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Jet engine performance

In fixed-wing aircraft driven by one or more jet engines, the performance of the jet engine is important to the operation of the aircraft. Performance of the jet engine includes measurement of thrust, fuel consumption, noise and engine emissions.

The thrust, noise and emission elements of the performance of a jet engine are of vital importance in the takeoff phase of operation of the aircraft. The thrust and fuel consumption elements, and their variation with altitude, are of vital importance in the climb and cruise phases of operation of the aircraft.

TS diagram
Temperature vs. entropy (TS) diagrams (see example RHS) are usually used to illustrate the cycle of gas turbine engines. Entropy represents the degree of disorder of the molecules in the fluid. It tends to increase as energy is converted between different forms, i.e. chemical and mechanical.

The TS diagram shown on the RHS is for a single spool turbojet, where a single drive shaft connects the turbine unit with the compressor unit. Apart from stations 0 and 8s, stagnation pressure and stagnation temperature are used. Station 0 is ambient. Stagnation quantities are frequently used in gas turbine cycle studies, because no knowledge of the flow velocity is required.

The processes depicted are:

 * Freestream (stations 0 to 1)
 * In the example, the aircraft is stationary, so stations 0 and 1 are coincident. Station 1 is not depicted on the diagram.

 * Intake (stations 1 to 2)
 * In the example, a 100% intake pressure recovery is assumed, so stations 1 and 2 are coincident.

 * Compression (stations 2 to 3)
 * The ideal process would appear vertical on a TS diagram. In the real process there is friction, turbulence and, possibly, shock losses, making the exit temperature, for a given pressure ratio, higher than ideal. The shallower the positive slope on the TS diagram, the less efficient the compression process.

 * Combustion (stations 3 to 4)
 * Heat (usually by burning fuel) is added, raising the temperature of the fluid. There is an associated pressure loss, some of which is unavoidable

 * Turbine (stations 4 to 5)
 * The temperature rise in the compressor dictates that there will be an associated temperature drop across the turbine. Ideally the process would be vertical on a TS diagram. However, in the real process, friction and turbulence cause the pressure drop to be greater than ideal. The shallower the negative slope on the TS diagram, the less efficient the expansion process.

 * Jetpipe (stations 5 to 8)
 * In the example the jetpipe is very short, so there is no pressure loss. Consequently, stations 5 and 8 are coincident on the TS diagram.

 * Nozzle (stations 8 to 8s)
 * These two stations are both at the throat of the (convergent) nozzle. Station 8s represents static conditions. Not shown on the example TS diagram is the expansion process, external to the nozzle, down to ambient pressure.

Design point performance equations
In theory, any combination of flight condition/throttle setting can be nominated as the engine performance Design Point. Usually, however, the Design Point corresponds to the highest corrected flow at inlet to the compression system (e.g. Top-of-Climb, Mach 0.85, 35,000 ft, ISA).

The design point net thrust of any jet engine can be estimated by working through the engine cycle, step by step. Below are the equations for a single spool turbojet.

==

Freestream
The stagnation (or total) temperature in the freestream approaching the engine can be estimated using the following equation, derived from the Steady Flow Energy Equation:

$$T_1 = t_0 \cdot (1 + ({\gamma}_c-1)\cdot M^2/2)$$

The corresponding freestream stagnation (or total) pressure is:

$$P_1 = p_0 \cdot (T_1/t_0)^ {{\gamma}_c/({\gamma}_c-1)}$$

Intake
Since there is no work or heat loss in the intake under steady state conditions:

$$T_2=T_1 \,$$

However, friction and shock losses in the intake system must be accounted for:

$$P_2=P_1 \cdot \mathrm{prf}$$

Compressor
The actual discharge temperature of the compressor, assuming a polytropic efficiency is given by:

$$T_3 = T_2 \cdot (P_3/P_2) ^ {{(\gamma}_c-1)/({\gamma}_c \cdot {\eta}pc)}$$

Normally a compressor pressure ratio is assumed, so:

$$P_3 = P_2 \cdot (P_3/P_2)$$

Combustor
A turbine rotor inlet temperature is usually assumed:

$$T_4 = \mathrm{RIT} \,$$

The pressure loss in the combustor reduces the pressure at turbine entry:

$$P_4 = P_3 \cdot (P_4/P_3)$$

Turbine
Equating the turbine and compressor powers and ignoring any power offtake (e.g. to drive an altenator, pump, etc), we have:

$$w_4 \cdot C_{\mathrm{pt}}(T_4-T_5) = w_2 \cdot C_{\mathrm{pc}}(T_3-T_2)$$

A simplyfying assumption sometimes made is for the addition of fuel flow to be exactly offset by an overboard compressor bleed, so mass flow remains constant throughout the cycle.

The pressure ratio across the turbine can be calculated, assuming a turbine polytropic efficiency:

$$P4/P5 = (T4/T5)^{{\gamma}_t/(({\gamma}_t-1).{\eta}_\mathrm{pt})}$$

Obviously:

$$P_5 = P_4 / (P_4/P_5) \,$$

Jetpipe
Since, under Steady State conditions, there is no work or heat loss in the jetpipe:

$$T_8 = T_5 \,$$

However, the jetpipe pressure loss must be accounted for:

$$P_8 = P_5 \cdot (P_8/P_5) \,$$

Nozzle
Is the nozzle choked? The nozzle is choked when the throat Mach number = 1.0. This occurs when the nozzle pressure ratio reaches or exceeds a critical level:

$$(P_8/p_{\mathrm{8s}})crit = (({\gamma}_t+1)/2))^{{\gamma}_t/({\gamma}_t-1)} \,$$

If $$(P_8/p_0) >= (P_8/p_{\mathrm{8s}})crit \,$$ then the nozzle is CHOKED.

If $$(P_8/p_0) < (P_8/p_{\mathrm{8s}})crit \,$$ then the nozzle is UNCHOKED.

Choked Nozzle
The following calculation method is only suitable for choked nozzles.

Assuming the nozzle is choked, the nozzle static temperature is calculated as follows:

$$t_{\mathrm{8s}} = T_8/(({\gamma}_t+1)/2) \,$$

Similarly for the nozzle static pressure:

$$p_{\mathrm{8s}} = P_8/(T_8/t_{\mathrm{8s}})^{{\gamma}_t/({\gamma}_t-1)}$$

The nozzle throat velocity (squared) is calculated using the Steady Flow Energy Equation:

$$V_8^2 = 2gJC_{pt}(T_8 - t_{\mathrm{8s}})$$

The density of the gases at the nozzle throat is given by:

$${\rho}_{\mathrm{8s}} = p_{\mathrm{8s}}/(R \cdot t_{\mathrm{8s}})$$

Nozzle throat effective area is estimated as follows:

$$A_8 = w_8/({\rho}_{\mathrm{8s}} \cdot V_8)$$

Gross thrust
There are two terms in the nozzle gross thrust equation; ideal momentum thrust and ideal pressure thrust. The latter term is only non-zero if the nozzle is choked:

$$F_g = C_\mathrm{x}((w_8 \cdot V_8/g) + A_8(p_{\mathrm{8s}} - p_0)) \,$$

Unchoked nozzle
The following special calculation is required, if the nozzle happens to be unchoked.

Once unchoked, the nozzle static pressure is equal to ambient pressure:

$$p_{\mathrm{8s}} = p_0 \,$$

The nozzle static temperature is calculated from the nozzle total/static pressure ratio:

$$t_{\mathrm{8s}} = T_8/(P_8/p_{\mathrm{8s}})^{{(\gamma}_t-1)/{\gamma}_t}$$

The nozzle throat velocity (squared) is calculated, as before, using the steady flow energy equation:

$$V_8^2 = 2gJC_{pt}(T_8 - t_{\mathrm{8s}})$$

Gross thrust
The nozzle pressure thrust term is zero if the nozzle is unchoked, so only the Momentum Thrust needs to be calculated:

$$F_g = C_\mathrm{x}((w_8 \cdot V_8/g) \,$$

Ram drag
In general, there is a ram drag penalty for taking air onboard via the intake:

$$F_r = w_0 \cdot V_0/g$$

Net thrust
The ram drag must be deducted from the nozzle gross thrust:

$$F_n = F_g - F_r \,$$

The calculation of the combustor fuel flow is beyond the scope of this text, but is basically proportional to the combustor entry airflow and a function of the combustor temperature rise.

Note that mass flow is the sizing parameter: doubling the airflow, doubles the thrust and the fuel flow. However, the specific fuel consumption (fuel flow/net thrust) is unaffected, assuming scale effects are neglected.

Similar design point calculations can be done for other types of jet engine e.g. turbofan, turboprop, ramjet, etc.

The method of calculation shown above is fairly crude, but is useful for gaining a basic understanding of aeroengine performance. Most engine manufacturers use a more exact method, known as True Specific Heat. High pressures and temperatures at elevated levels of supersonic speeds would invoke the use of even more exotic calculations: i.e. Frozen Chemistry and Equilibrium Chemistry.

Worked example
Question

Calculate the net thrust of the following single spool turbojet cycle at Sea Level Static, ISA, using Imperial units for illustration purposes:

Key design parameters:

Intake air mass flow, $$w_2 = 100 \ \mathrm{lb/s} \,$$ (use 45.359 kg/s if working in SI units)

Assume the gasflow is constant throughout the engine.

Overall pressure ratio, $$P_3/P_2 = 10.0 \,$$

Turbine rotor inlet temperature, $$T_4 = \mathrm{RIT}=1400 \ \mathrm{K} \,$$

(factor-up by 1.8, if working with degrees Rankine) Design component performance assumptions:

Intake pressure recovery factor, $$\mathrm{prf} = 1.0 \,$$

Compressor polytropic efficiency, $${\eta}pc = 0.89 \ (i.e. 89\%) \,$$

Turbine polytropic efficiency, $${\eta}pt = 0.90 \ (i.e. 90\%) \,$$

Combustor pressure loss 5%, so the combustor pressure ratio $$P_4/P_3 =0.95 \,$$

Jetpipe pressure loss 1%, so the jetpipe pressure ratio $$P_8/P_5 = 0.99 \,$$

Nozzle thrust coefficient, $$C_\mathrm{x} = 0.995 \,$$

Constants:

Ratio of specific heats for air, $${\gamma}_c = 1.4 \,$$

Ratio of specific heats for combustion products, $${\gamma}_t = 1.333 \,$$

Specific heat at constant pressure for air, $$C_{\mathrm{pc}} = 0.6111 \ \frac{\mathrm{hp} \cdot \mathrm {s}}{\mathrm{lb} \cdot \mathrm{K}} \,$$

(use 1.004646 kW·s/(kg·K) when working with SI units and use 0.3395 hp·s/(lb·°R) if working with American units)

Specific heat at constant pressure for combustion products, $$C_{\mathrm{pt}} = 0.697255 \ \frac{\mathrm{hp} \cdot \mathrm {s}}{\mathrm{lb} \cdot \mathrm{K}} \,$$ (use 1.1462 kW·s/(kg·K) when working with SI units and use 0.387363889 hp·s/(lb·°R) if working with American units) Acceleration of gravity, $$g = 32.174 \ \mathrm{ft}/\mathrm{s}^{2} \,$$ (use 1000 when working with SI units) Mechanical equivalent of heat, $$J = 550 \ \mathrm{ft} \cdot \mathrm{lb}/(\mathrm{s} \cdot \mathrm{hp}) \,$$ (use 1 when working with SI units)

Gas constant, $$R = 96.034 \ \mathrm{ft} \cdot \mathrm{lbf}/(\mathrm{lb} \cdot \mathrm{K}) \,$$ (use 0.287052 kN·m/(kg·K) when working with SI units and use 53.3522222 ft·lbf/(lb·°R) if working with American units including degrees Rankine)

Answer

Ambient conditions

A sea level pressure altitude implies the following:

Ambient pressure, $$p_0 =14.696 \ \mathrm{psia} \,$$ (assume 101.325 kN/m² if working in SI units)

Sea level, ISA conditions (i.e. Standard Day) imply the following:

Ambient temperature, $$t_0 =288.15 \ \mathrm{K} \,$$

(Note: this is an absolute temperature i.e. $$15 \ ^\circ \mathrm{C} + 273.15 \ ^\circ \mathrm{C} \,$$)

(Use 518.67 °R, if working with American units) Freestream

Since the engine is static, both the flight velocity, $$V_0 \,$$ and the flight Mach number, $$M \,$$are zero

So:

$$T_1 = t_0 = 288.15 \ \mathrm{K} \,$$

$$P_1 = p_0 = 14.696 \ \mathrm{psia} \,$$

Intake

$$T_2 = T_1 = 288.15 \ \mathrm{K} \,$$

$$P_2 = P_1 \cdot \mathrm{prf} \,$$

$$P_2 = 14.696 * 1.0 = 14.696 \ \mathrm{psia} \,$$

Compressor

$$T_3 = T_2 \cdot ((P_3/P_2) ^ {({\gamma}_c-1)/({\gamma}_c \cdot {\eta}pc)} = 288.15 * 10 ^ {(1.4-1)/(1.4 * 0.89)} = 603.456 \ \mathrm{K}$$

$$P_3 = P_2 \cdot (P_3/P_2) \,$$

$$P_3 = 14.696 * 10 = 146.96 \ \mathrm{psia} \,$$

Combustor

$$T_4 = \mathrm{RIT}=1400 \ \mathrm{K} \,$$

$$P_4 = P_3 \cdot (P_4/P_3) = 146.96 * 0.95 = 139.612 \ \mathrm{psia} \,$$

Turbine

$$w_4 \cdot C_{\mathrm{pt}}(T_4-T_5) = w_2 \cdot C_{\mathrm{pc}}(T_3-T_2) \,$$

$$100 * 0.697255 * (1400 - T_5)= 100 * 0.6111 * (603.456 - 288.15) \,$$

$$T_5 = 1123.65419 \ \mathrm{K} \,$$

$$P4/P5 = (T4/T5)^{{\gamma}_t/(({\gamma}_t-1).{\eta}_\mathrm{pt})} \,$$

$$P4/P5 = (1400/1123.65419)^ {1.333/((1.333-1) * 0.9)} \,$$

$$P4/P5 = 2.65914769 \,$$

Jetpipe

$$T_8 = T_5 = 1123.65419 \ \mathrm{K} \,$$

$$P_5 = P_4 /(P_4/P_5) \,$$

$$P_5 = 139.612/2.65914769 = 52.502537 \ \mathrm{psia}\,$$

$$P_8 = P_5 \cdot (P_8/P_5) \,$$

$$P_8 = 52.502537 * 0.99 = 51.9775116 \ \mathrm{psia} \,$$

Nozzle

$$P_8/p_0 = 51.9775116/14.696 = 3.53684755 \,$$

$$(P_8/p_{\mathrm{8s}})crit = (({\gamma}_t+1)/2))^{{\gamma}_t/(({\gamma}_t-1)} \,$$

$$(P_8/p_{\mathrm{8s}})crit  = ((1.333+1)/2)^{1.333/(1.333-1)} = 1.85242156 \,$$

Since $$P_8/p_0 > P_8/p_{\mathrm{8s}} \,$$, the nozzle is CHOKED

Choked Nozzle

$$t_{\mathrm{8s}} = T_8/(({\gamma}_t+1)/2) \,$$

$$t_{\mathrm{8s}} = 1123.65419/((1.333+1)/2) \,$$

$$t_{\mathrm{8s}} = 963.269773 \ \mathrm{K} \,$$

$$p_{\mathrm{8s}} = P_8/((T_8/t_{\mathrm{8s}})^{{\gamma}_t/({\gamma}_t-1)})$$

$$p_{\mathrm{8s}} = 51.9775116/ (1123.65419/963.269773)) ^ {1.333/((1.333-1))} \,$$ $$p_{\mathrm{8s}} = 28.059224 \ \mathrm{psia} \,$$ $$V_8^{2} = 2gJC_{pt}(T_8 - t_{\mathrm{8s}}) \,$$

$$V_8^{2} = 2 * 32.174 * 550 * 0.697255 * (1123.65419-963.269773) = 3957779.09 \,$$

$$V_8 = 3957779.09 ^ {0.5} = 1989.41677 \ \mathrm{ft}/\mathrm{s} \,$$

$${\rho}_{\mathrm{8s}} = p_{\mathrm{8s}}/(R \cdot t_{\mathrm{8s}}) \,$$

$${\rho}_{\mathrm{8s}} = (28.059224 * 144)/ (96.034 * 963.269773) = 0.0436782467 \ \mathrm{lb}/ \mathrm{ft}^3 \,$$

NOTE: inclusion of 144 in²/ft² to obtain density in lb/ft³.

$$A_8 = w_8/({\rho}_{\mathrm{8s}} \cdot V_8) \,$$

$$A_8 = (100 * 144)/ (0.0436782467 * 1989.41677) = 165.718701in^2 \,$$

NOTE: inclusion of 144 in²/ft² to obtain area in in².

Gross Thrust

$$F_g = C_\mathrm{x}((w_8 \cdot V_8/g) + A_8(p_{\mathrm{8s}} - p_0)) \,$$

$$F_g = 0.995 (((100 * 1989.41677)/32.174) + (165.718701 * (28.059224 - 14.696))) \,$$

$$F_g = 6152.38915 + 2203.46344 \,$$

The first term is the momentum thrust which contributes most of the nozzle gross thrust. Because the nozzle is choked (which is the norm on a turbojet), the second term, the pressure thrust, is non-zero.

$$F_g = 8355.85259 \ \mathrm{lbf} \,$$

Ram Drag

$$F_r = w_0 \cdot V_0/g \,$$

$$F_r = (100 * 0)/32.174 = 0 \,$$

The ram drag in this particular example is zero, because the engine is stationary and the flight velocity is therefore zero.

Net thrust

$$F_n = F_g - F_r \,$$

$$F_n = 8355.85259 - 0 = 8356 \ \mathrm{lbf} \,$$

To retain accuracy, only the final answer should be rounded-off.

Cooling Bleeds
The above calculations assume that the fuel flow added in the combustor completely offsets the bleed air extracted at compressor delivery to cool the turbine system. This is pessimistic, since the bleed air is assumed to be dumped directly overboard (thereby bypassing the propulsion nozzle) and unable to contribute to the thrust of the engine.

In a more sophisticated performance model, the cooling air for the first row of (static) turbine nozzle guide vanes (immeditely downstream of the combustor) can be safely disregarded, since for a given (HP) rotor inlet temperature it has no effect upon either the combustor fuel flow or the net thrust of the engine. However, the turbine rotor cooling air must be included in such a model. The rotor cooling bleed air is extracted from compressor delivery and passes along narrow passage ways before being injected into the base of the rotating blades. The bleed air negotiates a complex set of passageways within the aerofoil extracting heat before being dumped into the gas stream adjacent to the blade surface. In a sophisticated model, the turbine rotor cooling air is assumed to quench the main gas stream emerging from turbine, reducing its temperature, but also increasing its mass flow:

i.e.

$$w_{\mathrm{rotorexit}} \cdot C_{\mathrm{pt}}\cdot T_{\mathrm{rotorexit}} = w_{\mathrm{rotorbleed}} \cdot C_{\mathrm{pc}}\cdot T_{\mathrm{rotorbleed}} + w_{\mathrm{rotorentry}} \cdot C_{\mathrm{pt}}\cdot T_{\mathrm{rotorentry}} \, $$

$$w_{\mathrm{rotorexit}} = w_{\mathrm{rotorbleed}} + w_{\mathrm{rotorentry}} \, $$

The bleed air cooling the turbine discs is treated in a similar manner. The usual assumption is that the low energy disc cooling air cannot contribute to the engine cycle until it has passed through one row of blades or vanes.

Naturally any bleed air returned to the cycle (or dumped overboard) must also be deducted from the main air flow at the point it is bled from the compressor. If the some of the cooling air is bled from part way along the compressor (i.e. interstage), the power absorbed by the unit must be adjusted accordingly.

Cycle improvements
Increasing the design overall pressure ratio of the compression system raises the combustor entry temperature. Therefore, at a fixed fuel flow and airflow, there is an increase in turbine inlet temperature. Although the higher temperature rise across the compression system implies a larger temperature drop over the turbine system, the nozzle temperature is unaffected, because the same amount of heat is being added to the total system. There is, however, a rise in nozzle pressure, because turbine expansion ratio increases more slowly than the overall pressure ratio (which is inferred by the divergence of the constant pressure lines on the TS diagram). Consequently, net thrust increases, implying a specific fuel consumption (fuel flow/net thrust) decrease.

So turbojets can be made more fuel efficient by raising overall pressure ratio and turbine inlet temperature in unison.

However, better turbine materials and/or improved vane/blade cooling are required to cope with increases in both turbine inlet temperature and compressor delivery temperature. Increasing the latter may also require better compressor materials. Also, higher combustion temperatures can potentially lead to greater emissions of nitrogen oxides, associated with acid rain.

Adding a rear stage to the compressor, to raise overall pressure ratio, does not require a shaft speed increase, but it reduces core size and requires a smaller flow size turbine, which is expensive to change.

Alternatively, adding a zero (i.e. front) stage to the compressor, to increase overall pressure ratio, will require an increase in shaft speed (to maintain the same blade tip Mach number on each of the original compressor stages, since the delivery temperature of each of these stages will be higher than datum). The increase in shaft speed raises the centrifugal stresses in both the turbine blade and disc. This together with increases in the hot gas and cooling air(from the compressor) temperatures implies a decrease in component lives and/or an upgrade in component materials. Adding a zero stage also induces more airflow into the engine, thereby increasing net thrust.

If the increase overall pressure ratio is obtained aerodynamically (i.e. without adding stage/s), an increase in shaft speed will still probably be required, which has an impact on blade/disc stresses and component lives/material.

Other gas turbine engine types
Design point calculations for other gas turbine engine types are similar in format to that given above for a single spool turbojet.

The design point calculation for a two spool turbojet, has two compression calculations; one for the Low Pressure (LP) Compressor, the other for the High Pressure (HP) Compressor. There is also two turbine calculations; one for the HP Turbine, the other for the LP Turbine.

In a two spool unmixed turbofan, the LP Compressor calculation is usually replaced by Fan Inner (i.e. hub) and Fan Outer (i.e. tip) compression calculations. The power absorbed by these two "components" is taken as the load on the LP turbine. After the Fan Outer compression calculation, there is a Bypass Duct pressure loss/Bypass Nozzle expansion calculation. Net thrust is obtained by deducting the intake ram drag from the sum of the Core Nozzle and Bypass Nozzle gross thrusts.

A two spool mixed turbofan design point calculation is very similar to that for an unmixed engine, except the Bypass Nozzle calculation is replaced by a Mixer calculation (where the static pressures of the core and bypass streams at the mixing plane are usually assumed to be equal) followed by a Final (Mixed) Nozzle calculation.

General
An engine is said to be running off-design if any of the following apply:

 * a) change of throttle setting
 * b) change of altitude
 * c) change of flight speed
 * d) change of climate
 * e) change of installation (e.g. customer bleed or power off-take or intake pressure recovery)
 * f) change in geometry

Although each off-design point is effectively a design point calculation, the resulting cycle (normally) has the same turbine and nozzle geometry as that at the engine design point. Obviously the final nozzle cannot be over or underfilled with flow. This rule also applies to the turbine nozzle guide vanes, which act like small nozzles.

Simple Off-design Calculation

Design point calculations are normally done by a computer program. By the addition of an iterative loop, such a program can also be used to create a simple off-design model.

In an iteration, a calculation is undertaken using guessed values for the variables. At the end of the calculation, the constraint values are analyzed and an attempt is made to improve the guessed values of the variables. The calculation is then repeated using the new guesses. This procedure is repeated until the constraints are within the desired tolerance (e.g. 0.1%). Iteration variables

The three variables required for a single spool turbojet iteration are the key design variables:

1) some function of combustor fuel flow e.g. turbine rotor inlet temperature $$RIT\, $$

2) corrected engine mass flow i.e. $$w_{\mathrm{2cor}}\, $$

3) compressor pressure ratio i.e. $$P_3/P_2\, $$

Iteration constraints (or matching quantities)

The three constraints imposed would typically be:

1) engine match e.g. $$Fn\, $$ or $$w_{\mathrm{fe}}\, $$ or $$T_3\, $$, etc

2) nozzle area e.g. $$A_{\mathrm{8calc}}\, $$ vs $$A_{\mathrm{8 des pt}}\, $$

3) turbine flow capacity e.g. $$w_{\mathrm{4cor calc}}\, $$ vs $$w_{\mathrm{4cor des pt}}\, $$ The latter two are the physical constraints that must be met, whilst the former is some measure of throttle setting.

Note Corrected flow is the flow that would pass through a device, if the entry pressure and temperature corresponded to ambient conditions at sea level on a Standard Day. Results Plotted above are the results of several off-design calculations, showing the effect of throttling a jet engine from its design point condition. This line is known as the compressor steady state (as opposed to transient) working line. Over most of the throttle range, the turbine system on a turbojet operates between choked planes. All the turbine throats are choked, as well as the final nozzle. Consequently the turbine pressure ratio stays essentially constant. This implies a fixed $$\triangle T_{\mathrm{turb}}/RIT\,$$. Since turbine rotor entry temperature, $$RIT\,$$, usually falls with throttling, the temperature drop across the turbine system, $$\triangle T_{\mathrm{turb}}\,$$, must also decrease. However, the temperature rise across the compression system, $$\triangle T_{\mathrm{comp}}\,$$, is proportional to $$\triangle T_{\mathrm{turb}}\,$$. Consequently, the ratio $$\triangle T_{\mathrm{comp}}/T_1\,$$ must also fall, implying a decrease in the compression system pressure ratio. The non-dimensional (or corrected flow) at compressor exit tends to stay constant, because it 'sees', beyond the combustor, the constant corrected flow of the choked turbine. Consequently, there must be a decrease in compressor entry corrected flow, as compressor pressure ratio falls. Therefore, the compressor steady state working line has a positive slope, as shown above, on the RHS.

Ratio $$RIT/T_1\, $$ is the quantity that determines the throttle setting of the engine. So, for instance, raising intake stagnation temperature by increasing flight speed, at a constant $$RIT\, $$, will cause the engine to throttle back to a lower corrected flow/pressure ratio.

Fairly obviously, when an engine is throttled-back, it will lose net thrust. This drop in thrust is mainly caused by the reduction in air mass flow, but the reduction in turbine rotor inlet temperature and degradations in component performance will also contribute.

The simple off-design calculation outlined above is somewhat crude, since it assumes:

1) no variation in compressor and turbine efficiency with throttle setting

2) no change in pressure losses with component entry flow

3) no variation in turbine flow capacity or nozzle discharge coefficient with throttle setting

Furthermore, there is no indication of relative shaft speed or compressor surge margin.

Complex Off-design Calculation

A more refined off-design model can be created using compressor maps and turbine maps to predict off-design corrected mass flows, pressure ratios, efficiencies, relative shaft speeds, etc. A further refinement is to allow the component off-design pressure losses to vary with corrected mass flow, or Mach number, etc.

The iteration scheme is similar to that of the Simple Off-design Calculation.

Iteration variables

Again three variables are required for a single spool turbojet iteration, typically:

1) some function of combustor fuel flow e.g. $$RIT\, $$ 2) compressor corrected speed e.g. $$N_{\mathrm{cor}}\, $$

3) an independent variable indicative of the compressor operating point up a speed line e.g. $${\beta}\, $$.

So compressor corrected speed replaces corrected engine mass flow and Beta replaces compressor pressure ratio.

Iteration constraints (or matching quantities)

The three constraints imposed would typically be similar to before:

1) engine match e.g. $$F_n\, $$ or $$w_{\mathrm{fe}}\, $$ or $$T_{\mathrm{3}}\, $$, etc

2) nozzle area e.g. $$A_{\mathrm{8 geometricdesign}}\, $$ vs $$A_{\mathrm{8calc}}/C_{\mathrm{dcalc}}\, $$

3) turbine flow capacity e.g. $$w_{\mathrm{4cor calc}}\, $$ vs $$w_{\mathrm{4cor turb char}}\, $$

During the Complex Off-design calculation, the operating point on the compressor map is constantly being guessed (in terms of $$N_{\mathrm{cor}}\, $$ and $${\beta}\, $$) to obtain an estimate of the compressor mass flow, pressure ratio and efficiency. After the combustion calculation is completed, the implied compressor mechanical shaft speed is used to estimate the turbine corrected speed (i.e. $$N_{\mathrm{turb cor}}\, $$). Typically, the turbine load (power demanded) and entry flow and temperature are used to estimate the turbine enthalpy drop/inlet temperature (i.e. $$({\delta}H/T)_{\mathrm{turb}} \, $$). The estimated turbine corrected speed and enthalpy drop/inlet temperature parameters are used to obtain, from the turbine map, an estimate of the turbine corrected flow ($$w_{\mathrm{4cor turb char}}\, $$) and efficiency (i.e. $${\eta}_{\mathrm{pt}}\, $$). The calculation then continues, in the usual way, through the turbine, jetpipe and nozzle. If the constraints are not within tolerance, the iteration engine makes another guess at the iteration variables and the iterative loop is restarted.

Plotted on the LHS are the results of several off-design calculations, showing the effect of throttling a jet engine from its design point condition. The line produced is similar to the working line shown above, but it is now superimposed on the compressor map and gives an indication of corrected shaft speed and compressor surge margin.

Performance model
Whatever it's sophistication, the off-design program is not only used to predict the off-design performance of the engine, but also assist in the design process (e.g. estimating maximum shaft speeds, pressures, temperatures, etc to support component stressing). Other models will be constructed to simulate the behavior (in some detail) of the various individual components (e.g. rotor 2 of the compressor).

Installation effects
More often than not, the design point calculation is for an uninstalled engine. Installation effects are normally introduced at off-design conditions and will depend on the engine application.

A partially installed engine includes the effect of:

a) the real intake having a pressure recovery of less than 100%

b) air being bled from the compression system for cabin/cockpit conditioning and to cool the avionics

c) oil and fuel pump loads on the HP shaft

In addition, in a fully installed engine, various drags erode the effective net thrust of the engine:

1) an air intake spilling air creates drag

2) exhaust gases, exiting the hot nozzle, can scrub the external part of the nozzle plug (where applicable) and create drag

3) if the jet engine is a civil turbofan, bypass air, exiting the cold nozzle, can scrub the gas generator cowl and the submerged portion of the pylon (where applicable) and create drag

Deducting these throttle-dependent drags (where applicable) from the net thrust calculated above gives the streamtube net thrust.

There is, however, another installation effect: freestream air scrubbing an exposed fan cowl and its associated pylon (where applicable) will create drag. Deducting this term from the streamtube net thrust yields the force applied by the engine to the airframe proper.

In a typical military installation, where the engine is buried within the airframe, only some of the above installation effects apply.

Transient model
So far we have examined steady state performance modelling.

A crude transient performance model can be developed by relatively minor adjustments to the off-design calculation. A transient acceleration (or deceleration) is assumed to cover a large number of small time steps of, say, 0.01 s duration. During each time step, the shaft speed is assumed to be momentarily constant. So in the modified off-design iteration, $$N\, $$ is frozen and a new variable, the excess turbine power $${\delta}P_w\, $$, allowed to float instead. After the iteration has converged, the excess power is used to estimate the change in shaft speed:

Now:

Acceleration torque = spool inertia * shaft angular acceleration

$${\delta}\,{\tau}\, $$  = $$I\, $$ $$K\, $$ $$dN\, $$  /$$dt\, $$

Rearranging:

$$dN\, $$ = ( $${\delta}\,{\tau}\, $$/( $$I\, $$ $$K\, $$ )) $$dt\, $$ But:

$${\delta}P_w\, $$ = $$2\, $$ $${\pi}\,$$  $$N\, $$  $${\delta}\,{\tau}\, $$ /$$K_1\, $$

So:

$$dN\, $$ = ($$K_1\, $$ $${\delta}P_w\, $$/ ( $$2\, $$ $${\pi}\,$$ $$I\, $$ $$N\, $$ $$K\, $$)) $$dt\, $$

Or approximating:

$${\delta}N\, $$ = ($$K_2\, $$ $${\delta}P_w\, $$ / ($$I\, $$ $$N\, $$)) $${\delta}t\, $$

This change in shaft speed is used to calculate a new (frozen) shaft speed for the next time interval:

$$N_{\mathrm{new}}\, $$ = $$N_{\mathrm{old}}\, $$   + $${\delta}N\, $$

The whole process, described above, is then repeated for the new time:

$$t_{\mathrm{new}}\, $$ = $$t_{\mathrm{old}}\, $$ + $${\delta}t\, $$

The starting point for the transient is some steady state point (e.g. Ground Idle, Sea Level Static, ISA). A ramp of fuel flow versus time is, for instance, fed into the model to simulate, say, a slam acceleration (or deceleration). The transient calculation is first undertaken for time zero, with the steady state fuel flow as the engine match, which should result in zero excess turbine power. By definition, the first transient calculation should reproduce the datum steady state point. The fuel flow for $$tnew\, $$  is calculated from the fuel flow ramp and is used as the revised engine match in the next transient iterative calculation. This process is repeated until the transient simulation is completed.

It should be noted that the transient model described above is pretty crude, since it only takes into account inertia effects, other effects being ignored. For instance, under transient conditions the entry mass flow to a volume (e.g. jetpipe) needn't be the same as the exit mass flow; i.e. the volume could be acting as an accumulator, storing or discharging gas. Similarly part of the engine structure (e.g. nozzle wall) could be extracting or adding heat to the gas flow, which would affect that component's discharge temperature.

During a Slam Acceleration on a single spool turbojet, the working line of the compressor tends to deviate from the steady state working line and adopt a curved path, initially going towards surge, but slowly returning to the steady state line, as the fuel flow reaches a new higher steady state value. During the initial overfuelling, the inertia of the spool tends to prevent the shaft speed from accelerating rapidly. Naturally, the extra fuel flow increases the turbine rotor entry temperature, $$RIT\, $$. Since the turbine operates between two choked planes (i.e. the turbine and nozzle throats), the turbine pressure ratio and the corresponding temperature drop/entry temperature, $$\triangle T_{\mathrm{turb}}/RIT\,$$, remain approximately constant. Since $$RIT\, $$ increases, so must the temperature drop across the turbine and the turbine power output. This extra turbine power, increases the temperature rise across the compressor and, therefore, the compressor pressure ratio. Since the corrected speed of the compressor has hardly changed, the working point tends to move upwards, along a line of roughly constant corrected speed. As time progresses the shaft begins to accelerate and the effect just described diminishes.

During a Slam Deceleration, the opposite trend is observed; the transient compressor working line goes below the steady state line.

The transient behaviour of the high pressure (HP) compressor of a turbofan is similar to that described above for a single spool turbojet.

Performance software
Over the years a number of software packages have been developed to estimate the design, off-design and transient performance of various types of gas turbine engine. Most are used in-house by the various aero-engine manufacturers, but several software packages are available to the general public (e.g. GasTurb http://www.gasturb.de, EngineSim http://www.grc.nasa.gov/WWW/K-12//airplane/ngnsim.html, GSP http://www.gspteam.com).

Husk plot
A Husk Plot is a concise way of summarizing the performance of a jet engine. The following sections describe how the plot is generated and can be used.

Thrust/SFC loops
Specific Fuel Consumption (i.e. SFC), defined as fuel flow/net thrust, is an important parameter reflecting the overall thermal (or fuel) efficiency of an engine.

As an engine is throttled back there will be a variation of SFC with net thrust, because of changes in the engine cycle (e.g. lower overall pressure ratio) and variations in component performance (e.g. compressor efficiency). When plotted, the resultant curve is known as a thrust/SFC loop. A family of these curves can be generated at Sea Level, Standard Day, conditions over a range of flight speeds. A Husk Plot (RHS) can be developed using this family of curves. The net thrust scale is simply relabeled $$Fn/{\delta}\, $$, where $${\delta}\, $$ is relative ambient pressure, whilst the SFC scale is relabeled $$SFC/\sqrt{\theta}\, $$, where $${\theta}\, $$ is relative ambient temperature. The resulting plot can be used to estimate engine net thrust and SFC at any altitude, flight speed and climate for a range of throttle setting.

Selecting a point on the plot, net thrust is calculated as follows:

$$Fn = (Fn/{\delta}) \cdot {\delta}$$

Clearly, net thrust falls with altitude, because of the decrease in ambient pressure.

The corresponding SFC is calculated as follows:

$$SFC = (SFC/\sqrt{\theta}) \cdot \sqrt{\theta}$$

At a given point on the Husk Plot, SFC falls with decreasing ambient temperature (e.g. increasing altitude or colder climate).The basic reason why SFC increases with flight speed is the implied increase in ram drag.

Although a Husk Plot is a concise way of summarizing the performance of a jet engine, the predictions obtained at altitude will be slightly optimistic. For instance, because ambient temperature remains constant above 11,000 m (36,089 ft) altitude, at a fixed non-dimensional point the Husk plot would yield no change in SFC with increasing altitude. In reality, there would be a small, steady, increase in SFC, owing to the falling Reynolds number.

Thrust lapse
The nominal net thrust quoted for a jet engine usually refers to the Sea Level Static (SLS) condition, either for the International Standard Atmosphere (ISA) or a hot day condition (e.g. ISA+10 °C). As an example, the GE90-76B has a take-off static thrust of 76,000 lbf (360 kN) at SLS, ISA+15 °C.

Naturally, net thrust will decrease with altitude, because of the lower air density. There is also, however, a flight speed effect.

Initially as the aircraft gains speed down the runway, there will be little increase in nozzle pressure and temperature, because the ram rise in the intake is very small. There will also be little change in mass flow. Consequently, nozzle gross thrust initially only increases marginally with flight speed. However, being an air breathing engine (unlike a conventional rocket) there is a penalty for taking on-board air from the atmosphere. This is known as ram drag. Although the penalty is zero at static conditions, it rapidly increases with flight speed causing the net thrust to be eroded.

As flight speed builds up after take-off, the ram rise in the intake starts to have a significant effect upon nozzle pressure/temperature and intake airflow, causing nozzle gross thrust to climb more rapidly. This term now starts to offset the still increasing ram drag, eventually causing net thrust to start to increase. In some engines, the net thrust at say Mach 1.0, sea level can even be slightly greater than the static thrust. Above Mach 1.0, with a subsonic inlet design, shock losses tend to decrease net thrust, however a suitably designed supersonic inlet can give a lower reduction in intake pressure recovery, allowing net thrust to continue to climb in the supersonic regime.

The thrust lapse described above depends on the design specific thrust and, to a certain extent, on how the engine is rated with intake temperature. Three possible ways of rating an engine are depicted on the above Husk Plot. The engine could be rated at constant turbine entry temperature, shown on the plot as $$SOT/{\theta}\, $$. Alternatively, a constant mechanical shaft speed could be assumed, depicted as $$N_F/\sqrt{\theta}\, $$. A further alternative is a constant compressor corrected speed, shown as $$N_F/\sqrt{\theta}_T\, $$. The variation of net thrust with flight Mach number can be clearly seen on the Husk Plot.

Other trends
The Husk Plot can also be used to indicate trends in the following parameters:

1) turbine entry temperature

$$SOT = (SOT/{\theta}) \cdot {\theta}\, $$

So as ambient temperature falls (through increasing altitude or a cooler climate), turbine entry temperature must also fall to stay at the same non-dimensional point on the Husk Plot. All the other non-dimensional groups (e.g. corrected flow, axial and peripheral Mach numbers, pressure ratios, efficiencies, etc will also stay constant).

2) mechanical shaft speed

$$N_F = (N_F/\sqrt{\theta}) \cdot \sqrt{\theta}\, $$

Again as ambient temperature falls (through increasing altitude or a cooler climate), mechanical shaft speed must also decrease to remain at the same non-dimemsional point.

By definition, compressor corrected speed, $$N_F/\sqrt{\theta}_T\, $$, must remain constant at a given non-dimensional point.

Civil
Nowadays, civil engines are usually flat-rated on net thrust up to a 'kink-point' climate. So at a given flight condition, net thrust is held approximately constant over a very wide range of ambient temperature, by increasing (HP) turbine rotor inlet temperature (RIT or SOT). However, beyond the kink-point, SOT is held constant and net thrust starts to fall for further increases in ambient temperature. Consequently, aircraft fuel load and/or payload must be decreased.

Usually, for a given rating, the kink-point SOT is held constant, regardless of altitude or flight speed.

Some engines have a special rating, known as the 'Denver Bump'. This invokes a higher RIT than normal, to enable fully laden aircraft to Take-off safely from Denver, CO in the summer months. Denver Airport is extremely hot in the summer and the runways are over a mile above sea level. Both of these factors affect engine thrust.

Military
The rating systems used on military engines vary from engine to engine. A typical military rating structure is shown on the left. Such a rating system maximises the thrust available from the engine cycle chosen, whilst respecting the aerodynamic and mechanical limits imposed on the turbomachinery. If there is adequate thrust to meet the aircraft's mission in a particular range of intake temperature, the engine designer may elect to truncate the schedule shown, to lower the turbine rotor inlet temperature and, thereby, improve engine life.

At low intake temperatures, the engine tends to operate at maximum corrected speed or corrected flow. As intake temperature rises, a limit on (HP) turbine rotor inlet temperature (SOT) takes effect, progressively reducing corrected flow. At even higher intake temperatures, a limit on compressor delivery temperature (T3) is invoked, which decreases both SOT and corrected flow.

The impact of design intake temperature is shown on the right hand side.

An engine with a low design T1 combines high corrected flow with high rotor turbine temperature (SOT), maximizing net thrust at low T1 conditions (e.g. Mach 0.9, 30000 ft, ISA). However, although turbine rotor inlet temperature stays constant as T1 increases, there is a steady decrease in corrected flow, resulting in poor net thrust at high T1 conditions (e.g. Mach 0.9, sea level, ISA).

Although an engine with a high design T1 has a high corrected flow at low T1 conditions, the SOT is low, resulting in a poor net thrust. Only at high T1 conditions is there the combination of a high corrected flow and a high SOT, to give good thrust characteristics.

A compromise between these two extremes would be to design for a medium intake temperature (say 290 K).

As T1 increases along the SOT plateau, the engines will throttle back, causing both a decrease in corrected airflow and overall pressure ratio. As shown, the chart implies a common T3 limit for both the low and high design T1 cycles. Roughly speaking, the T3 limit will correspond to a common overall pressure ratio at the T3 breakpoint. Although both cycles will increase throttle setting as T1 decreases, the low design T1 cycle has a greater 'spool-up' before hitting the corrected speed limit. Consequently, the low design T1 cycle has a higher design overall pressure ratio.

Civil Engines
Modern (i.e. high bypass ratio) civil engines are normally sized to meet the the thrust requirements at the Top-of-Climb, which is often the design condition for the engine.

The throttle setting used at Take-Off depends upon the aircraft configuration: i.e. whether it has two, three or four-engines fitted. In the Western World civil engines operate to a "set and forget" throttle setting throughout Take-off. If the thrust of one engine is lost during Take Off, the remaining engine/s must have sufficient total thrust to clear any immediate obstruction beyond the end of the runway. If one engine is lost on a twin engine aircraft (e.g. Boeing 777), 50% of the nominal thrust is lost. Consequently the nominal T/O thrust must be very high, resulting in a very steep climb-out from the airport. On the other hand, if one engine is lost on a four engined aircraft (e.g. Boeing 747), it will only lose 25% of nominal thrust, so the nominal T/O thrust will be relatively low, giving a shallower climb-out from the airport.

Military Engines
The sizing point for a military engine is very much dependent upon the aircraft application.

As example, the Pegasus engine fitted in the Harrier is sized to meet the thrust requirements for a vertical landing in a hot climate, with a high level of stabilisation (i.e. reaction control) bleed from the HP compressor. These severe requirements mean there is more than sufficient thrust for normal wing-borne operation and so, in-flight, the engine is significantly derated (i.e. throttled back).

Nomenclature

 * $$A\, $$  flow area
 * $$A_{\mathrm{8calc}}\, $$ calculated nozzle effective throat area
 * $$A_{\mathrm{8 des pt}}\, $$ design point nozzle effective throat area
 * $$A_{\mathrm{8 geometricdesign}}\, $$ nozzle geometric throat area
 * $${\alpha}\, $$ shaft angular acceleration
 * $${\beta}\, $$ arbitrary lines which dissect the corrected speed lines on a compressor characteristic
 * $$C_{\mathrm{pc}}\, $$ specific heat at constant pressure for air
 * $$C_{\mathrm{pt}}\,$$ specific heat at constant pressure for combustion products
 * $$C_{\mathrm{dcalc}}\, $$ calculated nozzle discharge coefficient
 * $$C_x\, $$ thrust coefficient
 * $${\delta}\, $$ ambient pressure/Sea Level ambient pressure
 * $$({\delta}H/T)_{\mathrm{turb}} \, $$ turbine enthalpy drop/inlet temperature
 * $${\delta}N\, $$ change in mechanical shaft speed
 * $${\delta}P_w\, $$ excess shaft power
 * $${\delta}\,{\tau}\, $$ excess shaft torque
 * $${\eta}_{\mathrm{pc}}\, $$ compressor polytropic efficiency
 * $${\eta}_{\mathrm{pt}}\, $$ turbine polytropic efficiency
 * $$g\, $$  acceleration of gravity
 * $$F_g\, $$ gross thrust
 * $$F_n\, $$ net thrust
 * $$F_r\, $$ ram drag
 * $${\gamma}_{\mathrm{c}}\, $$ ratio of specific heats for air
 * $${\gamma}_{\mathrm{t}}\, $$ ratio of specific heats for combustion products
 * $$I\, $$  spool inertia
 * $$J\, $$  mechanical equivalent of heat
 * $$K\, $$  constant
 * $$K_1\, $$  constant
 * $$K_2\, $$  constant
 * $$M\, $$  flight Mach number
 * $$N\, $$ compressor mechanical shaft speed
 * $$N_{\mathrm{cor}}\, $$ compressor corrected shaft speed
 * $$N_{\mathrm{turb cor}}\, $$ turbine corrected shaft speed
 * $$p\, $$  static pressure
 * $$P\, $$  stagnation (or total) pressure
 * $$P_3/P_2\, $$ compressor pressure ratio
 * $$prf\, $$ intake pressure recovery factor
 * $$R\, $$  gas constant
 * $${\rho}\, $$ density
 * $$SFC\, $$ specific fuel consumption
 * $$RIT\, $$ (turbine) rotor inlet temperature
 * $$t\, $$  static temperature or time
 * $$T\, $$ stagnation (or total) temperature
 * $$T_1\, $$ intake stagnation temperature
 * $$T_3\, $$ compressor delivery total temperature
 * $${\theta}\, $$ ambient temperature/Sea Level, Standard Day, ambient temperature
 * $${\theta}_T\, $$ total temperature/Sea Level, Standard Day, ambient temperature
 * $$V\, $$ velocity
 * $$w\, $$ mass flow
 * $$w_{\mathrm{4cor calc}}\, $$ calculated turbine entry corrected flow
 * $$w_{\mathrm{2cor}}\, $$ compressor corrected inlet flow
 * $$w_{\mathrm{4cor des pt}}\, $$ design point turbine entry corrected flow
 * $$w_{\mathrm{4cor turb char}}\, $$ corrected entry flow from turbine characteristic (or map)
 * $$w_{\mathrm{fe}}\, $$ combustor fuel flow

title: Jet engine performance


text:
User talk:Geoffhodges

 Hello Geoffhodges, and welcome to Wikiversity! If you need help, feel free to visit my talk page, or contact us and ask questions. After you leave a comment on a talk page, remember to sign and date; it helps everyone follow the threads of the discussion. The signature icon in the edit window makes it simple. To get started, you may

 * Take a guided tour and learn to edit.
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 * Find out about research activities on Wikiversity.

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And don't forget to explore Wikiversity with the links to your left. Be bold to contribute and to experiment with the sandbox or your userpage, and see you around Wikiversity! --mikeu talk 13:27, 30 June 2009 (UTC)

Jet engine performance
I have used Import to transwiki copy the entire revision history of Jet engine performance to replace the text that you copy and pasted. This was done to preserve the edit history for reasons of license. I tried to restore the page to the last complete revision at wp. The page now requires some cleanup. Let me know if you need help with this. --mikeu talk 13:37, 30 June 2009 (UTC)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: User talk:Geoffhodges


text:
Reflections on McCarty

Teresa L. McCarty (2005) Language, literacy and power in schooling
Language, literacy and power in schooling includes a collection of articles from both novel (at the time) and renowned scholars in the field of educational research. The book is based on a symposium held by the American Anthropological Association ten years ago, but the texts in it bear an air of freshness and novelty. The volume is divided in three parts, and all the parts have a similar structure with a short introduction written by McCarty in the beginning, a core of chapters presenting educational ethnographic research from different angles in the middle and finally a commentary chapter, written by prominent scholars such as Jim Cummins, Luis C. Moll and Ray McDermott at the end of each part. I found this structure functional as the parts formed intelligible entities and the meta-commentaries added another dimension to the research presented. The structure also facilitated the process of reading.

The three parts have all different kinds of focus, even though the connections between them are easily seen. Part I with the title “Taking hold” of local literacies examines “the tensions between the local and the general (literacies), the margins and the center and the spaces in between” (p. xi). It presents research conducted mainly among indigenous peoples such as Maya people of Chiapas in Mexico, Hopi and other Native American peoples in the US, Alaskan Natives, Australian Aboriginals, and an in-depth ethnographic study where only one Mexican-American woman is in focus. The studies in part 1 highlight the complexity and meaning of literacy in local level, in communities, for individuals and their institutions.

Part II is titled Literacy practices in diverse classroom contexts and has a different kind of focus. The texts in part II are focused on examining face-to-face interactions around literacy in classrooms that have great diversity both ethnically and linguistically, therefore reinforcing the role of culture and language in learning. Themes presented include early literacy in multiethnic classrooms where the concept of race is – or is not – being discussed, argumentation for the coexistence of different varieties in multilingual classrooms, mathematics in bilingual-bicultural classrooms and local power construction through discourse in a multilingual classroom with socially marginalized students.

Part III, in its turn, positions literacy practices and politics in a larger context, namely that of globalization, seeing social, political and economic forces as interweaved with literacy education. All chapters present research with an ethnographic approach. A key question is deeply connected with power, wondering “what kind of and whose literacies and knowledges will predominate in an era of global capitalism” (p. 221). Possible answers are discussed from three different points of view in the chapters, ranging from a critical approach to current educational policies from the point of view of the “new capitalism” that demands a new set of principles in order to give more people a chance to succeed, to a critical examination of adult literacy education in the US-Mexico-border and to a discussion about education reform, followed by a “literacy crisis” in California.

In the book, literacy is presented as socially and historically situated, fluid, multiple and deeply connected with power. The access that certain type of literacy skills often grant to key intellectual, social, economic and political resources and rights are highlighted in all of the chapters from different points of view. One of the most interesting contributions in the book is Ray McDermott’s commentary on part 1. In a daring manner McDermott challenges our conceptions of the role of literacy in the society, making visible the contradictions, hierarchies, changes, settlements in societal structures and knowledge creation attached to it. Quoting and rewriting Marx, McDermott concludes “whatever a person learns takes its value from what others can make of it; whatever a person learns is taken from its maker and used to fulfill the intentions of others” (p.120), making it clear that literacy is and never has been a private issue, a skill that a person possesses without any social connections. McDermott’s commentary is at times very provocating but also refreshing. He points out that all actors (meaning all of us) in the “literacy market” are part of the problem and that if there is something we have succeeded in it is institutionalizing what he calls “crazy” ideas about language, education and their possible relations. Supported by the research presented in part I, McDermott pleads for a more consenting attitude towards different types of literacy.

In a commentary to part II, Luis C. Moll discusses language in a changing social context in the light of the previous chapters in the same section. Making a connection to the school arenas presented here, Moll concludes that the “presence of diversity in schools is being treated with alarm, suppression and attempts to impose uniformity on teaching and learning”, sending a clear message of who is in power and who is not to both students and their parents, but also to school personnel and decision-makers. Moll discusses also academic failure, turning the tables around when demanding the reader to reflect on whether failing in literacy (or in school in general) is something children do or something that is done to them.

Jim Cummins’ commentary to part III takes also a confronting point of view, asking whether it is possible through schools and literacy education to challenge the existing and evolving power relations in our globalizing world, and is complemented with a concluding afterword by the editor. A central theme for the book, as McCarty describes it, is “the richness and promise of multiple literacies and the pedagogies that nurture them”, but the reader never gets a chance to get too carried away as s/he is soon reminded of a different reality that still exists and dominates the views on language, culture and literacy in many societies. By extending a hand and inviting readers to join in critical literacy research, McCarty however succeeds in leaving us with a hopeful tone.

title: Reflections on McCarty


text:
User talk:Suresh Gottimukkala

 Hello Suresh Gottimukkala, and welcome to Wikiversity! If you need help, feel free to visit my talk page, or contact us and ask questions. After you leave a comment on a talk page, remember to sign and date; it helps everyone follow the threads of the discussion. The signature icon in the edit window makes it simple. To get started, you may

 * Take a guided tour and learn to edit.
 * Visit a (kind of) random project.
 * Browse Wikiversity, or visit a portal corresponding to your educational level: pre-school, primary, secondary, tertiary, non-formal education.
 * Find out about research activities on Wikiversity.

 * Read an introduction for teachers and find out how to write an educational resource for Wikiversity.
 * Give feedback about your initial observations
 * Discuss Wikiversity issues or ask questions at the colloquium.
 * Chat with other Wikiversitans on #wikiversity-en.

And don't forget to explore Wikiversity with the links to your left. Be bold to contribute and to experiment with the sandbox or your userpage, and see you around Wikiversity! --mikeu talk 14:48, 30 June 2009 (UTC)

title: User talk:Suresh Gottimukkala


text:
User:Aaronhorton

I am a graduate student in Ancient History and Classical Studies at the University of Wales, Lampeter. I hold a BA in History from Liberty University.

I am interested in the cultural exchange between the Greco-Roman world and the ancient Near East, especially Egypt and Babylon. At the moment I am researching the Hellenization of the socio-economic spheres in Egypt during the Ptolemaic administration.

I also have a deep interest in Maya civilization.

title: User:Aaronhorton


text:
User:CarrieBerg/2009 Literature Self Assessment

I realize that the class is not over yet... but I just had to write this. I'm sure you understand how that is: sometimes the words just flow out, needing to be said, even when the time is not ideal - much like the story I just had to write down late last night... despite the fact that I really wanted to sleep.

Going back and looking over what I have written for this class, I have to laugh. Usually what I enjoy writing the most is dialogue (it goes without saying that my dialogue is witty. Why write boring dialogue?  Yes, I'm being facetious.)  And then I looked through my stories posted here and found that, huh, I wrote almost no dialogue this entire quarter. Sacrilege!

Not only that, but while I usually write stories in limited third person (or third person omniscient), here I've been writing a slew of stories in first person. How completely out of character for me! I blame the book If I were an Evil Overlord. I seem to have had a change of heart. (Once I refused to read stories in first person. Now I find they are not as bad as I thought.  I wonder what horrible story originally made me stay away from them?)

Well, I guess I'm allowed to experiment as I see fit, but it still makes me laugh. It also means that this is not a full example of what I usually write. Maybe I'll add a dialogue heavy story, just to fix my omission...

And now for the question portion of this assessment.

What did I learn in this class. Hmmm... Oulipo is the big one for me. My, what a fun method of poetry! I shall have to try it with different limitations in the future. Like only using words with "st" in them... fascinating... I could spend hours lost in the intricacy of Oulipo. Hours I don't currently have.

My papers taught me much about Colonial healing properties of plants. And I learned more about modern healing properties of plants: next time you pull up that dandelion, eat the leaves in a salad - it's good for you! I also studied more into the Arthurian tradition, and delved back into my notes on alchemy and Chaucer.

I was also reminded how much I love writing. I really have to find more time to do so, despite all my other classes. There has to be a way to rearrange my schedule. And I was reminded as to how much I love tossing ideas back and forth between other people. I would love to write a book with someone else, where we trade off every other chapter and build upon our crazy tangents...

Which brings me to: what do I have left to learn? So much that I couldn't possibly write it all in this tiny space! As Socrates once said, "The only true wisdom is knowing you know nothing." There is still so much to learn - and I intend to spend my life making a tiny dent into that great mountain of knowledge. I do not see my task as impossible, though I know there is too much for just one person to know. I see it as a worthy challenge - to see how much knowledge I absorb, and then to test my use of it.

What did I do well? Ah, research. I love to do research. Research takes me anywhere from double to quadruple the amount of time it takes me to actually write the story or paper. Each page of typing takes about an hour. So for a five page short story, I spend 5 hours writing it and anywhere from 10 to 40 hours doing research on various topics. I think it pays off. And I learn a lot. But I'm sure not everyone has the extreme patience I have... or takes as copious quantities of research notes.

What could I have done better? Given more time to hone my writing skills, yes I could have done better in this class. But given to where I am right now in the matter of things? Then no. This is as good as my writing is currently. Sad, but true. Perhaps someday I will grace bookshelves with volumes of my work.

Until then, I will continue to read, and write, and eventually, by accident of brilliance, I will come to a greater understanding of the literary arts. Or I will find that I already have that understanding, I just chose to be blind to it at this time. That is the tricky part of hindsight...

Do I feel prepared or unprepared to continue my studies? This question is moot. Whether I'm prepared or not, I plan to spend the rest of my life studying! Have you seen my personal research library? No? Not surprising, but let me describe a small slice of it: it's filled with treatises on Medieval magic, Medieval alchemy, Medieval philosophy, Ancient Egyptian, Byzantine and Greek healing practices, astrology from around the world, herbs, religion from around the world, tomes upon tomes of mythology... and it is constantly growing based on whatever I find interesting or useful. Sufi poetry? Got it. Obscure religious texts (translated into English) from 15th Century Italy. Check. Thompson Tale-Type Motifs? Yep. Turkish folklore? Bottom shelf!

And if I don't have something, I know where to find it. Early English Books Online is a great source for those Medieval treatises on alchemy (eebo.chadwick.com/home). And www.theoi.com is possibly the most comprehensive site in the world for Ancient Greek Gods, Goddesses, Demi-Gods, monsters, heroes... There are so many great resources, and I have a feeling I'll be using all of them as I continue to write.

How did I contribute to the experiences of other students in this class? Ah, now this is a tricky question. I do not know. I am not the other students. Was I annoying with my in-class comments? Was I too aloof? Was I scary? Did I teach anyone anything? I guess I'll have to ask people about this one...

As I mentioned at the beginning, class is not yet over. So there may be more things that come up that I will feel the need to write about. I reserve this space for future comments - for I'm sure that they will come.


text:
Wikiversity:Colloquium/archives/June 2009

Arabic Wikiversity?
--Email4mobile 21:43, 4 June 2009 (UTC) Hi, all. I signed by accident into this site and was surprised not to see the Arabic main page or translation within Wikiversity. I was eager to start contributing in this site or translating some articles into Arabic but don't know how to do it. I'd appreciate your help. I usually translate English articles in Wikipedia into Arabic, update or create new Arabic articles.
 * Have you browsed these pages: ? I would say, you can also translate technical pages of this: . Wikiversity is something different, so I would recomend not to translate its content.--Juan de Vojníkov 04:41, 10 June 2009 (UTC)
 * Later on I could get a beta version for Arabic but I still face the problem in which I can append the English language link (e.g. abcd ) but can't make the reverse (or wxyz ) can any one please help me? --Email4mobile 05:40, 5 June 2009 (UTC)
 * You can cast your vote on the page Requests for new languages/Wikiversity Arabic. You might want to read betawikiversity:Wikiversity:Babel/archive/20080108 for your problem of linking to the Arabic beta version. The links made this way may have to be changed later on when pages are moved to the final Wikiversity Arabic. --fasten 11:06, 5 June 2009 (UTC)

 * That is not how a new Wikiversity language is created. Unlike other projects, Beta Wikiversity is responsible for new languages being created. You should begin creating Arabic resources on Beta Wikiversity and in time Arabic Wikiversity will be created. -- dark lama  12:07, 5 June 2009 (UTC)

project on information technology and its effect on student learning.

 * "Wikiversity Beta is also a place where Wikiversity projects which don't have a subdomain yet can develop." betawikiversity:Help:FAQ/En. To me that sounds as if it implies that you can develop resources that should be moved to the final project. The use may be uncommon but it is a possible use. Translations from other wikiversities may not be the most important projects to begin in beta state, though. --fasten 10:44, 7 June 2009 (UTC)

 * Well yes, once a project has been created for the language, the developed resources are moved from Beta to the new Wikiversity, but until then that is the place to develop them and activity there determines when and if a new language Wikiversity is ready to be created. Its not an uncommon use of Beta Wikiversity. Translations are also welcome and within the scope of Beta Wikiversity. -- dark lama  12:10, 7 June 2009 (UTC)

Template:free screenshot
Template:Software-screenshot links to Template:free screenshot. Is there a different option besides "Template:free screenshot"? --JWSchmidt 18:15, 10 June 2009 (UTC)

Theory ?
I prefer to ask first; I might have missed a policy. Do you mean that MY theory about infinite numbers is a good candidate for a page here at the Wikiversity ? I'm not totally sure anybody else didn't state it, but I didn't heard about it. I want to reassure you, it's not something completly funky about poly-dimentionnal wormhole ;) . It's quite straight forward in fact but I've not seen anybody postulate about it. Iluvalar 04:09, 21 June 2009 (UTC)
 * It seems like a decent candidate to me. Wikademia
 * How should I start then ? PS: I hanged on wp-fr for a long time (3000 edits). I know the basics. . I just want to know : Is there a specific namespace ? Any naming convention ? Where could I link my new page ? Those things... Iluvalar 15:14, 21 June 2009 (UTC)
 * I don't know what your theory is called, but you could just create a page which describes it, like writing a paper. The page name might sort of then be like picking the name of a paper, and then right the page as if you might be writing a paper. Naming conventions Wikademia
 * Here is the first draft. thanks. Defined infinity theory. Thinking about $$\infty+3$$ for so much time pushed me at the edge of pure madness. I think I've survived with a big load of humour. I hope the final result is not so bad and the idea can be understood. ... I'm taking a break. Iluvalar 01:10, 22 June 2009 (UTC)

 * Your theory sounds like "Original Research", so you should read, understand and agree to Wikiversity's OR policy. I looked over your page briefly -- what I would suggest is that you tap some math gurus to provide feedback and peer review and to try and punch holes in your Theory. Historybuff 15:31, 28 June 2009 (UTC)
 * I know my idea is a bit messy right now. I'm a bit rusty in integral and differential equation, but I would be glad to take a look to common calculus involving infinite values. And demonstrate how by thinking of an infinity as being defined, much more like others variables, we can end up with good answers. Often much more quickly then using conventional method. I don't have much spare time right now, to find those commons exemples which use those method. I quickly read WV:OR is there any template to warn that this theory is an original research ? Iluvalar 00:02, 29 June 2009 (UTC)
 * I don't think there is any template. If you think its important to let people know that your writing original research you can make such a template, otherwise don't worry about it. -- dark lama  22:23, 29 June 2009 (UTC)
 * I don't worry, but on another hand this might be used to determine critical mass in nuclear plant. Just in case, I put a warning. Iluvalar 19:24, 30 June 2009 (UTC)

Watchlist bug
When I change any of the following to "Hide" status, they won't change back:

 * "Hide minor edits | Hide bots | Hide anonymous users | Hide logged-in users | Hide my edits"

The workaround I've found is to edit the address bar to change the word "hide" to "show". Here's an example for "Show my edits":

 * " http://en.wikiversity.org/w/index.php?title=Special:Watchlist& showOwn=1&days=0"

How can we fix this ? StuRat 15:54, 15 June 2009 (UTC)

 * I'm not sure where the problem is, but this sounds like it might be in mediawiki. I would try looking around at http://www.mediawiki.org or at https://bugzilla.wikimedia.org.  --mikeu talk 12:31, 25 June 2009 (UTC)

 * Thanks. Can you confirm if the same problem happens for you ? StuRat 14:22, 25 June 2009 (UTC)
 * Show to Hide and back to Show works fine for me on both recent changes and my watchlist. I'm using Firefox. CQ 21:40, 28 June 2009 (UTC)

 * I seem to have this same problem. Tried it in Firefox on Windows 7, and Firefox and Internet Explorer on Vista. Also seems to effect other WMF Wikis. I suspect it will have been raised on bugzilla. Adambro 22:03, 28 June 2009 (UTC)

 * I can't find a report on Bugzilla on this. Can you ? StuRat 11:09, 29 June 2009 (UTC)

 * A kinda/sorta related bug is 17256. That was the only result of a search for "watchlist hide show". --mikeu talk 16:22, 5 July 2009 (UTC)

 * I don't quite understand that bug report. What's the "invert" it talks about ? StuRat 00:20, 6 July 2009 (UTC)

 * Just below the line with "hide minor edits" etc. there is a pulldown menu to select Namespace: to choose, for example, to only show edit in User_Talk: space. The Invert Selection checkbox shows all pages _except_ that one namespace.  --mikeu talk 00:25, 6 July 2009 (UTC)

 * Oh, that's what that does. I was thinking it was supposed to invert colors in the display. StuRat 09:45, 6 July 2009 (UTC)

 * The odd thing is that it seems to work fine in Recent Changes, but does not work in My Watchlist. Tested using:
 * Mozilla 1.7 for Sun Java Desktop System (Mozilla/5.0 (X11; U; SunOS sun4u; en-US; rv:1.7) Gecko/20070606)
 * Firefox 2.0.0.19 (Mozilla/5.0 (X11; U; SunOS sun4u; en-US; rv:1.8.1.19) Gecko/20090218 Firefox/2.0.0.19)
 * Opera 9.00 . Build 344 for SunOS. Qt library 3.3.5.
 * --mikeu talk 10:39, 29 June 2009 (UTC)

Thanks to everyone who tried to confirm this bug. StuRat 11:05, 29 June 2009 (UTC)

 * Same problem in el.wv --[[Image:Assassingr_signature.svg]]-- (profile | chit chat | email) 11:59, 29 June 2009 (UTC)

 * Thanks. That's Greek, right ? StuRat 13:48, 29 June 2009 (UTC)

 * Yes, el is greek. I also see the same bug on en-wikipedia, so it is not site specific.  --mikeu talk 16:26, 5 July 2009 (UTC)

 * OK, thanks. StuRat 00:20, 6 July 2009 (UTC)
 * Definately a bug in watchlist show/hide feature. CURRENTVERSION = 1.16alpha(r52088) • CQ 23:50, 11 July 2009 (UTC)


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User talk:B9 hummingbird hovering/Blog

Hello, if you are here regarding the Tibetan Language course please leave your name by signing with four tildes ( ~ ) following and follow the rest of the instructions in your initial point of contact:
 * B9 hummingbird hovering 06:04, 1 July 2009 (UTC)

title: User talk:B9 hummingbird hovering/Blog


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User:Jjb~enwikiversity

{| cellpadding="10" cellspacing="5" style="width: 100%; background-color: inherit; margin-left: auto; margin-right: auto"
 * style="width: 50%; background-color: LemonChiffon; border: 1px solid Gray; vertical-align: top; -moz-border-radius-topleft: 8px; -moz-border-radius-bottomleft: 8px; -moz-border-radius-topright: 8px; -moz-border-radius-bottomright: 8px;" |

About me

 * Name
 * Jordan

 * External Links

 * Location
 * Vancouver

 * School

 * Why I want to learn filmmaking.

 * Contact

 * }

 * Jjb has completed the following assignments in the course on Basic filmmaking (pre-production) for narrative motion pictures.

 * [[Image:Blancovinkjeup.png|16px]] Formatting the Script [[Image:Nuvola apps package wordprocessing.png|28px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Pop Quiz - What is the first shot? [[Image:Crystal Clear app clock.svg|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Creating the thumbnail storyboards [[Image:Crystal Clear app gimp.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Quick Exercise - Over-the-shoulder shot [[Image:Applications-accessories.svg|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Creating the 3D storyboards [[Image:Crystal Clear app Login Manager.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] A simple DVD-Video Editing Workshop [[Image:Crystal Clear device cdwriter unmount.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Learning about camera lenses [[Image:Crystal Clear app camera.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Record the dialog for the animatic [[Image:Crystal Clear app krec.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Intro to narrative filmmaking [[Image:Clapboard-Small.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Draw the movie poster for "Star Wars" [[Image:Crystal Clear app kcoloredit.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Understanding dailies [[Image:Clapboard-Small.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Create a matte painting [[Image:Crystal Clear app kcoloredit.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Understanding editing [[Image:Clapboard-Small.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Pop Quiz - Creating the moods (film scoring) [[Image:Crystal Clear app clock.svg|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Understanding "L-Cuts" [[Image:Clapboard-Small.png|24px]]
 * [[Image:Blancovinkjeemptysmall.png|16px]] Create the animatic [[Image:Clapboard-Small.png|28px]]

title: User:Jjb~enwikiversity


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Ejump/Designers

Designers of the Ejump course:

Satu Nurmela •	Email: satu.nurmela[at]utu.fi

•	Telephone: +358 40 531 8079

•	Second Life: Satu Constantine.

•	Facebook: Satu Nurmela

•	Blogs: http://satun.edublogs.org/

Sue Harrison

•	Email: S.Harrison[at]uel.ac.uk

•	Skype ID: sue.harrison.uel

Margarida Amaral •	Email mamaral[at]reit.up.pt

Alfredo Soeiro •	Email: soeiro.alfredo[at]gmail.com

Iskra Popova •	Email: iskpop[at]dsv.su.se

•	Skype ID: iskrapopova

•	Telephone: +46 8 16 16 06 (office) and +46 70 263 0345 (mobile)

Mauri Kantola •	Email: mauri.kantola[at]turkuamk.fi

•	Telephone & Text Messages: +358 50 385 4139

•	Facebook: Mauri Kantola

•	Second Life: Tutor Avatar Maka Inglewood

•      You can find Maka Inglewood also in Facebook and hopefully you will connect your avatar into the Facebook and to Maka Inglewood as well.

•      The Second Life address of edufinland: http://slurl.com/secondlife/EduFinland/110/184/25

•	Blog:The Blog of Maka Inglewood in the Blogger

Johanna Aaltonen

•	Finnish translation and localisation

title: Ejump/Designers


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Ejump/Orientation/Outcomes-based approach to the assessment of learning

An outcomes-based approach to the assessment of learning

David Baume did the orientation lecture with the title "An outcomes-based approach to the assessment of learning"20.1.2009. The session was an interactive one and you can see the File:Assessment of learning V3.pdfslides here http://beta.wikiversity.org/wiki/File:Assessment_of_learning_V3.pdf. Aim of this orientation was to give up-to-date information where are we at the moment in assessment and what are our future challenges in the near future. Continue working with questions of last slide.


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User:PS~enwikiversity

I have studied language at the University of Oslo (Norway) for two years. Mostly german, but also latin. I live by the motto "If the latin ablative case was a woman, I`d marry her on the spot."

title: User:PS~enwikiversity


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Ejump/Orientation/What is peer assessment?

Nancy Falchikov describes peer phenomenon in her book Learning Together: Peer Tutoring in Higher Education See at least the summary of the Introduction at page 5 and peer tutoring will become clearer for you.

In peer assessment, members of a class grade the work of performance of their peers using relevant criteria. Peer assessment may also involve students giving feedback to peers. As with self-assessment, in peer assessment, marks may be awrded by students or negotiated with teachers. Marks may or may not be used for formal grading purposes. For most practitioners, a key aim of peer assessment is to enhance learning. Student involvement in assessment can be peripheral or extensive. It can vary from a single simple decision taken by students, such as determining the submission date of assignments, or ascertaining preferred modes of assessment, to involvement in the entire process. Whre students are involved in all stages of assessment, the first thing that needs to be done is for teachers and learners to agree on the criteria by which work or performance will be judged. Sometimes, these criterias are supplied by the teacher. Very infrequently, students supply their own criteria in the absence of the teacher. Once criteria have been identified, self- or peer assessment may then follow. Nancy Falchikov has been collecting papers on peer assessment for a study which synthesizes results from investigations involving statistical comparisons (Falchikov and Goldfinch, 2000). Quantitative peer assessment studies which compared peer and teacher marks were subjected to meta-analysis, a technique which allows results collected in a wide variety of contexts to be compared. The analysis suggested that peer assessments more closely reseble teacher assessments when students are required to make a global judgements based on clear and explicit criteria, and when students are familiar with, and have some degree of ownership of, the criteria, rather than when grading involves assessing several individual dimensions. Assessment on professional practice appears to be more difficult than assessment of academic products and processes. Peer-teacher similarities were greater in well-designed studies than in poorly designed ones. (Falchikov, N. 2005. Learnin together. Peer tutoring in higher education. Routledge Falmer. Pages 1-2).


text:
Ejump/Orientation/Recommended Literature

Boud, D. (ed) (2007). Rethinking Assessment in Higher Education. Routledge. 978-0-415-39779-7.
 * Book revisits assessment in higher education and examines it from the point of view of what assessment does and can do. Challenging the overwhelming dominance of marks and grades, expert contributors from a range of countries suggest that we need to think differently about assessment if it is to make a useful contribution to the educational purposes of higher education.

Bryan, C. & Clegg, K. (2006). Innovative Assessment in Higher Education. Routledge. 978-0-415-35642-8.
 * Throughout higher education, assessment is changing, driven by incresed class size, changing curricula, and the need to support students better. At the same time assessment regulations and external quality assurance demands are constraining assessment options, driven by worries about standards, reliability and plagiarism. This book is about the difficult process of changing assessment in sometimes unhelpful contexts.

Falchikov, N. (2001). Learning Together. Peer tutoring in higher education. Routledge. 0-415-18261.
 * This book explores student learning within the context of peer tutoring and offers a practical guide to activities. Book contains chapters on: promoting and planning peer tutoring, preparing students for learning this way, theoretical frameworks underlying the practice and beneficial effects associated with peer tutoring.

Mason, R. & Rennie, F. (2008). E-Learning and Social Networking Handbook. Routledge. 978-0-415-42607-7.
 * Book describes the changes what using social media has to pedagogy. T


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Ejump/Orientation/Further Links and Useful Resources

 * Social Bookmarking Site for New Assessment Methods Course (Username: ejump2.0, Password: assessment1) http://delicious.com/e-jump2.0

Delicious will grow all the time with links of course participants.


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Wikis

The use of wikis in learning promotes collaboration. A wiki is a perfect place for process writing, studens' own homepages, and project working. When we use wikis as a learning space we concentrate thus also to assessment of groups and collaborative processes. Instead of single students we are now assessing processes and final outputs produced in some kind of groups. Assessment can be both feedback and feedforward and it can base to mixed modes of individual assessment, peer assessment and assessment of groups.

Here a couple of examples of educational wikis:

 * 1) Educational wikis
 * 2) A particularly innovative wiki use is DramaticIdentity — A DramaticIdentity is a temporary hat that you put on when you assume the role of another (nonhuman) entity, allowing it to speak on the topic at hand. (Peter Mereal in References, Category Wiki-5)

More can be found at: Educational wikis.

Assignment

 * 1) Get familiar with wikis and build your own wiki or use this wiki (create pages, modify content & discuss). There are lot of different wikis available but visit for example wikispaces, MediaWiki or wetpaint.
 * 2) Get familiar with assessment examples of wikis given in links and make your own plan how to assess learning when using wikis. Think who should assess learning, when and how.

If you wish to write your notes directly to wikiarticle, then please do so, creating titles and sub sections as you progress.

Research and discussion questions

 * Do any distributed/decentralized wiki technologies exist?

Wikipedia

 * Wikis and education

title: Wikis


text:
Blogs

 * YouTube Video on Wordpress Blog Creation
 * YouTube help videos for blogger
 * PDF Handout on Edublog Creation

Write your first Blog Entry
Once you have created your blogging site, write your first blog entry. This can cover anything you feel is appropriate, but a few suggestions as to topics are listed below:
 * Reasons for choosing the blogging software you opted for
 * Initial thoughts on the use of blogs for assessment

You may find it useful to read the Tips how to write better blog texts from Sue Waters

Link in to your peers blogs using RSS RSS (Really Simple Syndication) is an important tool in the Web 2.0 arena. Further details on RSS (including the set up and creation of an RSS Feed reader) are available from the RSS page. In order to keep up to date with the blogs of other participants, link them to your RSS Feed Reader. As before, choose whichever tool you feel would be most appropriate for you. As part of this course, you and your peer will be asked to identify and informally interview an educator who is involved in the use of blogs in education. The interviewee can come from whichever country and organisation you and your peer find interesting. Examples of educational blogs and bloggers are proved below:

 * Resourcing the Curriculum: Blogs in Education - Provides an overview of Blogs/Blogging and then list a number of useful blogging sites and resources.
 * Blogs on Educational Blogging - Extensive list of educational blogs.
 * Blogged Website Educational Directory

Interesting Blogs Commentary - Will Richardson's expression is worth thinking aout: By its very nature, assigned blogging in schools cannot be blogging. It's contrived. No matter how much we want to spout off about the wonders of audience and readership, students who are asked to blog are blogging for an audience of one, the teacher. When the semester ends, "students drop blogging like wet cement." Richardson wants to teach students to write with passion, but he notes: I can't let them do it passionately due to the inherent censorship that a high school served Weblog carries with it. Is assessement disturbing learning with blogging? Could it be vice versa and how? Things you really need to learn is not so positive towards assessement: "Your school will try to teach you facts, which you'll need to pass the test but which are otherwise useless. In passing you may learn some useful skills, like literacy, which you should cultivate." What kind of assessment we need in education?

The incorporation of diaries and journals as learning and assessment vehicles into programmes of study within higher education has enabled the further growth of reflection, creative writing, critical thinking and meta-cognitive processes of students' learning. However, there is currently little research that aims to compare how different types of diary are used and for what specific learning and teaching purposes, so, with this in mind, a study was carried out to investigate digital diary use within a group of undergraduates, to some of whom the authors allocated Personal Digital Assistants (PDAs), which they used to contribute to a blog (digital diaries), and to some of whom hard-backed format (paper diaries) were given. This paper is the first of two from this study. The findings indicated that whilst students found both forms of diary acceptable and convenient, differences emerged in the way that the diaries were being used on a day-to-day basis, both in the frequency of entry and in the length of entries made. Throughout the study, the digital were used more frequently, although the entries were often brief and incomplete. Conversely, students completing the paper diaries made significantly fewer entries in total, but those that were made were longer and more discursive in nature. Further, it was found that the paper diaries possessed positive qualities related to handling and attractiveness that promoted more prolonged use, whilst the negative qualities of the digital diaries were linked to technical limitations. The implications of this work are considered in relation to more general notions of using dynamic devices to encourage students to engage in reflexive criticism. (Assessment & Evaluation in Higher Education)

I chose this blogging software because it is very convenient, easy to use, educational and it will benefit me as a student.

Using a blog is quite hard. You have to find a specific topic and you should know the facts about your topic. You have to put a lot of effort on your blog. You should be artisitc when it comes to design so that it is very eye catching. Blogging is also fun because you can learn and experience new things.

Assignment
What kind of assessment is supported and promoted in the use of Blogs and Blogging software?

Further Resources and Links
YouTube Video from CommonCraft on Blogs in Plain English

Educational blogging

Using blogs for Formative Assessement and Interactive Teaching

article at wikipedia

Back

title: Blogs


text:
User talk:Satunu

 Hello Satunu, and welcome to Wikiversity! If you need help, feel free to visit my talk page, or contact us and ask questions. After you leave a comment on a talk page, remember to sign and date; it helps everyone follow the threads of the discussion. The signature icon in the edit window makes it simple. To get started, you may

 * Take a guided tour and learn to edit.
 * Visit a (kind of) random project.
 * Browse Wikiversity, or visit a portal corresponding to your educational level: pre-school, primary, secondary, tertiary, non-formal education.
 * Find out about research activities on Wikiversity.

 * Read an introduction for teachers and find out how to write an educational resource for Wikiversity.
 * Give feedback about your initial observations
 * Discuss Wikiversity issues or ask questions at the colloquium.
 * Chat with other Wikiversitans on #wikiversity-en.

And don't forget to explore Wikiversity with the links to your left. Be bold to contribute and to experiment with the sandbox or your userpage, and see you around Wikiversity! --mikeu talk 12:03, 1 July 2009 (UTC)

title: User talk:Satunu


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User:Daniel Souza

Olá, meu nome é Daniel de Souza Telles, sou um geek militante do software livre, seguidor do manifesto cypherpunk, pirata em horas vagas, leitor de livros científicos e de ficção cientifico, e um amante do puro lirismo, de vez em quando leio ficção pura e romances, exclua Sidney Sheldon, Veríssimo, e outras merdas que encontramos por aí. Também mostro minha outra face nerd e vejo bastante seriados, filmes e animes, desde que os mesmos se enquadrem nos meus interesses. Tenho várias idéias e projetos de sucesso na cabeça, mas me faltam estímulos para os mesmos, talvez se alguém quiser dar uma mãozinha. Então prefiro ficar por aí experimentando os jogos do Kong, visitando blogs e atualizando o twitter, e colaborando casualmente para algumas wikis.

title: User:Daniel Souza


text:
User:Aalia-shan

'''well i'm Aalia i'm 17- year-old from KSA i like learning a lot about computers and hope to help if i can i also want to learn a third language i looove wikipedia and now i'll be a member of this great site so please help me and i promise i'll be a good student that's all thanx'''

title: User:Aalia-shan


text:
User:Weathermanin

I am based in Coimbatore in India. I have a Diploma in Electrical and Electronic Engineering from P.S.G Tech in Coimbatore. I am supposed to have a very high IQ but it has not helped much personally. I am a very good out of the box thinker and can handle a variety of subjects and situations with ease. You can try me at answers to difficult problem or situations. Any thing from new inventions to advice.

title: User:Weathermanin


text:
User:Mholanzi

The page I prefer may be found here.

title: User:Mholanzi


text:
File:Example 01-01.pdf

Summary
"Shave-and-a-Haircut" Expectation and Fulfillment or Surprise

title: File:Example 01-01.pdf


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User:Adambro/monobook.css

div.imagemap-inline div { display: inline; }

title: User:Adambro/monobook.css


text:
Opportunity Cost

Opportunity cost is the value of the next best alternative forgone as a result of making a decision. Opportunity cost is a function of scarcity. Because of scarcity, people are faced with trade-offs in how they use their limited resources. For example, devoting the scarce resource of time to study economics means less time devoted to sleep. If, from an individual perspective, studying economics and sleeping are the two best alternatives for spending a given hour of time, then the cost of each can be expressed as the value of the other. So, an hour spent studying economics has an opportunity cost of one hour of sleep. As in the above example, opportunity cost is a convenient way to express the value of an item or course of action that has no explicit monetary cost or price.

Opportunity Cost vs. Accounting Cost
Though the concept of opportunity cost is used in financial applications such as capital budgeting, it is not used in accounting or in financial reporting. Accounting uses the concept of historical cost for valuation purposes.

title: Opportunity Cost


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Talk:Microeconomics/The Effects of Taxation

"A marginal tax on the sellers of a good will shift the supply curve to the left until the vertical distance between the two supply curves is equal to the per unit tax; when other things remain equal, this will increase the price paid by the consumers (which is equal to the new market price),"

The vertical distance between the old supply curve and the new supply curve would equal the per unit tax only if the demand curve is perfectly elastic. Since this is not generally the case, then per unit tax is better explained as the vertical distance between the price consumers pay and the price firms receive from a transaction.

Additionally, does the supply curve shift to the left as the result of a sales tax? I think that the effect of a sales tax changes the quantity suppliers are willing to provide, making it a change in the quantity supplied along the supply curve, not a shift of the supply curve.


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Elasticity, Consumers, Producers, and Market Efficiency

Elasticity

In practical terms, elasticity refers to the responsiveness of the quantity demanded and supplied to changes in price. A more technical definition is that elasticity is the ratio of the percent change in one variable to the percent change in another variable. The ratio is expressed as the change in quantity divided by the change in price demanded or supplied.

Elasticity = % Change in quantity / % Change in price

The elasticity of a good determines the slope or "steepness" of its supply and demand curves.

Elasticity of Demand

The elasticity of demand tells us how consumers modify their consumption behavior in response to a change in price for a given good. If a change in the price of a good results in a drastic change in the quantity demanded, the demand for the good can be described as highly elastic. For example, if the price of a good drops by 1% and the quantity demanded increases by 80%, the good is described as elastic. Conversely, an inelastic good is one for which the quantity demanded remains little changed by a change in price.

In economics, the elasticity of demand is a degree of change in the quantity demanded of a product in response to its determinants, such as the price of the product, price of substitutes, and income of consumers.

Lipsey defined as the ratio of the percentage change in demand to the percentage change in the price.

Economists have divided the elasticity of demand in three main categories. Three types of elasticity of demand are:
 * 1) Price Elasticity of Demand
 * 2) Income Elasticity of Demand
 * 3) Cross-Elasticity of Demand

What does the elasticity of demand tell us about the nature of the good it is describing? Let's first start with a highly elastic good.

When the demand for a good is highly elastic, consumers make drastic changes to the quantity they demand in response to relatively small changes in price. Let's say the cost of a movie ticket increases from $10 to $11, an increase of 10%. Now lets assume that as a result of this change in price ticket sales decrease from 100 per day to 10, a decrease of 90%. The elasticity of demand for movie tickets is 90%/10%, or 9/1, making it highly elastic. The nature of this change in demand illustrates that consumers feel that going to the movies is something they can easily sacrifice in response to an increase in price. Goods with high elasticities of demand are often described as luxury goods; that is, things that consumers feel they can go without. They also may be goods that are readily available in the market place or have plenty of substitutes. For instance, consumers may substitute renting movies and watching them at home in response to rising movie ticket prices. They may even find other forms of entertainment such as saving their money to go to a baseball game or to attend a concert.

Conversely, when the demand for a good is highly inelastic, consumers respond very little to changes in price. Let's use water as an example. Let's assume that the price for a gallon of water increases from $10 to $11, a 10% increase. Now lets assume that as a result of this change in price the quantity of water consumed drops from 100 gallons per day to 99 gallons per day, a 1% decrease. The elasticity of demand for a gallon of water is 1%/10%, or 1/10, making it highly inelastic. The nature of this change in demand illustrates that consumers feel that water is not something they are readily willing to sacrifice in response to an increase in price. Goods with highly inelastic demands are often described as necessities; that is, things that consumers feel they cannot do without. Examples of goods commonly described as inelastic are food and housing. These goods may also have few substitutes in the market place. For instance, there are few substitutes for the various roles water plays in our everyday lives.


text: User:Renaissancee

title: User:Renaissancee