Saïd N Mahjoub

S Habli

H Bournot

& G Le Palec

THE NEAR FIELD IN THE MIXING OF A THREE-DIMENSIONAL INCLINED POLLUTANT JET WITH A CROSSFLOW

Keywords: experimental study, numerical simulation, inclined jet, PIV, turbulent flow, recirculation zone

An experimental investigation was carried out to study the structure of the flow field resulting from the interaction of an inclined pollutant jet with a crossflow. The study of the flow field was conducted in a wind tunnel test by means of particle image velocimetry (PIV) system. As the jet was discharged with a variable angle, the resulting flow has been found to be quite complex owing to its three-dimensional nature and the interaction between several flow regions. Results showed the dependence of the emerging jet flow structure on its ratio velocity and the Reynolds number. Extensive wind tunnel experimental results are presented; they concern the Kelvin-Helmholtz vortical structures and the effect of the velocity ratio v0/u∞ on the interacting zone. A three-dimensional numerical model with a second-order turbulent model (RSM) and a nonuniform grid system is used to examine the behavior of the emerging jet. The comparison of the numerical and experimental results gives satisfactory agreement.

INTRODUCTION

Interactions between cool/hot jets with crossflows are highly interesting due to their wide presence in several industrial applications. Active flow control, aircraft performance and stability, mixing augmentation, film and effusion cooling, etc., are some of these applications. Perhaps the most familiar example in everyday life would be smoke rising from a chimney into a crosswind. This comes after film cooling, which is a technique extensively used in turbomachinery [START_REF] Azzi | Film cooling predictions of simple and compound angle injection from one and two staggered rows[END_REF]. The use of film cooling has particularly increased as a solution for the present trend towards the implementation of higher inlet temperatures for the generation of higher power. In addition to their wide application, jets in crossflow are interesting due to the complexity of the flowfield they generate. In fact once discharged, the jet is rapidly deflected in the direction of the crossflow, giving rise to a kidney-shaped cross section, dominated by a counterrotating vortex pair (CVP). As the potential core of the jet ends as a cone, a mixing layer develops at the periphery, slightly bent in the direction of the crossflow.

The great practical relevance of the generated mechanisms inspired several experimental, numerical, and theoretical studies. After the interaction between the inclined jet and the mainstream, one of the most experimentally highlighted features is the formation of the counterrotating vortex pair, its origin, and the mechanism of its formation. [START_REF] Taylor | An investigation of inclined jets in a crosswind[END_REF] are some of the pioneers that dealt with this feature, the CVP. Consideration was given to a turbulent jet discharged into a turbulent subsonic crosswind, under a variable inclination (15 • -90 • ) and momentum ratio. The results were given in terms of the jet paths (based on the maximum total pressure), deflection and penetration, the lift loss, and the pressure distribution. A decrease in the jet's inclination (from the position normal to the crosswind) reduced all these features together with a downstream move of the pressure center. In Broadwell and Breidenthal's paper (1984), the CVP vortices were suggested to rise from the impulse associ- Reynolds stress, m 2 /s 2 Superscripts u i , u j velocity components along the -Reynolds average i and j directions Favre average ated with the jet. It is then a global feature of the far field, in which the CVP are convected downstream by the crossflow. More detailed experimental studies, concentrated on the near-field, suggested that the CVP vortices are generated by the vortex sheet emanating from the jet nozzles or pipes [START_REF] Moussa | The near field in the mixing of a round jet with a cross-stream[END_REF][START_REF] Andreopoulos | Experimental investigation of jets in a crossflow[END_REF][START_REF] Fric | Structure in the near field of the transverse jet[END_REF][START_REF] Kelso | An experimental study of round jets in cross-flow[END_REF]. [START_REF] Moussa | The near field in the mixing of a round jet with a cross-stream[END_REF] focused on the near-field, defined as the region of the flow that stretches from the jet exit to a distance of a few diameters downstream of this exit. The confrontation between the discharged jet and the surrounding mainstream, in this region, brings three main adjustments on the jet's progression, which are closely dependent on the geometry of jet exit boundaries. A pair of bound vortices embedded within the lee side of the jet boundary develops and helps accelerate the development of the turbulent and mean vorticity. A vortex-shedding system then takes place and is accompanied by an increase in the entrainment rate of the mainstream into the jet. In addition to these observations, calculations of mass, momentum, and vorticity fluxes have been made and proved that the vorticity flux is at the origin of the rapid stretching and tilting of the vorticity vector field in the near-field region.

NOMENCLATURE

The following papers did not focus on a specific feature of the resulting field of a jet interacting with a crossflow. Attention was rather paid to the overall developed dynamic structures, and their evolution and growth either under constant or variable parameters. [START_REF] Chu | Oblique turbulent jets in a crossflow[END_REF], for example, described the jet's motion in a moving oblique coordinate system in the case of an oblique turbulent jet in a uniform crossflow by means of a line-impulse model.

The experiments of [START_REF] Lee | Experimental study on the flow characteristics of streamwise inclined jets in crossflow on flat plate[END_REF] highlighted the overall flow features induced by a normal and streamwise 35 • inclined jets, discharged into a turbulent crossflow boundary layer under a variable velocity ratio. The examined features include the turbulent activity enhanced by small velocity ratios in addition to the bound vortices and the downstream complex three-dimensional flow, which develop simultaneously regardless of the injection ratio and the initial inclination of the jets.

The numerical investigations of [START_REF] Jansson | Numerical simulation of inclined jets in a crossflow using a Reynolds stress model[END_REF] focused on the film cooling effectiveness and the velocity fields in an attempt to evaluate the efficiency of modeling of the finite volume calculations on a "jet in crossflow" configuration. The model efficiency was established with reference to two different turbulence models, namely the standard k -ε model and a full Reynolds stress model (RSM) in addition to hot wire measurements. Near the walls, the viscous effects on turbulence were determined by means of a one-equation model, elaborated by [START_REF] Norris | Turbulent Channel Flow with a Moving Wavy Boundary[END_REF] together with a mixing layer approach. A similar modeling evaluation was carried out by [START_REF] Donohue | Experimental and numerical study of swept ramp injection into a supersonic flowfield[END_REF], but on the efficiency of experimental iodine fluorescence-based data, over a swept ramp injection. A satisfying level of agreement was observed, though with some deviations, generally in the range of 5%, but larger such as in the base of the ramp. This evaluating investigation could also reveal asymmetry of the resulting flowfield and ramp-generated vortices, in addition to the turning and mixing of the jet plume.

Laser Doppler velocimetry measurements were used by [START_REF] Santiago | Velocity measurements of a jet injected into a supersonic crossflow[END_REF] and [START_REF] Zhang | Measurements of a longitudinal vortex generated by a rectangular jet in a turbulent boundary layer[END_REF] for the examination of inclined jets in crossflow. While the jet was circular and discharged within a supersonic crossflow within the first work [START_REF] Santiago | Velocity measurements of a jet injected into a supersonic crossflow[END_REF] it was rectangular, pitched, skewed, and discharged into a low speed wind tunnel crossflow within the second paper [START_REF] Zhang | Measurements of a longitudinal vortex generated by a rectangular jet in a turbulent boundary layer[END_REF]. Attention was given to the developed vortical structures in both works with a further exploration of the mean and fluctuating quantities within the first one and comparison of the developed vortices against the circular jet case in the second.

Further experimental techniques were used for the exploration of inclined jets in crossflow, such as the plane laser light illumination [START_REF] Nakabe | Visualisations of obliquely discharged jet flows and their heat transfer enhancement regions[END_REF], the planar laser-induced fluorescence (PLIF) [START_REF] Rivero | Organized motions in a jet in crossflow[END_REF], hot wire anemometry [START_REF] Milanovic | Highly inclined jet in cross-flow[END_REF], etc. [START_REF] Nakabe | Visualisations of obliquely discharged jet flows and their heat transfer enhancement regions[END_REF] combined laser light illumination, fluorescent dyes and color-to-temperature conversion of thermo-chromatic liquid crystal sheets to characterize the velocity field and the generated heat transfer. [START_REF] Rivero | Organized motions in a jet in crossflow[END_REF] used the PLIF visualizations to identify and provide plausible origin to the established vortical structures, namely the CVP and upright vortices, folded vortex rings, horseshoe vortices, and the newly observed handle-type structures. As to [START_REF] Milanovic | Highly inclined jet in cross-flow[END_REF], they focused rather on the velocity field and the generated turbulent stresses. The experiments carried out by [START_REF] Taslim | Discharge coefficient measurement for flow through compound-angle conical holes with cross-flow[END_REF] paid attention to the impact of the jets' inclination, the presence or not of a surrounding crossflow, the pressure ratio and the shape of the discharging hole on the coolant blowing rate, and consequently on the cooling effectiveness.

In the last decade, several numerical studies, based on Large Eddy Simulations (LES) [START_REF] Wegner | Comparative study of turbulent mixing in jet in crossflow configurations using LES[END_REF][START_REF] Guo | Large eddy simulations of film cooling flows[END_REF], were carried out on inclined jets in crossflow. The simulations of [START_REF] Wegner | Comparative study of turbulent mixing in jet in crossflow configurations using LES[END_REF] were validated against the experimental data of [START_REF] Andreopoulos | Measurements in a jet-pipe flow issuing perpendicularly into a cross stream[END_REF] and [START_REF] Andreopoulos | Experimental investigation of jets in a crossflow[END_REF]. [START_REF] Wegner | Comparative study of turbulent mixing in jet in crossflow configurations using LES[END_REF] checked whether active or passive means, including the jets' inclination, may help in controlling and enhancing the resulting mixing process, its vortical structures, and the induced secondary motion. [START_REF] Guo | Large eddy simulations of film cooling flows[END_REF] investigated the cooling performance of the discharged jets, the turbulent flow structures they produce, and the induced vortex dynamics. Particular attention was dedicated to the counter-rotating vortex pair (CVP), its first appearance, magnitude, and location under a variable injection ratio. In a prior paper, [START_REF] Guo | Flow characteristics of turbulent jets injected obliquely in crossflow[END_REF] used SIPLEC algorithm, body-fitted coordinates, the wall function method, and the RNG k -ε turbulence model for the modeling of the same configuration, namely a variably inclined jet in crossflow responding to different injection ratios. Once validated against experimental measurements, the model could describe the jet trajectories, define the separation events in the lee of the jet exit and allowed analyzing the different developing mechanisms. The numerical threedimensional simulation of [START_REF] Yang | Three-dimensional numerical simulation of an inclined jet with crossflow[END_REF] added the impingement mechanism within the jet in crossflow model to assess the generated heat transfer. The analysis is based upon the k -ε turbulence model and its associate wall function in addition to a control-volume-based finite-difference method with power-law scheme. [START_REF] Jia | A numerical and experimental investigation of the slot film-cooling jet with various angles[END_REF] combined numerical simulations and laser Doppler velocimetry (LDV) experiments on a jet variably inclined and sent at different injection ratios in an attempt to optimize the film cooling performance of the discharged jet. The cooling performance was determined in terms of the induced recirculation bubble. [START_REF] Jessen | Evolution of jets effusing from inclined holes into crossflow[END_REF] assessed this cooling performance experimentally by means of particle image velocimetry (PIV) measurements, in terms of the developed turbulent flow structures and vortex dynamics, under variable injection, density, and mass fraction ratios. A higher mass flux ratio enlarges the size of the recirculation region, leading to a more pronounced entrainment of hot outer fluid into the wake of the jet and a higher density ratio enhances the lateral spreading of the coolant downstream, which is crucial for the cooling efficiency.

The present paper checks some previous results through comparisons, and tries to extend them. Based upon PIV-based experiments, our investigation assesses the impact of both the jet inclination and the velocity ratio on the efficiency of mixing of a variably inclined jet within a uniform crossflow. The measured data, in terms of velocity fields, are combined with three-dimensional numerical results based upon the RSM (Reynolds stress model) turbulence closure model and a nonuniform grid system, to account for the jet's inclination impact on the generated field. Once validated, the effect of the jet's inclination impact is generalized in order to investigate both the thermal field and the dispersion process of the pollutants embedded within the discharged jet. Similar results are likely to offer engineers an extra consideration for practical applications of an inclined jet in crossflow, particularly for applications with direct impact on environmental issues.

PRESENTATION OF THE PROBLEM

Intuitively simple, the topology of an inclined jet injected into a transverse flow is in fact very complex. In fact, after its injection, the jet fluid is deflected in the direction of the crossflow as its cross section quickly assumes a kidney shape, dominated by a pair of counter-rotating vortices (Fig. 1 • Horseshoe swirls (along the wall); they are similar to that which appears near the junction of a wing and a plane plate (I)

• Strongly three-dimensional wake swirls resembling a Von Karman street downstream of a circular cylinder (III) (from jet to wall). The physical analogy between these two phenomena is only very partial because, in addition to the curvature of the jet, there is no production of vorticity on the boundary between the jet and the transverse flow, contrary to the wall of a cylinder where the condition of no-slip implies a production of vorticity.

• The contrarotating vortices pair (II), around which the flow organizes. The origin of this pair of contrarotating swirls (CVP for "counter-rotating vortex pair") was the subject of many experimental [START_REF] Kelso | An experimental study of round jets in cross-flow[END_REF] as well as numerical [START_REF] Cortelezzi | On the formation of the counter-rotating vortex pair in transverse jets[END_REF] investigations. It was thus established that the CVP appeared under the combined effects of the crumpling, the slope, and finally of the rolling up of the natural swirling structures of the jet under the effect of the transverse flow.

• Swirls of the sheared layer all around the jet.

Another dividing of the flow field is available in the literature and it depends on the nature of the fluid in the entire domain: near-field mixing, which is usually controlled entirely by the initial conditions, such as geometry of the jet, exit velocity, initial density difference, turbulence intensity, and velocity distribution in the supply pipe [START_REF] Fischer | Mixing in Inland and Coastal Waters[END_REF]. It is a region of rapid mixing and dilution caused by turbulence generated by the discharge.

Zone of flow establishment: This region refers to the distance immediately after the end of the nozzle, where a flow transition occurs between the efflux velocity profiles seen in the discharge pipe to the Gaussian profile exhibited in the jet [START_REF] Jirka | Technical Guidance Manual for Performing Waste Load Allocations, Book III[END_REF]. The fluid is "unaware" that it is suddenly in a different environment, and it takes some distance to adjust to the new flow characteristics.

Far-field mixing occurs beyond the near-field mixing process, where dynamic source characteristics lose their importance and ambient properties begin to control trajectory, advection, and mixing [START_REF] Roberts | Sea outfalls, in Environmental Hydraulics[END_REF].

EXPERIMENTAL SETUP

Measurements were carried out in a wind tunnel. This tunnel had a test section with a speed range of about 0-16 m • s -1 . The experiments were performed in an open circuit discharging to atmosphere outside the laboratory and with a parallel-sided, closed working section 3 m in length and 0.2 m × 0.3 m in cross section. For optical access, one side is made of Pyrex; the interior of the wind tunnel is painted black to reduce reflections. In all experiments, the airflow is seeded with oil droplets of approximately 0.8 μm diameter, and introduced at the ambient temperature into the tunnel nozzle. The jet was produced by means of a smooth pipe and 10 mm diameter (d) through which air at constant temperature was discharged. The pipe was positioned at the upstream end (20 cm from the tunnel nozzle) and along the centerline of the tunnel oriented at an angle of 60 • to the crossflow. The jet is seeded with approximately 1 μm diameter glycerin particles (seeding density ≈30 particles ml -1 of pure jet fluid). The turbulence intensity level of the crossflow was less than 0.2%. The Reynolds numbers for flow at the entry of the wind tunnel (Re F = u ∞ H T /υ) were in the range 2.7 × 10 4 -2.2 × 10 5 while within the jet the Reynolds numbers (Re = v 0 d/υ) were in the range 1.1 × 10 3 to 6 × 10 3 .

The particle image velocimetry system (Fig. 2) is based upon a TSI Power View system, including a 50 mJ dual YAG laser which produces two plan luminous pulses, the duration of one ranging from 5 × 10 -9 to 10 -8 seconds, a Power View 4M high resolution cross-correlation camera (2 k × 2 k resolution, 12 bits), a synchronizer, and "Insight" Windows-based software for acquisition, processing, and post-processing. This software allows the synchronization of pulsations according to the observed phenomena, and the adjustment of the time step between two images. This time step was 70 μs. In order to avoid errors, the velocity vectors were calibrated at 130 μm/pixel FIG. 2: Experimental setup: PIV. and limited to the representation of the velocity field in the regions where the luminance was strong enough.

Laser pulses from a neodymium-doped yttrium aluminum garnet (ND-YAG) laser were expanded to form a thin light sheet using a cylindrical lens. The light sheet was brought from the top of the wind tunnel using a 45 • mirror. Because of this arrangement, a shadow area upstream from the pipe was created where it was impossible to take measurements.

The light scattered from the seeded particles was captured and the resulted scattering signal is collected by an interline transfer CCD camera. The camera was oriented perpendicular to the plane of the sheet. The frame transfer capability of this camera allows each of the two closely spaced laser sheet pulses to be captured in a separate image. The collected images were transferred to the control computer. A target image was used to provide accurate scaling of the flow.

However, after the vector field is initially processed, filters are applied to the data to eliminate spurious vectors, and these vectors are linearly interpolated. Then the vector field is reprocessed. This permits the use of a crosscorrelation PIV algorithm [START_REF] Hasselbrink | Transverse jets and jet flames: Structure, scaling and effects of heat release[END_REF], which eliminates directional ambiguity and yields improved resolution over single-image autocorrelation techniques. In this way, the in-plane loss-of-correlation is minimized, and therefore the chance of valid vector detection is maximized.

Once an ensemble of instantaneous vector fields has been obtained from a set of images, several postprocessing calculations are made. Raw data are cast from pixel units into physical coordinates, and turbulence statistics and derived quantities such as vorticity and strain rate are calculated, using custom software. The final fields were averages performed with 200 successive acquisitions.

For each point, experimental uncertainties are estimated with the following criterion:

V max -V min V av
where V max , V min , and V av , respectively are the maximum velocity, the minimum velocity, and the average velocity measured during all the process. The uncertainties were about 5%. The estimates were inferred from estimated inaccuracies in the calibration data and from the observed scatter in the measurements.

The velocity profile of the main flow was measured with a hot wire anemometer together with a high precision electronic pressure transducer. With the help of an on-line micropressure calibration system, the uncertainty in the free-stream velocity was estimated to be as large as 3% of a reading.

The origin of the wake coordinate system is fixed on the axis of the pipe. The x axis is directed downstream, the y axis is perpendicular (defined as transverse) to the flow direction and the pipe axis, and the z axis lies along the axis of the pipe (defined as spanwise).

The visualized flow patterns and the measured velocities on the vertical symmetric plane are presented to highlight the interactions occurring between the discharged jet and the oncoming as well as the penetration and spreading of the jet. For each flow setting, PIV measurements were conducted on the cross plane located at z = 0.

The injection ducts are circular pipes whose diameter is equivalent to d = 10 mm. The injection hole resulted from the intersection of the injection pipe with the wind tunnel is ellipse shaped with d and D = d/(sin α) as minor and major diameters, respectively.

NUMERICAL STUDY

Consider a circular round jet of a pollutant of diameter d emitted through a wall with an ejection velocity v 0 , and a temperature T 0 . This jet is subjected to a transverse flow with a uniform velocity u ∞ and a temperature T ∞ . The ratio between the two velocities, R = v 0 /u ∞ is obtained by varying u ∞ whereas v 0 is maintained constant. Consideration is given to a steady, three-dimensional and turbulent flow. The equations describing this flow are obtained in a system of Cartesian coordinates, the origin of which are situated in the center of the section of ejection of the jet (Fig. 1). We have the following: Continuity:

∂ρ ∂t + ∂ (ρũ i ) ∂x i = 0 (1)
Momentum equations:

∂ (ρũ i ) ∂t + ∂ (ρũ j ũi ) ∂x j = - ∂p ∂x i + ∂ ∂x j μ ∂ ũi ∂x j -ρu i u j + (ρ ∞ -ρ) gδ ij (2)
Energy equation:

∂ ρũ j T ∂x j = ∂ ∂x j μ Pr + μ t σ t ∂ T ∂x j (3)
Species equations:

∂ ρũ j f ∂x j = ∂ ∂x j μ Sc + μ t σ f ∂ f ∂x j (4)
The introduction of the fluctuating sizes makes this system open. Its closing requires the use of a turbulence model which makes it possible to obtain a number of equations equal to the number of unknown parameters. Mahjoub ït al. (2003) show that the three first-order models (the standard k -ε model, the k -ε RNG model, and the realizable k -ε model) render identical results in the upstream and far-downstream regions of the jet. However, only the second-order model is shown to give good results in the exit region and in the trailing zone of the jet. Based on this last result, we choose this second-order closure model (also called Reynolds stress model) in this work. So the following equation is solved:

∂ ∂x k ρũ k u i u j = ∂ ∂x k μ ∂ ∂x k u i u j -ρ u i u k ∂ ũj ∂x k +u j u k ∂ ũi ∂x k +D T ij +G ij +φ ij +ε ij (5)
where

∂/(∂x k ) ρũ k u i u j = C ij ; ∂/(∂x k )xμ∂/(∂x k ) × u i u j = D L ij ; u i u k (∂ ũj )/(∂x k ) + u j u k (∂ ũi )/(∂x k ) = P ij . C ij being the convective term. D L ij , P ij , D T ij , G ij , φ ij , ε ij
are, respectively, the molecular diffusion, the stress production, the turbulent diffusion, the buoyancy production, the pressure strain, and the dissipation rate [START_REF] Schieste | Modélisation et simulation des écoulements turbulents[END_REF].

Equations of turbulent kinetic energy (k) and dissipation rate of kinetic energy (ε) associated with the secondorder model are defined as

∂ (ρũ j k) ∂x j = ∂ ∂x j (μ+μ t ) σ k ∂k ∂x j + 1 2 (P ii +G ii )-ρε (6) ∂ (ρũ j ε) ∂x j = ∂ ∂x j (μ + μ t ) σ ε ∂ε ∂x j + C ε1 1 2 ε k P ii -C ε2 ρ ε 2 k (7)
and

P ii = 2μ t ∂ ũi ∂x i 2 , G ii = 2 β g i μ t σ t ∂ T ∂x i , μ t = C μ ρ k 2 ε
The used constants are defined in Table 1.

The boundary conditions associated with the above system of differential equations are summarized in Table 2.

NUMERICAL PROCEDURE

Several important problems arise from the numerical simulation of this last system of equations. The topology of the flow requires a very fine meshing in a great part of the domain. In order to describe exactly any temperature or mass fraction variations, particularly near the jet, we adopted a nonuniform meshing, strongly tightened near the jet (Fig. 3).

The numerical code uses the finite volume method, the solution of equations being based on the algorithm SIM-PLER proposed by [START_REF] Patankar | A calculation procedure for heat, mass and momentum transfer in three dimensional parabolic flows[END_REF]. For the obtained algebraic equations we use an implicit scheme. The convection terms are interpolated from the values at the center of every face of the control volume, with a second-order upwind scheme, and the discretization of the diffusion terms is made with a second-order finitedifferences method. The elimination method of Gauss associated with an under-relaxation technique is used to solve the resulted tridiagonal matrix. The iterative process is stopped when the convergence criterion defined as FIG. 3: Schematic presentation of the grid at the symmetry plane.

f m+1 -f m f m+1 ≤ 10 -5 (8)
is satisfied. In Eq. ( 8), f stands for velocity components, turbulent kinetic energy, and its dissipation rate, while m is the iteration number.

RESULTS AND DISCUSSION

Figure 4 represents the evolution of an inclined jet characterized by a Reynolds number equal to 6000 (at rest flow) [START_REF] Demuren | Three dimensional numerical calculations of flow and plume spreading past cooling towers[END_REF] [START_REF] Demuren | Three dimensional numerical calculations of flow and plume spreading past cooling towers[END_REF] Figure 5 presents the evolution of a jet issuing at an angle of 60 • , deflected in the direction of the crossflow. In the periphery of the jet, as the potential core of the jet ends as a cone, a mixing layer develops, slightly bent in the direction of the crossflow. The resulted flow field is quite complex. Accurate predictions of the flow have been difficult to obtain, particularly in the near-field of the injected jet. In fact, the flow field is characterized by a spectrum of vortical structures including the wake vortices and the shear layer vortices. A sharp velocity gradient is detected upstream of the jet while a "wake" region develops downstream of the jet. Vortices on the leeward edge of the jet are observed, and the highest velocity gradient is associated with these vortical structures.

Jet hole ũ = v 0 cos α, T = T 0 f = f 0 k 0 = 0 -3 v 2 0 ε 0 = k 3/2 0 /0.5d ṽ = v 0 sin α,
w = 0 Crossflow ũ = u ∞ , T = T ∞ f = 0 k ∞ = 0.0005 u 2 ∞ ε ∞ = k 3/2 ∞ /0.2H T ṽ = 0,
w = 0 Ground ũ = 0, ∂ T ∂y = 0 ∂ f ∂y = 0 k = 0 ∂ε ∂y = 0 ṽ = 0, w = 0 Other ∂ ũ ∂n = 0, ∂ T ∂n = 0 ∂ f ∂n = 0 ∂k ∂n = 0 ∂ε ∂n = 0 boundaries ∂ṽ ∂n = 0,
Streamlines on the symmetry plane are also shown in Fig. 5, representing the path taken by the jet fluid as it interacts with the crossflow. Note that the jet is not symmetric about the mean streamline. The jet appears thinner on the upstream side of the streamline and thicker on the downstream side. of the wall shear stress.The normal injection of the jets is at the genesis of the observed greater penetration of the jet and the greater mixing between the jet and the mainstream. The blocking effect of the jet on the crossflow is significantly decreased due to the streamwise inclination. On the windward side of the jet exit no separation can be identified. The crossflow is only slightly deflected by the jet flow. The jet hardly penetrates into the crossflow and barely separates at the leeward edge of the hole. On the leeside of the jet exit the spanwise rollers originating from the trailing edge of the hole develop with a similar pattern as for the normal injection case. Their strength and the size of the affected domain, however, are smaller. Due to the reduced inclination angle the generation of vorticity is obviously reduced. The streamwise inclination then reduces the vertical jet velocity.

The confrontation of the calculated and measured results relatively to the longitudinal velocity component ũ (Fig. 7) gives a satisfying matching along all the variation of the feature for the both cases (α = 90 • , α = 60 • ). The results processed with the RSM model are closer to the experimental data which suppose that the second-order model is more adequate for the description of the experiments (Mahjoub ït al., 2003). The results coincide and comfort the obtained validation.

In Fig. 8, we proceeded in the same way with the vertical velocity component ṽ by superposing the experimental and the numerical results. Here, we do not obtain a total matching as with the longitudinal velocity. Just for the case of α = 90 • , we note a slight lack of experimental points. According to the above-discussed confronta-FIG. 7: Mean ṽ-velocity profiles at the plane of symmetry z = 0 and R = 2.3 at y = 0.0025 m with different injection angle α.

tions of the velocity components, and in accordance with the better description of the experiments with the RSM model, we can then conclude that our numerical modeling is acceptable and models well the experimental configuration of the inclined jet issuing within an oncoming crossflow.

We compared in Fig. 9 our numerical results to the experimental data of [START_REF] Crabb | A round jet normal to a crossflow[END_REF], obtained by hotwire anemometry. The evolution of the normal velocity ṽ is given in the symmetry plane (z = 0), for various injection angles (α = 90 • , α = 60 • , α = 45 • , α = 30 • ) and for a velocity ratio equivalent to R = 2.3 for y = 0.0025 m.

This figure shows the development of the jet near the ejection zone. For various injection angles, the profile of the velocity is uniform and symmetrical on the outlet side of the jet. The weaker the jet injection angle, the weaker the velocity. In fact, when the inclination angle is weak, the jet has the tendency to attach to the wall. It is well seen that for α = 90 • , the jet penetrates further in the transverse flow whereas for α = 30 • the jet "is crushed" by the crossflow.

Figure 10 shows the variation of the mean longitudinal velocity ũ according to the y distance for various posi-FIG. 8: Mean ũ-velocity profiles at the plane of symmetry z = 0 for R = 0.5. tions x, in the symmetry plane (z = 0): The profiles are obtained for a velocity ratio equal to R = 0.5 and various injection angles α The first three profiles correspond to x positions located at the top of the exit section and indicate a deceleration of the flow. The velocity increases tremendously for the weaker inclination at low and fixed values of y, i.e., near to the exit section of the jet. The last three profiles correspond to positions located downstream of the jet exit and indicate an acceleration of the flow in the wake region. The results are compared with those of [START_REF] Andreopoulos | Experimental investigation of jets in a crossflow[END_REF]. For the position x = 0.02 m, measurements of [START_REF] Bergeles | The near field character of a jet discharged normal to a main stream[END_REF] are also included within the comparison. The mean longitudinal velocity profiles show a peak which is considered as a locus of the jet trajectory. The peak's location is shifted downstream (increasing y) when the inclination angle decreases. Good agreement with the experiments is clearly indicated on this figure.

The study of the transverse component velocity allows determining the three-dimensional aspect of the considered flow. Figure 11 and for a velocity ratio equivalent to R = 2. The common feature between the plotted profiles is the alternation of a negative portion then of another positive. In fact, while emerging from the tube, the jet brings a dis-turbance to the transverse flow, which results in swirls into a horseshoe. These swirls turn on both sides of the jet column by intertwining; giving rise to a positive direction speed on the one hand and a negative direction speed on the other hand. We notice that the more we approach the edge downstream of the jet, the weaker the recorded gradient. We note also that the transverse com-ponent velocity decreases with x, which reveals that the more we move away from the jet, the less the training of the transverse current influences the flow. The 0.04, 0.05 and 0.06 m) under a constant velocity ratio equivalent to 5. The average swirl issued from the jet is reorientated and packed up in a pair of swirls, which limits the surface of the jet under the effect of the transverse flow. Turbulence causes the training of the deviated jet and the majority of the transverse fluid in the wake region. This counter-rotating vortex pair is much more intense than the horseshoe swirl, leading to the formation of a kidney-shaped swirl [START_REF] Moussa | The near field in the mixing of a round jet with a cross-stream[END_REF][START_REF] Foss | Interaction region phenomena for the jet in a crossflow[END_REF]. The counter-rotating vortex pair is primarily a manifestation of the field of the mean flow induced by the initial impulse of the jet. It starts to take form in the near field, as indicated on the figure, and becomes dominant in the far field. This point was elucidated by [START_REF] Broadwell | Structure and mixing of a transverse jet in incompressible, flow[END_REF]. The trajectory of the jet is conditioned by two elements: the movement tending to move the fluid away from the wall in the transverse direction, resulting from the initial impulse or the direction from the jet, and the bearing movement in the direction of the transverse flow [START_REF] Coehlo | The dynamics of the near field of strong jets in crossflows[END_REF].

In this part, we considered a fume jet discharged at the temperature of 110 • C within an air flow at a temperature equal to 18 • C. The fume is composed as follows: 20.9% carbon dioxide (CO 2 ), 76.9% nitrogen (N 2 ), 1.8% oxygen (O 2 ), 0.4% sulphur dioxide (SO 2 ).

Figure 13 to distance z for various emplacements x and a velocity ratio R = 5. For the positions x = 0.02, 0.03, 0.04, and 0.05 m, the profiles present two peaks corresponding to the centers of the pair of swirls. The latter adopts the kidney shape caused by the longitudinal vortices. The presence of the swirls pair is remarkable for the position x = 0.02 m. The two peaks attenuate and disappear for x = 0.06 m. Beyond the latter the temperature decreases.

We traced similarly in Fig. 14 the evolution of the temperature but at a single position x and at different levels y. The presence of the swirls pair is remarkable for the position y = 0.02 m. At y = 0.01 m, y = 0.015 m, we note only a slight dissymmetry of the foyers. This asymmetrical character and its existence in spite of the configuration's symmetry and its cohabitation with the symmetry under certain conditions were the subject of certain studies, though not too many. Those of [START_REF] Smith | Mixing, structure and scaling of the jet in crossflow[END_REF] and [START_REF] Yuan | Large-eddy simulations of a round jet in crossflow[END_REF] are included in that group since [START_REF] Yuan | Large-eddy simulations of a round jet in crossflow[END_REF] showed the existence of asymmetry for the scalar instantaneous field of the concentration in various transverse plans: They noted it on contours of the transverse vorticity. [START_REF] Smith | Mixing, structure and scaling of the jet in crossflow[END_REF] suggested that this character can exist even for the realized structures and this, under certain conditions, applied to the flow.

In ity ratio equivalent to R = 2. When the height y increases, the maximum of temperature is shifted far downstream of the jet. The curve created by the transverse flow reveals a lateral bending of the jet, on both sides, caused by the three-dimensional flow. The dispersion of the temperature is faster in the three-dimensional case than it would be in a two-dimensional case because of the additional mixture induced by the transverse swirls. The temperature peak is more obvious at higher levels (higher y) and at larger inclinations α.

In Fig. 16, we traced the isotherms in the central plan (z = 0), for a velocity ratio R = 2 and for various injection angles α This figure shows the well-known Gaussian distribution and reveals a more significant wall reattachment under weaker injection angles.

In Fig. 17, we analyzed the influence of the velocity ratio R (R = 0.5, 2, 1) over the temperature distribution in the symmetry plane z = 0, at a height equivalent to y = 0.0025 m and under an inclination angle of α = 60 • . In the interval -0.01 m ≤ x ≤ 0.01 m, the pollutants' temperature attains the lowest peak under the lowest rate of the transverse flow (R = 0.5). In fact, under these circumstances, the flow is constrained against the injection wall. The mixing process is consequently enhanced near the injection wall, leading to a significant decrease in the pollutant's temperature. When we move far downstream, the most significant temperature peak is still obtained under the lowest injection rate (R = 0.5). In fact, under this same rate, the flow is confined close to the injection wall and is oriented downstream. The jet plume is then less dispersed in the vertical direction than under higher ratios. The temperature of the jet plume is consequently further preserved justifying the higher registered temperature peak.

In Fig. 18, we analyzed the influence of the injection angle (α = 30 • , 45 • , 60 • , 90 • ) over the longitudinal distribution of the temperature in the symmetry plan z = 0 at a height equivalent to y = 0.0025 m and under a velocity ratio equal to R = 2. The temperature peak is attained over a whole stage, which is larger and slightly higher under weaker inclination angles. Far downstream, the highest thermal peak is also attained under the weakest initial inclinations (α = 30 • ) due to the confinement of the flow close to the wall. Figure 19 represents the distribution of the mass fraction of carbon dioxide under R = 2, at y = 0.0135 m and at various lateral locations (z = etc.). The pollutant's mass fraction decreases as one moves away from the jet exit section along the z direction due to the further pronounced dispersion process along this direction. We also note that the peak of the pollutant's mass fraction is shifted further downstream as the jet is less straightened. This is due to the further longitudinal impulse provided by the weaker inclination angles, as further emphasized in Table 3. At z = 0.02 m and z = 0.025 m, the dispersion process of the pollutant is already pronounced, justifying the weakness of the mass fraction of the carbon dioxide.

CONCLUSION

We have examined in this paper the dynamic and thermal fields as well as mass transfer generated by the interaction of an inclined jet with an oncoming crossflow. This study has been conducted both experimentally by means of the PIV technique and numerically by means of the finite volume method together with a turbulent closure model. The paper presents a three-dimensional experimental study of an inclined circular turbulent polluting jet issuing transversely into a uniform air stream. The dynamic field of a turbulent jet issuing transversely with velocity v 0 into a uniform air flow with velocity u ∞ is examined as a function of the velocity ratio R = v 0 /u ∞ . We also examined the structural behavior of the flow at different locations of the domain. The complexity of the observed vortical structures in the wake region as well as their interaction with the jet as it bends over after emission are discussed. Attention was also given to the Kelvin-Helmholtz vortex structures, established due to peripheral instabilities. We also studied the effect of the jet inclination angle on the various flow structures. The inclination angle of the jet is an important parameter that controls the development of the flow structures and the penetration and spreading of the jet. The results of a normal and an inclined jet in crossflow are performed to study the effect of the jet inclination on the penetration on the crossflow. In the perpendicular injection case a rather large separation region is found at the leading edge of the jet hole; whereas in the streamwise inclined injection cases no separation is observed. Compared with the normal injection case at the same blowing ratio, the streamwise inclination weakens the jet-crossflow interaction significantly. We also determined the distribution of the temperature and the mass fraction near the jet and downstream of it and examine the dispersion of a hot pollutant under the influence of the velocity ratio R = v 0 /u ∞ . The obtained results show mainly that the temperature of the pollutants is low when the velocity of the transverse flow is high because, in this case, the crossflow prevails in front of the jet flow and high temperature gradients are observed near the exit section of the jet. Moreover, turbulence is sufficiently significant to allow a better dilution of pollutants. The different plotted profiles and contours of the temperature showed that increasing the initial streamwise inclination angle highly affects the temperature. This impact is expressed through the development of a further vertical, longitudinal, and lateral diffusion of the heat contained within the potential core of the emitted jet. This diffusion allows a better mixing in these directions and results in a quicker homogenization of the global thermal field. The same trend is adopted by the mass fraction of the fume contained within the jet nozzle since it is lifted when its initial inclination is increased. That also limits the propagation of the fume in the longitudinal direction and then controls its dispersion on it. We can then conclude that the initial inclination angle highly affects both the thermal and mass transfer variations that result from the interaction of the emitted jet within the crossflow.

  FIG. 1: Scheme of the existing swirling structures of the interaction of an inclined jet and transverse crossflow.

  FIG. 4: (i)Mean velocity field, (ii) mean vorticity field, (iii) field structure for α = 60• , v 0 = 9 m • s -1 , u ∞ = 0 m • s -1 .

Figure 6

 6 FIG. 5:Various structures of an inclined jet.

  FIG. 9: Mean w-velocity profiles for R = 2 and α = 60 • at y = 0.02 m.

FIG. 10 :

 10 FIG. 10: Cross-sectional contours of the temperature at six planes and R = 5 = 60 • .

FIG. 11 :

 11 FIG. 11: Profiles of the temperature at y = 0.02 m, for R = 5 and α = 60 • .

  FIG. 13: Cross-sectional contours of the temperature at three planes and R = 2.

  FIG. 14: Temperature contours at the plane of symmetry z = 0 and R = 2.

FIG. 16 :

 16 FIG. 16: Profiles of the temperature at y = 0.0025 m and z = 0 for various inclined angles (R = 2).

FIG. 17 :

 17 FIG. 17: CO 2 mass fraction profiles at y = 0.0135 m for R = 2.

TABLE 1 :

 1 Constants of the second-order model

	C ε1	C ε2	σ k	σ ε
	1.44	1.92	0.82	1.0

TABLE 2 :

 2 Boundary conditions

	Boundaries	Velocity	Temperature Mass fraction	Kinetic energy	Rate of dissipation

TABLE 3 :

 3 Position of maximal values of the mass fraction according to x and z directions

	α	z	x	Maximal mass fraction
	90 •	0.005	0.484848	0.122
	Mahjoub et al. (2003)	0.01	0.767677	0.089
		0.015	1.9697	0.048
			2.60606	0.021
	60 •	0.005	0.0163636	0.122605
		0.01	0.0172727	0.0982105
		0.015	0.0236364	0.0425939
			0.0161479	0.0518182
	45 •	0.005	0.026061	0.185224
		0.01	0.030303	0.151212
		0.015	0.053636	0.0603705
			0.108788	0.0195276
	30 •	0.005	0.0515151	0.122965
		0.01	0.0706061	0.0806713
		0.015	0.11303	0.0323078
			0.115152	0.0107631

FIG. 19: CO 2 mass fraction profiles at y = 0.0135 m for R = 2.


Female, Ph. D Belcaid Aicha
email: belcaid_aicha@yahoo.fr

Le Palec Georges

Draoui Abdeslam

Numerical and experimental study of Boussinesq wall horizontal turbulent jet of fresh water in a static homogeneous environment of salt water *

Keywords: wall jet, turbulence, Boussinesq approximation, k ε model, buoyancy, cling length

come

Numerical and experimental study of Boussinesq wall horizontal turbulent jet of fresh water in a static homogeneous environment of salt water Aicha Belcaid, Georges Le Palec, Abdeslam Draoui

Introduction0 F

A wall turbulent jet is an effective means to promote high rates of heat and mass exchange especially in the near field. This jet configuration has been widely used in coastal sewage disposal projects. Indeed, it is necessary to ensure rapid mixing of the jet with the ambient fluid to minimize the impact on the marine environment and prevent a return flow of the jet towards the injection source. On this point, buoyant wall jets have a larger mixing zone than free jets and therefore it is possible to improve the initial dilution compared to the later. For a free turbulent jet, the expansion rate is the same in each normal direction to its centerline trajectory. However, it is not the case for wall turbulent jet.

When a wall turbulent jet is injected from sources of buoyancy and momentum, both effects of buoyancy and wall boundary are taken into account. In this case, the jet clings to the wall (obstacle) under the Coanda effect (definition in Section 1.1).The difference of pressure causes the jet cling to the wall and slip for some distance, called the cling length, before it leaves the floor. The Coanda effect of buoyant wall jets can increase the mixing zone between jet fluid and ambient so that the pollution in the near field can be effectively diluted. Singh and Ramamurthi [START_REF] Singh | Formation of Coanda jet from sharp-edged swirl nozzle with base plate[END_REF] investigated experimentally a gas turbulent plane wall jet. They used PIV technique to determine the conditions for which the jet would be affected by Coanda effect. Sharp and Vyas [START_REF] Sharp | The buoyant wall jet[END_REF] gave the relations between the cling length and densimetric Froude number through experimental research and theoretical analysis. Combining with Sharp's experimental data and theoretical results, Huai et al. [START_REF] Huai Wen-Xin | Numerical simulation of horizontal buoyant wall jet[J][END_REF] applied the realizable - k ε model to si- mulate horizontal buoyant wall jet and they gave the results of cling length, centerline trajectory and tem-perature dilutions at several sections. Li et al. [START_REF] Huai | Large eddy simulation of flow structure in the near region of a circular wall jet[END_REF] presented a LES study of the flow features in the near region of a turbulent circular wall jet discharging from a nozzle into a static ambient. They determined the mean and turbulent velocity characteristics in the near region.

In the current study, the aim is to build on these past observations by both numerical simulation and experimental investigation to analyze a Boussinesq turbulent horizontal buoyant wall jet of fresh water into a static and homogenous ambient of salt water with different values of salinity. Modeling is based on a Reynolds Averaged Navier Stokes finite volume method. The standard - k ε turbulence model for steady flow has been adopted with buoyancy related source terms in the momentum and turbulence governing equations. To validate numerical results, a set of laboratory experiments was conducted to observe photographically the jet boundaries, centerline trajectories and radius, and cling length over a range of initial conditions (initial jet velocity, nozzle diameter of injection and initial density difference between jet and ambient fluid of salt water). Numerical and experimental results are compared in order to validate the theoretical analysis.

Mathematical and numerical models

General hypothesis

We consider here mixed convection from a circular section source of fresh water placed tangentially on a horizontal adiabatic wall which is embedded in a static and homogenous ambient of salt water. At the source, the jet is characterized by the nozzle diameter, the injection velocity (supposed uniform), and the initial density gradient between the jet and the ambient fluid. The flow is tridimensional, turbulent and stationary. Since the domain temperature is assumed to be constant, density gradients are function of the mass concentration (salinity) only.

The applicability of Boussinesq approximation [START_REF] Zeytounian R | Boussinesq and his approximation: A contemporary view[END_REF][START_REF] Bois | A pioneer of mechanical modelling at the end of the 19th Century[J][END_REF] is limited to an initial fractional density 0 / a ρρ ∆ of 0.05 [START_REF] El-Amin M | Non-Boussinesq turbulent buoyant jet resulting from hydrogen leakage in air[END_REF] where 0 ρ is the density at the source and ρ a is the ambient density, but to generalize this approximation Swain et al. [START_REF] Swain | Hydrogen leakage into simple geometric enclosures[END_REF] suggested a condition of 0 /1 a ρρ ∆ 0 for jets of light fluid injected into an ambient environment of high density. In these cases where Boussinesq approximation is invalid, a density equation must be taken into consideration. For a wall flow, Coanda effect is usually adopted. The Coanda effect is the tendency of a fluid to cling to a surface that is near to an orifice from which the fluid emerges [START_REF] Vanierschot | Hysteresis in flow patterns in annular swirling jets[END_REF] . Some authors [START_REF] Chiekh | Synthetic jet control for flows in a diffuser: Vectoring, spreading and mixing enhancement[END_REF] consider both pressure difference and entrainment phenomena as examples of Coanda effect. Indeed, when two laminar jets injected from source of momentum (and/or buoyancy) are placed side by side, they tend to bent towards each other as a result of pressure difference. However, when the flow is turbulent, the jets bend due to the entrainment of ambient fluid. The present work will be based on the hypothesis that the attachment of turbulent round wall jet is caused by the momentum flux related to entrainment phenomena near the adjacent wall.

Entrainment concept

The entrainment assumption assumes that the velocity of ambient fluid entrained into the plume body is proportional to the mean centerline velocity of the plume. Thus, determining forced plume behavior leads to specify the rate of entrainment. The theory of plumes set out by Morton in 1956 assumed a constant coefficient of entrainment α . However, this la- tter cannot be a universal constant [START_REF] Jiang | Physical controls on mixing and transport within rising submarine hydrothermal plumes: A numerical simulation study[END_REF] . For forced plume which should behave more like a momentum plume near the source and like a plume at large distances, Fan and Brooks [START_REF] Fan | Discussion of Ref. 2[C[END_REF] used a value of 0.082 for α and their analysis agreed well with experimental data.

Based on the results of previous studies, Houf and Schefer [START_REF] Houf | Analytical and experiinvestigation of small-scale unintended releases of Hydrogen[END_REF] have demonstrated that the local rate of entrainment for buoyant plume (forced plume) increases as plume leaves the region dominated by momentum and enters a region dominated by buoyancy forces. Thus, the entrainment coefficient is related to the rate of entrainment E [START_REF] El-Amin M | Non-Boussinesq turbulent buoyant plume of a low-density gas leaks into a high-density ambient[END_REF] by

=2 E bU α π ( 1
)
where b is the width plume and U is the centerline velocity.

U Fr gd ρ ρρ ∞ - (5)
As the local Froude number decreases, the buoy E term begins to contribute and the buoyancy effect becomes more important. In Eq.( 4) it appears that the constant a, with a determination based on experiments developed by [START_REF] Tennekes | A first course in turbulence[END_REF] , is related to densimetric Froude number Fr by: Where the Froude number Fr is given by:

1/ 2 0 ² = () U Fr gd ρ ρρ ∞ -    (7)
1

.3 Governing equations

The mathematical model of the problem is given by the conservation equations of Navier-Stokes written using the Reynolds decomposition which refers to the separation of flow variables (velocity i u and mass concentration C′ ) into a mean (time averaged) component (mean velocity i u in the directions i x and mean mass concentration C ) and a fluctuating component (fluctuating velocity i u′ and fluctuating mass concentration C′ ):

=+ i ii uuu ′ , =+ CCC ′ (8)
Thus, the mass, momentum and concentration equations for steady round horizontal Boussinesq buoyant jet can be written as:

Mass =0 i i u x ∂ ∂ ( = 1, 2, 3) i (9) Momentum + 1 = ii a j ij ref a j ij j g x xx x u pu u uu ρρ ν ρ ρ ∂ ∂ ∂∂ - -- ∂ ∂∂ ∂  -  ′′   (10) Concentration () = i i i ii uC C D uC x xx  ∂ ∂∂ ′′ -  ∂ ∂∂  (11)
where i u are the mean velocity components in the di-rections i x . µ and ν are respectively the kinetic and the kinematic viscosities. p is the pressure and C is the the salt concentration of ambient fluid. D is the coefficient of salt diffusion in fresh water. The turbulent stresses ij uu ′′ and the turbulent mass fluxes i uC ′′ are unknown in the above equations and are approximated by the turbulence model.

Turbulence model

Turbulence model employed is the standard Averaged Reynolds-Number - k ε model which turbulent kinetic energy k and turbulence dissipation rate ε equations are respectively:

= ++ j i it jt j j ij j j k u uu kk u x x xx x x ν ε σ ν  ∂ ∂∂ ∂ ∂∂ -    ∂ ∂ ∂∂ ∂ ∂   (12) 2 12 =+ + j ii jt j j ij u uu uC C x kx x x k ε ε εε ε ν  ∂ ∂∂ ∂ -   ∂ ∂ ∂∂  t jj xx ε ν ε σ  ∂∂   ∂∂  (13)
where

2 = / t C k µ ν ε is the turbulent kinematic viscosi- ty. The empiric constants C µ , 1 C ε , 2 C ε , k σ and ε σ
which appear in Eqs.( 12) and ( 13) are the constant standard Averaged-Reynolds-Number -

k ε model: = 0.09 C µ , 1 = 1.44 C ε , 2 = 1.92 C ε , =1 k σ , =1 ε σ
It is known that the - k ε model is based on hy- potheses which are valid only for flows with high Reynolds numbers. In such flows, the predominance of viscous effects in a very thin area immediately through contact with the wall is negligible. However, the wall boundary represents a region where the velocity changes from the no-slip condition at the wall to its free flow value. The variation is usually the largest in the near-wall region, and hence strongest gradients are found here. Thus, one of the most common engineering problems is computing wall turbulent flows. Two remarkable effects of an adjacent wall are: damping the wall normal components, making the turbulent flow anisotropic and increasing the production of turbulence through the shearing mechanism in the flow.

In this work, to treat the boundary conditions in the presence of a wall boundary, friction forces are estimated by wall functions. These later resolve Eqs.( 12) and ( 13) in the region of fully turbulence and out of boundary layer. Wall functions method is used to reduce computational requirement and increase numerical stability. This approach is based on a mesh, where the first interior node is located in the inertial sublayer (where the viscous effects are small), then it is possible to use the law-of-the-wall to specify the boundary condition for the dependent variables j u , k and ε . We note here that the near-wall region may be sub-divided into three different areas [START_REF] Tennekes | A first course in turbulence[END_REF] : viscous sub-layer: where + y is a normalized value of the wall normal coordinate.

The standard wall function method is limited to flows where the turbulent kinetic energy becomes zero in separating and re-attachment points, by definition, where friction velocity u τ ( = / u τω τρ , where ω τ is the wall shear) is zero. Launder and Spalding models proposed a modification to the standard wall function method where they solve the turbulent kinetic energy with a modified integrated production and dissipation terms (Eq.( 14)), and they set ε with k (Eq.15)). where the subscript p is used for the first interior node, y is the wall normal coordinate, k is the Von-Karman constant, E is the wall roughness coefficient, p τ the wall shear stress.

Boundary conditions

According to the symmetry of the injection no-zzle, the simulation computes only the half of jet domain. When solving the governing equations, appropriate initial conditions and boundary conditions (Fig. 1) needed to be applied. Hence, the following conditions were taken into account:

(1) The initial velocity of jet corresponds to the mean velocity of discharges flow rate. This condition is applied to compute mass flow into the domain and fluxes of momentum and concentration.

(2) Bottom and lateral walls of the tank correspond to a slip boundary condition which assumes that there is no viscous interaction between the wall and the fluid.

(3) Flow exits where the details of the flow velocity and pressure are not known prior to solution of the flow problem, are defined by "pressure outlet" condition. Latter, is appropriate where the exit flow is close to a fully developed condition, as the outflow boundary condition assumes a zero gradient for all flow variables except pressure.

(4) The free surface is designed by a symmetry boundary that indicates no penetration and vanishing shear stresses.

The following table summarizes the boundary conditions and - k ε model conditions [START_REF] Mehta | Large eddy simulation of wind farm aerodynamics: A review[J][END_REF] : The computational domain (Fig. 1) has been generated in tridimensional by about 2.2×10 6 of non-structured tetrahedral cells. To have more precision of numerical results, the mesh density at the nozzle and its surroundings was more refined than the rest of computational domain.

Table 1 Generalized boundary and initial conditions

k d ε Outlet =0 i u n ∂ ∂ ( = 1, 2, 3) i =0 k n ∂ ∂ =0 n ε ∂ ∂ Bottom and lateral walls 12 == u u 3 =0 u =0 k y ∂ ∂ =0 y ε ∂ ∂ 1.

Resolution method

The resolution of steady governing equations in the presence of turbulence is done by the finite volume method with the solver Fluent-Ansys. The simulations were performed using 3-D segregated solver (pressure-based) and second order discretization. Implicit formulation was chosen. The SIMPLE algorithm was used for pressure-velocity coupling. The turbulence model used was the - k ε Realizable with the full buoyancy effects. Algebraic Equations for a discrete dependent variable Φ are constructed by integrating the governing equations over the separate control volumes. Hence, the result is given by

=+ P P nb nb nb A As ΦΦ ∑ (16)
where indices nb refer to adjacent cells to the cell P and P A are coefficients including the convection and the diffusion terms of Φ , whereas S is a source term.

Convection terms are interpolated from the cell center values. This is accomplished using an upwind scheme. The diffusion terms are central differenced and this approach is known as the central-difference scheme second-order accurate.

The residual R Φ is the imbalance in Eq.( 10), which summed over all the computational cells P . This is referred to as the "unscaled" residual. It may be written as

=+ nb nb P P P nb R A sA Φ ΦΦ - ∑∑ (17)
To scale this residual, a scaling factor representative of the flow rate of Φ through the domain is used.

Hence, the "scaled" residual is defined as

+ = nb nb P P P nb PP P A sA R A Φ ΦΦ Φ - ∑∑ ∑ ( 18
)
The latter is a more appropriate indicator of convergence for most problems. At convergence, All discrete conservation equations (momentum, species, etc.) are obeyed in all cells to a specified tolerance or the solution no longer changes with subsequent iterations. To monitor convergence, Fluent uses a residual history. Generally, a decrease in residuals by three orders of magnitude indicates at least qualitative convergence. At this point, the major flow features should be established. Fluent recommends the value of 10 -5 for concentration, 10 -6 for energy and 10 -3 for others quantities [17] . Starting from quiescent initial conditions, the equations are marched through time until converging to the steady-state solution. For each iteration, the momentum equations are solved using current values for pressure, to update the velocity field. The k and ε equations are solved using the previously up- dated values of the other variables. The fluid velocities are then updated, and a check for convergence of the system of equations is made. The steady-state solution is reached when the change in all of the calcula-ted variables is less than a chosen tolerance (residuals) [17] .

To minimize computation time, parallel calculation options have been set up by selecting Parallel under Processing Options in Fluent Launcher. Number of processes used is 4. Since our geometry involves enclosures connected via small-diameter nozzle injection, mean pressure levels in all zones can be quite large. Thus, the use of Double-precision calculations was necessary to resolve the pressure differences that drive the flow, since these will typically be much smaller than the pressure levels.

Experimental model

Numerical results obtained by the resolution of mathematical model are validating experimentally on a test bench in our laboratory. The experimental study of wall horizontal turbulent jet involves the behavior description, in the presence of a wall boundary, of fresh water jet injected into a homogenous and static ambient of salt water with different rates of salinity. Outgoing from the nozzle, the jet behavior is conditioned by: the nozzle diameter, initial velocity of injection and the initial density gradient between the jet and the ambient fluid. Experiments are carried out on a plexiglas tank with a cross-section of 0.3m×1m and a depth of 0.3 m. The tank is filled out by a static and homogenous ambient fluid of salt water. The salinity of this latter is deduced from the measure of solution conductivity by a mobile conductivity meter COND 3110 (Fig. 2). This later is of a conductivity range of 0 µS-1 000 mS with an accuracy of 0.5% ± full-scale 1 ± LSD. Deduced salinities vary between 36 g/l and 80 g/l.

Experimental apparatus is shown in Figs. 3 and4. Fresh water, conducted by gravity into the tank, is injected horizontally from a circular nozzle with inner diameter ranging between 0.012 m and 0.004 m. The flow of fresh water (colored by Indian ink) is controlled by a valve and measured by a flow meter which is capable of monitoring liquid fluids to 350 l/min with an accuracy of 0.5% ± . The flow visualizations are carried out by a speed camera HS-650 TSI which captures at up to 636 frames per second and has a high resolution (1 280×1 024 Pixels) for water flows, lower speed air flows, and biological flows. Captured images are analyzed by the Image J software. This treatment is used to determine the shape of the plume and the corresponding coordinates.

The following table summarizes the details of the experiments performed for each flow configuration:

Figures 5 and6 show some experiments of Table 2. Figure 5 presents the variation of flow behavior depending on salinity variation while the Fig. 6 shows the flow behavior depending on Reynolds number variation (variation of fresh water flow rate in the nozzle). Qualitatively, the first step to validate mathematical model is to compare between numerical and experimental flow visualizations. Then, for a quantitative validation, those visualizations are translated into encrypted data and curves that describe the mixture density between plume and ambient fluid.

Results and discussion

Jet boundaries

The turbulent flow ( 2 000) Re ≥ pattern is generated by a continuous source of momentum and buoyancy. Numerical and experimental results are compared for boundaries and centerline trajectory. The initial conditions of the centerline quantities are taken as their values at the source. Since the flow is generated by both momentum and buoyancy, the rate between momentum and viscous forces is defined by the Reynolds number Re while the Froude number Fr defines the rate between buoyancy and momentum. At the source, these numbers are defined by:

0 = Ud Re v , 1/ 2 2 0 0 = () a a U Fr gd ρ ρρ   - 
where 0 ρ is the fresh water jet density at the nozzle and a ρ is the density of ambient fluid (salt water).

In the following analysis, initial flow is represented by the initial velocity 0 U and the buoyancy by the initial gradient density 00 = a ρρρ ∆-. During its rising as a result of buoyancy forces, the plume takes a curved form due to combined effect of the horizontal component of momentum and the gravity. Outgoing from the nozzle, placed sufficiently close to the bottom, the jet seeps into the tank and the mixture process with ambient fluid starts. During its flow, the jet clings to the bottom for some distance. At the level of that boundary, the jet is submitted to frictional forces that brake the flow and decrease its kinetic energy. When this later becomes sufficiently weak, the flow is dominated by the positive buoyancy generated by initial density gradient 0 ρ ∆ . Thus, the jet leaves the bottom and rises to surface as a free jet. In principle, when a jet is injected horizontally from a nozzle with a certain momentum, it begins to ascend vertically as if the buoyancy forces predominates the inertia forces. However, in the case of horizontal jet of this study, for the same values of Froude number obtained by varying in the same time initial momentum flux, i.e., initial velocity 0 U , and buoya-ncy flux, i.e., initial density gradient 0 ρ ∆ between mixture injection fluid and ambient fluid, the jet rising depends on 0 ρ ∆ rather than 0 U . Even if the flow is generated by mixed convection, the buoyancy forces predominate: the higher these later are, i.e. low values of 0 ρ , the faster and the nearest (to the nozzle) plume rising is (due to the important buoyancy) [START_REF] Belcaid | Modélisation de la dispersion des pollutants dans un milieu marin via les oueds et les émissaires sous-marins[D]. Application to the pollution of the Bay of Tangier (Morocco)[END_REF] . Thus, in this work we analyze the combined effect of turbulence and wall boundary on the behavior of a wall horizontal turbulent jet. We notice that the higher initial density gradient 0 ρ ∆ is (the smaller ambient fluid salinity S is), the more important cling length L is (Fig. 7). In other words, the more Froude number decreases the more the attachment length to the wall is important. Now, jets are injected in ambient fluids with a same salinity = 50 g / l S , corresponding to a same initial density gradient 0 ρ ∆ , and where Froude numbers are obtained only by varying initial velocity 0 U (Fig. 8). In this case, with the decrease of Froude number, the cling length decreases progressively in order to be zero when the flow becomes laminar.

To test the turbulence effect on the jet cling to the wall, we treat now the case of laminar flow for Reynolds numbers varying between 100 and 350 (Fig. 9). In such flow, initial velocity 0 U at the source is very weak that the jet can't discharge too far over the nozzle. In this case, we notice that the wall boundary has no effect on the jet. This later, outgoing from the nozzle, raises up under the effect of buoyancy like a free jet.

For a wall turbulent jet injected from a source of momentum and positive buoyancy, the flow is conditioned by both turbulence effect and wall boundary that hits the jet. Jet cling to the wall depends strongly on the initial buoyancy flux where the lighter the jet is (more the initial density gradient is important), the weaker the jet cling to wall is. Indeed, when the jet is discharged from the nozzle, it merges with the ambient fluid under the effect of entrainment phenomena. However, for a light turbulent jet, entrainment processes is fast and the ambient fluid doesn't have the time to be entrained into the jet body. While this turbulent is combined to the positive buoyancy of the jet, this later raises up more rapidly when it is light. Thus, the jet doesn't cling to the wall for a long while. On the other hand, when the flow is laminar, the jet is discharged from the nozzle and guided by buoyancy effect with a behavior of free jet. In this case, the wall boundary has no effect on the jet flow.

In conclusion, the behavior of a wall horizontal turbulent jet depends on both initial Froude number Fr (that represents the ratio between buoyancy and momentum) and the effect of wall boundary (that the jet hit directly when it is discharged from the nozzle). Thus, this flow is characterized by its cling to the wall defined by a length L called the cling length.

Numerical results for boundaries are compared with experimental results for each flow configuration described above. The improved numerical model predicts well the boundaries jet. Near the nozzle, where the flow is dominated by horizontal momentum, the agreement is very satisfactory, but when the flow becomes purely buoyant, numerical model presents some little deviation of jet boundaries. This is due es-sentially to the rate of ambient fluid entrainment into the jet body: in the near field, the entrainment rate E , given by relations 4 and 5, is reduced to the component mom E (relation 6). This later depends only on the initial conditions which the values are known at the nozzle. That explains the accuracy of numerical results in the near field. When the jet leaves this later and arrives to the zone of established flow, the buoyancy dominates and the component buoy

Jet centerline radius

One of the most important characteristics to be determined for a flow jet is its radius r or whether its half-width. This parameter quantifies the entrainment rate of the ambient fluid into the jet body: the more the entrainment is important, the more the jet becomes wider and r increases. Thus, to continue the analysis of Section 3.1, we present in this section the variation of the jet radius r on its centerline.

Jet centerline radius r is determined and compared numerically and experimentally for each flow configuration described in Section 3.1. For each type of jet, round or plane, sample or double, free or with a wall boundary, with or without temperature (or density) gradient, the study of jet mean behavior in a static environment reveals that the mean velocity in the jet axis decreases and the jet ra-dius increases linearly (see for example Ref. [19]). Thus, for our case of wall horizontal turbulent jet and in accordance with the results of literature, the radius r increases linearly. However, this increase depends strongly on the jet cling to the wall. , the radius r increases linearly and the jet expansion is more important for the flows of high values of Froude number (Fig. 10). These later, correspond in the same time to the cases where the cling to the wall is important. Indeed, in the near field, these jets have the same behavior and keep practically the same width. However, from the moment where the inertia force damps and becomes equal to zero under the effect of friction with the wall, the jet behavior changes and becomes dominated by buoyancy. While this later isn't the same for those jets, in the far field the radius evolution changes: the lighter the jet (high values of 0 ρ ∆ ) is, the weaker its expansion is.

Proceeding with environments of the same salinity S , the density gradient 0 ρ ∆ is the same for flows of different values of Froude number Fr , initial velocity 0 U and Reynolds number Re . Jet radius at the extreme point of centerline trajectory is more important for high values of Froude number Fr and decreases with the decrease of Reynolds number Re (passing from turbulent to laminar flow) (Fig. 11). Indeed, more the flow is turbulent, more it entrains ambient fluid. This explains the decrease of radius r when we pass to laminar flow. To confirm this deduction, we analyze in the next section, the evolution of jet radius for flows purely laminar.

For laminar flows, jet inertia forces are very weak to entrain high quantities of ambient fluid into the jet body. Thus, the entrainment rate and jet expansion are weak. However, the flow is purely buoyant where the radius r decreases with the decrease of Reynolds number Re (Fig. 12).

Jet cling length to the wall

According to the previous analysis, the cling of a turbulent buoyant wall jet injected from a nozzle placed sufficiently near a wall depends, at the same time, on inertia forces and buoyancy forces. The flow is especially characterized by the Froude number Fr .

Near the wall, the mixture of the jet with the ambient fluid is defined by a length called the mixture length. This later is the product of the cling distance to the wall and the Von Karman constant (determined experimentally). This relation represents a law that leads to the identification of logarithmic profiles to the velocity near the wall [START_REF] Thual | Hydrodynamics of the environment[END_REF] . However, an ambiguity remains always to define the distance travelled by the jet on the wall. Thus, we define this region by the cling length L caused by Coanda effect.

Near the wall region, the buoyant turbulent jet is injected with an important momentum flux that generates a pressure difference between the jet and the wall.

In the near field (potential core), the inertia forces of the jet dominate the flow and lead the jet to cling to the wall under the effect of pressure difference. With the wall friction, the jet velocity decreases and becomes equal to zero. When the pressure forces become weak in comparison with the buoyancy forces, the jet leaves the wall and raises up vertically like a free jet. This point of detachment represents the limit of the cling length L . On this subject, the study of Ref. [2] introduced, analytically and experimentally, the relations between the cling length L of the wall jet and the Froude number. Recently, Huai et al. [START_REF] Huai Wen-Xin | Numerical simulation of horizontal buoyant wall jet[J][END_REF] , have compared their numerical results for the jet cling length with the results of Sharp. Here, we compare our numerical and experimental results with the literature, especially with those of Sharp and Huai et al. (Fig. 13). The jet cling to the wall under the Coanda effect is related to Froude number Fr by a linear law that shows the increase of cling length L with the increase of Froude number. According to Ref. [3], this law is given by: / = 3.2 L d Fr . The comparison of our numerical and experimental results with the experiments of Sharp shows a very satisfactory agreement.

Conclusions

In this paper, a numerical and experimental investigation of Boussinesq wall horizontal turbulent jet of fresh water in a static homogeneous environment of salt water is considered. Mathematical and experimental models have been used to determine jet boundaries, centerline jet radius and jet cling length to the wall. The solutions of jet behavior will be useful not only to the marine disposal problems but also to the problems of a similar nature such as the disposal of hot waste gases into the atmosphere or hot water from a thermal power plant into a lake.

Several flow configurations are obtained by varying initial injection conditions: nozzle diameter, injection velocity and density gradient between the jet and the ambient fluid (salt water). Mathematical approach is based on numerical resolution of conservation equations of mass, momentum and concentration, and turbulence equations by Reynolds Averaged Navier Stokes finite volume method. Numerical results are validated by comparison with experimental results (which apparatus was described in sect. 3) and a good level of agreement is observed.

The analysis focus essentially on the influence of the combined effect of turbulence and wall boundary on the jet behavior, especially its cling to the wall. In dimensionless values, numerical and experimental de-termine the boundaries, centerline radius and cling length of the jet to the wall.

Results show that the flow is dominated by buoyancy forces. Indeed, the jet cling to the wall, under the Coanda effect, depends strongly on the initial buoyancy flux: the lighter the turbulent jet is, the weaker its cling to the wall is. However, contrary to the case of free buoyant turbulent jet [START_REF] Belcaid | Modélisation de la dispersion des pollutants dans un milieu marin via les oueds et les émissaires sous-marins[D]. Application to the pollution of the Bay of Tangier (Morocco)[END_REF] , the turbulence effect influences remarkably the jet behavior. Thus, there is no jet cling to the wall for laminar flow. In this later, the flow is purely buoyant since the source and the wall has no effect on the jet.

During its development, the jet entrains the ambient fluid. Entrainment process promotes the jet expansion and increases its radius (half-width). In accordance with literature, our results show that the jet radius increases linearly and the jet expansion increases with the increase of initial Froude number. In others words, more the jet clings to the wall, for high values of Froude number Fr , more the jet becomes wide with an important entrainment of ambient fluid. Thus, a good jet dilution is established.

According to these analysis, a good concordance is established between the jet cling to the wall and the dependence of the flow on the ratio between inertia and buoyancy forces (represented by Froude number Fr ). Thus, a linear law is defined between this later and the jet cling length L , thus helping to delimit the mixture zone of a wall jet.

4 =

 4

Fig. 1

 1 Fig.1 Scheme of coordinates system and boundary conditions 1.5 Boundary conditionsAccording to the symmetry of the injection no-

Fig. 2

 2 Fig.2 Mobile conductivity meter COND 3110 used to measure the salinity

Fig. 3 Fig. 4

 34 Fig.3 Scheme of experimental apparatus

Fig. 5

 5 Fig.5 Experiments images of turbulent flow ( = 5 700) Re of fresh water jet into the tank of salt water

Fig. 7

 7 Fig.7 Comparison of jet boundaries between numerical and experimental models for 0 1.31 m / s U = and = 5 700 Re

Fig. 8

 8 Fig.8 Comparison of jet boundaries between numerical and experimental models for an ambient fluid of = 50 g / l S

Fig. 9

 9 Fig.9 Comparison in laminar flow of jet boundaries between numerical and experimental models for an ambient fluid of = 80 g / l S

  E (relation 7) takes part in the expression of entrainment rate E . That component introduces a new term θ , inclination angle of jet trajectory, which is unknown in advance of numerical model. Thus, the perturbations detected due to numerical resolution when the jet passes to buoyancy-dominated zone.

Fig. 10

 10 Fig.10 Comparison of jet centerline radius between numerical and experimental models for 0 1.31 m / s U = and

Fig. 11

 11 Fig.11 Comparison of jet centerline radius between numerical and experimental models for an ambient fluid of = S 50 g / l

Fig. 12

 12 Fig.12 Comparison of jet centerline radius between numerical and experimental models for an ambient fluid of = S 80 g / l

Fig. 13

 13 Fig.13 Comparison of the numerical and experimental results with the literature for the variation of the jet cling length L in function of initial Froude number

Table 2 Experiments details

 2

	Experiment	Velocity ( 0 U /m/s)	Froude number () Fr	Reynolds number	(Re	)	Salinity S of ambient fluid	Density ( 0 ρ /kg•m -3 )	Density ( a ρ /kg•m -3 )
	1	1.31	44	5 700			36	1 000	1 027
	2	1.31	36	5 700			50	1 000	1 038
	3	0.4	10	2 000			50	1 000	1 038
	4	0.07	2	300			50	1 000	1 038
	5	0.025	0.6	100			50	1 000	1 038
	6	1.31	23	5 700			80	1 000	1 062
	7	0.82	16	3 300			80	1 000	1 062
	8	0.38	7	1 400			80	1 000	1 062
	9	0.1	2	385			80	1 000	1 062
	10	0.05	1	183			80	1 000	1 062


C Nichita

G Caraene

N Badea

M Giurginca

C Vaca-Garcia

A Meghea

Vegetal bioproducts with antioxidant activity for prophylactic and therapeutic effect

Keywords: Vegetal bioproducts, Rosmarinus officina/is L., Polyphenols, Antioxidants, Chemiluminescence technique, Pharmacological tests

This paper presents the extractive technological process and processing of the selective vegetal extracts from the Rosmarinus officina!is L. species in order to obtain some vegetal bioproducts with proven antioxidant activity. By combining various active fractions, new vegetal bioproducts have been obtained and have been physically and chemically characterised (infrared, ultraviolet visible spectroscopy, chemiluminescence, determination of flavonoids, polyphenols, and polyphenolcarboxilic acids content) and finaly biologically tested. The antioxidant activity of Rosmarinus officinalis extracts have been evaluated by two techniques, in vitro chemilumines cence and ex vivo biological tests, both of them recommending the vegetal bioproducts for prophylactic and therapeutic purposes.

Introduction

Many investigations have correlated the pharmacody namie properties of some plant extracts with their anti oxidant activity and the capacity to defend the organism against oxidative stress, which generates numerous diseases of the digestive, cardiovascular and nervous system. The importance of the phenolic compounds as vegetal antioxidants is justified by their action over the free radicals. 1 -3 Phenolic compounds such as flavonoids, phenolic acids have been suggested as playing a preventive role in the development of cancer, heart diseases, and aging related diseases. 4 Among the plants of interest the species Rosmarinus officinalis L is also reported, since its chemical composi tion rich in essential oils, di-and triterpenes, flavonoids and inorganic components confers antioxidant and curative properties by the involvement of biological action mechanisms and due to the lack of toxicity as well. 5 Rosmarinus officinalis L. (family Lamiaceae), has been found to act both as a stimulant and as a mild analgesic, and has been in popular use to treat headaches, epilepsy and poor circulation. Its extracts have been incorporated into drugs and cosmetics, and used for flavours and fragrance in food. Leaves of Rosmarinus officinalis L. possess a variety of bioactivities, including antioxidant, antitumor, anti-inflamatory and anti-HIV effects. This work presents the quantitative characteristics of some flavonoidic fractions from Rosmarinus officinalis L. species and their spectral investigation in infrared (IR) and ultraviolet visible near infrared (UV-VIS-NIR) domains, in correlation with the antioxidant activity in order to assess their potential applications for prophy lactic and therapeutic purposes.

Experimental

Antioxidant character evaluation and physical chemical characterisation of vegetal bioproducts obtained from Rosmarinus officinalis L. species was performed by using the following methods and equipment: chemilumines cence (Turner Design TD 20/20 USA); UV-VIS-NIR spectroscopy (V-570 Jasco) with accessory for diffuse reflection ILN-472; Fourier transform infrared spectro scopy (FTIR 620 Jasco ); quantitative determination of flavonoids, polyphenols and poly-phenol-carboxylic acids by spectral technique.

Vegetal material: Rosmarinus officinalis L. from Fitoterapia SA Romania.

Pharmacological tests

Liver homogenates were prepared from male Wistar albino rats weighing 250 ± 10 g, intoxicated with car bon tetrachloride (CC1 4 ) (2 mL kg-1 po, 20% v/v in sun flower oil) or treated only with the vehicle. Liver homogenates from untreated animais served as control.

Rats were sacrificed 24 h after, followed by excision of the liver, its washing in ice cold 0• 15 saline and cutting into small pieces using scissors before homogenisation in ice cold 0• lM phosphate buffer, pH 7•4, at 4 °C with a Potter-Elvehjem glass homogeniser.

Aliquots of liver homogenates were incubated with 10 and respective 20 µg sample/mL in a termostat at 37 °C for 1 h. The incubation was stopped by adding ice cold Malondialdehide is an end product of peroxidative decomposition of polyenoic fatty acids in the lipid peroxidation process and its acumulation in tissues is indicative of the extent of lipid peroxidation. TBARS reagent (1 mL) was added to a 0•5 mL ofsample and the sample was heated for 15 min at l00 °C. [START_REF]Romanian Pharmacopoeia[END_REF] The amounts of peroxides formed in liver homo genates during incubation were determined spectro photometrically by measuring absorbance at 535 nm. The inhibition of lipid peroxidation as percentage was calculated by following equation

( T-M) %protection= 1----x 100 I-M
where T is the absorbance in the presence of the sample, M the absorbance of the positive control reaction and I the absorbance of the negative control reaction.

Results and discussion

The vegetal bioproducts (RA 1, RF 1, RZ 2, RZ2A) were obtained by a succession of technological stages consisting in the first stage in the solid-liquid extraction in a Soxhlet installation. Following the extraction procedure, the vegetal material used was removed, and the obtained filtrates were processed by vacuum concentration (Buchi type rotavapor B-480, with a constant temperature water bain) until obtaining a residue which, passed through successive precipitations with polar and non-polar solvents, centrifugation, filtering at low pressure and purification. The variation of the operational parameters, respec tively the fine degree of the plant, the solvent, used the plant/solvent ratio, extraction time and temperature, the type of concentration, precipitation and purification, resulted in obtaining four yellow, non-hygroscopie, fine powdery samples.

The samples were characterised by spectral tech niques (IR, UV-VIS-NIR), and by chemiluminescence, and the quantitative determination of the flavonoids, of the polyphenols, of the polyfenolcarboxilic acids and of specific physical chemical indicators, according to Romanian Pharmacopoeia and European Pharmacopoeia 9 • 10 (Table 1).

lnfrared characteristics of extracts

The analysis in the IR domain was made by including the samples in KBr pellets. The spectra of the samples (RAI, RFl, RZ2) are presented in Fig. 1. Comparing the spectra of the vegetal bioproducts (RAI, RFl, RZ2) with the spectra of the standards (rutin and quercetine), we note the presence of common bands, specific for phenolic and flavonoidic structures.11

Ultraviolet visible characteristics of samples

The samples in ethanol solvent have similar electronic spectra which corne from structures, with transitions of n�n* and n�n* type at the 286 and 345 nm. In the case of concentrated solutions the bands from 410 to 445 nm were also noticed in accordance with their light yellow ish colour, assessed to conjugated systems ofpolyphenol and/or flavonoid compounds.11

The bands of the solid fractions (Fig. 2) are assigned to the same transitions discussed for the tests in ethanol solution, but in addition the bands from 612 to 672 nm appear, assessed to extended conjugated systems with more than four aromatic cycles.

• =• ,... 60,-1- ��-� ,. ... -., rT'T . - - ..... ---• -- ----- � ---1- ' - - - -- .,0 )0 .::o � � ..... ---- -----� 10 � ..... ----- 0 it Il Il Il •j >!l <(

Results of lipid peroxidation

The bands in NIR domain can be assigned to harmonies and combinations of valence and deforma tion vibrations of CH 2 /CH 3 groups and OH existent in polyphenol structures.

Antioxidant activity

The antioxidant activity of the extracts RAI, RFl and RZ2 tested by chemiluminescence is comparable to that ofvitamin C (92•3%), of the extract obtained from green tee (97•8%), and other polyphenols/polyphenol acids (Table 2).

The qualitative and quantitative content in the phenolic and flavonoidic constituents in the samples, confirmed by spectral analysis and chemiluminescence determinations, explain the high value of the antioxidant activity, especially for the sample RAI.

Pharmacologie ex vivo tests on antioxidant activity of vegetal bioproducts

Antioxidant activity of the four fractions (RAI, RFl, RZ2, RZ2A) and of the reference substances (ascorbic acid, gallic acid and caffeic acid) was evaluated by quantifying the ability of different concentrations of the samples to suppress CC1 4 induced lipid peroxidation in rat liver homogenates. The results of lipid peroxidation assay (Fig. 3) showed that different fractions of Rosmarinus officinalis extract have a very strong antioxidant activity, successfully attenuating the effects of CC4, in a concentration dependent manner. At concentrations of 20 µg mL -t homogenate, two out of the four fractions were more effective (97•2% and respective 91%) than ascorbic acid (90•8%), gallic acid (80•3%) and caffeic acid (78•4%) in their antioxidant activity. A correlation between antioxidant activity and phenolic/flavonoidic content was observed for ail the four fractions, and a parallel behaviour with the antioxidant activity determined by ex vivo and in vitro chemiluminescence tests was also noted (Fig. 4).

Both series of ex vivo and in vitro tests on antioxidant activity suggest the use of selective extracts from Rosmarinus of.ficinalis L. for prophylactic and therapeu tic purposes.

Conclusions

By extractive process and processing of the selective vegetal extracts from Rosmarinus of.ficinalis L. species a number of four bioproducts were obtained.

Spectral investigations (IR, UV-VIS-NIR) on biopro ducts of vegetal antioxidants type emphasised the presence of some phenolic and flavonoidic structures, also confirmed by quantitative determination of the flavonoids, of the polyphenols and of the poliphenol carboxilic acids.

The results of the pharmacologie ex vivo tests revealed that the bioproducts obtained exhibit high antioxidant activity, being in accordance with the values provided by chemiluminescence in vitro tests, and suggesting thus their potential application for prophylaxy and therapy of various free radical related diseases.

  of vegetal bioproducts 20% trichloroacetic acid and the incubates were cen trifugated at 1000 g for 10 min. The assessement of the extent of lipid peroxidation relied on individual deter minations of malondialdehide (MDA) contents in sample supernatants by performing the barbituric acid assay (TBARS), as described by Draper and Hadley.8

4

  Correlation between antioxidant activity by in vitro che miluminescence [CL] and by ex vivo biological testes (BT)

6 • 7

1 National lnstitute for Chemical-Pharmaceutical Research and Develop ment, 112 Vitan Street, 031299, Bucharest, Romania 2 University Politehnica of Bucharest, 1 Polizu Street, 011061, Bucharest, Romania 3 Laboratoire de Chimie Agro-Industrielle, UMR 1010 INRA/INP ENSIACET, Toulouse France *Corresponding author, email a.meghea@gmail.com

Table 1 Physical chemical characteristics Samples RA1

 1

	Ash, %

1500 Wavelength (nm] 2 UV-VIS-NIR spectra of samples 2000 2200

Table 2 Chemiluminescence characteristics*

 2

	No.	Sample code	k ' s	-1	Vj, s -1	AA,%
	1	RA1	0•091	301-4	96-34
	2	RF1	0-096	100-00	88-51
	3	RZ2	0•089	143-54	90•50
	4	RZ2A	0•065	618-00	73•82
	5	Rutin	0•093	291-40	77•40
	6	Quercetin	0•100	118-84	92•80
	7	Gentisic acid	0•107	476-20	59•80
	8	Caffeic acid	0•070	318-00	82•90
	9	Rosmarinic acid	0•050	285-60	89•20

*k: ratio constant; 11;: ratio of reaction; AA: antioxidant activity.

Acknowledgement

The authors gratefully acknowledge the financial sup port from the Romanian National Authority for Scientific Research (project no. 61014/14•09•07).