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Experimental investigation of two heated oblique
 

Experimental investigation of two heated oblique

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    Experimental investigation of two heated oblique Experimental investigation of two heated oblique Document Transcript

    • INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERINGInternational Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, (IJMET) AND TECHNOLOGY Sep- Dec (2012) © IAEMEISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online)Volume 3, Issue 3, September - December (2012), pp. 669-681 IJMET© IAEME: www.iaeme.com/ijmet.aspJournal Impact Factor (2012): 3.8071 (Calculated by GISI)www.jifactor.com ©IAEME EXPERIMENTAL INVESTIGATION OF TWO HEATED OBLIQUE JETS INTERACTING WITH A TURBULENT FLOW Tcheukam-Toko D.*1 and Paranthöen P.2 1 Department of Energetic Engineering, University Institute of Technology. P. O. Box 455, Ngaoundere, Cameroon. 2 CNRS UMR 6614 CORIA, University of Rouen. P. O. Box 12 – 76801 Saint- Etienne du Rouvray, France * Corresponding author. Email: tcheukam_toko@yahoo.frABSTRACT The objective of this study is to analyse experimentally the thermal field of two air-jets inclined at 45° interacting with a turbulent longitudinal flow. The heating of the air-jetsbefore their entrance simulates the passive scalar. At the outlet, the air-jets generate somevortexes in the longitudinal flow. The measurement of temperature and fluctuations arecarried out with the help of a hot wire anemometer. The mean temperature fields andfluctuations are represented in the 0yz plane in different positions on longitudinal axis. Theresults show that the mode of the passive scalar dispersion verified previous works carriedout. The temperature fluctuations increase with the passive scalar dispersion as the jets goaway from the source.KEYWORDS: Jets, thermal field, passive scalar, turbulent flow, temperature fluctuations,vortex, experiments.I. INTRODUCTION Air pollution has become over time a worrying phenomenon in the world. One of thefactors contributing to this atmosphere pollution is the hot gas emitted by heat engines as jets.To better understand the movement of these jets and heat dispersion in the atmosphere, it isnecessary to study its transport from the moment they are issued until their total dispersion.Now days, many studies have been done on the dynamic aspect. In preliminary studies madein the wake of Ahmed body, Gosse [1] showed that the velocity of the longitudinal flowdominated the jet velocity gradually as one moves away from the source. The jets may alsobe issued at an angle for generating vortices in a longitudinal flow. On this subject, Küpper[2] used two numerical models to explain the control of boundary layer phenomena and heattransfer at the entrance of the reactors. Tilmann [3] showed in an experimental study the 669
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Sepinfluence that a discontinuous jet, emitted at a given frequency can have on a turbulent flow. Otherexperimental studies have shown that the heat contained in the jets moved in the longitudinal direction tudiesof the flow. For example those of Kothnur and Clemens [4], which in addition show that the ],directions of the scalar propagation and the normal shear stress are perpendiculars s.Despite thesenumerous studies, there are still gray areas including understanding the phenomena of temperature erefluctuations on the passive scalar dispersion. The aim of our study is to make an experimentalinvestigation of the thermal field of a turbulent flow interacting with two heated oblique jets. This willhelp to understand the influence of temperature fluctuations on the passive scalar dispersion in orderto better explain the phenomenon of air pollution. The design and construction of the model were ofmade in the laboratory. The choice of holes diameter jet emission has been based on the work of Gibb h nand Anderson [5], and more recently those of Gosse [1]. The jets’ emissions are inclined by 45 ], [ 45°,based on the work of Bray and Garry [6], this inclination is an optimal position to have good quality [jets and eddies in the longitudinal flow. To carry out this study, we first describe the experimentaldevice, and then, we do an analysis of mean temperature fields and of standard deviation of the ttemperature.II. MATERIEL AND METHODS METHOD In this study, the main flow is the air generated by a blower longitudinal plane type “open plane,circuit” which can generate flow velocities (U∞), between 3m.s-1 and 12.5m.s-1. We used hot wireanemometry as measurement technique. techniqueII.1 Blower type “open circuit” This blower, built by Delta Lab, is shown in Figure 1. It consists of a motor-driven fan of the Lab drivencentrifugal type providing a maximum flow rate of 0.32 m3.s-1. The revolutions number of the fan is viding 0.regulated by the intermediary of a variable speed transmission supplied with 220 V single single-phasecurrents. The air circuit comprises a diffuser located in the rectangular fan discharge. The two gratings(wire cloth) located downstream of the dust filter to reduce the level of turbulence and homogenizethe flow. In the output of the two-dimensional convergent (section 80x200 mm2), the maximum twovelocity of the flow is set between 3 m.s-1and 20 m.s-1. The level of turbulence at the nozzle outlet isin the order of 0.35%. Figure 1: Blower type “open circuit” 670
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME The two oblique jets are diverted 45° in a plane perpendicular to the main flow (flowin the outlet of the nozzle) through circular holes made on a plate fixed to the lower edge ofthe outlet nozzle. They have each one a diameter of 5 mm and are separate one of the otherby 40 mm as figure 2a shows it. The emission of pollutants is simulated by injecting hot airthrough the two holes at a velocity Uj through a small pipe with 5 mm of diameter under theplate as shown in Figure 2b. The temperature difference ∆Tref between the jet and the outsideis kept constant at 20°C using a regulated power supply. The thermostat of the heating systemis connected to the thermocouple control chamber. This small temperature difference avoidseffects gravitate. The velocity of the heated flow (Uj), is measured by a loss of loadconnected to a micro manometer Furness Control. This velocity is adjustable between 1 and10 m.s-1 as shown in figure 3.The origin 0 of the orthogonal axe (0x, 0y, 0z) is locatedequidistant from the two holes i.e, 20 mm of each axis. The two holes are symmetricalrelative to the 0x axis oriented in the direction of the main flow. 0y axis is vertical and the 0zaxis is perpendicular to the main flow. Figure 2: Plate; a) Front view; b) Top view Figure 3: the device of injection of the hot air The measured variable in this study is the temperature difference between the heatedzones and upstream fluid. In this study, the sign "+" indicates a normalized quantity. Lengthsare normalized by the distance between the hole and the main axis H equal to 20 mm, and thetemperature difference is normalized by the initial temperature difference ∆Tref. Moleculareffects are negligible compared to the turbulence, the report ∆T/∆Tref can be likened to aconcentration c, will vary between 1 and 0 emission to infinity. For convenience, the timeaverage and standard deviation of a quantity X are denoted respectively <X> and <X2>1/2.The outputs of the two jets heated are located respectively at the point S of coordinates (X+ =0, Y+ = 0, Z+ = -1), and S of coordinates (X+ = 0, Y+ = 0, Z+ = 1).II.2 Hot wire anemometry The Measure of a velocity flow using hot wire anemometry is based on convectiveheat exchange between the hot wire and the flow. This exchange is used to connect the wiretemperature to Nusselt number (Nu) which is a function of the flow velocity and the currentpower I shown by the equation (1). The figure 4 below, illustrates well this principle ofconvective exchange. The detail is clear in Paranthoën and Lecordier [7], and Rosset, and al[8]. 671
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Tw = Tg + ( ( )) R 0 1 + α Tg − T0 I² where, Nu = hd . (1) Nuπlλ g − αR 0 I² λg The hot wire anemometer operates at constant temperature. In this case, when theflow velocity varies, measuring the current I needed to keep the temperature Tw of the wire,constant. This technique provides a frequency response of approximately100 kHz. The electrode used is a set TSI, consisting of a sensor to a wire, a processor and anIFA conversion board 12-bit analog voltage, installed in a PC with high memory capacity andstorage. Probes conducted in the laboratory are made with platinum-rhodium10%, with 3 µmof diameter. A schematic of the probe used is presented in figure 5. The response of the wire as a function of the velocity is not linear. Calibration of thehot wire placed in the outlet section of the jet; is performed before each series ofmeasurements by varying the velocity of the flow. An example of a calibration curve isshown in figure 6. The experimental points are then approximated by a polynomial ofordernor with a selected interpolation function type "Cubic Spline". The temperature of theflow is measured by a thermocouple type K and recorded. If there are any changes in thetemperature of the flow, a correction can thus be applied to the measured voltage. L = lengthof the wire. D =diameter of the wire I = electrical current Rw = operating resistance of the hot wire at Tw Tw = Temperature of the hot wire. U = Flow velocity Tg = Temperature of the surrounding air Figure 4: Schematic of hot wire Table 4: Legend of figure 4 2 1.9 1.8 1.7 tension (V) 1.6 1.5 1.4 1.3 1.2 1.1 1 0 5 10 15 20 25Figure 5: Diagram of the hot wire probe used vitesse (m /s) Figure 6: Example of a calibration curve of a hot wire: voltage in function of the velocityII.3 Temperature measurement The instantaneous signal T(t) of temperature can be decomposed as: T(t) = <T> + T’(t) (2)<T> is the temporal mean value and T(t) is the temperature fluctuation. The signal ischaracterized by a mean value <T>, and centered moments that allow access to the standard 672
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEdeviation <T2>1/2. In our case, each mean time is calculated on a sample of more than200,000 points. 1 NMean temperature: < T >= ∑ Ti (3) N i =1 1 NVariance: < T 2 >= ∑ (Ti − < T >) 2 (4) N i =1 In the experiments of dispersion downstream from the linear sources or point sources,the variations in temperature which one must measure quickly become relatively weak. Thetemperature signal is thus influenced by the background noise as the distance from thesource. This requires making corrections to background noise to accurately measure theactual signal. Assuming that the instantaneous value of the temperature can be written in thefollowing form: Tmes (t) = <T>V + T’V (t) + TBF (t) (5)The subscripts “mes”, "V" and "BF" correspond respectively to the measured values, truevalues and background noise values. To make the corrections of noise on the variance, weused the following equation:Variance: < T 2 > V =< T 2 > mes − < T 2 > BF (6)III. RESULTS AND DISCUSSION We conducted several series of temperature measurements by choosing a singlelongitudinal flow velocity Ui = 5 m/s for different jets velocities Uj, equal to 5 m/s, 10 m/sand 20 m/s), corresponding to the Reynolds number (Re = Ud/ν), of 1200, 2400 and 4800. Toshow more details, we performed measurements in the plane (Y+, Z+) with a very small mesh.On the Z+ axis, the scan was between -2.5 to +2.5 values with 1/20 of step of measuring. Onthe Y+ axis, the scan was between 0 to 1.5 values with 1/20 of step of measuring. That makesa total of 3,000 points of space measurements.III.1 Means temperatures The figures 7a, 7b and 7c below represent the iso-values of mean temperature at thepositions X+ = 0.5; X+ = 2.5 and X+ = 5; for a jets velocity of 5 m/s (in this case, the jetsvelocities are equal to the longitudinal flow velocity, (Uj equal to Ui.). These figures showthat the two jets are symmetric with respect to the axes 0X+and 0Y+, and even when one is ina remote position (X+ = 5). We observe a low dispersion of the passive scalar in this positionand the area of the intermediate temperature (<T> = 0.099), becomes predominant. The twojets are still largely dominated by the longitudinal flow that prevents the plate off. The areawhere the temperature is high (<T> = 0.3) remains sticking to the plate along the longitudinalaxis 0X+. The figures 8a,8b, 8c and 8d below represent the iso-values of mean temperature inthe positions X+= 0.5; X+ = 1, X+= 2.5 and X+= 5, when the jets have a Reynolds number of2400. We note that the two jets take off from the plate upon release (X+= 0.5), and reach thecoast Y+ = 1 from the position X+= 2.5. The size of the hottest zone (<T> = 0.3), decreases asthe distance along the longitudinal axis. It disappears almost completely at the position X+ =5, and the intermediate zone (<T> = 0.099), becomes very dominant and invades the entirearea near the plate (Y+ =0). Coast Y+ = 1 appears as the maximum height reached by thehottest zone of the jets. The two jets are no longer symmetrical relative to the axes 0X+and0Y+ from the position X+= 1, also considered as the position where the scalar begins to 673
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEundergo a dispersion. This is very important when the jets reach the position X+ = 5, in thearea where Y+ ≤ 1, the temperature is greater than zero. The figures 9a, 9b, 9c and 9d below represent the iso-values of mean temperature indifferent positions of the plane (Y+, Z+), for jets with a Reynolds number of 4800. We notethat the two jets are less influenced by the longitudinal flow. They quickly take off the plateat the position X+ = 0.5 and cross the coast Y+ = 1.5 at the position X+ = 5. The size of thehottest zone (<T>= 0.33), decreases significantly from the position X+ = 0.5. It disappearscompletely in a jet and still a bit in the other, specifically one that is close to the axis 0X+.This shows that the scalar disperses less rapidly than in the previous case (Re = 2400). Thesize of the intermediate zone (<T> = 0.099), becomes dominant and the asymmetry of thetwo jets with respect to axes 0X+ and 0Y+ is even more significant. In these three sets of measures, we note that in the case where the jets could be lessinfluenced by the longitudinal flow (Re= 4800), there are quick release streams of the platebut the scalar disperses less. This is obvious for all three positions because at X+ = 5, thetemperature is <T> = 0 (dark blue) on the wall of the plate, and different from zero in theregion close to the wall for other cases Re = 1200 and Re = 2400. This heat dispersion on theplate is translated by the shape of the isotherms which spread much on the plate.a) TEMPERATURE 0.357274 0.335275 0.313276 0.291277 0.269278 0.247279 0.225279 0.20328 0.5 0.181281 Y+ 0.159282 0.137283 0.115284 0.0932846 0.0712855 0.0492863 0 -2 -1 0 1 2 Z+b) TEMPERATURE 0.267911 0.249998 0.232085 0.214172 0.196258 0.178345 0.160432 0.142519 0.5 0.124605 Y+ 0.106692 0.0887788 0.0708656 0.0529523 0.035039 0.0171258 0 -2 -1 0 1 2 Z+c) TEMPERATURE 0.14093 0.13416 0.12739 0.120619 0.113849 0.107079 0.100309 0.0935391 0.5 0.086769 Y+ 0.079999 0.0732289 0.0664588 0.0596887 0.0529186 0.0461485 0 -2 -1 0 1 2 Z+ Figure 7:Iso-values of mean temperature fields<T>in the plane (Y+, Z+),Re= 1200 a): X+= 0.5;b): X+= 1; c): X+ = 5 674
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEa) TEMPERATURE 0.31228 0.292557 0.272835 0.253112 0.233389 0.213667 0.193944 0.174221 0.154499 Y+ 0.5 0.134776 0.115053 0.0953308 0.0756082 0.0558855 0.0361629 0 -2 -1 0 1 2 Z+b) 1 TEMPERATURE 0.244115 0.227533 0.210951 0.194368 0.177786 0.161204 0.144621 0.128039 0.111457 Y+ 0.0948743 0.5 0.078292 0.0617097 0.0451273 0.028545 0.0119627 0 -2 -1 0 1 2 Z+c) TEMPERATURE 0.15801 0.147178 1 0.136345 0.125513 0.11468 0.103848 0.0930151 0.0821826 0.07135 Y+ 0.0605175 0.0496849 0.0388524 0.5 0.0280198 0.0171873 0.00635474 0 -2 -1 0 1 2 Z+d) 1.5 TEMPERATURE 0.1004 0.0929762 0.0855525 0.0781287 0.0707049 1 0.0632811 0.0558573 0.0484335 0.0410097 Y+ 0.0335859 0.0261621 0.0187384 0.0113146 0.5 0.00389077 -0.00353301 0 -2 -1 0 1 2 Z+ Figure 8:Iso-values of mean temperature fields<T>in the plane (Y+, Z+),Re= 2400 a): X+= 0.5;b): X+= 1; c): X+ = 2.5;d): X+ = 5 675
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEa) 1.5 TE M PE R A T U R E 0 .295613 0 .275175 0 .254737 0 .234299 0 .213861 1 0 .193424 0 .172986 0 .152548 0 .13211 Y+ 0 .111672 0 .0912341 0 .0707962 0 .0503583 0.5 0 .0299204 0 .00948254 0 -2 -1 0 1 2 Z+b) 1.5 TE M PE R A T U R E 0 .22666 0 .210599 0 .194539 0 .178478 0 .162417 1 0 .146356 0 .130295 0 .114234 0 .0981732 Y+ 0 .0821123 0 .0660514 0 .0499906 0 .0339297 0.5 0 .0178688 0 .00180789 0 -2 -1 0 1 2 Z+c) 1 .5 TEMPERATUR E 0 .159154 0 .14855 0 .137945 0 .12734 0 .116735 1 0 .106131 0 .0955258 0 .084921 0 .0743163 Y+ 0 .0637115 0 .0531067 0 .0425019 0 .0318971 0 .5 0 .0212924 0 .0106876 0 -2 -1 0 1 2 Z+d) 1.5 TEMPERATURE 0 .11203 0 .104573 0 .097117 0 .0896605 0 .0822041 1 0 .0747476 0 .0672912 0 .0598347 0 .0523783 Y+ 0 .0449218 0 .0374654 0 .0300089 0 .0225524 0.5 0 .015096 0 .00763954 0 -2 -1 0 1 2 Z+ Figure 9: Iso-values of mean temperature fields<T>in the plane (Y+, Z+),Re= 4800. a): X+= 0.5;b): X+= 1; c): X+ = 2.5;d): X+ = 5III.2 Standard deviation of means temperature We obtain the temperature fluctuations shown in the previous paragraph that werepresent through the standard deviations. The figures 10a, 10b, and 10c below represent the iso-values of the standard deviationof mean temperatures in different positions of the plane (Y+, Z+), for a Reynolds number of1200. We note that the symmetry of the two jets with respect to axes 0X+ and 0Y+ isconfirmed. The standard deviation of the mean temperature decreases when the jets move 676
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEaway along the longitudinal axis 0X+. At the position X+= 0.5, this iso-value is 0.04 in thehottest zone and it become 0.01 at the position X+ = 5. The influence of longitudinal flow onthe two jets is very important. The figures 11a, 11b, 11c and 11d below represent these standard deviations indifferent positions of the plane (Y+, Z+) for a Reynolds number of 2400. The decrease of thestandard deviation with distance along the longitudinal axis is confirmed. In the hottest zone,it is from 0.06 at X+ = 0.5, and 0.02 at X+ = 5. The asymmetry between the two jets isobserved from the position X+ = 1.a) EAT YE C R -T P 0.0494505 0.0461963 0.0429421 0.0396879 0.0364337 0.0331795 0.0299252 0.026671 0.5 0.0234168 Y+ 0.0201626 0.0169084 0.0136542 0.0104 0.00714577 0.00389156 0 -2 -1 0 1 2 Z+b) EAT YE C R -T P 0.0358285 0.0334971 0.0311658 0.0288344 0.026503 0.0241716 0.0218403 0.0195089 0.5 0.0171775 Y+ 0.0148462 0.0125148 0.0101834 0.00785206 0.00552069 0.00318932 0 -2 -1 0 1 2 Z+c) E T-T CAR YPE 0.018631 0.0174407 0.0162505 0.0150602 0.0138699 0.0126796 0.0114894 0.0102991 0.5 0.00910883 Y+ 0.00791856 0.00672829 0.00553802 0.00434775 0.00315748 0.00196721 0 -2 -1 0 1 2 Z+ Figure 10: Standard deviation of mean temperature<T2>1/2in the plane (Y+, Z+). Re= 1200. a): X+= 0.5; b): X+= 1; c): X+ = 5 677
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEa) EC ART-TYPE 0.0646835 0.0604049 0.0561262 0.0518476 0.047569 0.0432903 0.0390117 0.0347331 0.0304544 Y+ 0.5 0.0261758 0.0218972 0.0176185 0.0133399 0.00906128 0.00478265 0 -2 -1 0 1 2 Z+b) 1 ECART-TYPE 0.0518896 0.0484646 0.0450396 0.0416146 0.0381896 0.0347647 0.0313397 0.0279147 0.0244897 Y+ 0.0210647 0.5 0.0176398 0.0142148 0.0107898 0.00736482 0.00393984 0 -2 -1 0 1 2 Z+c) ECART-TYPE 0.0336098 1 0.0314054 0.0292009 0.0269965 0.0247921 0.0225876 0.0203832 0.0181788 0.0159743 Y+ 0.0137699 0.0115655 0.5 0.00936104 0.0071566 0.00495217 0.00274773 0 -2 -1 0 1 2 Z+d) 1.5 ECART-TYPE 0.0233372 0.0218155 0.0202938 0.0187721 0.0172504 1 0.0157287 0.014207 0.0126853 0.0111636 Y+ 0.00964191 0.00812021 0.00659851 0.00507681 0.5 0.0035551 0.0020334 0 -2 -1 0 1 2 Z+ Figure 11: Standard deviation of mean temperature<T2>1/2in the plane (Y+, Z+). Re= 2400. a): X+= 0.5; b): X+= 1; c): X+ = 2.5; d) X+ = 5. The figures 12a, 12b, 12c and 12d below represent these standard deviations in theprevious positions of the plane (Y+, Z+) for a Reynolds number of 4800. In the hottest zone,the standard deviation increases when the two jets move along the longitudinal axis. In general, we note that highest standard deviation of the mean temperaturecorresponds to the values of Reynolds number 2400. We saw in the previous section that thiscase of Re = 2400, was one where the dispersion of passive scalar was perfect. 678
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEa) 1 .5 E C A R T -T Y P E 0 .0 3 6 6 7 7 1 0 .0 3 4 2 5 2 2 0 .0 3 1 8 2 7 4 0 .0 2 9 4 0 2 5 0 .0 2 6 9 7 7 7 1 0 .0 2 4 5 5 2 8 0 .0 2 2 1 2 8 0 .0 1 9 7 0 3 2 0 .0 1 7 2 7 8 3 Y+ 0 .0 1 4 8 5 3 5 0 .0 1 2 4 2 8 6 0 .0 1 0 0 0 3 8 0 .0 0 7 5 7 8 9 6 0 .5 0 .0 0 5 1 5 4 1 2 0 .0 0 2 7 2 9 2 8 0 -2 -1 0 1 2 Z+b) 1 .5 E C A R T -T Y P E 0 .0 2 9 6 0 2 7 0 .0 2 7 6 9 2 1 0 .0 2 5 7 8 1 4 0 .0 2 3 8 7 0 8 0 .0 2 1 9 6 0 2 1 0 .0 2 0 0 4 9 6 0 .0 1 8 1 3 9 0 .0 1 6 2 2 8 4 0 .0 1 4 3 1 7 8 Y+ 0 .0 1 2 4 0 7 2 0 .0 1 0 4 9 6 6 0 .0 0 8 5 8 5 9 9 0 .0 0 6 6 7 5 3 8 0 .5 0 .0 0 4 7 6 4 7 8 0 .0 0 2 8 5 4 1 7 0 -2 -1 0 1 2 Z+c) 1 .5 E C A R T -T Y P E 0 .0 2 0 0 0 2 2 0 .0 1 8 6 8 2 8 0 .0 1 7 3 6 3 5 0 .0 1 6 0 4 4 1 0 .0 1 4 7 2 4 7 1 0 .0 1 3 4 0 5 3 0 .0 1 2 0 8 5 9 0 .0 1 0 7 6 6 5 0 .0 0 9 4 4 7 1 7 Y+ 0 .0 0 8 1 2 7 7 8 0 .0 0 6 8 0 8 4 0 .0 0 5 4 8 9 0 2 0 .0 0 4 1 6 9 6 4 0 .5 0 .0 0 2 8 5 0 2 6 0 .0 0 1 5 3 0 8 8 0 -2 -1 0 1 2 Z+d) 1 .5 E C A R T -T Y P E 0 .0 1 4 0 8 0 9 0 .0 1 3 1 7 8 2 0 .0 1 2 2 7 5 4 0 .0 1 1 3 7 2 7 0 .0 1 0 4 7 1 0 .0 0 9 5 6 7 2 3 0 .0 0 8 6 6 4 4 9 0 .0 0 7 7 6 1 7 6 0 .0 0 6 8 5 9 0 2 Y+ 0 .0 0 5 9 5 6 2 9 0 .0 0 5 0 5 3 5 5 0 .0 0 4 1 5 0 8 2 0 .0 0 3 2 4 8 0 8 0 .5 0 .0 0 2 3 4 5 3 5 0 .0 0 1 4 4 2 6 2 0 -2 -1 0 1 2 Z+ Figure 12: Standard deviation of mean temperature<T > in the plane (Y+, Z+). Re= 4800. 2 1/2 a): X+= 0.5;b): X+= 1;c): X+ = 2.5; d) X+ = 5IV. CONCLUSIONS The interaction between a longitudinal flow and two jets preheated has a greatinfluence on the passive scalar dispersion. In view of the figures shown in the previoussections, we can say that when the two jets are issued, the scalar is transported directlydownstream from a straight line by gradually dispersing. This has already been highlightedby Gosse [1], in the wake of Ahmed body. This dispersion is best done in the case where thejets are less influenced by the longitudinal flow. To further explore this issue, a study of thedynamic range must be made to understand the influence of the vortex on the dispersion ofpassive scalar in the turbulent flow.ACKNOWLEDGEMENT The authors acknowledge the CORIA UMR 6614 CNRS University of Rouen-France,and The University Institute of Technology of Ngaoundere, Cameroon. 679
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEREFERENCES[1] K. Gosse. Etude de la dissipation d’un scalaire passif en aval d’un corps d’Ahmed. Ph. D.Thesis. University of Rouen, France, 2006.[2] C. Kupper and F. S. Henry, Numerical simulation of flow in a circular duct fitted with air-jet vortex generators, Int. J. Numer. Meth. Fluids, 38: 919 – 943, 2002.[3] C. P. Tilmann, K. J. Langan, J. G. Betterton and M. J. Wilson, Characterization of pulsedvortex generator jets for active flow control. Symposium on “Active Control Technology forenhanced performance operational capabilities of military aircraft: Land vehicles and seavehicles”. RTO MP-051, 8 – 11. Germany, 2000.[4] P. S. Kothnur and N. T. Clemens, Effects of unsteady strain rate on scalar dissipationstructures in turbulent planar jets. Physics of fluid, 17, 2005.[5] J. Gibb and B. H. Anderson, Vortex flow control applied to aircraft intake ducts. CEASEuropeans Forum on high lift & separation control, Bath, UK, 1995.[6] T. P. Bray and K. P. Garry, Optimisation of jet vortex generators with respect to systemdesign parameters. The Aeronautical Journal, 1999.[7] P. Paranthoën and J. C. Lecordier, Mesure de température dans les écoulements. RevueGénérale de la Thermique, 34, pp. 286 – 308. Elsevier, Paris, 1996.[8] L. Rosset, P. Paranthoën, J. C. Lecordier and M. Gonzalez, Anisotropy of a thermal fieldat dissipative scales in the case of small-case injection. Phys. Fluids., 13, 3729 – 3737, 2001.[9] Kavitha T, Rajendran A, Durairajan A and Shanmugam A, “Heat Transfer EnhancementUsing Nano Fluids And Innovative Methods - An Overview"International Journal ofMechanical Engineering & Technology (IJMET), Volume3, Issue2, 2012, pp. 769 - 782,Published by IAEME.[10] Dr P.Ravinder Reddy, Dr K.Srihari and Dr S. Raji Reddy “Combined Heat And MassTransfer In Mhd Three-Dimensional Porous Flow With Periodic Permeability & HeatAbsorption” International Journal of Mechanical Engineering & Technology (IJMET),Volume3, Issue2, 2012, pp. 573 - 593, Published by IAEME.NOMENCLATURESmall lettersx = longitudinal coordinate (m)y = vertical coordinate (m)z = transversal coordinate (m)d = diameter of the holes on the plate (m)Capital lettersH distance between one of the two holds from the principal axe (m)∆Tréf Temperature difference between hot jet and the exterior (K)T’ Temperature fluctuations (K)Rw Hot wire resistance (Ω)Pui Electrical power supplied (Watt)Ui Flow velocity at the outlet of the nozzle (m.s-1)Uj Jet exit velocity (m.s-1)0x longitudinal axis0y vertical axis 680
    • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME0z transversal axisS The location point of the two jets sourcesGreeksymbolsν Kinetic viscosity of air (m2.s-1)ρ Volume mass (Kg.m-3)λ Thermal conductivity (J.m-2)No dimensional numbersRe Reynolds numberPrt Turbulent Prandtl numberNu Nusselt numberExponents, indices and specials characters+ Normalized value (H for lengths) and (∆Tréf for temperatures)<T> Mean temperature T<X> Means time of a quantity X 2 1/2<X > Standard deviation of a quantity X<X2> Variance of a quantity X 681