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NUMERICAL SIMULATIONS OF A PASSIVE SCALAR TRANSPORT IN A JET FLOW

NUMERICAL SIMULATIONS OF A PASSIVE SCALAR TRANSPORT IN A JET FLOW. L aboratoire de M odélisation en H ydraulique et E nvironnement. Prepared by : Nabil MRABTI Presented by : Zouhaier HAFSIA. Plan. Introduction. Mathematical model (chen profile at the inlet).

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NUMERICAL SIMULATIONS OF A PASSIVE SCALAR TRANSPORT IN A JET FLOW

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  1. NUMERICAL SIMULATIONS OF A PASSIVE SCALAR TRANSPORT IN A JET FLOW LaboratoiredeModélisationenHydrauliqueetEnvironnement Prepared by : Nabil MRABTI Presented by : Zouhaier HAFSIA

  2. Plan Introduction. Mathematical model (chen profile at the inlet). Rodi adjusments of the standard k-ε constants Numerical results. Conclusions.

  3. INTRODUCTION An important progress was made in the CFD It is possible to simulate a very large varieties of flow transport processes It is necessary to validate the transport model in a simple case : monophasic jet, for example Chen in 1979 adjust turbulence intensity at the inlet of the jet flow with Gaussian profile Since 1980, Rodi showed that the constants of the (k-eps) model depends on the decelaration of axial velocity We use the CFD code PHOENICS for numerical simulations. Numerical results are compared to experimental data of Hu (2000) associated with the establishment zone of the jet flow.

  4. THE JET FLOW PARAMETERS D= 30 mm; Win = 0.20 m/s

  5. GOVERNING EQUATIONS For a stationary single-phase flow and with no buoyancy for a quasi-parallel flow having axial symmetry, the transport equations is : - Momentum - Mass conservation - Kinetic equation : - εequation : - Scalar transport equation :

  6. The model in its form described previously has been applied with success in a lot of type of flow but the universality of its constants cannot be expected. The field of application of this model can be extended thus if its constants are substituted by functions of parameters of the flow. In this context comes the setting of Rodi and al. (1980) relative to jet flows which the constants are replaced by the equations:   : Maximal velocity   : (c: center and e: ambient fluid) The manipulation of the constants of the model can be done by the technique "PLANT" relative to PHOENICS. PLANT is an attachment to the PHOENICS-SATELLITE that allows the users to place in their files of entry, the formulas for which it cannot have an equivalent there in the source program.

  7. RODIADJUSMENTS Wc is the longitudinal mean velocity on the axis of the jet and is the width of the jet when the W is equal to 1%. The gradient of velocity term is approximated by : Thus, we can modify the term directly source of the dissipation rate while substituting, in the expression of, by:

  8. BOUNDARYCONDITIONS : - Standard inlet conditions  : For the kinetic energy and the dissipation rate at the inlet : These two coefficients are adjusted numerically in order to reproduce the experimental data. - Chen profile at inlet  (gaussian profile ) : - For a plane of symetry :

  9. Longitudinal variation of

  10. Longitudinal variation of

  11. Mean velocity profiles Fig. 4 : Velocity Profile at : Z=2D.

  12. Mean velocity profiles Fig. 5 : Velocity Profile at : Z=3D.

  13. RESULTS OF SIMULATIONS Mean velocity profiles Fig. 6 : Velocity Profile at : Z=4D.

  14. Turbulence Intensity profiles Fig.(5-a): Velocity fluctuations profiles at Z=2D.

  15. Turbulence Intensity profiles Fig.(5-a): Velocity fluctuations profiles at Z=3D.

  16. Turbulence Intensity profiles Fig.(5-a): Velocity fluctuations profiles at Z=4D.

  17. Concentrations profiles Fig.(5-a): Concentration profiles at Z=2D

  18. Concentrations profiles Fig.(5-a): Concentration profiles at Z=3D

  19. Concentrations profiles Fig.(5-a): Concentration profiles at Z=4D

  20. CONCLUSIONS * The monophasic jet transporting a passive scalar is affected by the conditions at the injection which describe the nature of the nozzle. * The Rodi adjustments for the jet flow provided significant improvements of hydrodynamic jet structure : for the mean velocity profiles and of the turbulent intensity at three sections in the establishment zone; however the concentrations profiles remain not acceptable. * Although, the modelling of the scalar transport by models which are based on a direct proportionality between diffusivities of momentum and that of the passive scalar appears insufficient. In fact, many authors such us Feath and al (1995) showed that the Schmidt number is variable through the cross-section of the stream discharge.

  21. THANKYOU THANKYOU

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