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Physics of jet turbulence and its RANS modeling

The turbulent jet discharged into a quiescent environment is a canonical turbulent flow that has abundant engineering applications. For industrial process design, the Reynolds-averaged Navier-Stokes (RANS) approach is often used because of its low computation costs and quick turnover time when compared to large-eddy simulations (LES). The faithfulness to jet physics of the turbulence closure model employed in a RANS simulation thus determines the quality of the simulation. Using the data from a time-resolved, stereoscopic particle image velocimetry (SPIV) experiment, the budgets of the turbulent kinetic energy and the turbulent dissipation rate were computed for a jet, and the model coefficients appearing in the standard k-epsilon turbulence closure model were evaluated.  An optimized set of coefficients is proposed for use in jet simulation. Further, the more sophisticated realisable k-epsilon model was found to be incompatible with the experimentally-observed constant eddy viscosity in the jet core; the model will have to use a spatially-varying turbulent Schmidt/Prandtl number to compensate for its predicted non-constant eddy viscosity.

Lai, C.C.K. and Socolofsky, S.A. (2018). Budgets of turbulent kinetic energy, Reynolds stresses and dissipation in a turbulent round jet discharged into a stagnant ambient, Environmental Fluid Mechanics, https://doi.org/10.1007/s10652-018-9627-3

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