The Role of Vortex Stretching In Turbulence Modeling
Traditional models for the turbulent dissipation rate assume an equilibrium in which the production by vortex stretching is exactly balanced by the leading order part of the viscous destruction term. In the present study, the effect of allowing for unbalanced vortex stretching is explored in an effort to describe departures from equilibrium. It is found that the presence of a small unbalanced vortex stretching term has a number of profound consequences for the calculation of isotropic decay, homogeneous shear flow, and more complex turbulent shear flows with separation. In the case of isotropic decay it accounts for enstrophy blow-up in the limit of zero viscosity, while for homogeneous shear flow it predicts a production-equals- dissipation equilibrium at large times instead of an unbounded exponential growth of turbulent kinetic energy. Preliminary calculations for turbulent flow over a backward facing step indicate that even a minute imbalance in vortex stretching can have a major influence on the reattachment length.
KeywordsVortex Vorticity Librium Rium Univer
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- Bernard, P. S. and Speziale, C. G. 1991 “Bounded Energy States in Homogeneous Turbulent Shear Flow—An Alternative View,” ASME J. Fluids Eng., in press.Google Scholar
- Eaton, J. and Johnston, J. P. 1980 “Turbulent Flow Reattachment: An Experimental Study of the Flow Structure Behind a Backward Facing Step”, Technical Report MD-39, Stanford University, Stanford, CA.Google Scholar
- Hinze, J. O., 1975 Turbulence, McGraw-Hill.Google Scholar
- Lesieur, M. 1990 Turbulence in Fluids, 2nd edition, Martinus Nijhoff.Google Scholar
- Speziale, C. G. and Bernard, P. S. 1991 “The Energy Decay in Self-Preserving Isotropic Turbulence Revisited”, ICASE Report No. 91-58, NASA Langley Research Center.Google Scholar
- Thangam, S. and Speziale, C. G. 1991 “Turbulent Separated Flow Past a Backward Facing Step: A Critical Evaluation of Two-Equation Turbulence Models,” AIAA J., in press.Google Scholar