FLUENT Fluent Software Trainin Ncct⊙tLD TRN-99-003 Why model Turbulence? Direct numerical simulation of governing equations is only possible for simple low-Re flows Instead, we solve Reynolds averaged Navier-Stokes(RANS equations aU Op aU aR p k ai ardr y(steady, incompressible flow +u w/o body forces where Rii=- pu;ul (Reynolds stresses) Time-averaged statistics of turbulent velocity fluctuations are modeled using functions containing empirical constants and information about the mean flow Large Eddy simulation numerically resolves large eddies and models c Fluent Inc. 2/20/01D3 © Fluent Inc. 2/20/01 Fluent Software Training TRN-99-003 Why Model Turbulence? u Direct numerical simulation of governing equations is only possible for simple low-Re flows. u Instead, we solve Reynolds Averaged Navier-Stokes (RANS) equations: where (Reynolds stresses) u Time-averaged statistics of turbulent velocity fluctuations are modeled using functions containing empirical constants and information about the mean flow. u Large Eddy Simulation numerically resolves large eddies and models small eddies. (steady, incompressible flow w/o body forces) Rij = - ruiu j j ij j j i k i i k x R x x U x p x U U ¶ ¶ + ¶ ¶ ¶ + ¶ ¶ = - ¶ ¶ 2 r m