Introductory FLUENT Notes Fluent User Services cente ANSYS LUENT v6. 3 December 2006 wwfluentusers. com FLUENT The closure problem The RaNS models can be closed in one of the following ways (1) Eddy viscosity Models(via the boussinesq hypothesis) Ou Ou,2 ai puiu 8n-=pkδ Boussinesq hypothesis Reynolds stresses are modeled using an eddy(or turbulent) viscosity, u. The hypothesis is reasonable for simple turbulent shear flows: boundary layers, round jets, mixing layers, channel flows, etc (2)Reynolds-Stress Models(via transport equations for Reynolds stresses Modeling is still required for many terms in the transport equations RSM is more advantageous in complex 3D turbulent flows with large streamline curvature and swirl, but the model is more complex, computationally intensive, more difficult to converge than eddy viscosity models C 2006 ANSYS. nc All ANSYS, Inc. Proprietar© 2006 ANSYS, Inc. All rights reserved. 6-8 ANSYS, Inc. Proprietary Fluent User Services Center www.fluentusers.com Introductory FLUENT Notes FLUENT v6.3 December 2006 The Closure Problem ◆ The RANS models can be closed in one of the following ways (1) Eddy Viscosity Models (via the Boussinesq hypothesis) ⚫ Boussinesq hypothesis – Reynolds stresses are modeled using an eddy (or turbulent) viscosity, μT. The hypothesis is reasonable for simple turbulent shear flows: boundary layers, round jets, mixing layers, channel flows, etc. (2) Reynolds-Stress Models (via transport equations for Reynolds stresses) ⚫ Modeling is still required for many terms in the transport equations. ⚫ RSM is more advantageous in complex 3D turbulent flows with large streamline curvature and swirl, but the model is more complex, computationally intensive, more difficult to converge than eddy viscosity models. i j i j k k i j j i i j i j k x u x u x u R u u  −     −            +   = −   =  3 2 3 2 T T