Computational study of turbulent separating flow in an asymmetric plane diffuser

Abstract

A computational study has been performed to compare the mean velocity and turbulent quantities with the experimental test case of Obi et ai. (1993a) which involves separation from a plane wall and subsequent reattachment in the downstream duct of an asymmetric diffuser. The diffusing section has a length of 21H, where H is the inlet channel height, and overall expansion ratio 4.7. The Reynolds number, based on an upstream reference velocity and H, is 21200. The incompressible Navier-Stokes equations for fully developed turbulent flow has been solved by using a standard finite volume CFD code. The convection and diffusion terms of all the equations, including the momentum equations in two directions and the model transport equations for turbulence quantities, have been approximated by the higher order differencing scheme. The SIMPLE algorithm has been used to obtain the pressure field. Standard k - E model and Hybrid turbulence model (Basara and Jakirlic, 2001) have been tested. The Hybrid turbulence model demonstrates an improved result for the mean velocity and turbulence quantities while standard k - E model fails to capture the downstream flow behavior. There are, however some shortcomings in these models particularly in the development of flow after reattachment, which is always predicted to be too slow.