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.
