The effect of opening angle and Reynolds number in a planar asymmetric diffuser studied using LES

The performance of diffuser-like flows occuring in many technical applications is strongly affected by separation and therefore flow control is needed. Here we study flow separation in a plane asymmetric diffuser by the means of LES. The numerical implementation follows the work by Kaltenbach et.al. using the code developed at CTR, Stanford. The incompressible Navier--Stokes equations are solved on a structured grid using a hybrid second order finite difference / spectral method with a dynamic subgrid model. Simulations have been conducted for two opening angles of $8.5^{\circ}$ and $10^{\circ}$ at the Reynolds number $Re_b=9000$ and at $Re_b=2000$ a simulation for an opening angle of $8.5^{\circ}$ matching the experimental configuration of Gullman-Strand et al. has been performed. We have found an increase in the separated region with increasing Reynolds number as well as for a wider opening angle. Future simulations of periodic forcing of the separated flow in the plane asymmetric diffuser will be presented at the conference. Gullman-Strand J. et al., Int. J. Heat and Fluid Flow, 25,pp. 451-460 (2004). Kaltenbach H. J. et. al, JFM, 390, pp. 151-185 (1999)