Viscous Computation of Steady/Unsteady Transonic Diffuser Flows

The lag model proposed by Olsen and Coakley (2001) is applied to simulate the steady and unsteady transonic flows in a diffuser. The unsteady flows are induced by imposing fluctuating back-pressures. A fully implicit time–accurate multigrid algorithm is used for solving the Navier-Stokes equations and the coupled k-ω turbulence model equations. Two test cases are investigated, one with a weak shock in the channel corresponding to a static-to-total pressure ratio Rp=0.82 at the diffuser exit and the other with a strong shock corresponding to Rp=0.72. The results with the implementation of the lag model are closer to the experimental data for the strong-shock case. However, the computational results are almost the same with and without the lag model for the weak-shock case.