Computation of transonic diffuser flows by a lagged κ-ω turbulence model

The lag model proposed by Olsen and Coakley is applied in combination with the baseline κ-ω two-equation turbulence model to simulate the steady and unsteady transonic flows in a diffuser. A fully implicit time-accurate multigrid algorithm is used to solve the unsteady Navier-Stokes equations and the coupled κ-ω turbulence model equations. Two test cases are investigated, one with a weak shock in the channel corresponding to an exit-static-to-inlet-total pressure ratio Rp=0.82 and the other with a strong shock corresponding to Rp=0.72. Unsteady flows are induced by imposing fluctuating backpressure. Computational results are compared with experimental data and demonstrate notable improvement by the lag model for flows with strong shock-boundary-layer interactions.