Computation of transonic diffuser flows by a lagged k-omega turbulence model

The lag model proposed by Olsen and Coakley is applied in combination with the baseline k–! 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 k–! turbulence model equations.Two test cases are investigated, one with a weak shock in the channel corresponding to an exit-static-toinlet-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.