A RANS Method for the Time-Accurate Simulation of Wake-Induced Boundary-Layer Transition in Turbine Flows

Abstract : A time-accurate multistage Navier-Stokes solver has been extended to simulate wake-induced transition in unsteady multistage turbomachinery flow. To this end, the Spalart-Allmaras turbulence model has been modified in several ways and coupled to a transition correlation on the basis of new modeling approaches by other authors. Application to an unsteady test case, a turbine cascade subject to the wake of a moving bar, shows very good agreement with the measurements. First, the turbine cascade is considered without any wake disturbance at two Reynolds numbers. It is shown that the model is capable of simulating laminar separation-bubble induced transition and reproducing correctly the observed Reynolds number effects. In the unsteady case, no separation occurs due to wake-induced transition. The migration of the transition start location is in remarkably good agreement with hot film measurement data.