Steady State Modeling of Unsteady Wake Induced Transition Effects in a Multistage Low Pressure Turbine

As low pressure turbine blade rows can operate at fairly low Reynolds numbers, long laminar boundary layers and transitional separation bubbles are not unusual in conventional blade design. Upstream wakes interact with the boundary layer in multistage low pressure turbine applications in a way that can alter the engine performance. In order to provide quick turnaround times, industrial applications involve steady state computations to a large extent which do not accurately model the unsteady wake effects. In this study, a two-stage low pressure turbine is computed at Reynolds numbers between 40,000 and 180,000 using unsteady and steady RANS methods in the flow solver TRACE by DLR and MTU Aero Engines. A quasi-unsteady wake model working together with the Gamma-ReTheta model by Langtry and Menter is applied to the steady state simulation in another step in order to improve the prediction accuracy of low cost simulations utilizing mixing plane interfaces. The steady state results with and without wake model are compared to the time-resolved reference solution and the computation time is evaluated in order to show that the additional model is able to improve steady state mixing plane simulation results without sacrificing the low computational effort provided by the status quo.