The Impact of Transition and Turbulence Modeling on the SPLEEN High-Speed Low-Pressure Turbine Cascade

In high speed low pressure turbines (LPTs) for geared turbofan engine applications, transonic flow conditions combined with low Reynolds number operation depict a flow scenario where shock waves can interact with laminar or turbulent boundary layers, and the resulting flow topologies pose serious challenges for computational fluid dynamics (CFD) analyses. In this work, two different in house developed Reynolds Averaged Navier Stokes (RANS) solvers are applied to the study of a transonic low pressure turbine cascade over a range of Mach and Reynolds numbers, with a focus on the performance of transition and turbulent closures. The selected test case consists of the SPLEEN (Secondary and Leakage Flow Effects in High Speed Low Pressure Turbines) C1 cascade, a state of the art high speed low pressure turbine blade section that has been investigated in an extensive experimental campaign at the von Karman Institute, in the framework of the SPLEEN European Research Programme. The considered transition sensitive turbulence closures are representative of the most advanced techniques for RANS methods and range from correlation based intermittency transport approaches to phenomenological model based on the laminar kinetic energy (LKE) concept and the k v'2 w framework. It is shown how realistic transition modeling is crucial for predicting blade loading distributions and then addresses design challenges for transonic LPT bladings. A discussion concerning the reproduction of wake loss profiles demonstrates how classical linear eddy viscosity closures can be adequate in the case of attached flow even in transonic flow conditions but fall short in predicting the intense wake mixing brought about by the thick turbulent boundary layers that are formed past laminar separation bubbles.