Multi-Fidelity Study of Secondary Flow and Transition in the SPLEEN Cascade With Endwalls

High-speed low-pressure turbines (LPTs) for geared turbofan engine application are affected by aggressive flow environments, characterized by high Mach numbers and low Reynolds numbers at the same time. Such operating conditions are very challenging from a flow modelling point of view, with shock-waves and three-dimensional effects that have the potential to influence boundary layer transition and losses. This paper offers a comprehensive CFD investigation of the SPLEEN C1 case study, a state-of-the art high-speed low pressure turbine test case tested experimentally at the von Karman Institute. The three-dimensional flow in the cascade is analyzed using different transition closures implemented in an in-house developed RANS/URANS solver (TRAF code), with particular focus on mutual interaction with shock waves and secondary flows. They include the gamma-ret model and a novel transition/turbulence closure based on the laminar kinetic energy concept. The study aims at the definition of a RANS numerical setup suitable for the design of high-speed low-pressure turbines for geared turbofan applications. RANS predictions are assessed by comparison with a large database of detailed experimental data in terms of blade surface distributions of relevant flow quantities and field measurements obtained with Particle Image Velocimetry. Preliminary LES calculations for the cascade midspan section are also discussed in order to gain more insights in the boundary layer structure provided by RANS analyses.