Direct Numerical Simulations of the SPLEEN cascade: a study of the impact of compressibility on transition and separation in a low-pressure turbine passage

A detailed experimental analysis of the flow in a representative high-speed low pressure turbine cascade, dubbed SPLEEN C1, was undertaken in the framework of the SPLEEN project. The latter is supplemented by a Direct Numerical Simulation campaign in view of interpreting the observed flow. The simulations are undertaken using ArgoDG, a high order discontinuous Galerkin code developed at Cenaero, which has been a.o. equipped for studying cascade flows. This paper presents subsonic (Ms,out = 0.7), transonic (Ms,out = 0.9) and choked conditions (Ms,out = 0.95) at two different Reynolds numbers (Res,out = 70×103 and 120×103) without inlet turbulence. Visualisations of the flow are provided through Mach contours and numerical Schlieren. Numerical and experimental results are compared based on pressure and skin friction distribution as well as boundary layer state and losses. The
impact of compressibility is highlighted, suppressing the separation on the suction side for choked conditions. Choking also prevents acoustic perturbations to propagate upstream. Separation and transition on the pressure side develop independently.