Analysis of rotor/stator interactions in a high-speed low-pressure turbine cascade using Large-Eddy Simulations.

Abstract

Turbomachinery flows are highly turbulent and prone to different types of instabilities. In low-pressure turbines (LPT), the wakes from the upstream bladerows provide the dominant source of unsteadiness. For Reynolds numbers at which LPT are generally operating, the majority of the blade boundary layer remains laminar. As a matter of fact, the suction side boundary layer of such flow is responsible for most of the efficiency loss. It is thus crucial to master the impact of the incoming wake turbulence and its effect on the transition of this boundary layer to master the generated losses. Such a rotor/stator interaction in new generation of low-pressure turbines, with the particularity of being locally transonic, is addressed numerically in this work. The considered geometry consists in a linear blade cascade in front of which bars rotate, acting as wake generators that periodically impact the blades leading edges, thereby influencing the aerodynamics of the cascade. For this study, Large-Eddy Simulations (LES) are carried out and compared to experimental results acquired at the Von Karman Institute during the Cleansky project SPLEEN. This paper investigates the interactions between the periodically incoming wakes and the turbine cascade. The transition of the suction side boundary layer, the pressure side separation bubble and the wall shear stress on the blade surface are specifically analysed along with the temporal evolution of the sonic pocket.