Local Spatial Linear Stability Analysis of Low-Pressure Turbine Endwall Boundary Layer

Abstract

An implicit large-eddy simulation of a low-pressure turbine cascade for an axial chord–based Reynolds number of 100,000 revealed steady longitudinal structures near the endwall that are reminiscent of crossflow vortices. A local spatial linear stability theory analysis with Newtonian eddy model of a profile extracted from the strongly curved section did not indicate any spatially growing steady modes. An unstable steady mode could be identified when the quasi-laminar assumption was made. The mode shape roughly agreed with the observed steady flow structures. Further analysis revealed that this mode was most strongly amplified when the frequency was nonzero. Based on a comparison of the Reynolds stress profiles upstream and inside the cascade, it is argued that the unstable mode may affect the mean flow through a modification of the Reynolds shear stresses.