Numerical Investigation of Active Flow Control of Low-Pressure Turbine Endwall Flow

The endwall flow in a highly loaded linear low-pressure turbine cascade has been numerically investigated for a chord-based Reynolds number of 100,000. Mean flow visualizations reveal a horseshoe vortex at the endwall-leading edge junction. The pressure side leg of the horseshoe vortex develops into a highly coherent passage vortex. The passage vortex is supported by a strong secondary flow that impinges on the endwall and spreads in the pitchwise direction. A dynamic mode decomposition reveals temporally growing three-dimensional modes that are susceptible to unsteady flow control. Based on the modal analysis and physical understanding of the mean flow topology, several different steady and unsteady flow control strategies were devised for weakening the passage vortex, countering the secondary flow, and reducing the suction side corner flow separation. Steady blowing that directly opposes the secondary flow effectively lowers the total pressure losses but requires large amplitudes, which makes it inefficient. Unsteady forcing is demonstrated to be an efficient way for decreasing the coherence of the passage vortex and for obtaining a moderate reduction of the total pressure losses.