Vortex development induced by part gap geometry and endwall configurations for variable stator vanes in a compressor cascade

Abstract

The article describes investigations on the three-dimensional (3D) flowfield development near the endwall of a linear compressor cascade which is caused by specific part gap and endwall concepts of adjustable stator vanes. Their beneficial or harmful characteristics, previously measured with outlet loss and flow turning distributions, are investigated inside the passage at different stagger angles to analyse the origin and the interaction of the geometry-induced vortex system. Qualitative blade-to-blade measurements were conducted with particle image velocimetry in several spanwise positions as well as oil flow visualisation on the blade surfaces and the endwall. Improved three-dimensional (3D) numerical Reynolds-averaged Navier–Stokes (RANS) calculations with Reynolds-stress turbulence models were carried out and enhance the experimental findings. Results indicate extensive interactions between secondary flow and leakage flow through a penny gap depending on the aerodynamic loading. The part clearance vortex development and its impact to the blade boundary layers downstream the passage is visualised and enhances the understanding of the geometry effect. Also, the impact of the endwall concepts without radial clearances to the endwall boundary layer is shown and explains their beneficial characteristics compared to a reference geometry.