Influence of Boundary Layer Skew on the Tip Leakage Vortex of an Axial Compressor Stator

Abstract

For an axial compressor stator with tip gap, the boundary layer (BL) in the hub endwall region has a significant influence on the development and progression of the tip leakage vortex. Herein, the so-called BL skew, which develops through relative motion of the hub, is of particular interest. Therefore, experimental and numerical investigations of a single axial compressor stator row with varying tip gap height (tip gap height/chord length =2.0%|5.4%|6.7%) have been conducted. Comparing cases with rotating or stationary hub endwall segments upstream of the examined vanes allowed to determine the effect of the skewed and un-skewed inflow BL. The steady-state flow fields up- and downstream of the stator row were measured using five-hole pressure probes. For validation and to improve the understanding of the existing flow phenomena, 3D-Reynolds-averaged Navier–Stokes (RANS) CFD simulations using a commercial flow solver were carried out. Furthermore, analog cases with no tip gap were examined and considered in the comparisons to extend the knowledge on this BL characteristic. The results show that the BL skew has a major influence on the trajectory and size of the tip leakage vortex for the cases with tip clearance. The effect of reduction of the produced losses decreases with increasing tip gap height.