Effects of moving endwall on the unsteadiness of tip leakage flow in compressor cascades

Abstract

The influence of the moving endwall on the behavior of the tip leakage flow in compressors holds substantial significance. This work investigates the unsteadiness of the compressor's tip leakage flow under the impact of the moving endwall, employing both experimental methods and unsteady Reynolds-averaged Navier–Stokes (URANS) simulations. First, a numerical decomposition technique is proposed to isolate the tip leakage flow within a controlled diffusion airfoil (CDA) cascade. Subsequently, URANS simulations based on the CDA cascade are conducted at various incidence angles (−6° to +7°), tip clearances (clearance to chord: 0.83% to 3.33%), and flow coefficients (0.4 to 0.6), and additional URANS simulations based on the Virginia Tech cascade are also performed. The results indicate that the moving endwall induces a greater inclination of the tip leakage flow in the pitchwise direction, allowing it to impinge upon the pressure side of the adjacent blade. The impingement, if sufficiently intense, leads to the periodic generation of unsteady tip leakage flow by altering the blade loading. Moreover, the degree of unsteadiness diminishes significantly as the endwall speed and clearance height decrease. Additionally, it is observed that the breakdown of the tip leakage vortex does not serve as the root cause of the periodic unsteadiness. These findings underscore the critical role played by the moving endwall in the unsteadiness of the compressor's tip leakage flow.