Effects of recessed blade tips on stall margin in a transonic axial compressor

In this paper, a recessed blade tip was applied to a transonic axial compressor in expectation of increasing the stable operating range. The internal flow has been calculated by a commercial flow solver for different recess cavities on the blade tip and the predicted performances for each case have been compared with one another. It was found that the recessed blade tip with a proper depth and length is effective to increase the stall margin. The tip leakage flow became weak due to a strong vortex generated in the recess cavity so that it was pushed backward by the main flow. This is why the recess cavity can increase the stall margin without any reduction of the adiabatic efficiency at the design point. Additionally, based on the comparison of the circumferential velocity between the numerical and the theoretical results, it was found that the rim of the recessed blade tip can work as the labyrinth seal and consequently reduce the mass flow rate through the tip clearance.