Combined control of variant clearance and casing aspiration on tip flow field and instability of a transonic compressor

To enhance the transonic compressor performance, the axially non-uniform variant tip clearance schemes and combined schemes with casing aspiration were applied and their effects on the tip flow field and flow instability were studied numerically. The results show that the expanding tip clearance can increase the stall margin and peak efficiency by reducing the tip leakage flow intensity within the first half chord, and cause the interface between the leakage flow and mainstream to move downstream. The effect of the shrinking clearance is on the contrary. The compressor performance can be further improved by the combination of expanding clearance and casing aspiration. When the circumferential suction groove is located at 35% of the axial chord length corresponding to the low-velocity region due to the leakage vortex breakdown, the stability enhancement is the largest, which is about 7.2% higher than that under the uniform clearance scheme. Casing aspiration decreases the blade tip loading and attenuates the tip leakage vortex, tip secondary vortex, and their interaction, which results in the suppression of vortex breakdown and tip flow blockage. Moreover, the oscillations and instability of the flow field are weakened. Therefore, the tip flow field is modified and the compressor performance is improved.