Effect of circumferential grooves casing treatment on tip leakage flow and loss in a transonic mixed-flow compressor

A numerical simulation of a single stage transonic mixed-flow compressor is presented. The simulation is run with a multi-passage grid that models the 3D, viscous, steady and unsteady flow field. The effect of circumferential grooves casing treatment on the compressor overall performance, tip leakage flow and loss has been studied. The results show that the narrow operating range has been significantly broaden by the casing treatment grooves, while the mismatching between the rotor and stator still exists and becomes even worse. Detailed analysis indicates that the fluid from circumferential grooves is injected into the blade passage near the suction surface and re-energizes the leakage flow, which makes mainly contribution to manipulation of the tip leakage flow and stall margin improvement. Since the pressure difference across the blade tip section has a great impact on the effectiveness of circumferential grooves, the positions of shock wave and tip leakage flow as well as where the interaction takes place ought to be taken into account through the casing treatment design procedure.