Mechanism of affecting ability of casing treatment to improve stall margin with varying axial position of circumferential grooves

The experimental and numerical investigations of three kinds of circumferential grooved casing treatment(CT)were performed to explore the mechanism of affecting the ability of casing treatment of improving stall margin with changing axial position of circumferential grooves. The experimental and numerical results show that the CT of unchanging axial position has the best ability to improve stall margin among three kinds of CT, and the ability of CT with forward axial position is better than that of CT with backward axial position. The experimental stall margin improvement is 10.3%, 7.82% and 5.65%, respectively. The detail analysis of flow-field in compressor tip indicates that the inlet blockage caused by the low energy tip clearance leakage flow appears near the leading edge of blade tip because there are not the positive effect made by grooves on leading edge of blade tip, when the CT moves backward along axial direction. Similarly, tip clearance leakage flow results in the outlet blockage due to the absence of the positive action of grooves near the tip blade tail when the CT moves forward along axial direction. The air flow status in blade tip is the best among three kinds of casing treatments when the axial position of casing treatment is unchanged, so the corresponding effect of improving stable operating range is optimal.