The Influence of Discrete Circumferential Grooves Casing Treatment on the Stability Margin of a Subsonic Axial Compressor

To promote the engineering application of casing treatment, this paper proposes the concept of discrete circumferential groove casing treatment. Taking a high-speed subsonic axial compressor rotor as the research object, with the circumferential treatment range fixed at 1/3, a multi-channel unsteady numerical simulation method is employed to investigate the effects of four circumferential groove casing treatment configurations with different distribution patterns on the aerodynamic performance and stability margin of the compressor. The results indicate that the distribution pattern of casing treatment has little impact on the total pressure ratio and adiabatic efficiency of the compressor but has a significant effect on its stability margin. The discrete casing treatment periodically connects the pressure surface and suction surface of the blade tip, reduces the pressure difference, weakens the mass flow rate and momentum of the tip leakage flow, and improves the tip flow state of several channels, which is the fundamental reason for the expansion of the compressor stability margin. In the six-channel simulation, the casing treatment structure distributed with an interval of one pitch exhibits the best stability expansion effect, with the overall stability margin improvement reaching 6.49%. The reason is that this structure reduces the momentum ratio of four tip channels, especially with a better effect on the middle channels, thus achieving the best stability expansion. The overall stability margin improvements of the casing treatment structures distributed with an interval of two pitches and continuous distribution are 6.42% and 5.38% respectively. The reason is that the action range of the circumferential grooves distributed with an interval of zero pitches is always limited to three channels; although the circumferential grooves distributed with an interval of two pitches can also reduce the momentum ratio of four blade tips, their effect on the middle channels is not as good as that of the structure with an interval of one channel, resulting in a slightly worse stability expansion effect. In the 15-channel simulation, the casing treatment structure with 5 consecutive channels distributed in the circumferential direction has the worst stability expansion effect, with the overall stability margin improvement only 3.86%.