Pitchwise casing treatment for effects of grooves on dynamics of vortices and loss of blade tip region of a compressor cascade

Abstract

In order to find the controlling mechanism of the pitchwise casing treatment (CT) on a compressor tip leakage vortex (TLV) breakdown and the complex flow on the blade tip, the pitchwise casing treatment of a compressor cascade with a gap is studied using a numerical simulation method. Firstly, the cascade is verified with some existing experimental data. Then, the controlling effect of single pitchwise CT grooves with different axial positions on the TLV breakdown and the tip flow field is studied, and the impact of pitchwise CT grooves about the tip loss is evaluated. Next, the effect of a single pitchwise CT groove on the tip loss is evaluated in cases of different incidences. Then, the controlling mechanism of the blade tip is studied on double pitchwise CT grooves. The obtained results show that the CT grooves at different axial positions can effectively reduce the range of the TLV breakdown, but they have different effects on the tip flow field. Based upon their influence on the tip loss, they can be divided into “Narrow region” CT grooves and “Wide region” CT grooves. When a “Wide region” CT groove is located at 48.7% of the axial chord, the range of the TLV breakdown becomes the smallest and the tip loss is reduced by 24.21%. A “Narrow region” CT groove mainly inhibits the TLV breakdown by delaying the formation of TLV, but the suction effect of the CT groove enhances other backflow structures in the blade tip region. A “Wide region” CT groove mainly inhibits the TLV breakdown by the injection acceleration of the CT groove, and it also reduces other backflow structures in the blade tip region. The “Wide region” CT grooves have better treatment effects than the “Narrow region” CT grooves. The “Wide region” CT groove significantly increases the incidence range of low loss, and the loss is lower than that of a solid wall in large incidence conditions. To a certain extent, it indicates the potential for the compressor that the “Wide region” CT groove to improve the stability margin. When the “Wide region” CT groove is combined with the “Wide region” CT groove, the double groove significantly reduces the tip loss.