Effect of different radial skewed angles of reversed blade-angle slot casing treatment on transonic axial flow compressor stability

Single-channel unsteady numerical simulation was carried out on NASA Rotor 35 to study the influence of radial skewed angle of reversed blade-angle slot casing treatment (RBSCT) on the aerodynamic performance and stall margin of a transonic compressor. Moreover, the influence mechanism is explained by detailed flow field analysis. The radial skewed angles were set to +0°, +30°, +60°, and +75° in the research. The calculated result shows that stall margin improvement (SMI) generated by the slots is increased when the radial skewed angle is gradually increased. The SMI of 17.47% for the slots with +75° radial skewed angle is the biggest among the four RBSCTs. As for the design efficiency improvement (DEI), it is increased first and then decreased with the radial skewed angle increasing. RBSCT with +60°radial skewed angle achieves the greatest DEI of 1.11%. The flow field analysis shows that the radial momentum of the injected and sucked flows is improved with the increasing of radial skewed angle. The improvement can reduce the relative airflow angle of mainstream near the stall condition. Furthermore, the excessive radial skewed angle will increase the flow losses in the slots. Consequently, the design efficiency is reduced at +75°.