The effect of radial skew angles of blade angle slots on the stability and performance of an axial flow compressor

The parametric numerical study was performed to explore the effect of radial skew angles of blade angle slot casing treatment(CT) on the stability and performance of an axial flow subsonic compressor. Five kinds of blade slot casing treatment with difference radial skew angles (0 degree, 30 degrees, 45 degrees, 60 degrees, and 75 degrees) were designed in the numerical investigations. The unsteady calculated results show that among the radial skew angles of 0 degree, 30 degrees, 45 degrees, 60 degrees, the bigger the radial skew angle of the slots is, the greater the stall margin improvement(SMI) generated by the slots is, and the slots with 60 degrees radial skew angle can generate 58.86% SMI. Moreover, the SMI for the slots with 60 degrees radial skew angle is 29.64% more than that for the slots with 75 degrees radial skew angle. Besides, the slots with radial skew angle of 75 degrees cause the least penalty in peak efficiency among five kinds of radial skew angle, and the peak efficiency for the slots with 75 degrees radial skew angle is 0.88% higher than that for smooth wall casing treatment. The slots with 0 degree radial skew angle generate the biggest peak efficiency loss of 5.94% among five kinds of radial skew angle. The flow field analyses show that the recirculated flows formed in the slots can generate momentum transport effects on the flow field in the blade tip. Under the effects of the momentum transport, the momentum balance between the tip leakage flow(TLF) and main flow(MF) is changed, and the momentum balance determines the trajectory of the TLF and the mainstream/tip leakage flows interface. As a result, the flow condition in the tip channel is also changed. By changing the radial skew angle of slots, the slots behave different capacities of momentum transport on the tip flow field, and the momentum balance between tip leakage flow and main flow is changed differently. So, the trajectory of the TLF and the mainstream/tip leakage flows interface are deflected differently. Different improvements of the compressor stability are obtained by the slots with different radial skew angles. The slots with radial skew angle of 60 degrees can largely deflect the trajectory of TLF and the mainstream/tip leakage flows interface to the blade suction surface. It improves the flow condition of the blade tip channel, and the slots generate 58.86% SMI. However, after the slots with radial skew angle of 0 degree and 30 degrees are applied, the tip leakage vortex breakdown is occurred. So, they generate few improvements of the stall margin. Furthermore, the interaction between recirculated flows inside slots and main flows inevitably causes additional flow losses. With the increase of radial skew angle, the efficiency loss caused by slot CT decreases. Thus, the slots with 75 degrees radial skew angle generate the least peak efficiency loss among five kinds of radial skew angle.