Experimental investigation of hole-type bleed for active flow control in an axial compressor cascade with tip clearance

Boundary layer aspiration using bleeding is a potential technique for active flow control. This study explores the influence mechanism of hole-type bleed on the secondary flow loss through a low-speed wind tunnel experiment. Compared with the suction slot, the hole-type bleed for boundary layer aspiration has the advantages of good flexibility and high strength. In this study, the tip leakage vortex (TLV) and passage vortex (PV) in a compressor cascade with a tip clearance are effectively controlled through the hole-type bleed experimentally. The optimal bleeding hole position is located at 25% c_x downstream of the blade leading edge near the blade suction surface. An 8.34% performance benefit in the C_pt with a bleed mass flow rate of 0.66% is obtained. It is found that the optimal bleeding hole position is highly correlated to the position where the TLV and PV originate in the baseline. Moreover, the balance between the controlling of the TLV and PV is considered to strongly determine the performance benefit obtained in the compressor cascade. The findings reveal that the secondary flow loss control mechanism under the hole-type bleed from two aspects: delayed vortex origination and clearance blockage.