Study of flow separation control by bleed slot and bleed holes in a transonic compressor cascade

Abstract

An extensive numerical investigation is carried out to study the effects of single-slot bleed and porous bleed on the flow separation control in a transonic compressor stator. Two single slots in different locations and three staggered rows of circular holes are placed on the suction surface. Five bleed pressure ratios are examined for each bleed scheme at the design inlet Mach number of 1.0. The numerical results show that the porous bleed performs similar to the downstream slot bleed in terms of pressure loss control when the bleed pressure ratio is below 1.0. The maximum relative reduction in total pressure loss is 73%. The stable working range of downstream slot bleed is between 0.75 and 1.0 bleed pressure ratio, which is narrower than the range of porous bleed. The bleeding acceleration and favorable pressure gradients on the suction surface are key reasons for keeping the boundary layer from separating. The position of the aft edge of the bleed configuration is a critical parameter. It determines the ultimate range of adverse pressure gradients that the blade surface boundary layer needs to withstand. The similar performance of porous bleed and slot bleed is caused by their identical aft edge position. The high shock losses caused by a single shock wave result in a narrow stable working range for single-slot bleed. Multiple shocks and side bleeding in porous bleed mitigate the influences of shock wave losses and extend its working range.