Experimental Study of Boundary Layer Control Through Tip Injection on Straight and Swept Compressor Blades

Abstract

Recent research on the use of three dimensional blade designs incorporating sweep and casing boundary layer control through tip injection have shown improved efficiency, stage loading and stable operating range Both methods are known to stabilize the flow at the tip trailing edge (Stall Inception Point) of the compressor blade under lower than design mass flow conditions and improve the compressor performance. This study, performed on a low speed axial flow fan, is aimed to improve the understanding and to assess the improved stall margin due to tip injection on swept and straight blades. Injection through flush mounted nozzles on the casing before the rotor blades is of practical importance because of the non-interference of the nozzles with the main flow. Benefits in terms of efficiency and operating range have already been established and swept blades were found to perform better than the baseline straight blades. The injection mechanism involves 12 symmetrically located flush mounted nozzles before the rotor blades in the casing. The number of injection nozzles used is an additional parameter of the study. Although there are manufacturing limitations in the air injection angle, two injection angles (10° and 30°) have been tried. The improvement in stall margin is more pronounced in the straight blades than in the swept blades and the 10° injection angle with 6 active injection holes gives the best performance in comparison to other combinations.