BOUNDARY LAYER SUCTION FOR SECONDARY FLOW CONTROL IN A COMPRESSOR CASCADE AT OFF DESIGN CONDITIONS

An experimental investigation of secondary flow control by boundary layer suction at discrete locations has been carried out throughout the last years. The focus in the investigations has been set to understanding the phenomena present at aspirated compressors and giving guidelines for practical implementation of suction into compressors. All experiments have been performed at the High Speed Cascade Wind Tunnel HGW of the German Aerospace Center DLR in Berlin. The chosen airfoil is a NACA 65 type due to its widely known characteristics and the good performance at the aerodynamic design point. Design conditions include a Mach number of 0.67 and a Reynolds number of 560.000 based on 40mm chord length. Former investigations have proven the working principles at design conditions, this work aims at presenting off design data which is of importance for the system integration. The results show that there is a wide range of incidence angles at which the boundary layer suction is effective. The total pressure loss can be decreased by substantial amounts. In the surge and stall area at low and high incidence angles, the efficiency of the suction depends strongly on the shape of the suction slots. Anyhow the flow control is not capable of affecting the flow if complete separation of the boundary layer has already occurred. The effectiveness of the suction is best near aerodynamic design conditions.