Influence of endwall boundary layer suction on the flow fields of a critically loaded diffusion cascade

Abstract

Boundary layer suction is an effective method used to delay separations in axial compressors. Most studies on boundary layer suction have focused on improving the performance of compressors, whereas few studies investigated the influence on details of the flow fields, especially vortexes in compressors. CFD method is validated with experimental data firstly. Three single-slot and one double-slot endwall boundary layer suction schemes are designed and investigated. In addition to the investigation of aerodynamic performance of the cascades with and without suction, variations in corner open separation, passage vortex, and concentration shedding vortex, which are rarely seen for the flow controlled blades in published literatures, are analyzed. Then, flow models, which are the ultimate aim, of both baseline and aspirated cascades are established. Results show that single-slot endwall suction scheme adjacent to the suction surface can effectively remove the corner open separation. With suction mass flow rate of 0.85%, the overall loss coefficient and endwall loss coefficient of the cascade are reduced by 25.2% and 48.6%, respectively. Besides, this scheme increases the static pressure rise coefficient of the cascade by 3.2% and the flow turning angle of up to 3.3° at 90% span. The concentration shedding vortex decreases, whereas the passage vortex increases. For single-slot suction schemes near the middle pitchwise of the passage, the concentration shedding vortex increases and the passage vortex is divided into two smaller passage vortexes, which converge into a single-passage vortex near the trailing edge section of the cascade. For the double-slot suction scheme, triple-passage vortexes are presented in the blade passage. Some new vortex structures are discovered, and the novel flow models of aspirated compressor cascade are proposed, which are important to improve the design of multi-stage aspirated compressors.