An Investigation of the Effect of Cascade Area Ratios on Transonic Compressor Performance

Transonic compressor rotor performance is highly sensitive to variations in cascade area ratios. This paper reports on the design, experimental evaluation and three-dimensional viscous analysis of four low aspect ratio transonic rotors that demonstrate the effects of cascade throat area, internal contraction and trailing edge effective camber on compressor performance. The cascade throat area study revealed that tight throat margins result in increased high speed efficiency with lower part speed performance. Stall line was also improved slightly over a wide range of speeds with a lower throat-to-upstream capture area ratio. Higher internal contraction, expressed as throat-to-mouth area ratio, also results in increased design point peak efficiency, but again costs performance at the lower speeds. Reducing the trailing edge effective camber expressed as throat-to-exit area ratio, results in an improvement in peak efficiency level without significantly lowering the stall line. Among all four rotors, the best high speed efficiency was obtained by the rotor with tight throat margin and highest internal contraction, but its efficiency was the lowest at part speed. The best compromise between high speed and part speed efficiency was achieved by the rotor with a large throat and a lower trailing edge effective camber. The differences in the shock structure and the shock boundary layer interaction of the four blades was analyzed using a three-dimensional viscous code. The analytical results are used to supplement the data and provide further insight into the detailed physics of the flow field.