Study of a transonic centrifugal compressor with high flow coefficient tailored for high-altitude long-endurance unman- aerial-vehicle (HALE UAV)

A high-efficient and lightweight high-pressure-ratio centrifugal compressor is the critical requirements for HALE UAV powered by piston-engine. But both factors, including the light-weight and high altitude, impose a challenge on the improvement of compressor efficiency due to large flow coefficient and low Reynolds number effect. This study comparatively investigates the performance and flow mechanism of a newly designed high-pressure-ratio centrifugal compressor with ultra large flow coefficient at high-altitude low Reynolds number conditions. Firstly, high-pressure-ratio centrifugal compressor with ultra-high flow coefficient (0.13) is designed in order to notably achieve significant compactness. The flow coefficient was increased by 44.4% compared with the original compressor. Next, the effect of high-altitude low Reynolds number on the compressor is studied comprehensively. At the cruise altitude 25 km, the peak efficiency, pressure ratio and choke mass flow rate of the compressor deteriorate significantly by 8.4%, 13.4%, and 6.7%, respectively. It is confirmed that performance deterioration is mainly caused by the interaction of strong shock and laminar flow separation on suction surface in the impeller inducer. The design concept of ultra-high flow coefficient significantly enhances the shock in the inducer as well as the sensitivity of laminar separation to blade geometry, thus the performance deterioration. Based on the loss mechanism, the design method is proposed attenuate the effects of interaction between shock and laminar separation due to low Reynolds number effect. Pressure ratio and efficiency are improved by 10% and 1.3%, respectively at high altitude conditions by the new method.