Improvement of the Flow Range of Transonic Centrifugal Compressors With a Low-Solidity Cascade Diffuser

Abstract

If the pressure ratio of a typical single-stage centrifugal compressor is larger than four, the velocity relative to the impeller and to the diffuser exceeds the velocity of sound. The flow range of transonic centrifugal compressors with a vaned diffuser is usually very narrow. Low-solidity cascade diffusers with solidity 0.69 have been successfully applied as a part of the diffuser system of a transonic centrifugal compressor. On the basis of this type of diffuser, a series of experiments to broaden the operating range are discussed focusing on the control of the geometry of impeller and/or diffuser; one was to reduce the inducer blade turning upstream of the throat, and the other was to reduce the inlet passage width of diffuser. The milder inducer blade camber realized the improvement in flow range by 1.5 times to the original one. Regarding the diffuser inlet passage width contraction, the flow range was not broadened so much owing to the change in impeller characteristics, but the input power was reduced and then the high speed efficiency was much improved.