Comparison of Two Diffusers in a Transonic Centrifugal Compressor

Abstract

Flow mechanisms suppressing the flow separation in two diffusers, a low‐solidity cascade diffuser and a vaned diffuser with additional small vanes near the inlet, were compared mainly by numerical simulation. As the superiority of the low‐solidity cascade diffuser was expected, a series of experiments was conducted using a transonic centrifugal compressor with a maximum pressure ratio of 7. The performance of the compressor with the vaned diffuser was comparable to that of the low‐solidity cascade diffuser only between the surge point and the design flowrate at a pressure ratio of 3.5. The maximum flowrate of the vaned diffuser was lower than that of the low‐solidity cascade diffuser. At higher rotational speeds, the pressure ratio at the surge point, the efficiency, and the flow range of the low‐solidity cascade diffuser exceded those of a vaned diffuser at a pressure ratio of 3.5.