J055032 遷音速遠心圧縮機の羽根なしディフューザにおける非定常流れ構造(〔J055-03〕流体機械の研究開発におけるEFD/CFD(3))

Abstract

Transonic centrifugal compressors for automotive turbochargers operate from near surge limit to choke limit. In order to improve the performance, it is indispensable to understand unsteady flow phenomena in the centrifugal compressors at off-design point. In this study, the flow fields in the vaneless diffuser of a transonic centrifugal compressor at off-design points have been investigated by DES(Detached Eddy Simulation). The numerical simulation results show that the jet-wake structure discharged from the impeller becomes larger with a decrease in the flow rate. At the disturbance onset point, the jet-wake structure flows into the scroll, so that non-uniform pressure distribution appears in the circumferential direction in the scroll. The high-pressure region in the scroll rotates in the impeller rotational direction with a speed close to the impeller rotating speed. At the developed disturbance point, the high-pressure region in the scroll causes steep adverse pressure gradient in the diffuser.