Mechanisms of Lean on the Performance of Transonic Centrifugal Compressor Impellers

摘要

Transonic centrifugal compressors with high performance are required in modern gas turbine engines and turbochargers. Lean of the blades is one of the crucial features that have a significant influence on their performance. This paper numerically investigates mechanisms by which lean affects the performance of a transonic impeller with twin splitters. Lean is defined relative to the tangential direction, and the variation range of lean angle has been chosen from -5 to +5 deg. Results show that the variation of efficiency value is 4.5% and the optimal lean angle occurs near 0 deg. Lean influences the flowfields through the effects on the shock structure, the spanwise pressure gradient, the axial-to-radial flow separation, and the secondary flow structure. The induced second blade surface vortex with positive lean tends to migrate the low-momentum flow from hub to shroud, whereas the induced inward spanwise pressure gradient with negative lean enhances the axial-to-radial flow separation, both of which increase the tip leakage loss and lead to the efficiency drop of leaned designs. The optimal lean angle is deduced to be the result of a trade-off between the suppression of axial-to-radial flow separation and the suppression of secondary flow.