Improvement in the performance of a high-pressure-ratio turbocharger centrifugal compressor by blade bowing and self-recirculation casing treatment

Abstract

Blade bowing together with a self-recirculation casing treatment was introduced into a high-pressure-ratio turbocharger centrifugal compressor in order to improve the performance. Experiments were conducted to investigate the effects of blade bowing and the self-recirculation casing treatment on the compressor performance. The results showed that, in comparison with the baseline (with radial blades), negative blade blowing increased the choke mass flow rate and the peak efficiency by 3.41% (relative value) and by 4.31% (absolute value) respectively at the designed speed. Furthermore, negative blade bowing together with the self-recirculation casing treatment improved the stable flow range of the compressor by 5.85% at the designed speed. Numerical simulation was conducted to analyse the flow mechanism. The result showed that, in the choke condition, bowing affects the actual throat area and thus changes the choke mass flow rate. Negative bowing enlarges the throat area. In the design condition, bowing affects the migrating process of the secondary flow at the suction surface and redistributes the low-energy fluids along the span. Negative bowing tends to advance the separation of the boundary layer flow at the suction surface and to alleviate accumulation of the low-momentum fluid near the blade tip; these lead to improvement in the compressor efficiency. The self-recirculation casing treatment decreases the effective flow area of the impeller passage and introduces a jet into the flow field near the blade tip, thereby increasing the axial velocity of the fluid near the shroud. This reduces accumulation of the low-energy fluid in the blade tip, thus delaying impeller stall.