Effects of recessed blade tips on the performance and flow field in a centrifugal compressor

Abstract

This article presents a numerical investigation of the influence of a recessed blade tip on the performance and flow field in a centrifugal compressor with a vaned diffuser. Steady computations were performed for three different blade tip geometries over their whole operating ranges. A flat tip blade was used as a baseline case to assess two different recessed blade geometries. It was found that recessed blade tip designs could improve the total-to-total pressure ratio and efficiency over whole operating ranges. The recessed tips were also effective in reducing the tip leakage flow. However, the recess cavity had an adverse effect on the efficiency due to the generation of a vortex in the cavity. As a result, the overall stage loss was reduced in the recessed cases because the positive effect of the reduced tip leakage flow ended up being superior to the negative effect of a strong vortex in the cavity. In addition, the diffuser performance of the centrifugal compressor could be enhanced with the recess cavity, because the pressure recovery coefficient was higher in the recessed cases than in the flat tip case. A parametric study was conducted to determine the geometry of a recess cavity with improved performance. This study revealed that as the cavity volume increases, the tip leakage flow continuously decreases but the strength of the cavity vortex increases. Therefore, it may be possible to optimize the recess cavity geometry further.