INVESTIGATION ON THE IMPACT OF CIRCUMFERENTIAL GROOVES ON AERODYNAMIC CENTRIFUGAL COMPRESSOR PERFORMANCE

Casing treatments are widely used in compressors for increasing range, stability and aerodynamic performance. However, applications in centrifugal compressors, as commonly used in turbochargers, are rare and mostly applied at the inlet region in terms of bleed slots. This paper presents the application of circumferential grooves, which are known to increase stability and performance in axial compressors, to the rear part of the impeller shroud casing in a centrifugal compressor. Experimental and numerical investigations of three different configurations have been performed and compared with the initial geometry. Experiments were conducted on a hot gas test facility where static pressure and temperature measurements up- and downstream of the compressor were acquired. The results indicate only small changes in operating range except for one speedline, where a considerable improvement is observed. Efficiency remains nearly unaffected for all configurations whereas the pressure ratio is increased at some operating points. For detailed examination of the compressor flow field, CFD analyses were conducted using steady-state RANS calculations. Structured meshes with node to node connections were used to suspend any possible influences stemming from interfaces in regions of interest. Validation with test data yields good agreement concerning choke margin and gradient trends. CFD results confirm that the investigated configurations of circumferential grooves have only small impact on efficiency and pressure ratio. Investigations on the mechanism which balances the additional losses due to increased groove surface friction and increases pressure rise are presented.