Influence of geometrical modeling on the results of numerical prediction for the centrifugal compressor with shrouded impeller

The overall perfomance of a centrifugal compressor prototype stage with shrouded impeller has been measured. Some factors influencing the numerical prediction accuracy and choke mass flow rate have been investigated numerically using different computational models generated by the component superposition method. A structure correction method using the equivalent blade thickness to replace the impeller fillet was proposed and verified. The main goal of this research was to find out a reasonable simulation strategy for the centrifugal compressor with shrouded impeller through assessing the influence of various fine structures and omitted treatments on the overall performance. A peak isentropic efficiency of 80.28% for the compressor stage was obtained experimently while the numerical model with the equivalent blade thickness correction achieved a peak efficiency of 82.02%. The results indicate that the shroud gap and seal, the impeller fillet as well as the blade machining error are the main geometric structure factors to influence the shrouded centrifugal compressor performance. The shroud gap leakage flow decreases the effective throat area of the shrouded impeller, which leads to the decrease of the choke mass flow rate, the acceleration of the fluid in the impeller passage and the reduce of the impeller diffusion ability. At a given exit pressure, the choke mass flow rate decreases with the increase of the impeller blade relative thickness. Using the equivalent blade thickness to replace the impeller fillet can make the compressor maintain an unchanged performance in the small mass flow conditions, but improve the numerical simulation accuracy in the large mass flow conditions.