Numerical investigation on the stage matching in a multistage centrifugal compressor

The performance of a multi-stage centrifugal compressor is commonly generated by stacking the individual stage's performance in the industry applications, which makes the proper stage matching vital in getting favorable performance of the whole machine. Taking a two-stage centrifugal refrigeration compressor as the research object, this paper numerically investigates the two key problems in the stage matching, i.e. 1) The accuracy of overall performance generated by stacking the individual stages' performance; 2) Effects of the inlet and outlet flow distortions on the individual stage performance and the axial thrust. It is found that the overall performance of the multi-stage centrifugal compressor predicted by the stagestacking method generally agrees well with that predicted by the CFD analysis at the small and moderate flow rates, and the difference is getting bigger at the large flow rate. The numerical investigations also show that the effect of inlet distortion on the isentropic efficiency and the total pressure ratio exist mainly at the large flow rate. The radial distortion of the inflow has little influence on the performance, while the circumferential distortion of the inflow affects remarkably. The outlet distortion also has an important influence on the performance of upstream stage. The effect of flow distortions at the inlet and outlet on the impeller thrust is presented as well.