Assessment of steady and unsteady predictions for a subsonic centrifugal compressor stage

Abstract

The most common procedure to obtain the performance of a centrifugal compressor in an industrial development process is based on the use of a steady RANS model with the mixing-plane approach. However some phenomena such as the flow interaction between the impeller and the diffuser can be the source of unsteady effects which can affect the steady model prediction. This paper investigates the ability of a steady simulation to predict the overall performance and the flow structures in a subsonic centrifugal compressor stage by comparison with time-dependent results. Simulations are performed considering three operating points : peak efficiency, close to the stability limit and close to the blockage. The results show that the steady model is accurate enough to predict the stage static-to-total pressure ratio. However, in location where high level of fluctuation are expected, the steady model shows some weakness to predict the time average quantities of the flow structure.