Prediction of impeller rotating stall onset using numerical simulations of a centrifugal compressor. Part 2: Evaluation of mass-flow fluctuations at rotor–stator interfaces

Rotating stall is an unsteady flow phenomenon that appears in both axial and centrifugal compressors. It is detrimental to the performance of the compressor, significantly narrowing its operating range. Numerical modeling of this phenomenon has been a major area of investigation for axial compressors with some success. While stall occurs less often in centrifugal compressors than axial ones, it can be much harder to predict. Some preventive measures are known but are mostly rules of thumb developed through experimental experience. This work focuses on the prediction of the onset flow rate of impeller rotating stall using computational fluid dynamics. Two different types of unsteady numerical simulations were performed on full 360° models of a compressor that exhibited rotating stall. The transient simulations were conducted using distributed processing on high-performance servers. Fast Fourier transform analysis was used to determine the mass-flow fluctuations in the impeller that can be associated to the phenomenon. The frequency analysis results were then used to determine the onset flow rate for impeller rotating stall. The simulation results and fast Fourier transform analysis were compared to experimental results for the same compressor and show a good correlation between the experimental and numerical tests.