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 simulation 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. Accurate modeling of rotating stall will allow for better understating of the onset conditions and possible preventive measures that may be adopted during the design stage, before testing.This work focuses on the prediction of impeller rotating stall using Computational Fluid Dynamics. A compressor was chosen that has demonstrated rotating stall instabilities with different diffuser lengths and return vanes. Unsteady numerical simulations were performed to establish the reliability with which rotating stall can be captured, as compared to the experimental results. Fast Fourier Transform analysis was used to determine the mass-flow fluctuations in the domain that can be associated to the phenomenon. These observations were then used to determine the onset flow rate for impeller rotating stall. Finally, a redesign of the compressor is proposed and analyzed using the developed methodology.
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