Predictability of rotating stall and surge in a centrifugal compressor stage with dynamic simulations

A testing campaign performed on a centrifugal compressor test-loop showed that multiple areas of stable operation existed that were not expected. It was shown during the tests that after a first region of instability at low flow rates, a second stable region would appear at even lower flow rates. Dynamic simulations based on a modified reitzer’s model have been performed in order to assess the predictability of these unsteady phenomena. The study is focused on watching the dynamic simulations and the experimental results, concerning the different stable and unstable regions. It was of particular interest to verify the simulation results for the first region of instability, where rotating stall is suspected to occur. In this region the time-averaged performance curve showed a positive, i.e. unstable, slope. The performance curve presents then two regions with negative, stable, slope. The model shows good agreement with the measured pressure fluctuations when operated in surge conditions, both in terms of fundamental surge cycle frequency and pulsation amplitude. Capturing the pressure variations for the rotating stall range proved more difficult and subject to the implemented performance curve, which is considered uncertain in this range. By tuning the performance curve in the corresponding range of flow rates, a satisfactory match with the test results could be achieved. The second range of stability was correctly captured by also modifying the compressor performance curve