Numerical Simulation and Evaluation of Velocity Fluctuations During Rotating Stall of a Centrifugal Pump

Flow instabilities like rotating stall can lead to severe vibrations in turbomachines if the eigenfrequency of the rotor is equal to the stall frequency. The goal of the present work is to shed some light on the origin of the rotating stall phenomenon in a centrifugal pump. The resulting fluctuating loads are quantified using numerical computations. For the chosen configuration transient PIV data are available for validation. In addition to measuring the stall frequency in the stationary frame, the CFD data is analyzed in the rotating frame. A Fourier analysis is done for a large number of sample points. This enables us to determine the local variation of amplitudes for a given frequency. Together with eigenfrequencies and eigenmodes of the rotor determined from modal analysis, it is possible to evaluate the risk of resonance vibration excited from fluctuating fluid forces.