Investigation on pressure fluctuations induced by flow instabilities in a centrifugal pump

Abstract

To investigate the pressure fluctuations induced by internal flow instabilities with flow rate variations in a centrifugal pump, combining numerical and experimental methods are applied to detect the complex flow state and identify safe and stable operating conditions of the pump. An analysis of the velocity and vorticity field based on the Q-criterion shows that a region of intensely unstable flow, including rotating stall, leakage vortices, wake flow, backflow and secondary flow, is concentrated upstream of the flow channel near the pump hump point. It was found from the experiments that the extremum of the main frequency of the pressure fluctuations at the pump inlet rapidly decreases to the local minimum value near the pump hump point. And an apparent broadband of the pressure fluctuations at the pump outlet is created between 100 and 150 Hz as the flow rate increases from 0 to 0.4 Qd. Relationships between the flow instabilities and the pressure fluctuations at the pump inlet and outlet are determined to formulate an effective detecting method for the flow state, while the pump outlet pressure fluctuations can serve as indicators of instabilities induced by flow rate variations in the centrifugal pump.