Numerical Simulation of the Internal Flow Stability in a Centrifugal Pump with High Specific Speed at Partial Load

The present paper aims to study the internal flow stability in a high specific speed centrifugal pump at partial load. Navier–Stokes equations combined with the SST k-ω model were used to numerically simulate internal flow. The Omega vortex identification method and the energy gradient theory were used to analyze the flow field. The results show that the internal flow instability in the centrifugal pump at partial load is due to the backflows at the inlet pipe, the volute tongue and the outlet of the volute, among which the backflow at volute tongue is dominant. It is found when the flow rate decreases to below Q/Qd = 0.792, the main frequency of pressure fluctuation of the centrifugal pump changes from the blade frequency to the shaft frequency. The closer the volute tongue is, the greater the pressure fluctuation is. With the decrease of the flow rate, the areas of stall vortex increase and move from the leading edge of the blade suction to the trailing edge of the pressure surface along the flow passage. Simultaneously, with the decrease of the flow rate, the shear effect near the inner wall of the volute increases, which makes the area of the stall vortex in the pump to increase and makes it easier to lose stability.