Numerical Study on Cavitation of Auxiliary Blades Centrifugal Pump under Low Flow Conditions

The auxiliary-blade impeller in a five-stage centrifugal pump was investigated through numerical simulation and experimental validation to ensure the accuracy of finite element analysis results. Based on the Homogeneous Equilibrium Cavitation Model, steady-state calculations were employed to evaluate the cavitation performance of the pump with auxiliary blades. The cavitation mechanism and its variation under different flow rates were studied, with transient cavitation simulations conducted to capture dynamic behaviors. The pressure pulsation coefficient under cavitating conditions was analyzed in the frequency domain using Fourier transform. This study focuses on exploring the cavitation flow mechanism in the auxiliary-blade pump under low-flow conditions and analyzing the evolution mechanism of transient cavitation flow induced by auxiliary blades.It was found that for the multi-stage centrifugal pump with auxiliary blades, a lower flow rate corresponds to a reduced the critical NPSH and enhanced cavitation resistance. When the flow rate decreases to 0.3Q (where Q represents the design flow rate), the critical NPSH decreases by 16% compared to the Q condition. Under varying inlet total pressures, cavitation initially occurs at the suction surface near the blade leading edge. As inlet pressure decreases, the cavitation area gradually expands from the blade suction surface to the entire impeller passage, resulting in a significant drop in pump head. The front chamber of the first-stage impeller maintains relatively high pressure, preventing cavitation during normal operation; after cavitation onset, the flow velocity in the front chamber decreases significantly compared to non-cavitating conditions. Following cavitation in multi-stage centrifugal pumps, internal water pressure exhibits unstable fluctuations. As the number of stages increases, the pressure fluctuation range at the outlet of each stage guide vane increased, and the frequency domain vibration amplitude rises. The water storage chamber at the pump outlet exerts a damping effect, reducing vibration amplitudes. Under this damping effect, the low-frequency vibration amplitude generated by cavitation at the pump outlet is lower than that at the guide vane outlet, with the maximum amplitude decreasing about by 2/3.