Numerical Examination of the Dynamic Evolution of Fluctuations in Cavitation and Pressure in a Centrifugal Pump during Startup

Rapid changes in the performance-related parameters of a pump during its startup operation lead to large pressure fluctuations and structural vibrations in it. In view of these problems, this study investigates the evolution of cavitation and the characteristics of fluctuations under pressure in a centrifugal pump during startup. We use the finite volume method to simulate this dynamic process. To characterize the acceleration, we assume that the rotational speed and rate of flow of the pump are not constant but vary with time. A steady-state numerical simulation is performed to examine the external characteristics of the pump to verify the accuracy of the numerical procedure. The evolution of fluctuations in the cavity and pressure over time is then analyzed in detail. We use the short-term Fourier transform for post-processing in light of its advantage in treating non-stationary signals. The results indicate that both the frequency and the amplitude of the fluctuations in pressure increase with the speed of the impeller. The transient operation causes the average pressure at the inlet of the impeller to decrease to the evaporation pressure, and this leads to an increase in the volume fraction of vapor. Moreover, both the impeller-tongue interaction and the impeller-diffuser interaction influence the fluctuations in cavitation.