Periodic transient pressure fluctuation in a high-speed centrifugal pump using variational mode decomposition combined with the Hilbert transform

Taking a high-speed centrifugal pump with a motor power of 280 kW and a rotational speed of 9685 r/min as the research object, large eddy simulations are conducted under transient and quasi-steady conditions. The flow rate of the former condition exhibits sinusoidal variation and oscillates between 0.25Qd and 0.75Qd (Qd represents the design flow rate). The low-frequency pressure fluctuation exhibits significant periodicity and is followed by a substantial number of high-frequency components. The dynamic features of the pressure fluctuation at the guide vane channel and near the volute tongue are examined using variational mode decomposition combined with the Hilbert transform. The number of intrinsic mode functions (IMFs) under transient condition is one greater than that under quasi-steady condition. The central frequency of the additional IMF is equal to the flow rate frequency, and the basic frequency remains at six times the rotational frequency. The amplitudes of the first three order modes are comparable, which is clearly observed at the guide vane channel inlet under transient conditions. The root mean square (RMS) value of the first intrinsic mode function (IMF1) component under transient condition is significantly greater than the corresponding value under quasi-steady condition near the volute tongue. Both the RMS value of the IMF1 component and the basic frequency amplitude generally decrease from upstream to downstream, and these trends have a small correlation with changes in the flow rate.