Effects of inlet gas volume fraction on vibration damping and noise reduction characteristics of marine pump

Abstract

This study experimentally investigates the effects of inlet gas volume fraction (C=0.0 %–0.75 %) on vibration damping and noise reduction in a marine centrifugal pump. Tests were conducted at three flow rates (0.8Q_d, 1.0Q_d, and 1.3Q_d), with measurements of external characteristics, outlet pressure pulsation, vibration, and outlet noise. Results show that when the inlet gas volume fraction is below 1 %, the pump head decreases by less than 0.20 %, and the efficiency reduction is less than 0.22 %, indicating minimal performance loss. An optimal inlet gas volume fraction of 0.50 % under 0.8Q_d and 1.0Q_d, and 0.75 % under 1.3Q_d, yields maximum vibration damping. Specifically, the overall vibration velocity level at the pump's base foot (M3) decreases by 0.26 dB, 0.33 dB, and 1.63 dB under the three flow rates, respectively. At the first axial passing frequency (1f_APF), the vibration velocity level decreases by up to 4.60 dB, 1.87 dB, and 0.98 dB, while at the first blade passing frequency (1f_BPF), it decreases by 3.13 dB, 2.53 dB, and 10.92 dB, respectively. In terms of noise, the overall sound pressure level (OASPL) at the outlet is reduced by up to 2.76 dB (under 1.3Q_d). Coherence analyses confirm that uniform gas distribution in the impeller flow passages weakens rotor-stator interaction, thereby reducing both vibration and noise, particularly at low characteristic frequencies. These findings provide a practical basis for improving the stability and acoustic performance of marine centrifugal pumps through controlled inlet gas injection.