An analysis of the cavitation noise in lubricating oil gear pumps under different gas contents: The important role of cavitation volume pulsation

Lubricating oil gear pumps are particularly susceptible to cavitation and noise generation due to the high content of dissolved gases in lubricating oil. Beyond the cavitation-induced flow pulsation, cavitation volume pulsation also acts as an acoustic source whose contribution in gear pumps has not been fully assessed. In this study, the three-dimensional unsteady flow field in a gear pump was simulated, and the acoustic characteristics with consideration of the additional excitation from cavitation volume pulsation were calculated using an acoustic finite element method combined with equivalent acoustic source approach. Results indicate that reducing gas content suppresses both flow pulsation and cavitation activity. As the mass gas fraction decreases from 1.2e-4 to 3e-5, flow pulsation drops by approximately 4.3 times, accompanied by a roughly 6 dB reduction in overall sound pressure level (OSPL). Cavitation volume pulsation contributes significantly to the cavitation-induced noise. If neglected, the calculated OSPL is underestimated by about 2.5 dB and 4.5 dB at gas contents of 1.2e-4 and 3e-5, respectively. This discrepancy primarily originates from pronounced peaks of cavitation volume pulsating radiated noise at the second harmonic frequency and its higher harmonics. Across the entire frequency range of 0-2500 Hz, the SPL of cavitation-induced noise is higher than that predicted without cavitation volume pulsation, confirming that cavitation volume pulsation amplifies the radiated noise of gear pump.