Rotational speed modulated air–cavitation interactions in centrifugal pumps

The high-power consumption and excessive heat generation in data centers present challenges to thermal management. As a critical component of liquid cooling systems, the circulation pump's stability and reliability are directly impacted by cavitation and air entrainment, which degrade performance. This study investigates the effects of cavitation with entrained air under various rotational speeds and air volume fractions on centrifugal pump performance, pressure pulsation, and cavitation behavior. Experiments were conducted using a closed-loop test rig at three rotational speeds (2900, 2300, and 1800 r/min). The impact of different air volume fractions on the time-domain and frequency-domain characteristics of pressure pulsations was systematically analyzed. The results reveal that: (1) The maximum efficiency under air entrainment conditions exceeds that under natural cavitation. This condition optimizes the pressure distribution within the impeller channels, particularly near the impeller outlet. (2) Air entrainment effectively suppresses high-amplitude pressure fluctuations caused by cavitation collapse, especially at high air volume fraction (1.6%), with varying effects observed during the cavitation stage depending on the air volume fractions. (3) The ratio of rotational speed to bubble volume fraction determines the frequency-domain characteristics, manifesting as a combination of blade frequency, broadband, and low-frequency signals, influencing flow field stability and energy distribution. (4) Cavitation and air–cavitation interference frequencies cluster around St = 6, indicating bubble aggregation, collapse, and fragmentation under impeller rotation, with distinct interaction patterns at different speeds. This study provides a novel theoretical explanation of the mechanisms by which bubble aggregation and fragmentation induce flow instability under low-speed conditions.