Cavity-dynamic modulation of pressure and hydroacoustic spectra in a cavitating axial-flow pump

Abstract

Cavitation-induced hydroacoustic variation in axial-flow pumps cannot be characterized solely by vapor volume or overall sound pressure level, but also depends on how evolving vapor structures reorganize rotor–stator pressure excitation. A box-culvert axial-flow pump is investigated using model-test validation, transient very-large-eddy simulation of cavitating flow, and a one-way surface-pressure-driven computational fluid dynamics–finite element method hydroacoustic calculation. Cavitation stages are identified from hydraulic degradation, vapor-volume statistics, and cavity morphology. Cavity-volume oscillation, section-resolved pressure and hydroacoustic spectra, blade passing-frequency (BPF)-centered energy ratios, and acoustic spectral entropy are then analyzed. Pressure-hydroacoustic spectral reorganization already appears during developing cavitation, when the head-drop ratio is only 1.91%, below the conventional 3% head-drop criterion. With decreasing cavitation number, vapor structures evolve from attached cavities with blade-passage-related modulation to longer-period vapor accumulation, blockage-like vapor structures, and blade-exit shedding. This transition weakens harmonic pressure organization, particularly in the impeller outlet–guide-vane inlet interaction region. The hydroacoustic response is therefore not uniformly amplified: the BPF remains dominant, whereas its energy contribution decreases and low-frequency components, fragmented fine spectral features, and non-BPF components become more pronounced under severe cavitation. The accompanying decrease in BPF-centered acoustic energy and increase in spectral entropy quantify the redistribution of acoustic energy over a broader frequency range. These results identify cavity-dynamic modulation of rotor–stator pressure excitation as the mechanism underlying cavitation-induced pressure-hydroacoustic spectral reorganization.