Generation and Propagation Mechanisms of Leak-Induced Acoustic Waves in Water Pipelines Based on Coupled Fluid–Acoustic–Structural Responses

Pipeline leakage acoustic signals are governed by the coupled effects of leakage excitation, acoustic–structural interaction, and propagation filtering, while the physical relationship between leakage conditions and measurable spectral characteristics remains insufficiently understood. In this study, a three-dimensional numerical framework combining leakage flow simulation, acoustic–structural coupling analysis, and dual-hydrophone experiments was developed to investigate the formation and propagation mechanisms of leak-induced acoustic signals in water pipelines. The investigated steel pipeline had an inner diameter of 50 mm, with leak hole diameters of 1–4 mm (d/D = 0.02–0.08). The leakage flow remained turbulent, with a Reynolds number of approximately 7.0 × 103, and the dominant acoustic response corresponded to Strouhal numbers of 1.7 × 10−3–2.1 × 10−2. The results show that supply pressure mainly controls leakage excitation intensity through hydraulic power, whereas the leak hole diameter primarily modifies the frequency-band distribution. A narrow-band pipe wall vibration enhancement was identified near 280 Hz, which was associated with the coupled pipe–water mode at 278.97 Hz. Experimental measurements further demonstrated strong propagation-induced frequency filtering, with more than 97% of far-field signal energy retained within the 20–250 Hz band. These findings establish a continuous relationship between hydraulic leakage input, local acoustic–structural response, and measurable leakage spectra, providing physical insights into acoustic-based pipeline leak detection.