The effect of nuclei population on cavitation evolution and load characteristics of a hemispherical–cylindrical structure

Surface cavitation flow is a critical issue affecting the reliability and stability of high-speed marine engineering structures such as underwater vehicles, propellers, and hydrofoils. The nuclei in water are a key medium factor in the inception of cavitation flow, and the effect of nuclei population further intensifies the uncertainties in flow and load of surface cavitation on structures. Therefore, to investigate the influence of nuclei population on the surface cavitation flow and the load evolution of unsteady moving structures, a vertical water-exit test system for vehicles with controllable nuclei size distributions and negative pressure is established in this paper. Three different nuclei size distributions with varying concentrations and distribution characteristics are constructed. The repeatability of nuclei size distributions, surface cavitation, and load evolution is verified. Unsteady vertical water-exit tests of the vehicle are conducted under different nuclei size distributions and cavitation numbers. The influence and mechanism of the nuclei population on the evolution of surface cavitation flow and the pressure load at the measuring point on the vehicle shoulder are compared and analyzed. The results indicate that the nuclei concentration in water modulates the inception time, position distribution, and shape of the surface cavitation flow on the vehicle. As the nuclei concentration increases, the mean value of pressure at the measuring point on the shoulder covered by the cavitation and the peak collapse value also increase. There is a wider frequency distribution range and a significantly increased proportion of high frequencies in the cavitation fluctuation load on the vehicle, resulting in increased uncertainty between loads.