Abstract
Ship fouling not only increases ship resistance and fuel consumption but is equally a type of biological invasion, which causes severe ecological damage. Submerged cavitation jet cleaning is an environmentally friendly, high-efficiency, and energy-saving cleaning method. The nozzle structure has an essential influence on the cleaning effect. Thus, a two-throat nozzle was designed for application in submerged cavitation jet cleaning. To investigate the cavitation characteristics of the two-throat nozzle, a high-speed photographic visualization experiment and an erosion experiment concerning the submerged cavitation jet were carried out in this study. The frame-difference method (FDM) was used to analyze the dynamic changes in the cavitation cloud in a single period. The dynamic changes in the cavitation cloud and the characteristics of the submerged cavitation jet were investigated under different inlet pressures. The sample mass loss and the macroscopic and microscopic changes in surface morphology were used to evaluate the cavitation intensity of the two-throat nozzle submerged jet. The experimental results demonstrate that the two-throat nozzle has a good cavitation effect, and the cavitation cloud of the submerged jet has obvious periodicity. With the increase in inlet pressure, the length, width, and area of the cavitation cloud continue to increase, and the shedding frequency of the cavitation cloud continues to decrease. The intensity of cavitation erosion is related to target distance and impact time. There is an appropriate target distance by which to achieve the optimal cavitation effect. The collapse of cavitation bubbles near the sample surface is related to the erosion distribution on the sample surface. Moreover, the magnitude of the absolute values of the root-mean-square surface roughness and surface skewness increase with cavitation intensity. The results in this paper are helpful for a better understanding of the cavitation characteristics of the two-throat nozzle submerged jet.
Highlights
After a ship has sailed in the ocean for a long time, the hull’s surface immersed in the seawater will be polluted by marine organisms, which consist of biological shellfish, algae plants, and other marine organisms
Submerged cavitation jet cleaning is a kind of ship fouling cleaning method with great potential and has attracted increasing attention
Submerged cavitation jet cleaning mainly uses micro-jets generated by the collapse of cavitation bubbles and extremely high collapse energy to achieve the purpose of cleaning
Summary
After a ship has sailed in the ocean for a long time, the hull’s surface immersed in the seawater will be polluted by marine organisms, which consist of biological shellfish, algae plants, and other marine organisms. Fujisawa et al [19] observed the collapse process of the cavitation cloud and the formation of excitation waves with and without the appearance of walls simultaneously by the frame-difference method (FDM) and the laser schlieren method. They obtained the same conclusion as that of Watanabe et al [18]. Cai et al [21] investigated the influence of different nozzle exit shapes of organ pipe nozzles on the cavitation erosion characteristics. Investigated the effect of the contraction ratio between the upstream and downstream of the resonant cavity of the organ pipe nozzle on the frequency and the erosion characteristics of self-excited oscillation cavitation jets. The macroscopic and microscopic evaluation of the cavitation characteristics of the two-throat nozzle submerged cavitation jet were carried out under different target distances and impact time
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