Influence of a hemispherical bulge on a flat wall upon the collapse jet of cavitation bubbles

Uneven sections along a wall cause local flow deterioration and can result in severe cavitation erosion. This paper investigates the influence of a hemispherical bulge on a flat wall upon the collapse dynamics of a cavitation bubble in terms of the Kelvin impulse theory and high-speed photography based on the Weiss theorem and the image method. The evolution and characteristics of the bubble collapse morphology, the flow field distribution, and the Kelvin impulse (in terms of strength, direction, and directional sensitivity) are analyzed for symmetric and asymmetric configurations. The results show that the bubble collapse jet can be divided into three scenarios: mainly induced by the hemispherical bulge, mainly induced by the flat wall, and broadly equivalent effects of both. Additionally, as the dimensionless distance between the bubble and the flat wall increases, the range of the jet attraction zone induced by the bulge initially increases, subsequently decreases, and ultimately converges to the diameter of the bulge. The maximum width of the attraction zone can reach 3.45 times the radius of the bulge. Finally, the spatial sensitivity of the jet direction is found to be significant near the junction between the flat wall and the bulge.