Non-spherical collapse of a cavitation bubble induced by a rigid filament

A combination of high-speed shadowgraph imaging and numerical simulations was used to study the collapse of a bubble near a rigid filament. The dynamic behavior of the collapsing bubble was investigated concerning two non-dimensional parameters: the filament radius (r*) and the initial near-wall distance (gamma(0)). The critical distance (1 < gamma(c) < 3) between spherical and non-spherical collapse was positively correlated with r*. The collapsing bubbles were found to exhibit three different morphologies with different gamma(0) values: flat two-dimensional necking with a strong jet, teardrop-shaped collapse with an weak jet, and spherical collapse with no jet. The first collapse time (T-1st) hardly varies with gamma(0), and the second collapse time (T-2nd) shows an increasing and then decreasing trend as gamma(0) increases, reaching a maximum at gamma(0) =1 and stabilizing after gamma(0) > gamma(c). In addition, when gamma(0) = 0.76, the pressure difference between the upper and lower surfaces of the bubble is high, the jet is strong, and the maximum pressure and maximum fluid velocity are found in the jet, producing a stronger impact on the rigid wall. When gamma(0) > 1, as gamma(0) increases, the jet weakens, the pressure on the wall is far less than the pressure on the bubble surface when it collapses. Our results would deepen the understanding of the kinetics of the bubble collapsing near a slender cylindrical wall and provide an important reference for the improvement of pulp pumps and interpreting the degradation of microfiber-reinforced plastics.