Cavitation bubble dynamics in a funnel-shaped tube

Abstract

Control of cavitation in confining geometries is vital to the safety of hydraulic conduits and structures. Here we investigate cavitation bubble dynamics in one typical type of open-ended tube with varying cross sections, i.e., a funnel-shaped tube, defined as a funnel-shaped section connected to a cylindrical section. In our experiments, single cavitation bubbles are generated by spark along the symmetric axis of the funnel-shaped tube at different positions, including in the funnel-shaped section (regime 1), near the throat (regime 2), and in the cylindrical section (regime 3). With high-speed photography, we observe that at the end of collapse, bubbles produce weak jets in regime 1, jets in a shape of an inverted cone in regime 2, and jets in a cylindrical shape with a rounded end in regime 3. With the help of OpenFOAM simulation, we better understand the surrounding flow fields during the bubble evolution. By capturing the main features of the flow fields, we derive dynamics equations for bubbles in each regime. Scaling laws are proposed for the bubble jet velocity, which depends on the position of bubble generation, the inner diameter of the cylindrical section of the tube, and the maximum distance where the bubble's upper surface can reach before the collapse. Our findings may be inspiring for understanding cavitation bubble dynamics in tubular conduits with complex geometries, e.g., cavitation in pipelines and draft tubes in hydrodynamic systems, and ultrasonic diagnosis in blood vessels.

Collapsing behavior of spark-induced cavitation bubble in rigid tube

“…For the convenience of observation and control of the size and position of cavitation bubble in rigid circular tube, in this study, the technique of inducing cavitation bubbles with low-voltage discharge underwater was employed [34] , [43] , [49] , [50] . The electrical circuit consists of a resistor, power supply, capacitor, and charging and discharging switch and a pair of copper electrodes with a thickness of 0.1 mm.…”

“…8 h - i , there is a slight distortion of the microjet tip. The reasons for this phenomenon may include two aspects: On the one hand, the surface of the bubble on the side close to the x -axis origin is less constrained by the tube compared to the bubble on the side away from the x -axis origin, which resulting an uneven distribution of liquid inertia on both sides of the bubble in the x -direction [34] . On the other hand, when the bubble deviates slightly from the tube axis, the bubble is not a perfectly axisymmetric cylindrical, which leads to a slight distortion of the bubble during its evolution.…”

“…In addition, Ren et al, 2022 [34] proposed a scaling law (Eq.6) for microjets velocity of bubble located in the straight section of a funnel shaped tube. …”

“…Additionally, a Rayleigh model was developed to describe the dynamics of these large cavitation bubbles within the tube. The evolution of bubbles at different positions (funnel-shaped section, near the throat, and cylindrical region) within a funnel tube was investigated through a combination of numerical simulations and experimental studies by Ren et al, (2022) [34] .They also analyzed the flow field characteristics around the bubbles and derived the dynamic equations for bubble evolution at different positions in the funnel-shaped tube. Scaling laws were proposed for the microjet velocity.…”

Numerical study of the behavior of a near-wall bubble under the influence of an acoustic wave

“…Hu et al [7] investigated the high-speed jet induced by a collapsing bubble influenced by a spherical particle. Ren et al [8] studied the bubble's evolution in a cone-shaped tube. They pointed out that the jet velocity is related to the position of the bubble's inception, the internal tube's diameter, and the maximal distance of the bubble surface.…”