Capture and inception of bubbles near line vortices

Abstract

Motivated by the need to predict vortex cavitation inception, a study has been conducted to investigate bubble capture by a concentrated line vortex of core size r c and circulation ⌫ 0 under noncavitating and cavitating conditions. Direct numerical simulations that solve simultaneously for the two phase flow field, as well as a simpler one-way coupled point-particle-tracking model ͑PTM͒ were used to investigate the capture process. The capture times were compared to experimental observations. It was found that the point-particle-tracking model can successfully predict the capture of noncavitating small nuclei by a line vortex released far from the vortex axis. The nucleus grows very slowly during capture until the late stages of the process, where bubble/vortex interaction and bubble deformation become important. Consequently, PTM can be used to study the capture of cavitating nuclei by dividing the process into the noncavitating capture of the nucleus, and then the growth of the nucleus in the low-pressure core region. Bubble growth and deformation act to speed up the capture process.

Numerical simulation of trajectory and deformation of bubble in tip vortex

“…The numerical results are compared with experimental data to validate the numerical model first. Figure 4 is the contrast between the numerical results and experimental data [19] . Here, the capture threshold is taken as r cri = a c /4, and the parameters are taken the same as those in the experiment, i.e., Γ = 0.290 m 2 /s, a c = 5.6 mm, and V ∞ = 10 m/s.…”

“…Figure 5 presents the trajectory of a bubble with the initial radius R 0 = a c /100 and the initial release position r 0 = 3a c , in which 'captured' denotes the position where bubble is captured. Furthermore, the PTM prediction is also compared with the direct numerical simulation (DNS) [19] based on the interface tracking method, as Fig. 6 shows.…”

“…The lift coefficient C l is a function of both the shear χ and the Reynolds number Re b . Here, C l is taken as 4χ/3 [19] .…”

Bubble–bubble interaction effects on dynamics of multiple bubbles in a vortical flow field

“…The experimental data on bubble rotating and captured by a vortex are rare, especially for multi-bubbles. Here, we adopted the photographic experimental data 11 of an initially static bubble releasing and moving in a line Gaussian vortex. The experimental parameters are G = 0:290 m 2 =s, a c = 5:6 mm, u ' = 10 m=s, s ' = 3, R 0 = a c =6 and r = a c .…”

“…The work by Hsiao and Chahine et al provided much insight on the single cavitation bubble captured by the vortex. Oweis et al 11 applied direct numerical simulations and point-particle tracking method to study capture and inception of bubbles near a line vortex under non-cavitating and cavitating conditions. Numerical results were compared and validated with their experimental data from Oweis et al 12 Choi et al 13 applied both axisymmetric and three-dimensional numerical models to examine the non-spherical growth, oscillation and collapse of a vortex cavitation bubble from a spherical nucleus.…”