Rosselló J M, Dellavale D, Bonetto F J
Instituto Balseiro-CONICET, Centro Atómico Bariloche, Río Negro R8402AGP, Argentina.
Instituto Balseiro-CONICET, Centro Atómico Bariloche, Río Negro R8402AGP, Argentina.
Ultrason Sonochem. 2015 Jan;22:59-69. doi: 10.1016/j.ultsonch.2014.06.003. Epub 2014 Jun 17.
In the present work, stable clusters made of multiple sonoluminescent bubbles are experimentally and theoretically studied. Argon bubbles were acoustically generated and trapped using bi-frequency driving within a cylindrical chamber filled with a sulfuric acid aqueous solution (SA85w/w). The intensity of the acoustic pressure field was strong enough to sustain, during several minutes, a large number of positionally and spatially fixed (without pseudo-orbits) sonoluminescent bubbles over an ellipsoidally-shaped tridimensional array. The dimensions of the ellipsoids were studied as a function of the amplitude of the applied low-frequency acoustic pressure (PAc(LF)) and the static pressure in the fluid (P0). In order to explain the size and shape of the bubble clusters, we performed a series of numerical simulations of the hydrodynamic forces acting over the bubbles. In both cases the observed experimental behavior was in excellent agreement with the numerical results. The simulations revealed that the positionally stable region, mainly determined by the null primary Bjerknes force (F→Bj), is defined as the outer perimeter of an axisymmetric ellipsoidal cluster centered in the acoustic field antinode. The role of the high-frequency component of the pressure field and the influence of the secondary Bjerknes force are discussed. We also investigate the effect of a change in the concentration of dissolved gas on the positional and spatial instabilities through the cluster dimensions. The experimental and numerical results presented in this paper are potentially useful for further understanding and modeling numerous current research topics regarding multi-bubble phenomena, e.g. forces acting on the bubbles in multi-frequency acoustic fields, transient acoustic cavitation, bubble interactions, structure formation processes, atomic and molecular emissions of equal bubbles and nonlinear or unsteady acoustic pressure fields in bubbly media.
在本研究中，对由多个声致发光气泡构成的稳定簇进行了实验和理论研究。使用双频驱动在充满硫酸水溶液（SA85w/w）的圆柱形腔室内声学产生并捕获氩气泡。声压场的强度足够强，能够在几分钟内维持大量位置和空间固定（无伪轨道）的声致发光气泡，这些气泡分布在一个椭球形三维阵列上。研究了椭球体的尺寸与所施加低频声压（PAc(LF)）的幅度以及流体中的静压（P0）之间的函数关系。为了解释气泡簇的大小和形状，我们对作用在气泡上的流体动力进行了一系列数值模拟。在这两种情况下，观察到的实验行为与数值结果非常吻合。模拟结果表明，位置稳定区域主要由零初级 Bjerknes 力（F→Bj）决定，被定义为以声场波腹为中心的轴对称椭球形簇的外周。讨论了压力场高频分量的作用以及次级 Bjerknes 力的影响。我们还通过簇的尺寸研究了溶解气体浓度变化对位置和空间不稳定性的影响。本文给出的实验和数值结果对于进一步理解和模拟当前许多关于多气泡现象的研究课题可能是有用的，例如多频声场中作用在气泡上的力、瞬态声空化、气泡相互作用、结构形成过程、等气泡的原子和分子发射以及气泡介质中的非线性或非稳态声压场。
