Experimental investigation of the acceleration statistics and added-mass force of deformable bubbles in intense turbulence
Experimental investigation of the acceleration statistics and added-mass force of deformable bubbles in intense turbulence
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DOI：
10.1017/jfm.2020.1121
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发表时间：
2021-02-18
影响因子：
3.7
通讯作者：
Ni, Rui
中科院分区：
文献类型：
--
作者：
Salibindla, Ashwanth K. R.;Masuk, Ashik Ullah Mohammad;Ni, Rui
本文对湍流中可变形气泡的加速度统计和附加质量张量进行了实验研究。通过同时跟踪气泡及其周围的三维流动，我们找到了两种独立的方法来估计气泡加速度：直接从三维气泡轨迹测量或间接从气泡的运动方程计算。当这样的方程被投影到气泡框架上时，附加质量系数变成了一个对角张量，其中三个元素与气泡加速度沿沿着三个气泡主轴的标准偏差相关联。该约束有助于通过实验确定附加质量系数张量。所得到的趋势似乎同意与兰姆的潜在的流动解决方案的球体，这表明可变形的气泡上的附加质量力可以使用具有相同的几何形状和方向的球体建模。此外，给出了变形气泡半长轴与湍流滑移加速度之间相对取向的概率密度函数。一个令人惊讶的发现是，由气泡的主轴表示的气泡取向在湍流中不是随机的，而是优先与滑移加速度对齐。随着气泡变形程度的增加，这种对齐的程度也会增加。因为沿更变形的气泡的长轴加速沿着需要减少的附加质量，所以可变形气泡的加速度标准偏差作为气泡纵横比的函数而增加。
We present an experimental investigation of the acceleration statistics and the added mass tensor of deformable gas bubbles in turbulence. By simultaneously tracking both bubbles and their surrounding flow in three dimensions, we find two independent ways of estimating the bubble acceleration: either directly measured from three-dimensional bubble trajectories or indirectly calculated from the bubble's equation of motion. When such an equation is projected onto the bubble frame, the added-mass coefficient becomes a diagonal tensor with three elements being linked to the standard deviation of bubble acceleration along three bubble principal axes. This constraint aids in experimentally determining the added mass coefficient tensor. The obtained trend of seems to agree with Lamb's potential flow solutions for spheroids, suggesting that the added-mass force on deformable bubbles can be modelled using spheroids with the same geometry and orientation. In addition, the probability density function of the relative orientation between the semi-major axis of deformed bubbles and the slip acceleration in turbulence is shown. A surprising finding is that the bubble orientation, indicated by the bubble's major axis, is not random in turbulence but rather is preferentially aligned with the slip acceleration. The degree of this alignment increases as bubbles deform more. Because accelerating along the major axis of a more deformed bubble entails reduced added mass, the acceleration standard deviation of deformable bubbles increases as a function of the bubble aspect ratio.