An experimental study on the multiscale properties of turbulence in bubble-laden flows
An experimental study on the multiscale properties of turbulence in bubble-laden flows
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DOI：
10.1017/jfm.2022.86
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发表时间：
2021-09
影响因子：
3.7
通讯作者：
Tian-xin Ma;H. Hessenkemper;D. Lucas;A. Bragg
中科院分区：
文献类型：
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作者：
Tian-xin Ma;H. Hessenkemper;D. Lucas;A. Bragg
摘要对不同尺度下含气泡湍流的特性进行了实验研究，着重研究了流动动能、能量传递和极端事件。实验采用粒子阴影测速仪测量两种不同气泡直径（2.7 $ mm和3.9 $ mm）和中等气体体积分数（0.26，1.31，1%$）的均质气泡群在水中上升时产生的柱中的流动。这两个速度分量在高分辨率下测量，并用于构造结构函数，以达到12阶，用于跨越流动中的小尺度到大尺度的分离。关于流动的各向异性，速度结构函数被发现在垂直和水平方向上的流动的分离不同，和较小的气泡的情况下是最各向异性的，依赖于空隙率。各向异性的程度示出增加的顺序的结构功能的增加，示出极端事件中的流是最各向异性的。结果表明，与三维单相湍流一样，水平速度分量的平均能量传递是下尺度的。然而，与流体速度的垂直分量相关联的能量传递是高档的。的速度增量的概率密度函数显示，极值变得更可能与雷诺数的减少，在单相湍流的行为相反。我们可视化这些极端事件，并发现激烈的小尺度速度增量的区域附近的湍流/非湍流界面的边界处的气泡尾流。
Abstract The properties of bubble-laden turbulent flows at different scales are investigated experimentally, focusing on the flow kinetic energy, energy transfer and extreme events. The experiments employed particle shadow velocimetry measurements to measure the flow in a column generated by a homogeneous bubble swarm rising in water, for two different bubble diameters ($2.7$ mm and $3.9$ mm) and moderate gas volume fractions ($0.26\,\%\sim 1.31\,\%$). The two velocity components were measured at high resolution, and used to construct structure functions up to twelfth order for separations spanning the small to large scales in the flow. Concerning the flow anisotropy, the velocity structure functions are found to differ for separations in the vertical and horizontal directions of the flow, and the cases with smaller bubbles are the most anisotropic, with a dependence on void fraction. The degree of anisotropy is shown to increase as the order of the structure functions is increased, showing that extreme events in the flow are the most anisotropic. Our results show that the average energy transfer with the horizontal velocity component is downscale, just as for the three-dimensional single-phase turbulence. However, the energy transfer associated with the vertical component of the fluid velocity is upscale. The probability density functions of the velocity increments reveal that extreme values become more probable with decreasing Reynolds number, the opposite of the behaviour in single-phase turbulence. We visualize those extreme events and find that regions of intense small-scale velocity increments occur near the turbulent/non-turbulent interface at the boundary of the bubble wake.