The dynamics of air bubbles in turbulent Rayleigh–Benard (RB) convection is described for the first time using laboratory experiments and complementary numerical simulations. We performed experiments at $Ra=5.5\times 10^{9}$ and $1.1\times 10^{10}$ , where streams of 1 mm bubbles were released at various locations from the bottom of the tank along the path of the roll structure. Using three-dimensional particle tracking velocimetry, we simultaneously tracked a large number of bubbles to inspect the pair dispersion, $R^{2}(t)$ , for a range of initial separations, $r$ , spanning one order of magnitude, namely $25\unicode[STIX]{x1D702}\leqslant r\leqslant 225\unicode[STIX]{x1D702}$ ; here $\unicode[STIX]{x1D702}$ is the local Kolmogorov length scale. Pair dispersion, $R^{2}(t)$ , of the bubbles within a quiescent medium was also determined to assess the effect of inhomogeneity and anisotropy induced by the RB convection. Results show that $R^{2}(t)$ underwent a transition phase similar to the ballistic-to-diffusive ( $t^{2}$ -to- $t^{1}$ ) regime in the vicinity of the cell centre; it approached a bulk behavior $t^{3/2}$ in the diffusive regime as the distance away from the cell centre increased. At small $r$ , $R^{2}(t)\propto t^{1}$ is shown in the diffusive regime with a lower magnitude compared to the quiescent case, indicating that the convective turbulence reduced the amplitude of the bubble’s fluctuations. This phenomenon associated to the bubble path instability was further explored by the autocorrelation of the bubble’s horizontal velocity. At large initial separations, $R^{2}(t)\propto t^{2}$ was observed, showing the effect of the roll structure.

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关于瑞利-贝纳德对流中气泡的动力学

使用实验室实验和补充数值模拟首次描述了湍流瑞利-贝纳德 (RB) 对流中气泡的动力学。我们在 $Ra=5.5\times 10^{9}$ 和 $1.1\times 10^{10}$ 进行了实验，其中 1 mm 气泡流从罐底部沿着滚动路径在不同位置释放结构体。使用三维粒子跟踪测速，我们同时跟踪大量气泡以检查对分散 $R^{2}(t)$ ，对于一系列初始分离 $r$ ，跨越一个数量级，即 $25\unicode[STIX]{x1D702}\leqslant r\leqslant 225\unicode[STIX]{x1D702}$ ; 这里 $\unicode[STIX]{x1D702}$ 是局部 Kolmogorov 长度尺度。对色散, $R^{2}(t)$ , 还确定了静止介质中气泡的数量，以评估 RB 对流引起的不均匀性和各向异性的影响。结果表明 $R^{2}(t)$ 经历了一个类似于弹道到扩散 ( $t^{2}$ -to- $t^{1}$ ) 状态的过渡阶段。细胞中心；随着远离细胞中心的距离增加，它在扩散状态中接近体积行为 $t^{3/2}$。在较小的 $r$ 处，$R^{2}(t)\propto t^{1}$ 显示在扩散状态中，与静止情况相比幅度较低，表明对流湍流降低了气泡的振幅波动。通过气泡水平速度的自相关进一步探索了与气泡路径不稳定性相关的这种现象。在较大的初始分离中，观察到 $R^{2}(t)\propto t^{2}$，