The dynamics of air bubbles in turbulent Rayleigh–Bénard (RB) convection is described for the first time using laboratory experiments and complementary numerical simulations. We performed experiments at Ra =5.5x10^9 and 1.1x 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 threedimensional particle tracking velocimetry, we simultaneously tracked a large number of bubbles to inspect the pair dispersion, R2(t), for a range of initial separations, r, spanning one order of magnitude, namely 25η < r < 225η; here η is the local Kolmogorov length scale. Pair dispersion, R2(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 R2(t) underwent a transition phase similar to the ballistictodiffusive (t^2tot^1) regime in the vicinity of the cell centre; it approached a bulk behavior t3/2 in the diffusive regime as the distance away from the cell centre increased. At small r, R2(t) ~ 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, R2(t) ∝ t^2 was observed, showing the effect of the roll structure
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On the dynamics of air bubbles in Rayleigh–Bénard convection
The dynamics of air bubbles in turbulent Rayleigh–Bénard (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 threedimensional 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 ballistictodiffusive ( $t^{2}$ 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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 Award ID(s):
 1912824
 NSFPAR ID:
 10157234
 Date Published:
 Journal Name:
 Journal of Fluid Mechanics
 Volume:
 891
 ISSN:
 00221120
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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