Motivated by numerous geophysical applications, we have carried out laboratory experiments of a reactive (i.e., melting) solid sphere freely falling by gravity in a stratified environment, in the regime of large Reynolds (Re) and Froude numbers. We compare our results to nonreactive spheres in the same regime. First, we confirm, for larger values of Re, the stratification drag enhancement previously observed for low and moderate Re. We also show an even more significant drag enhancement due to melting, much larger than the stratification-induced one. We argue that the mechanism for both enhancements is similar, due to the specific structure of the vorticity field sets by buoyancy effects and associated baroclinic torques, as deciphered for stratification by Zhang et al. [J. Fluid Mech. 875, 622 (2019)]. Using particle image velocimetry, we then characterize the long-term evolution (at time $t\gg 1/N$, with $N$ the Brünt-Väisälä frequency) of the internal wave field generated by the wake of the spheres. The measured wave field is similar for both the reactive and inert spheres: indeed, each sphere fall might be considered as a quasi-impulsive source of energy in time and the horizontal direction, as the falling time (the sphere radius) is much smaller than $N$ (than the tank width). Internal gravity waves are generated by wake turbulence over a broad spectrum, with the least damped component being at the Brünt-Väisälä frequency and the largest admissible horizontal wavelength. About 1% of the initial potential energy of each sphere is converted into kinetic energy in the internal waves, with no significant dependence on the Froude number over the explored range.

中文翻译：

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落入线性分层流体中的反应性球形颗粒的动力学

受众多地球物理应用的推动，我们进行了实验性实验，即在大雷诺数（Re）和弗洛德数的情况下，在分层环境中由于重力而自由下落的反应性（即熔融）固体球体。我们将结果与相同方案中的非反应性领域进行比较。首先，对于较大的Re值，我们确认以前在低和中等Re值下观察到的分层阻力增强。我们还显示由于融化而产生的阻力增加更为显着，远大于分层诱导的阻力增加。我们认为这两种增强作用的机制是相似的，这是由于张力等人解释为通过分层作用由浮力效应和相关的斜压力矩形成的涡旋场集合的特定结构。[ J.流体机械。 875，622（2019）]。然后使用粒子图像测速仪来描述长期演变（在时间$Ť\gg \mathrm{1个}/ñ$，带有 $ñ$球的尾波产生的内部波场的Brünt-Väisälä频率）。对于反应性和惰性球体，所测量的波场都相似：实际上，每个球体坠落在时间和水平方向上都可以视为准脉冲能量源，因为坠落时间（球体半径）比$ñ$（比水箱宽度大）。内部引力波是由宽范围内的尾流产生的，阻尼最小的分量是Brünt-Väisälä频率，最大允许的水平波长。每个球体大约1％的初始势能在内波中转换为动能，并且在所研究的范围内与弗洛德数无关。