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Turbulent bubble suspensions and crystal growth in microgravity. Drop tower experiments and numerical simulations

机译：湍流中的气泡悬浮液和微重力下的晶体生长。落塔实验和数值模拟

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[eng] We study the formation and spreading of a turbulent jet of bubbles in microgravity. This has been analyzed from the recordings obtained in previous experimental campaigns of microgravity. Results have been compared with a simplified model of passive bubbles, in which bubbles are advected by the mean flow and dispersed due to the local degree of turbulence at each point of the jet. Thanks to the expertise obtained with this part of the thesis, we have designed and built a new experiment that has been used 36 times in the 4.7 s drop tower of ZARM (“Center of Applied Space Technology and Microgravity”) in Bremen. With this experiment we have obtained, for the first time in history, a monodisperse suspension of bubbles, within a turbulent flow, in microgravity. From the resulting measures we have characterized the relaxation time of pseudo-turbulence (previously generated due to the effect of buoyancy forces upon the injected bubbles in normal gravity conditions). We have also studied the interaction between bubbles and the turbulent medium. Results have been compared with Lattice-Boltzmann simulations of the flow.On the other hand, we have also studied the impact of residual gravitational vibrations (known as g-jitters) upon the quality of semiconductors solidified in microgravity. The quality of the resulting crystals has been studied from the analysis of the inhomogeneities in their dopant concentration. This study has been based entirely on simulations, but g-jitters have been modeled from acceleration signals measured in real space missions.
机译：[eng]我们研究了微重力下湍流气泡的形成和扩散。从先前的微重力实验活动中获得的记录已经对此进行了分析。已将结果与被动气泡的简化模型进行了比较，其中被动气泡使气泡平均流动，并由于射流各点处的局部湍流程度而使气泡分散。得益于在本部分获得的专业知识，我们设计并建立了一个新的实验，该实验在不来梅ZARM（“应用空间技术和微重力应用中心”）的4.7 s下降塔中使用了36次。通过该实验，我们有史以来第一次获得了微重力下湍流中气泡的单分散悬浮液。根据所得到的度量，我们已经表征了伪湍流的弛豫时间（以前是在正常重力条件下，由于浮力对注入的气泡的作用而产生的）。我们还研究了气泡和湍流介质之间的相互作用。将结果与流动的Lattice-Boltzmann模拟进行了比较，另一方面，我们还研究了残余重力振动（称为g抖动）对在微重力下固化的半导体质量的影响。通过分析掺杂剂浓度的不均匀性，研究了所得晶体的质量。这项研究完全基于模拟，但是g抖动是根据实际太空任务中测得的加速度信号进行建模的。

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    Bitlloch Puigvert Pau;

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  • 年度 2012
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