在下降的冰球尾流中的热和水汽输送及其对云中二次冰形成的影响
Heat and water vapor transfer in the wake of a falling ice sphere and its implication for secondary ice formation in clouds
摘要：
我们进行直接的数值模拟的冰球在周围的流体中的热量和质量的传递会计的目的是在气象背景下研究的情况下，在潮湿的空气中下降的霰的解决方案。这项研究的动机是这样一个事实，即在云中下降的沙粒被加热的潜热释放过程中的液体水滴吸积。因此，它们可能比周围的温度要高得多，并蒸发出水蒸气，水蒸气与周围的空气混合，从而在那里形成短暂的过饱和区。本文将下落的<$球问题模拟为受热球体在重力作用下下落于静止流体中的问题。温度场和速度场之间的耦合是由Boussinesq近似。这个问题可以通过四个参数来参数化：粒子/流体密度比、伽利略数、普兰特数和理查森数。一个单独的标量输运方程帐户的蒸汽传输。典型的云条件包括球体和周围环境之间的小温差，产生相对较小的热量和质量传输的理查森数。我们特别强调伽利略数150，170，200和300，以分析每个解决方案的具体情况。在这项研究中解决的问题主要是方法和关注的影响的解决方案和流动性的领域的结构上的标量场，可能的影响适度的理查森数的结构上的唤醒，和可能的应用程序，这个模拟框架的调查饱和后下降的<$p。
英文摘要：
We perform direct numerical simulations of the settling of an ice sphere in an ambient fluid accounting for heat and mass transfer with the aim of studying in a meteorological context the case of falling graupel in humid air. The study is motivated by the fact that falling graupels in clouds are heated by the latent heat released during the accretion of liquid water droplets. They may therefore be considerably warmer than their surrounding and evaporate water vapor, which mixes with the surrounding air in the wake of the graupel, thereby creating transient zones of supersaturation there. The problem of a falling graupel is modeled as that of a heated sphere falling in a quiescent ambient fluid under the action of gravity. The coupling between the temperature and velocity fields is accounted for by the Boussinesq approximation. This problem can be parameterized by four parameters: the particle/fluid density ratio, the Galileo number, the Prandtl number, and the Richardson number. A separate scalar transport equation accounts for the vapor transport. Typical cloud conditions involve small temperature differences between the sphere and the surrounding, yielding relatively small Richardson numbers for both heat and mass transport. We give a special emphasis to the Galileo numbers 150, 170, 200 and 300 in order to analyze the specificities of each settling regime. The questions addressed in this study are mainly methodological and concern the influence of the settling regime and the mobility of the sphere on the structure of the scalar fields, the possible influence of modest Richardson numbers on the structure of the wake, and the possible application of this simulation framework to the investigation of the saturation in the wake of a falling graupel.
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