标题： 湍流羽流中的浓度分布 显示英文标题

标题： On the concentration distribution in turbulent thermals

摘要： 湍流热羽流出现在各种地理和工业流动中，例如大气积云对流和海洋及湖泊中的污染物扩散。当由于温度或组成密度差异产生的浮力流体体积从源头瞬间释放时，它们会形成。随着它们上升或下沉，与周围环境之间可能发生热量和质量的交换，这些交换跨越多个尺度，从宏观的环境流体掺混到微观的扩散过程。 尽管湍流热羽流通常通过其积分特性进行研究，但混合过程特别依赖于浓度或温度的内部分布。 在这里，我们使用实验室流体动力学实验和直接数值模拟来研究具有大雷诺数的湍流热羽流中被动标量的混合。我们追踪了浓度场的演变，计算了其矩和概率密度函数。 浓度分布随时间表现出自相似性，除了在高浓度情况下，这可能是由于存在未稀释的核心。 这些分布可以用指数概率密度函数很好地近似。 在所研究的范围内，我们发现浓度分布在很大程度上独立于佩克莱特数和雷诺数。 显示英文摘要

摘要： Turbulent thermals emerge in a wide variety of geophysical and industrial flows, such as atmospheric cumulus convection and pollutant dispersal in oceans and lakes. They form when a volume of buoyant fluid, arising from thermal or compositional density differences, is instantly released from a source. As they rise or sink, heat and mass transfers are likely to occur with the surrounding environment, spanning multiple scales from macroscopic entrainment of ambient fluid to microscopic diffusive processes. Although turbulent thermals are typically investigated through their integral properties, mixing processes specifically depend on the internal distribution of concentration or temperature. Here, we use laboratory fluid dynamics experiments and direct numerical simulations to investigate the mixing of a passive scalar in turbulent thermals with large Reynolds numbers. We track the evolution of the concentration field, computing its moments and the probability density function. The concentration distribution exhibits self-similarity over time, except at high concentrations, possibly because of the presence of undiluted cores. These distributions are well approximated by an exponential probability density function. In the investigated range, we find that concentration distributions are largely independent of the P\'eclet and Reynolds numbers.