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首页> 外文期刊>Bulletin of the American Physical Society >APS -70th Annual Meeting of the APS Division of Fluid Dynamics- Event - Particles and snowflakes falling through turbulence
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APS -70th Annual Meeting of the APS Division of Fluid Dynamics- Event - Particles and snowflakes falling through turbulence

机译：APS-APS流体动力学分部第70届年会-活动-湍流中的颗粒和雪花

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The question of how turbulence affects the settling of small heavy particles has proven surprisingly hard to answer. Previous investigations identified several mechanisms by which turbulence may alter the particle settling rate as compared to the still-fluid terminal velocity, but different studies often show large discrepancies. This is especially problematic in meteorology, where an accurate knowledge of the precipitation fall speed is a prerequisite for reliable weather forecasting. I will present laboratory and field measurements that demonstrate how turbulence may lead to a multifold increase of the particle fall speed. In the laboratory, a large chamber is used where hundreds of randomly actuated jets create a large volume of homogeneous air turbulence, and in which flow tracers and inertial particles are simultaneously tracked by laser imaging. Clusters of particles are identified and described in their self-similar nature. In the field, snowflakes settling in the atmospheric surface layer are imaged and tracked during nighttime snowfalls, using stage lights and high speed cameras. The Lagrangian acceleration statistics show that small and compact snowflakes (graupel) follow the classic phenomenology of inertial particles in homogeneous turbulence.
机译：湍流如何影响小的重颗粒的沉降问题已被证明很难回答。先前的研究确定了几种机制，与静止流体的最终速度相比，湍流可通过这些机制改变颗粒沉降速率，但是不同的研究通常显示出很大的差异。这在气象学中尤其成问题，因为对降水下降速度的准确了解是可靠天气预报的前提。我将介绍实验室和现场测量结果，以证明湍流如何导致粒子落下速度成倍增加。在实验室中，使用了一个大室，其中数百个随机驱动的射流会产生大量均匀的空气湍流，并在其中通过激光成像同时跟踪流动示踪剂和惯性粒子。可以识别和描述粒子簇，它们具有相似性。在野外，使用舞台灯和高速摄像头，可以在夜间降雪期间对沉降在大气表层的雪花进行成像和跟踪。拉格朗日加速度统计数据表明，小而紧凑的雪花（graupel）遵循均质湍流中惯性粒子的经典现象。

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