Droplet Transport in Flow Turbulence

在气相流动中，小液滴的稀多分散混合物是环境和工业过程的共同特征。例如：云层、加湿和冷却、燃烧、表面涂层、灭火、药物输送和农药应用。在许多实际情况下，液滴足够小，它们的运动受到气相湍流的强烈影响。湍流对液滴运动的影响取决于相对于湍流长度和速度尺度的液滴惯性和大小。一般来说，湍流引起液滴在流动中的扩散，并以这样一种方式在混合和耗散尺度上产生液滴浓度的间歇区域。***基于计算流体力学的液滴浓度及其输运预测方法对上述过程的分析具有重要意义。申请人是UNB一个研究小组的成员，该小组致力于开发一种大涡模拟（LES）工具，用于跟踪大气低层农药滴从释放到在地被物上沉积的过程。利用UNB开发的先进GPU计算技术，完成了1平方公里局地地形大气湍流的LES模拟。目前的挑战是建立一个有效而准确的液滴在大气湍流中的运动模型。其中一篇重要的文章描述了拉格朗日液滴跟踪下飞机尾迹的RANS模拟。下一个研究目标是LES模拟，其中包括飞机尾流和大气湍流以及液滴传输的欧拉模型。***目前的拨款提案描述了一个实验研究计划，这是支持上述更大目标所必需的。它为测试和开发基于欧拉LES计算模拟的现象学输运模型提供了湍流中液滴浓度和输运的测量。本文研究的模型问题是各向同性网格湍流中的水平轴对称喷射羽流，模型尺度选择近似于大气近地面大涡模拟的尺度。将选择液滴大小，以扩大目前文献中考虑的斯托克斯数和沉降速度的范围，以包括与农药运输相关的液滴大小。这些实验将与LES模拟大气湍流的模式试验相协调。**

Dilute poly-disperse mixtures of small liquid droplets in gas phase flow is a common feature of both environmental and industrial processes. For example: clouds, humidification and cooling, combustion, surface coating, fire suppression, drug delivery, and pesticide application. In many practical cases the droplets are small enough that their motion is strongly influenced by the gas phase turbulence. The effect of turbulence on the droplet motion depends on the droplet inertia and size relative to the length and velocity scales of the turbulence. In general terms, turbulence causes a diffusion of droplets across the flow and in such a manner as to generate intermittent regions of droplet concentration at the mixing and dissipation scales.***Prediction methods for droplet concentration and its transport based on Computational Fluid Dynamics are valuable to the analysis of the above mentioned processes. The applicant is a member of a research team at UNB focussed on development a Large Eddy Simulation (LES) tool for tracking pesticide droplets in the lower layer of the atmosphere from release to deposition on the ground cover. LES simulation of the atmospheric turbulence over local topography covering 1 sq km has been accomplished using advanced GPU based computing developed at UNB. The present challenge is developing an efficient and accurate model of droplet motion through the atmospheric turbulence. One of the articles provided as a significant contribution describes a RANS simulation of an aircraft wake with Lagrangian droplet tracking. The next research objective is a LES simulation which includes the aircraft wake and atmospheric turbulence together with an Eulerian model of droplet transport. ***The present grant proposal describes an experimental research program which is necessary to support the larger objectives described above. It provides measurements of droplet concentration and transport in turbulent flow for the purposes of testing and developing phenomenological transport models used in Eulerian LES based computational simulations. The model problem that will be studied is a horizontal axisymmetric spray plume in isotropic grid turbulence with model scales chosen to approximate the scales of a Large Eddy Simulation of the near ground layer of the atmosphere. The droplet sizes will be chosen to extend the range of Stokes number and settling velocity currently considered in the literature to include those of relevance to pesticide transport. The experiments will be coordinated with model testing in LES simulations of atmospheric turbulence. **