Droplet Transport in Flow Turbulence

小液滴在气相流中的稀释多分散混合物是环境和工业过程的共同特征。例如：云、加湿和冷却、燃烧、表面涂层、灭火、药物输送和农药施用。在许多实际情况下，液滴足够小，以至于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液滴的惯性和尺寸相对于湍流的长度和速度尺度。一般而言，湍流导致液滴在整个流动中扩散，并且以这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，该研究小组专注于开发一种大涡模拟（LES）工具，用于跟踪大气低层中农药液滴从释放到沉积在地面覆盖物上的过程。采用UNB开发的先进的基于GPU的计算技术，完成了覆盖1平方公里局部地形的大气湍流大涡模拟。目前的挑战是开发一个有效的和准确的模型通过大气湍流的液滴运动。作为重要贡献提供的文章之一描述了具有拉格朗日液滴跟踪的飞机尾流的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。 目前的拨款建议描述了一个实验研究计划，这是必要的，以支持上述更大的目标。它提供了测量液滴浓度和湍流中的运输的目的，测试和发展的现象学传输模型中使用的欧拉大涡模拟计算模拟。将要研究的模型问题是各向同性网格湍流中的水平轴对称喷雾羽流，模型尺度选择为近似大气近地层大涡模拟的尺度。液滴大小的选择将扩大目前文献中考虑的斯托克斯数和沉降速度的范围，以包括与农药运输有关的范围。实验将与大气湍流LES模拟中的模型测试相协调。

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.