Use of Direct Numerical Simulation and Lagrangian Methods inTurbulent Transport

该提议的目的是获得湍流混合和向分子物种和球形颗粒的壁上的湍流转移的统一处理。在过去的四十年里，这一领域的理论并没有显著的进步。然而，最近直接数值模拟的出现为取得长足进展提供了可能性。这项提议的一个主要目标就是利用这个机会。对于通道内的湍流和湍流Couette流，在较大的Prandtl数范围内，将得到三维随时间变化的速度场和温度场的结果。将对现有的理论进行评估。然而，我们将特别强调温度场结构与速度场结构的关系，以及分子输运如何改变湍流输运。将探索拉格朗日方法作为获得更好的物理理解的一种手段。温度场被认为是壁面源分布的结果。这种方法的开发是因为有可能在计算机上研究墙源的行为。球形颗粒的传输不同于分子物种的传输，因为重力、涡流作用和升力对传输有额外的贡献。这些效应将在计算机和实验室实验中进行研究。将特别注意获取有关惯性自由飞行到墙的迫切需要的信息。我们还将继续最近的工作，其中我们利用拉格朗日方法来分析泥沙运移。

The proposal is aimed at obtaining a unified treatment of turbulent mixing and of turbulent transfer to a wall of molecular species, and of spherical particles. Theory in this area has not advanced significantly over the past forty years. However, the recent availability of direct numerical simulations opens the possibility of making considerable progress. A main objective of this proposal is to exploit this opportunity. Results on the simultaneous three-dimensional time-dependent velocity and temperature fields will be obtained for a wide range of Prandtl numbers for turbulent flow in a channel and for turbulent Couette flow. Present theories will be evaluated. However, special emphasis will be placed on the relation of the structure of the temperature field to the structure of the velocity field and on how turbulent transport is modified by molecular transport. Lagrangian methods will be explored as a means to obtained better physical understanding. The temperature field is viewed as resulting from a distribution of wall sources. The exploitation of this approach has been opened up because of the possibility of studying, on the computer, the behavior of wall sources. The transport of spherical particles differs from transport of molecular species because of extraneous contributions to transport by gravity, turbophoresis and lift. These effects will be studied both in computer and in laboratory experiments. Particular attention will be given to obtaining much needed information about inertial free flight to the wall. We will also continue recent work in which we exploit Lagrangian methods to analyze sediment transport.