EAGER: Exploratory Research on DNS Modeling of Turbulent Heat Transfer in Porous Media

多孔介质中湍流传热的DNS模拟多孔介质中对流领域最有争议的话题之一是宏观湍流问题，这是由于高速流动而增强传输的已知过程。目前还不清楚宏观湍流是否会发生在流体饱和多孔介质中，如果是这样，它对对流传热有什么影响。在多孔介质中进行速度测量以确定湍流是否存在是非常困难的，因为它们通常是光学不透明的。与此同时，现在可以进行高清直接数值模拟（DNS）来研究这一现象。与大多数现有的多孔介质中的湍流研究相比，DNS依赖于某些未经验证的湍流模型，通过直接解决所有运输尺度，DNS允许人们了解其所有复杂性的现象。因此，本项目通过DNS检查在大流量（高雷诺数）下在多孔介质中发生的过程，试图准确描述它们并分析它们是否可以被标记为真正的湍流。这里的假设是，孔隙的大小决定了湍流涡流的最大大小。如果湍流涡流的大小不能超过孔隙的大小，那么多孔介质中的湍流现象可能与清澈流体中的湍流不同。事实上，这种尺寸限制必须有一个影响的能量级联，在明确的（多孔介质）流体的湍流动能主要是包含在大eddies.The研究进行广泛的DNS研究各种二维和三维多孔介质的几何形状。将研究具有不同孔径的多孔介质，以研究限定多孔介质填充通道的固体壁的影响。将多孔介质中出现的湍流结构与清澈流体中的湍流结构进行比较，分析它们对对流传热的影响。特别是，从大到小的涡的动能级联将被调查，并分析含能涡的频谱和尺寸，揭示湍流能量的产生，传递和耗散的机制，通过多孔介质的流动。通过将温度作为被动标量进行建模并研究瞬时温度分布，该项目旨在确定湍流对流中流体动力学和热过程之间的联系。此外，大量的固体障碍物，构成固体多孔基质，在湍流动能的量的影响将被揭示，以及它如何影响温度场。将考虑在双分散多孔介质中的第二雷诺数的可能性，这将通过对应于较大孔径的湍流涡流的出现来体现。将DNS结果与已发表的实验数据进行比较，以验证数值结果。

DNS Modeling of Turbulent Heat Transfer in Porous MediaOne of the most controversial topics in the field of convection in porous media is the issue of macroscopic turbulence, which is the known process of enhancing transport due to high speed flow. It remains unclear whether macroscopic turbulence can occur in a fluid saturated porous medium and, if so, what impact it has on convection heat transfer. It is extremely difficult to carry out velocity measurements within porous media to ascertain if turbulence exists on not in it, as they are typically optically opaque. At the same time, it is now possible to conduct high-definition direct numerical simulation (DNS) to study this phenomenon. In contrast to most existing work on turbulence in porous media, which relies on certain unverified turbulence models, DNS allows one to understand the phenomenon in all its complexities by directly resolving all the scales of transport. Hence, this project examines the processes that take place in porous media at large flow rates (high Reynolds numbers) via DNS, attempting to accurately describe them and analyze whether they can be labeled as true turbulence. The hypothesis here is that the size of the pores determines the maximum size of the turbulent eddies. If the size of turbulent eddies cannot exceed the size of the pores, then turbulent phenomena in porous media may differ from turbulence in clear fluids. Indeed, this size limitation must have an impact on the energy cascade, for in clear (of porous media) fluids the turbulent kinetic energy is predominantly contained within large eddies.The study entails carrying out extensive DNS studies for various 2D and 3D porous media geometries. Porous media with different pore sizes will be investigated to study the effects of solid walls bounding a porous medium filled channel. Turbulent structures that appear in a porous medium will be compared with those in a clear fluid; their effects on convective heat transfer will be analyzed. In particular, the kinetic energy cascade from larger to smaller eddies will be investigated, and the spectrum and size of energy-containing eddies analyzed to uncover the mechanisms of turbulence energy production, transfer, and dissipation in flow through porous media. By modeling temperature as a passive scalar and investigating instantaneous temperature distributions, this project aims at identifying connections between hydrodynamic and thermal processes in turbulent convection. Also, the effects of a large number of solid obstacles, constituting the solid porous matrix, on the amount of kinetic energy in turbulent flow will be unveiled and also how it affects the temperature field. The possibility of a second Reynolds number in a bi-disperse porous medium will be considered, which would manifest through the appearance of turbulent eddies corresponding to a larger pore size. Comparison of the DNS results with published experimental data will be performed to validate the numerical results.