Buoyancy-Dominated Turbulent Transport in Separated Flows

摘要/ ABSTRACT摘要：本文提出的研究是一项以浮力为主导的湍流分离流动的实验和数值研究，这些分离流动是在垂直和水平位置定向的后面向和前面向台阶几何形状上进行的。目的是提供在强浮力和低流速作用下分离流区和再附着流区动量和热输运的定量结果。重点将放在实验研究上，以检验自然对流和邻近这些几何形状的浮力主导的混合对流中的湍流传输特性（包括动量和传热）。现有的湍流模型，如高、低雷诺数的k-E模型、代数应力模型和RNG k-E模型，已经成功地应用于强迫对流，但它们还没有完全测试和验证浮力主导或浮力影响的复杂流动，包括流动分离和再附着。这是因为目前缺乏对浮力主导的湍流分离流的实验测量，即使是对像向后或向前台阶这样简单的几何形状。这些测量是为了测试、验证和/或改进现有的湍流模型，以应用于涉及流动分离的强湍流浮力流动。为了在浮力主导的湍流混合对流流动中建立一个实验和数值数据的基准，本研究选择了简单的前后台阶几何形状，类似于作者在层流混合对流流动中对相同几何形状所做的研究。将对这些基准几何形状在浮力主导的流动条件下的动量和热输运的平均量和湍流量进行测量，这些测量数据将用于拟议研究的数值阶段，希望验证或优化，如果需要，可能会修改现有的湍流模型。这些测量结果也将对未来其他人在浮力主导的分离流中模拟湍流输运的研究具有重要价值。所提出的研究结果将相互关联，以提供处理在许多工程设备中普遍存在的复杂的、以浮力为主的分离流中的湍流传输现象所需的构建块。

ABSTRACT -- CTS-9304485 PI -- Ta-Shen Chen The proposed research is a coordinated experimental and numerical study on buoyancy-dominated, turbulent separated flows over backward-facing and forward-facing step geometries that are oriented in vertical and horizontal positions. It is aimed at providing quantitative results for the momentum and thermal transport in the separates and reattached flow regions under the effect of strong buoyancy forces and low flow velocities. Emphasis will be placed on the experimental study to examine the turbulent transport characteristics (including momentum and heat transfer) in natural convection and in buoyancy-dominated mixed convection adjacent to these geometries. The existing turbulence models, such as the k-E models for high and low Reynolds numbers, the algebraic stress model, and the RNG k-E model have been applied with success to forced convection, but they have not been fully tested and validated for buoyancy- dominated or buoyancy-affected complex flows involving flow separation and reattachment. This is because at the present time there is a lack of experimental measurements of buoyancy-dominated turbulent separated flows, even for such simple geometry as a backward-facing or forward-facing step. Such measurements are needed in order to test, validate, and/or improve the existing turbulence models for applications in strong turbulent buoyant flows involving flow separation. Simple geometries of backward-facing and forward-facing steps are chosen for the proposed research in order to establish a benchmark of experimental and numerical data for these geometries in buoyancy-dominated turbulent mixed convection flows, similar to what has been done for the same geometries in laminar mixed convection flows by the authors. Measurements of the mean and turbulent quantities of the momentum and thermal transport under buoyancy-dominated flow conditions for these benchmark geometries will be carried out and these measured data will be used in the numer ical phase of the proposed study, with the hope of validating or optimizing, and maybe, if needed, modifying the existing turbulence models. These measurements will also be of great value for future studies by others in modeling turbulent transport in buoyancy-dominated separated flows. Results from the proposed research will be correlated to provide the building blocks that are needed in dealing with turbulent transport phenomena in complex, buoyancy-dominated separated flows that are prevalent in many engineering devices.