Buoyancy-Dominated Turbulent Transport in Separated Flows

摘要-- CTS-9304485 PI -- Ta-Shen Chen 拟议的研究是一个协调的实验和数值研究浮力主导的，湍流分离流后向和前向的步骤的几何形状，在垂直和水平的位置。 它的目的是提供定量的结果，在分离和再附着流区的动量和热量输运下的强浮力和低流速的影响。 重点将放在实验研究，以检查在自然对流和浮力为主的混合对流邻近这些几何形状的湍流传输特性（包括动量和热量传递）。 现有的湍流模型，如高雷诺数和低雷诺数的k-E模型、代数应力模型和RNG k-E模型已成功地应用于强制对流，但它们尚未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。 这是因为目前缺乏浮力主导的湍流分离流的实验测量，即使是对于像后向或前向台阶这样简单的几何形状。 为了测试、验证和/或改进现有的湍流模型，需要进行这种测量，以便在涉及流分离的强湍流浮力流中应用。 简单的几何形状的后向和前向的步骤被选择为拟议的研究，以建立一个基准的实验和数值数据，这些几何形状在浮力为主的湍流混合对流，类似于已经做了相同的几何形状在层流混合对流的作者。 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送的平均和湍流量进行测量，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，可能修改现有的湍流模型。 这些测量也将是非常有价值的未来的研究，由其他人在模拟浮力为主的分离流的湍流输送。 从拟议的研究结果将相互关联，以提供所需的积木，在处理复杂的，浮力为主的分离流，在许多工程设备中普遍存在的湍流传输现象。

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.