Abstract This research study investigated the three-dimensional nature and characteristics of buoyant thermals in the mixed convection turbulent boundary layer. Thermals were visualized using a multi-plane flow visualization technique. Experiments were performed in a variety of conditions where the bulk Richardson number was varied to cover a range describing both inertia dominant flow ( R i L = 0.05 ) and buoyancy dominant flow ( R i L = 2.0 ). Qualitative results define key interactions between thermals and the adjacent turbulent boundary layer flow. A robust algorithm for automatic thermal detection was developed and validated. This algorithm was then applied to experimental images to detect thermals and facilitate a quantitative analysis on the size and spatial distribution of buoyant thermals. Based on these findings an overall flow structure is proposed featuring convective cell like patterns at high Richardson numbers. A first approximation on the shape of thermals and velocity of key thermofluid interactions between thermals and turbulent boundary layer is made. Results indicate these thermal interactions can exhibit motion substantially different from the surrounding turbulent boundary layer flow.

中文翻译：

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加热湍流边界层中热量的可视化和表征

摘要 本研究研究了混合对流湍流边界层中浮力热流的三维性质和特征。使用多平面流动可视化技术可视化热量。实验是在各种条件下进行的，其中体积理查森数变化以涵盖描述惯性主导流（R i L = 0.05）和浮力主导流（R i L = 2.0）的范围。定性结果定义了热气流和相邻湍流边界层流之间的关键相互作用。开发并验证了一种用于自动热检测的稳健算法。然后将该算法应用于实验图像以检测热气流并促进对浮力热气流的大小和空间分布的定量分析。基于这些发现，提出了一种整体流动结构，其特征是在高理查森数下具有类似对流细胞的模式。对热流和湍流边界层之间关键热流体相互作用的热流形状和速度进行了第一次近似。结果表明，这些热相互作用可以表现出与周围湍流边界层流大不相同的运动。