Presidential Young Investigators Award: Experimental Investigations of Convective Heat Transfer in Complex Internal Flows

本研究的重点是实验 复合体对流传热研究 内部流动。 特别强调的是被迫的 电子设备的对流冷却，其中内部 由相邻的印刷电路板形成的通道促进了 高度扰动的流动。 其他复杂的、内部的 热传递发生在气体冷却热交换器中， 阵列形成通流区域， 先进燃气涡轮机叶片的流动和内部冷却 其中传热增强装置，例如短销 插入物或周期性的肋板，被浇铸到墙壁中。 所有 这些内部流动表现出现象学特征， 使它们难以预测，包括：（1） 分离和再附着流，（2）包含 二次运动，和（3）高水平的湍流， 平均流量 本研究以实验研究为主 三种典型的几何，它们共同展示了 这些特征。 这些几何形状是：（1） 二维后向台阶，或表面栅栏，（2） 具有重复的肋粗糙度的二维通道，以及 (3)二维通道与三维通道 一面或两面墙壁粗糙。 述第一配置 最不专业的。 在研究的这个分支中， 自由流湍流对管内换热的影响 再循环、再附着和再发展边界层 区域进行了检查。 具体而言，测量包括 湍流热传递和动量 运输，以澄清现有的湍流模型 非平衡壁流中的扩散。 的作用 再附着分离流中的自由流湍流， 尽管在真实的装置中的流动可能 由于上游的影响，高度“干扰”。 第二主 研究的分支以实验研究为中心 充分发展的通道流与分离区， 再附着，如二维通道所示， 重复肋粗糙度和三维通道 粗糙度大。 有一个显著的统一关系 在所有这些情况下的对流传热之间。 例如，无量纲传热速率、努塞尔（Nusselt） 数，增加约雷诺数的2/3次方 在所有这些案件中的数字。 此外，这种关系 似乎适用于小尺度粗糙度， 类型，和大规模的突起或肋。 运输 产生这种普遍行为的现象 希望能找出规模的作用， 粘性和分子扩散以及湍流输送。

The emphasis of this research is in Experimental Investigations of Convective Heat Transport in Complex Internal Flows. Particularly emphasized is forced convection cooling of electronics, wherein the internal passageways formed by adjacent printed circuit boards promote highly disturbed flow. Other examples of complex, internal heat transfer occur in gas-cooled heat exchangers where tube arrays form regions of through-flow interacting with separated flow and internal cooling of advanced gas turbine blades where heat transfer enhancement devices, such as short pin ins or periodic rib turbulators, are cast into the walls. All of these internal flows exhibit phenomenological features that make them difficult to predict including: (1) regions of separated and reattaching flow, (2) regions containing secondary motions, and (3) high levels of turbulence in the mean flow. This research focuses on experimental studies on three canonical geometries that together exhibit all of these features. These geometries are: (1) the two-dimensional rearward facing step, or surface fence, (2) the two-dimensional channel with repeated rib roughness, and (3) the two-dimensional channel with three-dimensional roughness on one or both walls. The first configuration is the least specialized. In this branch of the research, the effects of free-stream turbulence on the heat transfer in the recirculation, reattachment, and redeveloping boundary layer region are examined. Specifically, the measurements include turbulent heat transfer and, simultaneously, momentum transport, in order to clarify existing models of turbulent diffusion in non-equilibrium wall flows. The role of free-stream turbulence in reattaching separated flows is largely unexplored, even though flow in real devices may be highly "disturbed" due to upstream effects. The second major branch of the research centers on experimental investigations of fully-developed channel flow with regions of separation and reattachment as exhibited by the two-dimensional channel with repeated rib roughness and the channel with three-dimensional large roughness. There is a remarkable unifying relationship between the convective heat transfer in all of these cases. For example, the dimensionless heat transfer rate, the Nusselt number, increases as about the 2/3 power of the Reynolds number in all of these cases. Furthermore, this relationship seems to hold for both small-scale roughness, of certain types, and large-scale protrusions or ribs. The transport phenomena that produce this universal behavior are being examined with the hope of identifying the roles of scale, viscous and molecular diffusion, and turbulent transport.