Collaborative Research: Control of Natural Convection Alonga Heated, Inclined Plate

本文主要研究倾斜加热面平板边界层流向涡的产生和演化的主动控制。 由于这些涡流在表面附近的传输现象中起着重要的作用，因此对其发生和演变的主动控制可以成为操纵实际感兴趣的自由对流边界层的传热和表面沉积的有力工具，包括冷却技术和电子芯片的制造。 拟议的实验将在水中进行，并将使用镶嵌的单独控制的薄膜加热器齐平安装在一个淹没的测试表面上操纵的流动不稳定性，导致形成的流向涡。 这种操纵的一个重要特征是，随后的流动结构在时间和空间上是极其可重复的，从而允许相位锁定到激励波形的详细测量和流动可视化研究。 特别令人感兴趣的是流动机制，与流向涡的演变。 展向相互作用的这些涡似乎是一个前兆的发展，其次是快速过渡到湍流的二次不稳定。 将使用微型冷丝温度传感器的耙获得横流和展向随时间变化的温度分布的高分辨率测量，并且将使用灵敏的双程纹影系统来可视化流动。 所提出的工作的一个重要方面是测量从测试表面到邻近流体的热通量的全球和平面分布。 特别令人感兴趣的是强制和非强制流动之间的热传递的增量变化。 在本研究的后期阶段，将使用表面致动器来控制纵向涡的抑制或增强。

The proposed research focuses on the active control on the origin and evolution of the streamwise vortices in a flat plate boundary layer along an inclined heated surface. Because these vortices play important roles in transport phenomena near the surface, active control of their onset and evolution can become a powerful tool for the manipulation of heat transfer and surface deposition for free convection boundary layers of practical interest, including cooling techniques and manufacturing of electronics chips. The proposed experiments will be conducted in water, and the flow instabilities leading to the formation of the streamwise vortices will be manipulated using mosaics of individually-controlled film heaters flush-mounted on a submerged test surface. An important feature of such manipulation is that the ensuing flow structures are extremely repeatable in time and space, thus allowing for detailed measurements and flow visualization studies that are phase-locked to the excitation wave-form. Of particular interest are the flow mechanisms, associated with the evolution of the streamwise vortices. Spanwise interactions of these vortices appear to be a precursor to the development of a secondary instability that is followed by rapid transition to turbulence. High-resolution measurements of cross-stream and spanwise time-dependent temperature distributions will be obtained using rakes of miniature cold-wire temperature sensors, and the flow will be visualized using sensitive double-pass Schlieren system. An important aspect of the proposed work is the measurement of global and of planform distributions of heat flux from the test surface to the adjacent fluid. Of particular interest is the incremental change in heat transfer between the forced and unforced flows. At the later stages of this research, the surface actuators will be used to control suppression or enhancement of the longitudinal vortices.