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

本文的研究重点是对倾斜受热面平板边界层中流向涡的起源和演化进行主动控制。由于这些涡旋在表面附近的输运现象中起着重要的作用，因此，主动控制它们的开始和演化可以成为操纵具有实际意义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，并将使用齐平安装在水下测试表面上的单独控制的薄膜加热器的马赛克来操纵导致流向涡流形成的流动不稳定性。这种操作的一个重要特征是，随后的流动结构在时间和空间上是极其可重复的，从而允许进行详细的测量和流动可视化研究，这些测量和流动可视化研究是锁定在激励波形上的。特别令人感兴趣的是流动机制，与流向涡的演变有关。这些涡旋在展向上的相互作用似乎是二次不稳定发展的先兆，继而迅速转变为湍流。使用微型冷线温度传感器将获得横流和跨距随时间变化的温度分布的高分辨率测量，并将使用灵敏的双通道纹影系统显示流动。这项工作的一个重要方面是测量从测试表面到相邻流体的整体和平面热流密度分布。特别令人感兴趣的是强迫和非强迫流动之间的热量传递的增量变化。在本研究的后期阶段，表面致动器将用于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.