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.
