Spatial-temporal variation of heat transfer coefficient due to main vortex and local corner vortex downstream of a vortex generator

The relationship between the two longitudinal vortex structures generated by a right-angled triangular vortex generator placed in a laminar boundary layer on a flat plate and the local heat transfer coefficient was experimentally investigated. The shape of the vortex generator is a hypotenuse of 40 mm, a vertex angle of 22°, and a height of 15 mm, which is a height ratio of 1.5 to the boundary layer thickness of 10 mm. The flow field was visualized using a smoke wire method and measured by particle image velocimetry. For the heat transfer measurements, a 5 μm-thick titanium heating film was placed as the heat transfer surface, and the surface temperature distribution, including time changes, was measured using a high-speed infrared camera.The main vortex formed after passing over the vortex generator had a swirl width of approximately 1.5 times the boundary layer thickness and promoted heat transfer over a wide area, promoting heat transfer over a wide area and continuously.In contrast, the corner vortex, which is strongly concentrated near the wall, exhibits a locally higher heat transfer enhancement effect than the main vortex. Although it attenuates as it moves downstream, it exhibits a large time-varying component and is characterized by increasing again downstream. This suggests that it interferes with the main vortex and surrounding flow. The inclination angle of the vortex generator and its time change significantly affected the heat flow, and the maximum heat transfer coefficient was obtained at 120°.