Heat transfer visualization of transitional growth of turbulent spot on a wedge in Mach 5.2 hypersonic flow using fast-response TSP

In the present study, the propagation velocity and lateral spreading angle of turbulent spots on a wedge in transient hypersonic boundary layer flows were investigated and characterized by measuring the heat flux distribution using a fast-response temperature-sensitive paint (TSP) in a shock tunnel facility. The shock tunnel was operated under the over-tailored condition and provided with the low- to high-unit Reynolds number during a test duration, which was realized by the contact surface arrival in the shock tube that changed the temperature and density of the reservoir gas. Power spectral density estimated from the pressure recordings may indicate that the boundary layer flow was transitional. In TSP measurements, the global heat flux distribution on the wedge was accurately obtained qualitatively. Surprisingly, turbulent spots were visualized using TSP for each unit Reynolds number condition. The propagation velocities at the head, peak heat flux point, and tail of turbulent spots for low- and high-unit Reynolds number conditions were approximated from the TSP images to be 87 ~ 96%, 69 ~ 73%, and 52 ~ 57% of the boundary layer edge velocities at each condition, respectively. These results were in good agreement with the available data in previous investigations. The lateral spreading angle of turbulent spots was also measured to be 5° ~ 10° from the TSP images. This study showed that the fast-response TSP had the ability to visualize the temporally resolved turbulent spots by measuring the heat flux on the wedge.