Using a fast-response temperature-sensitive paint to spatially and temporally resolve transitional phenomena

Abstract

Time-resolved temperature-sensitive paint is employed in this work to investigate transitional boundary layer phenomena on a flat plate model under high Reynolds number and high subsonic Mach number conditions. Spatially and temporally resolved surface heat flux distribution are inferred from the surface temperature evolution. The experiments are conducted at a Mach number of 0.8, high chord Reynolds numbers of 6 and 7.5 million, and under streamwise favourable pressure gradients with an acquisition frequency of 20 kHz. The bimodal distribution of surface heat flux enables the identification of laminar and turbulent boundary layer states, allowing for the direct determination of the time-dependent transition front and the time-averaged intermittency distribution. It is demonstrated, that conventional time-averaged transition detection methods — specifically, the location of maximum temperature gradient and peak temperature fluctuation — accurately correspond to the location of 50% intermittency. Furthermore, the evolution of an isolated turbulent spot is spatially and temporally resolved and compared to hot-film traces.