Hypersonic Transitional Boundary Layer Profile Measurements with Molecular Tagging Velocimetry

Abstract Femtosecond laser electronic excitation tagging (FLEET) velocimetry was used to measure the evolution of the streamwise velocity profile in the transitional region on a hollow-cylinder model in a conventional Mach 7 tunnel with freestream Reynolds number of 8.11\((×)\) 10⁶ m⁻¹. Results showed increased momentum near the wall as the transition process occurs, and an analysis of the flow using the continuity equation and Crocco-Busemann relation suggested that the transition region is associated with a developed negative wall normal velocity, implying momentum is being pulled down towards the wall and contributing to an increase in heating. Finally, skin-friction values in the transitional region are estimated from velocity profiles using a canonical profile fitting technique similar to the original form of the Clauser chart method, but with scaling of nondimensionalized transitional boundary layer profiles from a simple CFD solution used in place of analytical theory. This new approach is also compared with viscous sublayer fitting, and evidence is provided suggesting it can give more precise answers, while also not imposing such a difficult to meet wall resolution constraint on experimental data.