Abstract
The hypersonic boundary layer transition over a concave wall is investigated in a Mach 6.5 quiet wind tunnel using temperature sensitive paint (TSP), CO2-enhanced filtered Rayleigh scattering flow visualization, PCB fast-response pressure sensors, and a high-frequency schlieren technique. The TSP shows that low- and high-temperature streaks are distributed in the spanwise direction. The wavelengths of naturally developing Görtler streaks are randomly distributed, with an average of approximately 7 mm, and change little as the unit Reynolds number increases. More importantly, three-dimensional waves are clearly visualized and quantitatively measured inside the Görtler streaks. This is the first time that the entire evolution of the Görtler instability has been visualized using the Rayleigh-scattering flow visualization in hypersonic flow. The results demonstrate that three-dimensional waves are amplified as a result of the Görtler instability, resulting in a localized high-shear layer around the interface of the three-dimensional waves, which contributes to the formation of hairpin vortices and mushroom-like structures. The three-dimensional waves grow and play an important role in Görtler instability-induced boundary layer transitions.
Highlights
The study of laminar–turbulent transition and turbulence production is very important for the safety of hypersonic vehicle flight.When a flow passes over a concave wall, the imbalance between the centrifugal force and the wall normal pressure causes the G€ortler instability.[1]
The results demonstrate that three-dimensional waves are amplified as a result of the G€ortler instability, resulting in a localized high-shear layer around the interface of the three-dimensional waves, which contributes to the formation of hairpin vortices and mushroomlike structures
This paper reports the use of temperature sensitive paint (TSP) and Rayleigh-scattering visualization to study the development of G€ortler streaks and three-dimensional instability waves
Summary
The study of laminar–turbulent transition and turbulence production is very important for the safety of hypersonic vehicle flight. G€ortler instability control was investigated by direct numerical simulations in both incompressible and compressible flows.[50,51]. Jiang et al.[56] systematically studied the structural evolution at the early stage of boundary layer transition through simulations and experiments. Jiang et al.[57] performed an experimental study of the low-speed streaks in a turbulent boundary layer They observed that the three-dimensional wave behavior of the detected low-speed streaks appeared to develop into associated nearwall vortex flow structures, in a process somewhat similar to transitional boundary layer behavior. Low-speed streak patterns and hairpin vortices appear frequently for G€ortler instability-induced boundary layer transitions. This paper reports the use of temperature sensitive paint (TSP) and Rayleigh-scattering visualization to study the development of G€ortler streaks and three-dimensional instability waves.
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