Abstract
This study investigates the effects of boundary layer transition on an oblique shock wave reflection. The Mach number was 1.7, the unit Reynolds number was 35 × 106 m?1, and the pressure ratio over the interaction was 1.35. Particle image velocimetry is used as the main flow diagnostics tool, supported by oil-flow and Schlieren visualizations. At these conditions, the thickness of the laminar boundary layer is only 0.2 mm, and seeding proved to be problematic as practically no seeding was recorded in the lower 40 % of the boundary layer. The top 60 % could, however, still be resolved with good accuracy and is found to be in good agreement with the compressible Blasius solution. Due to the effects of turbulent mixing, the near-wall seeding deficiency disappears when the boundary layer transitions to a turbulent state. This allowed the seeding distribution to be used as an indicator for the state of the boundary layer, permitting to obtain an approximate intermittency distribution for the boundary layer transition region. This knowledge was then used for positioning the oblique shock wave in the laminar, transitional (50 % intermittency) or turbulent region of the boundary layer. Separation is only recorded for the laminar and transitional interactions. For the laminar interaction, a large separation bubble is found, with a streamwise length of 96 ??i,0 . The incoming boundary layer is lifted over the separation bubble and remains in a laminar state up to the impingement point of the shock wave. After the shock, transition starts and a turbulent profile is reached approximately 80–90 ??i,0 downstream of the shock. Under the same shock conditions, the transitional interaction displays a smaller separation bubble (43 ??i,0 ), and transition is found to be accelerated over the separation bubble.
Highlights
Shock wave–boundary layer interactions (SWBLI) can be encountered in a wide range of applications that are relevant for the high-speed flight regime, such as supersonic intakes, the blade passages of jet engines and transonic wings
Their DNS simulations showed the development of Kelvin–Helmholtz vortices on the detached shear layer and revealed low-frequency unsteadiness present at the separation point, very similar to what has been recorded for turbulent SWBLIs (Clemens and Narayanaswamy 2014)
The particle image velocimetry (PIV) data that have been gathered during the experiments can be used to track the state of the boundary layer as it develops over the separation bubble
Summary
Shock wave–boundary layer interactions (SWBLI) can be encountered in a wide range of applications that are relevant for the high-speed flight regime, such as supersonic intakes, the blade passages of jet engines and transonic wings. The receptivity of the laminar separation bubble to outside disturbances was further investigated by Sansica et al (2014) Their DNS simulations showed the development of Kelvin–Helmholtz vortices on the detached shear layer and revealed low-frequency unsteadiness present at the separation point, very similar to what has been recorded for turbulent SWBLIs (Clemens and Narayanaswamy 2014). The goal is to describe the process of boundary layer transition in the interaction zone for the laminar and transitional interaction To this end, high-resolution (130 pix/mm) PIV measurements were performed that accurately capture the mean flow field for the different types of interactions. Page 3 of 20 113 the flow over the bubble is captured by tracing the development of the incompressible shape factor
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