Boundary-Layer Instabilities on a Cooled Flared Cone at Mach 6
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Date
2021-08-02
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Abstract
There are significant challenges involved in the design of hypersonic vehicles/projectiles, one of them being the fluid dynamics on the surface. The fluid dynamics can affect the thermal load, structural load and handling of the vehicle. Boundary-layer transition alone can account for an order of magnitude higher heating and thus it is important to understand how this transition process occurs. In this experiment the boundary layer on a sharp-tip, part-straight, part-flared actively cooled cone is being studied in a quiet Mach 6 wind tunnel. The Mack mode and its associated secondary instability dominate above Mach 4 as a cause of boundary-layer transition and is being focused on in this study. The role of curvature is also included in order to study the effects of Görtler vortices. Boundary-layer transition was tracked using embedded thermocouples, focusing schlieren and Focused Laser Differential Interferometry (FLDI). The Mack-mode disturbances were observed using a high-speed camera and spectral data were taken at a point in the boundary layer using focusing schlieren and FLDI. Constant Temperature Anemometry (CTA) was used in the form of hot-film probes that were traversed in the boundary layer to do azimuthal sweeps and showed periodic mass-flux variations with a wavenumber of 90, which were attributed to Görtler vortices. Distributed Roughness Elements (DREs) were placed at the neutral point with the same wavenumber seen from the hot-film data to force a 3-D breakdown. FLDI was used to probe six points in the boundary layer simultaneously and captured the Mack-mode instability and its harmonics. Computational work confirmed the experimental findings. This work creates a database for Direct Numerical Simulations (DNS) and Non-linear Parabolized Stability Equations (NPSE) computations and adds to the current knowledge of hypersonic boundary-layer transition.
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stability, transition, hypersonic, aerodynamics, fluid dynamics, aerospace