Hypersonic Ground Testing of Tangent Ogive Nose Cones: Investigating Turbulent Boundary Layers With Curvature-Driven Favorable Pressure Gradients
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Date
2023-11-30
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Abstract
Hypersonic flows create a difficult challenge to turbulence models due to their severe gradients, non-equilibrium conditions, and intense heating. Consequently, current models often fail to predict critical quantities such as heat transfer and skin friction on flight vehicles. To provide data for the advancement of new turbulence models, turbulent boundary layer and wall surface measurements were acquired in the Actively Controlled Expansion (ACE) tunnel and the Hypervelocity Expansion Tunnel (HXT) at Texas A&M’s National Aerothermochemistry and Hypersonic Laboratory. Results from the ACE facility included surface measurements of heat transfer, skin friction, static pressure, and pressure fluctuations. In the HXT facility, the surface measurements consisted of static pressure and pressure fluctuations. A laser diagnostic technique known as Focused-Laser Differential Interferometry (FLDI) characterized the test article’s boundary layer in each facility, providing convective velocity profiles and density gradient fluctuations at a measurement station located 3.81 cm from the trailing edge. The test article, a tangent ogive nosecone, enabled answers to a series of fundamental research questions pertaining to the influence of surface roughness and favorable pressure gradients. To answer those questions, the experiments targeted conditions ranging from laminar to turbulent flow with a constant Mach number of 5.7. To promote turbulent boundary layers on the test article in ACE, a 3D printed quasi-random roughness topology was designed using an axisymmetric Fourier series, and the design steps were listed in detail for others to replicate. A primary outcome of the experiments in ACE was the quantification of the Reynolds analogy factor, which relates the non-dimensional heat transfer to the local skin friction coefficient. The data revealed that the Reynolds analogy factor remained constant at approximately 0.6 when the boundary layer was turbulent. Additionally, the FLDI density gradient power spectra indicated that broadband turbulence was present after the Reynolds number reached Rex = 2e6 when using 3D printed roughness on the nose tip. In the HXT facility, the test article had a smooth nose tip, and the FLDI density gradient power spectra indicated that the boundary layer transitioned to turbulent between Rex = 13.5e6 and 22.6e6.
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hypersonic, ground testing, turbulence, boundary layer transition