Investigation of Hypersonic Laminar Heating Augmentation in the Stagnation Region

Laminar stagnation region heating augmentation is investigated in the AEDC Tunnel 9 at Mach 10 by performing high frequency surface pressure and heat transfer measurements on the Orion CEV capsule at zero degree angle-of-attack for unit Reynolds numbers between 0.5 and 15 million per foot. Heating augmentation increases with Reynolds number, but is also model size dependent as it is absent on a 1.25-inch diameter model at Reynolds numbers where it reaches up to 15% on a 7-inch model. Heat transfer space-time correlations on the 7-inch model show that disturbances convect at the boundary layer edge velocity and that the streamwise integral scale increases with distance. Therefore, vorticity amplification due to stretching and piling-up in the stagnation region appears to be responsible for the stagnation point heating augmentation on the larger model. This assumption is reinforced by the f(exp -11/3) dependence of the surface pressure spectrum compared to the f(exp -1) dependence in the free stream. Vorticity amplification does not occur on the 1.25- inch model because the disturbances are too large. Improved free stream fluctuation measurements will be required to determine if significant vorticity is present upstream or mostly generated behind the bow shock

Transition Within a Hypervelocity Boundary Layer on a 5-Degree Half-Angle Cone in Air/CO_2 Mixtures

Laminar to turbulent transition on a smooth 5-degree half angle cone at zero angle of attack is investigated computationally and experimentally in hypervelocity flows of air, carbon dioxide, and a mixture of 50% air and carbon dioxide by mass. Transition N factors above 10 are observed for air flows. At comparable reservoir enthalpy and pressure, flows containing carbon dioxide are found to transition up to 30% further downstream on the cone than flows in pure air in terms of x-displacement, and up to 38% and 140%, respectively, in terms of the Reynolds numbers calculated at edge and reference conditions

Transition Within a Hypervelocity Boundary Layer on a 5-Degree Half-Angle Cone in Air/CO_2 Mixtures

Laminar to turbulent transition on a smooth 5-degree half angle cone at zero angle of attack is investigated computationally and experimentally in hypervelocity flows of air, carbon dioxide, and a mixture of 50% air and carbon dioxide by mass. Transition N factors above 10 are observed for air flows. At comparable reservoir enthalpy and pressure, flows containing carbon dioxide are found to transition up to 30% further downstream on the cone than flows in pure air in terms of x-displacement, and up to 38% and 140%, respectively, in terms of the Reynolds numbers calculated at edge and reference conditions

Numerical and experimental investigation of laminar-turbulent boundary layer transition on a blunt generic re-entry capsule

Numerical and experimental results on laminar-turbulent transition in the boundary layer of a blunt Apollo-like capsule at 0° and 24° angle of attack are presented. Local stability analyses have been performed and a measurement campaign in the Hypersonic Ludwieg tube Braunschweig at a Mach number of 5.9 was carried out. Infrared thermography showed laminar and transitional surface heating in the unit Reynolds number range of Re_infinity = 6x10^6 /m to Re_infinity = 20x10^6 /m at a surface mean roughness of Ra = 10 micrometer, whereas for a mean roughness of Ra = 0.5 My micrometer no indications for a transitional boundary layer was noted. PCB and Kulite sensors used to measure pressure fluctuations inside the boundary layer do not show any peaks in the frequency spectra which might be related to boundary layer disturbances. The only relevant peak in the spectra does not change with unit Reynolds number and is currently attributed to a bow shock oscillation. Consistent with the experimental findings, the modal instability analysis does not provide any modal boundary layer disturbance growth at windtunnel conditions. Therefore, a scaling ansatz for the laminar boundary layer is introduced and evaluated in order to estimate the unit Reynolds numbers required for the onset of modal disturbance growth on Apollo-like capsules. Results for both first-mode and cross-flow instability are presented