Thermal Shielding of Reentry Vehicle by Ultra-High-Temperature Ceramic Materials
University of Naples Federico II, Napoli, Campania, ItalyJournal of Thermophysics and Heat Transfer (Impact Factor: 0.83). 07/2006; 20(3):500-506. DOI: 10.2514/1.17947
Reentry vehicles With enhanced aerodynamic performances and high maneuverability require sharp leading edges for the wings and control surfaces and a sharp tip of the fuselage nose where high localized heat fluxes occur. Ultra-high-temperature ceramics, for example, zirconium, hafnium, or titanium diborides, are candidate materials for the sharp edges of reentry Vehicles that make use of new thermal protection systems, positioning massive thermal protection systems only at the leading edge of the wings (or at the fuselage tip). The boundary-layer thermal protection concept is illustrated, and the requirements for the geometry and materials of the fuselage nose are identified. It is shown how a sharp nose will protect the fuselage, acting as a lightning rod for the rest of the structure when the vehicle flies at relatively low angles of attack. Systematic numerical analyses are shown for the sphere-cone nose vehicle to compute temperature distributions along the surface and inside the nose structure at different angles of attack. The effects of the chemistry and of the surface catalysis are discussed.
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- "Since a steady state is achieved, global radiative equilibrium is established, in the sense that the overall surface convective heat flux is balanced by the overall surface radiative heat flux and by the conduction heat transfer: a (relatively) lower equilibrium temperature is achieved if the base material composing the LE and operating at elevated temperature does not degrade significantly its own (high temperature) thermal conductivity. The heat flux distribution over a sharp LE exhibits a typical dependence by the inverse of the square root of the distance from the stagnation point decreasing as the boundary layer becomes thicker . Thus, less intense net heat fluxes take place, recommending as mandatory the need of installing strongly refractory thermal protections only in those parts of the vehicle where the heat fluxes reach the top magnitudes. "
ABSTRACT: Aim of this work is to analyze the response of an ultra-high temperature ceramic at typical heat flux conditions of thermal protection systems of a re-entry spacecraft. In particular, a ZrB2–SiC based ultra-high temperature advanced ceramic sharp leading edge demonstrator (1 mm nominal radius of curvature) was manufactured and tested in a non-equilibrium high enthalpy supersonic airflow, 20 MJ/kg of peak total enthalpy, by using an arc-jet ground facility. The surface temperature of the leading edge was monitored by infrared thermo-cameras coupled to a two-color pyrometer. The ultra-refractory advanced ceramic leading edge withstood stressful thermo-chemical loads successfully, without obvious failure. Ad-hoc computational fluid dynamics simulations rebuilt the adopted set-up and related experiment conditions: the numerical outputs matched fairly well the experimental in-situ determinations.International Journal of Heat and Mass Transfer 12/2015; 91:747–755. DOI:10.1016/j.ijheatmasstransfer.2015.08.029 · 2.38 Impact Factor
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ABSTRACT: Microstructure modifications of an ultra-high temperature ZrB2–SiC ceramic exposed to ground simulated atmospheric re-entry conditions were investigated and discussed. Fluid dynamic numerical calculations were carried out to correlate and explain the experimental results. The cross-sectioning of the ceramic models after exposure (examined by SEM) showed a compact scale of zirconia (20 μm thick) underlying an external silica thin coating. A partially SiC-depleted region, a few microns thick, underneath the zirconia sub-scale was also seen. The post-test analyses confirmed the potential of the ZrB2–SiC composite to endure re-entry conditions with temperature approaching 2000 °C, thanks to the formation of a steady-state external multiphase oxide scale. Numerical calculations, which simulated the chemical non-equilibrium flow around the ceramic model, matched well the experimental results only assuming a very low catalytic surface behavior.Journal of the European Ceramic Society 01/2007; 27(16-27):4797-4805. DOI:10.1016/j.jeurceramsoc.2007.02.201 · 2.95 Impact Factor
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ABSTRACT: The convective heat flux distributions over the surface are reproduced with stagnation point to simulate free-flight aerothermodynamic conditions in a wind tunnel such as a plasma wind tunnel (PWT) to get a complete duplication of all relevant flight conditions. The most appropriate wind tunnel settings simulating free-flight conditions are identified by approximating heat flux as a function of curvature radius and hypersonic speed as a function of density and velocity in freestream conditions. Heat flux distributions for sharp and blunt bodies at local radiative equilibrium shows that bow shock detaches from the nose and dissociation reactions take place in the shock layer for a blunt body. The sharp body numerical model suggests that the chemical reactions take place in a thin shock layer that surrounds leading edge, but near the stagnation point there is a nonegligible difference between catalytic and noncatalytic wall.Journal of Thermophysics and Heat Transfer 07/2007; 21(3):660-664. DOI:10.2514/1.26465 · 0.83 Impact Factor
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