Article

Thermal Shielding of a Reentry Vehicle by Ultra-High-Tempreature Ceramic Materials

Journal of Thermophysics and Heat Transfer - J THERMOPHYS HEAT TRANSFER 01/2006; 20(3):500-506. DOI: 10.2514/1.17947
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    ABSTRACT: Analytical modeling of thermal and mechanical response is a fundamental step in the design process for ultra-high-temperature ceramic components, such as nose tips and wing leading edges for hypersonic applications. The purpose of the analyses is to understand the response of test articles to high-enthalpy flows in ground tests and to predict component performance in particular flight environments. Performing these analyses and evaluating the results require comprehensive and accurate physical, thermal, and mechanical properties. In this paper, we explain the nature of the analyses, highlight the essential material properties that are required and why they are important, and describe the impact of property accuracy and uncertainty on the design process.
    Journal of The European Ceramic Society - J EUR CERAM SOC. 01/2010; 30(11):2239-2251.
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    ABSTRACT: This dissertation presents a detailed, computational study quantifying the effects of nonequilibrium on the surface properties of a hypersonic vehicle by comparing Navier-Stokes-based Computational Fluid Dynamics (CFD) and direct simulation Monte Carlo (DSMC) simulation results for the flow about a cylinder and a wedge. Physical submodels contained in both computational methods are ensured to be as equivalent as possible. Translational nonequilibrium effects are isolated by considering a monatomic gas, argon. Thermal nonequilibrium effects are included by considering a diatomic gas, nitrogen. Several different flow regimes are considered, from the continuum into the transitional (freestream Knudsen numbers are 0.002, 0.01, 0.05 and 0.25), with Mach numbers of 10 and 25. Effects on surface properties (total drag and peak heat transfer rate) are quantified at each flow condition. Flow field properties are also compared. Continuum breakdown parameter values are compared with other flow and surface properties. The effectiveness of several types of CFD slip boundary conditions is evaluated, and the velocity slip and temperature jump (including vibrational temperature jump) values are compared with those extracted from DSMC simulation results. The slip conditions of Gokcen (AIAA Paper 1989-0461) most accurately predict surface properties, while the slip conditions of Lockerby et al. (AIAA J. 43(6) (June 2005), 1391-1393) agree best with DSMC slip values. For flows of argon and nitrogen about a cylinder, CFD total drag predictions remain within 6% of DSMC predictions, and heat flux agreement is 8% or better. For flows about a wedge, total drag differences range between 2% and 34%, mostly due to friction force differences. Peak heating differences are between 70% and 100%; DSMC predicts a much higher temperature near the leading edge than CFD. Flow property differences near the wall surface are shown to be concentrated primarily in the Knudsen layer. Validation of the CFD code, as well as the effect of various levels of surface accommodation, are shown by considering a nitrogen flow over a flat plate and comparing the simulation results with experimental data. Ph.D. Aerospace Engineering University of Michigan, Horace H. Rackham School of Graduate Studies http://deepblue.lib.umich.edu/bitstream/2027.42/58370/1/ajloft_1.pdf
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    ABSTRACT: The article deals with arc-jet experiments on different ultra high temperature ceramics (UHTC) models in high enthalpy hypersonic non-equilibrium flow. Typical geometries of interest for nose tip or wing leading edges of hypersonic vehicles, as rounded wedge, hemisphere, and cone are considered. Temperature and spectral emissivity measurements have been performed using pyrometers, an IR thermocamera and thermocouples. The details of the experimental set-up, the test procedure and the measurement are discussed in the text. The UHTC materials have been tested for several minutes to temperatures up to 2050 K showing a good oxidation resistance in extreme conditions. Differences between the various model shapes have been analyzed and discussed. Numerical–experimental correlations have been carried out by a computational fluid-dynamic code. The numerical rebuilding also allowed to evaluate the catalytic efficiency and the emissivity of the materials at different temperature.
    Aerospace Science and Technology. 01/2010;