Science and technology of polymeric ablative materials for thermal protection systems and propulsion devices: A review

*The Hypersonic International Flight Research Experimentation (HIFiRE) program is a hypersonic flight test program executed by the Air Force Research Laboratories (AFRL) and Australian Defence Science and Technology Organization (DSTO). The test geometry consists of a 7-degree half angle cone with 2.5 mm bluntness followed by a cylinder and flare. The experiment test window is between Mach 7.2 and 7.4. The emphasis of flight one is aerothermodynamics, and boundary layer transition is the primary experiment. This makes it critical to specify allowable roughnesses and trips. No theory is available for estimating allowable roughness heights, so correlations must be used. This paper describes several correlations for distributed nose tip roughness and discrete frustum roughness. Generally, the correlations all give reasonable results about the same order of magnitude, but show considerable spread. Correlations based on integral parameters require fairly realistic walltemperature distributions in order to get integral values correct. When making roughness estimates, several correlations should be examined, and decisions on trips and roughness must be made using judgment based on how near one is to a specific criterion. Assessment of roughness effects is essentially an exercise in uncertainty management and risk mitigation.

Roughness Considerations for the HIFiRE-1 Vehicle

Heat transfer—a review of 1976 literature

: The first known gun barrel thermochemical erosion modeling code is presented. This modeling code provides the necessary missing element needed for developing a generalized gun barrel erosion modeling code that can provide analysis and design information that is unattainable by experiment alone. At the current stage of code development, single-shot comparisons can be made of either the same gun wall material for different rounds or different gun wall materials for the same round. This complex computer analysis is based on rigorous scientific thermochemical erosion considerations that have been validated in the reentry nosetip and rocket nozzle community over the last forty years. The 155-mm M2O3 Unicannon system example is used to illustrate the five module analyses for chromium and gun steel wall materials for the same round. The first two modules include the standard gun community interior ballistics (XNOVAKTC) and nonideal gas thermochemical equilibrium (BLAKE) codes. The last three modules, significantly modified for gun barrels, include the standard rocket community mass addition boundary layer (TDK/MABL), gas-wall chemistry (TDK/ODE), and wall material ablation conduction erosion (MACE) codes. These five module analyses provide recession, temperature, and heat flux profiles for each material as a function of time and axial position. In addition, this output can be coupled to PEA cracking codes. At the peak heat load axial position, predicted single-shot thermochemical wall erosion showed uncracked gun steel eroded by a factor of one hundred million more than uncracked chromium. For chromium plated gun steel, with its associated crack profile, it appears that gun steel ablation at the chromium cracks leaves unsupported chromium, which is subsequently removed by the high-speed gas flow,

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Unified Computer Model for Predicting Thermochemical Erosion in Gun Barrels

Unified computer model for predicting thermochemical erosion in gun barrels

Refractory metals are attractive candidates for re-entry vehicle nosetips due to their high resistance to water droplet and ice particle erosion. Ablation models are presented for tungsten, tungsten/25% rhenium, and molybdenum, including gas diffusion-limited thermochemical ablation and liquid phase removal. Chemical eqtilibrium is assumed in the gas phase with kinetics for tungsten ablation considered only at the ablating surface. These models have been incorporated into computer programs that also include shape change, boundarylayer transition, surface roughness, and two-dimensional transient conduction. Good correlation for highand low-pressure arcjet tests, ballistic range firings, and sounding rocket flights has been obtained with these models.

H. L. Moody

Papers

Tungsten and Molybdenum Ablation Modeling for Re-entry Applications

Tungsten and molybdenum ablation modeling for reentry applications