Crosshatched Ablation Patterns in Teflon

Nachtsheim, P. R.; Larson, H. K.

doi:10.2514/3.49963

Cited by 15 publications

(3 citation statements)

References 8 publications

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“…However, examination of Eq. (9) reveals that the magnitude of the amplification rate for an unstable (amplified) condition is primarily influenced by the function «c, ~ P> L (16) This result qualitatively explains the experimental evidence 7 that patterns are deeper in softer materials (low viscosity), and the depth distribution tends to correlate with the surface pressure distribution. However, it must be recognized that this functional dependence is based on a linear analysis, and is therefore applicable only in the early stages of pattern development.…”

Section: Pattern Onset and Growthsupporting

confidence: 69%

“…C ROSSHATCH surface patterns have been observed on a wide variety of dissimilar materials exposed to high-speed flow, including, among others, silicone fluid, 1 wax, 2 camphor, 3 " 6 ammonium chloride, 7 ' 8 plastics, 3 ' 9 " 13 Teflon, 7 ' 14 " 16 Phenolics, 14 and graphite. 7 Practical interest originally centered on flight dynamic perturbations, 1 and heating increments 7 associated with pattern onset.…”

Section: Introductionmentioning

confidence: 98%

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Crosshatch Surface Patterns-Comparison of Experiment with Theory

White

Grabow

1973

AIAA Journal

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Experimental crosshatch patterns from ablating, melting, and flowing materials in supersonic flow are compared with theory. Results from wind-tunnel, rocket motor, and flight test environments on cones from 4.5° to 40° halfangles are shown to have common characteristics and to correlate in terms of relatively simple parameters. The theories considered include differential ablation, inelastic deformation, and liquid layer instability mechanisms. The experimental data are best correlated by a theoretical model which encompasses both the inelastic deformation and liquid layer mechanisms. Nomenclaturec f = imaginary part of complex wave velocity c r -real part of complex wave velocity c p -specific heat G = shear modulus h = static enthalpy k = diffusivity parameter K = thermal diffusivity K* = proportionality between internal shear and pressure perturbations m = ablation rate M = Mach number M = molecular weight p = pressure p' = pressure perturbation F m = dimensionless pressure perturbation amplitude q = heat-transfer rate s = surface recession rate t = time T = temperature u = velocity x = distance normal to waves a = wave number, 2n/A N p = Mach angle y = ratio of specific heats d -boundary-layer thickness 6 f = frictional sublayer thickness S L = melt layer or viscoelastic layer thickness e = amplitude of surface wave A L = streamwise wavelength k N = wavelength normal to waves H = viscosity Q p = pressure perturbation parameter p = density A = thermal conductivity i = shear stress IK = material relaxation time (f) p = pressure phase angle from maximum slope point

p oj = wave angle Subscripts e -edge of boundary layer Presented as Paper 72-313 at

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Section: Pattern Onset and Growthsupporting

confidence: 69%

Section: Introductionmentioning

confidence: 98%

Crosshatch Surface Patterns-Comparison of Experiment with Theory

White

Grabow

1973

AIAA Journal

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p oj = wave angle Subscripts e -edge of boundary layer Presented as Paper 72-313 at

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“…Due to Teflon having a low ablation temperature and low thermal conductivity, it quickly reaches steady state ablation when placed in the arc jet flow [1]. Consequently, Teflon can be used to help define the arc jet test rhombus [1,11], infer heating [1,12,13], and can indicate whether the boundary layer is laminar or turbulent [14][15]. When exposed to high enthalpy arc jet flow, Teflon will sublime with its recession being very sensitive to variations in heating, including effects from shock interactions, radial and axial changes in enthalpy in the arc jet flowfield, and local vortex formation due to flow disturbances created by features on the test model surface, such as joints, grooves, and interfaces.…”

Section: Teflon Inferred Heatingmentioning

confidence: 99%

Calibration and Application of Gardon Gages for use in High Heat Flux Environments

Ferguson¹

2015

20th AIAA International Space Planes and Hypersonic Systems and Technologies Conference

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Gardon gages were calibrated at heat flux levels representative of those experienced in arc jet facilities for Thermal Projection System (TPS) material evaluations. This is the first known calibration of Gardon gages at high heat fluxes, which included values as high as 2,000 BTU/ft 2 -sec. The high heat flux calibration was accomplished using the Laser Hardened Materials Evaluation Laboratory (LHMEL) at Wright Patterson Air Force Base (WPAFB). The results demonstrate a linear response is maintained between the incident heating and voltage output of each Gardon gage at high heat fluxes with a correlation coefficient for the linear least squares regression for each gage exceeding 0.999. Agreement within 4% was obtained when comparing LHMEL calibration constants to manufacturer calibration constants, which were determined at heating levels approximately one order of magnitude lower than those experienced in an arc jet heating environment. The LHMEL calibrated Gardon gages were then tested in the Arnold Engineering Development Complex (AEDC) H1 arc jet, and the results were compared to heating results obtained from coaxial thermocouples and inferred heating using Teflon. Advantages and disadvantages of these different methods of heat flux measurement techniques are discussed relative to their application in arc jets, and recommendations are presented to further improve the understanding and characterization of incident heating on TPS sample surfaces in arc jet evaluations. NomenclatureB = thermochemical ablation potential δ = thickness Ch = Stanton number ε = emissivity E = emf output η = blowing correction H = enthalpy ρ = density ṁ = mass flux rate σ = Stefan-Boltzmann constant q = heat flux rate R = correlation coefficient Subscripts R 2 = coefficient of determination b = blowing s = ablation depth cw = cold wall T = temperature e = boundary layer edge u = velocity gw = gas wall α = absorptance o = no blowing Δt = arc jet dwell time Tef,o = Teflon at initial conditions

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A numerical method for the self-similar hypersonic viscous shear layer

Matarrese

Messiter

1991

Journal of Computational Physics

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Crosshatched Ablation Patterns in Teflon

Cited by 15 publications

References 8 publications

Crosshatch Surface Patterns-Comparison of Experiment with Theory

Crosshatch Surface Patterns-Comparison of Experiment with Theory

Calibration and Application of Gardon Gages for use in High Heat Flux Environments

A numerical method for the self-similar hypersonic viscous shear layer

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