Investigation of Graphite Ablation at IRS

Eswein, Nelli; Herdrich, Georg; Fasoulas, Stefanos; Röser, Hans‐Peter

doi:10.2514/6.2011-3615

Cited by 9 publications

(4 citation statements)

References 12 publications

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“…Some of these conditions were not met in the investigated subsonic flow. However, previous investigations of other subsonic flows in the same facility have shown that results obtained with this method are comparable to results of other measurement techniques [34,36,37]. Thus, the method was assumed to result in a reasonable estimate of the local mass-specific enthalpy.…”

Section: Facility Overviewmentioning

confidence: 62%

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Hermann

Löhle

Zander

et al. 2016

Journal of Thermophysics and Heat Transfer

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This paper presents the analysis of optical emission spectroscopic measurements from vacuum ultraviolet (120 nm) to near infrared (960 nm) in a high-enthalpy air plasma flow corresponding to superorbital reentry conditions. The vacuum ultraviolet measurements have been realized with a new experimental setup allowing measurements through a bore hole in the sample. Using the commonly applied optical emission spectroscopy from the side, the radiation transport along the line of sight of the vacuum ultraviolet measurements has been assessed. This allowed the determination of the local ground state densities of atomic oxygen and atomic nitrogen from a branching ratio analysis and the blackbody limiting correction of the vacuum ultraviolet radiation. Through the analysis of the absorption in the borehole, the spectra have been corrected, resulting in a stagnation point radiative heat flux in the vacuum ultraviolet of 235 kW∕m 2 .= local mass-specific enthalpy, MJ∕kg I = arc current, A K = proportionality constant for air, W∕MJ∕kg·Pa 0.5 ·m 1.5 k = Boltzmann constant, J∕K k cal = calibration factor, W∕m 2 · nm · sr∕counts∕s L λ = spectral radiance, W∕m 2 · nm · sr L λ;Limit = blackbody limit spectral radiance, W∕m 2 · nm · sr M = magnification _ m = mass flow, g∕s n = number density, m −3 n i = excited state population density, m −3 n 0 = ground state population density, m −3 P = electric power, kW P k = spectral line shape, nm −1 p = pressure, hPa _ q = heat flux, kW∕m 2 R eff = effective nose radius, mm r = radial distance, mm S = raw signal, counts/s s = distance from the probe surface, mm s 0 = distance between object and focusing element, mm= vibrational quantum number x = axial distance from the nozzle, mm y = horizontal distance from the nozzle, mm z = vertical distance from the nozzle, mm α λ = absorption coefficient, m −1 δ = full width at half-maximum of line broadening, nm ε λ = emission coefficient, W∕m 3 · nm · sr ε = spectrally integrated emission coefficient, W∕m 3 · sr λ = wavelength, nm σ λ = absorption cross section, m 2 Subscripts BB = blackbody DL = deuterium lamp exc = electronic excitation IS = integrating sphere l = lower state rot = rotational tot = total trans = translational u = upper state vib = vibrational

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Section: Facility Overviewmentioning

confidence: 62%

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Hermann

Löhle

Zander

et al. 2016

Journal of Thermophysics and Heat Transfer

Self Cite

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“…The conventional probe technique which is used in the present investigation for the carbon preform is used regularly for ablation material testing (see e.g. 8,15,16 ). Fig.…”

Section: Methodsmentioning

confidence: 99%

Photogrammetric Surface Recession Measurements on Ablative Samples of Various Shape

Reimer

Löhle

Öfele

2016

Processing, Properties, and Design of Advanced Ceramics and Composites: Ceramic Transactions

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Results from plasma wind tunnel testing of a lightweight carbon phenolic ablative material are presented. The tests were carried out in a high-enthalpy subsonic flow at a condition corresponding to the Hayabusa re-entry condition in 78 km altitude. The samples were produced from ZURAM which is a carbon-fiber structure impregnated with phenolic resin. The focus of the investigation was on the measurement method of the recession. Stereoscopic photogrammetry was applied to reconstruct the sample surface in three-dimensional space over the testing time. Two cameras were used to capture images simultaneously. Using a three-step process the sample surface for each image pair was reconstructed and the recession between the image pairs was calculated. The recession resolution is in the range of 45 µm. The advantage of the method is that the time-resolved in-situ surface recession measurement gives insight into the local recession distribution over the sample surface. This means that recession differences due to the sample geometry or due to material inhomogeneities can be identified. In order to verify this, samples were prepared that include distinct geometric features which influence the recession. Starting with a flat surface cylinder, samples with a rounded surface were prepared as well as a cone-sphere sample and one with a defined indentation in the form of a half-sphere. The temporally and locally resolved recession was successfully measured and related to the sample geometric features.

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“…To increase the number of measurements possible during each experiment, some probes were manufactured with two heads so that two tests could be performed within one experiment by rotating the probe. The present investigation was conducted with a probe that is usually used for the material investigation of ablative test materials [7,13]. The sample used was a carbon preform of type Calcarb with a probe diameter of 40 mm.…”

Section: Methodsmentioning

confidence: 99%

“…The significance of nitridation for recession has been shown to be rather low [6]. Sublimation, i.e., the phase change to gas of the carbon solid (char and fibers), becomes significant at high temperatures above 3000 K [5,7]. However, mechanical erosion can be important depending on the surface state and surface layer porosity.…”

Section: Introductionmentioning

confidence: 99%

Photogrammetric Surface Analysis of Ablation Processes in High-Enthalpy Air Plasma Flow

et al. 2015

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Results from an in situ analysis of ablative heat shield materials based on stereoscopic photogrammetry during plasma wind tunnel testing are presented. A carbon fiber preform material sample has been investigated in a highenthalpy airflow corresponding to a Hayabusa reentry condition at a 78 km altitude. The applied photogrammetry uses two digital single lens reflex cameras triggered at 3 frames∕s to acquire images simultaneously from two different perspectives of the sample exposed to the high-speed flow. The photogrammetric analysis resolves the surface with 25;000 px∕cm 2 , approximately 400 dpi, allowing the in situ analysis of the recession phenomena of ablators. Material inhomogeneities are identified during the ablation process, and surface recession is derived with an accuracy of 21 μm. The method is a useful tool for the investigation of temporally resolved volumetric ablation phenomena in low-density carbon phenolic materials.

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Investigation of Graphite Ablation at IRS

Cited by 9 publications

References 12 publications

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Characterization of a Reentry Plasma Wind-Tunnel Flow with Vacuum-Ultraviolet to Near-Infrared Spectroscopy

Photogrammetric Surface Recession Measurements on Ablative Samples of Various Shape

Photogrammetric Surface Analysis of Ablation Processes in High-Enthalpy Air Plasma Flow

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