Hot-Wall Reentry Testing in Hypersonic Impulse Facilities

Zander, Fabian; Morgan, Richard G.; Sheikh, U.; Buttsworth, David; Teakle, Philip

doi:10.2514/1.j051867

Cited by 78 publications

(53 citation statements)

References 9 publications

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“…Emission spectroscopy has been used in several experiments at UQ to observe the spectra of radiating flows around test models, particularly in the X2 facility [13][14][15][16][17]; both ratio-pyrometry and blackbody approximations have been used for temperature estimation [13,14]. Contamination of test gas flow is persistent: Eichmann [13] shows calcium contamination from a Mylar secondary diaphragm; a range of spectral lines due to neutral and singly ionized iron from damage to the test model rather than particles stripped from the tube walls; and a sodium doublet due to contamination from vacuum grease.…”

Section: Driver Gas Spectroscopymentioning

confidence: 99%

X3 expansion tube driver gas spectroscopy and temperature measurements

et al. 2017

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The University of Queensland's X3 facility is a large, free-piston driven expansion tube used for superorbital and high Mach number scramjet aerothermodynamic studies. X3's powerful test flow is initiated by firing its heavy piston into its driver gas -a mixture of argon and helium. Knowledge of the initial and transient temperature behavior of the driver gas is critical to correctly characterize the driver performance, losses and all subsequent expansion tube flow processes. However, the driver gas temperature is not currently measured during routine experimentation and there is limited evidence of its measurement in other international facilities. During recent scramjet flow development in X3, lower than expected experimentally measured shock speeds through helium indicated an effective driver temperature of approximately 2400 K, compared to a temperature of 3743 K at the time of diaphragm rupture for an ideal isentropic driver gas compression. These performance losses motivate this study, which examines initial and peak driver gas temperatures. The study shows that the initial steady-state driver gas temperature, once the filling process ceases, can be approximated by the external driver tube wall temperature. During filling, a net increase in driver gas temperature occurs due to compression heating, as well as, Joule-Thomson effect for helium. Optical emission spectroscopy was then used to resolve the peak driver gas temperature, during piston compression, for a Mach 10 scramjet operating condition. The driver gas emission spectrum exhibits a significant background radiation component, with prominent spectral lines attributed to contamination of the flow. A blackbody approximation of background radiation suggests a peak driver gas temperature of 3200±100 K. Application of the line-ratio method to two argon lines at 763.5 and 772.4 nm suggests a temperature of 3500±750 K. Comparison of these estimates to the ideal isentropic driver gas temperature at diaphragm rupture, 3743 K, suggests losses in the driver gas temperature during the compression process are not extensive for X3, and further that the lower than expected shock speeds are likely primarily due to pressure losses during driver gas expansion through the diaphragm and at the driver-to-driven tube area change. Nomenclature A = Einstein coefficient for spontaneous emission, s -1 a = sound speed, m/s c = speed of light = 3×10 8 m/s E = energy of the upper atomic state, eV g = statistical weight of upper atomic state h = Planck's constant = 4.136×10 -15 eV.s I = spectral intensity, counts K = Boltzmann's constant = 8.617×10 -5 eV/K L = spectral radiance, W/m 2 /sr/nm M = molecular weight, g/mol P i = driver gas initial pressure, Pa P p = driver gas pressure at rupture, Pa R = gas constant, J/mol/K T abs = absolute temperature, K T ex = excitation temperature, K T i = driver gas initial temperature, K T p = driver gas average peak temperature, K γ = ratio of specific heats λ = wavelength, m 1 Undergraduate, School of Mechanical and Mining Engineering, AIA...

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Section: Driver Gas Spectroscopymentioning

confidence: 99%

X3 expansion tube driver gas spectroscopy and temperature measurements

et al. 2017

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“…The Achilles' heel of impulse facilities is their inability to sustain the flow for long enough to accurately reproduce ablation and pyrolysis. In an attempt to eliminate the initial time requirement, Zander et al [6] developed a resistive heating technique to electrically heat a flat-faced model of a cylindrical section of reinforced carbon-carbon to approximately 2300 K before flow establishment, showing an increased production of CN due to wall temperature. Lewis et al [7] investigated CN violet emissions at a range of different wall temperatures for the same model.…”

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confidence: 99%

Venus Entry Flow over a Decomposing Aeroshell in X2 Expansion Tube

Banerji¹,

Leyland²,

Fahy³

et al. 2018

Journal of Thermophysics and Heat Transfer

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The effects of phenolic decomposition on shock-layer radiation were investigated experimentally in X2 expansion tube for a Venus entry flow. A carbon-phenolic composite aeroshell was subjected to a flow with a flight equivalent velocity of 9.35 km ⋅ s −1 . Emission spectroscopy was used to measure boundary-layer radiation in parts of the ultraviolet (380-480 nm) and visible (620-700 nm) spectrum, and it was compared to control measurements taken with a cold steel model. With the composite model in place, the calibrated spectral radiance measured was seen to increase for the O (645.598 nm) atomic line and the N 2 (391.22 nm) band head, but it decreased for the C 2 Swan band (420-480 nm). The recorded data were then compared to numerical spectra produced by two-dimensional axisymmetric computational fluid dynamic simulations coupled to a radiation solver. Both of the applied chemistry models overpredicted CN violet Δν 0 band radiation, which demonstrated strong self-absorption at these conditions. Better comparisons were achieved for the C 2 Swan band radiation. At visible wavelengths, peak intensities were underestimated by the numerical simulations. Several possible reasons were hypothesized for these discrepancies.

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“…Zander et al [25,26] addressed the problem of accurately reproducing the realistic ablative thermal boundary conditions relevant to flight. Reinforced carbon-carbon (RCC) models were manufactured using a filament winding technique, and electrically pre-heated to temperatures approaching 2500 K immediately before testing in the X2 facility.…”

Section: Studies Of Ablation In Impulse Facilitiesmentioning

confidence: 99%

“…Due to their extremely short test times, however (ranging from around 100 µs to several milliseconds), they are unable to aerothermally heat test models up to representative in-flight temperatures. A method for electrically preheating reinforced carbon-carbon (RCC) samples to temperatures approaching 2500 K was recently developed by Zander et al [25] to address this issue. It was shown that the surface thermochemistry was significantly promoted and the effects could be observed within the available test time of an impulse facility.…”

Section: Introductionmentioning

confidence: 99%

“…The measurements will be taken in an impulse facility to produce a full hypersonic shock layer around a test model. The models will be pure graphite and preheated to a number of representative surface temperatures using the methodology of Zander et al [25]. This preheating technique currently allows an upper temperature limit of around 2500 K, whereas previous studies of nitridation have been limited to 1900 K [54].…”

Section: Introductionmentioning

confidence: 99%

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Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Lewis¹

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During reentry into the atmosphere, a vehicle can encounter extreme convective and possibly radiative heating loads. Such spacecraft must rely on a carefully designed thermal protection system to maintain the integrity of the underlying structure, thus ensuring the survival of any cargo or crew it may contain. Despite many past developments and research efforts, to this day there remain large uncertainties associated with the prediction of heat shield performance. In particular, accurate modelling of ablation phenomena is critical to minimising uncertainties, reducing excess weight, and increasing safety. This includes thermochemical ablation by oxidation, nitridation, and sublimation, as well as the mechanical removal of material via spallation. Due to the high costs associated with in-flight testing, and the difficulty of mounting precision instruments and advanced diagnostics on flight vehicles, ground-based experiments stand as a cost-effective method for reducing modelling uncertainties.Ablation testing is generally conducted in long-duration facilities such as arc jets, which are well suited to investigating in-depth material response due to their ability to provide representative heating rates for extended periods. They are, however, unable to reproduce a realistic in-flight shock layer due to low Reynolds numbers and, depending on the facility type, a high degree of thermal and chemical nonequilibrium in the free-stream. In contrast, impulse facilities such as shock tubes and their variants are well suited to reproducing realistic flight conditions with free-streams that are a closer match for flows dominated by binary processes in terms of Reynolds number, temperature, and chemical composition. Due to their extremely short test times, however, ranging from the order of 10 µs to several milliseconds, they are unable to aerothermally heat test models up to representative in-flight temperatures, or recreate the quasi-steady heat and mass flux balance of flight. This key limitation of impulse facilities was recently overcome in experiments using the University of Queensland's X2 expansion tunnel by electrically pre-heating samples to temperatures approaching 2500 K immediately prior to a test.In this work, the pre-heating methodology was enhanced to generate maximum surface temperatures approaching 3300 K in order to study sublimation phenomena. It was found that although sublimation-regime temperatures could be achieved, the relevant surface processes themselves were suppressed due to the high pitot pressures of the conditions used. Instead, the nitridation process was studied by observing air shock layer CN emissions with pure graphite models heated to surface temperatures ranging from 1770-3300 K. These results were compared with numerical simulations which predicted a monotonic increase of emissions with surface temperature for all models considered, whereas the experiments showed an initial increase from 1770-2500 K and then remained relatively constant from 2500-3300 K. The simulations also su...

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Hot-Wall Reentry Testing in Hypersonic Impulse Facilities

Cited by 78 publications

References 9 publications

X3 expansion tube driver gas spectroscopy and temperature measurements

X3 expansion tube driver gas spectroscopy and temperature measurements

Venus Entry Flow over a Decomposing Aeroshell in X2 Expansion Tube

Hypervelocity shock layer emission spectroscopy with high temperature ablating models

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