Expansion Tunnel Experiments of Earth Reentry Flow with Surface Ablation

Lewis, Steven W.; Morgan, Richard G.; McIntyre, Timothy J.; Alba, Christopher R.; Greendyke, Robert B.

doi:10.2514/1.a33267

Cited by 44 publications

(22 citation statements)

References 23 publications

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“…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%

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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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confidence: 99%

“…Palmer et al [11] conducted a similar study for Mars and Titan gas mixtures. Alba et al [12] simulated radiation measurements obtained from the aforementioned experiments by Lewis et al [7], coupling a threedimensional (3-D) CFD solution to the radiation code NEQAIR, Version 13.2.…”

mentioning

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 experimental methodology is very similar to the authors' previous work [89]; therefore, only a summary is provided here, and readers are referred to the prior paper for further details.…”

Section: Experimental Descriptionmentioning

confidence: 99%

“…The methodology implemented by Zander et al [25] for electrically preheating carbon models was employed. In previous tests [89], the electrical supply settings were limited to approximately 10.75 V and 250 A, providing maximum surface temperatures of 2450 K with this model material and geometry. To overcome this limitation, a new power supply was sourced and tested [92].…”

Section: Test Modelmentioning

confidence: 99%

“…This technique does not create the true mass and enthalpy flux balance representative of the quasi-steady ablative cooling of flight, but it does provide the correct thermal boundary condition at the wall so that surface thermochemical processes may be studied. This methodology was implemented by Lewis et al [89] to investigate the nitridation process by observing shock layer CN emissions with pure graphite models heated to a number of surface temperatures from 1770 to 2410 K. CN emissions were seen to steadily increase inside the boundary layer with surface temperature, whereas numerical simulations by Alba et al [80] predicted relatively constant levels for all considered surface models within this temperature range. This study continues from the previous work by the authors with further measurements and simulations in an extended temperature range up to a maximum of 3300 K. These new results will be merged with prior data to view overall trends in the temperature range from 1770 to 3300 K. Additional numerical simulations will be conducted within this extended range for several surface reaction models.…”

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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Spectral Radiant Intensity Calculation of Air in Shock Tube

Lyu

Cheng

et al. 2019

31st International Symposium on Shock Waves 1

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Expansion Tunnel Experiments of Earth Reentry Flow with Surface Ablation

Cited by 44 publications

References 23 publications

Venus Entry Flow over a Decomposing Aeroshell in X2 Expansion Tube

Venus Entry Flow over a Decomposing Aeroshell in X2 Expansion Tube

Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Spectral Radiant Intensity Calculation of Air in Shock Tube

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