On the Current Limits of Simulating Gas Giant Entry Flows in an Expansion Tube

James, Christopher M.; Gildfind, David; Morgan, Richard G.; Lewis, Steven W.; Fahy, Elise; McIntyre, Timothy J.

doi:10.2514/6.2015-3501

Cited by 13 publications

(15 citation statements)

References 21 publications

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“…Table 1 provides the freestream conditions estimated using Pitot [15], which is an equilibrium expansion tube and shock tunnel analysis code that uses the tube configuration parameters and measured shock velocities as an input to calculate these properties.…”

Section: A Condition Selection and Testingmentioning

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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Section: A Condition Selection and Testingmentioning

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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“…Considering that the measurements themselves generally have an uncertainty of 0.2-0.3 km/s, this appears to be an acceptable range. To ensure, however, that this degree of variation would not significantly impact the results, an analysis was conducted using UQ's in-house code PITOT [103,104]. In this analysis, the shock speed in the shock tube was manually set to the nominal experimental value of 4.1 km/s (see Table 3.1), and the test section pressure was varied until the same difference in secondary shock speed was achieved.…”

Section: Discussionmentioning

confidence: 99%

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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“…Between 5 and 10% of flow enthalpy can be stored as static enthalpy and, as a result, while the total enthalpy of the free-stream can be achieved, the flow Mach number will be lower than desired [30]. Test conditions for scaled models will be different and determining scaled post-shock conditions is necessary.…”

Section: Post Shock Conditionsmentioning

confidence: 99%

Simulation of CubeSat re-entry trajectory

Apirana¹

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Von Karman Institute in partnership with Ecole Centrale Paris are launching the QB50 program, comprising 50 CubeSats capable of performing scientific experiments in the thermosphere. One of these Cubesats, QARMAN, is designed to make measurements of ablation to inform the design of thermal protection systems for re-entry vehicles.QARMAN will deploy a passive braking system upon re-entry to the atmosphere and peak-heating is expected to occur at an altitude of 50km. This was the design point for trajectory modelling. The re-entry velocity was determined to be in the range of 7.5 -7.57km/s. The resulting velocity at peak-heating was found to be 6.35km/s using the lower bound of the entry velocity range.A computational model was built to simulate the flow conditions over QARMAN during peak heating. The compressible flow code, eilmer3, was used and a 2D model was built subject to simplifying assumptions of the geometry of QARMAN. Bow-shock, boundary layer, and oblique-shock interactions were observed, and the boundary layer displacement thickness was measured to be 6.89mm at a distance 340mm downstream of the nose. A shock stand-off distance, influenced by boundary layer propagation, was observed, and measured to be 52.8mm upstream of the interface of fore-body and wedge-tip. This represents a stand-off distance that is 7.66 times the displacement thickness which is significantly larger than the commonly used 4x multiplier.A 3:10 scaled-model of QARMAN was designed and built. A recess within the model allows for gauges to measure heat data, and the location of 8 holes to house thin-film gauges has been outlines. Two additional mounting pieces were designed and built to hold the model in the test section and these can be used for mounting other models.An experiment has been designed for The University of Queensland's X2 expansion tube.The post-shock density was found and binary scaling was used to determine an appropriate driver gas configuration. Analytical calculation of the boundary layer thickness was compared with the CFD output and a difference between their predicted shock stand-off distances was found. The positioning of sensors was designed to capture this region of interest and comparison between experiments, CFD, and analytical predictions is recommended.

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On the Current Limits of Simulating Gas Giant Entry Flows in an Expansion Tube

Cited by 13 publications

References 21 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

Simulation of CubeSat re-entry trajectory

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