Convective and radiative heat transfer to an ablating body.

Hoshizaki, H.; Lasher, L. E.

doi:10.2514/3.4786

Cited by 31 publications

(5 citation statements)

References 7 publications

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“…A comparison of the radiative flux at the wall predicted by various researchers is shown in Figure 10 for various ablation rates. For the radiation calculation, Gupta et al 10 and Sutton 75 applied the RAD/EQUIL code 76 , Moss 9 applied the LRAD-3 code 77 , and Garrett et al 6 applied the RATRAP code 1 . The results of the various studies, including the present study, agree within about 10% for the entire range of ablation rates.…”

Section: Mars-return Benchmark Casementioning

confidence: 99%

“…Research in the late 1960s 1,2,3 and early 1970s 4,5,6,7,8,9 , which was based mostly on equilibrium viscous shock layer flowfield models and 1960s era radiation data, showed a radiation decrease of roughly 30% with m-dot values of 0.05 for conditions relevant to Mars return (15.24 km/s at 60.96 km). A later analysis by Gupta et al 10 confirmed these results with an updated flowfield model.…”

Section: Introductionmentioning

confidence: 99%

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The Influence of Ablation on Radiative Heating for Earth Entry

Johnston

Gnoffo

Sutton

2008

40th Thermophysics Conference

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Using the coupled ablation and radiation capability recently included in the LAURA flowfield solver, this paper investigates the influence of ablation on the shock-layer radiative heating for Earth entry. The extension of the HARA radiation model, which provides the radiation predictions in LAURA, to treat a gas consisting of the elements C, H, O, and N is discussed. It is shown that the absorption coefficient of air is increased with the introduction of the C and H elements. A simplified shock layer model is studied to show the impact of temperature, as well as the abundance of C and H, on the net absorption or emission from an ablation contaminated boundary layer. It is found that the ablation species reduce the radiative flux in the vacuum ultraviolet, through increased absorption, for all temperatures. However, in the infrared region of the spectrum, the ablation species increase the radiative flux, through strong emission, for temperatures above 3,000 K. Thus, depending on the temperature and abundance of ablation species, the contaminated boundary layer may either provide a net increase or decrease in the radiative flux reaching the wall. To assess the validity of the coupled ablation and radiation LAURA analysis, a previously analyzed Mars-return case (15.24 km/s), which contains significant ablation and radiation coupling, is studied. Exceptional agreement with previous viscous shock-layer results is obtained. A 40% decrease in the radiative flux is predicted for ablation rates equal to 20% of the free-stream mass flux. The Apollo 4 peak-heating case (10.24 km/s) is also studied. For ablation rates up to 3.4% of the free-stream mass flux, the radiative heating is reduced by up to 19%, while the convective heating is reduced by up to 87%. Good agreement with the Apollo 4 radiometer data is obtained by considering absorption in the radiometer cavity. For both the Mars return and the Apollo 4 cases, coupled radiation alone is found to reduce the radiative heating by 30 -60% and the convective heating by less than 5%. = thickness of the constant-property layers defined in Fig. 3, with i = 1 or 2 (cm) h = absorption coefficient (cm -1 ) = blowing reduction parameter = trasmissivity defined in Eq. (2) Subscripts h = indicates a spectral dependence in terms of eV Superscripts abl = refers to ablation species, meaning species containing any C or H atoms air = refers to air species, meaning species containing no C or H atoms Abbreviations eV = electron volts; the frequency in eV, labeled h , is equal to 1.24x10 -4 / c IR = infrared; refers here to the spectral region below 6 eV NIST = National Institute of Standards and Technology OP = Opacity Project VUV = vacuum ultraviolet; refers to the spectral region above 6 eV

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Section: Mars-return Benchmark Casementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Influence of Ablation on Radiative Heating for Earth Entry

Johnston

Gnoffo

Sutton

2008

40th Thermophysics Conference

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“…Degeneracy of electronic state i h w Enthalpy of gas at wall (J/kg) H Gas enthalpy (J/mol) I (0-6 eV) Wall-directed radiative intensity spectrally-integrated between 0 and 6 eV (W/cm 2 /sr) J (0-6 eV) Spectrally-integrated emission between 0 and 6 eV (W/cm 3 Frequency-dependent wall-directed radiative flux without radiation-flowfield coupling(W/cm 2 ) R Universal gas constant (J/mol/K) T Temperature (K) U Free-stream velocity for flight case or moving shock speed for shock tube case (km/s) x Curve fit variable, U (km/s) for shock tube cases and T (K) for constricted arc cases z Radial distance normal to the free-stream (cm) Part I…”

Section: Nomenclature a Imentioning

confidence: 99%

“…Stagnation line viscous shock layer solutions with coupled radiation only 2 and coupled radiation and ablation [3][4][5][6][7][8][9][10][11][12][13][14] were performed with various levels of fidelity in the flowfield and radiation models. These studies confirm the significant influence of coupled radiation and ablation on the radiative heating for a Mars-return case.…”

mentioning

confidence: 99%

Assessment of Radiative Heating Uncertainty for Hyperbolic Earth Entry

Johnston

Mazaheri

Gnoffo

et al. 2011

42nd AIAA Thermophysics Conference

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This paper investigates the shock-layer radiative heating uncertainty for hyperbolic Earth entry, with the main focus being a Mars return. In Part I of this work, a baseline simulation approach involving the LAURA Navier-Stokes code with coupled ablation and radiation is presented, with the HARA radiation code being used for the radiation predictions. Flight cases representative of peak-heating Mars or asteroid return are defined and the strong influence of coupled ablation and radiation on their aerothermodynamic environments are shown. Structural uncertainties inherent in the baseline simulations are identified, with turbulence modeling, precursor absorption, grid convergence, and radiation transport uncertainties combining for a +34% and −24% structural uncertainty on the radiative heating. A parametric uncertainty analysis, which assumes interval uncertainties, is presented. This analysis accounts for uncertainties in the radiation models as well as heat of formation uncertainties in the flowfield model. Discussions and references are provided to support the uncertainty range chosen for each parameter. A parametric uncertainty of +47.3% and −28.3% is computed for the stagnation-point radiative heating for the 15 km/s Mars-return case. A breakdown of the largest individual uncertainty contributors is presented, which includes C3 Swings cross-section, photoionization edge shift, and Opacity Project atomic lines. Combining the structural and parametric uncertainty components results in a total uncertainty of +81.3% and −52.3% for the Mars-return case.In Part II, the computational technique and uncertainty analysis presented in Part I are applied to 1960s era shock-tube and constricted-arc experimental cases. It is shown that experiments contain shock layer temperatures and radiative flux values relevant to the Mars-return cases of present interest. Comparisons between the predictions and measurements, accounting for the uncertainty in both, are made for a range of experiments. A measure of comparison quality is defined, which consists of the percent overlap of the predicted uncertainty bar with the corresponding measurement uncertainty bar.

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“…Extensive research on the topic was conducted in the late sixties [6,35,70,83,209] and early seventies [42,47,49,48,55,124,128,188]. These early efforts were motivated by a certain number of upcoming deep space exploration missions, including Apollo, Pioneer Venus Multiprobe (1978), and Galileo (launched in 1989).…”

Section: Radiative Couplingmentioning

confidence: 99%

On binary scaling and ground-to-flight extrapolation in high-enthalpy facilities

Looringhe¹,

Arwid²

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The binary scaling law is commonly used to study the aerothermodynamics of hypersonic vehicles in high-enthalpy facilities. It enables the duplication of the shock layer in the vicinity of the stagnation point, including binary chemistry and nonequilibrium processes, through the reproduction of the Péclet and wall Damköhler numbers. These are both conserved through the duplication of the composition of the gas, the free-stream enthalpy h ∞ and the product of a density and a length-scale of the flow ρL.Binary scaling is built on the assumption of a flow devoid of radiation coupling and governed by binary reactions. These two conditions drastically narrow down the envelope of flows for which binary scaling can be used. Moreover, diffusive transport and wall chemistry have never been addressed although they can have an important impact on the wall heat flux.The first part of this thesis consists in an effort to better understand the theoretical role and effect of the different assumptions done to build the binary scaling. It is first shown that diffusive transport and wall chemistry should scale appropriately. Second, that non-binary chemistry will cause the shock layer in the laboratory flow to be hotter and less dissociated. A methodology is proposed to identify clearly what free-stream conditions will affect the least the flow variables of interest. Lastly, that radiation coupling will be weaker in the laboratory flow than in flight, causing the enthalpy contained in the shock layer to be greater in the laboratory flow.These findings are verified in the second part with two experiments. The first experiment was performed in the Plasmatron plasma wind tunnel at the von Karman Institute, Belgium. Binary scaled boundary layers were obtained for flows where diffusion and wall chemistry contribute significantly to the heat flux. The stagnation point heat fluxes were measured and exhibit a good agreement with the theoretical scaling law. This also validates the use of the binary scaling law in subsonic high-enthalpy facilities.The second experiment was performed in the X2 expansion tube at the Centre for Hypersonics, Australia. Three flows were obtained over cylinders of different radii, adapting the free-stream density according to the binary scaling law. The free-stream conditions were determined in order to ensure a significant radiative coupling. Its effect could clearly be identified through measurements of the shock standoff distance, stagnation point heat flux, and shock layer radiation. A new method, based on a mix of experiments, computational fluid dynamics, and informed use of engineering correlations is proposed to perform ground to flight extrapolation for cases for which the radiative coupling is non-negligible. Declaration by authorThis thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have include...

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Convective and radiative heat transfer to an ablating body.

Cited by 31 publications

References 7 publications

The Influence of Ablation on Radiative Heating for Earth Entry

The Influence of Ablation on Radiative Heating for Earth Entry

Assessment of Radiative Heating Uncertainty for Hyperbolic Earth Entry

On binary scaling and ground-to-flight extrapolation in high-enthalpy facilities

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