Nonequilibrium Stagnation-Line Radiative Heating for Fire II

Johnston, Christopher O.; Hollis, Brian R.; Sutton, Kenneth

doi:10.2514/1.33008

Cited by 75 publications

(38 citation statements)

References 34 publications

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“…If these contributions are ignored along with the radiometer cavity absorption, good agreement with the flight data is obtained. However, previous comparisons with the Fire II flight data 83 support the inclusion of these contributions. …”

Section: Apollo 4 Peak Heating Analysismentioning

confidence: 92%

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: Apollo 4 Peak Heating Analysismentioning

confidence: 92%

The Influence of Ablation on Radiative Heating for Earth Entry

Johnston

Gnoffo

Sutton

2008

40th Thermophysics Conference

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“…The NEQAIR code computes the emission and absorption spectra along a line-of-sight (LOS) for atomic species, molecular species electronic band systems, and infrared band systems. Radiative heating rate is determined using either a tangent slab or spherical cap assumption [25]. Individual electronic transitions are evaluated for atomic and molecular species.…”

Section: Neqair Overviewmentioning

confidence: 99%

Coupled Fluids-Radiation Analysis of a High-Mass Mars Entry Vehicle

Palmer

Allen

Tang

et al. 2011

42nd AIAA Thermophysics Conference

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The NEQAIR line-by-line radiation code has been incorporated into the DPLR Navier-Stokes flow solver such that the NEQAIR subroutines are now callable functions of DPLR. The coupled DPLR-NEQAIR code was applied to compute the convective and radiative heating rates over high-mass Mars entry vehicles. Two vehicle geometries were considered -a 15 m diameter 70-degree sphere cone configuration and a slender, mid-L/D vehicle with a diameter of 5 m called an Ellipsled. The entry masses ranged from 100 to 165 metric tons. Solutions were generated for entry velocities ranging from 6.5 to 9.1 km/s. The coupled fluids-radiation solutions were performed at the peak heating location along trajectories generated by the Traj trajectory analysis code. The impact of fluids-radiation coupling is a function of the level of radiative heating and the freestream density and velocity. For the high-mass Mars vehicles examined in this study, coupling effects were greatest for entry velocities above 8.5 km/s where the surface radiative heating was reduced by up 17%. Generally speaking, the Ellipsled geometry experiences a lower peak radiative heating rate but a higher peak turbulent convective heating rate than the MSL-based vehicle.

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“…The absorbed radiative energy is calculated as a function of wavelength. 18 Simulations at two trajectory points are intended to illustrate capabilities at a strong thermochemical nonequilibrium condition (1636 seconds) and a near-equilibrium condition (1643 seconds).…”

Section: A Fire II Coupled Radiation Onlymentioning

confidence: 99%

Implementation Of Radiation, Ablation, And Free Energy Minimization Modules For Coupled Simulations of Hypersonic Flow

Gnoffo

Johnston

Thompson

2009

47th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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A description of models and boundary conditions required for coupling radiation and ablation physics to a hypersonic flow simulation is provided. Chemical equilibrium routines for varying elemental mass fraction are required in the flow solver to integrate with the equilibrium chemistry assumption employed in the ablation models. The capability also enables an equilibrium catalytic wall boundary condition in the non-ablating case. The paper focuses on numerical implementation issues using FIRE II, Mars return, and Apollo 4 applications to provide context for discussion. Variable relaxation factors applied to the Jacobian elements of partial equilibrium relations required for convergence are defined. Challenges of strong radiation coupling in a shock capturing algorithm are addressed. Results are presented to show how the current suite of models responds to a wide variety of conditions involving coupled radiation and ablation.

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Nonequilibrium Stagnation-Line Radiative Heating for Fire II

Cited by 75 publications

References 34 publications

The Influence of Ablation on Radiative Heating for Earth Entry

The Influence of Ablation on Radiative Heating for Earth Entry

Coupled Fluids-Radiation Analysis of a High-Mass Mars Entry Vehicle

Implementation Of Radiation, Ablation, And Free Energy Minimization Modules For Coupled Simulations of Hypersonic Flow

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