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

Gnoffo, Peter A.; Johnston, Christopher O.; Thompson, Richard A.

doi:10.2514/6.2009-1399

“…Recent work 32 has extended this capability to accommodate the injection of a gas containing the elements C, H, O, and N. The wall is assumed to be in chemical equilibrium at a specified wall temperature. The elemental composition at the wall is obtained by solving the elemental continuity equations 45 , which account for diffusion, convection, and mass injection of the char and pyrolysis gas.…”

Section: Flowfield Modeling With Ablation Products and Radiationmentioning

confidence: 99%

The Influence of Ablation on Radiative Heating for Earth Entry

Johnston

¹

,

Gnoffo

²

,

Sutton

³

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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“…The strong thermochemical equilibrium conditions cause sharp gradients in the temperatures and number densities at the shock (as a result of the abrupt change from the free-stream quantities to the post-shock quantities), which were found to cause stability problems in the flowfield solution procedure. To accommodate this, the recently developed 32 general chemical equilibrium option in LAURA was applied. This option treats a single temperature and solves the elemental continuity equations.…”

Section: Mars-return Benchmark Casementioning

confidence: 99%

“…Applying state-of-the-art flowfield (LAURA) and radiation (HARA) models, the present work examines the influence of ablation on the radiative heating for lunar and Mars return conditions. A T brief discussion of this recently developed capability 32 , which consists of a 22-species thermochemical nonequilibrium LAURA flowfield model with coupled HARA radiation and an ablating wall, is discussed in Section II. In Section III, the extension of HARA to treat carbon and hydrogen species is discussed and the sources of the required data are listed.…”

Section: Introductionmentioning

confidence: 99%

Influence of Ablation on Radiative Heating for Earth Entry

Johnston

¹

,

Gnoffo

²

,

Sutton

³

2009

Journal of Spacecraft and Rockets

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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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“…Program LAURA 11,15 simulates the coupled radiation and ablation in the shock layer over a vehicle entering a planetary atmosphere at hypersonic velocities. This code was chosen as a starting point for simulation of the production rig because the algorithms for dealing with high temperature, reacting gas mixtures and tightly coupled ablation and radiation for carbon based ablators are already well established.…”

Section: Methodsmentioning

confidence: 99%

“…10 In the case of flow in chemical equilibrium the elemental continuity equations are solved and a free energy minimization is implemented in every control volume to solve for species mass fractions as a function of elemental mass fraction, temperature, and pressure. 11 Early equilibrium simulations had been run with only a four species model that neglected B 2 . These simulations indicated that the presence of B 2 significantly diminished the amount of BN in the upper part of the plume.…”

Section: B Gas Propertiesmentioning

confidence: 99%

Modeling of Laser Vaporization and Plume Chemistry in a Boron Nitride Nanotube Production Rig

Gnoffo

¹

,

Fay

²

2012

43rd AIAA Thermophysics Conference

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Flow in a pressurized, vapor condensation (PVC) boron nitride nanotube (BNNT) production rig is modeled. A laser provides a thermal energy source to the tip of a boron fiber bundle in a high pressure nitrogen chamber causing a plume of boronrich gas to rise. The buoyancy driven flow is modeled as a mixture of thermally perfect gases (B, B 2 , N, N 2 , BN) in either thermochemical equilibrium or chemical nonequilibrium assuming steady-state melt and vaporization from a 1 mm radius spot at the axis of an axisymmetric chamber. The simulation is intended to define the macroscopic thermochemical environment from which boron-rich species, including nanotubes, condense out of the plume. Simulations indicate a high temperature environment (T > 4400K) for elevated pressures within 1 mm of the surface sufficient to dissociate molecular nitrogen and form BN at the base of the plume. Modifications to Program LAURA, a finite-volume based solver for hypersonic flows including coupled radiation and ablation, are described to enable this simulation. Simulations indicate that high pressure synthesis conditions enable formation of BN vapor in the plume that may serve to enhance formation of exceptionally long nanotubes in the PVC process.

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

Cited by 26 publications

References 13 publications

The Influence of Ablation on Radiative Heating for Earth Entry

The Influence of Ablation on Radiative Heating for Earth Entry

Influence of Ablation on Radiative Heating for Earth Entry

Modeling of Laser Vaporization and Plume Chemistry in a Boron Nitride Nanotube Production Rig

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