Coupled Flow Field Simulations of Charring Ablators with Nonequilibrium Surface Chemistry

Alkandry, Hicham; Boyd, Iain D.; Martin, Alexandre

doi:10.2514/6.2013-2634

Cited by 12 publications

(11 citation statements)

References 26 publications

(18 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, since the gas is eventually blown into the chemical reacting boundary layer [6], correct modeling of the pyrolysis gas is also important to help determine the surface boundary conditions. The gas flow within the charring ablator is often modeled as a porous media flow, for which steady-state Darcy's law is usually assumed [7][8][9][10].…”

mentioning

confidence: 99%

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Weng

Martin

2015

Journal of Thermophysics and Heat Transfer

Self Cite

View full text Add to dashboard Cite

An orthotropic material model is implemented in a three-dimensional material response code, and numerically studied for charring ablative material. Model comparison is performed using an iso-Q sample geometry. The comparison is presented using pyrolysis gas streamlines and time series of temperature at selected virtual thermocouples. Results show that orthotropic permeability affects both pyrolysis gas flow and thermal response, but orthotropic thermal conductivity essentially changes the thermal performance only. The pyrolysis gas flow is hypothesized to contribute to the thermal response of the material as it convects energy through the porous medium. Nomenclature A= face area of a control volume, m 2 A i = pre-exponential factor of solid component i, s −1 E i ∕R = activation energy of solid component i over universal gas constant, K E g = overall gas energy per unit volume, J∕m 3 or kg∕m s 2 E s = overall solid energy per unit volume, J∕m 3 or kg∕m s 2 Fo = Forcheimer number H = gas enthalpy, J∕kg K = material sample permeability, m 2 L = arc length; distance to the origin of Cartesian coordinate system,, kg∕m 2 s p = static pressure, Pa p w = sample surface pressure (p w 0 is the stagnation value), Pa q w = sample surface heat flux (q w 0 is the stagnation value), W∕m 2 S D = source term accounts for the energy loss in porous media flow, kg∕m s 3 T = temperature, K T react = reaction initiate temperature, K t = time, s V = volume of a control volume, m 3 Γ i = volume fraction of virgin solid composite i Δ = discretized term ϵ = small perturbations in numerical Jacobians calculation θ = rotation angle around z-axis (counterclockwise) λ = solid material thermal conductivity, W∕mK ρ g = overall density of pyrolysis gases, kg∕m 3 ρ s = overall solid density, kg∕m 3 ρ s i = density of solid component i, kg∕m 3 ϕ = porosity of material ψ i = phenomenological parameter of solid component i in reaction forumula ω = reaction rate of gas/solid species, kg∕m 3 s D = (D x , D y , D z ), diffusive source terms in momentum equations, Pa∕m F cond = (F cond;x , F cond;y , F cond;z ), conductive heat flux, W∕m 2 n = face normal direction P = vector of primitive variables Q = vector of conservative variables RHS = right-hand side of the linear system to be solved S = vector of source terms in a control volume u = (u, v, w), velocity components of Cartesian coordinates, m∕s F = convective flux through the face of a control volume F d = diffusive flux through the face of a control volume Subscripts c = char state of the material g = overall pyrolysis gas IP = in-plane orientation i = solid component i max, min = maximum and minimum values of boundary conditions s = overall solid TTT = through-the-thickness v = virgin state of the material w = sample surface wall x, y, z = components of Cartesian coordinate system

show abstract

mentioning

confidence: 99%

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Weng

Martin

2015

Journal of Thermophysics and Heat Transfer

Self Cite

View full text Add to dashboard Cite

show abstract

“…Pyrolysis is the process in which the phenolic polymer gradually carbonizes at high temperature, losing mass and generating pyrolysis gases. These gases are then expelled through the porous structure of the material and blown into the chemical reacting boundary layer [2]. The other phenomenon, ablation, occurs in a thin layer near the surface, and it refers to the mass removal of the char (composed of nonpyrolyzed and residual carbonized material) through oxidation, sublimation, and spallation.…”

mentioning

confidence: 99%

Multidimensional Modeling of Pyrolysis Gas Transport Inside Charring Ablative Materials

Weng

Martin

2014

Journal of Thermophysics and Heat Transfer

Self Cite

105

View full text Add to dashboard Cite

The behavior of pyrolysis gas transport in arcjet test samples is numerically studied. The simulation of the pyrolysis gas flow inside a porous material is presented, using two different geometries. The effects of allowing the gas to flow out of the sidewall are especially highlighted. Results show that the flow inside the test article is complex, and that the zero-dimensional or one-dimensional assumption made in most material response codes are not necessarily valid for certain geometries. The importance of three-dimensionality for modeling an ablative test article is addressed. Nomenclature A= face area of a control volume, m 2 A i = preexponential factor of solid component i, s −1 E g = overall gas energy per unit volume, J∕m 3 or kg∕ms 2 E i ∕R = activation energy of solid component i over universal gas constant, K E s = overall solid energy per unit volume, J∕m 3 or kg∕ms 2 F = matrix of convective fluxes through the face of a control volume F d = matrix of diffusive fluxes through the face of a control volume G = G x ; G y ; G z inviscid flux of momentum equation; e.g., G x is equal to ∂ϕρu 2 ∕∂x ∂ϕρuv∕∂y ∂ϕρuw∕∂z, Pa∕m H = gas enthalpy, J∕kg K = material sample permeability, m 2 k = solid material thermal conductivity, W∕m · K L = arc length; distance to the origin of Cartesian coordinate system;x 2 y 2 z 2 p , m _ m 0 0 = mass flow rate per unit area; ϕρ g u · n, kg∕m 2 s j _ m 0 0 j = gas momentum; ϕρ g u 2 v 2 w 2 p , kg∕m 2 s n = face normal direction P = vector of primitive variables p = static pressure, Pa p w = sample surface pressure, Pa Q = vector of conservative variables q w = sample surface heat flux, W∕m 2 R = R x ; R y ; R z ; residual of Darcy's law; e.g., R x is equal to −∂p∕∂x − ϕμ∕Ku, Pa∕m R HS = right-hand side of the linear system to be solved S = vector of source terms in a control volume S D = diffusive source term for flow through porous media; −ϕμ∕Ku 2 v 2 w 2 , kg∕ms 3 T = temperature, K T react = reaction initiate temperature, K t = time, s u = u; v; w; velocity, m∕s V = volume of a control volume, m 3 Γ i = volume fraction of virgin solid composite i ρ g = overall density of pyrolysis gases, kg∕m 3 ρ s = overall solid density, kg∕m 3 ρ s i = density of solid component i, kg∕m 3 ϕ = porosity of material ψ i = phenomenological parameter for component i ω g = pyrolysis gas generation rate, kg∕m 3 s ω s i = decomposition rate of solid component i, kg∕m 3 s Subscripts c = char state of the material g = overall pyrolysis gas i = solid species i s = overall solid v = virgin state of the material w = sample surface wall x = first component of Cartesian coordinate y = second component of Cartesian coordinate z = third component of Cartesian coordinate

show abstract

“…NASA's Stardust project in 2006 reentered the Earth's atmosphere from a solar orbit at a record 12.9 km/s [24], placing it still behind the 15 km/s prediction for Martian return missions. Measurement of the flow temperature within the plasma sheath surrounding Stardust was not directly measurable, however simulations by Alkandry et al in 2013 using the LeMANS hypersonic flow solver predicted a peak temperature of approximately 50, 000K whilst showing good agreement with the heat shield surface temperature measurements of ground based spectroscopy [75,2].…”

Section: The 5 11 and Doubly-ionized Species Gas Models For Airmentioning

confidence: 97%

“…Here an appreciable fraction of doubly-ionized monatomic plasma was predicted above temperatures of 30, 000K for both species. At the predicted 50, 000K produced during solar orbit reentry speeds [2], the molar fraction of second order ions O 2+ and N 2+ and higher is expected to be in excess of 90% [73,1,9].…”

Section: The 5 11 and Doubly-ionized Species Gas Models For Airmentioning

confidence: 98%

“…For reasonably temperatures in the 11 air species the translational degrees of freedom are typically assumed to be fully saturated -that is each axis of translation is assumed to be fully excited. Each translational mode is therefore assumed to contribute its maximum energy of 2 3 k B T to the system. This produces the additional 5 2 terms for the heat capacity and enthalpy definitions in Equations (3.1) and (3.2).…”

Section: Calculation Of Thermodynamic Propertiesmentioning

confidence: 99%

See 1 more Smart Citation

UQ eSpace

Murdoch¹

View full text Add to dashboard Cite

This thesis details the methodology and findings of a an extensive investigation into the definition and use of thermodynamic properties in the context of the hypersonic flight regime for air species. A surveying of common hypersonic flow solvers is presented, with the majority found to source their properties from the NASA Lewis/Glenn Chemical Equilibrium with Applications (CEA), including the University of Queensland's CFD package Eilmer4. A critical review was then performed on the sources of thermodynamic properties, in an effort to determine whether the current 20, 000K temperature limit of the CEA data could be increased, or more accurately modeled under this temperature. Despite its widespread use, flaws in the CEA modeling approach were identified for both atomic and molecular air species, making it erroneous when compared to the more modern and sophisticated publishings by Mario Capitelli. A complete build of the thermodynamic properties was then implemented using the Capitelli treatment of the internal partition function for both diatomic and monatomic species. Consideration in the monatomic species was made for the choice in ionization potential lowering technique, and a number of extrapolation methods were utilized to complete the electronic spectral levels where experimental observations were found to be lacking. Modeling of diatomic species was performed with consideration for the vibrational-rotational coupling of the atomic nuclei, using a Morse potential approach for determining the maximum permissible vibrational and rotational excitation modes. Quasi stable modes were identified and shown to good agreement with literature results. Good agreement was observed in the resulting thermodynamic properties to modern literature sources, which were then formatted for use in the Eilmer4 project. A preliminary evaluation of the influence these updated properties has on simulated results was presented, however insufficient evidence between the simulated results and available experimental data was found to conclusively validate the improvement made by these new results.

show abstract

Coupled Flow Field Simulations of Charring Ablators with Nonequilibrium Surface Chemistry

Cited by 12 publications

References 26 publications

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Multidimensional Modeling of Pyrolysis Gas Transport Inside Charring Ablative Materials

UQ eSpace

Contact Info

Product

Resources

About