Numerical study of iso-Q sample geometric effects on charring ablative materials

Weng, Haoyue; Bailey, Sean; Martin, Alexandre

doi:10.1016/j.ijheatmasstransfer.2014.09.040

Cited by 70 publications

(16 citation statements)

References 35 publications

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“…Recently, Weng and Martin [4] and Weng et al [5] showed that, due to the high enthalpy carried by the pyrolysis gas, the gas flow behavior within a charring ablator is crucial to the inner thermal response of the material. 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.…”

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“…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]. For unsteady charring ablation problems, however, Weng and Martin [4] and Weng et al [5] showed that the steady state of Darcy's law is not necessarily valid for the whole geometry of small test articles used in arc-jet facilities. Hirata et al [11] also proposed to use an unsteady, multidimension version of Darcy's law, and they identified a side wall blowing effect on arc-jet test samples.…”

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Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Weng

Martin

2015

Journal of Thermophysics and Heat Transfer

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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

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Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Weng

Martin

2015

Journal of Thermophysics and Heat Transfer

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“…Furthermore, the absence of internal material oxidation argues against the inflow or diffusion of hot boundary layer gases into the porous test sample. Such internal oxidation, as studied numerically by Weng et al for PICA 47 , could lead to a weaker fiber structure, causing mechanical failure of the material, for example, in the form of spallation 48,49 . Therefore, we highly suggest a general microscale analysis along with high-enthalpy testing of porous carbon-composite materials for heat shield applications.…”

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Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Helber

Chazot

Hubin

et al. 2016

JoVE

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Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions.Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties.The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale, results from a post-test microscopy analysis are presented.

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“…The methodology developed and presented here could be use to obtain accurate values of the effective conductivity of realistic three-dimensional material geometry, such as the ones obtained from computed X-ray microtomography [20]. These values could then be used in volume-averaged material response code [31,32] to increase the fidelity in heat transfer analysis.Moreover, performing such an analysis on a real material would allow to compare to experimental analysis.…”

Section: Discussionmentioning

confidence: 99%

Three dimensional radiative heat transfer model for the evaluation of the anisotropic effective conductivity of fibrous materials

Nouri

Martin

2015

International Journal of Heat and Mass Transfer

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Numerical study of iso-Q sample geometric effects on charring ablative materials

Cited by 70 publications

References 35 publications

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Three dimensional radiative heat transfer model for the evaluation of the anisotropic effective conductivity of fibrous materials

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