June 7th, 2016
A new report on the comparison of the MR code PATO with FIAT has been published:
This report provides a code-to-code comparison between PATO, a recently developed high fidelity material response code, and FIAT, NASA’s legacy code for ablation response modeling. The goal is to demonstrates that FIAT and PATO generate the same results when using the same models. Test cases of increasing complexity are used, from both arc-jet testing and flight experiment. When using the exact same physical models, material properties and boundary conditions, the two codes give results that are within 2% of errors. The minor discrepancy is attributed to the inclusion of the gas phase heat capacity (cp) in the energy equation in PATO, and not in FIAT.
Omidy, A. D., Panerai, F., Lachaud, J. R., Mansour, N. N., Cozmuta, I., and Martin, A., “Code-to-Code Comparison, and Material Response Modeling of Stardust and MSL using PATO and FIAT,” Contractor Report NASA/CR-2015-218960, NASA Ames Research Center, Moffett Field, CA, 2015.
May 30th, 2016
A new paper on the permeability of FiberForm has been published in the International Journal of Heat and Mass Transfer:
A series of experiments was performed to obtain permeability data on FiberForm®, a commercial carbon preform used for manufacturing thermal protection systems. A porous sample was placed in a quartz flow-tube heated by an isothermal furnace. The setup was instrumented to measure mass flow through and pressure drop across the sample. The intrinsic permeability and the Klinkenberg correction, which accounts for rarefied effects, were computed from the experimental data. The role of the gas temperature and pressure on the effective permeability is shown, and it is demonstrated that with proper data reduction, the intrinsic permeability is strictly a function of the micro-structure of the material. A function for the effective permeability of FiberForm, dependent on temperature, pressure, pore geometry, and type of gas is proposed. The intrinsic permeability was evaluated at K0=5.57×10-11 m2, with a Klinkenberg parameter of 8c/dp=2.51×105 m−1 and a reference porosity of ϕ†=0.87.
Panerai, F., White, J. D., Cochell, T. J., Schroeder, O. M., Mansour, N. N., Wright, M. J., and Martin, A., “Experimental measurements of the permeability of fibrous carbon at high temperature,” International Journal of Heat and Mass Transfer, Vol. 101, October 2016, pp. 267–273.
May 25th, 2016
A new paper has been published (online) in the CEAS Space Journal:
The spallation phenomenon was studied through numerical analysis using a coupled Lagrangian particle tracking code and a hypersonic aerothermodynamics com- putational fluid dynamics solver. The results show that car- bon emission from spalled particles results in a significant modification of the gas composition of the post-shock layer. Results from a test campaign at the NASA Langley HYM- ETS facility are presented. Using an automated image pro- cessing of short exposure images, two-dimensional velocity vectors of the spalled particles were calculated. In a 30-s test at 100 W/cm2 of cold-wall heat flux, more than 722 particles were detected, with an average velocity of 110 m/s.
Martin, A., Bailey, S. C. C., Panerai, F., Davuluri, R. S. C., Vazsonyi, A. R., Zhang, H., Lippay, Z. S., Mansour, N. N., Inman, J. A., Bathel, B. F., Splinter, S. C., and Danehy, P. M., “Numerical and experimental analysis of spallation phenomena,” CEAS Space Journal, Vol. 8, No. 3, September 2016.
March 21st, 2016
A new paper is available in the AIAA Journal of Thermophysics and Heat Transfer:
Omidy, A. D., Panerai, F., Lachaud, J. R., Mansour, N. N., and Martin, A., “Effects of water phase change on the material response of low density carbon phenolic ablators,” Journal of Thermophysics and Heat Transfer, 2016.
January 1st, 2016
The radiative heat transfer inside a low-density carbon fiber insulator is analyzed using a three- dimensional direct simulation model. A robust procedure is presented for the numerical calculation of the geometric configuration factor to compute the radiative energy exchange processes among the small discretized surface areas of the fibrous material. The methodology is applied to a polygonal mesh of a fibrous insulator obtained from three-dimensional microscale imaging of the real material. The anisotro- pic values of the radiative conductivity are calculated for that geometry. The results yield both directional and thermal dependence of the radiative conductivity. The combined value of radiative and solid conduc- tivity are compared to experimental data available in the literature, and show excellent agreement.
Nouri, N., Panerai, F., Tagavi, K. A., Mansour, N. N., and Martin, A., “Evaluation of the anisotropic radiative conductivity of a low-density carbon fiber material from realistic microscale imaging,” Interna- tional Journal of Heat and Mass Transfer, Vol. 95, 2016, pp. 535–539.
September 25th, 2015
New paper about carbon oxidation in the journal “Carbon”:
Oxidation is one of the main decomposition mechanisms of fibrous carbon/phenolic ablators employed in thermal protection systems for planetary entry capsules. The oxidation process is driven by two competing mechanisms: diffusion of reactants within the porous medium, and reaction rates at the surface of the fibers. These mechanisms are characterized by the Thiele number. Given that the Thiele number varies during an atmospheric entry, we aim to understand the effects of the diffusion/reaction processes on the decomposition of a porous carbon material in various regimes. We use a particle method for simulations of the oxidation process at microscale. The movement of oxygen reactants is simulated using a Brownian motion technique, and heterogeneous first-order reactions at the surface are modeled with a sticking probability law. To enable simulations of the fiber decomposition on actual materials, we use digitized computational grids obtained using X-ray micro-tomographic imaging. We present results for the oxidation of the substrate of the material used on the Mars Science Laboratory capsule that landed the Curiosity rover. We find that the depth of the reaction zone for this material is critically dependent on the Thiele number.
Ferguson, J. C., Panerai, F., Bailey, S. C. C., Lachaud, J. R., Martin, A., and Mansour, N. N., “Modeling the oxidation of low-density carbon fiber material based on micro-tomography,” Carbon, Vol. 96, January 2016, pp. 57–65.
May 7th, 2015
May 2nd, 2015
New paper just published in the AIAA Journal of Thermophysics and Heat Transfer!
 Davuluri, R. S. C., Zhang, H., and Martin, A., “Numerical study of spallation phenomenon in an arc-jet environment,” Journal of Thermophysics and Heat Transfer, vol. 29, no. 3, 2015.
April 19th, 2015
 Martin, A. and Boyd, I. D., “Modeling of heat transfer attenuation by ablative gases during the Stardust re-entry,” Journal of Thermophysics and Heat Transfer, Vol. 29, No. 3, July 2015.
 Weng, H. and Martin, A., “Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material,” Journal of Thermophysics and Heat Transfer, Vol. 29, No. 3, July 2015.