Micro scale simulations are performed of flow through porous (pyrolyzing) thermal protection system (TPS) materials using the direct simulation Monte Carlo (DSMC) method. DSMC results for permeability are validated with computational fluid dynamics (CFD) calculations and theory, for simple porous geometries under continuum flow conditions. An artificial fiber-microstructure generation code FiberGen is used to create triangulated surface geometry representative of FiberForm® (FiberForm) material. DSMC results for permeability of FiberForm are validated for a range of pressures (transitional flow conditions) and agree with experimental measurements. Numerical uncertainty is determined to be within 2% if sufficiently large portions of the microstructure are included in the computation. However, small variations in fiber size and angle bias can combine to give +30% uncertainty when comparing with experimental permeability data. X-ray microtomography scans of FiberForm are used to create microstructure geometry for incorporation within DSMC simulations of coupled oxygen diffusion and gas-surface chemistry in the presence of a blowing pyrolysis gas. In-depth penetration of atomic oxygen is limited to 0.2–0.4 mm for the range of Knudsen number and pyrolysis gas conditions studied.
Bibliographical noteFunding Information:
Savio Poovathingal would like to acknowledge support through Doctoral Dissertation Fellowship from University of Minnesota . Eric Stern was supported through a NASA Space Technology Research Fellowship under NASA Grant # NNX11AN42H . This work was also supported by the U.S. Air Force Office of Scientific Research (AFOSR) under Multidisciplinary University Research Initiative (MURI) grant FA9550-10-1-0563 . The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the AFOSR or the U.S. Government. Special thanks to Brian Bagley in the X-ray Computed Tomography lab at the University of Minnesota for performing the scans.
© 2018 Elsevier Inc.
- Numerical simulation
- Porous media
- Rarefied flow
- Thermal protection systems