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Multi-scale modeling of low-density carbon-phenolic ablators

Event Type: 
Date and Time: 
Friday, November 9, 2018 - 16:30
Location: 
CTR Conference Room 103
Event Sponsor: 
Parviz Moin, Director of Center for Turbulence Research
Speaker(s): 
Dr. Nagi N. Mansour

Protecting a spacecraft during atmospheric entry is one of highest risk factors that needs to be mitigated during design of a space exploration mission. At entry speeds from space, air turns into high-temperature plasma, and spacecraft Thermal Protection Systems (TPS) are needed to protect the vehicle payload. Modern successful material architectures of spacecraft shields use a porous carbon fiber substrate impregnated with phenolic as an ablator material. In the lecture, efforts to build a Predictive Material Modeling framework for porous ablators from micro-scale to macro-scale will be presented. Several numerical methods and techniques will be summarized that use voxelized images to compute geometrical properties of the porous substrate. These computed properties include porosity, specific surface area and tortuosity that are otherwise indirectly measured through experimental techniques. Direct simulation Monte Carlo (DSMC), a particle based method for approximating the Boltzmann equation, is used to compute the permeability coefficient of the porous substrate based on its digitized representation. The method computes the flow within the microstructure, where the size of the pores may approach the mean-free-path of the flow. Finally, a high-fidelity model implemented in PATO (Porous-material Analysis Toolbox) is discussed, and some examples of ablative material response are presented including for the first time 3D simulations of the full tiled heat-shield for the Mars Science Laboratory (MSL) capsule.

Bio: 
Dr. Mansour is currently Chief division Scientist at the NASA Advanced Supercomputing division. He received his Ph.D. in Mechanical Engineering at Stanford in 1978 where he carried out one of the earliest Large-Eddy simulations of a turbulent mixing layer. He also pioneered the use of direct numerical simulation for turbulence model development. He is the founding lead of the Heliophysics Modeling and Simulation (HMS) project at the NASA Advanced Supercomputing division. During his NASA career, Dr. Mansour has served in technical management positions including chief of the Reacting Flow Environments Branch, Chief of the Computational Physics Branch, and as deputy director of the Stanford Center for Turbulence Research, operated jointly with NASA. He is a fellow of the American Physical Society. Dr. Mansour’s current research interests include the development of high-fidelity models for Thermal Protection Systems used for spacecraft atmospheric entry, and development of realistic modeling of plasma with coupled radiative transfer and magneto-hydrodynamics effects on exascale computing systems; large eddy simulations of the solar convection zone, modeling sound propagation in plasma; and the development of emerging magnetic flux models. Dr. Mansour has published over 200 journal and conference articles in the fields of fluid mechanics, turbulence physics, solar physics, aerothermodynamics, magneto-hydrodynamics, and high-temperature material science.