NASA EPSCoR: R3 STMD RFA-067: Unsteady measurements of ultra-low permeability for TPS samples

Grants and Contracts Details

Description

Project: R3 STMD RFA-067: Unsteady measurements of ultra-low permeability for TPS samples 1. Abstract Ablative thermal protection systems (TPS) generate pyrolysis gases during heating that must flow out through the TPS porous structure. The TPS permeability is critically important since low permeability requires a large pressure to push the pyrolysis gases to the surface. This high pressure can result in material damage as has been observed on some modern TPS systems during flight tests. State-of-the-art models rely on material permeability to predict the internal flow and resulting internal stress, but this permeability can vary significantly across the material and can change by many orders of magnitude during ablation. Complete characterization of the permeability requires measurements spanning a large range of conditions. An experimental facility at the University of Kentucky (UK) has been developed for measurements of Darcy permeability from 10-10 m2 down to at least 10-15 m2. A unique process for sealing irregularly shaped TPS samples has also permitted measurements on TPS with varying degrees of char. However, virgin (uncharred) materials provided by NASA collaborators have permeabilities that are much lower than that accessible with the current approach. This proposal seeks to extend the capability of the UK facility by at least three orders-of-magnitude for lower permeabilities and permit measurements of NASA’s current TPS with ultra-low permeability. This new capability will be enabled by unsteady analysis of flow through the porous TPS. The current approach determines permeability from the steady state pressure drop across a TPS sample as a function of mass flow rate. Achieving steady state conditions with permeabilities below 10-15 m2 requires time periods exceeding days to weeks for a single measurement, which is not feasible. The proposed work will develop an unsteady measurement approach and analysis to determine permeability from dynamic pressure measurements following step changes in mass flow rate. The approach will be developed and tested against current samples with permeability in the range of 10-14 to 10-15 m2 that can be measured by both techniques. Following this development, measurement of materials with lower permeabilities provided by NASA collaborators will be measured in their virgin state. Using the UK facility for charring samples, these will then be charred over a range of mass loss focusing on low mass loss percentage, relevant to the early stages during the ablation process when high pressures from low permeability are most likely. The results of permeability versus char will be shared with collaborators and published for publicly available materials.
StatusActive
Effective start/end date9/1/248/31/25

Funding

  • National Aeronautics and Space Administration: $100,000.00

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