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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.
Status | Active |
---|---|
Effective start/end date | 9/1/24 → 8/31/25 |
Funding
- National Aeronautics and Space Administration: $100,000.00
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Projects
- 1 Active
-
NASA EPSCoR: SCIENCE: R3 STMD RFA-067: Unsteady measurements of ultra-low permeability for TPS samples
National Aeronautics and Space Administration
9/1/24 → 8/31/25
Project: Research project