Local Permeability Measurement for Porous Thermal Protection
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Solution Overview
Problem
Reusable thermal protection systems for hypersonic flights face challenges in characterizing the local permeability of complex carbon-carbon porous structures, which affects cooling efficiency and structural integrity due to non-uniform cooling and asymmetric flow paths caused by manufacturing defects and geometry variations.
Innovation Solution
A method and system for determining the local permeability of porous materials using a test probe to measure velocity and pressure gradients at multiple distances, employing Darcy's law and computed tomography to calculate effective permeability, and adjusting probe distance based on correlation coefficients to ensure accurate permeability measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a test probe measures velocity at a fixed distance from the porous surface, then the measurement process is simple, but the measurement precision is insufficient due to non-uniform flow distribution and asymmetric blowing capability
Solution Approach 1:
The patent divides the porous surface into multiple discrete measurement positions arranged in a grid pattern. Instead of measuring the entire surface at once, the system segments the measurement area and systematically probes each location to capture spatial variations in permeability, thereby achieving precise local characterization of the complex porous structure
Solution Approach 2:
The patent transitions from single-point measurements to a two-dimensional spatial mapping approach. By measuring velocity at multiple positions across the surface and correlating with pressure gradient data, the system creates a comprehensive permeability map that accounts for geometric variations and manufacturing defects across the entire porous structure
2Measurement precision
If the probe distance from the surface is not optimized, then the measurement process is faster, but the measurement precision decreases due to insufficient correlation between velocity and pressure gradient
Solution Approach 1:
The patent performs preliminary measurements at multiple distances from the porous surface before the actual permeability characterization. By establishing the optimal probe distance in advance through correlation analysis of velocity and pressure gradient data, the system eliminates the need for repeated distance optimization during subsequent measurements, reducing overall measurement time while maintaining precision
3Reliability
If overall material properties are used instead of local characterization, then the system complexity is reduced, but the reliability decreases due to non-uniform cooling and asymmetric flow paths
Solution Approach 1:
The patent applies the local quality principle by determining permeability at multiple discrete positions across the porous surface rather than using a single average value. This approach captures spatial variations in blowing capability caused by geometric features and manufacturing defects, enabling localized optimization of cooling performance and improving overall system reliability
Solution Approach 2:
The patent changes the permeability parameter from a single bulk material property to a spatially distributed field of local permeability values. By measuring and mapping permeability variations across different locations on the porous surface, the system accounts for non-uniform flow distribution and enables more accurate prediction of thermal protection system performance under realistic operating conditions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise characterization of permeability, preventing hot spots and improving thermomechanical response by optimizing coolant flow, thus enhancing the durability and efficiency of thermal protection systems for hypersonic vehicles.
Implementation Method 1
These measurements can be related to the pressure gradient across the local thickness of the material by using Darcy's law
Implementation Method 2
the coolant (air) mass flux blown from a conical porous surface can be measured by a hot-film probe
Implementation Method 3
employing Darcy's law and computed tomography to calculate effective permeability
Data Source
AI summary
Disclosed are various embodiments for measuring a local permeability of a porous material. A probe can be positioned perpendicular to the surface of the material. The probe can be configured to sense a velocity of a fluid flowing over the surface. The probe can be positioned at a distance determined based on an average porosity of the material. The probe can take measurements at various positions at the distance by moving a minimum dimension between each measurement.