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Completed TRL 6 (started at 2, targeting 6)
Arc jets are critical test facilities for leading edges and other thermal protection system (TPS) components, but demand exceeds national capacity, which can result in cost and schedule impacts for reentry and hypersonic flight programs at NASA and other agencies. The Leading Edge Irradiation Assembly (LEIA) research project at NASA Armstrong Flight Research Center in Edwards, California, is developing a radiant thermal test methodology to complement those at arc jet facilities and also adding a new ground test capability to impart combined thermal and mechanical loads to leading edge and other TPS components. The LEIA research leverages Armstrong expertise in refractory materials, measurements, and multimodal heat transfer analysis capabilities.
With resources from the Center Innovation Fund (CIF), the team identified flight-relevant aerothermal profiles; completed literature reviews and analytical studies to evaluate potential configurations and system performance; designed, analyzed, and fabricated a prototype test setup; and completed a test series with the prototype setup.
How does LEIA complement existing ground test facilities like arc jets?
The environments associated with atmospheric reentry and hypersonic flight are extreme, and it can be difficult to predict how leading edges, thermal protection systems (TPS), and hot structures will react to them through calculation or modeling alone. Ground testing is frequently used to understand the behavior of these technologies and to ensure that they can survive these extreme environments. However, it is impossible to simulate the entire flight environment in a single ground test facility.
Arc-heated wind tunnels are the gold standard for evaluating the thermochemical response of these technologies to flight environments for a good reason: they replicate fluid enthalpy, gas composition, stagnation heat flux, and other key parameters more closely than any other ground test facility. They are particularly well-suited for evaluating technologies where thermochemical effects are critical. Some examples include oxidation-resistant coatings, ablating heat shields, transpiration-cooled structures, and reusable tiles that must not chemically degrade during their lifespan.
LEIA does not replicate high-enthalpy flow, so it cannot evaluate flow-driven chemical effects. However, LEIA is particularly well-suited for evaluating technologies where thermal effects are critical. As manufacturing techniques advance, new methods of joining components and integrating them into larger structures must be evaluated. In some cases, a thermal-only early screening test can help designers de-risk new designs before moving on to arc jet or flight tests. In other cases like semi-active leading edges or control surfaces, fine time-resolved control of heating rates in many different areas of a structure may be required. For certain shapes and sizes of these test articles, it may be easier to achieve this LEIA than it is in other facilities. There are also cases where it is necessary to test an awkwardly shaped technology or one that is integrated into a vehicle, or to perform mechanical or dynamic loading at the same time as thermal loading. Although arc jets come in many sizes, LEIA doesn’t have to fit into a wind tunnel test section at all! This provides flexibility to test a wide variety of structures.
The bottom line is that any ground test requires some amount of compromise. Designers may be interested in a multitude of parameters like fluid enthalpy, shear, catalytic recombination, stagnation pressure, stagnation heat flux, integrated heat rate, vibratory loading, maneuver loading, or pressure loading. LEIA doesn’t replace any existing tools in their technology evaluation toolboxes, but it does add one more way to combine some of those parameters.
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