Tailorable Resistance Heating Layer and Silicon Carbide Protective Coating

Traditionally, unsteady pressure transducers have been the instrumentation of choice for investigating unsteady flow phenomena which can be time-consuming and expensive. The ability to measure and compute these flows has been a long-term challenge for aerospace vehicle designers and manufacturers. Results using only the pressure transducers are prone to inaccuracies, providing overly conservative load predictions in some cases and underestimating load predictions in other areas depending on the flow characteristics. NASA Ames has developed a new state-of-the-art method for measuring fluctuating aerodynamic-induced pressures on wind tunnel models using unsteady Pressure Sensitive Paint (uPSP). The technology couples recent advances in high-speed cameras, high-powered energy sources, and fast response pressure-sensitive paint. The unsteady pressure-sensitive paint (uPSP) technique has emerged as a powerful tool to measure flow, enabling time-resolved measurements of unsteady pressure fluctuations within a dense grid of spatial points on a wind tunnel model. The invention includes details surrounding uPSP processing. This technique enables time-resolved measurements of unsteady pressure fluctuations within a dense grid of spatial points representing the wind tunnel model. Since uPSP is applied by a spray gun, it is continuously distributed. With this approach, if the model geometry can be painted, viewed from a camera, and excited by a lamp source, uPSP data can be collected. Unsteady PSP (uPSP) has the ability to determine more accurate integrated unsteady loads.

In order to maintain the low cost, simplicity, and quick turnaround of cold-flow testing while improving accuracy, NASA evaluated unconventional gases for use as simulants. During such evaluations, NASA discovered that by adjusting stagnation temperature, the isentropic exponent of ethane can be tuned to approximate those of common rocket propellants (e.g., hydrogen, hypergols, alcohols, and hydrocarbons). Furthermore, due to ethane’s high auto-ignition temperature and resistance to condensation, tuned ethane enables testing of expansion ratios much larger than conventional inert-gas testing. To leverage this discovery, NASA developed a hardware-based system to treat ethane and obtain nozzle chamber conditions that match the appropriate aerodynamics for a specific test. The system, named HYPERFIRE, works in the following manner. Liquid ethane is transferred to a piston-style run tank, where it is pressurized. Then, the ethane is run through two insulated pebble beds where it is heated, vaporized, and stabilized. Finally, the treated ethane is transferred from the second pebble bed to a small thrust takeout structure, and through the test article. Control of valves and regulators is managed by an onboard computer, accessed via a LabVIEW™ interface. The system is mounted on a hurricane-resistant steel frame to enable transportation via forklift. Heated ethane reproduces the aerodynamics of combustion products at low temperatures relative to alternative testing methods. Thus, test articles can be manufactured using low-cost, low temperature rated, transparent materials (e.g., acrylic). In addition to reducing testing cost, this grants optical access to internal flowfields, enabling advanced diagnostic techniques (e.g., Schlieren imaging, particle image velocimetry) not possible with hot-fire testing and less meaningful with conventional cold-flow testing.

Low ice adhesion strength coatings are only useful insofar as they remain on the surface of interest, and aircraft leading edges experience extreme environmental conditions during flight. Ensuring durability while maintaining performance – in this case, reduction of impact (i.e., accreted in-flight) ice adhesion strength – is critical to meeting the needs of the aviation industry and other commercial applications. To that end, NASA engineers investigated coating compositions comprised of epoxy resins, including aromatic and aliphatic resins, and aromatic diamine hardeners. Several nonreactive additives were incorporated and tested. The first was holey graphene, a unique nanomaterial made by partly oxidizing areas of graphene that already have defects. This creates high energy functionalities that result in good dispersion throughout the matrix, enabling the mechanical properties of graphene to be imparted throughout the coating. Secondly, micrometer-sized core-shell rubber particles were dispersed throughout the epoxy resin to increase toughness. Finally, a series of polyhedral oligomeric silsequixones (POSS) were used for mechanical reinforcement. Several different coating formulations were development and tested, each incorporating different relative amounts of additives, with good results. Thus, the coatings can be tailored to meet different application-specific requirements. NASA's coating formulations, with further development, may be suitable for in-flight (i.e., impact) ice adhesion reduction on aircraft leading edges and other platforms exposed to harsh environments.

In one of NASA Glenn's innovations, a shaped recess can be formed on a surface associated with fluid flow. Often V-shaped, this shaped recess can be configured to create or induce fluid effects, temperature effects, or shedding effects. For example, the shaped recess can be paired (upstream or downstream) with a cooling channel. The configuration of the shaped recess can mitigate the lift-off or separation of the cooling jets that are produced by the cooling channels, thus keeping the cooling jets trained on turbine blades and enhancing the effectiveness of the film-cooling process. The second innovation produced to improve film cooling addresses problems that occur when high-blowing ratios, such as those that occur during transient operation, threaten to diminish cooling effectiveness by creating jet detachment. To keep the cooling jet attached to the turbine blade, and also to spread the jet in the spanwise direction, NASA Glenn inventors have successfully used cooling holes that reduce loss by blowing in the upstream direction. In addition, fences may be used upstream of the holes to bend the cooling flow back toward the downstream direction to further reduce mixing losses. These two innovations represent a significant leap forward in making film cooling for turbine blades, and therefore the operation of turbine engines, more efficient.

Advances in new polymers and composites along with growing industrial needs in below-ambient temperature applications have brought about the Macroflash development. Accurate thermal performance information, including effective thermal conductivity data, are needed under relevant end-use conditions. The Macroflash is a practical tool for basic testing of common materials or research evaluation of advanced materials/systems. The Macroflash can test solids, foams, or powders that are homogeneous or layered in composition. Test specimens are typically 75mm in diameter and 6mm in thickness. The cold side is maintained by liquid nitrogen at 77 K while a heater disk maintains a steady warm-side temperature from ambient up to 373 K. The steady boiloff of the liquid nitrogen provides a direct measure of the heat energy transferred through the thickness of the test specimen. Nitrogen or other gas is supplied to the instrument to establish a stable, moisture-free, ambient pressure environment. Different compression loading levels can also be conveniently applied to the test specimen as needed for accurate, field-representative thermal performance data. The Macroflash is calibrated from approximately 10 mW/m-K to 800 mW/m-K using well-characterized materials.