Improved Unsteady Pressure Sensitive Paint Formulation

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.

The retroreflective-enhanced system combines PSP/TSP with specially treated glass microspheres to enable simultaneous surface and flow field measurements. The process involves a multi-layer coating system including primer, epoxy base coat, and acrylic polymer/ceramic binder, with microspheres applied while the binder retains adhesive properties. The glass microspheres may be uncoated, half-coated with aluminum, or pre-processed to be coated in another chemical. The system leverages dual optical characteristics: the underlying PSP/TSP responds to pressure and temperature changes through luminescence intensity variations at specific wavelengths, while embedded microspheres provide retroreflective properties enabling focused SAFS, shadowgraph, or BOS visualization techniques. This configuration allows simultaneous capture of on-body surface measurements and off-body flow field disturbances. The invention enables measurements from a single viewing orientation rather than requiring orthogonal optical access points. While specific excitation lighting, wavelength filtering, and camera positioning are still necessary, the system significantly streamlines experimental setup compared to traditional separate approaches. While initially developed for aerodynamic testing and flow visualization research, this invention supports optical measurement and surface analysis applications. By enabling simultaneous measurements from a single optical access point, the retroreflective-enhanced PSP/TSP offers a streamlined solution for systems where optical access limitations are critical. The system is a TRL 6, having undergone successful validation in wind tunnel testing, and is available for patent licensing.

The heating layer uses a polyurethane binder loaded with carbon-based conductive filler, formulated to remain stable and crack-free across a wide temperature range. Applied as a thin film with copper-tape electrodes, it generates heat through electrical resistance when energized, functioning as a spray-on electric blanket that produces a precise, localized temperature step. The resistance can be tuned to match specific power and geometry requirements, offering a scalable alternative to the traditional temperature step method with lower energy consumption, faster setup, and reduced maintenance. The layer has been tested at NASA's National Transonic Facility (NTF), integrated into the CATNLF wing, and installed on test aircraft. The silicon carbide protective coating was developed after flight demonstrations revealed that minor surface damage from debris caused premature flow transition and compromised data quality. By incorporating beta silicon carbide into a polyurethane binder, the coating significantly increases surface hardness and abrasion resistance while retaining flexibility. It applies over the heating layer to protect against debris, water, and oil, and has demonstrated superior durability during surface preparation on in-flight models requiring infrared imaging. Together, the two coatings improve the accuracy, durability, and efficiency of aerodynamic testing in extreme environments. The heating layer is a TRL 6 and the silicon carbide coating is a TRL 4. The coatings are available for patent licensing.

This invention is an imaging method that requires very simple optics on an airborne vehicle, a camera with an appropriate lens, and an area on the ground that provides visual texture. The complexity with this method is in the image processing and not as much with the hardware or positioning, making Background Oriented Schlieren (BOS) an attractive candidate for obtaining high spatial resolution imaging of shock waves and vortices in flight. First, images are obtained of a visually textured background pattern from an appropriate altitude. Next, a series of images are collected of a vehicle in flight below the observer vehicle and over the same spot on the ground that serves as a background pattern. Shock waves are deduced from distortions of the background pattern resulting from the change in refractive index due to density gradients. The invention requires special software to create the schlieren images. The schlieren image is a contour plot of a two-dimensional data array of measured distortions, in pixel units. The results are used by researchers to help understand the flow phenomenon and compare to computational models. The BOS method also yields measured deflection distances, which can be used to determine the strength of a given density gradient. The system design and flight planning were based on the camera characteristics, airplane coordination, and airspace limitations.

The Projected BOS imaging system provides a significant advancement over other BOS flow visualization techniques. Specifically, the present BOS imaging method removes the need for a physically patterned retroreflective background within the flow of interest and is therefore insensitive to the changing conditions due to the flow. For example, in a wind tunnel used for aerodynamics testing, there are vibrations and temperature changes that can affect the entire tunnel and anything inside it. Any patterned background within the wind tunnel will be subject to these changing conditions and those effects must be accounted for in the post-processing of the BOS image. This post-processing is not necessary in the Projected BOS process here. In the Projected BOS system, a pattern is projected onto a retroreflective background across the flow of interest. The imaged pattern in this configuration can be made physically (a pattern on a transparent slide) or can be digitally produced on an LCD screen. In this projection scheme, a reference image can be taken at the same time as the signal image, facilitating real-time BOS imaging and allowing the pattern to be changed or optimized during measurements. The Projected BOS imaging technology has been proven to work by visualizing the air flow out of a compressed air canister taken with this new system. The Projected BOS is available for patent licensing.