Description: Pressure sensitive paint (PSP) systems are excellent tools for performing global pressure measurements in aerodynamic testing, especially in wind tunnel studies. The major limitation of PSP for pressure mapping is its dependence on an oxygen-containing flow, since those paints are actually oxygen sensors. Intelligent Optical Systems (IOS) is developing a unique coating in which fluorescence quenching can form high resolution images of the true pressure distribution on surfaces in transonic flow in oxygen-free atmospheres. The fluorescence in these unique coatings depends directly on absolute pressure, and oxygen permeation into the coatings is not required. The new coating, however, is completely compatible with the "legacy" (oxygen sensing) visualization equipment used in current transonic test facilities. With this novel pressure sensing technology, coating materials can be used that are not useful for oxygen-based PSPs, and coatings that can meet requirements not achievable with classical paints, like operation at extremely low temperature or in highly contaminated environments. In Phase I, IOS has created the oxygen-insensitive pressure-sensitive coating materials, and applied them to glass and stainless steel test coupons. The fluorescence emission lifetime and intensity of these test samples were measured at varying static pressures under pure nitrogen, showing significant correlation with pressure in the range studied (from 0.05 to 14.7 psi), and excellent repeatability. This sets the stage for Phase II development and delivery of a complete temperature-compensated true ambient pressure sensitive paint system that can be used to characterize flow around structures in hypersonic wind tunnels. At the end of Phase II, the coatings will have been tested at relevant environments (TRL5), and will be available for NASA to begin testing in a high-fidelity laboratory environment (TRL6).

Benefits: True ambient pressure sensitive (TAPS) paint will be immediately useful in wind-tunnel studies of hypersonic flow, where working fluids other than oxygen are often used to achieve Reynolds numbers characteristic of air flow at higher speeds, particularly in the study of real gas aerodynamic effects, including the world's largest pressurized cryogenic wind tunnel, the National Transonic Facility (NTF), the 0.3-Meter Transonic Cryogenic Tunnel and the Transonic Dynamics Tunnel (TDT). Advanced pressure sensitive coatings will be adopted rapidly by other aerodynamic test facilities where oxygen-independent pressure mapping is needed; for example, in the study of combustion-related phenomena (where the partial pressure of oxygen clearly does not depend exclusively on the local ambient pressure). Once the advantages of oxygen-free pressure mapping are demonstrated in these applications, TAPS-based PSPs will rapidly displace the conventional oxygen-sensitive paints in lower speed wind tunnels as well.

One very obvious advantage of TAPS PSPs is that they can be used in "water tunnels" for testing hydrodynamic structures. Thus, ship designers (including both the U.S. Navy and commercial naval architects) will be able to use the whole-surface image-based pressure mapping techniques now available to aerospace engineers. A large class of industrial and commercial structures that emit oxygen-reactive species – from tailpipes to smokestacks – that has hitherto been unaddressable by PSPs can be studied with TAPS paints. Pressure mapping of other non-aerodynamic structures (e.g., automobiles, trains, buildings) can be accomplished with conventional PSPs, but the increased shelf-life and stability of TAPS paints will make them attractive for these applications as well. Finally, the true-pressure-sensitive pigments developed in this project will also be useful in a host of spinoff applications, from "point sensors" (e.g., on the tips of optical fibers) to optical pressure switches.