Use of pressure sensitive paints in low speed flows

Low speed jet impingement tests are conducted to determine the accuracy and resolution of pressure sensitive paints (PSP). Aluminum plates are coated with PSP and a low speed jet is applied to the surface. A low power laser is scanned across the paint while the fluorescence is acquired with a photomultiplier tube. Three different methods are used to determine the pressure: intensity ratioing, phase sensitive detection, and two-color paints. Results show that the laser scanning system can accurately measure jets with total pressures below 0.05 psi utilizing ratioing techniques and lock-in amplification. Microheterogeneity of the luminophore and binder caused the phase (lifetime) to vary across the surface, causing the need for flow off references. Using this correction, phase sensitive detection was capable of pressures to 0.2 psi. Similarly, uneven mixing of the components in the two-color paints resulted in non-constant reference and pressure signal ratios. This necessitates flow-off ratioing for twocolor paints. However, temperature corrections can be easily made using the two-color paints.