Back-imaging of polymer-ceramic pressure-sensitive paint

The feasibility of back-imaging polymer-ceramic pressure-sensitive paint (PC-PSP) was investigated, with supersonic flow over a rectangular cavity being the test subject. A PC-PSP formulation in which the luminophore was fully-integrated into the binding layer created a PSP which luminesced from the top and bottom of the layer. This PSP was applied to a clear acrylic plate serving as the cavity ceiling. Two identical high-speed cameras imaged the paint; one viewed the top of the PSP layer (front-imaging) whereas the other viewed the bottom of the layer (back-imaging). The temporal, time-averaged, and spectral response measured by each camera were functionally identical. Specifically, the two data were found to be 90% correlated in time at zero delay. The minor differences can be attributed to random noise and the fact that the cameras viewed through two different materials (one through acrylic and the other through optically-polished glass). These results illustrate that back-imaging is a promising method for overcoming the optical access constraints of conventional PSP imaging techniques.