Luminescence Lifetime Response of Pressure-Sensitive Paint to a Pressure Transient

Abstract

Pressure-sensitive paint (PSP) is used to acquire high-fidelity images of steads pressure distributions across surfaces. The PSP luminescence emission response to excitation light depends in a straightforward way on the oxygen concentration (hence air pressure) and the irradiance incident on the PSP lumiphores. Often, however, the phenomenon of interest is unsteady. During a rapid change in pressure. the oxygen concentration within a PSP layer varies with depth. Moreover, the excitation irradiance varies with depth as a result of attenuation, and this affects signal generation when the spatial distribution of oxygen is also changing. Prior studies have been reported on the transient response of PSP using the radiometric technique to detect pressure, we have extended the study by applying a luminescence lifetime technique. Oxygen concentration as a function of time and depth are obtained by solving the mass diffusion equation. with appropriate initial and boundary conditions. We develop a luminescence emission model that takes the spatially varying oxygen concentration and excitation absorption profile into account and relate pressure to the lifetime of the luminescence emission. Oxygen concentration is governed by mass diffusion of oxygen through a PSP layer during a rapid change in pressure, and the absorption of excitation light is governed by Beer's law. The significance of both the mass diffusivity and the optical depth of PSP are assessed. A numerical method was used to solve the mass diffusion equation that allows modeling of the oxygen concentration within the PSP given an arbitrary pressure function. We have used a double-image digital camera to acquire PSP emission lifetime data from several paint thicknesses during a rapid change in pressure. These data were compared to the results predicted by the model.