Full-Field Uncertainty Determination for Pressure-Sensitive Paint Measurements
T HE principle behind pressure-sensitive paint (PSP) measurements is by nowwell known: a luminescent coating is applied to a test article, the test article is illuminated with light at a short wavelength (for example, blue), and emission from the paint (for example, red) is imaged by one or more digital cameras. Oxygen quenching of the luminescent signal produces the desired pressure sensitivity [1,2]. Pressure distributions are typically computed from the ratio of images based on a suitable calibration equation. In intensity-based measurements, these are images at a wind-off condition and images at the run condition. In lifetime-based measurements, both images are acquired at the run condition by choosing two different temporal gates with respect to a train of excitation pulses. Three-gate measurements are also being developed [3]. Many studies have been performed to assess the error sources in PSP measurements [4–11]. However, assessment of the measurement uncertainty in practice is typically limited to a comparison of PSP data in the vicinity of pressure taps with readings from these taps. The purpose of this paper is to show that two additional measures of uncertainty can easily be implemented. One is based on pixel-topixel variations within an image from a single camera, the other on camera-to-camera variations for points on the test article that are viewed by two or more cameras. In principle, these additional measures of uncertainty can be computed for every point on the surface of the test article. Both produce an estimate of the precision of the PSPmeasurement andmay be thought of as adding “error bars” to the processed data in full-field mode.