Accuracy Assessment of a Pressure-Sensitive Paint Measurement System

This paper describes the Boeing production pressure-sensitive paint (PSP) system as applied to a test of a Cessna Citation model late in the year 2000. Over 8000 visual images and 2000 infrared images were acquired in seven shifts of testing. The data accuracy is assessed by statistical analysis of comparisons between the PSP and conventional pressure transducers. Over 200 pressure transducers and 676 test points provided numerous comparisons over a wide range of pressures. The effect of applying a temperature correction based on infrared camera data is also assessed. Background and motivation Determining the accuracy of pressure-sensitive paint (PSP) measurement systems has long been elusive. This issue is particularly important when introducing PSP to customers or programs that have not previously incorporated this new technology into their design processes. Often, the use of PSP is necessitated by the lack of conventional instrumentation, which means that there are few if any pressure taps or strain-gauged surfaces with which to compare the PSP measurements. To characterize the accuracy of a PSP system, test data must be available from a model with a significant number of taps. Then, enough runs must be made to cover a variety of conditions that represent the target environments. * Copyright © 2001 by The Boeing Company. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Senior Specialist Engineer, Senior Member AIAA Associate Technical Fellow, Associate Fellow AIAA Senior Engineer Associate Technical Fellow, Senior Member AIAA Associate Technical Fellow Senior Engineer, Senior Member AIAA Some reports of PSP accuracy can be found in the literature. Bell et al. quotes typical accuracies of PSP, determined as the rms difference between pressure tap data and PSP data at the tap locations, as being 0.02 to 0.03 in Cp at transonic and supersonic speeds in a number of facilities. However, the sample sizes or conditions upon which these values were based were not reported. Mebarki et al. studied the performance of several PSP formulations. For the best formulation, they reported an accuracy of 0.02 to 0.03 Cp at Mach 0.74 and two different Reynolds numbers, corresponding to 0.24 and 0.16 psi, respectively. These statistics appear to be based on only two runs and 156 comparisons per run. In production environments, such accuracies are difficult to achieve consistently throughout a test. The first objective of this study is to characterize the accuracy of a PSP system in a typical production environment. Previous uncertainty studies indicate that temperature is the largest source of error in PSP measurements (see for example Refs. 3,4). The Boeing PSP system now incorporates infrared (IR) cameras to measure the temperature of the PSP coating. The second objective of this study is to assess the effectiveness of this approach. These objectives were accomplished through a joint Boeing/Cessna effort. Cessna provided a wellinstrumented commercial transport model in addition to tunnel time and test support. Boeing provided the PSP system. This cooperative effort produced a large number of comparisons between PSP and pressure taps over a range of Mach numbers and angles of attack in a production environment.