During the recent miniPSP test entry at ARA the images collected allowed the surface pressure contours over a portion of the ARA reference model wing to be measured. As this wing was relatively highly pressure plotted the PSP data recorded could be calibrated and the post-processing would provide surface contours of the absolute static pressure over the measurement region.
The calibration coefficients obtained through this in-situ calibration compare very well with those obtained during an apriori lab calibration of the PSP. Minimal differences in sensitivity were exhibited and changes are likely due to changes in temperature through the wind tunnel run as well as lighting and view angle effects.
Figure 1 shows a fully calibrated image with contours of static pressure. Within this image the shock footprint on the upper surface of the wing is clearly visible with the pressure rising from around 25kPa ahead of the shock up to around 50kPa after the shock. This demonstrates that the miniPSP setup has the sensitivity to be able to detect typical aerodynamic characteristics which would be of interest to civil aerospace customers. The accuracy of PSP measurements is often a difficult factor to both measure and quantify. Whilst this can be done through apriori calculations, often environmental factors such as temperature and lighting can have large impacts on the results. Therefore, the simplest measure of the accuracy is to compare to independently measured pressure values, where possible. Figure 2 shows a comparison between chord wise pressure values measured by traditional pressure taps and a through the miniPSP system. This comparison exhibits an excellent relationship between the traditionally measured pressure profile and the profile measured through the miniPSP system. The difference characteristics are presented in Table 1, where the mean difference is around 1.5kPa which corresponds to a pressure coefficient of around Cp=0.05. These values are typical of standard larger scale industrial PSP systems and certainly demonstrate the potential of the miniPSP system for accurate and reliable pressure measurements.
|Figure 1 - Fully calibrated PSP image for Mach 0.85 α =2°|
Figure 2 - Comparison between pressure measured from static tapping
|PSP pressure compared to tap measurement|