Sub-millimeter resolution pressure measurement on free flight model at Mach 1.5 using novel non-intrusive optical technique

Abstract

A motion-capturing pressure sensitive paint (PSP) system is developed and demonstrated by collecting transient pressure data on the surface of a 30 mm diameter sphere model in free flight at Mach 1.5, where a conventional pressure tap is unable to be mounted. The developed non-intrusive measurement technique is able to cancel out changes in signal intensity due to variations in illumination during free flight. Images of the sphere model are collected using a high-speed camera at a rate of 100 kHz with an exposure time of 3.75 μs. Motion blur is estimated as 6.5% of the sphere diameter. The sphere is fully in view for 7 frames, or 70 μs. Transient data from each frame is collected to produce a free flight pressure map on the surface. In order to validate the measurement, a time-averaged CFD simulation of a sphere model at Mach 1.5 is run using far field pressure boundary conditions and a mesh of 6.96 million cells. An uncertainty analysis is performed using the signal to noise ratio of the PSP measurement. The PSP measurement is in agreement with the CFD simulation quantitatively across a centerline pressure trace. The accuracy of the PSP measurement compared to the CFD simulation was within 7.4 kPa.