Comparison of Unsteady Pressure-Sensitive Paint Measurement Techniques

The current work focuses on the development and application of fast-responding polymer/ceramic pressure-sensitive paint (PSP) as an advanced optical surface pressure measurement technique for unsteady flowfields in large-scale wind tunnels. Three different data acquisition methods for PSP are evaluated and compared: phase averaging, real-time (high-speed) imaging, and single-shot lifetime imaging. All three techniques were applied to the measurement of the time-resolved, global surface pressure distribution on a hemispherical dome in Mach 0.6 freestream flow at a total pressure of 71.8 kPa, where the Reynolds number based on dome diameter (0.254 m) was 2.4 x 10(6). At this flow condition, a predominant shear layer oscillating at 400 Hz over the test model was detected by pressure transducer measurement, providing an appropriate trigger for the PSP optical instrumentation. In the phase-averaging technique, pulsed LED arrays were phase-locked to the shear-layer frequency, and a long camera exposure time captured the pressure distribution over many phase-averaged cycles. In the real-time approach, high-intensity continuous LED illumination was paired with a high-speed camera operating at a frame rate of 10 kHz to capture the pressure distribution without any image averaging. In the lifetime-based single-shot approach, instantaneous pressure information was acquired by exciting the paint with pulsed laser energy and ratioing two exposure gates, which covered the luminescent lifetime decay of the luminophore molecules resulting from each excitation pulse. An assessment of the three methods is presented, with the benefits and disadvantages of each technique evaluated through the ease study of the hemispherical dome.