Application of Fast-Responding Pressure-Sensitive Paint to a Hemispherical Dome in Unsteady Transonic Flow

The current work focuses on the application of fast-responding polymer/ceramic pressure-sensitive paint (PSP) as an advanced surface pressure measurement technique for the study of unsteady flow fields in large-scale wind tunnels. Three different PSP experimental methods are demonstrated to resolve the surface pressure distribution over a hemispherical dome placed in subsonic flow with freestream Mach number of 0.6 and a total pressure of 71.8 kPa, where the Reynolds Number based on dome diameter (0.254 m) is 2.4 x 10⁶. At this flow condition, a predominant shear layer oscillating at 400 Hz over the test model is observed. Three different PSP methods were employed to study this phenomenon: phase-averaged, real-time, and single-shot. In the phase-averaging technique, LED arrays are phase-locked to the shear layer frequency so that the strobed illumination freezes the motion of the oscillating fluid in one instant and the camera shutter stays open long enough to average the fluid motion over many cycles. In the real-time approach, a high-speed camera was used to capture the shear layer frequency at a shutter speed of 10 kHz without any averaging of the images. In the lifetime-based single-shot approach, the PSP information was acquired from one single laser pulse, which was also able to provide instantaneous surface pressures with high spatial resolution. An assessment of the three test methods is presented, with the advantage and disadvantage of each technique evaluated through example.