Unsteady pressure-sensitive paint (PSP) measurements were acquired on an articulated model helicopter rotor of 0.26 m diameter in edgewise flow to simulate forward flight conditions. The rotor was operated at advance ratios (free stream velocity normalized by hover tip speed) of 0.15 and 0.30 at a cycle-averaged tip chord Reynolds number of 1.1 9 10 5 , with collective and longitudinal cyclic pitch inputs of 10°and 2.5°, respectively. A single-shot data acquisition technique allowed a camera to record the paint luminescence after a single pulse of high-energy laser excitation, yielding sufficient signal-tonoise ratio to avoid image averaging. Platinum tetra(pentafluorophenyl) porphyrin (PtTFPP) in a porous polymer/ ceramic binder served as the PSP. To address errors caused by image blurring and temperature sensitivity, a previously reported motion deblurring algorithm was implemented and the temperature correction was made using temperature-sensitive paint measurements on a second rotor blade. Instantaneous, unsteady surface pressure maps at a rotation rate of 82 Hz captured different aerodynamic responses between the two sides of the rotor disk and were compared to the nominally steady hover case. Cycle-to-cycle variations in tip unsteadiness on the retreating blade were also observed, causing oblique pressure features which may be linked to three-dimensional stall.

A single-shot, lifetime-based pressure-sensitive paint (PSP) technique is proposed as a pressure sensor for applications requiring high pressure sensitivity on a moving model such as a rotor blade. The method is based on a single pulse of high-energy excitation light and a double-frame exposure on an interline transfer charge-coupled device camera for recording luminescent lifetime. Small pressures can be measured on surfaces that are moving in an aperiodic manner (which precludes phase averaging). Measurements in environments having overall surface pressure gradients as small as 1 kPa show that the technique is capable of accurately resolving small pressure fluctuations. The pressure sensitivity to the oxygen concentration of some commonly available PSP formulations has been investigated with respect to capabilities and limitations of the paints for this single-shot lifetime application. A system with ruthenium-based pressure-sensitive paint, 532 nm wavelength laser and a CCD camera is demonstrated on a 0.126 m diameter propeller rotating at 70 Hz. Pressure data are acquired within a single pulse of excitation light energy, with no image averaging required.

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