The Boeing/AFOSR Mach-6 Quiet Tunnel achieved quiet flow to a stagnation pressure of 163 psia in Dec. 2008, the highest value observed so far. It remains quiet at pressures above 160 psia. Under noisy conditions, nozzle-wall boundary-layer separation and the associated tunnel shutdown appear to propagate slowly upstream, whereas under quiet conditions, the propagation is very rapid. A new diffuser insert has been designed, fabricated, and installed in the tunnel in order to start larger blunt models and increase run time. A flared cone with a circular-arc geometry was designed to generate large second-mode N factors under quiet flow conditions. When the computed N factor was 13, large instability waves were measured under quiet flow conditions using fast pressure sensors, but the flow remained laminar. Transition was observed only under noisy conditions. A laminar instability was detected in the wake of an isolated roughness element in the boundary layer on the nozzle wall; this appears to be the first such measurement at hypersonic speeds.

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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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