Fast Responding PSP for Rotorcraft Aerodynamic Investigations

The proposed work focuses on implementing fast-response pressure-sensitive paint and Surface Stress Sensitive Films for measurements of unsteady pressure and skin friction in rotorcraft applications. Significant rotorcraft problems such as dynamic stall, rotor blade loads in forward flight, and blade-vortex interaction all have significant unsteady pressure oscillations that must be resolved in order to understand the underlying physics. Often these unsteady pressures are difficult to resolve in the rotating frame due to difficult installation of pressure transducers, and data is available only at discrete points. Pressure-sensitive paint formulations have been developed to provide surface pressure information in situations such as this, but conventional PSP formulations have slow response times. Conventional skin friction measurements, for example oil flow, do not offer significant frequency response. In order to improve the frequency response characteristics of PSP, sprayed porous paint binders have been developed for measurement of unsteady pressures. Fast-responding Surface Stress Sensitive Films provide both quantitative skin friction and qualitative flow visualization measurements. These techniques can provide high-spatial-resolution, time-resolved pressure and skin friction information that will provide unparalleled insight into the physical mechanisms driving certain rotorcraft problems. Both of these techniques will be demonstrated in Ohio State's unique 6"x22" transonic wind tunnel, where an airfoil may be tested for dynamic stall simulation in compressible flow. Successful demonstration of fast-responding PSP and S3F on a dynamic stall test in the 6"x22" tunnel will serve as a proof of concept that will allow transition of the technologies into larger-scale wind tunnels at NASA and elsewhere.