Unsteady Pressure-Sensitive Paint Measurements on an Articulated Model Helicopter in Forward Flight

Abstract

Unsteady pressure-sensitive paint (PSP) measurements are acquired on a two-bladed, articulated model helicopter rotor of 0.26-m diameter in edgewise flow to simulate forward flight conditions. The rotor operated at advance ratios of 0.15 and 0.3, while collective and cyclic pitch were set to 10o and 2.5o, respectively. A double-exposure, lifetime-based technique captured the paint luminescence after a single pulse of high-energy laser excitation, yielding a sufficient signal-to-noise ratio to avoid image averaging. In this way, transient pressure information on the blade can be measured to monitor cycle-to-cycle variations at a given azimuth position due to flow unsteadiness. The selection of porous polymer/ceramic PSP afforded high frequency response and pressure sensitivity, but the long lifetime of this paint caused blurring in the second exposure gate and the porous binder induces a large degree of temperature sensitivity. A recently-developed motion deblurring algorithm was implemented, and the temperature correction was made using temperaturesensitive paint (TSP) measurements. Surface pressure maps for the advancing and retreating blades captured a qualitatively different aerodynamic response between the two, including the signatures of tip relief, stall, and reversed flow.