An experimental study on the characteristics of transient deployment of hinged wing actuators within a boundary layer

Herein we investigate the flapping wing phenomenon in great detail. A 10cm x 10cm square winglet and a 10cm high, 10cm base isosceles triangular winglet are tested as they transiently deploy from a 0 degree position embedded in the wind tunnel floor, to 90 degrees with respect to the wind tunnel floor and the free stream flow. The two winglets were tested in two flow conditions. The first flow condition was a delta1 = 14cm thick boundary layer, with a free stream velocity of U01=11.03m/s, and a Re1 = 70300. The second flow condition was a delta 2 = 5cm thick boundary layer with a free stream velocity of U02 =10.69m/s, and a Re2 = 68133. Through these experiments we are trying to understand, both qualitatively and quantitatively, how drag is generated, increased beyond the steady state value under dynamic conditions, and then how drag falls back to its normal steady state values, after the transient phenomenon has ended. Our experiments used a novel aerodynamic balance design, developed for the exact purpose of acquiring very accurate low magnitude force measurements with high frequency response. Through this direct measurement method we acquired time-resolved and decoupled measurements of drag and lift that indicated the accurate timing and magnitude of these transient events. The controlling parameters in this transient drag generation phenomenon are the deployment speed and shape of the winglet, the range of deployment and the viscous effect of the boundary layer. The effect of these controlling parameters was then quantified. Load-cell measurements of drag and lift, along with accelerometer measurements of the tangential and radial acceleration, and encoder measurements of angle were taken for every experiment. These dynamic measurements helped us quantify the aerodynamic effects on the moving winglets within the two boundary layers.;The following overall conclusions were derived as a result of this study. (1) Faster deployment speed produces higher maximum dynamic coefficients of up to 360%. (2) The higher the final angle a winglet deploys to, the higher the dynamic drag it creates. (3) Square winglets had higher maximum dynamic and static drag coefficient under all flow and deployment conditions. (4) Higher h/delta produced higher dynamic drag for all shapes and deployment conditions.;After this dynamic phenomena were resolved in the time and magnitude domain, flow visualization experiments were obtained by using a video camera while seeding the flow with oil based smoke, and water vapor mist, and illuminating the flow using two different laser systems. Particle Image Velocimetry data were also used to further understand the underlying flow characteristics that lead to the quantitative results obtained with the aerodynamic balance.;Through our visual experiments we established that, at steady state conditions, there is a complex vortex system in place, that results in the measured steady state values for the coefficients of drag and lift. This steady state flow system is comprised of the horseshoe vortex, the left and right alternating side vortices and a shear layer steaming from the tip of the winglet propagating downstream. The creation of this steady state vortex system is delayed when the winglet deploys dynamically, and this is one of the reasons for the increased transient drag and lift forces that were observed. Furthermore, a series of tip vortices, that are formed continuously and shed downstream during dynamic deployments, are also responsible for the increased transient forces.