The Effect of Twisting on a Heaving Flat Pate

Remotely operated aerial vehicles are used extensively by the military, industry, and civilians alike. Current research into unsteady flapping flight has been concerned with rigid foils. The purpose of this study is to investigate how a dynamically morphing foil affects the fluid-structure interactions of unsteady flapping locomotion. The effects of non-dimensional heaving amplitude and reduced frequency were studied. Two morphing modes were investigated: spanwise twisting in the direction of upward pitch (Mode A), and spanwise twisting in the direction of downward pitch (Mode B). Force sensor data showed that Mode A recovered some lift during the upstroke. Mode A also maintained near-constant lift during the transition between downstroke and upstroke, suggesting more stable locomotion. Particle Image Velocimetry (PIV) data showed that Mode A limits circulation during the downstroke, keeping C_d ≅ 0 at the cost of reduced lift. By contrast, Mode B was found to increase circulation during the downstroke, resulting in higher lift and drag. Force sensor data for Mode B showed that this effect is reversed during the upstroke, where it causes negative lift. The effects of morphing were found to be caused by changes in shear layer velocity that occur as a result of spanwise twisting.