The Interaction Between a Plunging Wing and Gusty Environment*

There has been a great progress in unmanned vehicle's design and control, but these nature-inspired robots are still troubled while flying in gusty environments. However, birds and insects can easily stabilize themselves in complex gust environment. Therefore, we need to understand the gust-mitigation performance of flapping wings and flow physics of wing-gust interaction. A plunging wing, designed and built in-house, was tested in the presence of unsteady wake from a gust generator to investigate the effect of the flow disturbances on vorticity fields. The gust generator was made of multiple sinusoidally oscillating vanes placed in a closed-circuit water channel. The plunge amplitude and frequency of the oscillation were adjusted to bracket the range of Strouhal numbers relevant to the biological locomotion. Particle Image Velocimetry (PIV) was employed to quantitatively study the unsteady wake at different upstream flow speeds, oscillating frequencies, and amplitudes. We performed a flow measurement analysis to investigate the effects of vortical structures on the leading-edge vortex (LEV) of the wing. The results showed that the LEV is more strongly influenced by the gust structures at lower Strouhal numbers and the plunging wing with higher Strouhal numbers may have better performance in gust-mitigation. This research and its successive investigations may eventually lead to more efficient or better-performing Unmanned Aerial Vehicles, along with a better understanding of their fluid dynamics.