Investigation of Unsteady Aerodynamic Characteristics of a Seagull Wing in Level Flight

Unsteady aerodynamic characteristics of a seagull wing in level flight are investigated using a boundary element method. A new no-penetration boundary condition is imposed on the surface of the wing by considering its deformation. The geometry and kinematics of the seagull wing are reproduced using the functions and data in the previously published literature. The proposed method is validated by comparing the computed results with the published data in the literature. The unsteady aerodynamics characteristics of the seagull wing are investigated by changing flapping frequency and advance ratio. It is found that the peak values of aerodynamic coefficients increase with the flapping frequency. The thrust and drag generations are complicated functions of frequency and wing stroke motions. The lift is inversely proportional to the advance ratio. The effects of several flapping modes on the lift and induced drag (or thrust) generation are also investigated. Among three single modes (flapping, folding and lead & lag), flapping generates the largest lift and can produce thrust alone. For three combined modes, both flapping/folding and flapping/lead & lag can produce lift and thrust larger than the flapping-alone mode can. Folding is shown to increase thrust when combined with flapping, whereas lead & lag has an effect of increasing the lift when also combined with flapping. When three modes are combined together, the bird can obtain the largest lift among the investigated modes. Even though the proposed method is limited to the inviscid flow assumption, it is believed that this method can be used to the design of flapping micro aerial vehicle.