Unsteady Aerodynamics of Flapping Wing of a Bird

Abstract

Flow behavior and aerodynamic characteristics of flapping motion of a bird are investigated using a computational method. Seagull bird is chosen as a study case which has high aspect ratio wings with pointed wing-tips and higher camber wing section. Simulations are carried out order to know effects of flapping speed on flow behavior and aerodynamic characteristics. Two kind of simulations are performed, namely quasi-steady and unsteady flow simulations. The first approach is performed by hanging the bird wings on its body moving from lower position to higher position with no local vertical velocity to be produced. Meanwhile, the unsteady simulations are carried out by flapping the bird wing periodically with a given flapping frequency. The resulted of local vertical velocity due to the wing motion affects on flow behavior around wing which contributed in generating lift, thrust and moments. To mimic the movement of down-stroke and upstroke of the bird, the wing position changes in dihedral angles with respect to time with the path motion according to sinus function. The unsteadiness and viscous flows at low speed are evaluated using the solution of timedependent Reynolds Averaged Navier-Stokes with k-
turbulent model. In addition, multi-block structured grids are generated to provide more accurate viscous result and to model proper the complex wing-body bird. The results include mesh movement, velocity contours as well as aerodynamics coefficients of flapping motion of the bird at various flapping frequency.