The Effect of the Flapping Movements of the Wings of an Ornithopter on Aerodynamic Forces

In this article, we simulate the flow of an ornithopter flapping its wings. The wings are flat surfaces of zero thickness (which eliminates the creation of thrust through the Knoller-Bets effect). Flowing around an incoming stream at a speed of 20 m/s and with an angle of attack of 3 degrees implies the presence of a noticeable lifting force by itself, without flapping the wings. In addition, such a flow corresponds to the cruising flight mode of a bird actively flapping its wings. In this paper, the wing flap, which has a very complex kinematics, is represented as a superposition of a pair of simple periodic rotations.: 1) rotation of the wing planes around the longitudinal axis of the bird; 2) rotation of the wing planes around the axis of the wing itself. This simplified representation of the swing is used specifically to identify the relationship between the power characteristics of the swing and the parameters of each of the rotational vibrations of the wing. Calculations of the air flow are carried out on a deformable grid, which implies a conservative approximation scheme and a constant grid dimension. For this task, an author's algorithm was developed that allows wing flaps to be counted in a fairly wide range of flapping and rotation angles, which made it possible for the first time to apply the calculation on deformable grids to calculate the flow of flapping wings.

Keywords

ornithopter; aerodynamics; CFD; deformable computational grids.

References

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