Numerical Simulation of Unsteady Aerodynamics in Insect Flight using Generic Planform Shapes

摘要

The aim of this work is to provide a better understanding of the aerodynamic performance of various planform shapes undergoing various kinematics for flapping wing flight. There have been extensive analyses and experiments of 2D airfoils undergoing flapping motion. These studies reveal various mechanisms for unsteady aerodynamic lift and thrust generation such as the importance of the control of leading edge vortices. However, 3D analysis of flapping wing flight with various planform shapes is required to study 3D flow structures and their role in determining the lift and thrust for the design of a future flapping wing micro air vehicle.Firstly, CFD analysis has been carried out on 5 rigid simple planform shapes (rectangle, reverse ellipse, ellipse, triangle and four ellipse) at a Reynolds number of 13500 to determine the effect of planform shape on the aerodynamic performance of a flapping wing undergoing hover kinematics. The kinematics is described in terms of only 2 angles, sweep and pitch. The performance is compared through the use of force histories, pressure distribution plots, flow structure images, power utilized and lift generated. It is found that the area distribution near the wing tip contributes to the difference in lift generation between the five planforms. The rectangular planform is found to have the best performance with a suitable balance of power consumed and lift generated as compared to the reverse ellipse which has the highest lift generation.Secondly, the kinematics from a honeybee and thrips are used on the same 5 planform shapes to determine the effect of kinematics on the performance of each planform. These kinematics are more realistic as the variations of all the 3 angles (sweep, pitch and elevation) are considered. It is found from the analysis that the reverse ellipse planform performs the best in terms of lift generation but the ellipse performs better overall when power economy (ratio of average vertical force generated to the average power consumed) is considered. In thrips kinematics, the reverse ellipse is again seen to perform the best in terms of the power economy. For a given planforms, there is a reduction in lift generation in thrips kinematics compared to the honeybee kinematics except in the case of the rectangle where there is an increase.These results have been explained in terms of the flow structures and associated pressure distributions generated on the wings.