### Tech Briefs

Aerodynamics of Flapping Wings for Biomimetic Flying Devices

Inspired by biology (e.g., flying insects or birds), there are ongoing efforts for designing small flying devices called micro air vehicles (MAVs) [1] to achieve novel flight capabilities. An important step in developing such vehicles is to understand the aerodynamics of flapping wings of birds and insects. In this News, we present the experimental and numerical study of the aerodynamics of flapping wings of a hummingbird using ADINA FSI conducted by H.T. Oh and H.C. Choi [2]. A similar study has been conducted on beetle flight [3].

Figure 1 and the movie below show the experimental setup for this study. A model wing made of acryl with approximate dimensions of the hummingbird’s wing is used. The model wing is subjected to translations and rotations similar to that of the hummingbird’s wings during flight. The lift and drag forces acting on the wing are measured using force sensors. Note that due to difficulties in the measurement of the aerodynamic forces in air, the experiment is conducted in water.

Figure 1 Experiment

To study the flow structure around the wing during motion, a 2D model of the wing and the surrounding fluid is analyzed using ADINA FSI. The flow is assumed to be incompressible. To accommodate for the large motions of the wing in the fluid, the adaptive meshing capability of ADINA FSI is used (see our previous News for another example of Adaptive Meshing in FSI).

The animations above show the contour plots of the velocity and pressure distributions in the fluid during the flapping motion. Figure 2 shows the comparison between the numerical results and the experimental measurements of the lift and drag. The numerical results compare well with the experimental measurements, especially considering the fact that in the simulation, a 2D model was used while the experiment was conducted on a 3D curved wing.

 Lift Drag

Figure 2 Comparison of lift and drag coefficients between the 2D FSI and the 3D experimental results

Figure 3 shows the flow around the wing in different stages of the flapping motion. Note the changes in the structure of the vortices around the wing as it translates and rotates.

Figure 3 Flow around the wing

Some details of the velocity field during the flapping motion and the evolution of the computational grid are given in the following movies:
 mesh(> 4 MB) velocity(> 2 MB)

To illustrate the use of ADINA FSI, the ADINA Primer Problem 49 gives a tutorial on using adaptive meshing in FSI.

This example demonstrates some of the many powerful capabilities available in ADINA FSI for solving problems involving full coupling between fluids and structures. For more information on the modeling of such problems, see Fluid-structure Interaction Capabilities.

References

1. Wikipedia article on MAV. For a device in action, see this Youtube video.

2. Private Communication

3. T.Q. Le, D. Byun, Y.H. Yoo, J.H. Ko and H.C. Park, "Experimental and Numerical Investigation of Beetle Flight", Proc. 2008 IEEE Int. Conf. on Robotics and Biomimetics, 21-26 Feb. 2009, pp. 234-239

Keywords:
Bio-inspired, flapping wing, micro air vehicle, MAV, fluid-structure interaction, FSI, aerodynamics, biomimetic, robot, adaptive meshing

Courtesy of H.T. Oh (Korea University) and H.C. Choi (KIST)