Abstract
In nature, flying organisms change the flow field around their wings and produce fluid force by their flapping motion. This enables them to rapidly accelerate, turn, and hover. Therefore, the flow field around the flying organism's wing and the fluid force are of significant academic interest. In this research, we clarified the vortex ring generated over a butterfly wing in a downward and upward flapping motion using PIV measurement. We also estimated the dynamic lift from the circulation of the vortex ring generated over the butterfly wing. After that, we measured the dynamic lift using a sensor to verify the estimation result. The estimated and measured results for the dynamic lift are almost the same in the downward flapping motion. However, the estimated dynamic lift does not correspond to the measured dynamic lift. The reason is that we evaluated the vortex ring over the butterfly wing but did not evaluate the vortex ring generated in the wake field of the butterfly. Therefore, we then estimated the dynamic lift using the vortex ring over the butterfly wing and in the wake field of the butterfly, and we were able to show that the estimated dynamic lift corresponds to the measured dynamic lift.
