Aerodynamic interaction of collective plates in side-by-side arrangement

In tip-reversal upstrokes of bird flight, primary feathers twist individually and make gaps between them. Although this behavior was reported to allow individual feathers to function as individual airfoils, lift contribution of each feather and interaction of flow between feathers with a gap still remain unclear. To elucidate aerodynamic characteristics of each feather in tip-reversal upstrokes, we conduct numerical simulation at Reynolds numbers 100 and 1000. We model feathers as collective plates. The angle of attack of the collective plates is fixed at 90°, and the gap distance and the angle of attack of each plate are varied. Lift of the plates generally increases from the bottom plate to the top one. In some specific cases, lift coefficient and lift-to-drag ratio of the collective plates are higher than those of a single plate. These cases also exhibit low unsteadiness of the flow and low fluctuation of the lift. The model of our study may be able to be applied to micro air vehicle in that collective plates can have the better aerodynamic performance than that of a single plate. In addition, this study can give insights into understanding the principles of active flow control using multi-body system for the purpose of enhancing maneuverability.