Observations of flow structure changes with aspect ratio for rotating insect wing Planforms

The effect of wing aspect ratio for flapping and rotating wings in insect-like flight regimes is not well understood. In this study the effect of aspect ratio on the vortex structures formed over altered fly wings has been investigated. A numerical model was employed to simulate the flow over these wings which were rotating at a constant angular velocity. It was found that increasing the wing aspect ratio resulted in the formation of a dual co-rotating vortex structure near the leading-edge of the wing and the strengthening of the spanwise velocity within the core of the downstream vortex. Increasing the wing aspect ratio also resulted in an unsteady region of flow being developed out near the wing tip in which vortex structures are shed from the wing. The formation of this region was found to be due to the interaction of the leading-edge vortex with the vorticity at the trailing edge and not due to leading-edge vortex shedding as the dual leading-edge vortex structure was found to remain attached to the wing for all aspect ratios. This interaction did result in the reduction of the lift and drag coefficients for high aspect ratios.