A computational study of the aerodynamics and forewing-hindwing interaction of a model dragonfly in forward flight

Abstract

SUMMARY The aerodynamics and forewing-hindwing interaction of a model dragonfly in forward flight are studied, using the method of numerically solving the Navier-Stokes equations. Available morphological and stroke-kinematic parameters of dragonfly (Aeshna juncea) are used for the model dragonfly. Six advance ratios (J; ranging from 0 to 0.75) and, at each J, four forewing-hindwing phase angle differences(γd; 180°, 90°, 60° and 0°) are considered. The mean vertical force and thrust are made to balance the weight and body-drag, respectively, by adjusting the angles of attack of the wings, so that the flight could better approximate the real flight. At hovering and low J (J=0, 0.15), the model dragonfly uses separated flows or leading-edge vortices (LEV) on both the fore- and hindwing downstrokes; at medium J (J=0.30, 0.45), it uses the LEV on the forewing downstroke and attached flow on the hindwing downstroke; at high J (J=0.6, 0.75), it uses attached flows on both fore- and hindwing downstrokes. (The upstrokes are very lightly loaded and, in general, the flows are attached.) At a given J, at γd=180°, there are two vertical force peaks in a cycle, one in the first half of the cycle, produced mainly by the hindwing downstroke, and the other in the second half of the cycle, produced mainly by the forewing downstroke; atγ d=90°, 60° and 0°, the two force peaks merge into one peak. The vertical force is close to the resultant aerodynamic force[because the thrust (or body-drag) is much smaller than vertical force (or the weight)]. 55-65% of the vertical force is contributed by the drag of the wings. The forewing-hindwing interaction is detrimental to the vertical force (and resultant force) generation. At hovering, the interaction reduces the mean vertical force (and resultant force) by 8-15%, compared with that without interaction; as J increases, the reduction generally decreases (e.g. at J=0.6 and γd=90°, it becomes 1.6%). A possible reason for the detrimental interaction is as follows: each of the wings produces a mean vertical force coefficient close to half that needed for weight support, and a downward flow is generated in producing the vertical force; thus, in general, a wing moves in the downwash-velocity field induced by the other wing, reducing its aerodynamic forces.

Three-dimensional flow structures and evolution of the leading-edge vortices on a flapping wing

“…In fast forward flight, the structure of the LEV system could also be changed: the flows would become more attached to the wing as the increase of the flight speed (or advanced ratio) (Sun and Wu, 2003;Wang and Sun, 2005).…”

Deformable Overset Grid for Multibody Unsteady Flow Simulation

“…12(b), are set up the same as the forward flight case (advance ratio J=0. 3) presented in Wang and Sun [37] with the hind-wing leading the forewing in a phase of 180 o . Two kinematics of the motion were simulated: one is for rigid wings; the other is for flexible wings with camber deformation according to the data measured by Wang and Zeng [38].…”

“…15(b). The vertical forces computed by Wang and Sun [37] for rigid wings are also presented for comparison.…”

Implicit Virtual Boundary Method for Moving Boundary Problems on Non-Staggered Cartesian Patch Grids

“…In this branch of numerical methods, the grid system should be re-meshed at each time step and thus large CPU time is generally needed [1]. To improve the computational efficiency, the method of moving overset grids [2][3][4] generates a local non-inertial boundary-fitted grid system for each moving object that is allowed to move on the fixed global Cartesian grid system. However, the solution interpolation and data transfer among the grid systems are very complex and time consuming.…”