Aerodynamic forces and flows of the full and partial clap-fling motions in insects

Abstract

Most of the previous studies on Weis-Fogh clap-fling mechanism have focused on the vortex structures and velocity fields. Detailed pressure distribution results are provided for the first time in this study to reveal the differences between the full and the partial clap-fling motions. The two motions are studied by numerically solving the Navier–Stokes equations in moving overset grids. The Reynolds number is set to 20, relevant to the tiny flying insects. The following has been shown: (1) During the clap phase, the wings clap together and create a high pressure region in the closing gap between wings, greatly increasing the positive pressure on the lower surface of wing, while pressure on the upper surface is almost unchanged by the interaction; during the fling phase, the wings fling apart and create a low pressure region in the opening gap between wings, greatly increasing the suction pressure on the upper surface of wing, while pressure on the lower surface is almost unchanged by the interaction; (2) The interference effect between wings is most severe at the end of clap phase and the start of the fling phase: two sharp force peaks (8–9 times larger than that of the one-winged case) are generated. But the total force peaks are manifested mostly as drag and barely as lift of the wing, owing to the vertical orientation of the wing section; (3) The wing–wing interaction effect in the partial clap-fling case is much weaker than that in the full clap-fling case, avoiding the generation of huge drag. Compared with a single wing flapping with the same motion, mean lift in the partial case is enhanced by 12% without suffering any efficiency degradation, indicating that partial clap-fling is a more practical choice for tiny insects to employ.

Effect of clap-and-fling mechanism on force generation in flapping wing micro aerial vehicles

“…This aerodynamic force is upward if it is a trailing edge momentum jet, and is downward if it is a leading edge momentum jet. It was observed in some numerical studies that the presence of a trailing edge momentum jet need not necessarily imply enhancement in lift at that instant (Kolomenskiy et al 2011, Cheng and Sun 2017). The trailing edge momentum jet in these studies was also accompanied by a simultaneous leading edge momentum jet, as seen from the velocity plots.…”

Vortex trapping recaptures energy in flying fruit flies

“…1 d). The flexing motion of the wing chord accordingly reduces the elevated drag on the wing that results from both the viscous forces between the wing surfaces and wing acceleration during wing separation 30 , 31 . Figure 1 d shows that wing rotation occurs symmetrical in fruit flies with respect to the up- and downstroke, producing elevated lift for weight support compared to a delayed rotation 4 .…”

Flow visualization and force measurement of the clapping effect in bio-inspired flying robots

“…These results point to the important role played by closing gap at the end of clapping, which has not been duly studied in the literature using flexible wings (perhaps Cheng and Sun [42] is the most relevant effort that gave some attention to this study). Other research efforts have studied the effect of the gap at the end of the stroke, but did not find a major increase in the vertical force during those moments [45][46][47].…”

“…He realized that the majority have the same lift generation during takeoff except for the ones that exploit clap-and-fling, which created about 25% more lift. Later, Cheng and Sun [42] performed a comparative study between full clap and partial clap by numerically solving the Navier-Stokes equations. Based on their analysis of the pressure distribution over the wings, it was concluded that partial clap motion is more practical for insects.…”