A Numerical Study on Three-Dimensional Flapping Dragonfly Wings with Optimized Input Kinematics for hovering and forward flight*

Dragonflies are capable of hover, glide, forward flight, quick turning, etc., with substantial flight times. Previous studies found that dragonfly wings require distinctive input kinematics for different flight modes. For instance, in hovering/forward flight, the wings flap out-of-phase, whereas during quick maneuvers, the wings flap in-phase. In this study, we performed numerical simulation using a dynamic mesh to analyze the wake structure over a pair of tandem dragonfly wings and further optimized their aerodynamic performance with novel flapping kinematics. The wing geometries are based on structural studies. The input kinematics are selected as the mix of pure sinusoidal and periodic Eldredge functions.  The design parameters are taken similar to those of Berman and Wang (2007) and Geherke et al. (2019). Our study found that both wings' combined vertical lift coefficient is 1.56 times more than their individual lift coefficients when summed up. Moreover, the hindwing experiences most of the enhancement in lift resulting from the vortex synergy interaction. It was found the downwash-upwash wake interactions are insignificant in the in-phase flapping, which agrees with the results of Lua et al. (2018). The detailed flow physics will be discussed in the presentation.