Navigation in odor plumes: How do the flapping kinematics modulate the odor landscape?

Insects rely on their olfactory system to forage, prey, and mate. They can sense odor emitted from sources of their interest, use their highly efficient flapping-wing mechanism to follow odor trails, and track down odor sources. During such an odor-guided navigation, flapping wings not only serve as propulsors for generating lift and maneuvering, but also actively draw odors to the antennae via wing-induced flow. This helps enhance olfactory detection by mimicking “sniffing” in mammals. However, due to a lack of quantitative measuring tools and empirical evidence, we have a poor understanding of how the induced flow generated by flapping kinematics affects the odor landscape. In the current study, we designed a canonical simulation to investigate the impact of flapping motion on the odor plume structures. A sphere was placed in the upstream and releases odor at the Schmidt number of 0.71 and Reynolds number of 200. In the downstream, an ellipsoidal airfoil underwent a pitch-plunge motion. Both two- and three-dimensional cases are simulated with Strouhal number of 0.9. An in-house immersed-boundary-method-based CFD solver was applied to investigate the effects of flapping locomotion on the wake topology and odor distribution. From our simulation results, remarkable resemblances were observed between the wake topology and odor landscape. For the 2D case, an inverse von Kármán vortex street was formed in the downstream. For the 3D case, the wake bifurcates and forms two branches of horseshoe-like vortices. The results revealed in this study have the potential to advance our understanding of the odor-tracking capability of insects navigation and lead to transformative advancements in unmanned aerial devices that will have the potential to greatly impact national security equipment and industrial applications for chemical disaster, drug trafficking detection, and GPS-denied indoor environment.