CAREER: Aerial and Aquatic Flapping Flight at Low Reynolds Numbers

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The flapping of wings is a common locomotion technique for tiny animals in both air and water. Insects flap their wings to fly in air, and zooplanktonic marine snails called sea butterflies flap wing-like appendages (called parapodia) to "fly" in water. Further, some tiny insect species are able to locomote via wing flapping in both air and water. Despite the thousand-fold difference in density between air and water, the flight systems of these very different animals show surprising similarities in how the wings move and in how they generate lift. These similarities point towards the possibility of designing a bio-inspired micro-aerial vehicle capable of aerial and aquatic flapping flight, but the fluid dynamics of such flight systems are not well understood. The aim of this project is to investigate the fluid dynamics of small-scale biological flapping systems flying in air, in water, and in both. This research will occur within the larger context of an education program in which underrepresented engineering students prepare for graduate studies by learning research skills, creating an illustrated children's book about sea butterflies, and attending a graduate class field trip.Tiny insects and sea butterflies (pteropods) use similar wing kinematics and lift generation techniques to propel themselves in air and water, respectively. Further, some insects use their wings for both aerial flight and aquatic swimming. However, neither the fluid dynamics of aerial and aquatic flapping locomotion at low Reynolds numbers nor the adaptations these animals have made to fly in air, water, or both are well understood. This project will experimentally investigate these adaptations and the underlying fluid physics of flapping flight in air, water, and both by a diverse group of insects and pteropod species, with the following outcomes: 1) High speed kinematics and volumetric flow measurements of swimming pteropods will show how extreme wing flexibility affects lift production. 2) A novel, ultra-high-speed particle image velocimetry system will provide measurements of the 3D kinematics used by and the flow generated by freely flying tiny insects. 3) Kinematics and flow measurements of the swimming and flying of tiny aquatic insects will reveal how an aerial flight system can be adapted to aquatic operation. These outcomes will illuminate the core fluid dynamics principles underlying this locomotion technique, build understanding of the adaptations animals have made for flapping locomotion in air and water, and inspire design strategies for multimodal micro-aerial vehicles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.