Volumetric Lagrangian Particle Tracking, Air water interface, insect locomotion, surface tension

Abstract

Over a thousand animal species are capable of walking on the interface between air and water. These speciesinclude water striders, a family of insects from the order Hemiptera that has an almost unique ability to walk on the surface of the water without penetrating it. They achieve this outstanding feat by making use of the surface tension and their long hydrophobic legs. Experiments have revealed that water striders transfer some momentum to the underlying fluid through capillary waves and hemi-spherical vortices and that both waves and vortices contribute to the mechanism of propulsion. However, the exact momentum and energy carried by waves and vortices have never been quantified together, and only the energy of the surface waves has been quantified to date. An analysis of the complete energy balance between the interface and the body of the water requires measurement of the free surface topography, together with the three-dimensional (3D) flow field in the water under the surface. The ultimate aim of this work was to develop a method capable of doing this.