Role of appendage bending in metachronal paddling

Numerous species of aquatic invertebrates use metachronal paddling as their primary locomotion strategy. These invertebrates have widely varying body and appendage morphologies, ranging from soft-bodied organisms such as ctenophores that swim by beating many flexible cilia, to hard-bodied crustaceans that swim by oscillating pairs of jointed legs. We investigated how changing the bending angle and the time period needed to fully bend or straighten each paddle affect wake vorticity and momentum fluxes at realistic stroke frequencies and at paddle-based Reynolds numbers ranging from 0.1 to 1,000. A two-dimensional immersed boundary formulation (IB2D) was used to model the metachronal motion of flat plate paddles that each have a hinged joint approximately halfway along the length. We found that paddles that unbend quicker and have a smaller bending angle generate a more vertical wake, which can be useful for supporting the weight of negatively buoyant organisms. Comparisons between paddling and squirming strategies at different Reynolds numbers will also be presented.