Low Reynolds number swimming of helical structures in circular channels

Rotating helical structures are very effective in low Reynolds number swimming and propulsion. Helical rods are extensively studied theoretically and computationally with asymptotical methods, but the effects of the geometric variables in full-scale and the performance of other helical structures, such as ribbons and Archimedean screws, are also important for the understanding of swimming in confinements and design of micro swimming robots. In this study, a CFD model is developed to study swimming of helical rods, ribbons, screws and filaments, in circular channels under constant angular velocity or constant external torque. Effects of geometric parameters and the confinement radius on the swimming velocity and efficiency are demonstrated. Wavelength and amplitude of the helical wave, filament radius, thickness and width of ribbons, and eccentricity of tails are studied. Swimming performance of magnetically coated ribbons is compared with the ribbons with magnetic heads. Theoretical results in literature are used to validate the CFD results and to identify the role of hydrodynamic interactions between helical body and the channel wall.