Thrust generation by the coordinated suction and blowing of a cylinder array

Some animals, such as cephalopods, periodically expand and contract their highly flexible bodies to intake and eject surrounding fluid for propulsion. Motivated by such flexible bodies effective in suction and blowing of the fluid, we simplify the continuous deformation of the flexible body by segmenting it into multiple moving bodies in order to examine how the coordinated oscillating motions of the segmented bodies induce suction and blowing and generate propulsive force. In this study, several rigid circular cylinders are positioned in a circle with equal distance between adjacent cylinders. If the cylinders oscillate in a radial direction with the same amplitude and frequency, suction and blowing flows occur uniformly at every exit. However, slight variation in the phases of the cylinders can induce directional flow, generating net thrust on the entire structure. Kinematic parameters for the coordinated motion of the cylinder array, oscillation amplitude, frequency, and phase difference between the cylinders, are numerically investigated to find the optimal condition for the maximum thrust.