Shear-driven swimming in laminar flow inspired by tank treading

To study the feasibility of shear-stress-driven locomotion in the Reynolds number range of ⁡(10–102), we propose an aquatic swimming system characterized by an elongated barrel-shaped body with both ends open. The side wall of the body is enwraped within a flexible membrane, which circulates around the body similar to the tank treading motion of vesicles or erythrocytes (red blood cells). During the circulation, the membrane on the outer side of the barrel and the one on the inner side travel at opposite directions (one downstream and the other upstream), generating a net thrust force due to the inner-side versus outer-side asymmetry of the design. The performance of this system has been investigated numerically by using an immersed-boundary model. The results show that this device is able to achieve forward speeds that are comparable to the circulation speed of the membrane. Further study indicates that within the targeted Reynolds number range, when the membrane circulation speed is given the swimming speed is not sensitive to the Reynolds number, although it does depend on the diameter-to-length ratio of the body.