Numerical investigation of wake dynamics of tail-first "wriggling" swimmers

Natural invertebrate swimmers, such as mosquito larvae, move tail-first, which is unique among animals. In this study, the relationship between kinematics, stiffness of the body, and the resulting fluid-structure interaction (FSI) on swimming dynamics is investigated using a computational model consisting of a flexible body attached to a rigid head. The body stiffness and angular oscillation amplitude of the head were varied systematically, while the flow profile and forces were analyzed using an in-house two-way coupled IBM-based FSI solver. We found that the combination of the low bending rigidity of the body and small amplitude oscillation of the head resulted in anguilliform motion matching previous observations in the literature. However, for cases where bending rigidity of the body was low and pitching amplitude of the head was high, successive vortices are produced, first to one side and then to the other of the mean swimming path. The vortices convected anteriorly (from tail to head), exerting a net downward force. As a result, the net swimming direction of a body was backward, and the resulting kinematics mimicked the wriggling motion profile of mosquito larvae. The findings of this study corroborate the observations and measurements of natural aquatic swimmers.