THE 3-DIMENSIONAL HYDRODYNAMICS OF TADPOLE LOCOMOTION

Tadpoles are unusual among vertebrates in having a globose body with a laterally compressed tail abruptly appended to it, Compared with most teleost fishes, tadpoles swim awkwardly, with waves of relatively hig h amplitude at both the snout and tail tip, In the present study, we a nalyze tadpole propulsion using a three-dimensional (3D) computational fluid dynamic (CFD) model of undulatory locomotion that simulates vis cous and unsteady flow around an oscillating body of arbitrary 3D geom etry, We first confirm results from a previous two-dimensional (2D) st udy, which suggested that the characteristic shape of tadpoles was clo sely matched to their unusual kinematics, Specifically, our 3D results reveal that the shape and kinematics of tadpoles collectively produce a small 'dead water' zone between the head-body and tail during swimm ing precisely where tadpoles can and do grow hind limbs - without thos e limbs obstructing flow, We next use our CFD model to show that 3D hy drodynamic effects (cross flows) are largely constrained to a small re gion along the edge of the tail fin, Although this 3D study confirms m ost of the results of the 2D study, it shows that propulsive (Froude) efficiency for tadpoles is overall lower than predicted from a 2D anal ysis, This low efficiency is not, however, a result of the high-amplit ude undulations of the tadpole, This was demonstrated by forcing our ' virtual' tadpole to swim with fish-like kinematics, i.e. with lower-am plitude propulsive waves, That particular simulation yielded a much lo wer Froude efficiency, confirming that the large-amplitude lateral osc illations of the tadpole do, indeed, provide positive thrust, This, we believe, is the first time that the unsteady flow an undulating verte brate has been modelled in three dimensions, Our study demonstrates th e feasibility of using 3D CFD methods to model the locomotion of other undulatory organisms.