Effects of aspect ratio on the three-dimensional metachronal paddling wake

Drag-based paddling strategies are widely employed by aquatic invertebrates as a primary means of locomotion. Metachronal and metachronal-hybrid paddling strategies used by crustaceans involve the coordinated, phase-delayed stroking of a finite number of discrete appendages. Among these crustaceans there is a huge range of body and appendage morphologies. However, previous studies of the metachronal paddling strategy have primarily focused on the effects of varying paddle kinematics or spacing between adjacent paddles on the 2D wake by using idealized body and paddle shapes. We examined published images of the swimming legs of copepods (small crustaceans known for their rapid acceleration) and determined that the range of aspect ratios of the swimming legs (AR = paddle length / paddle width) of most copepods fall in the range 1<=AR<=4. We developed a robotic paddling model which was fitted with paddles of varying AR in order to determine the effects of paddle shape on propulsive forces and the paddle wake. The 3D structure of the paddle-tip vortices was quantified using 3D particle tracking velocimetry (shake-the-box). Forces, tip-vortex circulation, and 3D flow visualization will be presented.