TYTELL, Eric D.; Harvard University: Linking wake structure, kinematics, and mechanics for oscillatory propulsion

Many studies have examined either the kinematics or the hydrodynamics of fish swimming, but few have looked at both simultaneously. By directly observing the wakes that result from different kinematics, a more detailed description of the underlying mechanism may be produced. With high speed video and simultaneous digital particle image velocimetry (DPIV), the changes in both kinematics and wake structure over a range of speeds and for different swimming modes can be evaluated. For example, carangiform swimmers, which generally have a long body wavelength and a pronounced narrow caudal peduncle, produce a series of linked vortex rings with jets inclined to the swimming direction. In contrast, anguilliform swimmers, which usually have shorter body wavelengths and much less of a caudal peduncle, produce a more complex wake structure, primarily consisting of jets aligned at right angles to the swimming direction. While these two modes have clearly different kinematics and wake structures, without simultaneous measurements of both, it is unclear what these differences suggest about the underlying mechanism. In particular, the relative efficiency, power consumption, and cost of transport of the modes is poorly understood. To begin to examine how these performance parameters relate to swimming kinematics, the changes in these values are estimated from the wake structure over a range of swimming speeds and compared to the changes in kinematics. Additionally, using theoretical and physical models, the same values are estimated based on kinematics alone, and can be used to evaluate the accuracy of the wake measurements and the validity of the models.