ABSTRACTAquatic animals propel themselves using a wide variety of mechanisms. In manta rays, propulsion is achieved by combining oscillating and undulatory motions of flexible surfaces. We are interested in studying the unsteady hydrodynamics of such motions to understand and model the wake structure. Experiments have been conducted on flapping flexible membranes, flapping rigid plates, and mechanical models of manta rays. Our observations suggest a rich set of phenomena exist, depending on the non-dimensional frequency of flapping, the wavelength of the excitation, and the aspect ratio of the fin. The efficiency depends on a delicate balance among the actuation frequency, the structural resonance, and the wake resonance. In addition, the waveform of actuation can be crucial: pitching combined with heaving can be twice as efficient as pitching alone.

BIOGRAPHYDr. Smits is the Eugene Higgins Professor of Mechanical and Aerospace Engineering at Princeton, as well as a Professorial Fellow at Monash University in Australia. His research interests are centered on fundamental, experimental research in turbulence and fluid mechanics. In 2004, Dr. Smits received the Fluid Dynamics Award of the American Institute of Aeronautics and Astronautics (AIAA). In 2007, he received the Fluids Engineering Award from the American Society of Mechanical Engineers (ASME), the Pendray Aerospace Literature Award from the AIAA, and the President's Award for Distinguished Teaching from Princeton University. In 2014, he received the Aerodynamic Measurement Technology Award from the AIAA. He is a Fellow of the American Physical Society, the American Institute of Aeronautics and Astronautics, the American Society of Mechanical Engineers, the American Academy for the Advancement of Science, the Australasian Fluid Mechanics Society, and he is a Member of the National Academy of Engineering. He is currently the Editor-in-Chief of the AIAA Journal.