We extended our work on rigid airfoils and discovered that flexible panels also produce more thrust near a solid boundary. This time, we checked swimming speed directly and confirmed that flexible propulsors can swim faster near the ground. The enhancement is especially pronounced if the panel is operated at resonance. Flexible fish and fish-inspired vehicles can therefore swim faster near a solid boundary (e.g. substrate, sidewalls, ship hulls). (This work is from PI Quinn’s research prior to the SFS Lab and is archived here for reference.)
Authors: Daniel Quinn, George Lauder, Alexander Smits
Abstract: We present experimental evidence for the hydrodynamic benefits of swimming ‘in ground effect’, that is, near a solid boundary. This situation is common to fish that swim near the substrate, especially those that are dorsoventrally compressed, such as batoids and flatfishes. To investigate flexible propulsors in ground effect, we conduct force measurements and particle image velocimetry on flexible rectangular panels actuated at their leading edge near the wall of a water channel. For a given actuation mode, the panels swim faster near the channel wall while maintaining the same propulsive economy. In conditions producing net thrust, panels produce more thrust near the ground. When operating in resonance, swimming near the ground can also increase propulsive efficiency. Finally, the ground can act to suppress three-dimensional modes, thereby increasing thrust and propulsive efficiency. The planform considered here is non-biological, but the hydrodynamic benefits are likely to apply to more complex geometries, especially those where broad flexible propulsors are involved such as fish bodies and fins. Such fish could produce more thrust by swimming near the ground, and in some cases do so more efficiently.