Publication Detail

The boundary layer instability of a gliding fish helps rather than prevents object identification

Audrey Maertens, Michael Triantafyllou
28 pp.
MITSG 14-29
URL: doi:10.1017/jfm.2014.483

Inspired by the function of the lateral line in aquatic animals, we study the shape identification of a stationary cylinder through pressure measurements made by sensors located on the surface of a steadily moving foil, modelling a fish gliding in close proximity to an object. Comparing experimental results, potential flow predictions and viscous simulations, we first show that the pressure in the boundary layer of the foil is significantly affected by unsteady viscous effects, especially in the posterior half of the foil. Therefore, even after the effects of the boundary layer thickness are accounted for, potential flow predictions are inaccurate. Subsequently, we show that the spatial features of the unsteady patterns developing when the foil is moving near a cylinder can be predicted accurately through linear stability analysis of the average boundary layer velocity profile under open water conditions. Because these unsteady patterns result from amplification of the potential flow-like disturbance caused in the front part of the foil, they are specific to the cylinder that generated them and could be used to identify its shape. We develop and demonstrate a methodology to calculate the unsteady pressure based on combining potential flow predictions with results from linear stability analysis of the boundary layer. The findings can be useful for object identification in underwater vehicles, and support the intriguing possibility that the significant viscous effects caused by nearby bodies on the fish boundary layer, far from preventing detection, could actually be used by animals to identify objects.

type: Journal, book, proceeding reprints

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Parent Project

Project No.: 2013-R/RT-2/RCM-34
Title: Marine Center for Development of Biomimetic Underwater Sensors

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