Characterization of seal whisker morphology: implications for whisker-inspired flow control applications.

Seals with beaded whiskers-the majority of true seals (Phocids)-are able to trace even minute disturbance caused by prey fish in the ambient flow using only sensory input from their whiskers. The unique three-dimensional undulating morphology of seal whiskers has been associated with their capability of suppressing vortex-induced vibration and reducing drag. The exceptional hydrodynamic traits of seal whiskers are of great interest in renovating the design of aero-propulsion flow components and high-sensitivity flow sensors. It is essential to have well-documented data of seal whisker morphology with statistically meaningful generalization, as the solid foundation for whisker-inspired flow control applications. However, the available whisker morphology data is either incomplete, with measurements of only a few key parameters, or based on a very limited sample size in case studies. This work characterizes the morphology of 27 beaded seal whiskers (harbor seal and elephant seal), using high-resolution computer-tomography scanning at NASA's Glenn Research Center in Cleveland, OH. Over two thousand cross-sectional slices for every individual whisker sample are reconstructed, to generate three-dimensional morphology. This is followed by detailed statistical analysis of a set of key parameters, under an established framework (Hanke et al 2010 J. Exp. Biol. 213 2665-72). While the length parameters are generally consistent with previous studies, we note that the angle of incidence of elliptical cross-sections varies in a wide range, with a majority falling between [Formula: see text] and [Formula: see text]. Angles of incidence at both peaks and troughs appear to roughly follow a Gaussian distribution, but no clear preference of orientation is identified. We discuss the current knowledge of whisker-inspired flow studies, focusing on choices of morphology parameters. The new understanding of whisker morphology can better inform future design of high-sensitivity flow sensors and aero-propulsion flow structures.