Vortex Shedding Frequency Over Seal Whisker-Inspired Geometries of Varying Wavelength

The introduction of surface undulations to smooth bluff body geometry has important effects on flow. In particular, undulated cylinder geometry inspired by seal whiskers has been shown to alter shedding frequency and reduce fluid forces significantly compared to a smooth cylinder. In this work a rigid computational whisker model is used to systematically investigate the effects of varied undulation wavelength on unsteady lift force and shedding frequency. Prior research has parametrized the whisker-inspired geometry and demonstrated the relevance of geometric features on force reduction properties, but an analysis of the effects of wavelength variation alone has yet to be performed. A set of five whisker-inspired models at varying wavelengths are simulated at Reynolds number 250 and compared to a hydrodynamically equivalent elliptical cylinder. It is shown that nondimensional wavelength values of 3 and above result in reduced frequency and amplitude of vortex shedding and a reduction of oscillating lift force. Examining the flow physics as a function of span, the overall shedding frequency results from specific vortex structures that produce distinct local shedding modes with a dependence on undulation wavelength. The interaction of these modes produces a sophisticated lift frequency spectrum at wavelength values corresponding with maximum reduction in forces.