Flow past tandem vibrissae-inspired undulated cylinders in cross flow*

The undulated vibrissae of harbor seals significantly impact flow physics, enhancing their prey-tracking abilities compared to the smooth vibrissae of California sea lions. These effects include modifications to the wake vortex sheet and reduced vortex-induced vibrations. While previous studies focused on single vibrissae, this research investigates tandem vibrissae using force measurements, particle image velocimetry, and smoke visualizations in a series of wind tunnel experiments. The normalized streamwise separation (L*) between the whiskers was varied from 2 to 5 for subcritical Reynolds numbers (Re = 1.2-2.2 x 10^4), examining two configurations: in-phase and out-of-phase undulations. Results indicate that wake profiles of undulated geometries become decorrelated at shorter streamwise separations (L*) compared to smooth cylinders. Our signal-to-noise analysis of the force spectra identified an optimal separation and phase configuration, providing insights for designing mechanical flow sensors utilizing an array of vibrissae.