Vortex-induced vibrations of elastically mounted bluff bodies in response to unsteady vortex wake flows

We report on experiments designed to characterize the vortex induced vibration (VIV) experienced by bluff bodies immersed in both steady and unsteady flows. Using a real-time Cyber-Physical System (CPS) we are able to systematically prescribe the virtual mass, spring constant, and damping of elastically mounted models. This allows us to characterize the forces and displacements displayed during the free vibration of a circular cylinder, elliptical cylinder, and a seal whisker inspired vibrissae model with undulating elliptical geometry - known to reduce vortex induced vibrations (Hanke et al., 2010). We confirm extensive previous results, and also find that the onset of a high amplitude VIV occurs at lower reduced velocities as the Reynolds number is reduced. However, for a vibrissae geometry, regardless of Reynolds number, the vibration response is greatly reduced. Further, we characterize the VIV in response to an unsteady flow by generating vortices of different strength and frequency using a pitching and heaving hydrofoil positioned in the upstream flow. Understanding the nonlinear dynamics of these systems provides insight into effective geometries for sensing and vibration control applications.