| Popis: |
Whiskers in some mammals, such as rats and seals, have a mysterious level of sensing ability. A whisker interacting with the fluid flow can sense minuscule aero/hydrodynamic information and turn this information into an understanding of the environment. Our present work investigates the fluid-structure interaction of a flexible cantilever cylinder, as a canonical model of a whisker, to help understand how a rat or a seal whisker vibrates in response to low-speed air or water flow. We employ a fully-coupled fluid-structure solver based on the three-dimensional Navier-Stokes and structural equations to examine the dynamics of the cylinder. Of particular interest is to explore the possibility of flow-induced vibrations at laminar subcritical Reynolds numbers, where no periodic vortex shedding pattern is present. We show that the flexible cantilever cylinder could undergo sustained oscillations in this Reynolds regime when certain conditions are satisfied. The vibration frequencies are shown to match the cylinder's first- or second-mode natural frequency. The range of the frequency match, known as the lock-in regime, is found to have a strong dependence on the Reynolds number and mass ratio. Unlike the steady wake behind a stationary rigid cylinder, the wake of the flexible cantilever cylinder in the water flow is shown to become unstable at Reynolds numbers as low as 22 for a particular range of system parameters. We find that the cylinder could also experience sustained oscillations when positioned in the wake of a rigid stationary cylinder in a tandem configuration. For the cylinder in airflow, we show that a wavy pattern in the shear layer is the dominant feature of the wake. These findings provide a unified understanding of the flow-induced vibration phenomenon in flexible cantilever cylinders and lay the foundation for designing novel flow-measurement sensors for the next-generation underwater and aerial vehicles. |
