Vortex formation by a vibrating cantilever

Abstract

This paper presents a comparative investigation between numerical flow simulations and the experimental data of a vibrating cantilever. The unsteady flow fields were observed with smoke visualization, and the unsteady velocities were measured by high-resolution PIV (particle image velocimetry). Although the experimental results provide an intuitive understanding about the vortex formation from the vibrating cantilever, it is difficult to determine the underlying mechanism of vortex generation due to the limitation of temporal and spatial resolution. Numerical simulations were conducted using commercial code with a user-defined function describing the cantilever movement. The comparison between the experiment and simulation mainly covers velocity fields, vorticity distributions and the vortex location as well as the vortex size during one cycle. Qualitatively, velocity and vorticity distributions match well between the experiment and the simulation. The size and axial location (with respect to the cantilever tip) of the vortices are also in good agreement with the experimental data. Once validated, numerical simulations provide access to the whole flow field including pressure data. The flow has been evaluated in detail to understand vortex generation at the cantilever. It was found that the static pressure difference across the tip plays an important role in the formation and development of each individual vortex. In addition, it was possible to find the exact moment of vortex initiation using the static pressure difference across the cantilever tip.