Finite Amplitude Oscillations of Flanged Laminas in Viscous Flows: Vortex-structure Interactions for Hydrodynamic Damping Control

Abstract

In this thesis, we study the problem of a submerged flanged lamina undergoing harmonic oscillations in a quiescent, Newtonian, viscous fluid. This problem is of potential applicative relevance to a variety of research fields, such as atomic force microscopy, sensors and actuators based on micromechanical oscillators, biomimetic robotic propulsion, and microscale energy harvesting.We conduct a thorough computational fluid dynamics (CFD) simulation campaign with the goal of studying the fluid-structure interaction mechanisms resulting in added mass and hydrodynamic damping on the oscillating solid, with primary focus on evaluating the complex hydrodynamic function incorporating these effects via its real and imaginary parts, respectively. In this study, three nondimensional parameters are found to govern the flow evolution, that is, a nondimensional frequency parameter, a nondimensional amplitude of oscillation parameter, and a geometric parameter describing the flange to lamina width ratio. In particular, we determine that the addition of flanges results into complex and intriguing relations between hydrodynamic forcing, lamina geometry, and dynamic oscillation conditions.We investigate in detail the flow physics and the effects of nonlinearities on vortex shedding, convection, and diffusion in the vicinity of the oscillating structure. We find that the added mass effect is affected by the presence of the flanges, which results into larger fluid entrainment during the lamina oscillation. In addition, the hydrodynamic damping effects is remarkably affected by the interplay of geometric and dynamic parameters. We find the existence of a minimum in the hydrodynamic damping which can be attained by specific control of vortex-structure interaction dynamics. This peculiar interaction can be understood and discussed from physical grounds by inspection of the pertinent vorticity fields.