Experimental study of oscillating plates in viscous fluids: Qualitative and quantitative analysis of the flow physics and hydrodynamic forces

Abstract

In this paper, we present a comprehensive experimental study on harmonic oscillations of a submerged rigid plate in a quiescent, incompressible, Newtonian, viscous fluid. The fluid-structure interaction problem is analyzed from both qualitative and quantitative perspectives via a detailed particle image velocimetry (PIV) experimental campaign conducted over a broad range of oscillation frequency and amplitude parameters. Our primary goal is to identify the effect of the oscillation characteristics on the mechanisms of fluid-structure interaction and on the dynamics of vortex shedding and convection and to elucidate the behavior of hydrodynamic forces on the oscillating structure. Towards this goal, we study the flow in terms of qualitative aspects of its pathlines, vortex shedding, and symmetry breaking phenomena and identify distinct hydrodynamic regimes in the vicinity of the oscillating structure. Based on these experimental observations, we produce a novel phase diagram detailing the occurrence of distinct hydrodynamic regimes as a function of relevant governing nondimensional parameters. We further study the hydrodynamic forces associated with each regime using both PIV and direct force measurement via a load cell. Our quantitative results on experimental estimation of hydrodynamic forces show good agreement against predictions from the literature, where numerical and semi-analytical models are available. The findings and observations in this work shed light on the relationship between flow physics, vortex shedding, and convection mechanisms and the hydrodynamic forces acting on a rigid oscillating plate and, as such, have relevance to various engineering applications, including energy harvesting devices, biomimetic robotic system, and micro-mechanical sensors and actuators.

Wake vortex regimes of a pitching cantilever plate in quiescent air and their correlation with mean flow generation

“…The fluid motion along the length of the cantilever is essentially just upward or downward, and the velocity component in the forward direction is negligible. This is somewhat reminiscent of the flow regime observed by Shrestha et al [32], where isolated attached vortices are observed at low amplitudes and frequencies with no significant convection on the lateral side of a vibrating cantilever. We previously observed poor performance of piezoelectric fans operating in this regime [46].…”

“…More specifically, they observed that the transition from von Kármán to reverse von Kármán in a non-zero freestream velocity medium around a pitching airfoil takes place at a constant tip characteristic velocity Af for a fixed cord length. Shrestha et al [32] reported a critical value of Rec ~ 21 for the transition from the symmetric to asymmetric vortex regime for the lateral vortex generation of a submerged flat cantilever plate in water. In many applications, such as cooling enhancement using piezoelectric fans, the average flow generation in the streamwise direction due to the cantilever vibrations is of great interest.…”

“…Shrestha et al [32] proposed a 2D vortex regime map for a vibrating cantilever plate in the dimensionless frequency and amplitude domain. This past study was, however, concerned with flows generated from the lateral sides of a vibrating cantilever plate, as opposed to the downstream of its trailing edge, because the primary focus of the study was the relation between aerodynamic drag forces and observed vortex patterns.…”

Evaluation of drag and added mass forces acting on vibrating cantilever beams in the air

“…That allows to use a simplified quasi-two dimensional model of interaction between a beam and a gas, according to which the aerodynamic forces acting on each cross-section of the beam can be considered as a result of the planar flow past a section. This model is widely used in many studies [3,[6][7][8][9][10][11].…”

Three-dimensional characteristics of the jet flows induced by a pitching plate in a quiescent fluid

“…Eastman, Kiefer & Kimber (2012) studied thrust force generation by vibrating cantilever plates and proposed a correlation between the thrust and the vibration amplitude and frequency. Shrestha, Ahsan & Aureli (2018) studied the lateral vortex shedding in a pitching plate with a fixed geometry using particle image velocimetry (PIV) visualizations and proposed a 2-D vortex regime map to describe the observed patterns. These patterns were correlated with aerodynamic drag forces on the plate.…”