Wake-Induced Vibration of a flexible plate behind a cylinder: Effect of structural parameters

Abstract

The present Fluid flexible Structure Interaction (FfSI) study is on free-stream flow across a circular cylinder, with a detached flexible-plate that undergoes Wake-Induced Vibration. Effect of non-dimensional bending stiffness Kb0.01–0.521, and plate-fluid density ratio ρ∗10–500 is investigated numerically, for structural properties as well as cylinder–plate proximity induced coupled flow physics and vibrational characteristics of the plate. The study is performed at a Poisson’s ratio νs=0.4, Reynolds number Re=100, non-dimensional cylinder–plate gap G∗=1.5, and a constant size of the plate (non-dimensional length L∗=1 and thickness t∗=0.05). For most of the present simulated cases, the plate undergoes symmetric first-mode vibrations, for which three FfSI regimes are proposed. Regime-I corresponds to anti-phase ϕ≈180° periodic variation between the displacement Y of the plate-tip and lift coefficient CL,p, while Regime-III corresponds to in-phase ϕ≈0° variation, and Regime-II corresponds to a transition in the phase difference from anti-phase to in-phase with increasing Kb. For the transitional FfSI Regime-II, obtained at low and intermediate values of both ρ∗ and Kb, a larger plate-amplitude A∗ along with an oscillation frequency ratio f∗ close to lock-in (f∗=1) is found. Whereas Regime-I, obtained at intermediate ρ∗ for low Kb and high ρ∗ for all Kb, corresponds to low and intermediate amplitude A∗ and high or super-harmonic f∗; and Regime-III, obtained at low and intermediate ρ∗ for high Kb, corresponds to low A∗ and low or sub-harmonic f∗. Type of interaction between the cylinder-vortex and plate-vortex, in the near wake, is constructive for the Regime-II and destructive for the other regimes. The fluid-dynamic force-based damping is presented as positive in the Regime-I and negative in the other regimes. The qualitative vortex interaction-dynamics and the flow-induced damping show a strong correlation with quantitative vibrational parameters, indicating strongly coupled multi-physics characteristics of the present FfSI system.