Turbulence intensity effect on the axial-flow-induced vibration of an elastic cylinder

Abstract

A study is performed numerically to understand the effect of incident turbulence intensity Tu (0%–10%) on flow-induced vibration of an isolated elastic cylinder subjected to an axial tubular flow. The cylinder fix-supported at both ends is free to vibrate laterally. Large eddy simulation and the two-way coupled CFD-CSM calculation are employed to capture the characteristics of turbulent flow and fluid–structure interaction, respectively. The calculated root-mean-square (rms) vibration amplitude of the cylinder agrees reasonably well with experimental data at Tu=0.3%, thus providing a validation for the present numerical code. The dimensionless velocity u∗≡U∞L(ρfAc/EI)1∕2 is in the range of 1.52 – 9.67, where U∞, ρf, L, Ac and EI are the free-stream velocity, fluid density, length and cross-sectional area of the cylinder and the corresponding flexural rigidity, respectively. The Tu is found to produce a pronounced effect on dynamics of the cylinder at u∗≤ 9.67. At u∗=3.30, the vibration amplitude of the cylinder significantly increases with increasing Tu from 0 to 10%. Under the same Tu range, the onset of cylinder buckling does not depend on Tu, though the onset of flutter does. The cylinder buckles at u∗=7.92 and Tu = 0% and further undergoes flutter instability as Tu increases to 1.0%. It is proposed that interactions between the buckled cylinder and the higher-intensity turbulence amplifies the shear layer instability around the cylinder, forming uniform-low-pressure and nonuniform-high-pressure regions around the cylinder. These regions quasi-periodically reposition, thus generating unsteady lateral forces that are responsible for the flutter instability at Tu=1.0%. It is found that dimensionless rms vibration amplitude Arms∗ (= [(Axrms/D)2 + (Ayrms/D)2]1∕2, where D and the first letter of the subscript denote cylinder diameter and vibration direction, respectively) in flutter scales linearly with the effective velocity ueff∗=u∗TF, where turbulence factor TF is introduced to account for the effect of Tu.