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Vibration of two elastically mounted cylinders in an oscillatory flow at a Keulegan-Carpenter number of 10 is simulated numerically. The two cylinders are rigidly connected with each other and are allowed to vibrate in the cross-flow direction only. The aim of this paper is to identify the effects of the orientation of the cylinders and the gap between the cylinders on the vibration. The two-dimensional Reynolds-Averaged Navier-Stokes equations are solved to predict the flow and the cylinder vibration is predicted using the equation of motion. When the two cylinders are in a tandem arrangement, a combined single pair flow regime and attached pair flow regime are observed as reduced velocity exceeds 10 and this combined regime and the single pair regime occurs intermittently. Periodic vibration is found when the two cylinders are in a staggered arrangement with a 45° flow attack angle. When the two cylinders are in a side-by-side arrangement, a new single vortex regime is observed. This single vortex remains attached to the cylinder surface and rotates around the cylinder. The intermittent switch between this single vortex regime and the single pair regime are observed. [ABSTRACT FROM AUTHOR]

Vortex-induced vibration (VIV) of an elastically mounted rigid circular cylinder in an oscillatory flow is investigated by three-dimensional direct numerical simulations (DNS). The cylinder is allowed to vibrate only in the cross-flow direction. The main aim of the study is to investigate the correlation between the vibration, the lift coefficient, and the vortex shedding flow. The three-dimensional Navier-Stokes equations are solved using the Petrov-Galerkin finite-element method for predicting flow, and the equation of motion is solved for predicting the vibration of the cylinder. Simulations are carried out with a Reynolds number (R) of 500, Keulegan-Carpenter (KC) numbers of 10 and 20, and reduced velocities (Vr) in the range of 2-16. The dominant frequencies of the displacement and lift coefficient synchronize for both KC values when Vr is small. For KC = 10, the frequencies of the vibration and the lift coefficient deviate from each other at large Vr values. The cylinder vibrates at a frequency that is a multiple of the oscillatory flow frequency and is close to the natural frequency measured in water. For KC = 20, where the lift coefficient has multiple frequencies, the intermittent change of the vibration frequencies is observed at large reduced velocities. The number of vortices shed from the cylinder is increased by the vibration of the cylinder compared with the case of a stationary cylinder. Extra vortices are shed from the cylinder after flow reversal, and they do not significantly affect the overall vortex flow pattern because they are very weak. [ABSTRACT FROM AUTHOR]