Numerical simulation of flow-induced motion of three rigidly coupled cylinders in equilateral-triangle arrangement

In this study, the flow-induced motion (FIM) of three rigidly coupled cylinders arranged in an equilateral-triangular pattern is numerically investigated. The spacing ratio is set to four times the cylinder diameter, and simulations are conducted for flow incidence angles of α = 0°, 15°, 30°, 45°, and 60°. The reduced velocity U_r is varied from 1 to 30, with corresponding Reynolds numbers of ∼1000-30 000. The two-dimensional Reynolds-averaged Navier-Stokes equations are used in conjunction with the shear stress transport k-ω turbulence model to simulate the turbulent flow, and the vibration equations are solved using the Newmark-beta algorithm. The numerical results indicate that the flow incidence angles and reduced velocity have a significant effect on the FIM response and vortex shedding mode. The widest lock-in range (4 < U_r < 13) occurs when α = 45°, and the narrowest range (3 < U_r < 7) is observed when α = 60°. The optimal arrangement for suppressing the vibration of the cylinders is found to be α = 30°. The vibration and frequency responses for α = 0° and α = 15° are not the same as those of a single cylinder; in particular, galloping phenomena occur for α = 0° when U_r > 12 and become fully developed when U_r > 15.