CFD numerical simulation of flow-induced transverse vibration of a square cylinder

The galloping and vortex-induced vibrations of an elastic mounted square cylinder are investigated in this paper. The Reynolds number is kept at 500 for all calculations. The viscous incompressible flow field was calculated by the computational fluid dynamics (CFD) code of Fluent software, then the motion of square cylinder was modeled by a spring-damper-mass system, and the motion equation of the cylinder was solved by writing the Newmark-β method into the User-Defined-Function (UDF), moreover, the nonlinear coupling between square cylinder and flow field was carried out through the dynamic mesh technique. Results show that when the influence of mass ratio and reduced damping on flow-induced vibration is taken into consideration, the galloping in low frequency ratio is observed, the maximum oscillations can reach 2.5 times of side length under galloping, and the transition from galloping to vortex-induced vibration is found. Then the characteristic parameters of lift and drag coefficient, transverse displacement and vortex pattern in the wake of the square cylinder in different frequency ratios were studied in detail and the phenomena of "beat" and "phase switch" were confirmed. Thus the influence of galloping needs be considered for the design of square structures with low natural frequencies in engineering, and the section types which are not easy to induce galloping should be used in preference.