Three-dimensional Numerical Simulation Of Flow Around A Circular Cylinder And Vortex-induced Vibration

Fluid flow around a circular cylinder is one of the most common and important phenomena of flow around structures. It has been a hot topic in academic field for a long timg not only because it's widely used in engineering but also it's the basis of researching other flow around structures. Under certain conditions, pairs of symmetric counter-rotating vortices appear when flow around a cylinder, which will cause pulse pressure both in cross-flow direction and streamwise direction. This pulsating flow force will lead to the vibration of the cylinder, on the contrary, the cylinder vibration also can change the structure of wake, and this phenomenon is called VIV(vortex-induced vibration). With the cylinder's 'lock-in' phenomenon occurred, the cylinder vibration amplitude will be increased dramatically, resulting in material fatigue and even damage to the structure, which will affect the system's stability and safety.The problems of flow around a circular cylinder and VIV are studied numerically using the three-dimensional models which are built by immersed boundary method. The governing equations of incompressible viscous fluid flow are Navier-Stokes equations and the motion of circular cylinder is controlled by equations of Newton's second law. Extra singular body forces are added into the immersed boundary points on a Cartesian grid to simulate the effect of the cylinder's boundary condition. The iterative immersed boundary method is used to solve equations with a HD(half distribution) strategy and the WLM(wall-layer model). The numerical simulations of flow around a circular cylinder and VIV are carried out at Reynolds number of 100&3900. Results from numerical simulations of flow around a circular cylinder, including figures of streamline and vortice, pressure coefficient, drag coefficient, lift coefficient, Strouhal number, provide convincing evidences for the model's high accuracy after compared with the existing experimental data. In the results of VIV, we get some X-time curves in addition, where X represents displacement, velocity and so on. Besides, the three-dimensional effect of flow arround a circular cylinder is also studied on VIV at a high Reynolds number(Re=3900) and the 'self-limited' mechanism of VIV is clearly demonstrated.The purpose of this study is to provide convincing evidences for the model's high accuracy, to provide more belivable results for the numerical simulation of three-dimensional models and to discuss the influence of the VIV problems under the three-dimensional effect.