Numerical Investigation Of Fluid-structure Interaction And Flow Control At Low Reynolds Number

Cylindrical structures are widely used in ocean engineering, for example, deepwater risers and subsea pipelines. As the fluid passes the bluff bodies, periodic oscillating forces are caused by vortex shedding, which may result in vortex-introduced vibration (VIV). The VIV may bring the harmful effect on the structure stability and structure safety.In order to investigate the fluid-structure interaction of cylindrical structures and find the way of flow control, a two-dimensional laminar flow for incompressible viscous fluids is developed. The fluid-structure interaction of circular cylindrical system is solved by use the computational mesh update strategy in the frame of Arbitrary Lagrangian-Eulerian (ALE). The paper is consists of three aspects, as follows:the basic characteristics of a circular cylinder forced by the motions in-line and cross directions; the basic characteristics of a circular cylinder forced by a combination of oscillatory translational and rotational motions; reduction of flow force by using flow control device. The numerical model is validated carefully against the typical benchmark problems before it is utilised to do research.First of all, a circular cylinder is forced by the motions in-line and cross directions is investigated at different phase differences. The root mean square of lift force coefficient and mean drag force coefficient increase with the increase of the oscillating frequency; the force of circular cylinder is different under the different phase difference.Secondly, flow behind a circular cylinder forced by a combination of oscillatory translational and rotational motions is investigated, which focus on the effect of phase difference between the oscillatory translational and rotational motions on the vortex shedding mode and fluid forces. The study shows that there are no lock-in phenomenon were found at Stj<0.6. The force on the body is very small at the critical forced frequency while the locked status turns to unlocked status. When lock-in phenomenon occurred in the study, the vortex shedding mode is the 2S.Finally, numerical investigation of reduction of flow force by using flow control device, which is fairing, is carried out. The results indicate that the force of the system have a jump at reduced velocity Ur=4.8. The fairing has significant effect to reduce drag force of system by contrast with the results of the computation of stationary circular cylinder at the same Reynolds number. In a certain range of reduced velocity, the lift force of system is reduced by the fairing, however the situation of the lift force of system become lager was found in the other range of reduced velocity. In summary, the fairing is useful for reduce the drag and lift of the system under certain conditions, which is effective flow control device.