Study On The Flow Characteristics And Mechanism Of Flow Around A Finite-length Circular Cylinder

The phenomenon of flow around finite-length cylinder exists widely in shallow ocean engineering structures, submerged buoy system in deep sea, Civil engineering and construction and some other engineering applications. The engineering structures would generate certain dynamic response because of the effect of the flow, which plays an important role in the reliability and security of the structures. Meanwhile, there is still no a representative flow model of flow around finite-length cylinder at present, and a comprehensive and reasonable explanation of the essence of the flow phenomenon is still not revealed.A research on the flow around a surface-mounted circular cylinder at different length-to-diameter ratios is presented in this paper. The flow field characteristics, vorticity distribution and the force acting on the cylinder surface is analyzed. The studies are aimed at forming a comprehensive understanding of the flow phenomenon and its nature.On the basis of an infinite-length cylinder model, a research is carried out to make it clear of the effect of the turbulence simulation method and the mesh resolution on the calculation accuracy. The Large Eddy Simulation indeed has great advantage over the Reynolds Average Numerical Simulation. When the size of the first layer of the grid is less than 0.04 times of cylinder diameter, and increasing the number of nodes in the radial direction as much as possible, the calculation error could become quite small. The error of the two-dimension simulation can reach more than 50%, it should be avoided in the studies.Flow characteristics of flow around finite-length circular cylinder are studied by contrastive analysis. Due to the influence of the free end and the fixed wall, the upstream and downstream flow of the cylinder is obviously different from the flow around infinite-length circular cylinder. The recirculation zone behind the cylinder is partially or completely caused by the downwash movement of the fluid from the free end, the “horseshoe” vortex appears before the cylinder, and the alternate shedding vortex only occur in part of the region behind the cylinder. Its vortex is “triangular” distribution overall, and the vorticity of the near wake region is greater than the far field. The change of v ortex type further make big difference of the force acting on cylinder of the two kinds of flow model.The influence of the ratio of length to diameter on the flow characteristics of flow around finite-length circular cylinder is studied, and its action mechanism is also discussed. The three dimensional flow of the fluid around the cylinder is changed with different length to diameter ratio, and the change of the ratio directly affects the interaction strength between the free end vortex system and the fixed wall vortex system, and different vortex types and vorticity distribution after the cylinder are generated, the force acting on cylinder also show some regular change.The study of this paper provide a more precise simulation model for the flow around a circular cylinder. At the same time, it reveals the essence of this flow phenomenon, and provides a reliable basis for the improvement of the flow model. In this paper, the research on the flow around a finite-length cylinder is of great significance in the field of engineering practice and basic fluid mechanics.