Numerical Simulation Of Bluff Body Flow Under Free Surface And End Effect

The simplified single cylinders,such as rises,platform legs and bridge piers,which have appeared in practical engineering,have become one of the most common basic units in the current marine engineering structure.Many scholars at home and abroad have developed a single-phase infinitely long cylindrical flow with a lot of research work.However,under the condition of lower Reynolds number,there are relatively few studies on the finite-length flow,the flow around the free surface,and the flow under the end-effect and the free-surface interaction.The complexity of the flow field is also New and greater challenges have been raised for conducting experimental research.Therefore,it is especially important to use the appropriate turbulence model for numerical simulation.In this paper,the three-dimensional numerical simulation is used to compare and analyze the flow around the three cases.On the basis of the classical cylindrical flow,the first calculation of the single-phase infinitely long flow is carried out,and then the finite-length flow with the Reynolds number Re=200,500 and 1000,and the flow with free surface Numerical simulation of the flow around the cylinder under the interaction of the free surface and the end effect,In addition,the numerical simulation of the flow around a cylinder with only a free surface is performed for Reynolds number Re=5000 and Froude number Fr=0.8.According to the analysis of the drag coefficient and the lift coefficient,the velocity distribution of the flow field,the frequency of the vortex shedding,the change of the height of the free surface,the shedding pattern of the three-dimensional vortex structure and the flow field cloud diagrams and some other hydrodynamic characteristics such shows that the end effect and the free surface alone have a great influence on the wake field.The free end greatly changes the force of the cylinder and the distribution of mean streamwise velocity on the exhibition direction.At the same time,it suppresses the vortex shedding;while the free surface alone has a great influence on the mean streamwise velocity near the free surface,and a large number of irregular,small-scale vortices are generated in the vicinity of the free surface.The maximum height of the surface near the stagnation point,the liquid level difference before and after the cylinder,and the maximum water depth affected by the free surface are closely related to the Reynolds number,especially the Froude number;The characteristics of the flow field fusion under the interaction of the free surface and the end effect are the characteristics of the two.When analyzing a specific flow characteristic,the roles of the two are different.The influence of free surface on the force of the cylinder is dominant.the end effect has a greater influence on the mean streamwise velocity.The vortex diagram behind the cylinder combines the characteristics of the two under the action of the two.The end effect has a little effect on the maximum liquid level near the stagnation point,but the lowest height of the liquid level after the column is increased,and the magnitude of the increase increases with the increase of the Reynolds number and the Froude number.The phenomenon of flow around a cylinder is limited to a relatively small area between the free surface and the free end.