Numerical Simulation Research On Flow Past A Free Surface Piercing Circular Cylinder

The existence and development of human has close relations with free surface flows,the research of which has both widely practical engineering significance and important theoretic value.On the field of port,coast and offshore engineering,the research of free surface flows is also very important.When ocean deep water drilling,including drill pipe,riser,bridge pier,ship,mast and structure vertically pierce a free surface,it caused viscosity influence of cylinder surface, including the free surface phenomenon of a kind of wave,the thin shear layer of cylinder surface,air bubble entertainment,and 3D fluid separation etc.In ocean engineering,it focused on ship except cylinder structure piercing a free surface.Using the CFD software CFX and adopting the RNGk-εmodel, combination with the VOF(Volume of Fluid) method,in the Reynolds number from10⁴ to 10⁵,and Froude number from 0.15 to 0.88,this paper researched the flow around the three-dimensional circular cylinder piercing free surface. Analysed the deformation of free surface,the influence of free surface to fluid wake,concluded the rule of fluid which changed with the Reynolds number and Froude number.Meanwhile,researched the influence of free surface to some kind of force,and compared the numerical result with the result of other document. The main conclusions are as follows:1.At the stagnation of cylinder,the run-up L is less than Fr² * D/2.Because of the influence of free surface,the base pressure coefficient is -0.7～-0.5. The depression L₀ and base coefficient is C_pb = 2 gL₀ /V²2.Increase with Froude number the influence bound of free surface increased. The high Reynolds number confined the influence of free surface,and the influence of free surface was weaker. influence of free surface was weaker.3.The time averaged pressure coefficients of different depth cylinder section are similar with that of no-free surface fluid.In the influence range of free surface,the time averaged pressure coefficients of the same cylinder angle decreased with the increased depth.4.The total time averaged drag coefficient,pulse drag coefficient,pulse lift coefficient,and the same depth time averaged drag coefficient,pulse drag coefficient,pulse lift coefficient decreased with the increased Froude number and Reynolds number.