Numerical Simulation Of Flow Around The Three Dimensional Slender Body

With the rapid updating of marine oil and gas equipment technology,more and more deepwater resources are being investigated and developed.No matter what types of floating device are used,the riser system is always the key connecting component in the marine equipment.In the field of CFD,the numerical simulation of flows and vortex-induced vibrations of slender structures such as risers has been widely concerned by researchers.In recent years,the three-dimensional effect of the flow around is gradually known,so more and more research begin to develop 3D numerical simulation.Based on this,the numerical investigation of flow characteristics around three-dimensional slender structures is carried out.The main work includes:1st,the parallel technology of flow is studied in OpenFOAM software.2nd,the flow characteristics of slender bodies under uniform flow and shear flow conditions are analyzed.3rd,the vortex induced vibration of 3D model is calculated numerially.Firstly,the effects of the number of processors,the decomposition methods of different regions and the number of grids on the parallel performance are analyzed.This paper finds out the most suitable parallel processing method for our laboratory computer hardware.This paper also establishes a hybrid parallel model of MPI +openMP,and verifies its feasibility.The results show that the parallel computing technology using mixed programming can accelerate the computation speed.Secondly,the numerical calculation of the flow around a 3D cylinder with different slender ratios is carried out.We find that the drag coefficient,lift coefficient and Strouhal number of the 3D model are less than the 2D results.When the slender ratio is 30,the numerical results are very close to the experimental values.And the tail vortex of uniform flow is generally shown as 2S mode.Besides.We also find that the wake is less affected by the circumfluence in the flow field.In addition,the separation point will move with the increase of Reynolds number,and the recirculation zone length will decrease with the increase of slender ratio.Then,we analyze the flow around a three-dimensional model under shear flow,and the force situations of shear flow are larger than uniform flow.The shear flow wake vortex appears 2S mode and 2P mode.Besides,the shear flow also has obvious vertical vortex tube,and with the axial velocity gradually reduced from top to bottom,the vortex tube phenomenon is more significant.Finally,the VIV problem of three-dimensional cylinder model is numerically calculated.We find that under the same flow condition,the maximum amplitude and lock-in interval of the 3D model are closer to the experimental values than the 2D simulation results.In addition,the tail vortex exhibits 2S mode in the initial branch with smaller amplitude,while the tail vortex in the upper branch with larger amplitude appears 2p mode.In a word,the flow characteristics of 3D slender body are studied and summarized in detail by CFD software,which provides a reference for the large-scale parallel computation and vortex-induced vibrations study of slender body.