Drag Reduction Of Flow Around A Circular Cylinder Attached Prisms Base On OpenFOAM

In the research of bluff body flow,considering that the safety of high-altitude cables,super high-rise buildings and submarine pipelines is fully affected by the flow field,the research on the flow around a cylinder and related drag reduction schemes has always been a classic topic in the field of fluid mechanics.When the fluid flows through this kind of cylindrical structure,the flow velocity on the surface of the cylinder increases due to the contraction of the drainage area.At the same time,the existence of the viscous force of the fluid leads to the boundary layer separation on the wall of the cylinder,resulting in the Karman vortex street.The resulting periodic force and the shear force on the surface of the cylinder induce the vibration of the structure,which will cause resonance damage and bring serious economic losses.Therefore,it is of great significance to study various methods to suppress vortex shedding frequency and reduce the drag and lift of cylinder.In this paper,the open source computational fluid dynamics(CFD)software OpenFOAM based on Linux platform is used to carry out the numerical simulation work.Firstly,the model is validated and the appropriate mesh generation parameters are established.After using the single cylinder model to calculate and post process the data,combined with the previous experimental and numerical simulation data,the accuracy of the solution setting is verified.Then,the series double cylinder model is used to verify the disturbed cylinder model.The drag,lift coefficient and Strouhal number of the cylinder at low Reynolds number are discussed,and the relationship between the interaction of the two cylinders in series and the gap ratio is obtained.Considering that the common drag reduction schemes of passive control method are additional control rod,dividing plate and fairing.The disturbance effect of triangular structure on the flow field is different from that of circular structure,the influence of attached prisms scheme on the flow state around the cylinder is studied in this paper.Firstly,the disturbing prisms are arranged in series with the cylinder.Under different gap ratio and rotation angle,the variation of velocity and pressure around the cylinder,the distribution of transient vorticity and the rising and falling trend of drag and lift coefficients are analyzed when Re=200.The results show that the drag reduction efficiency can reach 44.56%when the gap ratio L/D=1.8.The double vortex mode makes the drag coefficient of the cylinder rise,and makes the disturbing prism lose the effect of restraining the lift fluctuation of the cylinder.When the gap ratio L/D=1.8,the suppression efficiency of the additional disturbing prism downstream of the cylinder to the lift coefficient of the cylinder can reach 73.26%.The suppression efficiency of the drag and lift coefficients of the cylinder can be further improved by setting the disturbing prisms at the corresponding position upstream and downstream of the cylinder,reaching 53.16%and 81.62%respectively.Then,the symmetrical double disturbing prisms with different angles and distances are arranged in front or behind the cylinder to analyze the pressure state of the cylinder surface when Re=200.The results show that the average drag coefficient of the cylinder can be reduced more effectively by the symmetrical double disturbing prisms upstream of the cylinder,and the drag reduction efficiency can reach 37.21%compared with the single cylinder.The symmetrical disturbing prisms downstream of the cylinder can better restrain the lift fluctuation of the cylinder,and the restraining efficiency can reach 99.86%.The drag coefficient and lift coefficient of the cylinder are further reduced by setting the disturbing prisms at the corresponding upstream and downstream positions.The suppression efficiency is 54.63%and 99.94%respectively,and the lift fluctuation is completely suppressed.Finally,the drag reduction efficiency of the optimal drag reduction scheme under six Reynolds numbers is studied.The results show that when Re>200,the drag reduction efficiency of series disturbing prisms scheme is higher than that of symmetrical double disturbing prisms scheme.