Numerical Study On Characteristics Of Single Or Two Fillet Cylinder Structure In Oscillatory Flow

The flow around cylinder is a common phenomenon of fluid movement in engineering and nature fields,such as offshore platform,submarine oil pipelines and isolated islands in the sea.On the one hand,the discovery of submarine resources has caused the cylinder structure are gradually build in the ocean,and the ocean fluid speed and direction of motion changing in any time just like an oscillating flow act on the cylinder structure surface,which will cause the cylinder structure to produce uneven fluid force and endanger it's safety under the long-term repeated action.On the other hand,the development of technology makes the fillet cylinder structure begin to be widely used in practical engineering,but the study of oscillatory flow mainly focuses on regular cylinder structure.Therefore,it's some of practical engineering significance to study zero-mean oscillatory flow around single fillet cylinder structure and two fillet cylinder structure group in tandem or side by side in this paper by adopt the numerical calculation software Fluent,and main analysis the influence of fillet radius,the angle of flow attack and spacing ratio on the flow field distribution and the fluid force coefficient,the main research work and related conclusions are as follows:(1)Numerical study on the two-dimensional flow around single fillet cylinder structure under oscillatory flow.It's found that the angle of flow attack not only change the number of wake vortices but also change the positions of the vortices and attached vortices,which leads to the symmetrical,asymmetrical and diagonal distribution of wake vortices.In addition,the increase of the angle of flow attack also cause the distribution of forward flow velocity change from "V" shape to "U" and the distribution of transcerse flow velocity will change from symmetric to asymmetric.On the other hand,large fillet radius will make the attached vortex disappear while small fillet radius has no significant influence on the flow field distribution,and fillet radius only has a large effect on the distribution of forward and transverse flow velocity at large angle of flow attack.However,the fluid force coefficient distribution and the shape of the Liassajous curve will change with the increase of the angle of flow attack and fillet radius.In addition,the increase of fillet radius will lead to the drag coefficient decrease,but the inertia coefficient first decrease and then increase,while the increase of the angle of flow attack has the opposite effect on the two coefficients.(2)Numerical study on the two-dimensional flow around two fillet cylinder structure group in tandem at oscillatory flow.It's found that fillet radius increase will cause the wakes of two cylinder structure group appear as "three oblique wake vortex","two oblique wake vortex" and "two parallel wake vortex" and attached vortex on the surface of each cylinder will disappear when spacing ratio is less than the critical value.On the one hand,spacing ratio and fillet radius increase have little effect on the distribution of forward and transverse flow velocity in the wake area of each cylinder,and thedistribution of forward flow velocity is "U" and symmetric about y/D=0 while the distribution of transverse flow velocity is antisymmetric.On the other hand,the fluid force coefficient distribution of the two fillet cylinder has a phase difference when arrange in tandem,and the effect of fillet radius on the flow field distribution depends on spacing ratio.In addition,the drag coefficient to decrease first and then increase with fillet radius increase while the inertial coefficient always decrease,but two coefficients first increase and then tend to a fixed value with spacing ratio increase.(3)Numerical study on the two-dimensional flow around two fillet cylinder structure group in side by side at oscillatory flow.It's found that the wake of the two fillet cylinders structure group are vortex patterns in the gap area and form parallel vortex streets at n?2.0 while the wakes of each cylinder is oblique vortex streets at n?3.0 and symmetrical distribution when fillet radius is small.On the one hand,the distribution of forward flow velocity of two cylinder at x/D=±0.06 are "U" shape and symmetrical about the center line of the gap area,while the distribution of transverse flow velocity are opposite to each other.On the other hand,the lift coefficient time-history curves of two fillet cylinder is opposition but the trend is same when they are arranged in side by side,and the distribution of the lift coefficient time-history curve and Liassajous curve shape will change of each cylinder with fillet radius and spacing ratio increase but has little effect on the FFT spectra of the lift coefficient.In addition,the drag coefficient and the inertia coefficient will reduce with fillet radius increase while spacing ratio increase would cause the two coefficients to decrease first and then remain unchanged.