| The structural damage caused by fluid-solid coupling is common in all fields.The fluid will produce regular vortex shedding within a certain Reynolds number range,and induce forces in the direction of the flow and perpendicular to the direction of the flow.Long-term repeated forces can cause damage or fatigue failure of the structure.Therefore,it is necessary to do research on the problem of controlling flow around the structure and drag reduction.Based on the CFD fluid mechanics calculation platform—Fluent software,this paper carries out a numerical simulation study on the three-dimensional flow around the structure of the wave-shaped cylinder and main cylinder with the auxiliary small cylinder under Reynolds number Re=3900.Mainly analyze the influence of two parameters,the wavelength ratio and the amplitude ratio of the wave-shaped cylinder structure on the flow control of the cylinder field.In addition,the research on the structure of the auxiliary small cylinders surrounding the main cylinder mainly focuses on the number n of auxiliary small cylinders,the diameter ratio d/D between the auxiliary small cylinders and the main cylinder,the wall spacing ratio G/D between the auxiliary small cylinders and the main cylinder and the influence of the angle?between the center line of the accessory small cylinder and the incoming flow on the flow control of the cylinder.Analyze the force conditions and flow field characteristics of various working conditions to provide a certain reference basis for actual engineering.The main research work of this paper is as follows:(1)Numerical simulation of the three-dimensional flow around a wave-shaped cylindrical structure under the condition of Reynolds number Re=3900.It mainly studies the influence of the two key parameters,the wavelength ratio?/D_m and the wave amplitude ratio a/D_m,on the force response of the cylinder structure,reveals the vortex shedding control law,and explores the evolution characteristics of the flow field.The research results show that in terms of drag coefficient,the wave-shaped cylinder wavelength ratio has the most unfavorable value?/D_m=2.75,the other wavelengths have better drag reduction control effects than the working conditions,and the wave amplitude ratio also has the most unfavorable value a/D_m=0.05,others have better drag reduction and control effect.Compared with a single cylinder with constant cross section,the boundary layer of the fluid flowing around a wavy cylinder will delay separation on the structure.When the wavelength ratio of the wave-shaped cylinder gradually increases from 1.8 to 5.0,the secondary vortex on the surface of the cylinder gradually disappears.As the amplitude ratio increases,the wake vortex suppression effect is better,and the vortex component?_x diffuses and transforms less to the wake region.(2)Numerical simulation of the three-dimensional flow around the main cylinder structure with two small attached cylinders under Reynolds number Re=3900.Mainly study the influence of three parameters,the diameter ratio d/D of the attached small cylinder and the main cylinder,the G/D spacing ratio between the attached small cylinder and the main cylinder,and the arrangement angle?on the flow control of the cylinder,and reveals Vortex shedding control law to explore the evolution characteristics of the flow field.The research results show that:in terms of drag coefficient,the arrangement angle of the attached small cylinders has the most unfavorable angle?=90°,and the spacing ratio has a greater influence in the range of G/D=0.05?0.2,while working conditions in G/D=0.2?0.5 have little effect on the drag coefficient.The frequency of vortex shedding is larger when the arrangement angle?=15°and?=30°.The Stouhal numbers of the other arrangement angles are close to the single-cylinder condition.As the spacing ratio increases,The Stouhal number is close to the single cylinder condition.The symmetrical arrangement of the two small attached cylinders has a greater impact on the generation mechanism of extension and the transformation from the main cylinder's surface vortex,which will increase the vorticity diffusion strength,and the overall effect of controlling the vortex space change is better.Compared with the other two parameters,the arrangement angle of the symmetrical arrangement of the attached small cylinders has a greater impact on the wake in the fluid-solid coupled field.The best arrangement angle for flow control is?=0°.(3)Numerical simulation of the three-dimensional flow around the main cylinder structure with four small attached cylinders under Reynolds number Re=3900.The main research is to study the influence of the diameter ratio d/D of the attached small cylinder to the main cylinder,the spacing ratio G/D between the attached small cylinder and the main cylinder,and the arrangement angle?on the flow control of the cylinder,and reveal law to control the vortex fall and explore the evolution characteristics of the flow field.The research results show that in terms of drag coefficient,there is the most unfavorable value?=0°for the arrangement angle of the symmetrically arranged four small attached cylinders.The Stouhal number is smaller when the spacing ratio is G/D=0.05.Compared with the single-cylinder condition,the symmetrical arrangement of the four small attached cylinders has a greater impact on generation mechanism of the stretching and transformation from the main cylinder surface vortex,and the effect of controlling the vortex space change is better.Compared with the other two parameters,the arrangement angle?of the symmetrical arrangement of the attached small cylinders has a greater influence on the wake in the fluid-solid coupled field.The best arrangement angle for flow control is?=45°. |
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