| Nowadays,under the background of energy crisis and environmental pollution,energy conservation and emission reduction has become a development trend.The development of energy-saving technology can effectively reduce energy consumption and alleviate the energy crisis.As a kind of additive drag reduction method,surfactant drag reduction can reduce the flow resistance in the circulating pipeline,thereby reducing the circulating power consumption of the pump and achieving energy saving in the field of pipeline transportation.Since Toms discovered the drag reduction effect in 1948,the effect and mechanism of surfactant drag reduction have been extensively studied by experiments and numerical simulations.However,most of the studies focus on straight tube structures,and the research on drag reduction performance in local components is still limited.At the same time,the flow loss at the local components of the circulating pipeline mainly comes from the vortex.It is of great significance to explore the influence of surfactants on the vortex range and evolution process for the exploration of the drag reduction mechanism.In this thesis,firstly,the research status of surfactant drag reduction and tee flow characteristics is investigated in depth.Based on the shear thinning and viscoelasticity of surfactant solution,the properties of drag reduction solution are described.Among them,the cross model of non-Newtonian fluid built-in CFD is used to characterize the shear thinning properties of drag reduction solution.The Giesekus model program is written by the UDF module,and the N-S equation is coupled to characterize the viscoelasticity of the drag reduction solution.Then,taking the T-type shunt tee structure commonly used in circulating pipelines as the research object,the grid and model parameters are verified,and the boundary conditions under steadystate and unsteady-state conditions are set up.Finally,the shear thinning model was used to study the variation of drag coefficient and drag reduction rate of pure water and surfactant drag reduction solution in the split tee,and the flow characteristics such as pressure distribution,velocity change,streamline distribution and vorticity distribution were analyzed.The difference of vortex length between pure water and surfactant solution under three-dimensional turbulence was studied by viscoelastic model,and the variation of pure water and viscoelastic fluid recirculation zone with flow parameters under two-dimensional laminar flow was explored.The main conclusions are as follows :(1)Through the study of shear thinning model : the straight pipe and branch pipe resistance coefficients of pure water and surfactant(CTAC)drag reduction solution decrease first and then increase with the increase of Reynolds number.As the split ratio increases,the resistance coefficient of the straight pipe gradually decreases,and the resistance coefficient of the branch pipe gradually increases.The drag reduction zone can be divided into incomplete drag reduction zone,complete drag reduction zone and over drag reduction zone.Compared with the straight pipe section,the branch pipe section is easier to reach the complete drag reduction zone.The drag reduction rate of straight pipe and branch pipe increases first and then decreases with the increase of Reynolds number.The drag reduction rate of the straight pipe decreases gradually with the increase of the split ratio,and the drag reduction rate of the branch pipe increases gradually with the increase of the split ratio.The comprehensive drag reduction rate is the largest when the Reynolds number is 44000 and the split ratio is 0.1,about 24.25 %.(2)The addition of surfactant(CTAC)increases the range of the high-speed flow region,reduces the radial length of the low-speed vortex region,and slightly increases the axial length of the vortex region.In the flow process of straight pipe and branch pipe,the addition of CTAC will delay the development of vortex structure.At the same time,the influence of the micelle structure of CTAC on the drag reduction effect is in the range of action.The region with high vortex intensity shows drag enhancement,which is concentrated in the central region of the vortex.The area with low vortex intensity is characterized by drag reduction,which is concentrated on the outer side of the vortex center and the wall surface.(3)Through the study of viscoelastic model : the velocity distribution and vortex length of viscoelastic drag reduction fluid and pure water are different.In the fully developed section,the velocity of the viscoelastic drag reduction fluid at the wall surface is smaller than that of pure water,and the velocity in the mainstream area is larger than that of pure water,so the velocity gradient from the wall surface to the center of the flow channel is larger than that of pure water.The viscoelasticity of the drag-reducing fluid has an effect on the vortex of both the straight pipe and the branch pipe,resulting in the axial length of the vortex structure being larger than that of pure water and the radial length being smaller than that of pure water.(4)The parameter changes of viscoelastic fluid will affect the recirculation zone of the shunt tee.The evolution of the recirculation zone can be divided into three stages with the increase of Reynolds number.The recirculation zone begins to appear in the straight pipe section at stage II,and two recirculation zones appear in the branch pipe section at stage III.The length of the recirculation zone increases with the increase of Reynolds number and split ratio,decreases with the increase of Wiesenberg number,and increases with the increase of solvent viscosity ratio. |
PDF Full Text Request