Research On The Drag Reduction Effect And Flow Characteristics Of Polymer Turbulent Flow In The Channel

When the fluid flows in the channel,the non-uniformity of the flow enhances the momentum transfer rate between the fluid and the solid wall of the channel,resulting in a sharp increase in the flow resistance.This surface friction resistance will eventually lead to a large consumption of energy resources.In order to effectively solve the problem of excessive energy consumption in the transportation process,many drag reduction technologies came into being and have been widely popularized and applied.Polymer additive drag reduction is favored because of its remarkable drag reduction effect and easy operation.It mainly depends on dissolving a small amount of long-chain polymer into the fluid to change the turbulent structure of the fluid,so as to greatly reduce the friction resistance of the flow.Therefore,this paper studies the effect and flow of polymer turbulent drag reduction in the channel under multiple working conditions and different parameters,deeply analyzes the drag reduction mechanism,and explores the influence of wall microstructure on polymer drag reduction flow.Firstly,based on the existing turbulent drag reduction theory and the basic structural characteristics of polymer molecules,the solution flow characteristics are simulated by using Reynolds average method and non-Newtonian fluid model,and the polymer drag reduction flow at the flow rate of 1 ? 10 m/s is obtained.The conclusions are as follows:(1)When the channel size is fixed,the drag reduction first increases with the increase of flow rate and then decreases;The drag reduction rate increases with the increase of polymer additive concentration,but when it increases to a certain concentration,the increase trend of drag reduction rate tends to be flat,and there is a saturated drag reduction concentration in the drag reduction process.(2)Compared with the pure water solution,after adding polymer drag reduction solution,the eddy viscosity coefficient,turbulent kinetic energy and Reynolds stress on the channel section are significantly reduced.This is because the turbulence structure of fluid flow changes,which weaken s the irregularity of turbulence and reduces the momentum exchange caused by turbulence pulsation,so that the additional stress caused by momentum exchange is also reduced and the flow resistance is reduced;The higher the concentration of polymer drag reduction solution,the more significant the drag reduction effect,and the smaller the eddy viscosity coefficient,turbulent kinetic energy and Reynolds stress.(3)After adding polymer drag reduction solution,the average velocity distribution curve near the wall moves upward compared with that in the pure water solution;The higher the concentration of polymer drag reduction solution,the closer the average velocity distribution curve is to the maximum limit drag reduction asymptote.From the mechanism,the thicker the buffer layer changes the velocity distribution,the increase of flow and the decrease of flow resistance.(4)Along the channel flow direction,normal direction and spanwise direction,the turbulence intensity tends to increase first and then decrease;The turbulence intensity in polymer drag reduction solution is smaller than that in the pure water solution,and the greater the concentration of polymer solution,the smaller the peak value of turbulence intensity.This is mainly because the momentum exchange and energy exchange between the fluid and the wall are weakened and the turbulence loss is reduced,which suppresses the turbulence intensity and improves the flow stability.(5)At the same Reynolds number,the turbulent drag reduction flow of polymer shows obvious pipe diameter effect,and the drag reduction rate increases with the decrease of channel equivalent diameter.The turbulent drag reduction flow coupled between polymer additives and wall microstructure is simulated.The conclusions are as follows:(1)The drag reduction of groove wall and polymer additives have synergistic effect.Compared with the smooth wall,the drag reduction rate of groove wall is slightly increased and the drag reduction performance is improved.(2)In the area near the wall,the flow velocity near the groove surface is lower than that on the smooth wall.The decrease of the velocity along the channel flow direction makes the pressure at the bottom of the pipeline free from violent disturbance,the momentum exchange between fluids is reduced,and the flow is more stable,so as to reduce energy loss and resistance.(3)Compared with the smooth wall,the shear stress,turbulent kinetic energy,eddy viscosity coefficient and Reynolds stress on the groove wall are reduced.The setting of the groove structure reduces the energy transfer generated by the turbulent vortex movement,and the turbulent fluctuating kinetic energy is weakened.Therefore,the resistance of fluid flow is reduced and the flow velocity is faster.This paper simulates and analyzes the drag reduction effect and flow characteristics of the turbulent flow of polymer in the channel and the flow of mutual coupling between polymer additives and wall microstructure,deeply explores the drag reduction mechanism,provides some help for the research of drag reduction in pipeline transportation process,and has a certain reference value for the engineering application of drag reduction technology.