Numerical Simulation Of Viscoelastic Fluid Flow Characteristics In A Curved Pipe

Adding an appropriate amount of drag reducing additive to the turbulent flow can effectively reduce the frictional resistance.This is the additive turbulent drag reduction technology.Since the 1st International Rheology Conference in 1948,Toms pointed out that since the turbulent drag reduction and mass transfer phenomenon of high molecular polymers,scholars at home and abroad have made extensive use of two kinds of drag reducing additives for high molecular polymers and surfactants.The experiment and the in-depth development of numerical simulation have obtained many important theoretical results on drag reduction and drag reduction mechanism.For the study of drag reduction mechanism,the current viscoelastic hypothesis has received considerable support.However,due to the complexity of the process of drag reduction of viscoelastic fluids,a lot of work still needs to be done in the future.In this thesis,the viscoelastic fluid is taken as the research object,and the control equations of the FENE-P viscoelastic model are derived.The C program is written according to the equation.The GAMBIT pre-processing software is used to construct the elbow geometry model,and the grid is divided,thenimported into FLUENT,and the C program is loaded by the custom function function for calculation.Using grid-independent verification,drag reduction range verification,and literature law comparison verification,the calculation cases and models have high reliability.Then,the drag reduction process under different working conditions was analyzed and compared with water.The establishment process of FENE-P viscoelastic model is introduced.Viscoelastic fluids are the most complex class of fluids in fluids,and the FENE-P model can be better described.By deriving the relevant formulas,the control equations of the FENE-P model and the component expansions in the Cartesian coordinate system are obtained.The solution flow of FLUENT software,the function of custom function and the writing method of C program are explained.The simulation calculation of the case was carried out in the simulation software.According to the size of the L-type compensator in the literature,the GAMBIT software is used to construct the 90° elbow physical model,and the high-quality ancient coin-shaped grid is divided.Import the mesh model into FLUENT,call the program that compiles the custom function to load the FENE-P viscoelastic model,and set related parameters,including turbulence model,boundary conditions,fluid materials,discrete methods,and so on.Observe the influence of different grid sizes on the calculation results,and consider the operating efficiency of the computer,and choose the best grid.The reliability of the numerical calculation was examined based on the asymptoticformula of the coefficient of friction of the viscoelastic fluid and water.Comparing the law of drag reduction exhibited by the calculation case with the previous research,it is further verified that the simulation effect on the viscoelastic fluid is better.By analyzing the calculation cases of three viscoelastic fluids and water under different Re in the elbow,the radial and axial changes of the drag reduction rate,pressure parameters,flow velocity parameters and turbulent kinetic energy are obtained.The results show that there is a linear relationship between the coefficient of artificial viscosity and Re.The larger the fluid concentration,the higher the slope of the curve.The viscoelastic fluid can obtain the best drag reduction effect at the critical Reynolds number and critical concentration.The rate of drag reduction is small and fluctuates;except for the curve part,the wall pressure coefficient of viscoelastic fluid and water decreases continuously along the axial direction of the pipe and the speed of water decreases faster.The part of the curve is affected by the centrifugal force,and the pressure coefficient appears.The phenomenon of separation between the inside and the outside is reflected as a radial gradient that decreases from the outside to the inside of the hydrostatic pressure distribution;the curved portion makes the high velocity region at the far wall end biased toward the inside of the curve,and the higher the drag reduction rate,the viscoelastic fluid The difference between the flow velocity distribution and the water is larger,and the degree of deviation is larger.The larger the polar angle of the curve,the greaterthe secondary flow intensity,and the strongest at 90°;the higher the drag reduction rate,the smaller the turbulent energy.The stronger the inhibition of turbidity by viscoelastic fluids;the effect of turbulent energy on the pipeline is mainly at the near-wall end,but it extends along the far-end end.