Numerical Simulation Of Non-Newtonian Fluid Flow And Miscibility In Trapezoidal Cavity

Fluid flow problems in confined space have a wide range of applications in petrochemical,medical technology,military armament and other fields,and the study of the flow mechanism has important scientific significance.The current research on fluid flow problems in confined spaces is mostly focused on Newtonian fluids,and relatively little research has been done on non-Newtonian fluid flow problems in confined spaces.Compared with Newtonian fluids,non-Newtonian fluids have special rheological properties and show more complex flow mechanisms in the flow,which are of great help to people’s production and life by understanding and using their flow mechanisms.In this paper,we simulate the non-Newtonian fluid cavity flow and the miscible cavity flow of non-Newtonian and Newtonian fluids in a two-dimensional isosceles trapezoidal cavity(ITC)driven by the lid based on the multi-relaxation time(LBM-MRT)model in the lattice Boltzmann method.The numerical results show that the Reynolds number(Re)variation has a more drastic effect on the flow structure of shear thinning fluid in the ITC flow of a single non-Newtonian fluid;the non-Newtonian effect in the trapezoidal cavity simplifies the flow structure,while the non-Newtonian effect in the square cavity has the opposite effect;the effect of the top angle on the flow structure of shear thinning fluids is more complex than that of shear thickening fluids,and both have a critical value that allows the bottom vortex to split.In addition,we also found that the shear thinning fluid has a complex flow state transition process(steady flow state-periodic flow state-chaotic flow state)similar to that of Newtonian fluid as Re increases,and carried out a detailed simulation study.Then we analyzed the simulation results of ITC miscible flow of non-Newtonian and Newtonian fluids and investigated the factors affecting the mixing effect of both fluids.The numerical results show that:in the miscible flow of non-Newtonian fluid and Newtonian fluid ITC,the larger the power law exponent of the low viscosity fluid the better the mixing effect of the two fluids at the same moment after the flow stabilization;the mixing effect is better when the low viscosity fluid is initially located in the left half of the cavity than when the low viscosity fluid is initially located in the right half of the cavity;the higher viscosity ratio,the better mixing effect of the two fluids,and the non-Newtonian characteristics of the fluid affect the mixing effect by affecting the viscosity ratio;the fluid viscosity will change further during the flow,thus affecting the fluid mixing effect;the greater the Peckley number(Pe),the better the mixing effect of the fluid after flow stabilization,indicating that the higher convection rate is beneficial to the mixing between the fluids;the angle of the top angle is negatively correlated with the mixing effect of the fluid.