Numerical Stduy Of Flows Over Bluff Bodies In Viscoelastic Fluid

The viscoelastic fluid can be obtained by adding small amount of long chain polymer into water.In this thesis,various related flows of viscoelastic fluids have been simulated by Fluent associated with UDF secondary development.Firstly,the thesis compares the exact solution of the viscoelastic fluid slit flow with the numerical results,and quantitatively compares the simulation results of the two-dimensional viscoelastic fluid flow over a circular cylinder with literature results.Furthermore a qualitative comparison is made for the flow field characteristics of the three-dimensional viscoelastic fluid over a circular cylinder.These comparisons validate that the present simulations show satisfied accuracy and computational stability for solving various flows of viscoelastic fluids.Secondly,the viscoelastic fluid flow over a NACA0012 airfoil at Reynolds number1000 with varies angle of attack from 0 to 20° has been studied.Furthermore the influence of polymer on the flow past a cylinder is checked by the two dimensional simulations at Reynolds number of 100 and three dimensional simulations at Reynolds number of 300.These studies show that at the moderate Reynolds number,the addition of polymer can greatly change the flow field and make the flows exhibit different patterns in different parameter spaces(Weissenberg number,the angle of attack,rotation speed).For Newtonian fluid,both large angles of attack and high rotation velocity make the wake field be asymmetrical and results in a non-zero lift coefficient.However,our simulation have demonstrated that the polymer addition can make the flow field more symmetrical by the reason of redistribution of pressure field for the appearance of elastic stress.Afterwards,the one degree freedom vortex-induced vibration of a viscoelastic fluid flow over a circular cylinder at the Reynolds numbers of 30 to 500 have been studied.Our studies have shown that the polymer additions can suppress vortex-induced vibration of a circular cylinder at low and moderate Reynolds number.Specifically,the polymer addition can increase the critical Reynolds number of vortex-induced vibrations at low Reynolds number range.At moderate Reynolds numbers,the vibration-reducing efficiency of polymer addition is positively correlated with the Weissenberg number and negatively related to the Reynolds number.In the last part,the three dimensional large eddy simulations have been applied to simulate the flow over a slender body at Reynolds number of 10,000.Polymer addition can greatly change the three-dimensional structures of the flow and make it more regular.At small Weissenberger numbers,the drag reduction of the cylinder is achieved.However,the drag reduction has not been observed at higher Weissenberg number.