Application Of Fluent Software In Numerical Simulation For Viscoelastic FLUENT Flow

The addition of polymer or surfactant into the water can bring drag reductionrate of80%to the turbulent flow. Its considerable practical value attracts a lot ofattention. However, currently turbulent drag reduction flow of viscoelastic fluid ismostly studied from the perspective of academic theory, and it is lack of numericalsimulation methodology which is suitable for engineering applications. In order toaddress this issue, the re-development of FLUENT software is presented in thispaper. An in-house subroutine modeling viscoelastic fluid is developed and thenembedded into the FLUENT code through utilizing the functionalization ofuser-defined function in the software, and thus the numerical simulation forviscoelastic fluid flow is achieved.Firstly, the computational models, governing equations, constitutive models ofviscoelastic fluid and numerical methods adopted in the numerical simulations onlid-driven cavity flow and planar sudden expansion flow are introduced. And theuser-defined function theory and the embedding of viscoelastic fluid model intoFLUENT by utilizing user-defined function are described in detail.Secondly, Oldroyd-B model is embedded into the software to conduct thenumerical simulations on the lid-driven cavity flows of viscoelastic fluid withdifferent Reynolds numbers and Weissenberg numbers, and the artificial viscosityterm is introduced into the calculations. The feasibility of the new numericalsimulation methodology for the viscoelastic fluid flow is proved by analyzing thechanges of velocity distribution, vorticity distribution, the location of primaryvortex center and secondary eddy with the increase of Weissenberg number andcomparing with previous research results. The study on the flow characteristics ofviscoelastic fluid shows that tertiary eddy with opposite rotational direction occursunder the secondary eddy at certain Weissenberg numbers, and complex changes ofthe velocity field and deformation field occur with the increase of Weissenbergnumber, such as the appearance of the secondary eddies under the promary vortexand at the upper left corner of the cavity and the increase of their sizes withincreasing Weissenberg number.Finally, FENE-P model is embedded into FLUENT to simulate the planarsudden expansion flows of viscoelastic fluid. The feasibility of the new numericalsimulation methodology for the viscoelastic fluid flow is further verified byanalyzing the onset Reynolds number for asymmetric flow, the variations of thevortex sizes and asymmetry with the change of Weissenberg number, extensibility,solvent viscosity ratio and Reynolds number, the overshoot of the streamwise velocity component along the centreline at low Reynolds numbers and the change ofenergy loss with the variation of Reynolds number and comparing with previousresearch results. The elastic instability at low Reynolds numbers is observed byanalyzing the information of velocity field and deformation field. Besides, theperiod of the different parameters at the same location are the same, while theparameters at different locations have different periods. The flow keeps thesymmetric state from the beginning to the form of steady flow. After the occurrenceof elastic instability, the flow changes from symmetric state at the beginning toasymmetric state. With the increase of Weissenberg number, the time from thebeginning of the flow to the form of steady flow increases, as well as the amplitudesof all the parameters within the periodic change, and the occurrence time of elasticinstability and the time from the appearance of instability to the form of periodicchange are both shortened, in addition, the period is slightly enlarged.