Effect of Weissenberg number on polymer-laden turbulence

Direct numerical simulation of polymer-laden turbulent flow is performed for the investigation of the two-way interaction. Lagrangian dynamic simulation is adopted for a finitely extensible nonlinear elastic (FENE-2) dumbbell model to observe polymer dynamics in turbulent flow. The impact of the polymers on fluid momentum is described using the elastic force between two beads. The elasticity of the polymer is characterized using the Weissenberg number, We*=tptk, where tp and tk denote the elasticity timescale and the Kolmogorov timescale, respectively. We observe that for We*=1.0 most of the polymers are in a coiled state and the hydrodynamic properties of fluid remain unchanged. The coil-stretch transition is observed at approximately We*=3.0. The highly stretched polymers in turn contribute to significant turbulence modification for large values of the Weissenberg number. The effect of the Weissenberg number on various turbulent statistics is computed and analyzed. The highly stretched polymers tend to rotate around the vortical structures. The feedback force effectively suppresses the turbulence structures for large values of the elasticity parameter. The effect of We* on the alignment between the end-to-end distance vector, vorticity vector, and the eigenvector of the rate of strain tensor is presented. A better insight into the effect of polymers on turbulence is obtained through the direct force modeling in stationary turbulence although the effect itself has been known for a long time.