Transition to turbulence against various perturbations and concentrations in viscoelastic flows*

The addition of small amounts of long-chain polymers to a flow has been well-studied thanks to their observed benefits, such as turbulent drag reduction. However, the study of the laminar-to-turbulent transition in the flow of polymer solutions flows is currently lacking. For this study, direct numerical simulations of viscoelastic flows are performed to investigate the turbulence transition of polymer solutions subject to various magnitudes of disturbances and polymer concentrations. Simulations are performed at friction Reynolds numbers up to 132. At a low friction Reynolds number of 94, viscoelastic flows start to transition at low polymer concentrations even against small perturbations, whereas the Newtonian counterpart and high concentration solutions still remain laminar. When subjected to higher disturbance magnitudes, higher concentration polymer solutions eventually undergo a transition at a similar time to lower concentrations but display reduced bursting magnitudes. For the highest Reynolds number of 132 studied, the transition seems delayed as the concentration is increased when subjected to small perturbations. As stronger perturbations are applied, the transition time becomes almost the same across all concentrations considered. More interestingly, there is no significant difference in the transition time between viscoelastic and Newtonian flows. The dependence of Reynolds number and detailed transition dynamics will be further discussed.