On the analysis of laminar-turbulent transition in viscoelastic channel flows*

It is well-known that adding small amounts of long-chain polymers to turbulent flows leads to a significant drag reduction compared to Newtonian flows. Therefore, numerous efforts have been made to understand the drag-reduction mechanisms. However, the study on the transitional behavior of viscoelastic flows remains limited as only early or delayed transition is often reported in the literature. In this study, we perform direct numerical simulations of viscoelastic turbulent channel flows to investigate the dynamics of the laminar-turbulent transition. Disturbance flows are added to perturb the laminar flow to induce the transition. Variables of interest are Reynolds number, polymer concentration, and perturbation magnitude. Preliminary results show that at low Reynolds numbers close to transition, the effect of polymer solutions is imperceptible. The probability of inducing the transition is similar for Newtonian and viscoelastic flows, regardless of the perturbation magnitude. However, at higher Reynolds numbers, viscoelastic flows appear to have a stabilizing effect, especially for higher perturbation magnitudes. At a given perturbation magnitude, polymer solutions show a lower probability of transition in comparison to the Newtonian flow. The effect of polymer concentration will also be discussed.