Flow Instability: Transition and Non Linearity

The addition of small amounts of long-chain polymers to a turbulent flow has been well reported because of its beneficial effect on drag reduction. Numerous experimental and numerical efforts have been made to understand the mechanisms of turbulent drag reduction. However, a better understanding of the transitional behavior of viscoelastic flows has yet to be fully investigated despite its fundamental importance for flow control. For this study, we perform direct numerical simulations of a laminar base flow disturbed by repeatable finite-amplitude disturbances in the laminar velocity field. These studies are performed at relatively low Reynolds numbers close to transition. Preliminary results show that at low Reynolds numbers, the effect of polymers is imperceptible. Interestingly, at higher Reynolds numbers, polymers appear to have a stabilizing effect, in comparison to the Newtonian flow. Similar behavior is observed when changing the disturbance amplitude at a fixed low-Reynolds number. The effect that different disturbance structures have on the flow and polymer dynamics, which result in earlier or delayed transition for viscoelastic flows in comparison to its Newtonian counterpart, should be further discussed.

Funding acknowledgement

This work was supported by the National Science Foundation through CBET-2154788 (CAREER Award).