Paper Number
PO48
Session
Poster Session
Title
Interplay of shear banding and wall slip
Presentation Date and Time
October 12, 2022 (Wednesday) 6:30
Track / Room
Poster Session / Riverwalk A
Authors
- McCauley, Patrick J. (University of Minnesota, Chemical Engineering and Materials Science)
- Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)
- Kumar, Satish (University of Minnesota, Department of Chemical Engineering and Materials Science)
Author and Affiliation Lines
Patrick J. McCauley, Michelle A. Calabrese and Satish Kumar
Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
Speaker / Presenter
McCauley, Patrick J.
Keywords
flow-induced instabilities; surfactants
Text of Abstract
Shear banding, the separation of flow into distinct regions of shear rate, is well studied in wormlike micelles (WLMs) and often accompanied by some degree of wall slip, a phenomenon where the velocity of a fluid at a moving surface is less than the surface velocity. Despite being observed simultaneously, the relationship between wall slip and shear banding is still not fully understood. A significant complication is the inconsistent manifestation of wall slip; sometimes wall slip is observed near the onset of flow while sometimes wall slip is observed after shear-banded flow has developed. Additionally, wall slip is difficult to quantify in shear-banding experiments because of large shear-rate gradients near the interface. To investigate the interplay between these phenomena, the evolution of shear banded flows with and without wall slip is simulated using the Germann-Cook-Beris (GCB) model of WLMs. Motivated by the few datasets that quantify wall slip with shear banding, simple shear-rate and stress-dependent slip laws are postulated and applied at the moving boundary. Wall slip is found to preclude shear banding at low shear rates where shear banding may otherwise be expected, consistent with experimental observations. During shear startup, wall slip dampens the magnitude of shear-rate gradients, which extends the time for shear-banded flow to develop. Additionally, wall slip reduces the magnitude of flow reversal, a phenomenon where portions of the fluid move opposite to the imposed wall velocity, which is predicted by the GCB model but only observed in select WLM systems. In cases where wall slip precludes shear banding, the evolution of stress appears qualitatively similar to a shear-banded flow, highlighting the importance of local measurements of the flow field to confirm the presence of shear banding. The interplay of wall slip and shear banding is complex, and this work emphasizes the need for new experiments to quantify wall slip to improve models of both shear banding and wall slip.