Transient rod-climbing in an Oldroyd-B fluid

TL;DR

This paper analyzes the transient behavior of the rod-climbing effect in an Oldroyd-B fluid using asymptotic analysis, revealing boundary layer dynamics and the interplay of inertia and viscoelasticity.

Contribution

It introduces a time-dependent analysis of the rod-climbing phenomenon in Oldroyd-B fluids, extending previous steady-state models with transient and inertial effects.

Findings

Identification of a boundary layer in the transient interface rise

Derivation of short-time transient velocity and interface profiles

Proposed criteria for rod-climbing occurrence considering inertia

Abstract

The Weissenberg effect, or rod-climbing phenomenon, occurs in non-Newtonian fluids where the fluid interface ascends along a rotating rod. Despite its prominence, theoretical insights into this phenomenon remain limited. In earlier work, Joseph \& Fosdick (\emph{Arch. Rat. Mech. Anal.}, vol. 49, 1973, pp. 321--380) employed domain perturbation methods for second-order fluids to determine the equilibrium interface height by expanding solutions based on the rotation speed. In this work, we investigate the time-dependent interface height through asymptotic analysis with dimensionless variables and equations using the Oldroyd-B model. We begin by neglecting surface tension and inertia to focus on the interaction between gravity and viscoelasticity. In the small-deformation scenario, the governing equations indicate the presence of a boundary layer in time, where the interface rises rapidly over a short time scale before gradually approaching a steady state. By employing a stretched time variable, we derive the transient velocity field and corresponding interface profile on this short time scale and recover the steady-state profile on a longer time scale. Subsequently, we reintroduce small but finite inertial effects to investigate their interplay with viscoelasticity and propose a criterion for determining the conditions under which rod-climbing occurs.