# Start-up inertia as an origin for heterogeneous flow

## TL;DR

This paper demonstrates that start-up inertia in simple yield stress fluids can induce transient shear banding even under homogeneous stress conditions, challenging previous assumptions about the necessity of non-monotonic flow curves.

## Contribution

It introduces a novel mechanism where fluid start-up inertia causes shear banding, supported by CFD simulations, in simple yield stress fluids under realistic conditions.

## Key findings

- Inertia can initiate shear banding without stress heterogeneity.
- Transient shear banding occurs even with homogeneous stress conditions.
- The mechanism is relevant to experimental setups.

## Abstract

For quite some time non-monotonic flow curve was thought to be a requirement for shear banded flows in complex fluids. Thus, in simple yield stress fluids shear banding was considered to be absent. Recent spatially resolved rheological experiments have found simple yield stress fluids to exhibit shear banded flow profiles. One proposed mechanism for the initiation of such transient shear banding process has been a small stress heterogeneity rising from the experimental device geometry. Here, using Computational Fluid Dynamics methods, we show that transient shear banding can be initialized even under homogeneous stress conditions by the fluid start-up inertia, and that such mechanism indeed is present in realistic experimental conditions.