Axially strained flow in a porous duct of circular-sector cross-section

TL;DR

This study investigates the complex flow patterns in a porous circular-sector duct under axial strain, revealing how flow symmetry breaks at higher Reynolds numbers and how geometry influences pressure gradients.

Contribution

It provides new insights into flow symmetry loss, vortex structures, and the impact of duct geometry on pressure gradients in porous ducts under axial strain.

Findings

Flow remains symmetric at low Reynolds numbers.

Symmetry breaks and asymmetric vortices form at higher Reynolds numbers.

Pressure-gradient coefficient depends on duct geometry and flow symmetry.

Abstract

A canonical problem of axially strained flow in a duct of circular-sector cross-section, with fluid injection through the circular arc, is examined for a range of Reynolds numbers and sector angles. At small Reynolds numbers, the flow remains symmetric about the mid-plane; however, symmetry is rapidly lost as the Reynolds number exceeds order one, giving rise to asymmetric structures. These flows are characterised by dominant vortices on one side of the duct and secondary vortices on the other when the Reynolds number is sufficiently large. The interaction between interior vortex structures and boundary layers on porous and impermeable walls governs the separation and attachment of the latter. The axial pressure-gradient coefficient, which also determines the axial strain rate, approaches a constant value at large Reynolds numbers; yet, in contrast to the classical Taylor-Culick result, its value depends sensitively upon duct geometry and flow symmetry. The results underscore the significance of considering partial-wall injection and asymmetric solutions in practical applications.