Numerical Study of Bifurcating Flow through Sudden Expansions: Effect of divergence and geometric asymmetry

TL;DR

This study numerically investigates how divergence and asymmetry in channels affect laminar flow bifurcations and symmetry breaking during sudden expansions, revealing that geometric asymmetries smoothen bifurcations and lead to unique flow solutions.

Contribution

It introduces a comparative analysis of flow symmetry and bifurcation behavior using CFD and Lattice Boltzmann methods under various geometric asymmetries.

Findings

Wall divergence disrupts flow symmetry and bifurcation patterns.

Small asymmetries smoothen bifurcation transitions.

Large asymmetries eliminate bifurcation, leading to unique flow solutions.

Abstract

A numerical study of laminar flow through symmetric and slightly asymmetric sudden expansion, of expansion ratio 1:3, in channels with increasing cross section, is carried out using two different approaches - Conventional CFD and Lattice Boltzmann Method. The effect of divergence of walls of the channel, after a sudden expansion, on the symmetry of flow and recirculation is studied for various Reynolds numbers. It is seen that the angles of the walls play an active role in disrupting the symmetry of flow. For non-parallel walls, the symmetry breaking bifurcation phenomenon no longer exists and the loss of symmetry is a gradual process. The effect of asymmetry of geometry on flow is also studied by considering two types of asymmetry - First type is at the plane of expansion where the steps on either side are of unequal heights, while the second one deals the walls of the channel are at a different inclination with the direction of inflow. The present study reveals that small asymmetry impedes the sharp transition and thus smoothens the pitchfork bifurcation. Increased asymmetry finally leads to the unique solution of the governing Equations, indicating complete loss of bifurcation pattern.