Laminar Separation Bubbles in Two-Dimensional Straight-Diverging-Straight Channel Flows

Abstract

Geometries with sudden expansion have been a subject of study for decades now, owing to its engineering applications. While attention has been lavished on flow through symmetric channels with sudden expansion (SE) and backward-facing step (BFS), channels with other divergent angles are studied far less. Straight-diverging-straight (SDS) channels with finite angle of divergences have been studied here. Our focus is on the formation of the laminar separation bubble, typically in the diverging region, and its reattachment downstream. Computations have been carried out to estimate the effect of various parameters such as the angle of divergence $(\alpha )$, the outlet to intet height ratios $(D/d)$ and the Reynolds numbers $(Re)$ on the formation of the recirculation bubble. The extreme case with $\alpha = 90^\circ$ can be compared to the flow through a symmetric sudden-expansion (SE) flow. The base flow obtained from the two open source codes is characterized for the formation of laminar separation bubble for very low Reynolds numbers $(Re)$ in the parametric space including the angle of divergence, $\alpha$ and the expansion ratio, $\kappa =D/d$ and $Re$.