On flow through furrowed channels. Part 2. Observed flow patterns

Abstract

Observations of flow in furrowed channels support the calculations of part 1 (Sobey 1980). If the mainstream flow is steady there is a critical Reynolds number below which separation does not occur. Above that Reynolds number vortices form and fill the furrow. When the mainstream is oscillatory, the flow may separate during the acceleration to form strong vortices. During the deceleration the vortices grow to fill the furrow and channel. As the mainstream reverses the vortices are ejected from the furrows as the fluid flows between the wall and the vortex. Photographs show that this pattern occurs for sinusoidally varying walls, furrows that are arcs of circles and rectangular hollows.