Visualization of an annular viscoplastic jet

The current study investigates the global flow field characteristics of a submerged annular viscoplastic jet. The mass and momentum conservation equations, governing the steady laminar flow field, along with the Bingham rheological model, are numerically solved using a finite-difference scheme. Central and outer recirculation regions typically characterize the flow of a Newtonian annular jet. However, the current visualizations demonstrate the existence of new and unique-to-viscoplastic-fluids flow features. When the yield numbers are small, central and outer recirculation regions exist. However, the extent of the outer region and recirculation intensity of the outer and central regions are found to substantially diminish with the yield number. At intermediate yield numbers, a stagnant, attached-to-the-wall region replaces the outer recirculation while a central, yet weaker one, exists. At high yield numbers, stagnant regions replace the recirculating ones, i.e., flow recirculation throughout the whole flow field is eliminated once a critical yield number is exceeded.Graphical Abstract