Flow Structure and Penetration Behavior of a Submerged Annular Jet of a Bingham Fluid

The flow and penetration characteristics of a submerged annular jet of a Bingham non-Newtonian fluid were investigated numerically within the steady laminar flow regime. Central and outer recirculation regions typically characterize the flow of a Newtonian annular jet. However, in the case of a Bingham jet, once a critical yield number is exceeded, flow recirculation throughout the whole flow field is eliminated and stagnant, attached-to-the-wall regions are formed. Extent of the outer recirculation region and the recirculation strength of both the outer and central regions are found to significantly diminish with the yield number. The axial penetration of a submerged annular jet decreases with the inner-to-outer annular nozzle diameter ratio and the yield numbers. Annular jets of yield stress fluids decay continuously, very rapidly, and can vanish within the initial few jet diameters. The point at which the axial momentum of the jet vanishes shifts upstream with both the yield number and the annular diameter ratio.