The Flow and Decay Behavior of a Submerged Shear Thinning Jet With Yield Stress

Abstract

The flow and decay characteristics of submerged jets of shearthinning fluids with yield stress are studied. Numerical solutions to the governing mass and momentum conservation equations, along with the Herschel–Bulkley rheological model, are obtained using a finitedifference scheme. A parametric study is implemented to investigate the influence of flow inertia and rheology over the following range of parameters: Reynolds number, 50 ≤ Re ≤ 200; yield number, 0 ≤ Y ≤ 1; and shearthinning index, 0.6 ≤ n ≤ 1. A large recirculation region exists for Newtonian and shearthinning nonNewtonian jets. However, the extent and strength of the recirculation region substantially diminish with the yield number and, to a lesser extent, when the shearthinning index is reduced from 1 to 0.6. Increasing the yield number beyond a critical value eliminates flow recirculation. The centerline velocity and momentum decay of shearthinning jets with yield stress, in general, increase with the yield number. Velocityand momentumbased depths of penetration, DPU, and DPM, respectively, are introduced and presented. DPU and DPM are the downstream locations corresponding to 90% decay in the initial centerline velocity and jet momentum, respectively. A substantial decrease in DPU and DPM is observed when the shearthinning index is reduced from 1 to 0.6 for Y = 0. The presence of yield stress significantly reduces both DPU and DPM of submerged jets. The impact of shearthinning on the decay characteristics of the jet is more pronounced at low yield numbers.