Dimensionless Yield Stress Research Articles

Finite‐Element Simulation of Laminar Viscoplastic Flows with Regions of Recirculation

Solutions are obtained for steady‐state low Reynolds number flow of viscoplastic materials in systems with recirculating eddies using the finite‐element method. The reattachment length and eddy intensity in planar and axisymmetric abrupt expansions are correlated with Reynolds number and dimensionless yield stress for Bingham and Casson materials. Flow in a stenosis is examined using Newtonian and Casson constitutive relationships. The separation zones in a 180 degree planar bifurcation with straight and bent inlets are compared for Bingham and Newtonian fluids. The results show that the size and strength of recirculation is reduced for viscoplastic materials.

Numerical solution of a casson fluid flow in the entrance of annular tubes

The solution of the momentum equation for a Casson fluid flowing in the entrance region of an annular tube has been obtained. The results have been presented for a large range of radii ratio and dimensionless yield stress. The mathematical accuracy of the numerical procedure is demonstrated by comparing the asymptotic velocity profiles at large axial distance with fully developed solution [1]. In addition, the results of the numerical solution for the case of yield stress equal to zero are compared with the entrance flow solution for a Newtonian fluid [2].

Behavior of a Bingham Solid in Hydrodynamic Lubrication : Part 2, Application to Step Bearing

There are few papers in which the effects of the core formation on bearing performances were investigated experimentally and compared with the theoretical results. The process of the core formation has not been observed precisely.We have investigated the behavior of a Bingham solid in hydrodynamic lubrication. The general theory on a Bingham solid was already presented in the first paper.In this paper, we applied this theory to the step bearing and clarified theoretically how the existence of a yield value in shear stress affects the core formation and the bearing performances.After confirming that grease had the behavior of a Bingham solid, we observed the core distribution in the step bearing using grease as a lubricant. And comparing the experimental results with the theory, we found that both agreed and the film pressure and the range of the core formation increased as the dimensionless yield stress increased.