Herschel–Bulkley fluid

About: Herschel–Bulkley fluid is a research topic. Over the lifetime, 1946 publications have been published within this topic receiving 49318 citations.

Shear Stress Fluctuations in the Granular Liquid and Solid Phases

Abstract: We report on experimentally observed shear stress fluctuations in both granular solid and fluid states, showing that they are non-Gaussian at low shear rates, reflecting the predominance of correlated structures (force chains) in the solidlike phase, which also exhibit finite rigidity to shear. Peaks in the rigidity and the stress distribution's skewness indicate that a change to the force-bearing mechanism occurs at the transition to fluid behavior, which, it is shown, can be predicted from the behavior of the stress at lower shear rates. In the fluid state stress is Gaussian distributed, suggesting that the central limit theorem holds. The fiber bundle model with random load sharing effectively reproduces the stress distribution at the yield point and also exhibits the exponential stress distribution anticipated from extant work on stress propagation in granular materials.

The sedimentation of a sphere through an elastic fluid Part 2. Transient motion

Abstract: Direct comparisons of time-dependent finite-element simulations and experimental observations are presented for the transient benchmark problem of a sphere accelerating from rest in a cylindrical tube of viscoelastic fluid. Finite-element calculations of the trajectory of the sphere using a nonlinear dumbbell model and a nonlinear network model are compared with experimental measurements obtained using a digital video-imaging system. The test fluid is a highly elastic polyisobutylene Boger fluid, and comparisons are carried out over a wide range of Deborah numbers, 0≤De≤11, and for a range of sphere/tube radius ratios, 0.12≤ a R ≤0.63 . In the experiments, the sphere shows a velocity overshoot with a magnitude that is a strong function of the density of the sphere, the radius ratio of the geometry and the Deborah number of the flow. This transient motion is heavily over-damped as a result of the high solvent viscosity of the Boger fluid. The numerical calculations show that significant differences in the transient velocity of the sphere are predicted by the network and dumbbell models, partly as a consequence of the variations in the time-dependent viscometric functions predicted in the start-up of simple shear flow. At short times, the flow is governed by the linear viscoelastic response of the fluid; however, at longer times and higher strains, nonlinear fluid rheology becomes increasingly important. A good description of the experimentally observed trajectory of the sphere can be obtained with a multimode formulation of the nonlinear Phan-Thien-Tanner network model by incorporating both a spectrum of relaxation times and a set of nonlinear model parameters which accurately describe the normal stress response of the fluid in steady shear and in transient uniaxial elongation.

Lagrangian viscoelastic flow computations using a generalized molecular stress function model

Abstract: A new finite element technique for the numerical simulation of 3D time-dependent flow of viscoelastic fluid is presented. The technique is based on a Lagrangian kinematics description of the fluid flow. It represents a further development of the 3D Lagrangian integral method (3D-LIM) from a Rivlin–Sawyers fluid to a fluid described by a generalized molecular stress function (MSF) model allowing the use of dissipative convective constraint release in the constitutive equation. The convergence of the method is demonstrated on the axis-symmetric problem of the inflation of a polymeric membrane only restricted by a clamping ring.