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.

Effect of Slip Condition on Unsteady Flows of an Oldroyd-B Fluid between Parallel Plates

Abstract: The unsteady flows of an incompressible Oldroyd-B fluid between two infinite parallel plates are considered when the slippage between the plate and the fluid is valid. The relative velocity between the fluid and plate is assumed to be proportional to the shear rate at the plates. The flow is generated by moving one of the plates or application of the constant pressure gradient giving arise to two unsteady boundary value problems. Analytical solutions of the problems are obtained. Effects of various dimensionless parameters emerging in the model on velocity field are presented graphically. It is shown that the solution exists for all values of non-Newtonian parameters. The solutions with no-slip condition for Maxwell, second grade and viscous fluid appear as limiting cases of the present results .

Comparing thixotropic and Herschel–Bulkley parameterizations for continuum models of avalanches and subaqueous debris flows

Abstract: . Avalanches and subaqueous debris flows are two cases of a wide range of natural hazards that have been previously modeled with non-Newtonian fluid mechanics approximating the interplay of forces associated with gravity flows of granular and solid–liquid mixtures. The complex behaviors of such flows at unsteady flow initiation (i.e., destruction of structural jamming) and flow stalling (restructuralization) imply that the representative viscosity–stress relationships should include hysteresis: there is no reason to expect the timescale of microstructure destruction is the same as the timescale of restructuralization. The non-Newtonian Herschel–Bulkley relationship that has been previously used in such models implies complete reversibility of the stress–strain relationship and thus cannot correctly represent unsteady phases. In contrast, a thixotropic non-Newtonian model allows representation of initial structural jamming and aging effects that provide hysteresis in the stress–strain relationship. In this study, a thixotropic model and a Herschel–Bulkley model are compared to each other and to prior laboratory experiments that are representative of an avalanche and a subaqueous debris flow. A numerical solver using a multi-material level-set method is applied to track multiple interfaces simultaneously in the simulations. The numerical results are validated with analytical solutions and available experimental data using parameters selected based on the experimental setup and without post hoc calibration. The thixotropic (time-dependent) fluid model shows reasonable agreement with all the experimental data. For most of the experimental conditions, the Herschel–Bulkley (time-independent) model results were similar to the thixotropic model, a critical exception being conditions with a high yield stress where the Herschel–Bulkley model did not initiate flow. These results indicate that the thixotropic relationship is promising for modeling unsteady phases of debris flows and avalanches, but there is a need for better understanding of the correct material parameters and parameters for the initial structural jamming and characteristic time of aging, which requires more detailed experimental data than presently available.

Progressive fluid deformation in low Reynolds number flow past a falling cylinder

Abstract: A new laboratory technique is outlined by which the flow of a very viscous fluid can be made visible and finite strains and fluid rotations in the flow can be measured. The technique involves the emplacement of a pattern of grid lines in a plane through the fluid before the flow begins. The grid lines are in fact formed by placing an ‘‘unfixed’’ photocopy in contact with a surface of the fluid, thereby transferring carbon particles from the photocopying paper on to the fluid, and then bringing that surface of the fluid into contact with another similar volume of fluid. The carbon particles are therefore embedded within the working volume of fluid. Use of the technique, and some of the results that can be obtained, are demonstrated by the example of flow about a falling cylinder.

Vehicle heat generator and viscous fluid therefor

Abstract: A non-Newtonian fluid (for instance, a specific silicone oil) having a tendency that the apparent viscosity decreases as the shearing speed of a rotor (33) increases is used as a viscous fluid (F) that is contained in a vehicle heat generator provided with the rotor (33). The nominal viscosity of the viscous fluid (F) ranges from 10,000 cSt to 200,000 cSt. By using the viscous fluid, the shearing heat generating function of the viscous fluid (F) can be maintained for a long time even when the viscous fluid bears excessive shearing due to excessive rotation of the rotor (33), and the rotor (33) can be easily activated from the stationary state at a lower temperature.