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Velocity gradient
About: Velocity gradient is a research topic. Over the lifetime, 3013 publications have been published within this topic receiving 77120 citations.
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TL;DR: In this paper, an ellipsoidal model was constructed to describe the morphological evolution and rheological properties of a mixture of two immiscible viscoelastic components.
Abstract: An ellipsoidal model was constructed to describe the morphological evolution and rheological properties of a mixture of two immiscible viscoelastic components. The phenomenological parameters in the model were determined by comparing the interfacial velocity gradient with the viscoelastic theory for small deformation. The model was then applied to various model blend systems to predict the steady deformation, transient deformation, and relaxation after cessation of step shear flow. The model predictions were also compared with some available numerical simulations. The predictions on droplet deformation both in steady and transient regimes as well as the relaxation process were found to be in good agreement with the experimental results in literatures. The rheological properties predicted by the present model were also found to agree with the experimental results.
46 citations
TL;DR: In this paper, a mixed convection flow and heat transfer of pseudo-plastic power law nanofluid past a stretching vertical plate is investigated, where three types of nano-particles, such as copper (Cu), aluminum oxide (Al2O3) and titanium oxide (TiO2), are considered.
46 citations
01 Jul 1990
TL;DR: In this paper, the authors investigated the nature of the momentum transport processes responsible for the Reynolds shear stress using several ensembles of fluid particle paths obtained from a direct numerical simulation of turbulent channel flow and found that the Reynolds stress can be viewed as arising from two fundamentally different mechanisms.
Abstract: The nature of the momentum transport processes responsible for the Reynolds shear stress is investigated using several ensembles of fluid particle paths obtained from a direct numerical simulation of turbulent channel flow. It is found that the Reynolds stress can be viewed as arising from two fundamentally different mechanisms. The more significant entails transport in the manner described by Prandtl in which momentum is carried unchanged from one point to another by the random displacement of fluid particles. One-point models, such as the gradient law are found to be inherently unsuitable for representing this process. However, a potentially useful non-local approximation to displacement transport, depending on the global distribution of the mean velocity gradient, may be developed as a natural consequence of its definition. A second important transport mechanism involves fluid particles experiencing systematic accelerations and decelerations. Close to the wall this results in a reduction in Reynolds stress due to the slowing of sweep-type motions. Further away Reynolds stress is produced in spiralling motions, where particles accelerate or decelerate while changing direction. Both transport mechanisms appear to be closely associated with the dynamics of vortical structures in the wall region.
46 citations
TL;DR: In this paper, the authors examined flow birefringence and flow modification effects for two-dimensional extensional flows of polystyrene solutions at two concentrations in the semidilute regime.
Abstract: We examine flow birefringence and flow modification effects (polymer‐induced changes in the flow field) for two‐dimensional extensional flows of polystyrene solutions at two concentrations in the semidilute regime. The concentrations of the polymer solutions are 1500 and 4500 ppm. This corresponds to ∼0.33 and 1.0×c*, the critical concentration for domain overlap of coiled polymer molecules at equilibrium. Results from a dilute 100 ppm solution of the same polymer sample are also presented for comparison. From the steady flow birefringence results, it appears that polymer chain extension is inhibited due to intermolecular interactions as the concentration is increased. In addition, inception of steady flow experiments show distinctive overshoots in birefringence. The main result of the velocity gradient measurements in this study is that the semidilute polymer solutions (1500 and 4500 ppm) show significant inhibition of high strain rates. The onset of flow modification corresponds to a critical effective ...
46 citations
TL;DR: In this paper, the velocity of solid particles flowing in an inclined open channel of which the bottom plate was covered with very rough sandpaper was measured for three kinds of particle, and the observed velocity distributions were analyzed based on the variational principle, by which the velocity distribution could be obtained as the solution which minimized a certain integral consisting of several energy terms.
Abstract: The velocity of solid particles flowing in an inclined open channel of which the bottom plate was covered with very rough sandpaper was measured for three kinds of particle. Except for the region near the bottom plate, the velocity distribution normal to the bottom plate appeared to be linear. The velocity gradient in that region was almost independent of the thickness of the particle layer and increased as the slope of the channel became steep. These observed velocity distributions were analyzed based on the variational principle, by which the velocity distribution could be obtained as the solution which minimized a certain integral consisting of several energy terms. It was found that such analysis could explain the main feature of the particle flow in an inclined channel, and the following relation between stress and rate of deformation was obtained. τyz=kτy-kμy(dvz/dy) It was also found that the critical inclination angle of the channel, which was anticipated by the analysis, corresponded to the angle of repose.
46 citations