Topic
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, the authors analyzed the behavior of thin films of Reiner-Philippoff fluid in the changeable heat transmission and radiation over a time-dependent stretching sheet in 2D.
Abstract: The current investigation is carried out on the thin film flow of Reiner-Philippoff fluid of boundary-layer type. We have analyzed the flow of thin films of Reiner-Philippoff fluid in the changeable heat transmission and radiation over a time-dependent stretching sheet in 2D. The time-dependent governing equations of Reiner-Philippoff fluid model are simplified with the help of transformation of similarity variables. To investigate the behavior of the Reiner-Philippoff fluid with variable stretching surface for different physical effects, we considered thermophoresis and Brownian motion parameters in the flow. The Homotopy Analysis Method is implemented in the reduced model to achieve a solution of the original problem. A numerical convergence of the implemented method is also analyzed. The behavior of temperature, velocity, and concentration profiles have been investigated with the variation of skin friction, Nusselt number, and Sherwood number. A comparative graphical survey is presented for the velocity gradient, under different parameters. An analytical analysis is presented for the time-dependent parameter over thin film flow. The results we obtained are better than the previously available results. For the survey, the physical representation of the embedded parameters, like, β depends on the stretching parameter ζ , and the Reiner-Philippoff fluid parameter ϵ are discussed in detail and plotted graphically. Prandtl number P r , Brownian motion parameter N b , thermophoretic number N t , and Schmidt number S c are presented by graphs and discussed in detail.
52 citations
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TL;DR: In this article, the torsional vibration of size-dependent viscoelastic nanorods embedded in an elastic medium with different boundary conditions is investigated, which consists of combining the nonlocal theory with the strain and velocity gradient theory to capture both softening and stiffening sizedependent behavior of the nanorod.
52 citations
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TL;DR: In this paper, the full diffusion tensor of shear-induced self-diffusion has been measured experimentally for the first time and the coefficients Dxx and Dxy have been determined for concentrated suspensions of noncolloidal hard spheres as a function of particle volume fraction.
Abstract: The full diffusion tensor of shear-induced self-diffusion has been measured experimentally for the first time. In addition to the well-known components in the velocity gradient, Dyy, and vorticity direction, Dzz, the coefficients Dxx and Dxy have been determined for concentrated suspensions of noncolloidal hard spheres as a function of particle volume fraction. Owing to the shear-induced nature of the phenomenon, these four coefficients are the only nonzero elements of the diffusion tensor. The newly determined diffusion quantities have been obtained by extending our correlation based technique [J. Fluid Mech. 375, 297 (1998); Phys. Rev. E 63, 021403 (2001)] with a method to subtract convective displacements due to the shear flow. The diffusion in the velocity direction, Dxx, is almost an order of magnitude larger than the other components and the only nonzero off-diagonal component, Dxy, is negative and small compared to the diagonal components of the diffusion tensor. In principle the applied technique is also feasible for measuring other anisotropic diffusion mechanisms, e.g., Brownian diffusion in steady shear flow.
52 citations
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TL;DR: In this paper, the mean flow distributions and turbulent statistics inside a canopy with complex geometry and multiple scales consisting of fractal, tree-like objects are studied and the results show that the trees leave their signatures in the flow by imprinting wake structures with shapes similar to the trees.
Abstract: Particle image velocimetry laboratory measurements are carried out to study mean flow distributions and turbulent statistics inside a canopy with complex geometry and multiple scales consisting of fractal, tree-like objects. Matching the optical refractive indices of the tree elements with those of the working fluid provides unobstructed optical paths for both illuminations and image acquisition. As a result, the flow fields between tree branches can be resolved in great detail, without optical interference. Statistical distributions of mean velocity, turbulence stresses, and components of dispersive fluxes are documented and discussed. The results show that the trees leave their signatures in the flow by imprinting wake structures with shapes similar to the trees. The velocities in both wake and non-wake regions significantly deviate from the spatially-averaged values. These local deviations result in strong dispersive fluxes, which are important to account for in canopy-flow modelling. In fact, we find that the streamwise normal dispersive flux inside the canopy has a larger magnitude (by up to four times) than the corresponding Reynolds normal stress. Turbulent transport in horizontal planes is studied in the framework of the eddy viscosity model. Scatter plots comparing the Reynolds shear stress and mean velocity gradient are indicative of a linear trend, from which one can calculate the eddy viscosity and mixing length. Similar to earlier results from the wake of a single tree, here we find that inside the canopy the mean mixing length decreases with increasing elevation. This trend cannot be scaled based on a single length scale, but can be described well by a model, which considers the coexistence of multi-scale branches. This agreement indicates that the multi-scale information and the clustering properties of the fractal objects should be taken into consideration in flows inside multi-scale canopies.
52 citations
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TL;DR: In this article, an extensive set of nonlinear gyrokinetic simulations are performed based on the experimental discharges, investigating the physical mechanism behind the observations, and the impact on the ion heat flux of various parameters that differ within the data-set are explored.
Abstract: Recent experimental observations at JET show evidence of reduced ion temperature profile stiffness. An extensive set of nonlinear gyrokinetic simulations are performed based on the experimental discharges, investigating the physical mechanism behind the observations. The impact on the ion heat flux of various parameters that differ within the data-set are explored. These parameters include the safety factor, magnetic shear, toroidal flow shear, effect of rotation on the magnetohydrodynamic equilibrium, R/L-n, beta(e), Z(eff), T-e/T-i, and the fast-particle content. While previously hypothesized to be an important factor in the stiffness reduction, the combined effect of toroidal flow shear and low magnetic shear is not predicted by the simulations to lead to a significant reduction in ion heat flux, due both to an insufficient magnitude of flow shear and significant parallel velocity gradient destabilization. It is however found that nonlinear electromagnetic effects due to both thermal and fast-particle pressure gradients, even at low beta(e), can significantly reduce the ion heat flux, and is a key factor in explaining the experimental observations. A total of four discharges are examined, at both inner and outer radii. For all cases studied, the simulated and experimental ion heat flux values agree within reasonable variations of input parameters around the experimental uncertainties.
52 citations