The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Arnaud Perrot - One of the best experts on this subject based on the ideXlab platform.
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Two-scale nonlocal Shear Rate formulation of Bingham plastic fluid
Applied Mathematical Modelling, 2015Co-Authors: Vincent Picandet, Noel Challamel, Arnaud PerrotAbstract:This paper deals with a phenomenological model based on a nonlocal Bingham constitutive law. This nonlocal viscoplastic law accounts for possible microstructured effects of a heterogeneous fluid. Thermodynamic arguments are presented for the justification of this two-scale nonlocal Shear Rate law, which can be specialized either as a purely nonlocal or a gradient-type Bingham law. Plane Shearing and uniaxial flow assumptions between parallel walls are basic and tractable hypotheses for a first investigation of nonlocal and gradient Shear Rate law. Analytical solutions are presented for the plane Poiseuille stationary flow inside a straight smooth channel of infinite width. Two higher boundary conditions at the walls are assumed for this so-called micromorphic medium, a static higher-order boundary condition and a kinematic one. A boundary layer phenomenon can be observed for such nonlocal problems. Parametric studies show the key role of the characteristic lengths of the nonlocal model on the Shear flow phenomena. Consequently, the heterogeneous nature of microstructured yield-stress fluids may significantly affect velocity profiles, maximum velocity and total flow Rate, which have been recently reported in literature.
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processing the couette viscometry data using a bingham approximation in Shear Rate calculation
Journal of Non-newtonian Fluid Mechanics, 2008Co-Authors: Patrice Estellé, Christophe Lanos, Arnaud PerrotAbstract:Abstract This paper presents an approach to computing the Shear flow curve from torque–rotational velocity data in a Couette rheometer. The approximation techniques in Shear Rate calculation are generally dictated by the radius ratio between coaxial cylinders and the rheological behaviour of fluid tested. Here, the approach consists in analysing the Sheared material as a Bingham fluid and computing an average Shear Rate when the fluid in the cylindrical gap is partially and fully Sheared. We focus in particular on the applicability of the Bingham approximation in Shear Rate calculation. First, the approach is assessed by examining synthetic data geneRated with Newtonian, non-Newtonian and yield stress materials with known properties, varying the gap radius ratio. The results, which are compared with commonly used techniques in Shear Rate calculation, prove the relevance of the proposed approach. Finally, its efficiency is examined by applying it to process Couette data of yield stress fluids taken from published works.
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Processing the Couette viscometry data using a Bingham approximation in Shear Rate calculation
Journal of Non-Newtonian Fluid Mechanics, 2008Co-Authors: Patrice Estellé, Christophe Lanos, Arnaud PerrotAbstract:This paper presents an approach to computing the Shear flow curve from torque-rotational velocity data in a Couette rheometer. The approximation techniques in Shear Rate calculation are generally dictated by the radius ratio between coaxial cylinders and the rheological behaviour of fluid tested. Here, the approach consists in analysing the Sheared material as a Bingham fluid and computing an average Shear Rate when the fluid in the cylindrical gap is partially and fully Sheared. We focus in particular on the applicability of the Bingham approximation in Shear Rate calculation. First, the approach is assessed by examining synthetic data geneRated with Newtonian, non-Newtonian and yield stress materials with known properties, varying the gap radius ratio. The results, which are compared with commonly used techniques in Shear Rate calculation, prove the relevance of the proposed approach. Finally, its efficiency is examined by applying it to process Couette data of yield stress fluids taken from published works. © 2008 Elsevier B.V. All rights reserved.
Parviz Moin - One of the best experts on this subject based on the ideXlab platform.
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structure of turbulence at high Shear Rate
Journal of Fluid Mechanics, 1990Co-Authors: Parviz MoinAbstract:The structure of homogeneous turbulence subject to high Shear Rate has been investigated by using three-dimensional, time-dependent numerical simulations of the Navier–Stokes equations. The instantaneous velocity fields reveal that a high Shear Rate produces structures in homogeneous turbulence similar to the ‘streaks’ that are present in the sublayer of wall-bounded turbulent Shear flows. Statistical quantities such as the Reynolds stresses are compared with those in the sublayer of a turbulent channel flow at a comparable Shear Rate made dimensionless by turbulent kinetic energy and its dissipation Rate. This study indicates that high Shear Rate alone is sufficient for generation of the streaky structures, and that the presence of a solid boundary is not necessary. Evolution of the statistical correlations is examined to determine the effect of high Shear Rate on the development of anisotropy in turbulence. It is shown that the streamwise fluctuating motions are enhanced so profoundly that a highly anisotropic turbulence state with a ‘one-component’ velocity field and ‘two-component’ vorticity field develops asymptotically as total Shear increases. Because of high Shear Rate, rapid distortion theory predicts remarkably well the anisotropic behaviour of the structural quantities.
Frantisek Stepanek - One of the best experts on this subject based on the ideXlab platform.
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Wall Shear Rate distribution for flow in random sphere packings
Physical Review Letters, 2008Co-Authors: Patrick B Warren, Frantisek StepanekAbstract:The wall Shear Rate distribution P(I) is investigated for pressure-driven Stokes flow through random arrangements of spheres at packing fractions 0.1Ï•0.64. For dense packings, P(I) is monotonic and approximately exponential. As Ï0.1, P(I) picks up additional structure which corresponds to the flow around isolated spheres, for which an exact result can be obtained. A simple expression for the mean wall Shear Rate is presented, based on a force-balance argument. © 2008 The American Physical Society.
Petr Filip - One of the best experts on this subject based on the ideXlab platform.
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effect of Shear Rate on aggregate size and structure in the process of aggregation and at steady state
Powder Technology, 2013Co-Authors: Petra Bubakova, Martin Pivokonsky, Petr FilipAbstract:Abstract The paper deals with the dependence of aggregate properties on the Shear Rate ( G ) in the aggregation process and at steady state. Natural raw water and ferric sulphate were aggregated in a Taylor–Couette reactor. The methods of image and fractal analysis were used to determine the aggregate size and structure. It was observed that at the early phase of aggregation, the aggregate growth Rate is higher for lower Shear Rates. At G ≤ 150 s − 1 , the time aggregation curve contains the local maximum before reaching the steady state. Moreover, the different extent of break-up and restructuring was proved for different values of Shear Rate. At G ≥ 200 s − 1 , the aggregation curve misses the local extreme completely. It was found that with increasing Shear Rate ( G = 21.2–347.9 s − 1 ), the aggregates are smaller ( d = 1504–56 μm), more compact ( D 2 = 1.54–1.91) and more regular ( D pf = 1.37–1.10). A relationship for the description of dependence of fractal dimension on the Shear Rate was also suggested.
Leonard Kritharides - One of the best experts on this subject based on the ideXlab platform.
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Flow recirculation zone length and Shear Rate are differentially affected by stenosis severity in human coronary arteries
American Journal of Physiology-Heart and Circulatory Physiology, 2013Co-Authors: Ashkan Javadzadegan, Andy S. C. Yong, Austin C. C. Ng, John Yiannikas, Michael Chang, Martin K C Ng, Masud Behnia, Leonard KritharidesAbstract:Flow recirculation zones and Shear Rate are associated with distinct pathogenic biological pathways relevant to thrombosis and atherogenesis. The interaction between stenosis severity and lesion eccentricity in determining the length of flow recirculation zones and peak Shear Rate in human coronary arteries in vivo is unclear. Computational fluid dynamic simulations were performed under resting and hyperemic conditions on computer-geneRated models and three-dimensional (3-D) reconstructions of coronary arteriograms of 25 patients. Boundary conditions for 3-D reconstructions simulations were obtained by direct measurements using a pressure-temperature sensor guidewire. In the computer-geneRated models, stenosis severity and lesion eccentricity were strongly associated with recirculation zone length and maximum Shear Rate. In the 3-D reconstructions, eccentricity increased recirculation zone length and Shear Rate when lesions of the same stenosis severity were compared. However, across the whole population of coronary lesions, eccentricity did not correlate with recirculation zone length or Shear Rate (P = not signficant for both), whereas stenosis severity correlated strongly with both parameters (r = 0.97, P < 0.001, and r = 0.96, P < 0.001, respectively). Nonlinear regression analyses demonstRated that the relationship between stenosis severity and peak Shear was exponential, whereas the relationship between stenosis severity and recirculation zone length was sigmoidal, with an apparent threshold effect, demonstrating a steep increase in recirculation zone length between 40% and 60% diameter stenosis. Increasing stenosis severity and lesion eccentricity can both increase flow recirculation and Shear Rate in human coronary arteries. Flow recirculation is much more sensitive to mild changes in the severity of intermediate stenoses than is peak Shear.
