The Experts below are selected from a list of 17316 Experts worldwide ranked by ideXlab platform
Tianshou Zhao - One of the best experts on this subject based on the ideXlab platform.
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effect of the forcing term in the multiple relaxation time lattice boltzmann equation on the shear stress or the strain Rate Tensor
Physical Review E, 2012Co-Authors: Zhenhua Chai, Tianshou ZhaoAbstract:In this work, the effect of the forcing term (or external force) in the multiple-relaxation-time lattice Boltzmann equation (MRTLBE) on the shear stress or the strain Rate Tensor is studied theoretically and numerically. Through a Chapman-Enskog analysis and numerical simulations, we show that the shear stress (or the strain Rate Tensor) derived from the MRTLBE is second-order accuRate in space. We then examine the influence of the forcing term on the shear stress or the strain Rate Tensor, and demonstRate that the forcing term effect must be included when the shear stress or the strain Rate Tensor is computed with the nonequilibrium part of the distribution function.
Zhenhua Chai - One of the best experts on this subject based on the ideXlab platform.
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the computation of strain Rate Tensor in multiple relaxation time lattice boltzmann model
Computers & Mathematics With Applications, 2018Co-Authors: Wenhuan Zhang, Changsheng Huang, Yihang Wang, Baochang Shi, Shibo Kuang, Zhenhua ChaiAbstract:Abstract The multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is an important class of LB model with lots of advantages over the traditional single-relaxation-time (SRT) LB model. Generally, the computation of strain Rate Tensor is crucial for the MRT-LB simulations of some complex flows. At present, only two formulae are available to compute the strain Rate Tensor in the MRT LB model. One is to compute the strain Rate Tensor using the non-equilibrium parts of macroscopic moments (Yu formula). The other is to compute the strain Rate Tensor using the non-equilibrium parts of density distribution functions (Chai formula). The mathematical expressions of these two formulae are so different that we do not know which formula to choose for computing the strain Rate Tensor in the MRT LB model. To overcome this problem, this paper presents a theoretical study of the relationship between Chai and Yu formulae. The results show that the Yu formula can be deduced from the Chai formula, although they have their own advantages and disadvantages. In particular, the Yu formula is computationally more efficient, while the Chai formula is applicable to more lattice patterns of the MRT LB models. Furthermore, the derivation of the Yu formula in a particular lattice pattern from the Chai formula is more convenient than that proposed by Yu et al.
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effect of the forcing term in the multiple relaxation time lattice boltzmann equation on the shear stress or the strain Rate Tensor
Physical Review E, 2012Co-Authors: Zhenhua Chai, Tianshou ZhaoAbstract:In this work, the effect of the forcing term (or external force) in the multiple-relaxation-time lattice Boltzmann equation (MRTLBE) on the shear stress or the strain Rate Tensor is studied theoretically and numerically. Through a Chapman-Enskog analysis and numerical simulations, we show that the shear stress (or the strain Rate Tensor) derived from the MRTLBE is second-order accuRate in space. We then examine the influence of the forcing term on the shear stress or the strain Rate Tensor, and demonstRate that the forcing term effect must be included when the shear stress or the strain Rate Tensor is computed with the nonequilibrium part of the distribution function.
Philippe Coussot - One of the best experts on this subject based on the ideXlab platform.
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Yielding and Flow of Soft-Jammed Systems in Elongation
Physical Review Letters, 2018Co-Authors: X. Zhang, Omar Abdoulaye Fadoul, Elise Lorenceau, Philippe CoussotAbstract:So far, yielding and flow properties of soft-jammed systems have only been studied from simple shear and then extrapolated to other flow situations. In particular, simple flows such as elongations have barely been investigated experimentally or only in a nonconstant, partial volume of material. We show that using smooth tool surfaces makes it possible to obtain a prolonged elongational flow over a large range of aspect ratios in the whole volume of material. The normal force measured for various soft-jammed systems with different microstructures shows that the ratio of the elongation yield stress to the shear yield stress is larger (by a factor of around 1.5) than expected from the standard theory which assumes that the stress Tensor is a function of the second invariant of the strain Rate Tensor. This suggests that the constitutive Tensor of the materials cannot be determined solely from macroscopic shear measurements.
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Breaking of non-Newtonian character in flows through a porous medium
Physical Review E : Statistical Nonlinear and Soft Matter Physics, 2014Co-Authors: Thibaud Chevalier, Stéphane Rodts, Xavier Chateau, Christophe Chevalier, Philippe CoussotAbstract:From NMR measurements we show that the velocity field of a yield stress fluid flowing through a disordered well-connected porous medium is very close to that for a Newtonian fluid. In particular, it is shown that no arrested regions exist even at very low velocities, for which the solid regime is expected to be dominant. This suggests that these results obtained for strongly nonlinear fluid can be extrapolated to any nonlinear fluid. We deduce a generalized form of Darcy's law for such materials and provide insight into the physical origin of the coefficients involved in this expression, which are shown to be moments of the second invariant of the strain Rate Tensor.
Lennart Lofdahl - One of the best experts on this subject based on the ideXlab platform.
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an estimate of the pressure strain Rate Tensor in a plane cylinder wake
Fifth European Turbulence Conference in Siena Italy July 5-8 1994, 1995Co-Authors: Dag Aronson, Lennart LofdahlAbstract:The far wake of a cylinder has been studied in order to provide accuRate experimental information on the normal component of the pressure-strain Rate Tensor by balancing the turbulent kinetic energy budget and Reynolds stress transport (RST) equations. A non-isotropic dissipation Rate Tensor was found, thus fulfilling the basic physical integral constraint of the diffusion and indicating an energy redistribution as described by the pressure-strain Rate correlations.
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the plane wake of a cylinder an estimate of the pressure strain Rate Tensor
Physics of Fluids, 1994Co-Authors: Dag Aronson, Lennart LofdahlAbstract:The modelling of the pressure strain Rate terms is an important issue in the improvement of the generality of closure models for the Reynolds stress transport (RST) equations. A part of these efforts is to provide accuRate experimental information on the pressure-strain Rate Tensor, which in turn requires equally accuRate information on the dissipation and diffusion Tensors. Here the far wake of a cylinder was studied in order to enable the required balances of the RST equations. The experimental results indicate a nonisotropic dissipation Tensor, and show the energy redistribution between the different components as described by the pressure-strain Rate correlations. Comparisons are made between the experimentally determined pressure-strain Rate distributions and the corresponding distributions predicted by closure models.
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measured and modelled component 11 of the dissipation Rate Tensor
13th Turbulence Conference in Missouri-Rolla Missouri, 1992Co-Authors: Dag Aronson, Lennart LofdahlAbstract:The anisotropy of the dissipation Rate Tensor has been studied in the self-preserving region of a cylinder wake. Hot-wire techniques have been employed to measure velocity derivatives in the stream-wise, lateral and normal direction. From these measurements the stream-wise diagonal component of the dissipation Rate Tensor was determined and compared to that predicted by an anisotropic dissipation model. It was found that the dissipation Rate anisotropy could essentially be accounted for by the employed model. Triple velocity correlations were also measured and compared with corresponding profiles obtained from closure models.
James R Dawson - One of the best experts on this subject based on the ideXlab platform.
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invariants of the reduced velocity gradient Tensor in turbulent flows
Journal of Fluid Mechanics, 2013Co-Authors: Jose Cardesa, Dhiren Mistry, James R DawsonAbstract:In this paper we examine the invariants p and q of the reduced 2 2 velocity gradient Tensor (VGT) formed from a two-dimensional (2D) slice of an incompressible three-dimensional (3D) flow. Using data from both 2D particle image velocimetry (PIV) measurements and 3D direct numerical simulations of various turbulent flows, we show that the joint probability density functions (p.d.f.s) of p and q exhibit a common characteristic asymmetric shape consistent with hpqi < 0. An explanation for this inequality is proposed. Assuming local homogeneity we derive hpiD 0 and hqiD 0. With the addition of local isotropy the sign ofhpqi is proved to be the same as that of the skewness of @u1=@x1, hence negative. This suggests that the observed asymmetry in the joint p.d.f.s of p‐q stems from the universal predominance of vortex stretching at the smallest scales. Some advantages of this joint p.d.f. compared with that of Q‐R obtained from the full 3 3 VGT are discussed. Analysing the eigenvalues of the reduced strain-Rate matrix associated with the reduced VGT, we prove that in some cases the 2D data can unambiguously discriminate between the bi-axial (sheetforming) and axial (tube-forming) strain-Rate configurations of the full 3 3 strain-Rate Tensor.
