The Experts below are selected from a list of 10578 Experts worldwide ranked by ideXlab platform
Yuelong Xiao - One of the best experts on this subject based on the ideXlab platform.
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vanishing viscosity limit for the 3d nonhomogeneous incompressible navier stokes equations with a Slip Boundary Condition
2017Co-Authors: Pengfei Chen, Yuelong Xiao, Hui ZhangAbstract:In this paper, we investigate the vanishing viscosity limit for the 3D nonhomogeneous incompressible Navier–Stokes equations with a Slip Boundary Condition. We establish the local well-posedness of the strong solutions for initial Boundary value problems for such systems. Furthermore, the vanishing viscosity limit process is established, and a strong rate of convergence is obtained as the Boundary of the domain is flat. In addition, it is needed to add some additional Condition for density to match well the Boundary Condition. Copyright © 2017 John Wiley & Sons, Ltd.
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vanishing viscosity limit for the 3d nonhomogeneous incompressible navier stokes equations with a Slip Boundary Condition
2016Co-Authors: Pengfei Chen, Yuelong Xiao, Hui ZhangAbstract:In this paper, we investigate the vanishing viscosity limit for the 3D nonhomogeneous incompressible Navier-Stokes equations with a Slip Boundary Condition. We establish the local well-posedness of the strong solutions for initial Boundary value problems for such systems. Furthermore, the vanishing viscosity limit process is established and a strong rate of convergence is obtained as the Boundary of the domain is flat. In addition, it is needed to add some additional Condition for density to match well the Boundary Condition.
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vanishing viscosity limit for the 3d nonhomogeneous incompressible fluids with a Slip Boundary Condition
2016Co-Authors: Pengfei Chen, Yuelong XiaoAbstract:In this paper, we investigate the vanishing viscosity limit for the 3D nonhomogeneous incompressible Navier-Stokes equations with a Slip Boundary Condition. We establish the local well-posedness of the strong solutions for initial Boundary value problems for such systems. Furthermore, the vanishing viscosity limit process is established and a strong rate of convergence is obtained as the Boundary of the domain is flat. In addition, it is needed to add some additional Condition for density to match well the Boundary Condition.
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vanishing viscosity limit for the 3d magnetohydrodynamic system with a Slip Boundary Condition
2009Co-Authors: Yuelong Xiao, Zhouping XinAbstract:Abstract This work investigates the solvability, regularity and vanishing viscosity limit of the 3D viscous magnetohydrodynamic system in a class of bounded domains with a Slip Boundary Condition.
B U Felderhof - One of the best experts on this subject based on the ideXlab platform.
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broadside mobility of a disk in a viscous fluid near a plane wall with no Slip Boundary Condition
2012Co-Authors: B U FelderhofAbstract:The broadside motion of a disk in a viscous fluid towards a planar wall with no-Slip Boundary Condition is studied on the basis of the steady-state Stokes equations. It is shown that flow velocity and pressure of the fluid can be found conveniently from a superposition of elementary complex stream functions. The two amplitude functions characterizing the superposition are found from the numerical solution of a pair of integral equations for the axial and radial velocity components at the disk. The numerical procedure converges fast, provided the distance to the plane is not much smaller than the radius of the disk. For small distance the flow is well approximated by lubrication theory.
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time dependent poiseuille flow of a viscous compressible fluid confined between two planar walls with dynamic partial Slip Boundary Condition
2012Co-Authors: B U FelderhofAbstract:: Time-dependent Poiseuille flow of a viscous compressible fluid confined between two planar walls is studied for a partial Slip Boundary Condition with frequency-dependent Slip length. After an initial uniform impulse parallel to the walls, the flow pattern quickly becomes nearly parabolic. For a narrow gap, a dynamic Slip length can lead to damped oscillations of total fluid momentum.
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hydrodynamic force on a particle oscillating in a viscous fluid near a wall with dynamic partial Slip Boundary Condition
2012Co-Authors: B U FelderhofAbstract:: The hydrodynamic force on a particle oscillating in a viscous fluid near a wall with partial-Slip Boundary Condition is studied on the basis of the linearized Navier-Stokes equations. Both incompressible and compressible fluids are considered. It is assumed that the Slip length characterizing the partial-Slip Boundary Condition depends on frequency. The consequences of this assumption for the spectrum of Brownian motion near a wall are investigated and compared with a recent experiment.
Parviz Moin - One of the best experts on this subject based on the ideXlab platform.
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dynamic Slip wall model for large eddy simulation
2019Co-Authors: Hyunji Jane Bae, Adrian Lozanoduran, Sanjeeb Bose, Parviz MoinAbstract:Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the Boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-Slip Boundary Condition at the wall with a Neumann Boundary Condition in the wall-parallel directions while maintaining the no-transpiration Condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (Slip) Boundary Condition with transpiration (non-zero wall-normal velocity) in the context of wall-modelled LES. The effect of the Slip Boundary Condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and a flat-plate turbulent Boundary layer. It is shown that the Slip Condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting non-zero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models (Jimenez & Moser, AIAA J. , vol. 38 (4), 2000, pp. 605–612). Second, we discuss the requirements for the Slip Condition to be used in conjunction with wall models and derive the equation that connects the Slip Boundary Condition with the stress at the wall. Finally, a dynamic procedure for the Slip coefficients is formulated, providing a dynamic Slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow at varying Reynolds numbers, non-equilibrium three-dimensional transient channel flow and a zero-pressure-gradient flat-plate turbulent Boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers and grid resolutions.
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dynamic Slip wall model for large eddy simulation
2018Co-Authors: Jane H Bae, Adrian Lozanoduran, Sanjeeb Bose, Parviz MoinAbstract:Wall modelling in large-eddy simulation (LES) is necessary to overcome the prohibitive near-wall resolution requirements in high-Reynolds-number turbulent flows. Most existing wall models rely on assumptions about the state of the Boundary layer and require a priori prescription of tunable coefficients. They also impose the predicted wall stress by replacing the no-Slip Boundary Condition at the wall with a Neumann Boundary Condition in the wall-parallel directions while maintaining the no-transpiration Condition in the wall-normal direction. In the present study, we first motivate and analyse the Robin (Slip) Boundary Condition with transpiration (nonzero wall-normal velocity) in the context of wall-modelled LES. The effect of the Slip Boundary Condition on the one-point statistics of the flow is investigated in LES of turbulent channel flow and flat-plate turbulent Boundary layer. It is shown that the Slip Condition provides a framework to compensate for the deficit or excess of mean momentum at the wall. Moreover, the resulting nonzero stress at the wall alleviates the well-known problem of the wall-stress under-estimation by current subgrid-scale (SGS) models. Secondly, we discuss the requirements for the Slip Condition to be used in conjunction with wall models and derive the equation that connects the Slip Boundary Condition with the stress at the wall. Finally, a dynamic procedure for the Slip coefficients is formulated, providing a dynamic Slip wall model free of a priori specified coefficients. The performance of the proposed dynamic wall model is tested in a series of LES of turbulent channel flow, non-equilibrium three-dimensional channel flow, and flat-plate turbulent Boundary layer. The results show that the dynamic wall model is able to accurately predict one-point turbulence statistics for various flow configurations, Reynolds numbers, and grid resolutions.
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turbulence intensities in large eddy simulation of wall bounded flows
2018Co-Authors: Hyunji Jane Bae, Adrian Lozanoduran, Sanjeeb Bose, Parviz MoinAbstract:A persistent problem in wall-bounded large-eddy simulations (LES) with Dirichlet no-Slip Boundary Conditions is that the near-wall streamwise velocity fluctuations are overpredicted, while those in the wall-normal and spanwise directions are underpredicted. The problem may become particularly pronounced when the near-wall region is underresolved. The prediction of the fluctuations is known to improve for wall-modeled LES, where the no-Slip Boundary Condition at the wall is typically replaced by Neumann and no-transpiration Conditions for the wall-parallel and wall-normal velocities, respectively. However, the turbulence intensity peaks are sensitive to the grid resolution and the prediction may degrade when the grid is refined. In the present study, a physical explanation of this phenomena is offered in terms of the behavior of the near-wall streaks. We also show that further improvements are achieved by introducing a Robin (Slip) Boundary Condition with transpiration instead of the Neumann Condition. By using a Slip Condition, the inner energy production peak is damped, and the blocking effect of the wall is relaxed such that the splatting of eddies at the wall is mitigated. As a consequence, the Slip Boundary Condition provides an accurate and consistent prediction of the turbulence intensities regardless of the near-wall resolution.
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a dynamic Slip Boundary Condition for wall modeled large eddy simulation
2014Co-Authors: Sanjeeb Bose, Parviz MoinAbstract:Wall models for large-eddy simulation (LES) are a necessity to remove the prohibitive resolution requirements of near-wall turbulence in high Reynolds turbulent flows. Traditional wall models often rely on assumptions about the local state of the Boundary layer (e.g., logarithmic velocity profiles) and require a priori prescription of tunable model coefficients. In the present study, a Slip velocity Boundary Condition for the filtered velocity field is obtained from the derivation of the LES equations using a differential filter. A dynamic procedure for the local Slip length is additionally formulated making the Slip velocity wall model free of any a priori specified coefficients. The accuracy of the dynamic Slip velocity wall model is tested in a series of turbulent channel flows at varying Reynolds numbers and in the LES of a National Advisory Committee for Aeronautics (NACA) 4412 airfoil at near-stall Conditions. The wall-modeled simulations are able to accurately predict mean flow characteristics, including the formation of a trailing-edge separation bubble in NACA 4412 configuration. The validation cases demonstrate the effectiveness of this wall-modeling approach in both attached and separated flow regimes.
Guoxiang Hou - One of the best experts on this subject based on the ideXlab platform.
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lattice boltzmann simulations of liquid flows in microchannel with an improved Slip Boundary Condition
2019Co-Authors: Liuming Yang, Huijie Pei, Yuan Gao, Guoxiang HouAbstract:Abstract Flow characteristics in channels are critical in chemical engineering. Slip velocity has a great influence on the microchannel flows. The lattice Boltzmann simulations of some typical channel flows are conducted with an improved Slip Boundary Condition. Through theoretical analysis, the defects of the existing Slip Boundary Conditions are clarified. To solve these problems, the Slip Boundary Condition of Kuo et al. is ameliorated by considering the tangential momentum change generated by the external force. Besides, the Navier’s Slip model is adopted to specify the improved Slip Boundary Condition. With this improved scheme, we study five cases, namely the Couette flow, the force driven Poiseuille flow, the time-dependent force driven Womersley flow, the porous plate flow and the channel flow with a surface-mounted block. Our method is accurate and reliable enough even with a coarse grid. The mass leakage at the wall is avoided and the numerical error generated by the external force is eliminated.
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Slip Boundary Condition for lattice boltzmann modeling of liquid flows
2018Co-Authors: Kai Wang, Guoxiang Hou, Zhenhua Chai, Wei ChenAbstract:Abstract Boundary Slip phenomenon has been widely studied for microscale gas flow in recent years. However, researches on this topic for liquid flow are still rare. Boundary Slip of liquid flow is caused by roughness and micro bubbles, while that of gas flow is caused by rarefied effect. Despite this difference, researchers found that some Slip Boundary Conditions for gas flow can also be applied to liquid flow, except the different way of treating accommodation coefficients. Currently, a measurable physical parameter, Slip length, is widely used for liquid flow, which can be obtained through experiential methods. If the relationship between the Slip length and the accommodation coefficients can be found theoretically, these Slip Boundary Conditions for liquid flow will be powerful tools to research Slip related flow characteristics, for example, drag reduction with superhydrophobic surface. Based on the Navier Slip model, this paper deducts the relationship between the accommodation coefficients and the Slip length with the half-way and the modified Slip Boundary Conditions, under the framework of the lattice Boltzmann method (LBM). The effectiveness of the proposed Slip Boundary Conditions are verified with the Couette flow, the Poesueille flow, the water Cu nanofluid flow, and the 2-D Womersley flow. Results indicate that these Boundary Conditions are suitable for both linear and non-linear liquid flow.
Steve Granick - One of the best experts on this subject based on the ideXlab platform.
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limits of the hydrodynamic no Slip Boundary Condition
2002Co-Authors: Yingxi Zhu, Steve GranickAbstract:A controversial point in fluid dynamics is to distinguish the relative importance of surface roughness and fluid-surface intermolecular interactions in determining the Boundary Condition. Here hydrodynamic forces were compared for flow of Newtonian fluids past surfaces of variable roughness but similar, poorly wetted, surface chemistry. The critical shear stress and shear rate to observe deviations from predictions using the no-Slip Boundary Condition increased nearly exponentially with increasing roughness and diverged at $\ensuremath{\approx}6$ nm rms roughness. We conclude that local intermolecular interactions dominated when the surface was very smooth, but roughness dominated otherwise. This quantifies the limits of both ideas.
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No-Slip Boundary Condition switches to partial Slip when fluid contains surfactant
2002Co-Authors: Yingxi Zhu, Steve GranickAbstract:Physisorbed surfactant can change the hydrodynamic Boundary Condition of oil flow from “stick” to “partial Slip”, provided that the shear stress on the wall exceeds a threshold level that decreases with increasing surface coverage of surfactant. To demonstrate this, Newtonian alkane fluids (octane, dodecane, tetradecane) were placed between molecularly smooth surfaces that were either wetting (muscovite mica) or rendered partially wetted by adsorption of surfactant (0.2 or 0.1 wt % hexadecylamine). The surface spacing was vibrated at spacings so large that the fluid responded as a continuum. The resulting hydrodynamic forces agreed with predictions from the no-Slip Boundary Condition when flow rate, peak velocity normalized by surface spacing, was low but implied partial Slip when it exceeded a critical level. In other words, the “Slip length” depended on reduced velocity. When the reduced velocity was sufficiently high, a plateau shear stress was observed, ≈1.3 N m-2 for 0.2 wt % hexadecylamine, but also...
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rate dependent Slip of newtonian liquid at smooth surfaces
2001Co-Authors: Steve GranickAbstract:: Newtonian fluids were placed between molecularly smooth surfaces whose spacing was vibrated at spacings where the fluid responded as a continuum. Hydrodynamic forces agreed with predictions from the no-Slip Boundary Condition only provided that flow rate (peak velocity normalized by spacing) was low, but implied partial Slip when it exceeded a critical level, different in different systems, correlated with contact angle (surface wettability). With increasing flow rate and partially wetted surfaces, hydrodynamic forces became up to 2-4 orders of magnitude less than expected by assuming the no-Slip Boundary Condition that is commonly stated in textbooks.
