Search results for "boundary"
showing 10 items of 1626 documents
Effect of the Schrödinger functional boundary conditions on the convergence of step scaling
2012
Recently several lattice collaborations have studied the scale dependence of the coupling in theories with different gauge groups and fermion representations using the Schrodinger functional method. This has motivated us to look at the convergence of the perturbative step scaling to its continuum limit with gauge groups SU(2) and SU(3) with Wilson fermions in the fundamental, adjoint or sextet representations. We have found that while the improved Wilson action does remove the linear terms from the step scaling, the convergence is extremely slow with the standard choices of the boundary conditions for the background field. We show that the situation can be improved by careful choice of the …
BEM Formulation of the Trailing Edge Condition
1995
This paper deals with a BEM formulation of the trailing edge condition to determine the potential flow field around an airfoil. It is seen the trailing edge condition is not sufficient to give an unique solution. It is necessary to assign a further condition to eliminate the nonuniqueness of the solution. The approach allows to adopt a discretization into superior order elements. Some preliminary applications show the validity of the formulation.
Two-Dimensional Boundary Layer Equations: High Resolution Capturing Methods
1993
In this paper we apply the piecewise hyperbolic and parabolic essentially non-oscillatory (ENO) capturing schemes (see [2] and [4]) to approximate the solution to the boundary layer equations for two-dimensional incompressible flow. We have tested several numerical examples analyzing their resolutive power and efficiency with respect to small values of the kinematic viscosity of the flow.
Wetting in fluid systems. Wetting and capillary condensation of lattice gases in thin film geometry
1994
Monte Carlo studies of lattice gas models with attractive interactions between nearest neighbors on a simple cubic lattice are carried out for a L×L×D geometry with two hard walls of size L×L and periodic boundary conditions parallel to the wall. Two types of short-range forces at the walls are considered: (i) Both walls are of the same type and exert an attractive force of the same strength (in Ising model terminology, surface fields HD = H1 occur). (ii) The walls differ, one attracts and the other repels particles, again with the same strength (HD = −H1). In the first case, capillary condensation occurs at a chemical potential differing from its value for phase coexistence in the bulk, an…
On the Weak Solution of the Fluid-Structure Interaction Problem for Shear-Dependent Fluids
2016
In this paper the coupled fluid-structure interaction problem for incompressible non-Newtonian shear-dependent fluid flow in two-dimensional time-dependent domain is studied. One part of the domain boundary consists of an elastic wall. Its temporal evolution is governed by the generalized string equation with action of the fluid forces by means of the Neumann type boundary condition. The aim of this work is to present the limiting process for the auxiliary \((\kappa,\varepsilon,k)\)-problem. The weak solution of this auxiliary problem has been studied in our recent work (Hundertmark-Zauskova, Lukacova-Medvid’ova, Necasova, On the existence of weak solution to the coupled fluid-structure in…
Numerical Study of Forced MHD Convection Flow and Temperature Around Periodically Placed Cylinders
2016
In this paper we consider 2D stationary boundary value problems for the system of magnetohydrodynamic (MHD) equations and the heat transfer equation. The viscous electrically conducting incompressible liquid moves between infinite cylinders with square or round sections placed periodically. We also consider similar 2D MHD channel flow with periodically placed obstacles on the channel walls. We analyse the 2D forced and free MHD convection flow and temperature around cylinders and obstacles in homogeneous external magnetic field. The cylinders, obstacles and walls of the channel with constant temperature are heated. The distributions of electromagnetic fields, forces, velocity and temperatur…
Application of Tunable-Slip Boundary Conditions in Particle-Based Simulations
2014
Compared to macroscopic systems, fluids on the micro- and nanoscales have a larger surface-to-volume ratio, thus the boundary condition becomes crucial in determining the fluid properties. No-slip boundary condition has been applied successfully to wide ranges of macroscopic phenomena, but its validity in microscopic scale is questionable. A more realistic description is that the flow exhibits slippage at the surface, which can be characterized by a Navier slip length. We present a tunable-slip method by implementing Navier boundary condition in particle-based computer simulations (Dissipative Particle Dynamics as an example). To demonstrate the validity and versatility of our method, we ha…
Estimation of the Roughness Function in Turbulent Flows Using the Slope of the Roughness
2019
In the last decades, important efforts have been made to better understand the effects of surface roughness on the mean flow. These studies have been performed investigating turbulent channel flows, turbulent boundary layers or pipe flows. The most evident effect of the roughness is the increase of the overall resistance, corresponding to a decrease of the mean streamwise velocity profile in the logarithmic region. This reduction is known as roughness function \(\varDelta U^+\) (the symbol \(^+\) represents quantities made non dimensional using the friction velocity \(u_{\tau }\), or the viscous length scale \(\nu /u_{\tau }\)).
The build-up and relaxation of stresses in a glass-forming soft-sphere mixture under shear: A computer simulation study
2009
Molecular-dynamics computer simulations in conjunction with Lees-Edwards boundary conditions are used to investigate a glass-forming binary Yukawa fluid under shear. The transition from the elastic response to plastic flow is elucidated by studying the stress relaxation after switching off the shear. We find a slow stress relaxation starting from states in the elastic regime and a fast one starting from states in the plastic-flow regime. We show that these relaxation patterns are related to a different distribution of local microscopic stresses in both cases.
Large Eddy Simulations of Rough Turbulent Channel Flows Bounded by Irregular Roughness: The Role of Geometrical Parameters
2020
Almost all bounded flows, in nature and industry, are bounded by rough boundaries. Important efforts have been made, in fact, to analyse the physics of the fluids over such geometries. Basically, rough walls strongly influence the total energy dissipation, with important consequences in the form of higher costs especially in industrial applications.