Three-Dimensional Simulations of Anisotropic Slip Microflows Using the Discrete Unified Gas Kinetic Scheme

Abstract

The specific objective of the present work study is to propose an anisotropic slip boundary condition for three-dimensional (3D) simulations with adjustable streamwise and spanwise slip length by the discrete unified gas kinetic scheme (DUGKS). The present boundary condition is proposed based on the assumption of nonlinear velocity profiles near the wall instead of linear velocity profiles in a unidirectional steady flow. Moreover, a 3D corner boundary condition is introduced to the DUGKS to reduce the singularities. Numerical tests validate the effectiveness of the present method, which is more accurate than the bounce-back and specular reflection slip boundary condition in the lattice Boltzmann method. It is of significance to study the lid-driven cavity flow due to its applications and its capability in exhibiting important phenomena. Then, the present work explores, for the first time, the effects of anisotropic slip on the two-sided orthogonal oscillating micro-lid-driven cavity flow by adopting the present method. This work will generate fresh insight into the effects of anisotropic slip on the 3D flow in a two-sided orthogonal oscillating micro-lid-driven cavity. Some findings are obtained: The oscillating velocity of the wall has a weaker influence on the normal velocity component than on the tangential velocity component. In most cases, large slip length has a more significant influence on velocity profiles than small slip length. Compared with pure slip in both top and bottom walls, anisotropic slip on the top wall has a greater influence on flow, increasing the 3D mixing of flow. In short, the influence of slip on the flow field depends not only on slip length but also on the relative direction of the wall motion and the slip velocity. The findings can help in better understanding the anisotropic slip effect on the unsteady microflow and the design of microdevices.

Slip Flow Analysis in an Experimental Chamber Simulating Differential Pumping in an Environmental Scanning Electron Microscope

“…These facts can be seen in Figure 20 , where the distribution of Mach disks for the NO SLIP and LOW SLIP variants corresponds to the theory whereby the location of the first Mach disk corresponds to [ 21 , 22 ]. …”

Kinetic Theory-Based Methods in Fluid Dynamics

“…After a year-long preparation and a rigorous peer-review process, 12 articles were finally accepted for publication in this Special Issue. These articles report the latest developments in kinetic-theory-related numerical schemes [1,2] and typical applications in multiphase flows [3], thermal flows [4], micro/nano flows [5,6], flows in porous media [7], and compressible flows [8,9], as well as other areas of fluid dynamics [10][11][12]. Specifically, Song et al [1] proposed a simplified linearized Boltzmann method for the effective simulation of acoustic propagation with a lower cost of virtual memory.…”

“…Wu and Zhou [5] presented an application of the lattice Boltzmann flux solver to the modelling of the natural convection process within a square cavity filled by nanofluid. Guo and Hou [6] derived an anisotropic slip boundary condition based on nonlinear velocity profiles near the wall, consolidated this new boundary treatment into the discrete unified gas kinetic scheme, and investigated the effects of anisotropic slip on the two-sided orthogonal oscillating micro-lid-driven cavity flow through three-dimensional simulations. Liu et al [7] carried out a series of simulations using the smoothed particle hydrodynamics method to shed light on the physics under the imbibition phenomenon in porous media.…”