第18届国际电加工会议综述

对第18届国际电加工会议论文进行了综述,介绍了近年来国际特种加工领域的最新研究进展。主要内容包括电火花成形加工、电火花线切割加工、电化学加工、超声加工、激光加工、增材制造、微细特种加工及相关复合加工工艺的研究成果。     

Depth-averaged Lattice Boltzmann and Finite Element methods for single-phase flows in fractures with obstacles

We use Lattice Boltzmann Method (LBM) MRT and Cumulant schemes to study the performance and accuracy of single-phase flow modeling for propped fractures. The simulations are run using both the two- and three-dimensional Stokes equations, and a 2.5D Stokes–Brinkman approximate model. The LBM results are validated against Finite Element Method (FEM) simulations and an analytical solution to the Stokes–Brinkman flow around an isolated circular obstacle. Both LBM and FEM 2.5D Stokes–Brinkman models are able to reproduce the analytical solution for an isolated circular obstacle. In the case of 2D Stokes and 2.5D Stokes–Brinkman models, the differences between the extrapolated fracture permeabilities obtained with LBM and FEM simulations for fractures with multiple obstacles are below 1%. The differences between the fracture permeabilities computed using 3D Stokes LBM and FEM simulations are below 8% . The differences between the 3D Stokes and 2.5 Stokes–Brinkman results are less than 7% for FEM study, and 8% for the LBM case. The velocity perturbations that are introduced around the obstacles are not fully captured by the parabolic velocity profile inherent to the 2.5D Stokes–Brinkman model.     

Aerodynamic simulation of high-speed trains based on the Lattice Boltzmann Method (LBM)

Aerodynamic simulation of high-speed trains has been carried out by using Lattice Boltzmann Method (LBM). Non-simplified train model was used and the number of space grids reached tens of millions. All results under different working conditions reflected the actual situation.     

Prediction of hypo eutectoid steel softening due to tempering phenomena in laser surface hardening

The paper presents a mathematical model for predicting material mechanical property variation, in laser hardening of hypo eutectoid steel, when the softening effects due to the overlapping trajectories are considered. This generally occurs during laser hardening of industrial parts, especially when wide areas have to be treated, due to the tempering phenomena.An original tempering model for the prediction of the hardness reduction is presented in this paper. The proposed model is integrated in a Laser Hardening simulation package, previously developed by the authors. Experimental activities are also presented to validate the model.     

NUMERICAL STUDY OF THE RELATIONSHIP BETWEEN APPARENT SLIP LENGTH AND CONTACT ANGLE BY LATTICE BOLTZMANN METHOD

The apparent slip between solid wall and liquid is studied by using the Lattice Boltzmann Method (LBM) and theShan-Chen multiphase model in this paper. With a no-slip bounce-back scheme applied to the interface, flow regimes under differentwall wettabilities are investigated. Because of the wall wettability, liquid apparent slip is observed. Slip lengths for different wallwettabilities are found to collapse nearly onto a single curve as a function of the static contact angle, and thereby a relationshipbetween apparent slip length and contact angle is suggested. Our results also show that the wall wettability leads to the formation of alow-density layer between solid wall and liquid, which produced apparent slip in the micro-scale.     

基于格子波尔兹曼法的热障陶瓷涂层凝固生长过程模拟

热障涂层(TBCs)在使用过程中表面陶瓷层的脱落是影响其使用寿命的关键,针对以上问题,建立了凝固生长过程流动及传热传质模型,用格子波尔兹曼法(LBM)研究了涂层凝固生长过程。结果显示:不考虑对流影响时,晶体生长的形貌呈现对称十字枝晶形状;在考虑对流的情况下,迎流部分生长快,背流部分生长受到抑制。在大的过冷度影响下,晶界出现波动,出现二次枝晶生长。等离子喷涂涂层在温度梯度下朝向正温度梯度方向呈柱状晶生长。枝晶生长受到对流的影响和侧向温度梯度的影响。迎流方向和大温度梯度方向枝晶形貌发达,背流方向和小温度梯度处枝晶生长受到抑制。     

Numerical simulation of hemodynamic interactions of red blood cells in micro-capillary flow

The hemodynamic interactions of red blood cells （RBCs） in a microcapillary flow are investigated in this paper. This kind of interaction is considered as the non-contact mutual interaction of cells, which is important in the suspension flow of blood, but not sufficiently understood. The distributed Lagrange multiplier/fictitious domain method in the lattice Boltzmann framework is used to solve the suspension of the RBCs. The modification of the flow due to the cells, the dependence of the cell deformation on the flow and the cell-cell interaction via the fluid are discussed. It is revealed that the long-range hydrodynamic interaction with a long interacting distance, more than about 5 times of the RBC equivalent radius, mainly has effect on the rheology properties of the suspension, such as the mean velocity, and the short-range interaction is sensitive to the shape of the cell in the microcapillary flow. The flow velocity around the cell plays a key role in the cell deformation. In the current configuration of the flow and cells, the cells repel each other along the capillary.     

Numerical study of flow and heat transfer characteristics of alumina-water nanofluids in a microchannel using the lattice Boltzmann method

In the present study, mathematical modeling is performed to simulate force d convection flow of Al₂O₃/water nanofluids in a microchannel using the lattice Boltzmann method (LBM). Simulations are conducted at low Reynolds numbers (Re ≦ 16). Results indicate that the average Nusselt number increases with the increase of Reynolds number and particle volume concentration. The fluid temperature distribution is more uniform with the use of nanofluid than that of pure water. Furthermore, great deviations of computed Nusselt numbers using different models associated with the physical properties of a nanofluid are revealed. The results of LBM agree well with the classical CFD method for predictions of flow and heat transfer in a single channel and a microchannel heat sink concerning the conjugate heat transfer problem, and consequently LBM is robust and promising for practical applications.     

质量力作用下液滴变形及破裂现象的LBM模拟

基于伪势模型的两相格子Boltzmann方法(lattice Boltzmann method-LBM)模拟研究了液滴在质量力作用下的运动、变形和破裂现象.根据Young-Laplace定律确定模拟中所需的表面张力系数值,并对模型中表面张力所应具有的各向同性特性进行验证;计算了不同Bond数和Ohnesorge数时液滴的运动和变形过程.结果表明:随着Bond数的增大,液滴变形不断加剧并最终破裂;随着Ohnesorge数的增大,液滴趋向于维持其原始形状,运动过程中破裂现象的发生将受到抑制.