二维非结构网格有限体积格式的壁热现象和人工热流方法

基于Noh人工热流方法的思想,推导出任意多边形网格人工热流的格式,将Noh的结构网格人工热流方法推广到任意多边形非结构网格的拉氏有限体积方法中,抑制或消除了壁热现象.几个数值实验,包括Noh激波反射问题和两块钢金属碰撞问题,验证了方法的可行性.     

CGNS API和FVM在非结构混合网格计算中的应用

用CGNS API（CFD General Notation System Application Programming Interface）作为非结构混合网格求解器的前处理和后处理,用FVM（Finite Volume Method）作为偏微分方程求解方法．在前处理过程中,用hash表法对内部网格面和边界网格面进行编号,并计算出相应的几何信息,以满足FVM求解器的需要．从FVM求解器计算出来的各种场信息可以写入原来的CGNS文件,该文件可以被许多专业商业后处理软件（如Tecplot,Fluent,CFX等）读取和进行可视化;对于求解器,用基于网格中心的FVM及SIMPLEC（Semi Implicit Methodfor Pressure Linked Equation Consistent）方法求解压力速度耦合．最后给出两个说明算例．     

非结构网格上温度扩散方程的能流计算方法

讨论非结构网格上温度扩散方程的能流计算方法.应用有限点方法(Finite Point Method,简称FPM)导出基于有限点两点公式和三点公式的能流计算公式,该公式适用于任意多边形及非匹配网格等非结构网格;给出网格角点温度新的计算公式.数值试验表明:基于两点公式的离散解和基于三点公式的离散解均具有平方阶的收敛速度;基于三点公式的离散解的精度总优于基于两点公式的离散解.     

热传导方程的一类无网格方法

构造求解热传导方程的一类无网格方法,只要选择好每个节点的适当的邻点集合,便可利用节点信息顺利进行计算.作为特殊情形,也可在各种结构或非结构网格上进行计算.在矩形或均匀平行四边形网格上进行计算时具有二阶精度,当在任意的不规则四边形或三角形网格上计算时仍然是守恒的和相容的,且至少具有一阶精度.作为数值试验,将该方法用于在不规则四边形网格上及四边形与三角形混合网格上求解二维非线性抛物型方程,并在不规则四边形网格上求解二维三温辐射热传导方程,均获得了较为理想的数值结果.     

Numerical analysis of conservative unstructured discretisations for low Mach flows

Unstructured meshes allow easily representing complex geometries and to refine in regions of interest without adding control volumes in unnecessary regions. However, numerical schemes used on unstructured grids have to be properly defined in order to minimise numerical errors. An assessment of a low Mach algorithm for laminar and turbulent flows on unstructured meshes using collocated and staggered formulations is presented. For staggered formulations using cell‐centred velocity reconstructions, the standard first‐order method is shown to be inaccurate in low Mach flows on unstructured grids. A recently proposed least squares procedure for incompressible flows is extended to the low Mach regime and shown to significantly improve the behaviour of the algorithm. Regarding collocated discretisations, the odd–even pressure decoupling is handled through a kinetic energy conserving flux interpolation scheme. This approach is shown to efficiently handle variable‐density flows. Besides, different face interpolations schemes for unstructured meshes are analysed. A kinetic energy‐preserving scheme is applied to the momentum equations, namely, the symmetry‐preserving scheme. Furthermore, a new approach to define the far‐neighbouring nodes of the quadratic upstream interpolation for convective kinematics scheme is presented and analysed. The method is suitable for both structured and unstructured grids, either uniform or not. The proposed algorithm and the spatial schemes are assessed against a function reconstruction, a differentially heated cavity and a turbulent self‐igniting diffusion flame. It is shown that the proposed algorithm accurately represents unsteady variable‐density flows. Furthermore, the quadratic upstream interpolation for convective kinematics scheme shows close to second‐order behaviour on unstructured meshes, and the symmetry‐preserving is reliably used in all computations. Copyright © 2016 John Wiley & Sons, Ltd.     

Hybrid mesh generation with embedded surfaces using a multiple marching direction approach

This paper proposes a method for the creation of hybrid meshes with embedded surfaces for viscous flow simulations as an extension of the multiple marching direction approach (AIAA J. 2007; 45 (1):162–167). The multiple marching direction approach enables to place semi‐structured elements around singular points, where valid semi‐structured elements cannot be placed using conventional hybrid mesh generation methods. This feature is discussed first with a couple of examples. Elements sometimes need to be clustered inside a computational domain to obtain more accurate results. For example, solution features, such as shocks, vortex cores and wake regions, can be extracted during the process of adaptive mesh generation. These features can be represented as surface meshes embedded in a computational domain. Semi‐structured elements can be placed around the embedded surface meshes using the multiple marching direction approach with a pretreatment method. Tetrahedral elements can be placed easily instead. A couple of results are presented to demonstrate the capability of the mesh generation method. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface Extension in Layered Structures with the Use of Metal Meshes for Heat-Transfer Enhancement

The properties of multilayer metal-fiber coverings superimposed on plane base layers, which consist of various combinations of a copper mesh and different-length copper wires, are examined. Coverings from discrete copper microwires, two-layer coverings including a mesh and microwires, and three-layer coverings consisting of a mesh and two layers of microwire are investigated. The contacts between the fibers, the copper mesh, and the base layer are analyzed by using the metallography technique. Quantitative estimates for these contacts are presented. The side effects connected with the hydrogen disease of copper are discussed. The thermal properties of the porous structures are analyzed with the use of a termographic chamber. It is shown that the porous metal-fiber structures have good mechanical and heat-transfer properties.     

钝体后湍流预混燃烧的PDF模拟

本文采用PDF方法对矩形燃烧室内钝体后的湍流预混火焰进行了数值模拟。脉动速度-频率-标量联合的PDF输运方程用Monte Carlo方法求解,质量、动量和能量的平均值由基于无结构网格的有限体积法求解,压力通过状态方程获得。PDF方程中所需的平均密度、平均速度和压力由有限体积法提供,并将用Monte Carlo方法求出的雷诺应力、化学反应源项和比热比传递给有限体积法。本文对丙烷和空气燃烧的不同简化化学反应机理进行了研究,并与实验结果进行比较,获得满意的结果。     

A conservative unstructured scheme for rapidly varied flows

This article introduces a new semi‐implicit, staggered finite volume scheme on unstructured meshes for the modelling of rapidly varied shallow water flows. Rapidly varied flows occur in the inundation of dry land during flooding situations. They typically involve bores and hydraulic jumps after obstacles such as road banks. Near such sudden flow transitions, the grid resolution is often low compared with the gradients of the bathymetry. Locally the hydrostatic pressure assumption may become invalid. In these situations, it is crucial to apply the correct conservation properties to obtain accurate results. An important feature of this scheme is therefore its ability to conserve momentum locally or, by choice, preserve constant energy head along a streamline. This is achieved using a special interpolation method and control volumes for momentum. The efficiency of inundation calculations with locally very high velocities, and in the case of unstructured meshes locally very small grid distances, is severely hampered by the Courant condition. This article provides a solution in the form of a locally implicit time integration for the advective terms that allows for an explicit calculation in most of the domain, while maintaining unconditional stability by implicit calculations only where necessary. The complex geometry of flooded urban areas asks for the flexibility of unstructured meshes. The efficient calculation of the pressure gradient in this, and other semi‐implicit staggered schemes, requires, however, an orthogonality condition to be put on the grid. In this article a simple method is introduced to generate unstructured hybrid meshes that fulfil this requirement. Copyright © 2008 John Wiley & Sons, Ltd.