基于Matlab的径向基函数数值计算软件包

为推动基于无网格方法的计算软件的发展,介绍基于Matlab自主开发的径向基函数（Radial Basis Function,RBF）数值计算软件包,阐述软件的理论基础、设计思路以及该软件包的功能和特点,并结合边界节点法（Boundary Knot Method,BKM）的数值实例给出软件的使用过程．该软件包可以根据不同的数学物理模型选择合适的数值算法来求解多种实际物理问题,也可对不同数值算法得到的结果进行比较．最后,总结应用Matlab进行数值计算软件开发的优缺点．     

压气机三维流场数值仿真及湍流模型研究

本文利用商用CFD软件对压气机转子通流部分建立了一个三维的数值模拟计算平台.对NASA Rotor 37跨音速压气机转子全工况特性进行了计算,与NASA Rotor37的实验结果对比表明,本文的网格生成技术和数值模拟方法都是比较成功的,满足一定的数值求解精度,具有工程技术应用价值.在湍流模型方面引入Baldwin-Lonax(B-L)湍流模型和Spalart-All-maras(S-A)湍流模型,并对模拟结果进行了分析对比研究.对跨音速压气机转子内流场的数值模拟结果表明:S-A湍流模型对跨音速压气机转子的模拟能力优于B-L湍流模型.     

汽车换热器风室试验台的CFD分析

为给汽车前端和发动机舱内气流数值计算提供参考依据,基于FLUENT对某汽车换热器风室试验台进行建模和数值模拟;分析风室内部空气流动状况,针对流动特征,给出风室计算流体力学（Computational Fluid Dynamics,CFD）校核的评价．网格采用四面体结构,模型中采用三维不可压的雷诺平均N．S方程,速度压力耦舍采用SIMPLE方法．空间离散格式为2阶迎风格式,时间离散格式为2阶隐式．选用realizable k-ε占模型模拟风室内部空气的湍流流动．固体壁面采用无滑移边界条件和非平衡壁面函数边界条件．模型进口采用速度入口来给定风量,出口采用压力出口．比较计算结果与试验设计标准,喷嘴压差的相对偏差范围在5％以内,基本达到对设备的精度要求,对风室设计有一定指导意义．     

分区域变尺度网格的社区火灾场景数值仿真

目的 火灾场景数值仿真对消防救援和应急疏散具有重要意义。火灾场景仿真需要对室内外地物及环境进行精细建模和大量数值计算,而传统地图和空间分析无法满足日趋复杂的建筑物消防场景表达。为此本文基于室内外地图研究基础,构建面向社区安全的火灾场景数值仿真模型。方法 通过传统制图技术建立社区地物分布模型,利用室内制图技术建立建筑物内部场景,利用3维建模技术重建社区室内外3维模型,引入火灾数值模拟方程进行仿真计算。根据社区建筑物分布和其内部结构复杂程度的差异,提出分区域变尺度的网格划分方法,以提高计算效率。结果 通过对红树湾社区进行"精细"、"粗糙"和"分区域变尺度"3种不同方法的仿真实验,分析火灾模型的计算速度、温度场及烟气扩散情况。与精细网格方法相比,分区域变尺度方法和粗糙网格方法的计算速度是其8倍和24倍,烟气最低能见度误差为2 m和13.5 m,分区域变尺度方法相较于粗糙网格方法与精细网格方法的温度变化曲线更加吻合。分区域变尺度方法的模拟精度更接近于精细网格方法,同时效率得到提升。结论 本文提出的火灾场景仿真模型将室内制图应用扩展到社区消防研究,实验结果表明,所提出的分区域变尺度网格划分方法能够在保证数值模拟精度的前提下提高仿真效率,具有重要的应用价值。     

Navier-Stokes方程的三种两层稳定有限元算法计算效率分析

讨论分析了定常Navier-Stokes（N—S）方程的三种两层稳定有限元算法．它们将局部高斯积分稳定化技术和两层算法的思想充分结合,采用不满足Inf-Sup条件的低次等价有限元P1-P1或Q1-Ql对N—S方程进行数值求解,在粗网格上解定常N—S方程,在细网格上只需求解一个Stokes方程．误差分析和数值实验都表明,当它们的粗、细网格尺度比分别为H=h1/3。｜logh｜-1／6,H=O（h1／2）和H=O（h1/2）时,它们与在细网格上的标准有限元算法具有相同的收敛速度．而两层稳定有限元算法却节省了大量的计算时间．相比之下,简单两层稳定有限元算法具有更高的计算效率,Oseen两层算法次之,Newton两层算法较低．而且进一步发现较小粘性系数对Newton两屡算法数值精席影响较大．     

基于稳定节点光滑有限元法的纯电动汽车电磁场仿真

针对纯电动汽车电磁场数值分析时传统有限元法（finite element method, FEM）因数值“过硬”而计算精度低的问题，在传统FEM的基础上引入梯度光滑技术和稳定项修正，采用基于稳定节点的光滑有限元法（stable node based smoothed FEM, SNS FEM）对长直接地金属槽和纯电动汽车整车电磁场算例进行仿真分析。结果表明，SNS FEM可显著降低前处理网格划分难度，在一定程度上软化数值模型，具有计算效率高、精度高、收敛速度快和抗网格畸变能力强等优点，在工业应用中具有较大潜力。     

Ω形双螺杆泵流场仿真与实验研究

研究螺杆转子转动过程中的流场变化有助于对双螺杆泵运行参数的优化。采用计算流体力学(CFD)方法,对双螺杆泵流场进行三维瞬态动网格仿真分析。针对Ω形双螺杆泵,建立内流场数值模型,通过仿真得到一个转动周期内泵内压力分布,同时研究了不同粘度下泵外特性的变化规律。仿真结果表明,泵内压力由吸入端到排出端逐级增大,与容积腔推挤增压规律相吻合;在吸入端容积腔截面和螺杆啮合缝隙内均存在负压,且由于泄露的原因,密封腔两端的压力分布并非完全一致,存在轻微差异;流量随着压差的增大而呈近似线性下降趋势,粘度越大,流量受压差的影响就越小;泵效随压差的变化曲线呈抛物线形,达到峰值后先逐渐减小,最后趋于平稳。实验结果与仿真一致,证明了仿真方法的有效性。     

求二维非定常流数值解的主从网格方法

0．前言二维非定常流的拉格朗日型数值方法,是计算多种介质问题的常用的数值方法．最早是建立在随流体运动的四边形网格上的有限差分方法[1,2]．这种方法的优点显著,缺点是网格容易相交重复（两个网格同时占用一份空间）,致使计算不能进行,因此出现了三角网格方法[3]和邻域可变的任意多边形网格方法[4]．三角网格方法基本上不出现网格相交,但是人为粘性和边角的朝向可能引起大的误差．任意多边形网格的邻域关系确定不好也会引起很大的误差甚至错的计算结果．因此使用最广泛的还是建立在固定邻域的四边形网格上的拉格朗日方法．为了避…     

油罐清洗机器人低压自激脉冲喷嘴的仿真设计

为实现安全、环保的油罐清洗方式,需要研制配有低压自激脉冲喷嘴的油罐清洗机器人。运用计算流体力学技术,结合油罐清洗的特殊作业环境和罐底油泥特性,对油罐清洗机器人的低压自激脉冲喷嘴进行了仿真设计。通过对自激脉冲射流发生机理和非定常空化模型研究,利用fluent软件对不同的结构设计进行数值仿真,对比分析出不同方案的优劣,选出油罐清洗机器人自激脉冲喷嘴腔径、腔长、上下喷嘴直径、碰撞壁锥度等各结构参数的最优范围,从而为实际设计提供了参考依据。     

基于抗磁悬浮的气流能量采集器

研究了一种由外壳、提升磁体、上热解石墨板、线圈、永磁体转子和下热解石墨板构成的气流能量采集器,自由悬浮于两热解石墨板之间的永磁体转子可在外界气流的作用下转动,并在线圈中产生感应电压。采用有限元软件COMSOL Multiphysics 5.3和ANSYS Maxwell 16.0建立仿真模型,对能量采集器的悬浮特性、驱动特性和输出特性进行仿真分析通过实验验证,发现当喷嘴为83°时转子所受的气流驱动力矩最大;实验测试永磁体转子悬浮高度56.5 mm,与仿真高度57.5 mm误差仅为1.77%;能量采集器稳定工作的气流量范围为137 sccm^733 sccm,最大输出电压可达160 mV。     

A pressure-correction method and its applications on an unstructured Chimera grid

In this paper, an unstructured Chimera mesh method is used to compute incompressible flow around a rotating body. To implement the pressure correction algorithm on unstructured overlapping sub-grids, a novel interpolation scheme for pressure correction is proposed. This indirect interpolation scheme can ensure a tight coupling of pressure between sub-domains. A moving-mesh finite volume approach is used to treat the rotating sub-domain and the governing equations are formulated in an inertial reference frame. Since the mesh that surrounds the rotating body undergoes only solid body rotation and the background mesh remains stationary, no mesh deformation is encountered in the computation. As a benefit from the utilization of an inertial frame, tensorial transformation for velocity is not needed. Three numerical simulations are successfully performed. They include flow over a fixed circular cylinder, flow over a rotating circular cylinder and flow over a rotating elliptic cylinder. These numerical examples demonstrate the capability of the current scheme in handling moving boundaries. The numerical results are in good agreement with experimental and computational data in literature.     

An efficient and high-order sliding mesh method for computational aeroacoustics

This paper presents an efficient sliding mesh method to simulate the noise emission from aero-engines. The vortexes shed from the rotating blade and interact with the downstream stationary outlet guide vanes (OGVs), producing noise. The challenges in simulating the problem are the accurate modelling of the wake turbulence, and the capabilities to capture the acoustic waves, the energy of which is several orders lower than the turbulent components. To model the relative motion between the rotors and OGVs, a sliding mesh method is developed to account for the rotation of the rotor blades and wakes, which can lead to efficiency and accuracy challenges. In this work, an advanced treatment is developed for efficient and high-accuracy interpolation by combining both patch and sliding interfaces. The grid along the sliding interface is uniformly distributed taking advantage of the patch interface, providing huge benefits to the overall performance by reusing data and omitting repeated calculation. The algorithm using message passing interface is well designed for maintaining ideal performance of the code. The fan–OGV geometry is represented as unwrapped two-dimensional cascades with isotropic and anisotropic turbulence synthesised and injected to simulate the fan-wake. The numerical results are compared to analytical solutions for accuracy validation. The simulations numerically reveal the effect of turbulence intensity, length scale and anisotropy in the fan wake on the noise emission due to the turbulence-OGV interaction. Also the blockage effect of rotating blades on the noise propagation and its impact on the hearing of observers are discussed. Moreover, it is shown that the new method is able to maintain a high accuracy for acoustic computation and an ideal performance is obtained from the numerical code using a parallel computing algorithm.

     

Quasi-angle-preserving mesh deformation using the least-squares approach

We propose an angle-based mesh representation, which is invariant under translation, rotation, and uniform scaling, to encode the geometric details of a triangular mesh. Angle-based mesh representation consists of angle quantities defined on the mesh, from which the mesh can be reconstructed uniquely up to translation, rotation, and uniform scaling. The reconstruction process requires solving three sparse linear systems： the first system encodes the length of edges between vertices on the mesh, the second system encodes the relationship of local frames between two adjacent vertices on the mesh, and the third system defines the position of the vertices via the edge length and the local frames. From this angle-based mesh representation, we propose a quasi-angle-preserving mesh deformation system with the least-squares approach via detail-preserving mesh editing examples are presented to handle translation, rotation, and uniform scaling. Several demonstrate the effectiveness of the proposed method.     

层适应网格上求解奇异摄动问题的粒子群算法

针对一类奇异摄动对流扩散问题,将粒子群算法与差分格式相结合,在Bakhvalov-Shishkin网格上进行求解。对于Bakhvalov-Shishkin网格中的网格参数,采用粒子群算法进行优化,构造了求误差范数最小值的目标函数。对两个算例进行了数值计算,实验结果表明,与选择固定的网格参数相比,采用粒子群算法计算能得到更好的数值结果,并且数值结果具有收敛性,验证了该方法的有效性和优越性。     

Adaptive mesh refinement for chevron nozzle jet flows

In this paper an adaptive mesh generation procedure is presented for improving the resolution of the numerical simulation of a turbulent jet exhausting from a chevron nozzle. This procedure is based on the minimization of a variational integral whose integrand depends on the metric (also called the monitor function) induced by a curvilinear grid generated in the physical domain. Specifically, it leads to solving parabolic equations involving the monitor function, which is carefully designed to resolve the flow gradients, and which, in the present instance, is determined by the time-averaged axial velocity profile within the jet. This mesh redistribution strategy is incorporated into a flow computation code (that solves the compressible three-dimensional Navier-Stokes equations using a prefactored optimized fourth-order compact difference scheme for spatial derivatives and the Beam-Warming method for the time derivative on a multi-block overset grid) and is demonstrated to be efficient and effective.     

Simulation of liquid micro-jet in free expanding high-speed co-flowing gas streams

We present the development of an experimentally validated computational fluid dynamics model for liquid micro jets. Such jets are produced by focusing hydrodynamic momentum from a co-flowing sheath of gas on a liquid stream in a nozzle. The numerical model based on laminar two-phase, Newtonian, compressible Navier–Stokes equations is solved with finite volume method, where the phase interface is treated by the volume of fluid approach. A mixture model of the two-phase system is solved in axisymmetry using?~?300,000 finite volumes, while ensuring mesh independence with the finite volumes of the size 0.25 µm in the vicinity of the jet and drops. The numerical model is evaluated by comparing jet diameters and jet lengths obtained experimentally and from scaling analysis. They are not affected by the strong temperature and viscosity changes in the focusing gas while expanding at nozzle outlet. A range of gas and liquid-operating parameters is investigated numerically to understand their influence on the jet performance. The study is performed for gas and liquid Reynolds numbers in the range 17–1222 and 110–215, and Weber numbers in the range 3–320, respectively. A reasonably good agreement between experimental and scaling results is found for the range of operating parameters never tackled before. This study provides a basis for further computational designs as well as adjustments of the operating conditions for specific liquids and gases.     

旋翼无人机大气探测设备布局仿真优化设计

为了提高多旋翼无人机气象探测的准确度,基于CFD方法对偶数桨旋翼无人机的流场进行分析,比较了不同旋翼数和不同旋翼间距离的无人机的流场,分析了流场的特点。同时,结合大气探测设备对温湿度、气体浓度及颗粒物浓度测量的基本原理,分析了多旋翼无人机扰流场对探测设备测量精度的影响及其原因。由此确定了进行大气探测的多旋翼无人机尽量根据情况选择旋翼数较多、翼间距较大的机型,探测设备安装位置应当靠近无人机中心轴靠近旋翼旋转平面处的相对静风区,经实验对比,通过优化可以有效减小测量的误差。并提出可利用多旋翼无人机流场特点设计多旋翼无人机专用探测设备的构想。     

A decade of progress on anisotropic mesh adaptation for computational fluid dynamics

In the context of scientific computing, the mesh is used as a discrete support for the considered numerical methods. As a consequence, the mesh greatly impacts the efficiency, the stability and the accuracy of numerical methods. The goal of anisotropic mesh adaptation is to generate a mesh which fits the application and the numerical scheme in order to achieve the best possible solution. It is thus an active field of research which is progressing continuously. This review article proposes a synthesis of the research activity of the INRIA Gamma3 team in the field of anisotropic mesh adaptation applied to inviscid flows in computational fluid dynamics since 2000. It shows the evolution of the theoretical and numerical results during this period. Finally, challenges for the next decade are discussed.     

基于流线的重新网格化及多分辨率表示

提出基于场的重新三角网格化和多分辨率表示生成算法.首先,在原三角网格模型上建立拉普拉斯标量场,据此生成两组夹角为60(的流线.然后,从这两组流线构造以菱形面为主的网格并三角化得到三角基网格.最后,在基网格的基础上,再次使用流线技术对原始数据进行向上重采样,得到模型的多分辨率表示.一般地,基网格的三角形接近等边三角形,实验也表明该方法能够得到较高质量的结果.