用DES分离涡方法数值模拟串列双圆柱绕流问题

主要开发了SST-DES和SST-DDES两种分离涡方法,并集成到基于开源代码平台Open-FOAM开发的CFD求解器naoe-FOAM-SJTU中.选用高Reynolds(雷诺)数下串列双圆柱绕流问题作为标准算例来验证所开发的分离涡方法.该标准算例此前在美国国家航空航天局兰利研究中心的两个不同风洞做过物理试验.该研究将数值模拟得到的时均流场信息和一些其他物理量同物理试验结果比较,同时讨论分析了三维瞬态流场结构.结果表明该文开发的SST-DES和SST-DDES分离涡方法能够解决高Reynolds数下有大量流动分离的复杂流动问题.     

直管束流固耦合振动的数值模拟

为了研究反应堆结构中的诸如燃料棒、蒸汽发生器和其它换热器传热管束等的流体-结构交互作用问题,利用有限体积法离散大涡模拟(large eddy simulation, LES)的流体控制方程,用有限元方法求解结构动力学方程,并结合动网格技术,建立三维流体诱发振动的数值模型,模拟直管束中流体的流动及结构振动,实现计算结构动力学(computational structure dynamics, CSD)与计算流体力学(computational fluid dynamics, CFD)之间的联合仿真．首先,基于流固耦合方法对单管的流致振动特性进行了详细分析,得到了其动力学响应与流场特性;其次基于建立的传热管束流致振动计算模型,研究了两并列管、两串列管以及3×3正方形排列管束的流致振动行为．     

用DES分离涡方法数值模拟串列双圆柱绕流问题（英文）

主要开发了SST-DES和SST-DDES两种分离涡方法,并集成到基于开源代码平台Open-FOAM开发的CFD求解器naoe-FOAM-SJTU中.选用高Reynolds(雷诺)数下串列双圆柱绕流问题作为标准算例来验证所开发的分离涡方法.该标准算例此前在美国国家航空航天局兰利研究中心的两个不同风洞做过物理试验.该研究将数值模拟得到的时均流场信息和一些其他物理量同物理试验结果比较,同时讨论分析了三维瞬态流场结构.结果表明该文开发的SST-DES和SST-DDES分离涡方法能够解决高Reynolds数下有大量流动分离的复杂流动问题.     

计算流体力学在大型风力机空气动力学的应用进展北大核心CSCD

针对大型风力机设计中的关键空气动力学问题,比较系统地介绍了计算流体力学(computational fluid dynamics,CFD)方法的主要应用,特别是在大型风力机翼型气动分析、风力机流动的数值模拟、风轮空气动力特性的数值计算以及大型风力机叶片的多目标气动优化设计方面的进展.基于CFD方法分别实现了风力机翼型与叶片二维/三维气动特性的准确预测,风力机尾流场涡系结构的准确捕捉;并结合多目标遗传算法对1.5 MW风力机叶片进行了优化,获得了具有高风能利用效率的叶片方案.     

基于有限体积法的非结构网格大涡模拟离散方法研究

非结构网格下的大涡模拟是解决复杂几何体高Reynolds(雷诺)数流动的有效途径.首先,基于有限体积法,研究了对流项和扩散项非结构网格下的离散方法.研究结果表明:基于TVD(total variation diminishing)限制器的限制中心差分格式保证了对流项的二阶精度并抑制了非物理振荡,同时,线性迎风格式虽然稳定,但数值耗散过大,且不能保证有界,中心差分格式引起了周期性非物理振荡;扩散项的超松弛非正交修正减小了网格非正交带来的离散误差,但修正系数须根据网格非正交的程度进行合理选取.为验证所述离散方法对大涡模拟的适用性,数值计算了Re=1.14×10~6下的非定常三维小球绕流,计算方法包括:计算网格用基于Delaunay三角剖分和Netgen前沿推进算法的四面体非结构网格;湍流模型用改进的延迟分离涡大涡模型;在离散格式的选取上,对流项用限制中心差分,扩散项加入非正交修正,插值格式用最小二乘法,时间项用二阶后向差分.计算结果表明,所用离散方法稳定收敛并且与实验数据基本吻合.     

关于幂零π-块中B_(π′)-特征标个数的一个注记

Broué和Puig给出了幂零p-块的概念,并指出了幂零p-块的存在性以及幂零p-块的一个性质:幂零p-块中仅含一个Brauer特征标.利用Slattery,Robinson等的一些工作,将上述思想推广到π-可分群的π-块论中,给出了幂零π-块的合理定义,并证明:幂零π-块中仅含一个B_(π′)-特征标.     

海上浮式风力机及其动力学问题

深水风资源更为丰富,随着科技进步风电场正逐步向水深百米及以上的海域发展．海上浮式风力机、浮式基础以及系泊系统作业时,受到风浪流等的联合作用．就不同海上浮式风力机形式及其典型结构对应的气动载荷、水动力载荷,浮式风力机系统与环境动力的耦合问题、处理方法和可能的发展方向作了简要的评述．充分考虑作业背景的环境流场和风力机尺度,针对不同的流动特征综合各种理论方法和计算手段,更为准确地进行空气动力学-水动力学-控制系统-结构耦合分析是研究的难点和发展方向.     

电磁力控制下圆柱绕流的涡度拟能

Okubo-Weiss函数与流元的容变、畸变以及涡量相关,可以用来评估流场的涡结构．经该文数学证明,对于边界无滑移的,低Reynolds数的二维不可压缩流动,Okubo-Weiss函数的全流场积分为0．还以电磁控制的圆柱绕流为例,通过数值计算,对该结论进行了验证．根据计算结果,依据Okubo-Weiss函数值,对流场进行了划分,讨论了总涡度拟能、总变形率和Okubo-Weiss函数在流场中的分布规律,以及电磁力对分布的影响．     

基于非结构自适应网格的复合有限体积法

利用文献[1]中将Lax-Wendroff格式和Lax-Friedrichs格式整体复合作用构成二维无结构网格上的复合型有限体积法,同时利用Delaunay方法,根据流场流动特性变化的梯度值为指示器对网格进行加密和粗化,实现自适应,并将此方法应用到二维浅水波方程的求解上,进行了二维部分溃坝,倾斜水跃的数值实验.结果表明,该方法是一个计算稳定、能适应复杂的求解域、能很好地捕捉激波、且计算速度快的算法.     

二元海水液滴对心碰撞过程数值模拟

为研究海水循环冷却系统中液滴碰撞的基本规律及碰撞结果预测模型,采用流体体积函数(volume of fluid,VOF)方法捕捉两相交界面,利用动态网格自适应技术提高求解精度,对二元海水液滴的对心碰撞过程进行直接数值分析与模拟.首先对氮气中正十四烷液滴的碰撞实验进行数值模拟,验证了数值模型的可靠性.开展了常温常压下等尺寸二元海水液滴对心碰撞数值研究,分析了液滴碰撞过程流场结构及流动机理,研究了不同液滴直径和不同海水浓度对碰撞过程的影响规律,得到了聚合和自反分离两种碰撞结果类型以及二者的临界Weber数.总结出不同Ohnesorge数下海水液滴碰撞结果诺模图.     

Adaptive Runge-Kutta Discontinuous Galerkin Methods with Modified Ghost Fluid Method for Simulating the Compressible Two-Medium Flow

In this paper, we investigate using the adaptive Runge-Kutta discontinuous Galerkin (RKDG) methods with the modified ghost fluid method (MGFM) in conjunction with the adaptive RKDG methods for solving the level set function to simulate the compressible two-medium flow in one and two dimensions. A shock detection technique (KXRCF method) is adopted as an indicator to identify the troubled cell, which serves for further numerical limiting procedure which uses a modified TVB limiter to reconstruct different degrees of freedom and an adaptive mesh refinement procedure. If the computational mesh should be refined or coarsened, and the detail of the implementation algorithm is presented on how to modulate the hanging nodes and redefine the numerical solutions of the two-medium flow and the level set function on such adaptive mesh. Extensive numerical tests are provided to illustrate the proposed adaptive methods may possess the capability of enhancing the resolutions nearby the discontinuities inside of the single medium flow region and material interfacial vicinities of the two-medium flow region.     

Crack growth modeling via 3D automatic adaptive mesh refinement based on modified-SPR technique

In this paper, the three-dimensional automatic adaptive mesh refinement is presented in modeling the crack propagation based on the modified superconvergent patch recovery technique. The technique is developed for the mixed mode fracture analysis of different fracture specimens. The stress intensity factors are calculated at the crack tip region and the crack propagation is determined by applying a proper crack growth criterion. An automatic adaptive mesh refinement is employed on the basis of modified superconvergent patch recovery (MSPR) technique to simulate the crack growth by applying the asymptotic crack tip solution and using the collapsed quarter-point singular tetrahedral elements at the crack tip region. A-posteriori error estimator is used based on the Zienkiewicz–Zhu method to estimate the error of fracture parameters and predict the crack path pattern. Finally, the efficiency and accuracy of proposed computational algorithm is demonstrated by several numerical examples.     

A parallel adaptive grid algorithm for computational shock hydrodynamics

Adaptive Mesh Refinement (AMR) algorithms that dynamically match the local resolution of the computational grid to the numerical solution being sought have emerged as powerful tools for solving problems that contain disparate physical scales. In particular several workers have demonstrated the effectiveness of employing an adaptive, hierarchical block-structured grid system for time-accurate simulations of complex shock wave phenomena. Here we present an overview of one such block-structured AMR algorithm. Our formulation has progressed far beyond the development stage to become a reliable numerical tool for performing detailed investigations of complex flows. While our refinement machinery is not tied to a specific application and is intended for general use, in this paper we adopt detonation phenomena as a theme so as to provide a sense of purpose.     

Adaptive mesh method for topology optimization of fluid flow

In order to solve the topology optimization problems of fluid flow and obtain higher resolution of the interface with a minimum of additional expense, an automatic local adaptive mesh refinement method is proposed. The optimization problem is solved by a simple but robust optimality criteria (OC) algorithm. A material distribution information based adaptive mesh method is adopted during the optimization process. The optimization procedure is provided and verified with several benchmark examples.     

Mesh quality control for multiply-refined tetrahedral grids

A new algorithm for controlling the quality of multiply-refined tetrahedral meshes is presented in this paper. The basic dynamic mesh adaption procedure allows localized grid refinement and coarsening to efficiently capture aerodynamic flow features in computational fluid dynamics problems; however, repeated application of the procedure may significantly deteriorate the quality of the mesh. Results presented show the effectiveness of this mesh quality algorithm and its potential in the area of helicopter aerodynamics and acoustics.     

Four-triangles adaptive algorithms for RTIN terrain meshes

We present a refinement and coarsening algorithm for the adaptive representation of Right-Triangulated Irregular Network (RTIN) meshes. The refinement algorithm is very simple and proceeds uniformly or locally in triangle meshes. The coarsening algorithm decreases mesh complexity by reducing unnecessary data points in the mesh after a given error criterion is applied. We describe the most important features of the algorithms and give a brief numerical study on the propagation associated with the adaptive scheme used for the refinement algorithm. We also present a comparison with a commercial tool for mesh simplification, Rational Reducer, showing that our coarsening algorithm offers better results in terms of accuracy of the generated meshes.     

Adaptive least-squares finite element approximations to transonic-flow problems

This work concerns solutions of compressible potential flow problems based on weighted least-squares finite element approximations. The model problem considered is that of the potential flow past a circular cylinder. To capture the transonic flow region, an adaptive algorithm based on mesh redistribution with local mesh refinement and smoothing is developed for suitably weighted least-squares approximations. Numerical results for the model problem are given for the transonic case with shocks. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Parallel Algorithm for Adaptive Local Refinement of Tetrahedral Meshes Using Bisection

Local mesh refinement is one of the key steps in the implementations of adaptive finite element methods. This paper presents a parallel algorithm for distributed memory parallel computers for adaptive local refinement of tetrahedral meshes using bisection. This algorithm is used in PHG, Parallel Hierarchical Grid (http: //lsec. cc. ac. cn/phg/J, a toolbox under active development for parallel adaptive finite element solutions of partial differential equations. The algorithm proposed is characterized by allowing simultaneous refinement of submeshes to arbitrary levels before synchronization between submeshes and without the need of a central coordinator process for managing new vertices. Using the concept of canonical refinement, a simple proof of the independence of the resulting mesh on the mesh partitioning is given, which is useful in better understanding the behaviour of the bisectioning refinement procedure.AMS subject classifications: 65Y05, 65N50     

Adaptive mesh refinement for the control of cost and quality in finite element analysis

Adaptive strategies are a necessary tool to make finite element analysis applicable to engineering practice. In this paper, attention is restricted to mesh adaptivity. Traditionally, the most common mesh adaptive strategies for linear problems are used to reach a prescribed accuracy. This goal is best met with an h-adaptive scheme in combination with an error estimator. In an industrial context, the aim of the mechanical simulations in engineering design is not only to obtain greatest quality but more often a compromise between the desired quality and the computation cost (CPU time, storage, software, competence, human cost, computer used). In this paper, we propose the use of alternative mesh refinement criteria with an h-adaptive procedure for 3D elastic problems. The alternative mesh refinement criteria (MR) are based on: prescribed number of elements with maximum accuracy, prescribed CPU time with maximum accuracy and prescribed memory size with maximum accuracy. These adaptive strategies are based on a technique of error in constitutive relation (the process could be used with other error estimators) and an efficient adaptive technique which automatically takes into account the steep gradient areas. This work proposes a 3D method of adaptivity with the latest version of the INRIA automatic mesh generator GAMHIC3D.     

RBF Neural Network Based Prediction on Blade Surface Pressure Fields in Compressors北大核心CSCD

The airflow characteristics of the internal flow path of an aero-engine compressor are complex, and the vortex flow field around the blade is characterized by high pressure, high speed, rotation, and unsteadiness. Therefore, there is an urgent need to calculate and predict the aerodynamic characteristics of the complex flow field around the compressor blade efficiently and accurately. The computational fluid dynamics (CFD) method was used to generate the aerodynamic load distribution on the blade surface under different operating conditions for the study of the complex flow fields around aero-engine blades. The radial based function (RBF) neural network was applied to establish the pressure surface aerodynamic load prediction model, and the neural network modeling method was combined with the flow field calculation. The neural network method can learn and train the CFD-based data set to properly compensate the errors from the CFD, which provides a reference for the effective prediction of the complex flow fields around aero-engine compressor blades. © 2023 Editorial Office of Applied Mathematics and Mechanics. All rights reserved.