大展弦比气弹机翼柔性非线性变形的气动力效应分析与风洞试验

从飞行器刚弹耦合动力学模型出发，引入柔性机翼准定常假设，建立大柔性飞行器非线性静气动弹性气动力方程，利用非线性迭代求解思路模拟了柔性飞行器的静气动弹性响应行为，开展了大展弦比飞机静气动弹性风洞试验验证，采用气动力有限基本解与机翼的耦合计算，发现了大柔性飞机大变形状态下载荷及结构变形形式随风速的变化规律.传统基于小变形假设的线性分析方法和刚体分析由于无法考虑气动面随结构变形的曲面气动力因素和结构变形后的非线性刚度特性，均与风洞试验存在一定的误差.对于大展弦比柔性飞机的非线性静气动弹性分析十分必要.      

激光辐照高超声速舵面热力响应研究

建立了基于流固耦合的高超声速飞行器舵面结构在激光辐照下静气动弹性模型,流体控制方程为三维雷诺平均N-S方程,分别采用了中心格式和AUSM+up格式对粘性项和对流项进行空间离散,时间推进采用了高斯-塞德尔隐式推进方法,湍流粘性系数求解使用Menter SST模型。利用冯·卡门研究所高超风洞实验结果对模型进行了校核,预估了激光辐照对高超舵面的热力影响。结果表明,气动力/热计算模型与实验数据符合较好,能够准确模拟高超飞行器的热力参数,根据模型外推结果,激光在较低功率下加热高超飞行器舵面可能导致舵面材料弹性模量大大降低,继而发生弯曲发散而折断,高超飞行器可能因此发生气动失稳而坠毁。     

CFD在高速飞行器热气弹问题中的应用

采用气动力/热/结构耦合的方法对高速细长体飞行器结构热静气动弹性问题进行了研究.为保证耦合计算精度，达到准确预测热气动弹性特性的能力，气动力和气动热计算采用CFD数值模拟方法，热应力和热变形计算采用有限元方法并通过热考核试验验证.以该简单细长体飞行器模型为研究对象，对其热静气动弹性特性进行了计算与分析，计算结果表明:CFD/CSD耦合可准确模拟热气弹问题，且气动加热造成结构温升不均衡是结构变形的主导因素，力热耦合静气弹变形与单纯受力分析变形形式不同，对飞行器气动特性影响规律不同.准确预测飞行器热气动弹性特性对飞行器结构设计十分必要.      

利用N-S方程模拟机翼气动弹性的一种计算方法

利用一种双时间方法求解三维非定常N-S方程,得到与任意非定常运动对应的气动力,在求解非定常气动力的同时,在时间域内用二阶龙格 库塔方法求解机翼弹性运动方程,从而模拟粘性流动中的气动弹性全过程.为保证网格生成效率,采用无限插值理论生成O-H型代数网格,考虑了机翼变形时的网格生成问题,并得到计算结果.     

高超声速飞行器热气动弹性仿真计算方法综述

高超声速飞行器遭遇的热气动弹性问题具有危险性和复杂性，而型号设计又对计算环境下的热气动弹性仿真提出了效率和精度的双重要求.针对此问题，首先回顾了热气动弹性分析中气动力、气动热、结构热传导、热结构动力学等子学科的仿真计算方法，包括工程方法、数值模拟及降阶建模方法.其中，降阶建模方法有望解决目前计算效率和精度的矛盾，是调研的重点.之后，从时空耦合的角度总结了热气动弹性分析的多场耦合计算架构，包括单向、双向空间耦合策略，以及全耦合、松耦合、时域-频域耦合等时间耦合策略.在结论中，提出了基于子学科降阶模型进行多场耦合仿真的思路，并对热气动弹性分析的发展趋势进行了展望.      

贯流风扇气动声场数值模拟及分析

针对贯流风扇气动噪声传播特性,采用基于非结构网格的CE/SE算法对其气动流场进行数值模拟,并模拟了气动噪声的传播.湍流模拟采用大涡模型,搭接式滑移网格模型处理动静干涉.噪声传播采用完全欧拉方程作为控制方程,远场采用无反射边界条件.将使用该方法得到的远场噪声频谱与实验数据进行对比分析,结果表明与实验测量得到宽带频谱不同,采用大涡模拟湍流模型进行声源模拟时,会加强部分离散频率上的声级,从而产生误差.     

Stokes流动中液滴变形的数值模拟

数值模拟研究Stokes流动中的液滴变形问题。采用边界积分方法计算液滴表面的运动,建立在网格能量最小化基础上的自适应表面离散及网格局部重建方法以准确的分辨出变形液滴的形状,并将数值模拟结果与实验结果进行了比较,模拟结果表明,本方法能够较好的模拟液滴变形的动力学特性。     

用DES数值模拟分离绕流中的旋涡运动

脱体涡模拟(Detached-Eddy Simulation,DES)是近年来出现的一种结合雷诺平均方法和大涡数值模拟两者优点的湍流模拟方法.采用基于Spalart-Allmaras方程模型的DES方法,数值求解Navier-Stokes方程,模拟绕流发生分离后的旋涡运动.其中空间区域离散采用有限体积法,方程空间项和时间项的数值离散分别采用Jameson中心格式和双时间步长推进方法.通过模拟圆柱绕流以及翼型失速绕流,观察到了与物理现象一致的旋涡结构,得到与实验数据相吻合的计算结果.     

吸气式高超声速飞行器气动力气动热的数值模拟方法及应用

对吸气式高超声速飞行器而言,物面热流和摩阻的准确预测对飞行器设计及安全十分关键.介绍采用CFD准确预测气动力和气动热的方法,包括流动的控制方程、湍流模型及湍流的先进壁面函数边界条件,介绍流动的数值求解方法.对典型超声速层流和湍流流动的摩擦阻力和热流进行详细的验证与确认,考察CFD工具在使用先进壁面函数边界条件后,湍流计算的法向网格无关性能力.对设计的一种吸气式高超声速飞行器的气动力和气动热进行数值模拟,为飞行器的气动设计及热防护提供了可靠的数据.     

叶栅内定常及非定常粘性流动数值模拟

本文给出了一个模拟叶栅内准三维定常和非定常粘性流动的数值方法。对于定常流动,采用ＴＶＤ Ｌａｘ－Ｗｅｎｄｒｏｆｆ格式和代数湍流模型求解雷诺平均Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程,使用当地时间步长和多网格技术使计算加速收敛到定常状态;对于非定常流动,使用双时间步长和全隐式离散,采用与求解定常流动相似的多网格方法求解隐式离散方程。文中给出了ＶＫＩ透平叶栅内的定常流结果和１．５级透平叶栅内的非定常数值结果。     

Investigation on transonic flutter active auppression with CFD-Based ROMs

The calculation of accurate unsteady aerodynamic forces is critical in the analysis of aeroelastic problems,however the efficiency is low because of high computational costs of the computational fluid dynamics(CFD)portion.Additionally,direct integrated CFD and computational structural dynamics(CSD)technique is unsuitable for the analysis of ASE and the flutter active suppression in state-space form.A reduced-order model(ROM)based on Volterra series was developed using CFD calculation and used to predict the flutter coupled with the structure.The closed-loop control systems designed by the sliding mode control(SMC)and linear quadratic Gaussian(LQG)control were constructed with ROM/CSD to suppress the AGARD 445.6wing flutter.The detailed implementation of the two control approaches is presented,and the flutter suppression effectiveness is discussed and compared.The results indicate that SMC method can make the controlled object response decay to the stable equilibrium more rapidly and has better control effects than the LQG control.     

三维机翼跨音速颤振的分布式并行计算

以多台微机组成分布式计算系统,利用无限插值方法(TFI)生成三维多块贴体运动网格,以Navier Stokes方程为控制方程,求解三维机翼的跨音速非定常气动力,并与颤振方程耦合迭代计算,求解机翼广义位移响应的时间历程,根据广义位移的时间历程的衰减、等幅和发散振荡等情况确定机翼跨音速颤振临界条件.通过算例验证,计算结果与实验结果和理论分析相吻合.     

隐-显积分因子间断Galerkin方法求解二维辐射扩散方程

提出一种求解二维非平衡辐射扩散方程的数值方法.空间离散上采用加权间断Galerkin有限元方法,其中数值流量的构造采用一种新的加权平均;时间离散上采用隐-显积分因子方法,将扩散系数线性化,然后用积分因子方法求解间断Galerkin方法离散后的非线性常微分方程组.数值试验中在非结构网格上求解了多介质的辐射扩散方程.结果表明:对于强非线性和强耦合的非线性扩散方程组,该方法是一种非常有效的数值算法.     

Detailed numerical simulation of laminar flames by a parallel multiblock algorithm using loosely coupled computers

A parallel algorithm for the detailed multidimensional numerical simulation of laminar flames able to work efficiently with loosely coupled computers is described. The governing equations have been discretized using the finite volume technique over staggered grids. A SIMPLE-like method has been employed to solve the velocity–pressure fields while the species equations have been calculated in a segregated manner using an operator-splitting technique. The domain decomposition method is used to optimize the domain's discretization and to parallelize the code. The main attributes and limitations, together with the computational features (computational effort, parallel performance, memory requirements, etc), are shown, taking into account different degrees of chemical modelling and two benchmark problems: a premixed methane/air laminar flat flame and a confined co-flow non-premixed methane/air laminar flame. In order to assess the validity of the numerical solutions, a post-processing procedure, based on the generalized Richardson extrapolation for h-refinement studies and on the grid convergence index, has been used.     

有限差分法中的贴体坐标变换

分析了有限差分法曲线贴体坐标系下守恒型控制方程的推导过程,认为在离散条件下所采用的数学恒等式不成立,推断目前CFD广泛采用的齐次方程是原始Descartes直角坐标系下方程的近似,提出增加源项的非齐次方程作为离散等价方程.采用数值实验研究了源项,结论是大部分情况下源项不等于0,且对数值解的影响大于差分格式的截断误差,在分析了引起源项非0的原因和推导过程后,提出源项离散的相容性准则.利用坐标变换系数和守恒型方程对流通量的特性,建立了源项隐式计算的耦合算法,通过数值实验证明耦合算法有效消除了坐标变换引起的误差.      

Coupling discontinuous Galerkin methods and retarded potentials for transient wave propagation on unbounded domains

This work deals with the numerical simulation of wave propagation on unbounded domains with localized heterogeneities. To do so, we propose to combine a discretization based on a discontinuous Galerkin method in space and explicit finite differences in time on the regions containing heterogeneities with the retarded potential method to account the unbounded nature of the computational domain. The coupling formula enforces a discrete energy identity ensuring the stability under the usual CFL condition in the interior. Moreover, the scheme allows to use a smaller time step in the interior domain yielding to quasi-optimal discretization parameters for both methods. The aliasing phenomena introduced by the local time stepping are reduced by a post-processing by averaging in time obtaining a stable and second order consistent (in time) coupling algorithm. We compute the numerical rate of convergence of the method for an academic problem. The numerical results show the feasibility of the whole discretization procedure.     

直接甲醇燃料电池膜及阴极模拟

本文提出一个针对直接甲醇燃料电池膜及阴极的二维、多组分稳态数学模型．模型根据直接甲醇膜燃料电池膜及阴极运行工况特性,考虑质量、动量、组分守恒以及电池中的电化学过程而建立,并应用了计算流体动力学(CFD)技术．模拟结果表明传质对直接甲醇燃料电池的性能影响很大;本文还进行了直接甲醇燃料电池阴极水管理的初步探讨．     

On the Fully Implicit Solution of a Phase-Field Model for Binary Alloy Solidification in Three Dimensions

A fully implicit numerical method, based upon a combination of adaptively refined hierarchical meshes and geometric multigrid, is presented for the simulation of binary alloy solidification in three space dimensions. The computational techniques are presented for a particular mathematical model, based upon the phase-field approach, however, their applicability is of greater generality than for the specific phase-field model used here. In particular, an implicit second order time discretization is combined with the use of second order spatial differences to yield a large nonlinear system of algebraic equations as each time step. It is demonstrated that these equations may be solved reliably and efficiently through the use of a nonlinear multigrid scheme for locally refined grids. In effect, this paper presents an extension of earlier research in two space dimensions (J. Comput. Phys., 225 (2007), pp. 1271-1287) to fully three-dimensional problems. This extension is validated against earlier two-dimensional results and against some of the limited results available in three dimensions, obtained using an explicit scheme. The efficiency of the implicit approach and the multigrid solver are then demonstrated and some sample computational results for the simulation of the growth of dendrite structures are presented.