三维非结构混合网格高超声速流场并行计算

在非结构混合网格上对三维高超声速化学非平衡粘性绕流进行了基于PC-Cluster的分布式并行数值模拟.本采用区域分裂思想,研究了三维非结构混合网格区域自动分解技术,并以此为基础对高超声速化学非平衡绕流进行了并行数值计算.控制方程为多组分N-S方程,空间离散采用有限体积格心格式,时间推进为显式Runge-Kutta格式.化学非平衡动力学模型为七组元带电离反应模型,对化学反应源项进行了点隐式处理,温度场的计算采用牛顿迭代法.在PC-Cluster上对三维双椭球模型的高超声速绕流流场进行了基于区域分解技术的并行数值模拟,所得数值结果与参考献中的结果作了对比验证。     

边界条件对三维空腔流动振荡的影响

基于全隐式无分裂方法,数值求解三维非定常雷诺平均的N av ier-S tokes方程,紊流模型采用修正的B-L代数模型。运用此方法,本文数值模拟了三维开式空腔的超声速、跨声速、亚声速流动。研究了空腔口处剪切层的非定常运动现象,着重探讨了入口边界条件对三维空腔流自持性振荡的影响。数值计算结果表明,与层流速度型相比,入口条件为紊流速度型和特征边界型得到的结果能够吻合。     

高超声速小钝锥尾流转捩规律与光电特性

显式有限差分方法用于求解小钝锥高超声速化学非平衡尾流的轴对称边界层方程。该方法既适用于层流也适用于湍流。应用 Goldburg 转捩准则确定转捩初始位置。详细地计算了小钝锥尺寸、飞行速度、高度对尾流转捩和光电特性的影响。从计算中得到转捩和光电特性变化的一些有用规律。对湍流亚密部分的雷达散射截面进行了规律性分析。计算结果具有实用参考价值。     

Lattice Boltzmann Flux Solver： An Efficient Approach for Numerical Simulation of Fluid Flows

A lattice Boltzmann flux solver （LBFS） is presented for simulation of fluid flows. Like the conventional computational fluid dynamics （CFD） solvers, the new solver also applies the finite volume method to discretize the governing differential equations, but the numerical flux at the cell interface is not evaluated by the smooth function approximation or Riemann solvers. Instead, it is evaluated from local solution of lattice Boltzmann equation （LBE） at cell interface. Two versions of LBFS are presented in this paper. One is to locally apply one-dimensional compressible lattice Boltzmann （LB） model along the normal direction to the cell interface for simulation of compressible inviscid flows with shock waves. The other is to locally apply multi-dimensional LB model at cell interface for simulation of incompressible viscous and inviscid flows. The present solver removes the drawbacks of conventional lattice Boltzmann method （LBM） such as limitation to uniform mesh, tie-up of mesh spacing and time interval, limitation to viscous flows. Numerical examples show that the present solver can be well applied to simulate fluid flows with non-uniform mesh and curved boundary.     

Model for Asymmetry of Shock/Boundary Layer Interactions in Nozzle Flows

The reason for the asymmetry phenomenon of shock/boundary layer interactions(SBLI)in a completely symmetric nozzle with symmetric flow conditions is still an open question.A model for the asymmetry of nozzle flows was proposed based on the properties of fluid entrainment in the mixing layer and momentum conservation.The asymmetry model is deduced based on the nozzle flow with restricted shock separation,and is still applicable for free shock separation.Flow deflection angle at nozzle exit is deduced from this model.Steady numerical simulations are conducted to model the asymmetry of the SBLIs in a planar convergent-divergent nozzle tested by previous researchers.The obtained values of deflection angle based on the numerical results of forced symmetric nozzle flows can judge the asymmetry of flows in a nozzle at some operations.It shows that the entrainment of shear layer on the separation induced by SBLTs is one of the reasons for the asymmetry in the confined SBLIs.     

盒式机翼布局气动特性研究

采用数值模拟的方法研究了盒式机翼布局的气动特性。在数值模拟过程中,控制方程为雷诺平均N-S方程,采用基于非结构网格的有限体积方法进行求解。空间离散采用了Osher逆风格式,时间离散则采用五步Runge-Kutta格式。紊流模型采用了S-A方程模型。对盒式机翼布局外形在不同状态下的流场进行了数值模拟,给出了每个状态下的气动参数,并进行了分析,结果显示盒式机翼布局具有较好的气动特性。     

ON SPECTRAL PROBLEM FOR VISCOUS SHEAR FLOWS

INTRODUCTIONLarge- scale complex eigenvalue problemsarising in continuum physics and engineering ap-plications are important not only because theyyield fundamental knowledge on the systems be-ing studied,they also provide a challenging con-textforthe developmentof numerical and analyt-ical techniques in their solution.In this paper,we re- examine the well- known Orr- Sommerfeldproblem which governs the linear stability of par-allel shear flows.More specifically,we are con-cerned with the …     

Adaptive Backstepping Control for Hypersonic Vehicles with Actuator Amplitude and Rate Saturation

This paper presents a constrained control strategy for the hypersonic vehicle with actuator amplitude,rate constraints and aerodynamic uncertainties. First,a vehicle-actuator control model is derived in consideration of actuator dynamics properties explicitly. Second, a nonlinear disturbance observer is designed to estimate the aerodynamic uncertainties, and then an adaptive backstepping control technique is adopted with a modified first-order-filter to eliminate the"explosion of terms"problem. Next,for handling the actuator amplitude and rate constraints,a novel auxiliary compensation system is constructed to generate quickly compensating signals to ensure tracking performance of command signal. By the Lyapunov stability proof,the proposed control scheme can enssure that the tracking errors converge to an arbitrarily small neighborhood around zero when the actuator constraints and aerodynamic uncertainties exist. Finally,numerical simulations are implemented to illustrate the effectiveness of the proposed control method.     

含化学反应流动的TVD格式及其在燃气射流中的应用

以Harten标准TVD格式为基础，结合固体火箭燃气射流的特点，以数学方法系统地推导了适合于高温、高压和高速流体流动的数值格式，给出了压力偏导数的合理计算公式；利用化学动力学知识，对火箭燃气射流流场中存在的多组分、含有限速率的化学反应问题进行了论述，阐明了化学反应质量源项的求解方法。以12组分9反应方程模型为例，利用编制的计算程序，对某火箭燃气自由射流流场进行了模拟。通过对结果的分析，肯定了数值格式的正确性。     

CONSERVATIVE FRONT TRACKING IN HIGHER SPACE DIMENSIONS

INTRODUCTIONWe propose and demonstrate a tracking fi-nite difference algorithm which is( a) fully con-servative and ( b) improves local truncation errorby one order( from O( 1 ) to O( Δx) near trackeddiscontinuities.Discontinuities in the solutions of systems ofnonlinear hyperbolic conservation laws are widelyrecognized as a primary difficulty for numericalsimulation.Surprisingly,the nonlinearities actu-ally help,as they cause information,which flowsalong solution characteristics,to flow…     

后掠机翼欧拉方程数值模拟

本文对后掠机翼用保角转绘加剪切变换生成C-H型网格,并在这类网格拓扑上,用Jameson的三维欧拉方程有限体积法,四步Runge-Kutta时间推进格式,研制出可供分析三维后掠机翼亚、跨、超声速绕流的计算程序。本方法的特色是改进了机翼表面网格点的分布,使机翼后缘与网格线一致。在数值计算中,通过附面层位移厚度计算,引入了附面层粘性修正,改善了计算结果。     

基于环状超声速气流引射作用的靶式气流磨研究

气流磨作为生产超精细粉末的设备在工业界得到了广泛应用。通过数值模拟和试验验证,提出了一种超声速靶式气流磨。该气流磨采用环状超声速气流引射颗粒流,使其达到超声速状态并获得极大动能,以颗粒束形式维持于气流中心,准确碰撞靶头,实现超声速粉碎。对颗粒速度和运动轨迹的两相流数值模拟结果表明:在总压1.5 MPa、马赫数3.0的超声速气流引射作用下,粒径为25~1 μm的颗粒可加速至440~530 m/s,并精准地碰撞靶头。在此基础上,设计制造了超声速靶式气流磨并进行了铁粉粉碎试验和靶头侵蚀试验,结果表明:颗粒具有极大的碰撞能量,且与靶头发生了聚焦式碰撞。     

收敛形进气道数值研究的验证

介绍一种新型的、具有最小喉道面积的三维高超声速进气道 (称之为收敛形进气道 )的数值和实验研究结果。表明使用这种形式的进气道 ,在整个飞行速度范围内可以降低阻力和高超声速发动机表面的热防护要求 ,通过降低外压缩表面的倾斜度和减少进气道及燃烧室壁的面积就可以做到这一点。在采用低维次流动的气体动力设计方法的基础上设计成这种形式的进气道。计算是在无粘气体模型构架内用有限体积法进行的。同时用边界层方程计算出计及粘性的气流特性和进气道特性。数值算法是通过收敛形进气道的有限宽楔形外压缩表面的计算和实验数据来验证的。进行实验研究的马赫数M=2～ 1 0 7,基于模型进气道高度的雷诺数Re=( 1～ 5) × 1 0 6。数值计算与实验结果一致性很好。这些结果也和通常的二维进气道的数据作了比较。     

超声速化学反应流场迎风格式数值模拟及并行计算

基于有限体积迎风格式对超声速燃烧流场进行了的数值模拟.由于超声速燃烧流场绕流的复杂性,要求对多组分Euler/N-S方程求解的数值模拟方法应具有较高的计算精度及效率.本文引用辅助点方法建立了具有空间二阶精度的van Leer迎风矢通量分裂格式,并应用于超声速燃烧流场绕流的数值模拟.化学反应为氢气/空气十反应模型,采用考虑了化学反应特征时间的当地时间步长显式Runge-Kutta时间推进格式.对钝头体模型爆轰现象、后向台阶氢气喷射及二维内外流超声速燃烧流场模型进行了区域分裂技术的并行计算.计算结果与参考文献作了对比,得到了满意的结果.     

圆弧激波缓聚点火及后续燃烧传播

采用激波管实验和准一维数值模拟的方法,对预混可燃气体中圆弧汇聚激波的自点火现象及后续燃烧波的传播特性进行研究。其中圆弧汇聚激波由平面运动激波通过精确设计的弧形过渡管段转变得到。研究表明:收缩段中圆弧汇聚激波波后的非均匀梯度环境由激波在平直段、弧形过渡段和扇形收缩段中传播所分别诱导的3个梯度区共同构成。随着圆弧汇聚激波的不断增强,圆弧激波后某处首先形成一个无激波的温和反应区。该反应区逆流锋面的初期运动速度远超Chapman-Jouguet（CJ）爆轰波速,而反应产物区流动则呈现出一定弱爆轰波特征。进一步分析发现,该反应锋面本质上是一种"自发反应波"（spontaneous reaction wave）,而非常规意义上的动力学波,其速度与汇聚激波波后气流点火时间梯度的倒数吻合。而后,反应区的扩张速度很快降至CJ爆轰波速以下,伴随反应锋面附近激波的产生以及激波-火焰复合结构的形成。激波-火焰结构最终加速演变为反向传播的爆轰波。在一定的条件下,由于入射激波转变过程和汇聚所构造的特定点火环境,自发反应波可再次赶超爆轰波,成为新的燃烧波前;而当自发反应波速度再次低于CJ爆轰波速时,它将再次转变为爆轰波;在此过程中,原先的爆轰波阵面蜕变为反应产物中传播的激波。     

应用确定性优化算法求解多目标气动设计问题的Pareto阵面

将确定性优化算法和Pareto阵面概念结合起来处理了多目标优化设计问题；给出了结合算法及数值过程的细节，并将其应用到了气动优化设计中；描述了如何用确定性优化算法快速抓获多目标优化问题的Pareto阵面以及能够抓获哪些类型的Pareto阵面。数值实验结果表明，确定性优化算法可以准确高效地抓获任意凸的和某些凹的Pareto阵面，故对于此类多目标气动优化问题，可用确定性算法代替进化算法。     

一种轨道式动态目标跟踪算法

研究了一种轨道式动态目标跟踪的算法,建立轨迹式目标跟踪模型;分析了目标跟踪的基本原理,研究跟踪平台的光学结构和转台角度与轨道目标运动的跟踪算法,给出了物像动态跟踪的计算方法;研究Mean shift跟踪算法,利用它的核密度估计和跟踪图像的帧图像关系,确定目标检索中心位置,以达到动态目标跟踪目的。通过试验验证,提出的算法在外弹道轨道目标动态跟踪系统中是可行的。     

圆转方非轴对称喷管无粘流动的多层网格法求解

本文利用多层网格法求解三维无粘亚音和跨音速圆转方非轴对称喷管的流动,基本格式是把Ni[1]的二维有限体积积分格式推广到三维流场。边界条件采用文[2]中的“预测一修正”处理方法。为了进一步提高格式稳定性,在计算流动变量的一阶时间变化量时,采用单元体积平均法而不是文[1]中的算术平均法。引入当地时间步及多层网格方法,以加快格式的收敛速度。文中还对多层网格构造形式及其收敛效果作了讨论。通过对两种喷管模型流动的计算和与试验数据的对比,验证了该算法的精度。     

Numerical Study on Flow-Induced Vibration of Ejector Structure

High-speed airflow in wind tunnel tests usually causes dramatic vibration of ejector structure,which may lead to fatigue and even destruction of the wind tunnel. Therefore,analyzing and solving the flow-induced vibration problem is a tough and indispensable part of the wind tunnel security design. In this paper,taking a kind of two-stage ejector as the study object,multiple numerical simulation methods are adopted in order to carry out research on the analysis technique of the flow-induced vibration characteristics of ejector structure. Firstly,the structural dynamics characteristic is analyzed by using the ejector structural dynamics numerical model,which is built on the basis of finite element method. Secondly,the complex flow phenomenon is explored applying numerical fluid-dynamics model of the inner flow field of the ejector,which is constructed on the basis of finite volume method. Finally,based on the two numerical models above,the vibration response of the ejector structure induced by the high-speed airflow is computed via the fluid-solid coupling technique. The comparison of the simulation results with the actual vibration test indicates that these numerical simulation methods can accurately figure out the rule of flow-induced vibration of ejectors.