适用于参数可调结构的非定常气动力降阶建模方法

基于计算流体力学(CFD)的非定常气动力降阶模型(ROM)可以极大提高气动弹性分析效率,然而现有的ROM只能针对固定参数结构,即只适合于固定模态振型,这使得现有ROM在气动弹性优化设计和不确定性分析等结构变参问题中应用受限。针对该问题,在文献[20]基础上提出了一种新的适用于任意模态振型的非定常气动力建模方法。首先将待设计/分析的结构进行参数化抽样和模态分析,之后通过主成分分析(PCA)得到若干基振型,再将这些基振型线性叠加即可拟合抽样空间内任何参数下结构的前若干阶振型。当结构参数改动时,仅仅是叠加系数发生变化。算例表明,仅用很少的基振型就能达到理想的拟合精度。经典的气动力降阶方法可用于基振型坐标下的气动力降阶,进一步变换可得到适用于不同结构的ROM,这意味着,结构参数可以在抽样空间内任意调节改动,而ROM却是通用的。该方法能广泛用于气动弹性优化设计和不确定性分析工作,可提高颤振分析精度和效率。     

Numerical simulation of multi-dimensional inviscid compressible flows by using TV-HLL scheme

This paper deals with the numerical solution of inviscid compressible flows. The threedimensional Euler equations describing the mentioned problem are presented and solved numerically with the finite volume method. The evaluation of the numerical flux at the interfaces is performed by using the Toro Vazquez-Harten Lax Leer(TV-HLL) scheme. An essential feature of the proposed scheme is to associate two systems of differential equations, called the advection system and the pressure system. It can be implemented with a very simple manner in the standard finite volume Euler and Navier–Stokes codes as extremely simple task. The scheme is applied to some test problems covering a wide spectrum of Mach numbers, including hypersonic, low speed flow and three-dimensional aerodynamics applications.     

基于高阶谱差分的扑翼面运动学数值优化(英文)

基于高阶谱差分(SD)格式的高成本效益的优化方法被用以优化扑翼面的运动学,从而达到最大推进效率。具体来说,基于梯度的优化算法与高阶谱差分的纳维-斯托克斯流动求解器被耦合用以研究一系列NACA对称翼型的最优运动学。在此研究中,翼型做沉标和俯仰运动。数值优化在粗网格上进行。得到最优解后,在密网格上用高阶SD求解器捕获处于最优运动学状态下扑翼面的详细涡结构。提出的数值优化框架被用以研究翼型厚度,雷诺数和俯仰中心位置对最佳巡航飞行的影响。通过研究相关流场,气动力以及等效攻角(AOA)的变化,我们解释了与最佳扑翼面运动相关的流动物理特性。     

数据融合技术在空气动力学研究中的应用

气动力数据通常通过风洞试验、数值计算和飞行试验三种途径获得,三者各有优缺点,为了得到更加完善准确的气动数据,可采用数据融合技术对不同来源的数据进行深加工和利用。针对数据融合技术在空气动力学中的应用进行讨论和探索,首先介绍了数据融合技术在空气动力学中的应用背景、发展现状及数据融合的基本思想,此后综合提出了建立气动数据融合准则的基本思路和两种具有应用价值的融合算法:基于不确定度的数据融合方法和基于气动力建模的数据融合方法,并给出了部分研究应用结果。最后,文章对气动数据融合技术在气动领域的应用前景进行了展望。研究发现,采用数据融合技术后,可以进一步提高气动数据的完整性和准确性,但由于气动数据融合工作不仅需要进行算法研究,同时还需要工作人员的大量经验,融合结果包含较多的人为因素,因此具体采用何种融合方法要根据具体情况而定。     

Numerical investigation of unsteady vortex breakdown past 80°/65° double-delta wing

An improved delayed detached eddy simulation （IDDES） method based on the k-x-SST （shear stress transport） turbulence model was applied to predict the unsteady vortex breakdown past an 80o/65o double-delta wing （DDW）, where the angles of attack （AOAs） range from 30° to 40°. Firstly, the IDDES model and the relative numerical methods were validated by simulating the massively separated flow around an NACA0021 straight wing at the AOA of 60°. The fluctuation properties of the lift and pressure coefficients were analyzed and compared with the available measurements. For the DDW case, the computations were compared with such mea-surements as the mean lift, drag, pitching moment, pressure coefficients and breakdown locations. Furthermore, the unsteady properties were investigated in detail, such as the frequencies of force and moments, pressure fluctuation on the upper surface, typical vortex breakdown patterns at three moments, and the distributions of kinetic turbulence energy at a stream wise section. Two dominated modes are observed, in which their Strouhal numbers are 1.0 at the AOAs of 30°, 32° and 34° and 0.7 at the AOAs of 36o, 38° and 40°. The breakdown vortex always moves upstream and downstream and its types change alternatively. Furthermore, the vortex can be identified as breakdown or not through the mean pressure, root mean square of pressure, or even through correlation analysis.     

跨声速轴流压气机失速边界预测方法

研究了跨声速、单级设计压比为1.82的Stage 35轴流压气机与单级设计压比为2.05的Stage37轴流压气机在不同转速下的特性.在HARIKA原型程序基础上,改进了其叶排效率、落后角、理论能头计算模型,采用了两种轴流压气机失速边界的预测方法,第1种为HARIKA原型程序的分离流量预测方法,第2种为Koch所提出的失速静压升系数预测方法,所得特性计算结果与实验点吻合较好,Stage 35设计点效率的误差由原型的3.9%降低到改进后的1.5%,Stage 37设计点效率的误差由3.1%降低到1.9%.两种预测方法对失速边界流量的预测误差最小分别可达1.3%与1.6%,表明两种失速边界预测方法都是可行的.     

弹性飞机阵风减缓研究

阵风响应减缓可有效抑制飞机由于离散突风和紊流引起的附加过载。以某民机为研究对象,基于飞机结构动力学方程和非定常空气动力学模型,建立弹性飞机在突风作用和控制面偏转联合激励下的开环气动弹性方程。引入坐标变换,建立飞机刚体模态对应的广义坐标与飞行动力学运动变量之间的关系,从而实现气动弹性方程与飞行动力学方程的融合。并以副翼和升降舵为突风减缓控制面。采用俯仰角速率,翼尖加速度和质心加速度作为反馈信号,针对连续突风和离散突风,分别设计相应的控制律。仿真结果表明,减缓系统对翼尖过载、翼根弯矩具有较好的抑制能力。     

飞艇气动特性分析与设计的一种新趋向

在飞艇气动研究中,将气动计算特别是计算流体力学与优化算法相结合的数值方法非常便于在计算机上应用,实现设计的自动化,相比传统的设计方法具有明显的优势,在最近的研究中多被采用.本文针对新近的若干篇代表性的飞艇气动优化设计的文章,分析其所用的气动计算方法和优化算法,以及优化的结果,指出气动外形优化需要注意的问题,为相关研究提供有益的参考.     

Physical Body Impact After High Altitude Bail-out

In most of the emergency circumstances,the aircrew leaves the aircraft under unsatisfied conditions,such as too high relative velocity to the ambient air or low partial oxygen pressure.The aircrew must pass through this area as quickly as possible before opening the parachute safely,viz.,free-fall.Numerical simulations are conducted in this paper to explore the major characteris-tics of the aircrew free-fall process by using a commercial computational fluid dynamic(CFD) software,FLUENT.Coupled with the classical pressure-altitude and temperature-altitude relations,Navier-Stokes(N-S) equations for compressible flow are solved by using finite volume method.The body velocity and the attitude are predicted with six-degree of freedom(6DOF) module.The evolution of velocities,including horizontal,vertical components and angular velocity,is obtained.It is also analyzed further according to the particle kinetic theories.It is validated that the theories can predict the process qualitatively well with a modi-fied drag effect,which mainly stems from the velocity pressure.An empirical modification factor is proposed according to the fitting results.     

H2O污染对超燃冲压发动机燃烧室性能影响的三维数值模拟

为了解来流污染对超燃冲压发动机性能的影响,需要大量的实验和CFD模拟。基于纯净空气和污染空气(H2O)来流下燃烧对比实验,采用较为详细的化学反应动力学模型(13组分33方程),对三个试验条件的燃烧室反应流场进行了三维大规模并行CFD模拟。模拟结果与对比试验测得的壁面压强比较接近,能"分辨"试验气体中H2O的污染影响。模拟结果显示,从燃烧室整体性能看,7.4%H2O和18.3%H2O污染导致燃烧室单位流量的空气对应推力分别下降4.1%和10.7%,而燃烧室燃烧效率分别下降5.5%和9.5%。