基于误差估计的伴随网格自适应方法

网格自适应是一种有效减少解与网格相关性,改善计算结果的重要途径。给出了一种基于误差估计的伴随网格自适应计算技术,定义了基于误差估计的自适应准则,给出了非结构四面体网格单元细化剖分规则,以及一般的网格自适应流程,介绍了一种基于Rechardson外推的网格收敛技术,运用本文提供的方法对NLR7301翼型进行了数值计算研究,数值试验表明给出的网格自适应具有较高的可有效改善计算结果。     

An SOR Implicit Time-accurate Scheme in Calculating Unsteady Flows

A new time-accurate marching scheme for unsteady flow calculations is proposed in the present work. This method is the combination of classical Successive Over-Relaxation (SOR) iteration method and Jacobian matrix diagonally dominant splitting method of LUSGS. One advantage of this algorithm is the second-order accuracy because of no factorization error. Another advantage is the low computational cost because the Jacobian matrices and fluxes are only calculated once in each physical time step. And, the SOR algorithm has better convergence property than Gauss-Seidel. To investigate its accuracy and convergency, several unsteady flow computa- tional tests are carried out by using the proposed SOR algorithm. Roe’s FDS scheme is used to discritize the inviscid flux terms. Un- steady computational results of SOR are compared with the experiment results and those of Gauss-Seidel. Results reveal that the numerical results agree well with the experimental data and the second-order accuracy can be obtained as the Gauss-Seidel for unsteady flow computations. The impact of SOR factor is investigated for unsteady computations by using different SOR factors in this algorithm to simulate each computational test. Different numbers of inner iterations are needed to converge to the same criterion for different SOR factors and optimal choice of SOR factor can improve the computational efficiency greatly.     

Finite-time sliding mode attitude control for a reentry vehicle with blended aerodynamic surfaces and a reaction control system

This paper proposes a finite-time robust flight controller, targeting for a reentry vehicle with blended aerodynamic surfaces and a reaction control system(RCS). Firstly, a novel finite-time attitude controller is pointed out with the introduction of a nonsingular finite-time sliding mode manifold. The attitude tracking errors are mathematically proved to converge to zero within finite time which can be estimated. In order to improve the performance, a second-order finite-time sliding mode controller is further developed to effectively alleviate chattering without any deterioration of robustness and accuracy. Moreover, an optimization control allocation algorithm, using linear programming and a pulse-width pulse-frequency(PWPF) modulator, is designed to allocate torque commands for all the aerodynamic surface deflections and on–off switching-states of RCS thrusters.Simulations are provided for the reentry vehicle considering uncertain parameters and external disturbances for practical purposes, and the results demonstrate the effectiveness and robustness of the attitude control system.     

类X-37B航天器气动力天地相关性数值模拟

随着高性能计算机的发展,CFD已成为飞行器设计和流场分析不可缺少的重要手段,风洞试验与飞行数据的天地相关性问题正是其中一项重要的研究内容,X-37B作为继航天飞机之后美国发展的最成功的可跨大气层在轨飞行器,从气动特性角度分析其大气层内飞行走廊的状态对中国类似航天器的研制具有重要的借鉴意义。首先,对计算类X-37B布局飞行器的网格无关性及网格修正开展了研究,在此基础上提出的网格规模影响修正方法对该类飞行器的计算结果修正经过验证是可信的;然后,分别对比分析了雷诺数的影响和试验状态支架干扰的影响,完成了基于数值模拟的高空飞行与风洞试验气动特性差异分析。结果表明,网格规模主要对亚声速来流计算状态压差产生的轴向力影响较大,对法向力系数、俯仰力矩系数和纵向压心影响较小;雷诺数对该类飞行器气动特性特别是轴向力系数、阻力系数和升阻比有较大的影响,但随着马赫数的增加,影响特性开始变的非常复杂;由于风洞试验状态支杆存在,亚跨声速来流条件对该类飞行器的底阻影响很大,需要采取一定的方法和手段对支杆影响进行修正。     

基于Galerkin法的机载甚低频拖曳天线振动分析

通过对拖曳天线运动状态及其受力进行分析,建立了其动力学模型;针对模型复杂的非线性和耦合性,在考虑天线旋转平衡时构型的基础上,采用Galerkin法研究求解了其末端锥袋的非线性振动。通过仿真并对多阶Galerkin方法截断求解结果进行比较,验证了Galerkin方法求解时的收敛性和可靠性。仿真结果表明,在无风条件下,拖曳天线的末端锥袋振动不会对机载甚低频通信系统的通信质量产生明显的影响。     

流体网络节点残量修正算法的改进

为了提高流体网络求解的收敛性与稳定性,对网络节点残量修正算法进行改进。基于理论分析,提出使残量修正算法大范围收敛的初值赋值规律,并通过简单模型的数值分析加以验证;在节点残量修正显式迭代的基础上,提出隐式梯形迭代格式,扩大最大迭代步长。基于改进方法,以某典型航空发动机空气系统为例进行计算,获得空气系统各节点的压力、温度以及各支路的质量流量。该计算过程显示,相对于残量修正显式迭代,改进计算振荡大幅度减弱,收敛速度提高了80%以上。结果表明:改进算法有效地提高了流体网络求解的稳定性和收敛性。     

非结构混合网格高雷诺数流动计算中一种改进的LU-SGS隐式格式(英文)

The lower-upper symmetric Gauss-Seidel (LU-SGS) implicit relaxation has been widely used because it has the merits of less dependency on grid topology,low numerical complexity and modest memory require...     

地面效应中悬停旋翼的自由尾迹计算

发展了一种具有良好收敛性的自由尾迹模型,用于对地面效应(IGE)状态下的旋翼悬停尾迹进行数值模拟。其中使用直涡元对桨尖涡丝进行离散,使用面元法模拟地面对流场的影响。针对以往类似研究中旋翼高度较低时自由尾迹迭代不易收敛的问题,引入了地下尾迹等比例修正并提出了环式地面面元分布等多项修改办法来改善计算模型的收敛性,同时这些改进也起到了削减计算量的作用。为了对新构建模型进行验证,以多个高度下的旋翼有地效状态为算例,对其尾迹几何结构进行了计算并与实验值进行了对比,结果显示二者符合得较好,证实了该模型具有较高的准确性。     

基于广义Richardson外插方法的阻力预测精度分析

利用计算流体力学(CFD)方法预测阻力是飞行器气动设计中的关键环节。采用广义Richardson外插方法分别对数值方法预测二维简单构型的压差阻力、摩擦阻力和三维复杂构型的总阻力的精度进行了分析。在NACA 0012翼型无黏绕流和平板湍流边界层两个算例中验证了NSAWET程序和广义Richardson外插方法,分别得到数值算法预测压差阻力和摩擦阻力能达到的名义精度。进而模拟三维通用研究模型(CRM)翼身组合体绕流,得到的阻力名义精确值在DPW 5的统计误差带范围之内;综合DPW 5的计算结果来看,不同CFD解算器的结果之间存在一定差别,阻力预测精度总体上不符合二阶。可见,标准Richardson方法采用的二阶精度假设难以普遍适用,有必要采用广义Richardson外插方法得到名义精度。针对不合理的名义精度,采用Roache建议的方法加以限制。广义Richardson外插方法有助于提高误差分析的合理性,可以进一步降低网格对阻力预测的影响。     

信息化与工业化合力驱动的产业发展新趋势——产业融合

当前,信息产业融合型的增长模式正在快速改变着社会经济的运行方式。产业融合正在加速产业结构的变动,也在推动产业转型升级。产业间的融合渗透促进了新兴业务的活跃爆发,为产业发展带来了一股全新的力量。应当以此为契机,培育新一代产业增长极,以产业融合有力地推动战略性新兴产业发展。