全机绕流Euler方程多重网格分区计算方法

全机三维复杂形状绕流数值求解只能采用分区求解的方法,本文采用可压缩Euler方程有限体积方法以及多重网格分区方法对流场进行分区计算。数值方法采用改进的van Leer迎风型矢通量分裂格式和MUSCL方法,基于有限体积方法和迎风型矢通量分裂方法,建立一套处理子区域内分界面的耦合条件。各个子区域之间采用显式耦合条件,区域内部采用隐式格式和局部时间步长等,以加快收敛速度。计算结果飞机表面压力分布等气动力特性与实验值进行了比较,二者基本吻合。计算结果表明采用分析“V”型多重网格方法,能提高计算效率,加快收敛速度达到接近一个量级。根据全机数值计算结果和可视化结果讨论了流场背风区域旋涡的形成过程。     

代数多重网格方法在紊流数值预测中的应用

机械和矿山工程中广泛使用锥形渐扩管。将DLR型k-ε紊流模型中非线性偏微分方程基于全隐式高精度迎风差分格式离散,得到差分方程的系数矩阵为五对角块十三对角带状稀疏矩阵,基于一种"三元组"方式进行压缩存储,节约内存。提出了一种基于DLR型k-ε紊流模型与代数多重网格方法结合的新算法,阐述了代数多重网格方法的实施过程。对具有逆压梯度流动的锥形渐扩管内紊流进行了数值预测。数值实验表明,代数多重网格方法对求解紊流模型离散方程组非常有效,同此前该紊流数值模拟中使用的Point-SOR方法相比,计算效率有了显著提高,计算结果与实验结果吻合较好。     

求解一类网格结构模型的代数多重网格法

针对网格结构离散模型的特点,设计了一类适用于求解大规模二维网格结构数值计算的代数多重网格方法,详细描述了代数多重网格方法中粗化策略与插值算子的构造,并在此基础上得到了一类以该代数多重网格为预条件子的预处理方法。数值试验表明,本文建立的代数多重网格方法及相应的预处理方法是健壮的,具有较好的数值效率,非常适合于大规模网格结构材料的数值计算。近似连续模型的建立为代数多重网格方法的可靠性和计算的准确性提供了有效的理论基础。     

无网格法在三维复杂超音速流场模拟中的应用研究

对最小二乘无网格方法在含复杂外形三维超音速流场中的应用进行了研究.选用分解法求解采用最小二乘法得到的对称方程组,针对最小二乘无网格方法的计算特点生成近似正交均匀分布的离散点,对B1AC2R常规导弹超音速流场采用最小二乘无网格方法进行了无粘数值模拟,计算了B1AC2R常规导弹在不同攻角下的轴向力、法向力及俯仰力矩系数,并将数值结果与实验结果进行了比较.结果表明,最小二乘无网格方法在求解含复杂外形超音速流场时具有较高的准确度,将其应用于三维含复杂外形超音速流场的模拟是完全可行的.     

侧向多喷口干扰复杂流动数值模拟研究

采用具有高分辨率的NND格式,通过数值求解N-S方程对典型外形多喷口侧向喷流复杂干扰流动进行了数值模拟. 为了提高计算效率,采用了LU-SGS隐式算法. 采用分块对接网格技术,生成高质量的贴体计算网格,精确模拟喷口截面. 对比分析了不同计算格式、限制器形式、网格拓扑及流动形态(层流与湍流)对喷流干扰流场结构和压力分布特性的影响,研究和分析了喷口附近流场的涡系结构、波系结构和喷流干扰引起的气动力特性. 在上述研究的基础上,针对典型飞行器外形的侧向喷流干扰特性进行了详细的数值模拟,得到了喷口参数(喷口位置、数目等)及来流条件对喷流干扰流场结构、气动力特性的影响规律,并对其流动机理进行了相应的分析. 研究表明,发展的针对多喷口侧喷干扰的数值计算方法是成功的,可以应用于飞行器侧向喷流干扰的流场结构分析及气动力特性数值预测.      

计算含动边界非定常流动的无网格算法

在无网格算法中考虑了含动边界的流动问题,研究了可以计算处理包含一定位移及扭转动边界非定常流动的算法.创建了无网格算法的动点法则,并引入抗扭方法对弹簧方法进行改进来处理离散点运动,提高了方法的可用度及精度.发展了求解基于无网格的ALE方程组的算法,在点云离散的基础上采用曲面逼近计算空间导数及HLLC格式计算数值通量,运用四步龙格-库塔法进行时间推进.在跨、超音速条件下,计算模拟了典型翼型简谐振动流场,计算结果与实验结果及文献对比吻合,验证了该算法的正确性.     

非结构重叠网格方法研究及应用

航空、航天和兵器技术等领域的研究中存在大量包含运动边界的流场。非结构重叠网格方法是一种高效的处理动边界问题的新方法。围绕相对运动的每个物体单独生成非结构网格,在网格重叠区域通过搜索和插值完成网格系之间的信息传递,提出了动态八叉树搜索算法,发展了绝对坐标系和相对坐标系相结合的流场求解方式,采用二阶精度Van Leer/Hanel格式和四阶Runge-Kutta法分别进行空间和时间离散,形成了一种新的非结构重叠网格算法。对三维Riemann问题的求解结果与精确解能很好吻合,证明了本文的重叠网格算法具有较好的时空离散精度和插值精度。对7.62mm步枪射击过程进行了数值模拟,描述了弹丸离开膛口后膛口流场的发展过程,与实验结果体现的发展过程较为吻合,验证了本文提出的非结构网格算法体系具有较好的计算性能,是研究含动边界复杂流场的一种有效手段。     

某型电动飞机气动特性数值模拟与风洞实验

为了验证某型大展弦比电动飞机气动设计的合理性以及为飞行性能及品质计算提供数据,采用有限体积法离散求解三维可压雷诺平均Navier-Stokes方程,并选用Spalart-Allmaras湍流模型对该电动飞机流场进行CFD数值模拟。结果表明,该型电动飞机气动设计合理,巡航速度升阻比最高可达23,具有较高气动效率;通过CFD数值模拟得到了全机升力系数、阻力系数和升阻比。为了验证CFD计算结果,对该型电动飞机进行了缩比模型风洞实验,结果显示,CFD数值模拟法计算结果与风洞实验结果高度吻合,说明CFD计算结果准确。该方法可为大展弦比电动飞机气动设计提供指导。     

基于SIMPLER算法的多重网格方法研究

以二维方腔顶盖驱动流为模型,将多重网格方法和SIMPLER算法进行耦合,对不同雷诺数下多重网格加速SIMPLER算法和SIMPLER算法的计算效率进行了对比,数值计算表明:多重网格加速SIMPLER算法不仅能够解决SIMPLER算法不能准确模拟较高雷诺数流场的问题,而且其计算效率远远高于SIMPLER算法.本文也对松弛因子的选取、多重网格实现形式以及网格层数对多重网格加速SIMPLER算法的影响进行了研究,从而为多重网格加速SIMPLER算法的实施提供了计算技术.     

AUFS格式在无网格方法中的应用

将计算量小,激波分辨率高的AUFS(artificially upstream flux vector splitting)格式应用于无网格方法.所发展算法基于多项式基函数最小二乘无网格方法,采用线性基函数曲面拟合及AUFS格式计算各离散点的空间导数,应用四阶Runge--Kutta法进行时间显式推进.为验证算法健壮性、精度以及计算效率,对Riemann问题、超音速平面流动,以及不同攻角NACA0012翼型跨音速流场进行了数值模拟,其结果同采用HLLC(Harten-Lax-van Leer-contact)格式的无网格方法以及文献报道结果吻合较好,并且计算量较形式简单HLLC格式减少约15%.     

Computation of the stability derivatives via CFD and the sensitivity equations

The method to calculate the aerodynamic stability derivates of aircrafts by using the sensitivity equations is ex- tended to flows with shock waves in this paper. Using the newly developed second-order cell-centered finite volume scheme on the unstructured-grid, the unsteady Euler equations and sensitivity equations are solved simultaneously in a non-inertial frame of reference, so that the aerodynamic stability derivatives can be calculated for aircrafts with complex geometries. Based on the numerical results, behavior of the aerodynamic sensitivity parameters near the shock wave is discussed. Furthermore, the stability derivatives are analyzed for supersonic and hypersonic flows. The numerical results of the stability derivatives are found in good agree- ment with theoretical results for supersonic flows, and variations of the aerodynamic force and moment predicted by the stability derivatives are very close to those obtained by CFD simulation for both supersonic and hypersonic flows.     

Lift force on rotating sphere at low Reynolds numbers and high rotational speeds

The lift force on an isolated rotating sphere in a uniform flow was investigated by means of a three-dimensional numerical simulation for low Reynolds numbers (based on the sphere diameter) (Re<68.4) and high dimensionless rotational speeds (Г5). The Navier-Stokes equations in Cartesian coordinate system were solved using a finite volume formulation based on SIMPLE procedure. The accuracy of the numerical simulation was tested through a comparison with available theoretical, numerical and experimental results at low Reynolds numbers, and it was found that they were in close agreement under the above mentioned ranges of the Reynolds number and rotational speed. From a detailed computation of the flow field around a rotational sphere in extended ranges of the Reynolds number and rotational speed, the results show that, with increasing the rotational speed or decreasing the Reynolds number, the lift coefficient increases. An empirical equation more accurate than those obtained by previous studies was obtained to describe both effects of the rotational speed and Reynolds number on the lift force on a sphere. It was found in calcttlations that the drag coefficient is not significantly affected by the rotation of the sphere. The ratio of the lift force to the drag force, both of which act on a sphere in a uniform flow at the same time, was investigated. For a small spherical particle such as one of about 100μm in diameter, even if the rotational speed reaches about 10^6 revolutions per minute, the lift force can be neglected as compared with the drag force.     

高速列车头型长细比对气动噪声的影响

高速列车的头尾车外形对气动噪声具有重要的影响.工程实践中随着车速的增加,车辆头部越来越细长,日本高速磁悬浮列车实践中甚至出现了具有极端长细比的头部形状.本文以讨论头型长细比对列车气动噪声的影响规律为出发点,应用非线性声学求解器(NLAS)和FW-H声学比拟法的混合算法,在3种运行速度下对基于CRH380A高速列车头型概化的4种不同头型长细比的模型车的气动噪声进行了数值模拟.给出了不同头型长细比列车的流场特征、气动阻力和气动噪声.结果表明,列车的气动总阻力随头型长细比的增大而减小,且头型长细比对列车总气动阻力的影响随运行速度的增加而增强.而头型长细比对气动噪声的影响呈现出较为复杂的影响,并不存在单调的影响关系;综合考虑气动阻力和气动噪声,长细比最大的头型综合性能较优,但差异并不显著,因此在不考虑微气压波等因素的条件下,简单增加车头长细比并不一定能带来明显的气动噪声性能提升.     

基于流固耦合的跨声速压气机叶片静气动弹性分析

采用时域推进的双向流固耦合方法对一级跨声速压气机叶片流场和固体域进行数值模拟,研究跨声速转子叶片静气动弹性变形及其对气动性能的影响,对比分析了100%转速下转子叶片的气动特性和固有频率的变化.结果表明:转子叶片在气动力和离心惯性力共同作用下的弹性变形以扭转变形为主,气动力对叶尖前缘变形量的影响可达总变形量的20%.转子叶片变形后通道流通能力增强,气动特性曲线向大流量方向偏移.     

Delay of finite-span excrescence-induced transition using plasma-based control

Direct numerical simulations are carried out to explore the use of flow control that delays transition generated by excrescence on a plate-like geometry in subsonic flow. Both forward-facing and rearward-facing steps of small roughness heights are considered in the investigation. These are representative of joints and other surface imperfections on wing sections that disrupt laminar flow, thereby increasing skin friction and configuration drag. Unlike previous studies, the steps have a finite lateral extent, such that sharp edges occur in both the spanwise and streamwise directions, and provide a more realistic characterisation of misaligned panels in aerodynamic configurations. The effect of spanwise corners upon transition is examined, and dielectric barrier discharge plasma-based flow control is applied to delay transition and increase the extent of the laminar flow region. Solutions are obtained to the Navier– Stokes equations that were augmented by source terms used to represent body forces imparted by plasma actuators on the fluid. A simple phenomenological model provided these forces resulting from the electric field generated by the plasma. The numerical method is based upon a high-fidelity scheme and an implicit time-marching approach, on an overset mesh system that is used to represent the finite-span steps. Very small-amplitude numerical forcing is employed to generate perturbations, which are amplified by the geometric disturbances and result in transition, similar to the physical situation. Both continuous and pulsed operations of actuators are considered, and the effectiveness of the control is quantified. Transition with the forward-facing step is considerably exacerbated by the presence of a spanwise edge. Plasma control is minimally effective, even with the use of multiple actuators and increased applied force. For the rearward-facing step, transition is substantially delayed by plasma control with small force application.     

汽车外流场数值仿真中的湍流模型分析与应用

采用较为合理的计算流体力学分析技术对汽车高速行驶时其外部气动特 性进行研究. 以带有轮胎、侧后视镜以及天线等突出部件的某轿车外流场模型为研究对象, 在稳态下采用RNS法中Realizable $k$-$\varepsilon$两方程湍流模型结合增强壁 面函数法对不同车速工况下整车外流场进行数值仿真计算. 研究表明：沿车辆X纵 向上所形成压力差是产生气动阻力的主要原因; 随车速的提高, 气动阻力 的增长速度快于气动升力的增长.     

Bifurcation and dynamic behavior analysis of a rotating cantilever plate in subsonic airflow

Turbo-machineries, as key components, have wide applications in civil, aerospace, and mechanical engineering. By calculating natural frequencies and dynamical deformations, we have explained the rationality of the series form for the aerodynamic force of the blade under the subsonic flow in our earlier studies. In this paper, the subsonic aerodynamic force obtained numerically is applied to the low pressure compressor blade with a low constant rotating speed. The blade is established as a pre-twist and presetting cantilever plate with a rectangular section under combined excitations, including the centrifugal force and the aerodynamic force. In view of the first-order shear deformation theory and von-Kármán nonlinear geometric relationship, the nonlinear partial differential dynamical equations for the warping cantilever blade are derived by Hamilton's principle. The second-order ordinary differential equations are acquired by the Galerkin approach. With consideration of 1:3 internal resonance and 1/2 sub-harmonic resonance, the averaged equation is derived by the asymptotic perturbation methodology. Bifurcation diagrams, phase portraits, waveforms, and power spectrums are numerically obtained to analyze the effects of the first harmonic of the aerodynamic force on nonlinear dynamical responses of the structure.     

Nonlinear analysis of orbital motion of a rotor subject to leakage air flow through an interlocking seal

A nonlinear mathematical model for orbital motion of the rotor under the influence of leakage flow through a labyrinth seal was established in the present study. An interlocking seal was chosen for study. The rotor–seal system was modeled as a Jeffcot rotor subject to aerodynamic forcing induced by the leakage flow. Particular attention was placed on the serpentine flow path by spatially separating the aerodynamic force on the rotor surface into two parts, e.g., the seal clearance and the cavity volume. Spatio-temporal variation of the aerodynamic force on the rotor surface in the coverage of the seal clearance and the cavity volume was delineated by using the Muzynska model and perturbation analysis, respectively. The governing equation of rotor dynamics, which was incorporated with the aerodynamic force integrated over all seal clearances and cavity volumes, was solved by using the fourth-order Runge–Kutta method to obtain the orbit of the whirling rotor. Stability of the rotating rotor was inspected using the Liapunov first method. The results convincingly demonstrate that the destabilization speed of the rotor was reduced due to the aerodynamic force induced by the leakage flow through the interlocking seal. The nonlinear analysis method proposed in the present study is readily applied to dynamics of various rotor–seal systems with labyrinth seals.     

航空发动机轴承腔润滑的气液两相均匀流研究

基于轴承腔中润滑油的两相均匀流动模型,采用湍流模式和有限差分数值方法计算轴承腔内三维定常N-S方程,对腔内润滑油的气液两相均匀流动特性进行研究,以获得气液两相均匀流条件下润滑油流场、压力场和速度场在轴承腔内的分布情况,分析转子转速、含气率和润滑油进口速度对润滑油出口压力以及润滑油与壁面之间剪切力的影响,同时对单相流和两相均匀流润滑性能差异进行比较.结果表明,转子转速、含气率和润滑油进口速度对润滑油出口压力和腔内壁面与润滑油间的平均剪切力具有不同影响,而采用2种流动模型计算出的轴承腔润滑油出口压力的差异较大,同时支持了开展航空发动机轴承腔润滑两相流动分析的必要性.