不可压粘性流动N—S耦合方程的有限元解法—1理论

本文对不可压粘性流动非定常N－S方程组在耦合条件下应用有限元方法直接求解，并对在高雷诺数下如何提高计算的精度，稳定性以及收敛速度等方面进行了讨论，从而建立起不可压粘性流动N－S耦合方程的有限元解法。     

三维不可压非定常流动的数值计算

采用多重网格法对三维不可压非定常粘性流动进行了数值实验，控制方程在非结构网格上用有限体积法进行离散，本文计算了雷诺数为100情况下的圆柱绕流问题，计算结果与实验结果和国外的计算结果基本吻合，说明了该方法的准确性和有效性。     

基于无网格伽辽金法的非线性流动数值模拟

基于无网格伽辽金方法针对典型的非线性流动问题进行数值研究,对Navier-Stokes方程使用Galerkin方法离散,方程中的惯性项分别采取速度项提出法和直接推导法进行离散,使用罚函数法施加压力和速度边界条件,建立了基于EFG法的二维N-S方程的离散形式。针对定常非线性流动问题,对矩形域上下平板相向运动流动进行数值模拟,结果表明该方法求解精度比较高,计算误差不超过3.66%;针对非定常非线性流动问题,采取θ加权法对N-S方程中的时间项进行离散,建立了EFG法非定常求解方程。以方柱绕流问题为例,证明了文中所建立的非定常算法的精度及收敛性。     

激波绕尖劈障碍物运动粘性流场的数值模拟研究

本文以数值方法研究了运动激波绕射的非定常粘性流的发展过程．计算中采用二阶ＴＶＤ差分格式求解二维非定常薄层Ｎａｖｉｏｒ－Ｓｔｏｋｅｓ方程，得到了清晰的流场结构图谱，分析了产生局部粘性分离的现象．研究结果表明，本文的方法可以很好地描述激波绕射的复杂流动，对流场间断有较高的捕获能力，同时表明在激波障碍物干扰的绕射场研究中局部粘性效应作用是不可忽视的重要因素     

旋翼跨声速流动气动噪声的一种高效算法

采用Euler/Kirchhoff方法,计算了直升机旋翼悬停流场的远场噪声。在采用CFD方法求解非定常旋翼悬停流动的Euler方程的基础上,采用Kirchhoff公式计算了直升机悬停流动的远场噪声。中对Kirchhoff面的选取、源点延迟时刻的确定方法进行了研究,并提出了一种由Euler方程解确定Kirchhoff面上物理参数及其空间法向导数的高效三维线性插值方法。对UH－1H直升机旋翼跨声悬停流动的远场噪声进行了定量计算,计算结果与实验值相比较,符合较好,验证了本方法的正确性。     

非牛顿钻井流体流动计算机智能解析方法

钻井液体在环形钻杆空间中的运动,可归结为幂律流体管内流动和螺旋流动。由于幂律流体的本构方程,在运动方程中产生速度梯度的非线性项,求解过程比较复杂。因此应用计算机符号运算、改进的Kantorovich变分法和幂律流体模型相结合,并采用局部线性化的方法,提出了解决运动方程中出现的非线性问题的方法,即计算智能解析方法应用于非线性问题,研究了幂律流体管内非定常流动,研究方法及其结果可以推广到幂律流体螺旋流动情形。     

抽水蓄能电站水力过渡过程的可压缩管流基本方程和计算方法

给出了抽水蓄能电站的水力过渡过程中弹性管道内可压缩非定常流动的基本方程组，讨论了稳定工况时弹性管道内可压缩定常流动的数值计算的方程和方法，并利用特征线方法得到了水力过渡过程中弹性管道内可压缩非定常流动的特征方程和计算公式。     

结合定常CFD技术的当地流活塞理论

结合定常CFD技术和超音速非定常气动力工程计算方法——活塞理论，发展了一种基于超音速、高超音速定常流场求解非定常气动力的当地流活塞理论。适用于超音速、高超音速飞机颤振中的小振幅非定常气动力计算。通过与非定常Euler方程求解结果的比较，发现在马赫数不太高或大迎角的超音速流动中，其精度比原始活塞理论高得多，也能够计算超音速、高超音速下大钝头和考虑机身干扰的复杂外形非定常气动力，扩大了活塞理论的应用范围。与非定常Euler方程或N-S方程的数值求解相比，计算效率很高。     

粘性不可压缩流体平面流动的有限差分解法

本文使用上风差分格式求解了二维非定常粘性不可压缩流体非守恒的Navier-Stokes方程,讨论了相应的差分方程的精度、收敛性和人工粘性.发现当雷诺数增大时,使用非守恒型方程比守恒型方程易于收敛、更为适宜.本文还对壁面拐角上点的涡量计算提出了一种新的方法.以曲折流道内粘性流体的流动为例进行了数值计算,结果表明与实验结果具有较好的一致性.     

轴流压气机稳定性预估的改进模型

推导并建立了进口非定常扰动条件下多轴流压缩系统动态响应及其稳定性分析的理论模型，基于逐级特性，又建立了该模型轴力和轴功的准定常计算方法，导出了基于特征线理论的流动方程数值求解方法，应用本模型对两个中等负荷的多级轴流压缩系统进行了数值分析，数值结果与实验结果的一致性较好，表明了所建立的理论模型是可行的。     

中国采用近似边界条件的振荡翼型欧拉方程数值解

This paper presents an efficient numerical method for solving the unsteady Euler equations on stationary Cartesian grids.Wall boundary conditions are implemented on nonmoving mean wall positions by assuming the airfoil being thin and undergoing small deformation,but the mean angle of attack of the body can still be large and we use the full nonlinear Euler equation in the field for accurate resolution of shock waves and vorticity.The method does not require the generation of moving body-fitted grids and thus can be easily deployed in any fluidstructure interaction problem involving relatively small deformation of a thin body.We use the first-order wall boundary conditions in solving the full Euler equation.Unsteady transonic flow is calculated about an oscillating NACA 0012 airfoil at free stream Mach number M∞=0. 755, mean angle of attack αm=0. 016,amplitude of pitching oscillation αo=2.51,reduced frequency k=0.0814.The computed results,including surface pressure distribution,instantaneous lift and moment coefficients are compared with known experimental data.It is shown that the first-order boundary conditions are satisfactory for airfoils of typical thicknesses with small deformation for unsteady calculations.     

非定常条件下大迎角机动控制

针对推力矢量飞机在非定常气动影响下的机动控制问题,提出一种大迎角俯仰机动的控制器设计方案.采用干扰观测器方法对机动过程中的非定常俯仰力和力矩进行估计,并在控制端进行俯仰力矩补偿以及适当的升力补偿,建立了统一参数下飞机线性参变(LPV)模型和外部干扰LPV模型,并基于LPV模型设计了标称控制器和干扰观测器.从大迎角机动仿真中可以看出,控制系统能够控制迎角较好地跟踪输入指令,同时对机动过程中存在的非定常干扰能进行有效地抑制.仿真结果表明利用干扰观测器的方法较其他方法具有更好的控制性能.     

应用Realizable k-ε湍流模型的振荡水翼绕流数值模拟研究

采用计算流体力学软件Fluent提供的Realizable k-ε湍流模型计算了振荡水翼的绕流问题,利用有限体积法求解雷诺平均N-S方程,空间离散应用二阶迎风格式,速度—压力耦合格式为SIMPLEC格式;为了验证该数值格式及湍流模型,计算了文献中的算例并做了对比;考察了不同参数对振荡水翼周围流场及受力特征的影响,研究表明在一定水翼攻角条件下,水翼振幅及振荡频率均对振荡水翼的涡结构产生发展及其受力特征具有明显的影响.     

Study of control effects of vortex generators on a supercritical wing

Flows around vortex generators (VGs), which serve as one of the important flow control methods, are investigated by solving Reynolds-averaged Navier-Stokes (RANS) equations. The influences on the main flow of VGs are intended to explore. Firstly, the flow around a single VG on a flat plane is computed to validate the schemes and to acquire basic knowledge of this kind of flow. Secondly, transonic flow past a standard model, named by ONERA-M6 wing, is predicted to investigate the flow features of shockwave/boundary-layer interactions (SWBLI). Thirdly, the effects of a row of VGs mounted about 25% local chord on a supercritical wing are analyzed in transonic condition with strong SWBLI. Lastly, VGs are mounted more upwind (about 3.5% local chord) to explore the effects at low speed and high incidence condition. The numerical results show that seven VGs can effectively suppress the separations behind the strong SWBLI and decrease spanwise flow and wing-tip vortex in transonic condition. VGs also can decrease the large scope of separation over the wing at low speed with high angle of attack.     

翼型厚度和弯度对前飞扑翼气动性能的影响

扑翼飞行器是一种模仿鸟类和昆虫飞行方式的新型飞行器.翼型参数设计对提高扑翼飞行器性能至关重要,为研究扑翼翼型厚度和翼型弯度对前飞扑翼气动性能的影响,基于自然界中飞行生物的实验观测结果建立了前飞扑翼气动特性计算模型,针对不同厚度和弯度的NACA系列标准翼型,采用计算流体力学方法求解二维不可压缩非定常Navier-Stokes方程,基于有限体积法并结合动态网格技术,分析了低雷诺数条件下对应不同来流速度的刚性前飞扑翼气动力、能耗、气动效率以及周围流场结构随翼型厚度和弯度的变化规律.结果表明,不同来流速度条件下扑翼推力和能耗均随翼型厚度的增大而逐渐减小,随着翼型厚度的增大,扑翼推进效率最大降幅达15.9%;翼型厚度的增加,降低了前缘涡强度并延迟了前缘涡的脱落.翼型弯度可以改变翼型的有效气动攻角,翼型弯度的增加可以显著提高翼型升力和升举效率,并促使尾流中心线向右下方倾斜;正向弯度扑翼在下扑行程能产生更大的升力,而负向弯度扑翼则在上挥行程中产生了更大的推力.     

振荡翼捕获能量系统的流体动力性能

采用Fluent求解绕二维振荡翼层流流场的非定常、不可压缩Navier-Stokes方程,将域动网格策略用在滑移交界面内流体域,使之与翼一起运动,该方法可保证核心区域网格质量。研究了Re=1100、θ0=76.33°、y0=5、k=0.88时,俯仰轴位置对NACA0015振荡翼气动特性和能量捕获性能的影响,以及升沉--俯仰相位差和俯仰轴位置对系统的耦合影响。结果表明,俯仰轴位置会影响振荡翼的升力特性、俯仰力矩特性及能量捕获性能,当系统因俯仰轴位置偏离平均压力中心而造成能量捕获性能下降时,改变升沉--俯仰相位差可改善系统的能量捕获性能。     

A wake bending unsteady dynamic inflow model of tiltrotor in conversion flight of tiltrotor aircraft

The aerodynamics, dynamic responses and aeroelasticity of tiltrotor aircraft in the tilting of rotor i.e. in conversion flight are extraordinarily complicated. The traditional quasi-steady assumption model can not reflect the unsteady aerodynamic problems in the tilting of rotor. The CFD method based on the vortex theory can get better results, but it consumes a lot of computing resources. In this paper, a wake bending dynamic inflow model of tilting rotor was established firstly based on the Peters-He dynamic inflow model used in helicopter. Then combining with the ONERA unsteady aerodynamic model, a wake bending unsteady dynamic inflow model of tilting rotor in conversion flight of tiltrotor aircraft was established. The wake bending unsteady dynamic inflow model of tilting rotor was verified by using the experimental data of an isolated rotor model in large angle pitching up maneuver and was used to calculate the dynamic responses of tilting rotor in conversion flight of a tiltrotor aircraft model. The calculated results were analyzed to be physically reasonable.     

Numerical investigation of an advanced aircraft model during pitching motion at high incidence

An unsteady Reynolds averaged Navier–Stokes(URANS) method combined with a rigid dynamic mesh technique was developed to simulate unsteady flows around complex configurations during pitching motion. First, a test case with the NACA0012 airfoil was selected to validate the numerical methods and our in-house codes. Then, we evaluated the unsteady flows around an advanced aircraft model during harmonic pitching motion at high incidence. The effects of pitching motion on the hysteresis of aerodynamic force, the evolution of the leading-edge vortex, and the distribution of pressure on the model's surface were analyzed in detail. The roles of several significant parameters such as the reduced frequency and pitching amplitude were revealed. Several conclusions were found: pitching motion would delay the initiation of the leading-edge vortex, strengthen the vorticity, postpone the occurrence of vortex breakdown, and weaken the massively separated flows, thus causing additional aerodynamic force. Two categories of critical reduced frequency have been found, which divide the influence of reduced frequency on aerodynamic force into three stages, called the linear increasing range, slowly increasing range, and constant range. The first-order phase lag between the aerodynamic force and the incidence is a constant that is independent of the amplitude when the reduced frequency is sufficiently high. A scaled maximum value of C_L is proposed; it depends only on the reduced frequency(instead of the amplitude), and increases linearly when the reduced frequency is sufficiently low.     

叶栅流场尾迹中非定常涡系的数值模拟

叶栅通道内包含复杂非定常流动特征的涡系结构，二维直叶栅的尾迹涡系中粘性、尺寸效应十分明显，进行数值模拟时计算量较大，因此时分离涡产生与脱落过程的准确、清晰的捕捉要求有更高效率的数值解法。应用隐式格式、全场统一时间步长和Baldwin—Lomax紊流模型求解二维Navier—Stokes方程，时二维直叶栅流场非定常涡系进行了数值模拟分析，在大攻角、不同进口马赫数的2种工况下，通过对比分析不同时刻叶栅流场的熵和压力瞬态图，捕捉到分离涡产生与脱落过程，并合理地反映了紊流流动特征。通过计算结果看出，所采用的非定常粘性流动数值模拟方法有效，计算效率较高，能够较好地捕捉复杂的尾迹非定常涡系，较为清晰地反映叶栅流场涡系的形成、发展和消失过程，为进一步研究孤立转子和多叶排环境下的非定常流动效应提供了初步的基础。     

双水翼耦合振荡捕获潮流能系统2维数值模拟

提出了一种双水翼耦合振荡捕获潮流能的系统,该系统在河床及浅海具有良好的适应性。建立了相应系统的数学模型及网格模型,将域动网格策略用在滑移交界面内部流体域,利用Fluent求解绕2维双振荡翼流动的数值模型。研究了折算频率、俯仰振幅及雷诺数对NACA0015型双水翼水动力特性及捕获潮流能性能的影响,以及在不同运动参数下水翼的升阻力、俯仰力矩、功率系数的变化规律。结果表明,振荡水翼的折算频率、俯仰振幅和雷诺数会影响水翼边界层的分离及周围漩涡的产生和脱落,继而影响振荡翼的升阻力特性和俯仰力矩特性。折算频率与俯仰振幅对振荡水翼系统的捕能效果有较大影响。当水翼的振荡频率为0.28、俯仰振幅为75°、雷诺数为5×10⁵时双水翼耦合振荡捕获潮流能系统的水动力和捕能性能较好,捕能效率可达40%。