多排叶片内部流动以及叶片排与排气系统相互作用研究

本文采用高分辨率格式和多块多网格方法求解雷诺平均Navier-Stokes方程,数值模拟多排叶片内的三维粘性流动;使用数值激盘模拟叶片排的存在,研究叶片排与非轴对称排气部件之间的相互作用以及复杂的内部流动。文中描述了数值方法,给出了NASA透平导叶和单级透平内部流场的数值结果及其与相应实验结果的对比,也给出了多级透平内部流场的数值结果,以及透平与排气部件之间的耦合流场的结果。     

亚音速轴流压气机转子非轴对称轮毂端壁的数值研究

修改端壁型线是减小二次流损失提高压气机性能的有效方法之一.本文针对某高亚音速压气机转子,首先利用三角函数造型法完成了非轴对称轮毂端壁造型,然后对带非轴对称端壁结构的轴流压气机内部流场进行了详细的数值模拟,数值计算所获得的总性能与试验结果符合较好,该非轴对称轮毂端壁结构的引入能使得压气机的峰值效率提高约0.3285%.详细分析了非轴对称端壁结构对压气机内部流场结构的影响,结果表明:非轴对称轮毂端壁结构的采用能够改善轮毂端壁附近载荷分布,有效地降低叶片通道的二次流流动,从而提高轴流压气机的性能.     

非均匀来流下等压力梯度曲面压缩二维进气道性能

本文选用性能较好的设计点马赫6三楔压缩二维进气道为基准模型,精心设计了设计点马赫6性能与基准模型相当,采用等压力梯度曲面压缩的二维进气道。数值模拟分析了两进气道在非设计点和非均匀来流下的流场和性能。结果表明:非设计点,采用等压力梯度曲面压缩二维进气道,其流量系数、总压恢复和压比均高于三楔压缩二维进气道;在非均匀来流下,采用等压力梯度曲面压缩二维进气道比基准进气道性能要好,低马赫数下起动性能也较好,值得进一步研究。     

柱形容器内部爆炸流场的数值模拟

采用NND差分格式,同时利用点爆炸解作为计算初值,对圆柱形容器内部的二维轴对称非定常流场进行了数值模拟,清楚地反映了内部流场的变化过程,得到了容器壁面上各点的压力-时间关系。对计算结果进行了讨论,与文献中结果作了比较。     

跨音速进气道内外流场的一种镶嵌数值解法

提出了一种计算跨音速进气道内外流场的方法,它把求解小扰动势流方程的混合差分法以及求解欧拉方程的时间相关扫描有限元素法结合起来使用。利用有限差分法先对整个流场做计算。然后,在求解域內的局部地区镶嵌使用扫描有限元素法以改善当地流场的参数。计算了来流马赫数为1.14与1.22的皮托管式和带中心锥式的两种轴对称进气道流场,获得了与实验相一致的结果。     

轴对称流场干涉条纹折射率的模拟计算

提出一种获取流场干涉条纹折射率分布的新方法。该方法首先采用不等间隔的环带分割轴对称流场,使折射率变化大的地方获得的数据点密,然后通过对Abel变换进行离散数值计算来获取流场的折射率分布。通过模拟轴对称流场的实时全息干涉条纹证明了该方法不仅简单易行,而且所获取的折射率分布精度高。     

抗爆容器内爆炸流场数值模拟

 采用计算流体动力学中的二阶精度TVD差分格式和特殊算子分裂法,按轴对称问题,对半球顶圆柱筒密闭式抗爆容器内部爆炸流场进行了数值模拟。计算得到的容器壁面载荷分布与实验结果基本一致。不同时刻爆炸流场压力分布图像清晰地描述了容器壁面的冲击波加载过程。     

基于弯曲激波特征线法的两级压缩内收缩流场设计与分析

进气道是超声速飞行器的关键部件,设计核心是无黏超声速流场的确定,而波系结构又直接决定了流场的性能。考虑到实际应用价值,基于给定激波的超声速流场反设计至关重要。传统单道入射波的流场结构简单,压缩效率不高,且传统特征线法（method of characteristics,MOC）无法获得高阶的气动参数。为了拓展设计思路,首先利用弯曲激波特征线法展示了内收缩超声速流场不同的单元过程,随后基于此法提出了一种已知入射和反射激波的两级压缩内收缩流场的概念及反设计方法。基于此法设计的基准流场与数值模拟结果吻合良好,双入射激波可以提高压缩效率并缩短长度,能够实现波系结构和出口参数的分布可控,在非均匀来流条件下也能得到相应型面。在给定激波的条件下,求解分析了一系列具有中心体的轴对称流场,讨论入射和反射激波激波角分布对流场气动参数和几何参数的影响。弯曲激波特征线法的精确性和有效性使其成为平面/轴对称超声速流场反设计的良好候选。      

叶栅非轴对称端壁成型技术的初步研究

本文根据叶栅内部二次流形成和发展的机理,应用级数函数建立了一种非轴对称端壁成型方法.采用三维时均可压缩N-S求解程序,对采用非轴对称端壁造型的某一后加载亚音速直列叶栅进行了数值研究,分析讨论了非轴对称端壁对叶栅内二次流的影响。计算结果显示:非轴对称端壁可有效地抑制和延迟通道中马蹄涡、通道涡的生成和发展,造型后叶栅内二次流损失减少了1%,效率提高了0.73±0.24%.     

局域能量注入对高超声速进气道流动影响研究

研究了局域能量脉冲注入条件下高超声速进气道流场的扰动情况。数值模拟采用三维雷诺平均N-S方程,分别利用ROE格式和二阶中心格式对对流通量和粘性通量进行离散处理;用高斯-赛德尔隐式格式对方程进行时间推进求解,采用k-ε两方程模型用于湍流的数值模拟。开展了高超风洞平板流场能量注入实验,获取了高速纹影图像,并对实验结果与计算结果进行比较。研究表明,能量注入产生的冲击波能与高超流动产生的斜激波发生强烈干扰,脉冲能量的引入可能引起高超声速进气道流量俘获率产生剧烈震荡,从而导致进气道流场的性能急剧下降。     

A numerical method for the study of nonlinear stability of axisymmetric flows based on the vector potential

We develop in this paper a numerical method to simulate three-dimensional incompressible flows based on a decomposition of the flow into an axisymmetric part, in terms of the stream function and the circulation, and a non-axisymmetric part in terms of a potential vector function. The method is specially suited for the study of nonlinear stability of axially symmetric flows because one may follow neatly the raising of the different non-axisymmetric modes, their nonlinear development, and their nonlinear interaction. The numerical technique combines finite differences on a non-uniform grid in the axial direction, a Chebyshev spectral collocation technique in the radial direction, and a Fourier spectral method in the azimuthal direction for the non-axisymmetric vector potential. As an example to check the efficiency and accuracy of the method we apply it to the flow inside a rotating circular pipe, and compare the resulting travelling waves with previous stability results for this problem, for different values of the Reynolds and the swirl numbers.     

A computational fluid dynamic technique valid at the centerline for non-axisymmetric problems in cylindrical coordinates

A technique is described for the numerical solution of non-axisymmetric flow problems posed in cylindrical coordinates when the z-axis is included in the flowfield. The highlight of the technique is the manner in which the singularities at the centerline are handled. Specifically, the governing flowfield equations at R = 0 are put in a special form by applying L'Hospital's Rule. The required radial derivatives are evaluated using a one-sided, second-order accurate, first-difference. This leads to a smooth, convergent calculation of the flow-field at the centerline. This appears to be the first generally applicable numerical method for avoiding coordinate system singularites in the context of a finite-difference scheme, and could have application to many non-axisymmetric flows. The technique is illustrated by specific results for the time-dependent flowfield inside an internal combustion engine.     

基于喷管节流的轴流转子非轴对称间隙布局研究

实际工作中的压气机转子叶尖间隙往往存在着非轴对称性,对压气机性能及稳定性产生影响.本文以上海交通大学LSRC压气机实验台的第一级转子为研究对象,开展了转子非轴对称间隙布局的数值模拟研究.在数值模拟中,通过在转子出口设置喷管的方式模拟节流过程,分析了喷管结构对压气机性能的影响,并对该方法与常规背压节流方法进行了对比验证....     

旋风分离器上部空间各种二次涡的数值模拟

采用改进的雷诺应力模型对旋风分离器上部环形空间内的强旋湍流流动进行了数值模拟,重点分析了顶板和升气管附近的局部二次涡。数值模拟结果与实验对比表明雷诺应力模型对环形空间内的强旋流动有良好的预报精度。旋风分离器上部环形空间不仅在顶板下存在有二次涡,而且在升气管外壁附近还存在有局部二次涡,局部二次涡的尺度比较小,而且沿周向有变化,呈现非轴对称分布。     

The Radial-Azimut ha1 Inst ability of an Isothermal Magnetized Accretion Disk

The radial-azimuthal instability of an isothermal magnetized accretion disk is examined in this paper. We find that the azimuthal perturbation enhances the instability of the magneto-acoustic and non-axisymmetric modes. The magnetic field induces and enhances the instability of magneto-acoustic modes, but stabilizes the non-axisymmetric modes in the outer disk. The viscous modes are always stable. The instability of magneto-acoustic modes are dominant in this disk.     

High frequency sound emission from moving point multipole sources embedded in arbitrary transversely sheared mean flows

Formulas are derived for the high frequency sound emission from moving point multipole sources embedded in an arbitrary uni-directional transversely sheared mean flow. The results are used to study the sound generated by non-axisymmetric turbulent jets. The effect of the asymmetry in both the mean flow and the source distribution is accounted for by a “circumferential directivity factor”, which is easily calculated from the solution of a second order ordinary differential equation in the general case and from an explicit formula when the mean flow is symmetric but the source location is not. This factor is used to assess the potential of employing asymmetric velocity profiles that redirect the sound upward to reduce the noise radiation below the flight path of a jet aircraft.     

Rotordynamical simulations of a fibre refiner during production

A key component in panel board production is the refiner, whose task is to break raw cellulose wood chips into slender fibres, done by a relative angular motion between stator and rotor. The main problem in predicting the dynamics of these machines is to model the complicated fibre breaking process, since the refining process leads to a three-phase flow (solid wood, water and steam) between the stator and rotor. By modelling the rotor as a rigid body, the process can only contribute by a resulting force and a resulting moment. Through this approach and axial force measurements, it has been shown that the refining process can be treated as a time dependent stiffness matrix and external load. The objective for this paper is to predict and explain dynamical characteristics of fibre refiners during production in such a way that the results can be used already at early stages of the product development process. Two different pressure distribution cases are studied, i.e. one axisymmetric with only radial variations and one non-axisymmetric. It is found that the axisymmetric case only excited forward modes, while the non-axisymmetric case excited all modes. The time dependent stiffness matrix resulted in unstable domains, but also in stable domains with intermittent high amplitudes.     

Thermal stresses around a circular inclusion with functionally graded interphase in a finite matrix

Based on the theory of the complex variable functions, the analysis of non-axisymmetric thermal stresses in a finite matrix containing a circular inclusion with functionally graded interphase is presented by means of the least square boundary collocation technique. The distribution of thermal stress for the functionally graded interphase layer with arbitrary radial material parameters is derived by using the method of piece-wise homogeneous layers when the finite matrix is subjected to uniform heat flow. The effects of matrix size, interphase thickness and compositional gradient on the interfacial thermal stress are discussed in detail. Numerical results show that the magnitude and distribution of interfacial thermal stress in the inclusion and matrix can be designed properly by controlling these parameters.     

Instabilities of Taylor columns in a rotating stratified fluid

We numerically solve for the flow in a differentially rotating spherical shell, with a stable stratification imposed along the rotation axis. The axisymmetric basic state evolves from a Stewartson layer in the unstratified limit to a Taylor column in the strongly stratified limit. For the Taylor columns, we next compute the linear onset of non-axisymmetric instabilities, and show that small (0.1) and large (10) Prandtl numbers yield very different results. For Pr=10, positive and negative differential rotations also yield fundamentally different instabilities.     

稠密颗粒射流倾斜撞击颗粒膜特征

采用高速摄像仪对稠密颗粒射流倾斜撞击形成的类液体颗粒膜特征进行实验研究,考察了颗粒粒径、射流速度以及射流含固率等因素对颗粒膜形态及动态特征的影响.结果表明:随着颗粒粒径增大,稠密颗粒倾斜撞击流由颗粒膜向散射模式转变;随着射流速度增加,气固不稳定增强,射流流量出现脉动,正面与侧面分别表现为颗粒膜的非轴对称振荡和表面波纹结构;颗粒膜非轴对称振荡的振荡频率和振荡幅度随射流速度的增大而增大;表面波纹速度和波长沿传播方向增大,波纹间存在叠加现象.颗粒膜出现非轴对称振荡主要是因为喷嘴出口由气固不稳定性引起的射流流量脉动,射流流量脉动频率与撞击面振荡频率基本相当.