考虑气动热对粘性系数μt影响的压气机流场计算

根据气动热影响叶片壁面附面层粘性系数tμ的理论,把考虑气动热对粘性系数tμ影响的粘性体积力计算方法运用于压气机叶栅三维粘性流场计算。计算时使用有限体积显式时间推进法解算Navier-Stokes方程,用Baldwin-Lomax模型模拟湍流流动。所得结果比不考虑气动热影响的三维计算结果更接近实验结果,能更真实地反映压气机叶栅流场的流动。     

湿空气非平衡凝结对压气机叶栅性能影响的数值研究

跨音速流动条件下湿空气中的水蒸气由于快速膨胀而发生非平衡凝结,凝结潜热与跨音速气流耦合会显著改变流场结构。本文建立了湿空气非平衡凝结流动的数学物理模型,对三种工况下压气机叶栅内湿空气凝结流动进行计算分析。计算结果表明:湿空气压气机叶栅流动中,湿空气中水蒸气有可能发生非平衡凝结从而对叶栅通道内的流动产生强烈影响,改变流场内的激波结构,叶栅内压力系数减小最大幅度由1.38减小到0.76。     

DIRECT NUMERICAL SIMULATION OF TURBINE CASCADE FLOW WITH HEAT TRANSFER EFFECTS

低雷诺数流动对高空动力装置, 特别是涡轮部件的性能产生重要的影响. 本文采用具有7阶精度的差分格式, 通过直接求解二维瞬态可压缩Navier-Stokes方程组, 对雷诺数为241 800 (基于叶片弦长)时的叶片表面带有热传导效应的平面涡轮叶栅流动进行了二维直接数值模拟, 对低雷诺数平面涡轮叶栅流动的非定常流动现象作了初步的探索.数值结果表明:在叶栅通道入口处, 流场的非定常性很弱;在叶栅尾缘处, 具有正负涡量的尾涡交替地从压力面和吸力面上脱落;周期性的涡脱落使得叶栅通道内和尾迹区的总压发生(准)周期的变化, 并且, 尾迹区总压变化主频率是通道内总压变化主频率的2倍;在时均流场中, 叶片表面压力的分布与实验值吻合良好, 表征热传导效应的斯坦顿数除湍流区外与实验值基本吻合;尾迹区速度脉动的2阶统计量与圆柱绕流尾迹区速度脉动2阶统计量具有基本相似的分布特征.     

跨音涡轮叶栅底压的无粘模型

本文提出一个无粘的底部压力模型。证明了在给定反压的情况下,超音出口的涡轮叶栅的叶片尾缘的底压以及叶型损失可由该模型确定。与无粘的流场计算相结合,可用该模型计算二维叶栅的底压。对模型的参数研究表明:具有正曲率的喉道下游叶背型面将有利于减少损失;而出口为音速时流动则最为不利。     

气固耦合振动叶栅非定常流动分析研究

引入结构动力学方程建立了二维N-S/结构振动耦合方程组,采用双时间法建立了气固耦合方程组的非定常数值求解体系,研究了叶栅间的二维非定常粘性流动及叶栅振动特性。对两种叶型分别计算了不同折合振动频率下的流场,振动叶栅位移随时间变化的曲线表明,采用气固耦合得到的叶栅振动频率与非耦合自振频率相比均有所下降;振动位移-时间曲线在不同振动折合频率下有显著差别。在气固耦合情况下叶栅振动规律及其稳定性与非耦合情形差异较大,因此研究叶栅振动稳定性应当考虑气动/结构的耦合。     

快速求解叶栅流动的边界元方法

本文利用边界元方法，通过ｋｒｉｃｈｈｏｆｆ变换将描述叶栅流动的控制方程转换成线性方程。并将广义ｋ－Ｊ条件与边界积分方程联立求解，避免了非线性项和叶片出气角的迭代计算。完成了一种快速求解任意迥转面叶栅流场的计算程序，实用表明与其它数值方法及实验结果符合较好，具有快带、简明、实用的特点。     

平面跨音速叶栅正、反混合问题的一种高效率解法

本文在文献[1]的基础上提出了平面跨音速叶栅正、反混合问题的一种高效率解法,它保持了文献[1]中方法的优点,避免了打靶,从而达到了扩大适用范围,减少了计算时间。 文中导出了以Von Mises坐标为自变量的流线控制方程,简单而有效地处理了速度的双值问题,作为考核,计算了两个跨音速平面叶栅和一个拉伐尔喷管的流场,结果令人满意,本方法具有精度高、收敛快的特点,即使对于624所跨音涡轮动叶中部叶栅中比较复杂的流场,也只需迭代50次,费时不到1分钟(DPS-8机),即可获得满意的结果。     

二维扩压叶栅非定常分离流控制途径探索

二维扩压叶栅非定常黏性数值模拟结果表明,在一定攻角范围内,叶片前缘点附近的周期性吹吸气激励能有效控制混乱的非定常分离流．详细研究了非定常激励频率、幅值、位置对流场的影响．满足一定条件的非定常激励能够使流动由无序变为有序,时均气动性能提高。     

进口受控非定常来流同振荡叶栅相互作用的Euler方程数值解

将 Dcnton 的四角点有限面积格式用于求解变换坐标系下的非定常 Euler 方程组,在振荡叶片附近局部子域构造了一种按等差级数分布的动态网格,从而节省了计算时间,对于本方法的正确性进行了初步检验并与相应的实验进行了对比,在进口总压简谐振荡的束流条件下,计算了零安装角平板叶栅和53°安装角双凸叶栅扭转振荡的非定常流场,结果表明,进口受控扰动同振荡叶栅之间的相互作用在有压力梯度的情况下可以定性地改变叶栅的气动阻尼。     

纳米示踪平面激光散射技术在激波复杂流场测量中的应用

在激波以及激波边界层相互作用这类含激波的复杂流场中,流场结构具有明显的三维特征.研究这类流场,采用纹影、阴影和干涉等传统流动显示技术空间分辨率较低,难以分辨流场的三维特性.基于纳米示踪的平面激光散射技术(nano-tracer planar laser scattering,NPLS),是作者近年来开发的一种新的研究超声速流场的测试与显示技术,可对超声速复杂三维流场进行高时空分辨率流动显示与测量.NPLS技术的特点使其成为测量激波复杂流场的有力手段.近年来,作者以NPLS技术为主要手段,对航空航天领域典型的激波复杂流场进行了试验研究,包括超声速弹头绕流、超声速混合层、超声速边界层,以及激波边界层相互作用流场,显示出NPLS技术在激波复杂流场精细测试与流动显示中优势.本文简要介绍NPLS技术在激波复杂流场测量中应用的研究进展.      

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.     

Turbulence measurements in a transonic two-passage turbine cascade

This paper presents detailed turbulence measurements in a two-dimensional, transonic, double passage turbine cascade. Particle image velocimetry was used to obtain mean velocity and turbulence measurements all around a single turbine blade within about 2 mm of the blade and wall surfaces. The passage walls were designed using an optimization procedure so that the blade surface pressure distribution matches that of the blade in an infinite cascade. The resulting experimental model captures much of the complexity of a real turbine stage (including high streamline curvature, strong accelerations, and shocks) in a passage with a continuous wall shape, allowing for high measurement resolution and well controlled boundary conditions for comparison to CFD. The measurements show that in the inviscid regions of the passage the absolute level of the turbulent fluctuations does not change significantly as the flow accelerates, while the local turbulence intensity drops rapidly as the flow accelerates. These results provide a benchmark data set that can be used to improve turbulence models.     

Computation of cascade flutter by uncoupled and coupled methods

A computational method for flutter prediction of turbomachinery cascades is presented. The flow through multiple blade passages is calculated using a time-domain approach with coupled aerodynamic and structural models. The unsteady Euler/Navier-Stokes equations are solved in quasi-three-dimensions using a second-order implicit scheme with dual time-stepping and a multigrid method. A structural model for the blades with bending and torsion degrees of freedom is integrated in time together with the flow field. Information between structural and aerodynamic models is exchanged until convergence in each real-time step. Computational results for a cascade are presented and compared with those obtained by the conventional energy method and with experimental and numerical data by other authors. Significant differences are found between the coupled and uncoupled methods at low mass ratios. A transonic test case with strong nonlinear phenomena is investigated with the fluid-structure coupled method. Results for inviscid flow are compared with results of Navier-Stokes computations.     

Progresses in application of computational fluid dynamic methods to large scale wind turbine aerodynamics

The computational fluid dynamics (CFD) methods are applied to aerodynamic problems for large scale wind turbines. The progresses including the aerodynamic analyses of wind turbine profiles, numerical flow simulation of wind turbine blades, evaluation of aerodynamic performance, and multi-objective blade optimization are discussed. Based on the CFD methods, significant improvements are obtained to predict two/three dimensional aerodynamic characteristics of wind turbine airfoils and blades, and the vortical structure in their wake flows is accurately captured. Combining with a multi-objective genetic algorithm, a 1.5 MW NH-1500 optimized blade is designed with high efficiency in wind energy conversion.     

A finite element solution of unsteady two-dimensional flow in cascades

A theory is presented for unsteady two-dimensional potential transonic flow in cascades of compressor and turbine blades using a mesh of triangular finite elements. The theory leads to a computer program, FINSUP, which is fast and has moderate storage requirements, so that it can be run on a personal computer. Comparisons with other theories in special cases show that the program is accurate in subsonic flow, and that in supersonic flow, although the wave effects are smeared by the numerical process, the results for overall blade force and moment have acceptable accuracy. The program is useful for engineering assessment of unstalled flutter of actual compressor and turbine blades.     

Research status and trend of wind turbine aerodynamic noise

The main components of the wind turbine aerodynamic noise are introduced. A detailed review is given on the theoretical prediction, experimental measurement, and numerical simulation methods of wind turbine noise, with specific attention to applications. Furthermore, suppression techniques of wind turbine aerodynamic noise are discussed. The perspective of future research on the wind turbine aerodynamic noise is presented.     

3D pressure imaging of an aircraft propeller blade-tip flow by phase-locked stereoscopic PIV

The flow field at the tip region of a scaled DHC Beaver aircraft propeller, running at transonic speed, has been investigated by means of a multi-plane stereoscopic particle image velocimetry setup. Velocity fields, phase-locked with the blade rotational motion, are acquired across several planes perpendicular to the blade axis and merged to form a 3D measurement volume. Transonic conditions have been reached at the tip region, with a revolution frequency of 19,800 rpm and a relative free-stream Mach number of 0.73 at the tip. The pressure field and the surface pressure distribution are inferred from the 3D velocity data through integration of the momentum Navier-Stokes equation in differential form, allowing for the simultaneous flow visualization and the aerodynamic loads computation, with respect to a reference frame moving with the blade. The momentum and pressure data are further integrated by means of a contour-approach to yield the aerodynamic sectional force components as well as the blade torsional moment. A steady Reynolds averaged Navier-Stokes numerical simulation of the entire propeller model has been used for comparison to the measurement data.     

A check on the energy method of predicting blade transonic stall flutter

An improved structural dynamic model of an oscillating blade in two degrees of freedom is combined with an unsteady aerodynamic model for the transonic flow about a cascade with separation, which results in a coupled system. The system is solved in an iterative way between the two models. As a check on the current energy methods, the stall flutter boundaries for two real rotors are predicted by using the present method and the results are compared with the experiments and those predicted by using an energy method.     

A numerical modelling of stator–rotor interaction in a turbine stage with oscillating blades

In real flows unsteady phenomena connected with the circumferential non-uniformity of the main flow and those caused by oscillations of blades are observed only jointly. An understanding of the physics of the mutual interaction between gas flow and oscillating blades and the development of predictive capabilities are essential for improved overall efficiency, durability and reliability. In the study presented, the algorithm proposed involves the coupled solution of 3D unsteady flow through a turbine stage and the dynamics problem for rotor-blade motion by the action of aerodynamic forces, without separating the outer and inner flow fluctuations. The partially integrated method involves the solution of the fluid and structural equations separately, but information is exchanged at each time step, so that solution from one domain is used as a boundary condition for the other domain. 3-D transonic gas flow through the stator and rotor blades in relative motion with periodicity on the whole annulus is described by the unsteady Euler conservation equations, which are integrated using the explicit monotonous finite volume difference scheme of Godunov–Kolgan. The structural analysis uses the modal approach and a 3-D finite element model of a blade. The blade motion is assumed to be constituted as a linear combination of the first natural modes of blade oscillations, with the modal coefficients depending on time. A calculation has been done for the last stage of the steam turbine, under design and off-design regimes. The numerical results for unsteady aerodynamic forces due to stator–rotor interaction are compared with results obtained while taking into account blade oscillations. The mutual influence of both outer flow non-uniformity and blade oscillations has been investigated. It is shown that the amplitude-frequency spectrum of blade oscillations contains the high-frequency harmonics, corresponding to the rotor moving past one stator blade pitch, and low-frequency harmonics caused by blade oscillations and flow non-uniformity downstream from the blade row; moreover, the spectrum involves the harmonics which are not multiples of the rotation frequency.     

Thermochromic liquid crystal temperature measurements through a borescope imaging system

Thermochromic liquid crystals (TLCs) have proven to be a valuable tool for the collection of full-field, high-resolution heat transfer data. This paper presents an extension of previously developed calibration techniques to a simplified transonic linear cascade for a highly cambered turbine blade geometry. This required the introduction of miniature periscopes to image the measurement surfaces. The procedures and equipment used to ensure high-accuracy wide-band TLC measurements are presented. These included a geometry-matched calibration device, mechanisms to accurately position the borescope imaging optics, an algorithm to automatically divide the imaging region into a large number of calibration subregions (termed as cells), and algorithms to correct for geometric and optical image distortions. The cell calibration approach is shown to halve calibration times and dramatically reduce memory requirements when compared to a pixel-by-pixel calibration. The results of an extensive validation study are presented. This work was funded by the General Electric Aircraft Engines Strategic Alliance Program.