Transverse shear behavior on the aeroelastic stability of composite rotor blades

The aeroelastic stability of a composite hingeless rotor blade, idealized as a laminated thin-walled box-beam, has been investigated using a finite element formulation based on Hamilton’s principle. First-order shear deformation theory and quasi-steady aerodynamic theory have been employed for the analysis. In order to consider the sectional distribution of shear stresses for the box-beam in an effective manner, Timoshenko beam assumption has been made and the formula of shear correction factor of isotropic box section has been used to describe the motion. Three dimensional stress analysis of composite box-beam by using a detailed finite element analysis program has been performed to identify the distribution of shear of the box section and to correlate the results of shear correction factor of isotropic material with that of composite material. Free vibration tests of rotating composite box-beams have showed fairly good agreement between the current results and the experimental data. Transverse shear behavior on the aeroelastic stability has been studied for a specific box-beam configuration. The results displayed in this article have revealed that the transverse shear coupling has a significant role on the flutter boundary of the rotor, especially in case of anti-symmetric configuration.     

Determination of the principal directions of composite helicopter rotor blades with arbitrary cross sections

Modern helicopter rotor blades with non-homogeneous cross sections, composed of anisotropic material, require highly sophisticated structural analysis because of various cross sectional geometry and material properties. They may be subjected by the combined axial, bending, and torsional loading, and the dynamic and static behaviors of rotor blades are seriously influenced by the structural coupling under rotating condition. To simplify the analysis procedure using one dimensional beam model, it is necessary to determine the principal coordinate of the rotor blade. In this study, a method for the determination of the principal coordinate including elastic and shear centers is presented, based upon continuum mechanics. The scheme is verified by comparing the results with confirmed experimental results.     

The coupled vibration in a rotating multi-disk rotor system with grouped blades

The influence on coupling vibrations among shaft-torsion, blade-bending and lacing wire coupling vibrations of a multi-disk rotor system with grouped blades was investigated analytically. The natural frequencies and the mode shapes of the system were solved for one-to four-disk cases as examples. First, numerical results showed how the natural frequencies varied by lacing wires and disks in a multidisk rotor system. The diagrams of the coupling mode shapes were drawn. From the results, the inter-blade (BB) modes, the shaft-blade (SB) modes and the lacing wires-blade (LB) modes change rules were given in this paper. Numerical calculation also revealed three interesting results that the natural frequencies were affected by lacing wire constant, lacing wire location and the disk distance. In the rotation effects, the multi-disk has drawn three important phenomena. The times of instability will due to the number of disk, the more disk rotor causes instability earlier than the less disk case and the lacing wires could not affect the system instability.     

Optimization model for rotor blades of horizontal axis wind turbines

This paper presents an optimization model for rotor blades of horizontal axis wind turbines. The model refers to the wind speed distribution function on the specific wind site, with an objective to satisfy the maximum annual energy output. To speed up the search process and guarantee a global optimal result, the extended compact genetic algorithm (ECGA) is used to carry out the search process. Compared with the simple genetic algorithm, ECGA runs much faster and can get more accurate results with a much smaller population size and fewer function evaluations. Using the developed optimization program, blades of a 1.3 MW stall-regulated wind turbine are designed. Compared with the existing blades, the designed blades have obviously better aerodynamic performance. __________ Translated from Journal of Shantou University (Natural Science), 2006, 21(1): 44–49 [译自: 汕头大学学报 (自然科学版)]     

复合材料飞轮转子设计

考虑到转子与驱动机构的连接,给出了一种金属轮毂加复合材料轮缘结构飞轮转子的设计方法。分析了转子材料、结构、连接及制作工艺等因素对储能密度的影响,分析结果表明:复合材料轮缘内外径比值α是影响其储能密度的关键,根据轮缘材料选取合理值,对轮毂进行优化可以进一步提高转子的储能密度。分析中所用复合材料及胶粘剂力学常数的准确性是影响仿真结果的主要因素,通过实验对其理论值进行修正可以进一步提高仿真结果的准确性。对实际应用中一个具体飞轮转子进行了设计并制作出了转子,在20 000 r/min转速范围内进行了旋转应力实验,仿真分析与实验结果取得了较好的一致性,证明了本文设计方法的正确性。     

Design of composite flywheel rotor

A design method for a flywheel rotor composed of a composite rim and a metal hub is proposed by studying the connection between the rotor and the driving machine. The influence of some factors such as the rotor material, configuration, connection, and fracture techniques on energy density is analyzed. The results show that the ratio of the inner radius to outer radius of the rim is the key factor, and is determined by the rim material. Optimizing the hub can further efficiently improve energy density. The composite flywheel rotor is produced and its rotation stress has been tested at the speed of 20 krpm. The emulation results are consistent with testing results, which proves that the introduced design method is useful. __________ Translated from Optics and Precision Engineering, 2007, 15(6): 852–857 [译自: 光学精密工程]     

Vibration of higher-order-shearable pretwisted rotating composite blades

The free and forced vibration of a rotating, pretwisted blade modeled as a laminated composite, hollow (single celled), uniform box-beam is studied. The structural model includes transverse shear flexibility, restrained warping, and centrifugal and Coriolis effects. A key element of this model is its ability to satisfy the zero shear–traction requirement on the external bounding surfaces. The governing system possesses complicated and eigenvalue-dependent natural boundary conditions. Hence an extended Galerkin method using admissible functions is employed. Free-vibration results obtained for the present higher-order shearable model are compared with those of the existing first-order shearable and the non-shearable models. For the data considered, the present theory provides conservative predictions. This suggests that through-the-thickness variations of transverse shear strains are significant and should be considered when pursuing non-resonant designs. The effect of pretwist, while marginal for the lowest eigenfrequency, is substantial for the higher ones especially for lower rotation speeds and larger ply angles. A combination of softening and stiffening effects are also possible for the same eigenfrequency when pretwist is varied. Tailoring studies using the present model show an enhancement of eigenfrequency characteristics and also reveal the potential for passive mitigation of forced response.     

On the occurrence of self-synchronization of autooscillations of turbocompressor rotor blades

The self-synchronization of the spectral parameters of turbocompressor blades is studied, as well as its connection with nonlinear resonance during fluttering. The evolution of blade oscillations during the growth of turbocompressor rotor revolutions is characterized by the concurrence of torsional and flexural oscillation modes, a change of the base frequencies of the rotor blades, and the appearance of a common synchronization frequency in their spectrum. Fluttering comes with a loss of stability of the blades’ oscillation mode at the synchronization frequency. Estimates are obtained on the basis of the spectral analysis of the recording of transient processes of axial and centrifugal turbocompressors. The parameters of the blade oscillation modes and their power have been identified by means of the construction of models of the processes on the basis of the technology of Proni spectral analysis.     

低压压气机转子叶片振动特性计算与分析

利用优化的八节点超参数单元法对某型发动机低压压气机转子叶片的振动特性进行了计算分析,并结合转子结构和发动机工作状态深入分析了可能发生的危险共振情况,发现第二级转子叶片抗振性能不好,为转子叶片的在线监测与故障预报提供了重要依据。     

Resonance bifurcation during self-oscillations of the rotor blades of a turbocompressor

Bifurcation of the trajectory of the resonance for the blades of an axial rotor, which leads to flutter of the blade cascade, is investigated. For this purpose, a spectral analysis of readouts of the transient period of blade oscillation is performed. As opposed to the resonance with a constant phase difference and excited oscillations of the blades, the shift of the phase of collective synchronous oscillations of the blades during flutter depends on their number and the form of the diametral mode of the blade cascade. The flutter of the blades is associated with one diametral mode of pressure pulsations of the air flow.     

基于立体视觉的旋翼共锥度动态测量系统精度分析

为了提高基于立体视觉的直升机旋翼共锥度动态测量系统的精度和可操作性,全面分析了其测量误差。首先,介绍了测量系统模型及误差来源;其次,分析了双目立体视觉静态三维测量的误差;再次,针对旋翼共锥度的多目标动态测量特点,分析了系统安装误差对共锥度解算精度的影响;最后,利用原理样机进行了6 058次静态测量重复实验,通过统计分析可知静态测量误差小于1.4 mm。对动态测量误差进行了仿真实验分析,给出了各参数对精度影响的量化结果,为实际共锥度测量的误差控制提供了理论依据。在标记点安装精度小于10 mm的情况下,动态测量误差小于3.5 mm,合成产生的总测量误差小于4.9 mm,能满足旋翼共锥度动态测量精度要求。     

Non-linear stability analysis of a rigid rotor on tilting pad journal bearings

This paper describes a method for conducting non-linear stability analysis on the synchronous motion of the journal axis and tilting pads in a system consisting of a symmetrical rigid rotor mounted on tilting pad journal bearings with two pads. The method makes it possible to obtain the limit curves separating the stable operating condition, characterized by the above motion, from the so-called unstable one characterized by motions of the pads and journal with a fundamental frequency equal to one half the rotor angular speed. A variational method is used to carry out stability analysis on the synchronous solution of the non-linear equations of motion, obtained in an approximated analytical form using a particularized harmonic balance method.     

A simple mixed-based approach for thin-walled composite blades with two-cell sections

In this work, a mixed beam approach that combines both the stiffness and the flexibility methods has been performed to analyze the coupled composite blades with closed, two-cell cross-sections. The Reissner’s semi-complementary energy functional is used to derive the beam force-displacement relations. Only the membrane part of the shell wall is taken into account to make the analysis simple and also to deliver a clear picture of the mixed method. All the crosssection stiffness coefficients as well as the distribution of shear across the section are evaluated in a closed-form through the beam formulation. The theory is validated against experimental test data, detailed finite element analysis results, and other analytical results for coupled composite blades with a two-cell airfoil section. Despite the simple kinematic model adopted in the theory, an accuracy comparable to that of two-dimensional finite element analysis has been obtained for cases considered in this study.     

Aerodynamic shape optimization of wind turbine rotor blades considering aeroelastic deformation effect

An aerodynamic shape optimization framework of two modules is developed for improving the aerodynamic performance of wind turbine rotor blades. The first module conducts CFD-based aeroelastic analysis for the complete blade configuration to evaluate the turbine performance and to extract the sectional flow conditions at selected blade sections. The second module performs 2-D shape optimization of blade sections to maximize the lift-to-drag ratio under given sectional flow conditions. When the optimization is completed for all selected blade sections, the performance and sectional flow characteristics of the new blade reconfigured from the optimized sections are evaluated again by the CFD-based aeroelastic analysis. The above procedure is repeated until the solution converges satisfactorily. Applications were made for the NREL phase VI and the NREL 5MW reference wind turbines. The results showed that the optimization framework can be effectively utilized in enhancing the aerodynamic performance of wind turbine blades.

     

复合材料加筋壁板稳定性影响分析

分别运用特征值法和弧长法开展T字型加筋壁板稳定性及其影响因素分析.分析表明:特征值法和弧长法所得结果相近,弧长法分析结果较为安全,特征值法可作为观察模型屈曲位置及模态图的分析方法.加筋壁板屈曲载荷随筋条间距的变化呈抛物线状,较平均的筋条布置有利于加筋壁板的整体稳定性.加筋壁板屈曲载荷随凸缘宽度的变化呈抛物线状,保持筋条横截面面积不变,筋条凸缘宽为60mm时屈曲载荷达到最大值.较小的凸缘宽度会导致筋条屈曲的发生,应在实际设计中予以避免.     

Value range optimization of ply parameter for composite wind turbine blades based on sensitivity analysis

Journal of Mechanical Science and Technology - Blade ply parameters are important design factors that influence the performances of wind turbine blades. This paper proposes a sensitivity analysis...     

Dynamic stability of a rotor with shear-flexible shaft under axial loads

The dynamic stability of shear-flexible rotating shaft with a disk under axial forces has been studied by employing the transfer matrix method. The conventional transfer matrix was modified to include both the applied axial force and the shear deformation. The shear effect is considered based on Engesser’s and Haringx’s buckling theories for shear-flexible beam. A computer program was developed to investigate the influence of both the axial force and the shear deformation on the stability and the natural frequencies of general rotor systems. Two rotor system models are considered: the overhung rotor with or without an intermediate support and the simply supported Jeffcott rotor. The effect of shear deformation and the difference between the Engesser and Haringx approaches increase with an intermediate support for an overhung rotor.