Intrinsic physical relationships between rotor modal shapes and instantaneous vibrational energy flow transmission characteristics: Theoretical and numerical analysis and application

The modal vibration of the rotor is the main cause of excessive vibration of the aero-engine overall structure. To attenuate the vibration of the rotor under different modal shapes from the perspective of energy control, the intrinsic physical relationships between rotor modal shapes and instantaneous vibrational energy flow transmission characteristics is derived from the general equation of motion base on the structural intensity method. A dual-rotor-support-casing coupling model subjected to the rotor unbalanced forces is established by the finite element method in this paper. The transmission, conversion and balance relationships of the vibrational energy flow for the rotors in the first-order bending modal shape, the conical whirling modal shape and the translational modal shape are analyzed, respectively. The results show that the vibrational energy flow transmitted to the structure can be converted into the strain energy, the kinetic energy and the energy dissipated by the damping of the structure. The vibrational energy flow transmission characteristics of rotors with different modal shapes are quite different. Especially for the first-order bending modal shape, the vibrational energy flow and the strain energy are transmitted and converted to each other in the middle part of the rotor shaft, resulting in large deformation at this part. To attenuate this harmful vibration, the influences of grooving on the shaft on the first-order bending vibration are studied from the perspective of transmission control of vibrational energy flow. This study can provide theoretical references and guidance for the vibration attenuation of the rotors in different modal shapes from a more essential perspective.     

垂直于叶片弦线方向喷气对转子稳定性的影响研究

以NASA Rotor37为研究对象,采用数值模拟的方法进行叶顶喷气对转子稳定性的影响研究。研究表明,在叶顶垂直于叶片弦线方向喷气可以达到扩稳效果,其扩稳机理在于通过喷口喷射出的高速射流把叶顶泄漏流吹向转子吸力面,减弱了叶顶泄漏流对主流的影响,使得转子叶顶堵塞区域减小,改善了叶顶区域的流通状况,从而得到扩稳效果。在喷气流量对转子稳定性的研究中,喷气流量越大,对增强稳定性越有利。在所选取的1%,1.5%和2%三种喷气流量水平下,2%的喷气流量可以使转子的流量裕度提高4.24%,综合裕度改进量提高5.16%。此外,不同喷气流量对转子的流场影响不同,随着喷气流量的增大,除了可以降低叶顶前缘负荷外,还可以通过将激波位置推向下游,从而有利于减弱流动分离,对转子稳定性的提升更为有利。     

航空发动机盘腔积液的故障识别

针对航空发动机盘腔积液故障难于监测和诊断的问题,将积液问题分为早期积液和严重积液,分别进行振动特征提取。研究了不平衡量和早期积液对转子振动的影响规律,基于幅频特性曲线区域面积分布特点,提出一个早期积液故障识别准则;分析了严重积液转子失稳振动特征,发现积液转子在发生失稳时会出现振动幅值突增、次谐波分量突增和拍振,基于振动特征提出三个严重积液故障识别准则。结合航空发动机实际工况,提出一套完整的积液故障监测方法和诊断流程,能够实现在转子失稳前发出预警,避免故障升级。通过30组实验数据进行验证,所提出的积液故障识别方法准确率达96%,具备工程应用价值。     

风扇转子的气动优化设计研究

风扇转子气动优化设计是结合CFD、遗传算法和风扇特性的跨学科自动设计方法,这种设计较少依赖经验,能实现多目标和多设计参数组合的优化设计。先研究了四个关键技术：具有耗时少、计算较准确的叶片通道流场数值计算方法;具有良好寻优能力的数值最优化方法;三维叶片造型的参数化方法;以气动性能为目标的多目标函数构建方法。再将上述四个关键技术模块整合,构建简易的气动优化设计软件。三维叶片优化算例证明了该软件的设计能力,其设计结果较满意、设计效率较高、设计周期短。     

Panel/full-span free-wake coupled method for unsteady aerodynamics of helicopter rotor blade

A full-span free-wake method is coupled with an unsteady panel method to accurately predict the unsteady aerodynamics of helicopter rotor blades in hover and forward flight. The unsteady potential-based panel method is used to consider aerodynamics of finite thickness multi-bladed rotors, and the full-span free-wake method is applied to simulating dynamics of rotor wake. These methods are tightly coupled through trailing-edge Kutta condition and by converting doublet-wake panels to full-span vortex filaments. A velocity-field integration technique is also adopted to overcome singularity problem during the interaction between the rotor wake and blades. Helicopter rotors including Caradonna-Tung, UH-60A, and AH-1G rotors, are simulated in hover and forward flight to validate the accuracy of this approach. The predicted aerodynamic loads of rotor blades agree well with available measured data and computational fluid dynamics (CFD) results, and the unsteady dynamics of rotor wake is also well simulated. Compared to CFD, the present method obtains accurate results more efficiently and is suitable to rotorcraft aeroelastic analysis.     

直升机飞行/推进系统综合模型的建立

利用递阶,分散的控制思想,将直升机对象划分为三个具有独立功能,便于建模的子系统,即直升机,旋翼,发动机子系统,再在各子系统模型基础上根据各子系统间的耦合关系,建立了整个系统的模型。其中四片铰接式旋翼模型起着纽带作用,只有充分考虑机体／旋翼及发动机／旋翼间耦合关系才能建立直升机飞行／推进综合模型,仿真结果证明了建模方法的有效性,为直升机飞行／推进综合控制系统的建立奠定了基础。     

Aerodynamic design optimization of helicopter rotor blades including airfoil shape for hover performance

This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight. The trim condition must be attainable. This paper considers rotor blade configuration for the hover flight condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.     

旋翼螺旋桨巡航及悬停状态气动特性研究

为了提高旋翼螺旋桨的综合气动性能,本文基于叶素-动量组合理论,并耦合了计算流体力学（Computational fluid dynamics,CFD）方法,设计了一款旋翼螺旋桨,进行了螺旋桨巡航及悬停状态的气动特性计算及流场仿真,计算结果与风洞试验数据进行了对比分析。研究结果表明,在进行网格无关性研究基础上,数值计算与风洞试验的误差较小,设计点平均计算误差为3.0%左右,所采用的CFD计算方法具有较高准确性和可信度。设计的旋翼螺旋桨巡航效率高于80%,悬停效率高于70%,具备了较好的巡航及悬停的综合气动性能。     

转子叶尖开缝对跨声速轴流压气机性能及流场结构影响机理研究

为了研究转子叶尖开缝对跨声速轴流压气机性能和流场结构的影响机理,设计了一种渐缩式射流缝,并提出在转子叶尖不同相对位置开缝的流动控制方案,通过数值计算的方法对各开缝方案与压气机的流场进行对比分析。结果表明,开缝位置靠近前缘时压气机总压比提升了1.39%,但综合稳定裕度降低了0.18%;开缝位置靠近尾缘时,压气机总压比提升了2.78%,综合稳定裕度也提升了1.38%。分析发现,转子叶尖开缝能有效控制转子叶片表面流动分离,缓解叶尖通道堵塞,在所研究范围内,开缝位置越靠近尾缘,对静叶通道流场性能改善越明显,削弱气流分离的同时还能抑制气流沿叶高方向潜移,极大程度提高了压气机流场性能。     

转子越过临界转速的振动特性试验研究

以盘偏置单盘双简支试验器转子为对象,由加速与减速的幅频特性曲线确定转子的临界转速。以幅频特性曲线模态计算法确定盘处的偏心距和阻尼比,用弯、扭耦合传递矩阵法计算临界转速及稳态不平衡响应,同时分析了偏心距及初始弯曲按一阶振型分配时,转子越过临界之振动特性。由试验与理论分析结果表明,加速度对振动特性有明显的影响。