单叶风轮与三叶风轮的动力学特性的比较

风力机风轮的模态分析是了解风力机结构动态特性的基础,准确地得到风轮的固有频率和模态振型具有十分重要的意义.采用试验模态分析方法和计算模态分析方法分别对单叶片和三叶片风轮进行模态分析,得到了它们的模态振型.研究结果显示,单个叶片的模态振型和多叶片的模态振型有较大不同,单叶片风轮的动力学特性不能代替三叶片风轮的动力学特性.     

Lessons from Rotor 37

INTanDUCTIONhi1992theturbomachinerycommittee0ftheIoter-nationalGasTurbineInstitute(IGTI)decidedtosetuPatestcaseforCFDcalculations.Aftersomedebateitwasdecidedthatthetestcasesh0uldbecalculated'blind',i.e.thattheexperimentalresultssh0uldn0tbemadeawilableulltilafterthesolutionshadbeensubndtted.NASA(LewisResearchCenter)offeredasuitabletestca-seintheformofahighlyloadedtransoniccompressorrot0rwhichwasthenbeingtestedwitheXtensiveuseoflaseranemometrytomeasuretheiliternalflow.Themeasurementsw…     

Decoupled control of rotor torque and rotor electric power delivered in a salient-pole, synchronous machine

A drive system with a control algorithm that provides independent control of rotor torque and rotor electric power is described in this paper. One electromechanical machine is used for two purposes, viz., firstly to provide electromagnetic torque to rotate a rotor mounted load and secondly to provide electric power to equipment mounted on the rotor. The technique eliminates the need for slip rings. Simulation and practical results verifying the analysis are given. The system has applications such as rotational antennas and turret systems.     

Comparative study of a three-bucket Savonius rotor with a combined three-bucket Savonius–three-bladed Darrieus rotor

The vertical axis wind turbines are simple in construction, self-starting, inexpensive and can accept wind from any direction without orientation. A combined Savonius–Darrieus type vertical axis wind rotor has got many advantages over individual Savonius or individual Darrieus wind rotor, such as better efficiency than Savonius rotor and high starting torque than Darrieus rotor. But works on the combined Savonius–Darrieus wind rotor are very scare. In view of the above, two types of models, one simple Savonius and the other combined Savonius–Darrieus wind rotors were designed and fabricated. The Savonius rotor was a three-bucket system having provisions for overlap variations. The Savonius–Darrieus rotor was a combination of three-bucket Savonius and three-bladed Darrieus rotors with the Savonius placed on top of the Darrieus rotor. The overlap variation was made in the upper part, i.e. the Savonius rotor only. These were tested in a subsonic wind tunnel available in the department. The various parameters namely, power coefficients and torque coefficients were calculated for both overlap and without overlap conditions. From the present investigation, it is seen that with the increase of overlap, the power coefficients start decreasing. The maximum power coefficient of 51% is obtained at no overlap condition. However, while comparing the power coefficients (C_p) for simple Savonius-rotor with that of the combined configuration of Savonius–Darrieus rotor, it is observed that there is a definite improvement in the power coefficient for the combined Savonius–Darrieus rotor without overlap condition. Combined rotor without overlap condition provided an efficiency of 0.51, which is higher than the efficiency of the Savonius rotor at any overlap positions under the same test conditions.     

Motor temperature estimation incorporating dynamic rotor impedance

The estimation of induction motor temperature at different system, motor, and load conditions is investigated. Motor temperature is estimated using comprehensive interactive electrical, thermal, and mechanical models. The electrical model accounts for the skin effect in the rotor bars and predicts the dynamic motor impedance as motor speed changes. The thermal model accounts for the heating and cooling process in the motor. The interactive model is used to study motor behavior during balanced system condition, unbalanced system condition, high inertia load, locked rotor, and overload situations. Motor temperature during these states is predicted. It is shown that under certain conditions motor starting time may exceed the locked rotor time. Rotor thermal limit curves during an unbalanced voltage condition are presented     

Copper die-cast rotor efficiency improvement and economicconsideration

Significant motor efficiency improvement can be achieved by substituting aluminum with copper die-cast rotor in a squirrel cage induction motor. This paper summarizes the experiments conducted by Westinghouse Motor Company Canada Ltd. in our copper die-cast rotor induction motors project     

Transient thermal characteristics of induction machine rotor cage

Thermal analysis of an induction machine cage rotor during stall conditions forms an important part of design calculations. The study of rotor circuit thermal behavior is also useful to identify causes of failure in large cage rotor induction machines. The authors present a three-dimensional finite-element-based electrical-thermal analysis of the bar and end-ring area of a large rotor to examine its thermal characteristics during a stall. Details of temperature variations at key locations in the bar and end ring are provided. The calculations are compared to experimental results, and the advantages and limitations of the solution technique for rotor analysis are discussed     

燃气轮机转子模态试验与分析

介绍了某型燃气轮机转子模态试验,试验测得转子静态固有频率和模态振型。利用传递矩阵法对该转子进行了相应计算与对比分析,分析与试验结果为进一步研究该类型燃机转子的结构刚度问题提供了依据。     

Numerical investigation of airflow through a Savonius rotor

The aim of this report is to present a model of a rigid‐rotor system based on computational fluid dynamics (CFD), which is applied on a vertical axis wind turbine (VAWT) research. Its originality results from the use of the average value of the variable rotational speed method taken in a periodic steady‐state (PSS) of the VAWT rotor instead of the classical fixed rotational speed method. This approach was chosen in order to determine the mechanical and aerodynamic parameters of the wind turbine. The modeling method uses an implicit Euler iterative solution strategy, which resolves the coupling between fixed and moving rotor domains. The main methods that were adopted are based on the three‐dimensional modeling of the interaction of the fluid flow with a rigid‐rotor. The strategy consists of using the Reynolds averaged Navier Stokes (RANS) equations with the standard k‐ ? and SST k‐ ω models to solve the fluid flow problem. To perform the rigid‐rotor motion in a fluid, the one degree of freedom (1‐DOF) method was applied. In the present study, the steady‐state and dynamic CFD simulations of the Savonius rotor are adopted to contribute to the validation elements of the VAWT models that are used. The dynamic study allows the investigation of the rotor behavior and the relation between velocity, pressure, and vorticity fields in and around the rotor blades. The flow fields generated by the rotation of the Savonius rotor were investigated in the half revolution period of the rotor angle θ from 0° to 180°. In this range of θ, the focus is on generating and dissipating vortices. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigation of 3D printed Savonius rotor performance

In this study increasing the performance of Conventional Savonius wind rotor has been investigated by a 3D (three dimensional) printer which is one of the rapid prototyping techniques. For this purpose, some design changes have been introduced to increase the performance of conventional Savonius wind rotor. Here, 3D digital designing of Savonius wind rotors have been easily manufactured tangible as a physical model by a 3D printer. Experimental data concerning produced Savonius wind rotors have been acquired by using a wind tunnel. Some numerical data have been obtained from the CFD (Computational Fluid Dynamics) analysis carried out under the same conditions. The effects of the additional blade end design have been examined to obtain more torque increase on improved classical Savonius wind rotor. Furthermore, by means of introducing straight blade, the effects of the flow compression inside the blade have been reduced and rotor performance increased. Based on such optimizations, optimum additional design parameters have been designated as that (1/r) ratio is 0.3, (s/r) is 1, and (α) additional straight blade angle is 135°. It has been determined that power coefficient is increased at a ratio of around 20% together with all these design changes.     

Refurbishment of low pressure rotor last stage blades

Abstract

Work performed to refurbish last stage blades (LSBs) with articulated tip struts on low pressure steam turbine rotors is described. During the late 1990s, a series of erosion shield failures occurred on these high twist last stage blades, resulting in significant damage to tip struts and blades and causing generation downtime. Metallurgical investigation revealed the shield braze bond had degraded during cyclic service, resulting in shield detachment from the blade. Repair options considered included welding of Stellite bar to the blade leading edge, deposition of hardfacing weld metal on the blade leading edge and replacement of the complete blade tip with a laser hardened blade insert. From initial stress corrosion cracking tests, the laser hardened insert was selected. Trials to optimise welding parameters, joint set-up and weld bead deposition sequence are reported. The completed joint requires post-weld heat treatment to reduce residual stress and produce acceptable hardness across the weldment. Further high cycle fatigue and stress corrosion cracking testing of the aerofoil weld confirmed the suitability of this repair method. The susceptibility of the laser hardened insert to fatigue and environmentally assisted cracking was also found to be acceptable. Examples of the successful application of this patented repair technique are given.     

FEM analysis of inverter-induction motor rotor conduction losses

A direct method to simulate the steady-state stator and rotor currents in an inverter-induction machine of known geometry and winding design is developed, and the FEM (finite element method) analysis of the skin effect problem is used to determine the variation of rotor resistance with rotor current frequency. The rotor conduction loss can be calculated from these two sets of information. The total losses incurred for a particular mode of inverter operation are determined both experimentally and using the analytical procedure developed here. The total calculated loss is only 3.5% greater than the measured amount, which confirms the validity of the theory developed and its computer implementation. Furthermore, experimental and simulation results of the standstill condition with sinusoidal input were also found to be in close agreement. Finally, the proposed procedure yields information on the instantaneous current distribution throughout the machine, which permits the accurate determination of the flux pattern and optimization of the lamination design     

Finite element calculation of double-cage rotor equivalent circuitparameters

This paper describes the use of a saturable single slot finite element model to determine the resistances and reactances of a double-cage rotor, allowing for the MMF balancing effect of the stator currents. The method is verified by comparing the impedances calculated for an unsaturated rotor with rectangular bars with their analytically determined counterparts. The model requires the user to specify both rotor frequency and current per slot. The effect of magnetic saturation is examined, and it is demonstrated that care must be taken in the choice of current at low frequencies, to avoid conditions of excessive saturation, leading to unrealistic values for inductances     

Broadband noise radiation analysis for an HAWT rotor

The paper demonstrates a computational methodology for the noise prediction of an horizontal axis wind turbine (HAWT) rotor in time domain. The aeroacoustic modeling is based on the Ffowcs Williams and Hawkings equation considering only the surface monopole and dipole noise sources. The accurate solution of the noise problem is strongly influenced by the unsteadiness of the rotor flowfield, the nonuniform inflow effects and the blade aerodynamic parameters which are included in the numerical model. The aerodynamic analysis uses a three-dimensional low-order panel method combined with a boundary layer correction model for the calculation of the blade pressure distribution, obtaining satisfactory agreement with experimental data. Acoustic pressure predictions for the NREL downwind rotor are presented for several cases proving that broadband noise propagation dominates at low- and mid-frequency ranges. Sound pressure level contours occur via Fourier transformations, while the directivity for a single frequency source is also examined.     

垂直轴螺旋式风力叶轮的动态特性研究

采用风力叶轮直接驱动盘式发电机的方式,针对一种垂直轴螺旋式风力叶轮进行旋转状态下的动态特性试验研究,分别在自然风条件下和拖车试验条件下(来流速度为1～12 m/s),对试验装置的空载转速、空载电压进行测定,并对叶尖速比进行统计分析。研究结果表明:在自然风条件下,风速波动大,导致瞬态采集的风速与风轮转速不对应;在拖车试验条件下,来流速度相对稳定,且较易控制,风速与输出电压的对应关系较为明显。研究结果为相应的控制系统的设计与优化提供了参考。     

Experimental investigations on fiber motion within rotor spinning unit

An experimental platform is constructed to photograph fibers' motion within rotor spinning unit,which is mainly composed of a transparent rotor and a transport channel based on the similarity theory.The fibers will stretch and gather into a fiber bundle in the transport channel.The velocity of fibers is increasing along the inlet to the outlet of the transport channel,and the fibers' maximum velocity appears at the outlet of transport channel.The straightness of the fiber bundle is related to the convergence degree of the transport channel,and the greater the convergence degree is,the straighter the fiber bundle stretches.The results will provide a useful insight to the yam-forming mechanism of rotor spirming.     

转轴振动可靠性计算的模糊方法研究

转轴振动的可靠性计算中存在着大量的模糊信息,如何通过这些模糊信息获得模糊安全事件－－不发生共振的隶属函数是计算模糊共振可靠度的关键。将共振准则模糊化,构建模糊共振区域和相应的隶属函数,并将其应用于转轴的振动可靠性计算,取得了合理的计算结果。     

On the near-wall effects induced by an axial-flow rotor

Laboratory experiments were performed to quantify the near-wall flow characteristics and the bed shear stress in the vicinity of an axial-flow rotor model. It was placed in a smooth-wall open channel flow under subcritical conditions and operated at two heights. A laser Doppler velocimeter was used to collect profiles of the streamwise and vertical velocity at few locations within the rotor symmetry plane as close as one wall unit from the bed. Local estimates of the mean bed shear stress were obtained from the mean velocity profiles in the viscous and logarithmic regions. Results show that the bed shear stress is sensitive to the distance from the rotor and to the relative height of the rotor. Maximum bed shear stress occurred downstream of the rotor with the rotor closer to the bed. Flow statistics shows a reduction of turbulence intensity and turbulent shear stress near the wall and close to the rotor due to flow acceleration and changes in the pressure distribution. Spectral analysis of the streamwise velocity evidences a reduction of the energy content across scales spanning two decades right below the turbine. The increase of bed shear is due to mainly flow accelerating but not to turbulence.     

电站风机转子出厂平衡方法

介绍出厂前风机转子的平衡方法。根据转子速度及转子的宽度与直径之比的大小进行单面静平衡或双面动平衡校准,从而实现风机理想平衡状态。