A tip clearance prediction model for multistage rotors and stators in aero-engines

Tip clearances of multistage rotors and stators greatly affect aero-engines’ aerodynamic efficiency, stability and safety. The inevitable machining and assembly errors, as well as the complicated error propagation mechanism, cause overproof or non-uniform tip clearances. However, it is generally accepted that tip clearances are difficult to predict, even under assembly state. In this paper, a tip clearance prediction model is proposed based on measured error data. Some 3 D error propagation sub-models, regarding rotors, supports and casings, are built and combined. The complex error coupling relationship is uncovered using mathematical methods. Rotor and stator tip clearances are predicted and analyzed in different phase angles. The maximum, minimum and average tip clearances can be calculated. The proposed model is implemented by a computer program,and a case study illustrates its performance and verifies its feasibility. The results can be referred by engineers in assembly quality judgement and decision-making.

Experimental Study of Bowed-twisted Stators in an Axial Transonic Fan Stage

Bowed-twisted stators with large camber angles have been developed to replace the conventional tandem stators in an axial transonic fan stage working at high subsonic speeds. Experimental study is carried out on both stages with tandem stators and with bowed-twisted stators. Compared to the tandem stators, the bowed-twisted stators change the distribution of the low-energy fluid and the potential high-energy fluid at the compressor outlets, reduce the endwall loss significantly, improve the aerody- namic matching of rotors and stators, and eventually increase the fan stage performances. The aerodynamic performances of the fan stage at different operating points are compared and contrasted. The results show that the transonic fan stage with bowed-twisted stators has better aerodynamic performances. It is thus suggested that the bowed-twisted stators with large camber angles be popularized into the high-loaded transonic fan designs.

Enhancement of Torque Density in Wound Field Switched Flux Machines with Partitioned Stators Using Assisted Ferrites

In this paper,ferrites are applied in a partitioned stator wound field switched flux(PS-WFSF)machine to increase the air-gap flux density,and hence,the average electromagnetic torque and overload capability.Introducing short-circuited ferrites in the inner stator in the PS-WFSF machine can increase the open-circuit phase fundamental back-EMF and average electromagnetic torque at a 60 W copper loss by 2.33%and 3.77%,respectively.Moreover,the proposed PS-WFSF machine with ferrites can exhibit a better overload capability than conventional PS-WFSF machines without ferrites,e.g.,a 7.36%torque increment can be achieved when the copper loss is 120 W.The torque increment mechanism is analyzed and verified using finite element(FE)analysis.Moreover,the demagnetization of the ferrites in the proposed machine under rated on-load and overload conditions is investigated.Both prototypes of the proposed PS-WFSF machine with ferrites and a conventional one without ferrite are built and tested to validate the analytical and FE analyses.

Influence of Rotor Iron Bridge Position on DC-winding-induced Voltage in Wound Field Switched Flux Machine Having Partitioned Stators

In this study,the influence of the position of the rotor iron bridge on the DC-winding-induced voltage pulsation in a partitioned stator wound field switched flux machine is investigated.Analytical and finite element(FE)analyses show that both the open-circuit and on-load DC-winding-induced voltages can be minimized by positioning the rotor iron bridge adjacent to the inner air gap closer to the DC winding.This is due to a smoother inner air-gap magnetic reluctance while maintaining the average electromagnetic torque at 92.59%of the maximum value.The analyzed machine with the rotor iron bridge adjacent to the inner air gap is prototyped,and the experimental results validate the analytical and FE results.

A Fault Feature Extraction Model in Synchronous Generator under Stator Inter-Turn Short Circuit Based on ACMD and DEO3S

This paper proposed a new diagnosis model for the stator inter-turn short circuit fault in synchronous generators.Different from the past methods focused on the current or voltage signals to diagnose the electrical fault,the sta-tor vibration signal analysis based on ACMD(adaptive chirp mode decomposition)and DEO3S(demodulation energy operator of symmetrical differencing)was adopted to extract the fault feature.Firstly,FT(Fourier trans-form)is applied to the vibration signal to obtain the instantaneous frequency,and PE(permutation entropy)is calculated to select the proper weighting coefficients.Then,the signal is decomposed by ACMD,with the instan-taneous frequency and weighting coefficient acquired in the former step to obtain the optimal mode.Finally,DEO3S is operated to get the envelope spectrum which is able to strengthen the characteristic frequencies of the stator inter-turn short circuit fault.The study on the simulating signal and the real experiment data indicates the effectiveness of the proposed method for the stator inter-turn short circuit fault in synchronous generators.In addition,the comparison with other methods shows the superiority of the proposed model.

前置预旋定子泵喷推进器辐射噪声数值预报

The requirement of low radiated noise is increasing for underwater propulsors as the noise significantly affecting the comfort and quietness of ships,submarines,and vessels.To broaden the view of noise characteristics of pump-jet propulsors(PJPs),this paper considers the radiated noise of a pre-swirl stator PJP with the effects of the advance coefficient and rotor rotational speed.Radiated noise is obtained by the“hybrid method”approach,which combines a hydrodynamic solver with a hydroacoustic solver.The turbulence flow is obtained through improved delayed detached eddy simulation(IDDES),which show good agreement with the experiment,including the performance and flow field.The solver precision,permeable surface size,and sampling frequency notably affect the noise calculation.The spectra of thrust fluctuation and radiated noise are characterized by the tonal phenomenon around the blade passing frequency and its harmonics.The spectrum of radiated noise and overall sound pressure level(OSPL)are considerably affected by both the advance coefficient and the rotor rotational speed.Overall,the numerical results and analysis given in this paper should be partly helpful in deepening the understanding of the radiated noise characteristics of PJPs.

Analysis of electromagnetic characteristics of typical faults in permanent magnet wind generators

Due to the harsh actual operating environment of the permanent magnet wind turbine,it is easy to break down and difficult to monitor.Therefore,the electromagnetic characteristics identification of major fault types of large-scale permanent magnet wind turbines is studied in this paper.The typical faults of rotor eccentricity,stator winding short circuit and permanent magnet demagnetization of permanent magnet wind turbines are analyzed theoretically.The wavelet analysis algorithm is used to decompose and reconstruct the abnormal electromagnetic signal waveform band,and the characteristic frequency of the electromagnetic signal is obtained when the fault occurs.In order to verify the effectiveness of the proposed method,a 3.680MW permanent magnet wind turbine was taken as the research object.Its physical simulation model was established,and an external circuit was built to carry out field co-simulation.The results show that the motor fault type can be determined by detecting the change rule of fault characteristic frequency in the spectrum diagram,and the electromagnetic characteristic analysis can be applied to the early monitoring of the permanent magnet wind turbine fault.

Design of Online Vision Detection System for Stator Winding Coil

The quality of the stator winding coil directly affects the performance of the motor.A dual-camera online machine vision detection method to detect whether the coil leads and winding regions were qualified was designed.A vision detection platform was designed to capture individual winding images,and an image processing algorithm was used for image pre-processing,template matching and positioning of the coil lead area to set up a coordinate system.After eliminating image noise by Blob analysis,the improved Canny algorithm was used to detect the location of the coil lead paint stripped region,and the time was reduced by about half compared to the Canny algorithm.The coil winding region was trained with the ShuffleNet V2-YOLOv5s model for the dataset,and the detect file was converted to the Open Neural Network Exchange(ONNX)model for the detection of winding cross features with an average accuracy of 99.0%.The software interface of the detection system was designed to perform qualified discrimination tests on the workpieces,and the detection data were recorded and statistically analyzed.The results showed that the stator winding coil qualified discrimination accuracy reached 96.2%,and the average detection time of a single workpiece was about 300 ms,while YOLOv5s took less than 30 ms.

变轴向间隙下压气机近失速工况时弯曲静叶改善流场的实验研究(英文)

The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of the straight stator stages are investigated and compared to those of the bowed stator stages. The results show that using bowed stator stages could alleviate the flow separation at both upper and low corners of the suction surface and the endwalls, and decrease the losses along the flow passage as well as the outlet flow angle. As the rotor/stator axial gap decreases, although the diffusion capacity of the compressor increases obviously, the outlet flow field in the straight stator stages deteriorates quickly. By contrast, little changes occur in the bowed stator stages, indicating that as the rotor/stator axial gap decreases, improved performance is achieved in the bowed stator stages.

VSV系统对CFM56发动机喘振的影响分析

航空发动机喘振是发动机衰退过程中的常发的故障,而发动机VSV系统的工作状态直接影响发动机的喘振裕度。以CFM56—3发动机的VSV系统为研究对象,讨论其工作机理,分析其对处于衰退期的CFM56—3发动机稳定工作的影响,提出相应的维修注意事项。从而为研究以VSV故障为诱因的喘振提供理论依据,为相关维修提供工程参考。

Development of Energy-Saving Devices for a 20,000DWT River–Sea Bulk Carrier

A reduction of fuel consumption and an increase in efficiency are currently required for river–sea bulk carriers.Pre-swirl and ducted stators are widely used devices in the industry and efficiency gains can be obtained for single-screw and twin-screw vessels.Based on the hydrodynamic characteristics of the 20,000DWT river–sea bulk carrier,in this study,we proposed,designed,and tested a series of pre-swirl energy-saving devices(ESDs).The experimental results demonstrate that the proposed ESDs improved the propulsive efficiency and reduced the delivered power.The results confirm the success of our ESD for the 20,000DWT river–sea bulk carrier.We validated the role of Reynolds-averaged Navier–Stokes(RANS)computational fluid dynamics(CFD)in the twin-skeg river–sea vessel ESD design and found the circumferential arrangement and number of stators to be important factors in the design process.

A New Fault-Tolerant Switched Flux Machine With Hybrid Permanent Magnets

This paper put forward a new fault-tolerant hybrid switched-flux PM(HSFPM)machine design employing the synergy of NdFeB and Ferrite Magnet.The key of the proposed HSFPM designed machine is the unique design E-core laminated stator with the hybrid magnet to ensure a drastic reduction of NdFeB magnet without compromising the output performances and efficiency in the conventional SFPM machine design to avert the huge demand of NdFeB and its associated volatile high price increase.Additionally,the fault-tolerant stator teeth designed principle implemented in the proposed HSFPM machine provides enhanced segregation among the various phases and ensures continuity of operation with acceptable operating performance under fault-condition.For fair evaluation and comparison,both the proposed HSFPM and the conventional SFPM(CSFPM)machine have the same slot-pole combination,winding arrangements,and stator/rotor dimensions except for the unique outer-stator of the proposed design.Meanwhile,compared to the CSFPM machine,the proposed HSFPM machine design makes use of only 60%of the PM(NdFeB)length.Finally,the evaluation of the no-load in conjunction with the load condition performances was carefully investigated by the Finite Element Method(FEM)of the ANSYS Maxwell software.The results depicted that the proposed HSFPM exhibits similar sinusoidal back electromotive force,comparable output torque,and slightly higher efficiency compared to that of the CSFPM machine.

无速度传感器永磁同步电机直接转矩控制系统(英文)

The direct torque control theory has achieved great success in the control ofinduction motors. However, in the DTC drive system of Permanent Magnet Synchronous Machine (PMSM)proposed a few years ago, there are many basic theoretical problems that must be clarified. Thispaper describes an investigation about the effect of the zero voltage space vectors in the DTCsystem of PMSM and points out that if using the zero voltage space vectors rationally, not only canthe DTC system be driven successfully but also the torque ripple is reduced and the performance ofthe system is improved. This paper also studies the sensorless technique in the DTC system of PMSMand configures the DTC system of PMSM with sensorless technique including zero voltage spacevectors. Numerical simulations and experimental tests have proved the theory correct. In thecondition of sensor-less, the DTC system of PMSM is wide-rangely speed adjusting, and the ratio ofspeed adjustment is 1: 100.

压气机直、弯静叶Clocking效应实验研究(英文)

This paper is focused on the experimental study of the effects of stator clocking on the performance of a low-speed repeating stage axial compressor with compound-lean stators as well as the one with conventional stators （the baseline） for comparison. The experimental results show that as the clocking positions vary, the upstream stator wake enters the following passage at different circumferential positions, and then mixes with the local fluid in the following passage. This is the main reason for the variation of the compressor performance resulted from the stator clocking effects. The variation of the compressor performance due to the clocking effect is less pronounced for the compressor with compound-lean stators than with the baseline. At a certain clocking position, the efficiency of the compressor with compound-lean stators is increased in comparison with that of the baseline, especially on small mass flow rate conditions, e.g., 0.7% at design condition and 3.5% at near-surge condition in this case. The maximum 1.22% and the minimum 0.07% increases in efficiency on design condition are obtained through the combined effects of the stator compound-lean and the stator clocking in this case.

风力发电机定子绕组雷电过电压分布的仿真(英文)

This paper analyzes lightning surge on the stator windings of wind turbine generators.The path of lightning in the wind turbines was analyzed.An equivalent circuit model for megawatt direct-driven wind turbine system was developed,in which high-frequency distributed parameters of the blade conducts,tower,power cables and stator windings of generator were calculated based on finite element method,and the models of converter,grounding,loads, surge protection devices and power grid were established.The voltage distribution along stator windings,when struck by lightning with 10/350μs wave form and different amplitude current between 50 kA and 200 kA,was simulated using electro-magnetic transient analysis method.The simulated results show that the highest coil-to-core voltage peak appears on the last coil or near the neutral of stator windings,and the voltage distribution along the windings is nonuniform initially.The voltage drops of each coil fall from first to last coil,and the highest voltage drop appears on the first coil.The insulation damage may occur on the windings under lightning overvoltage.The surge arresters can restrain the lightning surge in effect and protect the insulation.The coil-to-core voltage in the end of windings is nearly 19.5 kV under the 200 kA lightning current without surge arresters on the terminal of generator,but is only 2.7 kV with arresters.

Feasibility of a New Ironless-stator Axial Flux Permanent Magnet Machine for Aircraft Electric Propulsion Application

With the development of aviation electrification,higher demands for electrical machines are put forward in aircraft electric propulsion systems.The aircraft electric propulsion requirements and propulsion motor features are analyzed in this paper.Comparing with conventional PM machines,ironless stator axial flux permanent magnet(AFPM)machine topologies with Litz wire windings allow designs with higher compactness,lightness and efficiency,which are suitable for high-frequency and high-power density applications.Based on the motor requirements and constraints of aircraft electric propulsion systems,this paper investigates a high-power 1 MW multi-stack ironless stator AFPM machine,which is composed of four 250kW modular motors by stacking in axial.The design guidelines and special attentions are presented,in term of electromagnetic,thermal,and mechanical performance for the high-frequency coils and Halbach-array PM rotor.Finally,an ironless stator AFPM motor is manufactured,tested and evaluated with the consideration of cost and processing cycle.The results show that the output power is up to 53.8kW with 95%efficiency at 9000r/min at this stage.The proposed ironless stator AFPM machine with oil immersed forced cooling proves to be a favorable candidate for application in electric aircraft as propulsion motors.

Visual study on the characteristics of liquid and droplet in a novel rotor-stator reactor

Rotor–stator reactor(RSR), an efficient mass transfer enhancer, has been applied in many fields. However,the hydrodynamic characteristics of liquid flow in RSR are still a mystery despite they are fundamental for the mass transfer performance and processing capacity. In view of the above, this paper studies the liquid–liquid flow and liquid holdup in RSR under various conditions with a high-speed camera. The paper firstly demonstrates two flow patterns and liquid holdup patterns that we obtained from our experiment and then presents in succession a flow pattern and a liquid holdup criterion for the transition of film flow to filament flow and complete filling to incomplete filling. It is found that experimental parameters, including rotor–stator distance, rotational speed and volume flow rate exert great influence on the average droplet diameter and size distribution. Besides, by comparison and contrast, we also find that the experimental values match well with our previous predicted calculations of the average diameter, and the relation between the average diameter and the mean energy dissipation rate.

THE RESONANCES OF PARAMETRIC VIBRATION WITH FORCED VIBRATION OF THE STATOR SYSTEM OF HYDROELECTRIC-GENERATOR STIMULATED BY ELECTROMAGNETISM

The resonances of parametric vibration with forced vibration isanalyzed, the bifurca- tion equation of the system is obtained andthe singularity analysis is made. Some of the laws and phe- nomenaare revealed. The transition variety and bifurcation diagram of thephysical parameteric plane are given. the results can be used inengineering.

燃气轮机发动机内流及二次流系统（英文）

The challenging conditions at which gas turbine engines operate mean that careful management of component temperatures is necessary, in order to ensure component integrity and reasonable service life. Pressurised flows extracted from the compressor can be used for cooling, sealing and balancing of components throughout the engine. Cooling is typically necessary for some combustor and turbine components, and sealing flows may be needed to exclude high temperature gases. In addition to cooling and sealing requirements, there is also a need to balance thrust loads in an engine, to limit loads on bearings, arising from the pressure differentials across compressor and turbine disc assemblies. The diverse tasks of cooling, sealing and balancing are generally assigned to a system known as the internal air system or secondary flow system. This paper describes the technologies associated with this system for both industrial gas turbine engines and aero-engines, and the current state of the art and challenges in component and subsystem design.

A New Switching Sequences of SVPWM for Six-Phase Induction Motor with Features of Reduced Switching Losses

In this paper,new SVPWM switching sequences for six-phase asymmetrical induction motor drives are derived with the aim to reduce inverter’s switching losses.Total three switching sequences are introduced in this paper.These sequences are derived such that the phases get continuously clamped when a current of the phases is around its peak magnitude and hence reduced switching losses are recorded.The comparative performances of these modulation techniques are studied with two existing switching sequences.Simulation,analytical and experimental results are presented.Based on these results,it is found that new switching sequences reduce switching losses effectively in dual three phase inverters.