During the rotor assembly of aeroengines,the combined effect of blade mass moment variations and fixed tenon slot constraints makes single-phase rotor unbalance optimization strategies insufficient for real-world indu...During the rotor assembly of aeroengines,the combined effect of blade mass moment variations and fixed tenon slot constraints makes single-phase rotor unbalance optimization strategies insufficient for real-world industrial assembly scenarios.This often leads to excessive residual unbalance after assembly,resulting in engine vibrations and compromised operational stability.To address the lack of blade selection strategies and low qualification rates due to tenon slot constraints in industrial settings,this paper proposes a co-optimization method for blade selection and sequencing under industrial assembly constraints.A two-stage data-driven optimization framework is developed.In the first stage,a Dynamic Replacement Roulette Selection(DRWS)algorithm is introduced for global multi-set blade selection,improving blade utilization and avoiding selection failure caused by excessive moment dispersion.In the second stage,under fixed tenon slot constraints,blade sequencing is optimized using a Constrained Adaptive Genetic Algorithm(CAGA),effectively suppressing residual unbalance.Experimental results demonstrate that the proposed method achieves a blade utilization rate of 92.4%on 145 samples,with well-balanced group sets.Under tenon slot constraints,the residual unbalance is reduced from 58 g·mm and 94 g·mm(random assembly)to 7 g·mm and 10 g·mm,respectively.This study offers a novel solution and technical support for improving assembly precision and enabling intelligent decision-making in aeroengine rotor assembly lines.展开更多
This paper proposes a new approach to eliminate aerodynamic lift oscillation,called the Dominant Sector Individual Blade Control(DS-IBC)method for rigid rotor helicopters.An Advancing Blade Concept(ABC)rotor model for...This paper proposes a new approach to eliminate aerodynamic lift oscillation,called the Dominant Sector Individual Blade Control(DS-IBC)method for rigid rotor helicopters.An Advancing Blade Concept(ABC)rotor model for aerodynamic analysis based on the free-wake method is applied.DS-IBC avoids applying active control on the rotor's retreating side by employing and restricting active control inputs to a sector area of the rotor disc.Outside this sector,only primary collective and cyclic pitch control are used.Each blade takes turns entering the sector,creating a“relay”active control form to ensure continuous control inputs.The method also includes outer-trim and inner-trim iteration modules.Results show that DS-IBC can eliminate aerodynamic lift oscillation using much smaller control inputs than the sine-trim method.By focusing active control on the rotor's advancing side,DS-IBC improves the effective lift-to-drag ratio and reduces the implementation difficulty of active rotor control for aerodynamic oscillation elimination,especially at a large lift-offset.展开更多
The unsteady 3D flow fields in a single-stage transonic compressor under designed conditions are simulated numerically to investigate the effects of the curved rotors on the stage performance and the aerodynamic inter...The unsteady 3D flow fields in a single-stage transonic compressor under designed conditions are simulated numerically to investigate the effects of the curved rotors on the stage performance and the aerodynamic interaction between the blade rows. The results show that, compared to the compressor with unurved rotors, the compressor under scrutiny acquires remarkable increases in efficiency with significantly reduced amplitudes of the time-dependent fluctuation. The amplitude of the pressure fluctuation around the stator leading edge decreases at both endwalls, but increases at the mid-span in the curved rotors. The pressure fluctuation near the stator leading edge, therefore, becomes more uniform in the radial direction of this compressor. Except for the leading edge area, the pressure fluctuatinn amplitude declines remarkably in the tip region of stator surface downstream of the curved rotor, but hardly changes in the middle and at the hub.展开更多
In this paper, an identification method to estimate the unbalances is introduced, which is based on the boundary element method (BEM). By using the vibration response measured at some points on the flexible rotor the ...In this paper, an identification method to estimate the unbalances is introduced, which is based on the boundary element method (BEM). By using the vibration response measured at some points on the flexible rotor the unbalances can be identified conveniently. Therefore, the rotor can be balanced without test runs.展开更多
Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of th...Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.展开更多
A control system aims at vibration reduction in a two-span rotor system with two shear mode magnetorheological （MRF） dampers is designed. A finite element model of the MRF damper- rotor system is built and used to a...A control system aims at vibration reduction in a two-span rotor system with two shear mode magnetorheological （MRF） dampers is designed. A finite element model of the MRF damper- rotor system is built and used to analyze the rotor vibration characteristics. Based on Hooke and Jeeves algorithm and the numerical simulation analysis, an optimal appropriate controller is proposed and designed. Experimental results show that rotor vibration caused by unbalance is well controlled （ first critical speed region 37% , second critical speed region 42% ）. To reflect advantages of optimi- zing strategy presented and validate the intelligent optimization control technology, detailed experi- ments were developed on a two-span rotor-vibration-control platform. The influence on accuracy, rapidity and stability of optimizing control for rotor vibration are analyzed. It provides a powerful technical support for the extension and application in target and control for shafting vibration.展开更多
This paper presents a method of general geometrical definitions of screw machine rotors and their manufacturing tools.It describes the details of lobe shape specification,and focuses on a new lobe profile,which yields...This paper presents a method of general geometrical definitions of screw machine rotors and their manufacturing tools.It describes the details of lobe shape specification,and focuses on a new lobe profile,which yields a larger cross-sectional area and shorter sealing lines resulting in higher delivery rates for the same tip speed.A well proven mathematical model was used to determine the optimum profile,compressor housing size,and compressor ports to achieve the superior compressors.展开更多
Gurney Flaps(GFs) are used for improving the performance of variable speed tail rotors. A validated analytical helicopter model able to predict the main and tail rotor power is utilized. The fixed height GF has substa...Gurney Flaps(GFs) are used for improving the performance of variable speed tail rotors. A validated analytical helicopter model able to predict the main and tail rotor power is utilized. The fixed height GF has substantially small influence on the tail rotor power in hover and low to medium speed forward flight, and can obtain significant power reduction in high speed flight.This ability can be enhanced by decreasing the tail rotor speed. With the deployment of GF, the collective pitch of the tail rotor decreases, and the maximum tail rotor thrust increases. The GF can compensate the reduction of the maximum thrust by the decrease in the tail rotor speed. The GF with a height of 5% of the chord length can almost remedy 50% of the thrust reduction introduced by decreasing 10% of the tail rotor speed. With the increase of GF height, the maximum thrust generated by the tail rotor increases. The GF with larger height can cause the increase in the tail rotor power in hover and low to medium speed flight. The retractable GF can obtain more power savings than the fixed height GF. However, the benefit is substantially small even in high speed flight. Considering the side effects introduced by the active GF, the fixed height GF may be more preferable. The mechanism for the retractable GF to generate more tail rotor thrust is to increase the lift in advancing side due to the higher dynamic pressure.展开更多
The nonlinear properties of rotating machinery vibration signals are presented. The relationship between faults and quadratic phase coupling is discussed. The mechanism that gives rise to quadratic phase coupling is a...The nonlinear properties of rotating machinery vibration signals are presented. The relationship between faults and quadratic phase coupling is discussed. The mechanism that gives rise to quadratic phase coupling is analyzed, and the coupling models are summarized. As a result, higher order spectra analysis is introduced into fault diagnosis of rotors. A brief review of the properties of higher order spectra is presented. Furthermore, the bicoherence spectrum is employed to extract the features that signify the machinery condition. Experiments show that bicoherence spectrum patterns of different faults are quite different, so it is proposed to identify the faults in rotors.展开更多
A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling.The experimental rotor system is established using ...A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling.The experimental rotor system is established using a fluted disk and a speed sensor which is applied in an actual aero engine for speed measurement.Through simulating calculation and experiments,the effects of tightening torque on the dynamic characteristics of the rotor system connected by a spline coupling including critical speeds,vibration modes and unbalance responses are analyzed.The results show that when increasing the tightening torque,the first two critical speeds and the amplitudes of unbalance response gradually increase in varying degrees while the vibration modes are essentially unchanged.In addition,changing axial and circumferential positions of the mass unbalance can lead to various amplitudes of unbalance response and even the rates of change.展开更多
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 me...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.展开更多
The pressure increasing process within a twin screw multiphase pump, under the condition of high gas volume fractions (GVFs), induces large temperature and pressure changes that cause the rotors to deform. Rotor defor...The pressure increasing process within a twin screw multiphase pump, under the condition of high gas volume fractions (GVFs), induces large temperature and pressure changes that cause the rotors to deform. Rotor deformations heavily influence the backflow of the multiphase fluid through clearances within the twin screw multiphase pump and these deformations may even lead to pump failures. An accurate temperature and pressure distribution on the screw rotors need be obtained before the deformation analysis can be carried out. By means of small temperature and pressure sensors embedded into the groove at the root of the rotors, the temperatures of 12 points on the rotors and the pressure distributions of a twin screw multiphase pump under high GVFs conditions were recorded. Temperature test results were adopted to perform a heat transfer analysis for determining the temperature distribution on the screw rotors. Then deformation analyses, including thermal deformation, force deformation, and total deformation, were conducted according to the pressure and temperature distributions. Deformation analysis for different materials was also conducted under the same boundary conditions. A material was suggested for the manufacturing of rotors in a twin screw multiphase pump under the condition of high gas volume fractions.展开更多
Switched reluctance motors(SRM)with full-pitch windings and segmental rotors are particularly suitable for the drive systems in aerospace environments because of low wind(oil)resistance and iron losses at high speed.I...Switched reluctance motors(SRM)with full-pitch windings and segmental rotors are particularly suitable for the drive systems in aerospace environments because of low wind(oil)resistance and iron losses at high speed.In this paper,the authors have been studying electromagnetic design of this motor.展开更多
The SiCp/Al-alloy composite front brake rotors designed for Shanghai Santana cars were prepared by semi-solid stirring+liquid forging process. The composite brake rotors were subjected to dynamometer tests on a SCHENC...The SiCp/Al-alloy composite front brake rotors designed for Shanghai Santana cars were prepared by semi-solid stirring+liquid forging process. The composite brake rotors were subjected to dynamometer tests on a SCHENCK brake testing system, referring to TL110 standard of VOLKSWAGEN Co. The friction coefficient and thermal response during fade testing and the wear performance of the composite rotors were studied as the functions of various parameters such as braking pressures, initial speeds, initial temperatures, torque and decelerations, and were compared with those of conventional cast iron rotors. The results show that the properties of the composite rotors can achieve the requirements of commercial cast iron rotors. The results also show that the friction coefficients of the composite rotors under different braking conditions are within the deviation band specified by the TL110 standard, and the temperature rise of composite rotors is lower than that of cast iron rotors at the end of each fade stop. The wear resistance of composite rotors is higher than that of cast iron rotors. The friction mechanism and wear mechanism were analyzed.展开更多
The dynamic response of the rotor depends on not only itself but also the dynamical characteristics of the structures that support it. In this paper, the coupling vibration characteristics of the rotor and supporting ...The dynamic response of the rotor depends on not only itself but also the dynamical characteristics of the structures that support it. In this paper, the coupling vibration characteristics of the rotor and supporting structure are studied using one simple rotor-supports model firstly, and then the dynamic stiffness of the typical supporting structure of an aero-engine is investigated in use of both numerical and experimental methods. While, one simulation strategy is developed to include dynamic stiffness of realistic supports in the dynamical analysis of the rotor system. The simulated and tested results show that the dynamic stiffness of the supporting structure not only depends on the structural parameters but also is related to the frequency of the excitation force. The dynamic stiffness is affected by the damping and inertia effect when the excitation frequency is high and closed to the resonance frequency of the support, which may decrease the dynamic stiffness sharply.More resonance frequencies may be induced and the critical speed could be reduced or increased.While higher vibration response peak and overload of the bearing may also be caused by the varied dynamic stiffness, which needs to be avoided in the design of the rotor-supports system.展开更多
To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluid- lastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to ch...To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluid- lastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to change the tuning port area ratio, which can change the tuning frequency of the isolator. A rotor model including the model of fluidlastic isolator is coupled with a fuselage model to predict the steady responses of the rotor system in forward flight. The aeroelastic analyses indicate that distinct performance improvement in pitch link load control can be achieved by the utilization of variable frequency isolators compared with the constant tuning frequency isolators. The 4/rev （per revolution） pitch link load is observed to be reduced by 87.6% compared with the increase of 56.3% by the constant frequency isolator, when the rotor speed is reduced by 16.7%. The isolation ability at different rotor speeds in different flight states is investigated. To achieve overall load reduction within the whole range of rotor speed, the strategy of the variation of tuning frequency is adjusted. The results indicate that the 4/rev pitch link load within the whole rotor speed range is decreased.展开更多
The Actuator Line/Navier-Stokes model is validated against wind tunnel measurements for flows past the yawed MEXICO rotor and past the yawed NREL Phase VI rotor. The MEXICO rotor is operated at a rotational speed of 4...The Actuator Line/Navier-Stokes model is validated against wind tunnel measurements for flows past the yawed MEXICO rotor and past the yawed NREL Phase VI rotor. The MEXICO rotor is operated at a rotational speed of 424 rpm, a pitch angle of ?2.3。, wind speeds of 10, 15, 24 m/s and yaw angles of 15。, 30。 and 45。. The computed loads as well as the velocity field behind the yawed MEXICO rotor are compared to the detailed pressure and PIV measurements which were carried out in the EU funded MEXICO project. For the NREL Phase VI rotor, computations were carried out at a rotational speed of 90.2 rpm, a pitch angle of 3。, a wind speed of 5 m/s and yaw angles of 10。and 30。. The computed loads are compared to the loads measured from pressure measurement.展开更多
A sudden increase of vibration amplitude with no foreboding often results in an abrupt breakdown of a mechanical system.The catastrophe of vibration state of a faulty rotor is a typical nonlinear phenomenon,and very d...A sudden increase of vibration amplitude with no foreboding often results in an abrupt breakdown of a mechanical system.The catastrophe of vibration state of a faulty rotor is a typical nonlinear phenomenon,and very difficult to be described and predicted with linear vibration theory.On the basis of nonlinear vibration and catastrophe theory,fhe eatastrophe of the vibration amplitude of the faulty rotor is described;a way to predict its emergence is developed.展开更多
We present an immersed array of four rotors whose promoted flow can be mathematically modeled with a creeping flow solution from the incompressible Navier-Stokes equations. We show that this solution is indeed represe...We present an immersed array of four rotors whose promoted flow can be mathematically modeled with a creeping flow solution from the incompressible Navier-Stokes equations. We show that this solution is indeed representative of the two-dimensional experiment and validate such class of solution with experimental data obtained through the Particle Image Velocimetry technique and time-lapsed particles visualizations.展开更多
Twin-rotor cylinder-embedded piston engine is proposed for dealing with the sealing problems of rotors in twin-rotor piston engine where the existent mature sealing technologies for traditional reciprocating engine ca...Twin-rotor cylinder-embedded piston engine is proposed for dealing with the sealing problems of rotors in twin-rotor piston engine where the existent mature sealing technologies for traditional reciprocating engine can be applied.The quantity and forms of its sealing surfaces are reduced and simplified,and what's more,the advantages of twin-rotor piston engine are inherited,such as high power density and no valve mechanism.Given the motion law of two rotors,its kinematic model is established,and the general expression for some parameters related to engine performance,such as the trajectory,displacement,velocity and acceleration of the piston and centroid trajectory,angular displacement,velocity and acceleration of the rod are presented.By selecting different variation patterns of relative angle of two rotors,the relevant variables are compared.It can be concluded that by designing the relative angle function of two rotors,the volume variation of working chamber can be changed.However,a comprehensive consideration for friction and vibration is necessary because velocity and acceleration are quite different in the different functions,the swing magnitude of rod is proportional to link ratio λ,and the position of rod swing center is controlled by eccentricity e.In order to reduce the lateral force,a smaller value of λ should be selected in the case of the structure,and the value of e should be near 0.95.There is no relationship between the piston stroke and the variation process of relative angle of two rotors,the former is only proportional to the amplitude of relative angle of two rotors.展开更多
基金supported by Basic Research Project for Young Students of the National Natural Science Foundation of China(grant number:524B2070)National Key Research and Development Program of China National Key R&D Program of China(2024YFF0726600,2024YFF0726601,2024YFF0726602,2024YFF0726604)+2 种基金Fundamental Research Funds for the Central UniversitiesNational Natural Science Foundation of China 52275525Postdoctoral Fellowship Program of CPSF under Grant Number BX20240476.
文摘During the rotor assembly of aeroengines,the combined effect of blade mass moment variations and fixed tenon slot constraints makes single-phase rotor unbalance optimization strategies insufficient for real-world industrial assembly scenarios.This often leads to excessive residual unbalance after assembly,resulting in engine vibrations and compromised operational stability.To address the lack of blade selection strategies and low qualification rates due to tenon slot constraints in industrial settings,this paper proposes a co-optimization method for blade selection and sequencing under industrial assembly constraints.A two-stage data-driven optimization framework is developed.In the first stage,a Dynamic Replacement Roulette Selection(DRWS)algorithm is introduced for global multi-set blade selection,improving blade utilization and avoiding selection failure caused by excessive moment dispersion.In the second stage,under fixed tenon slot constraints,blade sequencing is optimized using a Constrained Adaptive Genetic Algorithm(CAGA),effectively suppressing residual unbalance.Experimental results demonstrate that the proposed method achieves a blade utilization rate of 92.4%on 145 samples,with well-balanced group sets.Under tenon slot constraints,the residual unbalance is reduced from 58 g·mm and 94 g·mm(random assembly)to 7 g·mm and 10 g·mm,respectively.This study offers a novel solution and technical support for improving assembly precision and enabling intelligent decision-making in aeroengine rotor assembly lines.
基金supported by the National Natural Science Foundation of China(No.12372229)the Aeronautical Science Foundation of China(No.2020Z006063001)+1 种基金the Science and Technology on Rotorcraft Aeromechanics Laboratory Foundation,China(No.61422202110)the Fundamental Research Funds for the Central Universities of China(No.DUT22LK12)。
文摘This paper proposes a new approach to eliminate aerodynamic lift oscillation,called the Dominant Sector Individual Blade Control(DS-IBC)method for rigid rotor helicopters.An Advancing Blade Concept(ABC)rotor model for aerodynamic analysis based on the free-wake method is applied.DS-IBC avoids applying active control on the rotor's retreating side by employing and restricting active control inputs to a sector area of the rotor disc.Outside this sector,only primary collective and cyclic pitch control are used.Each blade takes turns entering the sector,creating a“relay”active control form to ensure continuous control inputs.The method also includes outer-trim and inner-trim iteration modules.Results show that DS-IBC can eliminate aerodynamic lift oscillation using much smaller control inputs than the sine-trim method.By focusing active control on the rotor's advancing side,DS-IBC improves the effective lift-to-drag ratio and reduces the implementation difficulty of active rotor control for aerodynamic oscillation elimination,especially at a large lift-offset.
基金National Natural Science Foundation of China (506460210) Chinese Specialized Research Fund for the Doctoral Program of Higher Education (20060213007)Development Program for Outstanding Young Teachers in Harbin Institute of Technology (HITQNJS.2006.046)
文摘The unsteady 3D flow fields in a single-stage transonic compressor under designed conditions are simulated numerically to investigate the effects of the curved rotors on the stage performance and the aerodynamic interaction between the blade rows. The results show that, compared to the compressor with unurved rotors, the compressor under scrutiny acquires remarkable increases in efficiency with significantly reduced amplitudes of the time-dependent fluctuation. The amplitude of the pressure fluctuation around the stator leading edge decreases at both endwalls, but increases at the mid-span in the curved rotors. The pressure fluctuation near the stator leading edge, therefore, becomes more uniform in the radial direction of this compressor. Except for the leading edge area, the pressure fluctuatinn amplitude declines remarkably in the tip region of stator surface downstream of the curved rotor, but hardly changes in the middle and at the hub.
文摘In this paper, an identification method to estimate the unbalances is introduced, which is based on the boundary element method (BEM). By using the vibration response measured at some points on the flexible rotor the unbalances can be identified conveniently. Therefore, the rotor can be balanced without test runs.
基金China Postdoctoral Science Foundation (20100481368)National Key Laboratory Foundation of China
文摘Three-dimensional unsteady Euler equations are numerically solved to simulate the unsteady flows around forward flight helicopter with coaxial rotors based on unstructured dynamic overset grids. The performances of the two coaxial rotors both become worse because of the aerodynamic interaction between them, and the influence of the top rotor on the bottom rotor is greater than that of the bottom rotor on the top rotor. The downwash velocity at the bottom rotor plane is much larger than that at the top rotor plane, and the downwash velocity at the top rotor plane is a little larger than that at an individual rotor plane. The downwash velocity and thrust coefficient both become larger when the collective angle of blades is added. When the spacing between the two coaxial rotors increases, the thrust coefficient of the top rotor increases, but the total thrust coefficient reduces a little, because the decrease of the bottom rotor thrust coefficient is larger than the increase of the top rotor thrust coefficient.
基金Supported by the National Program on Key Basic Research Project(973Program)(2012CB026000)Ph.D Programs Foundation of Ministry of Education of China(20110010110009)
文摘A control system aims at vibration reduction in a two-span rotor system with two shear mode magnetorheological （MRF） dampers is designed. A finite element model of the MRF damper- rotor system is built and used to analyze the rotor vibration characteristics. Based on Hooke and Jeeves algorithm and the numerical simulation analysis, an optimal appropriate controller is proposed and designed. Experimental results show that rotor vibration caused by unbalance is well controlled （ first critical speed region 37% , second critical speed region 42% ）. To reflect advantages of optimi- zing strategy presented and validate the intelligent optimization control technology, detailed experi- ments were developed on a two-span rotor-vibration-control platform. The influence on accuracy, rapidity and stability of optimizing control for rotor vibration are analyzed. It provides a powerful technical support for the extension and application in target and control for shafting vibration.
文摘This paper presents a method of general geometrical definitions of screw machine rotors and their manufacturing tools.It describes the details of lobe shape specification,and focuses on a new lobe profile,which yields a larger cross-sectional area and shorter sealing lines resulting in higher delivery rates for the same tip speed.A well proven mathematical model was used to determine the optimum profile,compressor housing size,and compressor ports to achieve the superior compressors.
基金supported from the National Natural Science Foundation of China (No. 11472129)the Science and Technology on Rotorcraft Aeromechanics Laboratory Foundation of China (No. 6142220050416220002)+2 种基金the Foundation of Graduate Innovation Center in NUAA of China. (No. KFJJ20170102)the Fundamental Research Funds for the Central Universities of Chinaa project funded by the Priority Academic Program Development of Jiangsu Higher Educational Institution of China
文摘Gurney Flaps(GFs) are used for improving the performance of variable speed tail rotors. A validated analytical helicopter model able to predict the main and tail rotor power is utilized. The fixed height GF has substantially small influence on the tail rotor power in hover and low to medium speed forward flight, and can obtain significant power reduction in high speed flight.This ability can be enhanced by decreasing the tail rotor speed. With the deployment of GF, the collective pitch of the tail rotor decreases, and the maximum tail rotor thrust increases. The GF can compensate the reduction of the maximum thrust by the decrease in the tail rotor speed. The GF with a height of 5% of the chord length can almost remedy 50% of the thrust reduction introduced by decreasing 10% of the tail rotor speed. With the increase of GF height, the maximum thrust generated by the tail rotor increases. The GF with larger height can cause the increase in the tail rotor power in hover and low to medium speed flight. The retractable GF can obtain more power savings than the fixed height GF. However, the benefit is substantially small even in high speed flight. Considering the side effects introduced by the active GF, the fixed height GF may be more preferable. The mechanism for the retractable GF to generate more tail rotor thrust is to increase the lift in advancing side due to the higher dynamic pressure.
文摘The nonlinear properties of rotating machinery vibration signals are presented. The relationship between faults and quadratic phase coupling is discussed. The mechanism that gives rise to quadratic phase coupling is analyzed, and the coupling models are summarized. As a result, higher order spectra analysis is introduced into fault diagnosis of rotors. A brief review of the properties of higher order spectra is presented. Furthermore, the bicoherence spectrum is employed to extract the features that signify the machinery condition. Experiments show that bicoherence spectrum patterns of different faults are quite different, so it is proposed to identify the faults in rotors.
文摘A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling.The experimental rotor system is established using a fluted disk and a speed sensor which is applied in an actual aero engine for speed measurement.Through simulating calculation and experiments,the effects of tightening torque on the dynamic characteristics of the rotor system connected by a spline coupling including critical speeds,vibration modes and unbalance responses are analyzed.The results show that when increasing the tightening torque,the first two critical speeds and the amplitudes of unbalance response gradually increase in varying degrees while the vibration modes are essentially unchanged.In addition,changing axial and circumferential positions of the mass unbalance can lead to various amplitudes of unbalance response and even the rates of change.
基金co-supported by the Equipment Pre-Research Foundation (No. 61409230204)the National Basic Research Project (No. 2017-VII-0010-0104)+2 种基金the Defense Industrial Technology Development Program (No. XXXX2018213A001)the National Natural Science Foundation of China(No. 51875475)the Key Development Program of Shaanxi Province (Nos. 2018ZDXM-GY-068 and 2016KTZDGY4-02)。
文摘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.
基金Project supported by the National High-Tech R&D Program (863) of China (No. 2007AA05Z208)the Scientific Research Foundation for Returned Scholars (No. 50706034), China
文摘The pressure increasing process within a twin screw multiphase pump, under the condition of high gas volume fractions (GVFs), induces large temperature and pressure changes that cause the rotors to deform. Rotor deformations heavily influence the backflow of the multiphase fluid through clearances within the twin screw multiphase pump and these deformations may even lead to pump failures. An accurate temperature and pressure distribution on the screw rotors need be obtained before the deformation analysis can be carried out. By means of small temperature and pressure sensors embedded into the groove at the root of the rotors, the temperatures of 12 points on the rotors and the pressure distributions of a twin screw multiphase pump under high GVFs conditions were recorded. Temperature test results were adopted to perform a heat transfer analysis for determining the temperature distribution on the screw rotors. Then deformation analyses, including thermal deformation, force deformation, and total deformation, were conducted according to the pressure and temperature distributions. Deformation analysis for different materials was also conducted under the same boundary conditions. A material was suggested for the manufacturing of rotors in a twin screw multiphase pump under the condition of high gas volume fractions.
文摘Switched reluctance motors(SRM)with full-pitch windings and segmental rotors are particularly suitable for the drive systems in aerospace environments because of low wind(oil)resistance and iron losses at high speed.In this paper,the authors have been studying electromagnetic design of this motor.
文摘The SiCp/Al-alloy composite front brake rotors designed for Shanghai Santana cars were prepared by semi-solid stirring+liquid forging process. The composite brake rotors were subjected to dynamometer tests on a SCHENCK brake testing system, referring to TL110 standard of VOLKSWAGEN Co. The friction coefficient and thermal response during fade testing and the wear performance of the composite rotors were studied as the functions of various parameters such as braking pressures, initial speeds, initial temperatures, torque and decelerations, and were compared with those of conventional cast iron rotors. The results show that the properties of the composite rotors can achieve the requirements of commercial cast iron rotors. The results also show that the friction coefficients of the composite rotors under different braking conditions are within the deviation band specified by the TL110 standard, and the temperature rise of composite rotors is lower than that of cast iron rotors at the end of each fade stop. The wear resistance of composite rotors is higher than that of cast iron rotors. The friction mechanism and wear mechanism were analyzed.
基金the financial support from the National Natural Science Foundation of China(No.52075018)the National Science and Technology Major Project of the Ministry of Science and Technology of China(Nos.2017-Ⅳ-0011-0048 and 2017-I-0008-0009)。
文摘The dynamic response of the rotor depends on not only itself but also the dynamical characteristics of the structures that support it. In this paper, the coupling vibration characteristics of the rotor and supporting structure are studied using one simple rotor-supports model firstly, and then the dynamic stiffness of the typical supporting structure of an aero-engine is investigated in use of both numerical and experimental methods. While, one simulation strategy is developed to include dynamic stiffness of realistic supports in the dynamical analysis of the rotor system. The simulated and tested results show that the dynamic stiffness of the supporting structure not only depends on the structural parameters but also is related to the frequency of the excitation force. The dynamic stiffness is affected by the damping and inertia effect when the excitation frequency is high and closed to the resonance frequency of the support, which may decrease the dynamic stiffness sharply.More resonance frequencies may be induced and the critical speed could be reduced or increased.While higher vibration response peak and overload of the bearing may also be caused by the varied dynamic stiffness, which needs to be avoided in the design of the rotor-supports system.
基金co-supported by the National Natural Science Foundation of China (Nos. 11202097 and 11472129)Aeronautical Science Foundation of China (No. 2013ZA52014)the Fundamental Research Funds for the Central Universities (No. NS2014007)
文摘To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluid- lastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to change the tuning port area ratio, which can change the tuning frequency of the isolator. A rotor model including the model of fluidlastic isolator is coupled with a fuselage model to predict the steady responses of the rotor system in forward flight. The aeroelastic analyses indicate that distinct performance improvement in pitch link load control can be achieved by the utilization of variable frequency isolators compared with the constant tuning frequency isolators. The 4/rev （per revolution） pitch link load is observed to be reduced by 87.6% compared with the increase of 56.3% by the constant frequency isolator, when the rotor speed is reduced by 16.7%. The isolation ability at different rotor speeds in different flight states is investigated. To achieve overall load reduction within the whole range of rotor speed, the strategy of the variation of tuning frequency is adjusted. The results indicate that the 4/rev pitch link load within the whole rotor speed range is decreased.
文摘The Actuator Line/Navier-Stokes model is validated against wind tunnel measurements for flows past the yawed MEXICO rotor and past the yawed NREL Phase VI rotor. The MEXICO rotor is operated at a rotational speed of 424 rpm, a pitch angle of ?2.3。, wind speeds of 10, 15, 24 m/s and yaw angles of 15。, 30。 and 45。. The computed loads as well as the velocity field behind the yawed MEXICO rotor are compared to the detailed pressure and PIV measurements which were carried out in the EU funded MEXICO project. For the NREL Phase VI rotor, computations were carried out at a rotational speed of 90.2 rpm, a pitch angle of 3。, a wind speed of 5 m/s and yaw angles of 10。and 30。. The computed loads are compared to the loads measured from pressure measurement.
文摘A sudden increase of vibration amplitude with no foreboding often results in an abrupt breakdown of a mechanical system.The catastrophe of vibration state of a faulty rotor is a typical nonlinear phenomenon,and very difficult to be described and predicted with linear vibration theory.On the basis of nonlinear vibration and catastrophe theory,fhe eatastrophe of the vibration amplitude of the faulty rotor is described;a way to predict its emergence is developed.
文摘We present an immersed array of four rotors whose promoted flow can be mathematically modeled with a creeping flow solution from the incompressible Navier-Stokes equations. We show that this solution is indeed representative of the two-dimensional experiment and validate such class of solution with experimental data obtained through the Particle Image Velocimetry technique and time-lapsed particles visualizations.
文摘Twin-rotor cylinder-embedded piston engine is proposed for dealing with the sealing problems of rotors in twin-rotor piston engine where the existent mature sealing technologies for traditional reciprocating engine can be applied.The quantity and forms of its sealing surfaces are reduced and simplified,and what's more,the advantages of twin-rotor piston engine are inherited,such as high power density and no valve mechanism.Given the motion law of two rotors,its kinematic model is established,and the general expression for some parameters related to engine performance,such as the trajectory,displacement,velocity and acceleration of the piston and centroid trajectory,angular displacement,velocity and acceleration of the rod are presented.By selecting different variation patterns of relative angle of two rotors,the relevant variables are compared.It can be concluded that by designing the relative angle function of two rotors,the volume variation of working chamber can be changed.However,a comprehensive consideration for friction and vibration is necessary because velocity and acceleration are quite different in the different functions,the swing magnitude of rod is proportional to link ratio λ,and the position of rod swing center is controlled by eccentricity e.In order to reduce the lateral force,a smaller value of λ should be selected in the case of the structure,and the value of e should be near 0.95.There is no relationship between the piston stroke and the variation process of relative angle of two rotors,the former is only proportional to the amplitude of relative angle of two rotors.
