A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine.Three perforated-rib layouts are considered,wherein a perforated rib is installed at(A)the Suc...A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine.Three perforated-rib layouts are considered,wherein a perforated rib is installed at(A)the Suction-Side squealer(SS-rib),(B)the Pressure-Side squealer(PS-rib),and(C)the additional squealer along the blade Camber Line(CL-rib).A numerical method is used to show how the novel rib layouts affect the aerodynamic performance of the tip leakage flow.Results show that the coolant jets issuing from the perforated-rib injection holes penetrate deeper into the tip clearance than those in the baseline squealer-tip case,and how the perforated-rib coolant injection affects the tip leakage flow depends strongly on the rib layout.The PS-rib and CL-rib layouts appear promising for controlling the tip leakage flow,playing a significant role in reducing the total pressure loss and improving the turbine blade’s isentropic efficiency.In particular,under an injection mass flow ratio of 1%and a tip clearance of 1%blade span,the PS-rib layout reduces the leakage mass flow rate by 27%and increases the isentropic efficiency by 1.25%compared with those in the baseline squealer-tip case.Meanwhile,the advantages of the PS-rib layout in tip leakage control are confirmed under small and large tip clearances.展开更多
Actuator faults can be critical in turbofan engines as they can lead to stall,surge,loss of thrust and failure of speed control.Thus,fault diagnosis of gas turbine actuators has attracted considerable attention,from b...Actuator faults can be critical in turbofan engines as they can lead to stall,surge,loss of thrust and failure of speed control.Thus,fault diagnosis of gas turbine actuators has attracted considerable attention,from both academia and industry.However,the extensive literature that exists on this topic does not address identifying the severity of actuator faults and focuses mainly on actuator fault detection and isolation.In addition,previous studies of actuator fault identification have not dealt with multiple concurrent faults in real time,especially when these are accompanied by sudden failures under dynamic conditions.This study develops component-level models for fault identification in four typical actuators used in high-bypass ratio turbofan engines under both dynamic and steady-state conditions and these are then integrated with the engine performance model developed by the authors.The research results reported here present a novel method of quantifying actuator faults using dynamic effect compensation.The maximum error for each actuator is less than0.06%and 0.07%,with average computational time of less than 0.0058 s and 0.0086 s for steady-state and transient cases,respectively.These results confirm that the proposed method can accurately and efficiently identify concurrent actuator fault for an engine operating under either transient or steady-state conditions,even in the case of a sudden malfunction.The research results emonstrate the potential benefit to emergency response capabilities by introducing this method of monitoring the health of aero engines.展开更多
Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spot...Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spots,and inclusions.These defects are intricately linked to the electromagnetic effects,temperature distribution,and fluid dynamics during the melting process.The self-induced magnetic field created by the electric current,along with the axial magnetic field applied to stabilize the arc,significantly influences the solidification of titanium alloy ingots.A mathematical model optimized for the integrated analysis of multiple fields—electromagnetic,fluid,and thermal—was developed for the VAR solidification process of titanium alloys.The influence mechanism of electromagnetic field on the macroscopic solidification process of titanium alloy was investigated.The findings indicate the presence of two competing forces within the VAR molten pool,namely,thermal buoyancy and the Lorentz force.Introducing a coupled self-induced magnetic field and elevating the current to 15 kA led to an increase in the molten pool depth by 42.9%and a reduction in the thickness of the mushy zone by 25.2%.The application of a constant axial magnetic field enhances a unidirectional momentum buildup within the molten pool,thereby enhancing the flow velocity and cooling efficiency of melt.展开更多
Superalloys are commonly used in aircraft manufacturing;however,the requirements for high surface quality and machining accuracy make them difficult to machine.In this study,a hybrid electrochemical discharge process ...Superalloys are commonly used in aircraft manufacturing;however,the requirements for high surface quality and machining accuracy make them difficult to machine.In this study,a hybrid electrochemical discharge process using variable-amplitude pulses is proposed to achieve this target.In this method,electrochemical machining(ECM)and electrical discharge machining(EDM)are unified into a single process using a sequence of variable-amplitude pulses such that the machining process realizes both good surface finish and high machining accuracy.Furthermore,the machining mechanism of the hybrid electrochemical discharge process using variable-amplitude pulses is studied.The mechanism is investigated by observations of machining waveforms and machined surface.It is found that,with a high-frequency transformation between high-and low-voltage waveforms within a voltage cycle,the machining mechanism is frequently transformed from EDM to pure ECM.The critical discharge voltage is 40 V.When pulse voltages greater than 40 V are applied,the machining accuracy is good;however,the surface has defects such as numerous discharge craters.High machining accuracy is maintained when high-voltage pulses are replaced by low-voltage pulses to enhance electrochemical dissolution.The results indicate that the proposed hybrid electrochemical discharge process using variable-amplitude pulses can yield high-quality surfaces with high machining accuracy.展开更多
In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of...In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of acoustic emission(AE)signals after completing the tensile tests at ambient temperature.Using in-plane tensile at 800 and 1000°C as implementing examples,supervised recognition(K-nearest neighbor(KNN))was used to identify damage mode in real time.According to the damage identification results,four main tensile damage modes of 2D C/SiC composites were identified:matrix cracking(122.6–201 kHz),interfacial debonding(201–294.4 kHz),interfacial sliding(20.6–122.6 kHz)and fiber breaking(294.4–1000 kHz).Additionally,the damage evolution mechanisms for the 2D C/SiC composites were analyzed based on the characteristics of AE energy accumulation curve during the in-plane tensile loading at ambient and elevated temperature with oxidation.Meanwhile,the energy of various damage modes was accurately calculated by harmonic wavelet packet and the damage degree of modes could be analyzed.The identification results show that compared with previous studies,using the AE analysis method,the method has higher sensitivity and accuracy.展开更多
Dry friction damping structures are widely-used in aero-engines to mitigate vibration.The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately an...Dry friction damping structures are widely-used in aero-engines to mitigate vibration.The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately and efficiently predict the forced response of frictionally damped structures.The state-of-the-art Multi-Harmonic Balance Method(MHBM)on quasi-3D contact model in engineering cannot precisely capture the kinematics on the friction interface although the efficiency is high.The full-3D contact model can describe the constitutive relationship of the interface in a more accurate manner;however,the efficiency and convergence are not guaranteed for large-scale models.In this paper,a semi-analytical MHBM on full-3D contact model is proposed.The original Trajectory Tracking Method(TTM)for evaluating the contact force is reformulated to make the calculation more concise and the derivation of the Analytical Jacobian Matrix(AJM)feasible.Based on the chain rule of derivation,the AJM which is the core to upgrade the performance is deduced.Through a shrouded blade finite element model,the accuracy and efficiency of the proposed method are compared with both the MHBM on full-3D contact model with numerical Jacobian matrix and the MHBM on quasi-3D contact model with AJM.The results show that the AJM improves significantly the efficiency of the MHBM on full-3D contact model.The time cost of the proposed method is in the same order of magnitude as that of the MHBM on quasi-3D contact model.We also confirm that the full-3D contact model is necessary for the dynamic analyses of shrouded blades.If one uses the quasi-3D model,the estimation relative error of damping can even reach 31.8%in some cases.In addition,the AJM also brings benefits for stability analysis.It is highly recommended that engineers use the MHBM on full-3D contact model for the dynamic analysis and design of shrouded blades.展开更多
The accessory gearbox is a crucial component of the power transmission system of an aero-engine.The current design of the accessory gearbox case heavily relies on engineering experience,resulting in a bulky and heavy ...The accessory gearbox is a crucial component of the power transmission system of an aero-engine.The current design of the accessory gearbox case heavily relies on engineering experience,resulting in a bulky and heavy structure.This makes it increasingly challenging to meet the design requirements of high-power density.This work proposes a multi-objective topology optimization method based on the compromise programming method for the aero-engine accessory gearbox case.By locally thinning the gearbox case wall thickness,the case weight is reduced by 12.7%,and the maximum Mises stress is also reduced by 19.7%compared to the initial design scheme.Furthermore,the maximum vibration acceleration amplitude is reduced by 23.9%.These results provide a new solution for the lightweight design of the aero-engine accessory gearbox case.展开更多
In order to reveal the different effect mechanisms of blade sweep on the aerodynamic performance when a transonic rotor operates alone or in fan stage environment,two series of forward and backward swept rotors were d...In order to reveal the different effect mechanisms of blade sweep on the aerodynamic performance when a transonic rotor operates alone or in fan stage environment,two series of forward and backward swept rotors were designed and utilized in the first stage of the dual-stage NASA CR-120859 fan.Results show that,the influence of sweep on the single rotor and the whole stage is different,indicating swept designs for rotor alone may not be suitable for the stage operations.The distinct effect of sweep is account for the difference of the flow field characteristic and stall mechanism of the single rotor and the rotor in the stage environment.The single rotor is tip limited and its stall mechanism is shock/tip leakage vortex(TLV)interaction,whereas the fan stage is hub limited and its stall mechanism is the severe corner separation at stage hub region.For the single rotor,forward sweep increases the stall margin(SM)for all sweep schemes,while backward sweep reduces it in general.For the fan stage,however,backward swept rotor significantly increases stall margin and the stall mechanism is changed to shock/TLV interaction.On the contrary,forward sweep reduces stall margin in general.The flow mechanism is that forward sweep reduces blade loading at tip region near leading edge(LE)and causes the shock to move downstream.Both the variations improve flow field at tip region,while backward sweep exerts an opposite effect.At hub region,backward sweep reduces radial flow tendency by varying radial pressure gradient,causing reduction of corner separation at rotor hub,while forward sweep enhances corner separation.Moreover,with increasing of swept height and swept angle,the chock mass flow,peak efficiency and total pressure ratio of forward sweep are reduced in general,while an opposite effect can be found for backward sweep.展开更多
基金supported by the National Science and Technology Major Project,China(No.2017-III-0001-0025)the Interdisciplinary Innovation Foundation for Graduates at Nanjing University of Aeronautics and Astronautics in China(No.KXKCXJJ202002).
文摘A novel perforated-rib configuration is proposed for controlling the tip leakage flow at the rotor tip of an axial turbine.Three perforated-rib layouts are considered,wherein a perforated rib is installed at(A)the Suction-Side squealer(SS-rib),(B)the Pressure-Side squealer(PS-rib),and(C)the additional squealer along the blade Camber Line(CL-rib).A numerical method is used to show how the novel rib layouts affect the aerodynamic performance of the tip leakage flow.Results show that the coolant jets issuing from the perforated-rib injection holes penetrate deeper into the tip clearance than those in the baseline squealer-tip case,and how the perforated-rib coolant injection affects the tip leakage flow depends strongly on the rib layout.The PS-rib and CL-rib layouts appear promising for controlling the tip leakage flow,playing a significant role in reducing the total pressure loss and improving the turbine blade’s isentropic efficiency.In particular,under an injection mass flow ratio of 1%and a tip clearance of 1%blade span,the PS-rib layout reduces the leakage mass flow rate by 27%and increases the isentropic efficiency by 1.25%compared with those in the baseline squealer-tip case.Meanwhile,the advantages of the PS-rib layout in tip leakage control are confirmed under small and large tip clearances.
基金support by the National Natural Science Foundation of China(Grant No.52402520)。
文摘Actuator faults can be critical in turbofan engines as they can lead to stall,surge,loss of thrust and failure of speed control.Thus,fault diagnosis of gas turbine actuators has attracted considerable attention,from both academia and industry.However,the extensive literature that exists on this topic does not address identifying the severity of actuator faults and focuses mainly on actuator fault detection and isolation.In addition,previous studies of actuator fault identification have not dealt with multiple concurrent faults in real time,especially when these are accompanied by sudden failures under dynamic conditions.This study develops component-level models for fault identification in four typical actuators used in high-bypass ratio turbofan engines under both dynamic and steady-state conditions and these are then integrated with the engine performance model developed by the authors.The research results reported here present a novel method of quantifying actuator faults using dynamic effect compensation.The maximum error for each actuator is less than0.06%and 0.07%,with average computational time of less than 0.0058 s and 0.0086 s for steady-state and transient cases,respectively.These results confirm that the proposed method can accurately and efficiently identify concurrent actuator fault for an engine operating under either transient or steady-state conditions,even in the case of a sudden malfunction.The research results emonstrate the potential benefit to emergency response capabilities by introducing this method of monitoring the health of aero engines.
基金financially supported by the National Natural Science Foundation of China(Nos.52422408 and 52171031)the Excellent Youth Fund of Liaoning Natural Science Foundation(No.2023JH3/10200001)the Liaoning Xingliao Talents-Top-notch Young Talents Project(No.XLYC2203064).
文摘Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spots,and inclusions.These defects are intricately linked to the electromagnetic effects,temperature distribution,and fluid dynamics during the melting process.The self-induced magnetic field created by the electric current,along with the axial magnetic field applied to stabilize the arc,significantly influences the solidification of titanium alloy ingots.A mathematical model optimized for the integrated analysis of multiple fields—electromagnetic,fluid,and thermal—was developed for the VAR solidification process of titanium alloys.The influence mechanism of electromagnetic field on the macroscopic solidification process of titanium alloy was investigated.The findings indicate the presence of two competing forces within the VAR molten pool,namely,thermal buoyancy and the Lorentz force.Introducing a coupled self-induced magnetic field and elevating the current to 15 kA led to an increase in the molten pool depth by 42.9%and a reduction in the thickness of the mushy zone by 25.2%.The application of a constant axial magnetic field enhances a unidirectional momentum buildup within the molten pool,thereby enhancing the flow velocity and cooling efficiency of melt.
基金the National Natural Science Foundation of China(No.51705239)the Natural Science Foundation for Distinguished Young Scholars of Jiangsu Province(BK20170031)of China。
文摘Superalloys are commonly used in aircraft manufacturing;however,the requirements for high surface quality and machining accuracy make them difficult to machine.In this study,a hybrid electrochemical discharge process using variable-amplitude pulses is proposed to achieve this target.In this method,electrochemical machining(ECM)and electrical discharge machining(EDM)are unified into a single process using a sequence of variable-amplitude pulses such that the machining process realizes both good surface finish and high machining accuracy.Furthermore,the machining mechanism of the hybrid electrochemical discharge process using variable-amplitude pulses is studied.The mechanism is investigated by observations of machining waveforms and machined surface.It is found that,with a high-frequency transformation between high-and low-voltage waveforms within a voltage cycle,the machining mechanism is frequently transformed from EDM to pure ECM.The critical discharge voltage is 40 V.When pulse voltages greater than 40 V are applied,the machining accuracy is good;however,the surface has defects such as numerous discharge craters.High machining accuracy is maintained when high-voltage pulses are replaced by low-voltage pulses to enhance electrochemical dissolution.The results indicate that the proposed hybrid electrochemical discharge process using variable-amplitude pulses can yield high-quality surfaces with high machining accuracy.
基金the National Natural Science Foundation of China(Grant No.12172304)the 111 Project(Grant No.BP0719007).
文摘In this study,unsupervised and supervised pattern recognition were implemented in combination to achieve real-time health monitoring.Unsupervised recognition(k-means++)was used to label the spectral characteristics of acoustic emission(AE)signals after completing the tensile tests at ambient temperature.Using in-plane tensile at 800 and 1000°C as implementing examples,supervised recognition(K-nearest neighbor(KNN))was used to identify damage mode in real time.According to the damage identification results,four main tensile damage modes of 2D C/SiC composites were identified:matrix cracking(122.6–201 kHz),interfacial debonding(201–294.4 kHz),interfacial sliding(20.6–122.6 kHz)and fiber breaking(294.4–1000 kHz).Additionally,the damage evolution mechanisms for the 2D C/SiC composites were analyzed based on the characteristics of AE energy accumulation curve during the in-plane tensile loading at ambient and elevated temperature with oxidation.Meanwhile,the energy of various damage modes was accurately calculated by harmonic wavelet packet and the damage degree of modes could be analyzed.The identification results show that compared with previous studies,using the AE analysis method,the method has higher sensitivity and accuracy.
基金financially supported by the National Natural Science Foundation of China(Nos.52175071,91860205)the Major Projects of Aero-engines and Gas turbines(No.J2019-IV-023-0091)。
文摘Dry friction damping structures are widely-used in aero-engines to mitigate vibration.The nonlinear nature of friction and the two-dimensional in-plane motion on the contact interface bring challenges to accurately and efficiently predict the forced response of frictionally damped structures.The state-of-the-art Multi-Harmonic Balance Method(MHBM)on quasi-3D contact model in engineering cannot precisely capture the kinematics on the friction interface although the efficiency is high.The full-3D contact model can describe the constitutive relationship of the interface in a more accurate manner;however,the efficiency and convergence are not guaranteed for large-scale models.In this paper,a semi-analytical MHBM on full-3D contact model is proposed.The original Trajectory Tracking Method(TTM)for evaluating the contact force is reformulated to make the calculation more concise and the derivation of the Analytical Jacobian Matrix(AJM)feasible.Based on the chain rule of derivation,the AJM which is the core to upgrade the performance is deduced.Through a shrouded blade finite element model,the accuracy and efficiency of the proposed method are compared with both the MHBM on full-3D contact model with numerical Jacobian matrix and the MHBM on quasi-3D contact model with AJM.The results show that the AJM improves significantly the efficiency of the MHBM on full-3D contact model.The time cost of the proposed method is in the same order of magnitude as that of the MHBM on quasi-3D contact model.We also confirm that the full-3D contact model is necessary for the dynamic analyses of shrouded blades.If one uses the quasi-3D model,the estimation relative error of damping can even reach 31.8%in some cases.In addition,the AJM also brings benefits for stability analysis.It is highly recommended that engineers use the MHBM on full-3D contact model for the dynamic analysis and design of shrouded blades.
基金supported by the Chongqing Outstanding Young Scientist Fund(Grant No.CSTB2023NSCQJQX0016)the National Natural Science Foundation of China(Grant No.52322504)。
文摘The accessory gearbox is a crucial component of the power transmission system of an aero-engine.The current design of the accessory gearbox case heavily relies on engineering experience,resulting in a bulky and heavy structure.This makes it increasingly challenging to meet the design requirements of high-power density.This work proposes a multi-objective topology optimization method based on the compromise programming method for the aero-engine accessory gearbox case.By locally thinning the gearbox case wall thickness,the case weight is reduced by 12.7%,and the maximum Mises stress is also reduced by 19.7%compared to the initial design scheme.Furthermore,the maximum vibration acceleration amplitude is reduced by 23.9%.These results provide a new solution for the lightweight design of the aero-engine accessory gearbox case.
基金the supports of National Natural Science Foundation of China(No.51806174)National Science and Technology Major Project(J2019-Ⅱ-0011-0031)+1 种基金and National Natural Science Foundation of China(No.51790512)the funding from AECC Sichuan Gas Turbine Research Establishment。
文摘In order to reveal the different effect mechanisms of blade sweep on the aerodynamic performance when a transonic rotor operates alone or in fan stage environment,two series of forward and backward swept rotors were designed and utilized in the first stage of the dual-stage NASA CR-120859 fan.Results show that,the influence of sweep on the single rotor and the whole stage is different,indicating swept designs for rotor alone may not be suitable for the stage operations.The distinct effect of sweep is account for the difference of the flow field characteristic and stall mechanism of the single rotor and the rotor in the stage environment.The single rotor is tip limited and its stall mechanism is shock/tip leakage vortex(TLV)interaction,whereas the fan stage is hub limited and its stall mechanism is the severe corner separation at stage hub region.For the single rotor,forward sweep increases the stall margin(SM)for all sweep schemes,while backward sweep reduces it in general.For the fan stage,however,backward swept rotor significantly increases stall margin and the stall mechanism is changed to shock/TLV interaction.On the contrary,forward sweep reduces stall margin in general.The flow mechanism is that forward sweep reduces blade loading at tip region near leading edge(LE)and causes the shock to move downstream.Both the variations improve flow field at tip region,while backward sweep exerts an opposite effect.At hub region,backward sweep reduces radial flow tendency by varying radial pressure gradient,causing reduction of corner separation at rotor hub,while forward sweep enhances corner separation.Moreover,with increasing of swept height and swept angle,the chock mass flow,peak efficiency and total pressure ratio of forward sweep are reduced in general,while an opposite effect can be found for backward sweep.
