The current paper focuses on the prediction of residual stresses and distortions in the Laser Powder Bed Fusion(LPBF)built Ti6Al4V thin-walled geometries using Ansys Additive Print(AAP)software which employs a layer-b...The current paper focuses on the prediction of residual stresses and distortions in the Laser Powder Bed Fusion(LPBF)built Ti6Al4V thin-walled geometries using Ansys Additive Print(AAP)software which employs a layer-by-layer accumulation of inherent strain to calculate the deformations.Isotropic and anisotropic strain scaling factors were calibrated initially within the APP software for the Ti6Al4V based single cantilever beam geometry.Subsequently,the numerical simulations were performed in APP software and computed the residual stresses and distortions for the varied process parameters including laser power,scan speed and hatch distance while maintaining the layer thickness constant for all the design iterations.The numerical predictions were compared;they were found to match reasonably well with the XRD measurements within the calibrated regime.展开更多
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
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
Contra-rotating turbines offer enhanced performance over their conventional corotating configurations.In addition,vaneless contra-rotating turbine stages offer lesser stage length along with improved performance.Contr...Contra-rotating turbines offer enhanced performance over their conventional corotating configurations.In addition,vaneless contra-rotating turbine stages offer lesser stage length along with improved performance.Contra-rotating turbines with a vaned LP stages offer a controlled work-split between the stages over a wider range of operating conditions by maintaining inlet swirl to the second rotor.The objective of the present work is to design an equivalent vaned contra-rotating turbine for an existing co-rotating configuration of a two-spool turbo fan engine.The contra-rotating turbine is designed by retaining the existing flow path and HP turbine,and redesigning the LP turbine for fixed radial distributions of inlet total temperature,pressure and swirl.A comparative study between performance of the co-rotating and contra-rotating turbines is carried out for different speeds.Cascade testing of the LP stator and rotor mean sections was carried out to validate the analysis.The LP stage of contra-rotating turbine exhibits a performance improvement by 2%points at design point,as per flow predictions.The reduced flow deflection in stator row is the primary reason for significant reduction in profile and secondary losses in contra-rotating turbine,which contributed to the performance improvement.A significant reduction of 23%in blade weight and 45% in LP stator vane count is obtained.展开更多
Self-lubrication is one of the smart material properties required for producing components with enhanced wear resistance and low coefficient of friction.Bidirectional(BD)satin weave polyacrylonitrile(PAN)based carbon ...Self-lubrication is one of the smart material properties required for producing components with enhanced wear resistance and low coefficient of friction.Bidirectional(BD)satin weave polyacrylonitrile(PAN)based carbon fiber(Cf)fabric preform was successfully infiltrated with Al 6061 alloy by squeeze infiltration process.The infiltrated composite shows uniform distribution of carbon fibers in the matrix with the elimination of porosities,fiber damage and close control on the formation of deleterious aluminum carbide(Al4C3)phase.Cf/Al composite exhibits remarkable wear resistance compared to unreinforced alloy due to the formation of self-lubricating tribolayer on the pin surface,which intercepts the contact of matrix metal to counter surface.The BD carbon fiber enhanced the hardness and compressive strength of the composite by restraining the plastic flow behavior of matrix.High resolution transmission electron microscopy shows the presence of Al2O3 and MgAl2O4 spinel,confirmed by EDS and SAD pattern,at the composite interface.The composite shows a lower density of 2.16 g/cm^3 which is a major ad vantage for weight reduction compared to the monolithic alloy(2.7 g/cm^3).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 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
文摘The current paper focuses on the prediction of residual stresses and distortions in the Laser Powder Bed Fusion(LPBF)built Ti6Al4V thin-walled geometries using Ansys Additive Print(AAP)software which employs a layer-by-layer accumulation of inherent strain to calculate the deformations.Isotropic and anisotropic strain scaling factors were calibrated initially within the APP software for the Ti6Al4V based single cantilever beam geometry.Subsequently,the numerical simulations were performed in APP software and computed the residual stresses and distortions for the varied process parameters including laser power,scan speed and hatch distance while maintaining the layer thickness constant for all the design iterations.The numerical predictions were compared;they were found to match reasonably well with the XRD measurements within the calibrated regime.
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Authors acknowledge GATET-GTRE,DRDO,India forthe financial assistance in this projectAuthors would like tothank Director and Head-Propulsion Division of CSIR-NAL for their support in carrying out this workAuthorsalso thank‘Turbine Group-GTRE’and Versatile Turbine Test Rig team members.
文摘Contra-rotating turbines offer enhanced performance over their conventional corotating configurations.In addition,vaneless contra-rotating turbine stages offer lesser stage length along with improved performance.Contra-rotating turbines with a vaned LP stages offer a controlled work-split between the stages over a wider range of operating conditions by maintaining inlet swirl to the second rotor.The objective of the present work is to design an equivalent vaned contra-rotating turbine for an existing co-rotating configuration of a two-spool turbo fan engine.The contra-rotating turbine is designed by retaining the existing flow path and HP turbine,and redesigning the LP turbine for fixed radial distributions of inlet total temperature,pressure and swirl.A comparative study between performance of the co-rotating and contra-rotating turbines is carried out for different speeds.Cascade testing of the LP stator and rotor mean sections was carried out to validate the analysis.The LP stage of contra-rotating turbine exhibits a performance improvement by 2%points at design point,as per flow predictions.The reduced flow deflection in stator row is the primary reason for significant reduction in profile and secondary losses in contra-rotating turbine,which contributed to the performance improvement.A significant reduction of 23%in blade weight and 45% in LP stator vane count is obtained.
文摘Self-lubrication is one of the smart material properties required for producing components with enhanced wear resistance and low coefficient of friction.Bidirectional(BD)satin weave polyacrylonitrile(PAN)based carbon fiber(Cf)fabric preform was successfully infiltrated with Al 6061 alloy by squeeze infiltration process.The infiltrated composite shows uniform distribution of carbon fibers in the matrix with the elimination of porosities,fiber damage and close control on the formation of deleterious aluminum carbide(Al4C3)phase.Cf/Al composite exhibits remarkable wear resistance compared to unreinforced alloy due to the formation of self-lubricating tribolayer on the pin surface,which intercepts the contact of matrix metal to counter surface.The BD carbon fiber enhanced the hardness and compressive strength of the composite by restraining the plastic flow behavior of matrix.High resolution transmission electron microscopy shows the presence of Al2O3 and MgAl2O4 spinel,confirmed by EDS and SAD pattern,at the composite interface.The composite shows a lower density of 2.16 g/cm^3 which is a major ad vantage for weight reduction compared to the monolithic alloy(2.7 g/cm^3).
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 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.