The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to...The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to train safety,significantly lowering the critical wind velocity.Therefore,developing strategies to enhance crosswind stability is essential.This study focuses on the leeward region adjacent to the train body,where separated flows with large vortices generate significant negative surface pressure.Enhancing this negative pressure distribution is proposed as a potential method to improve a train’s resistance to overturning.To achieve this,winglets are installed on the leeward side as a flow control measure,and their effects at different deflection angles are evaluated.The influence of five deflection angles on the leeward-side flow field and aerodynamic loads is analyzed,considering the head,middle,and tail cars.Results indicate that a deflection angle of 90°optimally reduces the overall overturning moment by 27.6%compared to the baseline model in a three-car configuration.These findings highlight that optimizing the winglet deflection angle to approximately 90°can significantly enhance a train’s resistance to overturning,offering valuable insights for aerodynamic optimization in strong wind conditions.展开更多
In this paper we discussed the development of a morphing wingtip device or winglet for aircraft.The aim of this research is enhancing the aerodynamic of aircrafts,by optimizing the winglet shape,angle and torsion,to r...In this paper we discussed the development of a morphing wingtip device or winglet for aircraft.The aim of this research is enhancing the aerodynamic of aircrafts,by optimizing the winglet shape,angle and torsion,to reduce wingtip vortices at each flight stage,reduce drag,fuel consumption and increase its endurance.The development of a working physical wingtip device with morphing functionality,is possible by using piezoelectric MFCs(Macro Fiber Composites)as actuators in wing structures.Due to their excellent properties like flexibility,light weight,tolerant to damage and long term stability MFC fit most of the requirements and specifications of morphing structures.Unfortunately,they are based on the toxic compound of PbZrxTi1-xO3(PZT).Lead-free materials can replace lead based compounds.Also,other aim of this inquiry is the development of piezoelectric lead-free compounds based on the solid solution Ba1-xCaxTi0.9Zr0.1O3(BCZT)with x=0.1,0.125,0.15.The reason for choosing these compositions is because BZCT compounds could reach a piezoelectricity coefficient d33~400 pC/N.This value is comparable with commercial PZT,therefore it is a great candidate to replace it.展开更多
The tip leakage flow has an important influence on the performance of transonic com- pressor. Blade tip winglet has been proved to be an effective method to control the tip leakage flow in compressor, while the physic...The tip leakage flow has an important influence on the performance of transonic com- pressor. Blade tip winglet has been proved to be an effective method to control the tip leakage flow in compressor, while the physical mechanisms of blade tip winglet have been poorly understood. A numerical study for a highly loaded transonic compressor rotor has been conducted to understand the effect of varying the location of blade tip wing]et on the performance of the rotor. Two kinds of tip winglet were designed and investigated. The effects of blade tip winglet on the compressor over- all performance, stability and tip flow structure were presented and discussed, It is found that the interaction of the tip winglet with the flow in the tip region is different when the winglet is located at suction-side or pressure-side of the blade tip. Results indicate that the suction-side winglet （SW） is ineffective to improve the performance of compressor rotor. In addition, a significant stall range extension equivalent to 33.74% with a very small penalty in efficiency can be obtained by the pressure-side winglet （PW）. An attempt has been made to explain the fundamental mechanisms of blade tip winglet in detail.展开更多
Installing winglets can notably improve the aerodynamic performance of solar aircraft.This paper proposes a multi-constraints optimization method of winglets for solar aircraft,aiming to enhance the corresponding unin...Installing winglets can notably improve the aerodynamic performance of solar aircraft.This paper proposes a multi-constraints optimization method of winglets for solar aircraft,aiming to enhance the corresponding uninterrupted cruising capability.An optimization objective function is formed and is separately studied in aerodynamic and structural terms.Qualitative analysis shows that the winglet design parameters are restricted by four special constraints(geometry,aerodynamics,energy and stability)of solar aircraft.The optimization process is constructed on the basis of a multi-island genetic algorithm,and carried out for a 15 m wingspan solar aircraft.Although the designed winglet is not as good as the traditional winglet in terms of drag and structural weight,the designed winglet provides a better 24 h cruising capability.The sensitivity between the objective function and the design parameters is investigated,and the winglet effects vary with respect to the wing aspect ratio(AR=10,15,19.6).The effect of the constraints is analysed quantitatively,and some basic laws are obtained.Moreover,the feasible design region and the possible optimal design parameters of winglets for different wing configurations are explored.The calculation results show that when the aspect ratio exceeds a certain value,the winglets will not benefit the aircraft.展开更多
Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with ...Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with a spacing of 2.0 mm. The flow disturbers studied include rectangular winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications, as well as square prism, triangular prism, and circular cylinder, which are used here to mimic the traditional spacer filaments for comparison of their abilities in enhancing the convective mass transfer near the membrane surface to alleviate the concentration polarization. The disturber performance was evaluated in terms of concentration polarization factor versus consumed pumping power, with a larger factor meaning a more serious concentration polarization.Calculations were carried out for Na Cl solution flow with Reynolds numbers ranging from 400 to 1000. The results show that the traditional flow disturbers can considerably reduce the concentration polarization but cause a substantial pressure drop, while the rectangular winglets can effectively reduce the concentration polarization with a much less pressure drop penalty. The rectangular winglets were optimized in geometry under equal pumping power condition.展开更多
Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:pun...Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:punched delta-and elliptical-winglets(P-DW and P-EW)with four punched-hole sizes were tested at a fixed attack angle,optimal relative pitch and height.Also,data of solid delta-and elliptical-winglets(DW and EW)were included for comparison.The investigation has shown that the P-DW yields higher thermal-performance enhancement factor(η)than the P-EW.Although the solid DW and EW with no punch have the highest heat transfer and friction loss,the PWs yield betterηthan the solid ones.For PWs,the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct,respectively but the optimumηof 2.17 is seen for the one with a certain hole size.The PWs provideηat about 5%–8%above the solid winglets.展开更多
Taking a two-stage variable-pitch axial fan as the research object,five schemes,including a single counter-flow rib layout grooved tip,are numerically simulated using the fluent software.The results indicate that,comp...Taking a two-stage variable-pitch axial fan as the research object,five schemes,including a single counter-flow rib layout grooved tip,are numerically simulated using the fluent software.The results indicate that,compared with the original blade tip,the total pressure rise and efficiency of the four proposed schemes have been improved to various degrees,with Scheme 4(groove tip with double counterflow ribs)displaying the best performances.The total pressure and efficiency are increased by 113.44 Pa and 0.955%,respectively.The blade tip leakage flow is reduced to varying degrees under different schemes,according to the following order:Scheme 1,Scheme 2,Scheme 4,and Scheme 3 leading to a reduction of 7.44%,6.46%,5.36%,and 4.35%,respectively.Steady results are used as the initial condition for the ensuing strength check and modal analysis.展开更多
基金Project(2020YFA0710903)supported by the National Key Research and Development Program of ChinaProject(2025ZZTS0623)supported by the Graduate Student Independent Innovation Project of Central South University,ChinaProject(202406370145)supported by the China Scholarship Council。
文摘The stability of high-speed trains under crosswind conditions has become a key consideration in aerodynamic design.As running speeds continue to increase and car body weight decreases,crosswinds pose a greater risk to train safety,significantly lowering the critical wind velocity.Therefore,developing strategies to enhance crosswind stability is essential.This study focuses on the leeward region adjacent to the train body,where separated flows with large vortices generate significant negative surface pressure.Enhancing this negative pressure distribution is proposed as a potential method to improve a train’s resistance to overturning.To achieve this,winglets are installed on the leeward side as a flow control measure,and their effects at different deflection angles are evaluated.The influence of five deflection angles on the leeward-side flow field and aerodynamic loads is analyzed,considering the head,middle,and tail cars.Results indicate that a deflection angle of 90°optimally reduces the overall overturning moment by 27.6%compared to the baseline model in a three-car configuration.These findings highlight that optimizing the winglet deflection angle to approximately 90°can significantly enhance a train’s resistance to overturning,offering valuable insights for aerodynamic optimization in strong wind conditions.
文摘In this paper we discussed the development of a morphing wingtip device or winglet for aircraft.The aim of this research is enhancing the aerodynamic of aircrafts,by optimizing the winglet shape,angle and torsion,to reduce wingtip vortices at each flight stage,reduce drag,fuel consumption and increase its endurance.The development of a working physical wingtip device with morphing functionality,is possible by using piezoelectric MFCs(Macro Fiber Composites)as actuators in wing structures.Due to their excellent properties like flexibility,light weight,tolerant to damage and long term stability MFC fit most of the requirements and specifications of morphing structures.Unfortunately,they are based on the toxic compound of PbZrxTi1-xO3(PZT).Lead-free materials can replace lead based compounds.Also,other aim of this inquiry is the development of piezoelectric lead-free compounds based on the solid solution Ba1-xCaxTi0.9Zr0.1O3(BCZT)with x=0.1,0.125,0.15.The reason for choosing these compositions is because BZCT compounds could reach a piezoelectricity coefficient d33~400 pC/N.This value is comparable with commercial PZT,therefore it is a great candidate to replace it.
基金co-supported by the National Natural Science Foundation of China(Nos.51436002,51406021)the Scientific Research Fund of Education Department of Liaoning Province(No.L2014197)+1 种基金the Program for Liaoning Innovative Research Team in University(No.LT2015004)the Fundamental Research Funds for the Central Universities(Nos.3132016014,3132014319)
文摘The tip leakage flow has an important influence on the performance of transonic com- pressor. Blade tip winglet has been proved to be an effective method to control the tip leakage flow in compressor, while the physical mechanisms of blade tip winglet have been poorly understood. A numerical study for a highly loaded transonic compressor rotor has been conducted to understand the effect of varying the location of blade tip wing]et on the performance of the rotor. Two kinds of tip winglet were designed and investigated. The effects of blade tip winglet on the compressor over- all performance, stability and tip flow structure were presented and discussed, It is found that the interaction of the tip winglet with the flow in the tip region is different when the winglet is located at suction-side or pressure-side of the blade tip. Results indicate that the suction-side winglet （SW） is ineffective to improve the performance of compressor rotor. In addition, a significant stall range extension equivalent to 33.74% with a very small penalty in efficiency can be obtained by the pressure-side winglet （PW）. An attempt has been made to explain the fundamental mechanisms of blade tip winglet in detail.
文摘Installing winglets can notably improve the aerodynamic performance of solar aircraft.This paper proposes a multi-constraints optimization method of winglets for solar aircraft,aiming to enhance the corresponding uninterrupted cruising capability.An optimization objective function is formed and is separately studied in aerodynamic and structural terms.Qualitative analysis shows that the winglet design parameters are restricted by four special constraints(geometry,aerodynamics,energy and stability)of solar aircraft.The optimization process is constructed on the basis of a multi-island genetic algorithm,and carried out for a 15 m wingspan solar aircraft.Although the designed winglet is not as good as the traditional winglet in terms of drag and structural weight,the designed winglet provides a better 24 h cruising capability.The sensitivity between the objective function and the design parameters is investigated,and the winglet effects vary with respect to the wing aspect ratio(AR=10,15,19.6).The effect of the constraints is analysed quantitatively,and some basic laws are obtained.Moreover,the feasible design region and the possible optimal design parameters of winglets for different wing configurations are explored.The calculation results show that when the aspect ratio exceeds a certain value,the winglets will not benefit the aircraft.
基金Supported by Tsinghua University Initiative Scientific Research Program(20131089319)
文摘Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with a spacing of 2.0 mm. The flow disturbers studied include rectangular winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications, as well as square prism, triangular prism, and circular cylinder, which are used here to mimic the traditional spacer filaments for comparison of their abilities in enhancing the convective mass transfer near the membrane surface to alleviate the concentration polarization. The disturber performance was evaluated in terms of concentration polarization factor versus consumed pumping power, with a larger factor meaning a more serious concentration polarization.Calculations were carried out for Na Cl solution flow with Reynolds numbers ranging from 400 to 1000. The results show that the traditional flow disturbers can considerably reduce the concentration polarization but cause a substantial pressure drop, while the rectangular winglets can effectively reduce the concentration polarization with a much less pressure drop penalty. The rectangular winglets were optimized in geometry under equal pumping power condition.
文摘Thermal performance of a heat exchanger duct with punched winglets(PWs)mounted on the upper duct wall has been examined for Reynolds number(Re)ranging from 4100 to 25,500.In the present experiment,two types of PWs:punched delta-and elliptical-winglets(P-DW and P-EW)with four punched-hole sizes were tested at a fixed attack angle,optimal relative pitch and height.Also,data of solid delta-and elliptical-winglets(DW and EW)were included for comparison.The investigation has shown that the P-DW yields higher thermal-performance enhancement factor(η)than the P-EW.Although the solid DW and EW with no punch have the highest heat transfer and friction loss,the PWs yield betterηthan the solid ones.For PWs,the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct,respectively but the optimumηof 2.17 is seen for the one with a certain hole size.The PWs provideηat about 5%–8%above the solid winglets.
基金This research is supported by the Fundamental Research Funds for the Central Universities(No.2021 MS121).
文摘Taking a two-stage variable-pitch axial fan as the research object,five schemes,including a single counter-flow rib layout grooved tip,are numerically simulated using the fluent software.The results indicate that,compared with the original blade tip,the total pressure rise and efficiency of the four proposed schemes have been improved to various degrees,with Scheme 4(groove tip with double counterflow ribs)displaying the best performances.The total pressure and efficiency are increased by 113.44 Pa and 0.955%,respectively.The blade tip leakage flow is reduced to varying degrees under different schemes,according to the following order:Scheme 1,Scheme 2,Scheme 4,and Scheme 3 leading to a reduction of 7.44%,6.46%,5.36%,and 4.35%,respectively.Steady results are used as the initial condition for the ensuing strength check and modal analysis.
