Smart materials,especially shape memory composites and 4D printing materials,are widely used in aerospace.Deflectors are essential equipment in wind tunnel construction.Classical deflectors are made of metal materials...Smart materials,especially shape memory composites and 4D printing materials,are widely used in aerospace.Deflectors are essential equipment in wind tunnel construction.Classical deflectors are made of metal materials and have a relatively high structural weight.The deflector made of smart material has the advantage of being lighter in weight compared to classical structure,and it could change the bending angle of the deflector structure under external excitation.In this study,the corresponding mechanical property test and finite element simulation of the smart material are carried out,and the deflector made of smart material is further studied and analyzed.Maxwell viscoelasticity model for the material is established,and relevant parameters are obtained through stress relaxation test fitting.According to relevant parameters and literature,finite element simulation of intelligent deflector structure is carried out.The pressure loss coefficient,airflow deflection angle,and velocity uniformity are studied.The numerical model of the minimum pressure loss coefficient is established with reference to the relevant data,and the formula for calculating the optimal upwind radius of the deflector is obtained.Combined with the numerical simulation results of the flow deflection angle and velocity uniformity of the flow field,it provides a reference for the selection of the size of the deflector.展开更多
Rigid barrier deflectors can effectively prevent overspilling landslides,and can satisfy disaster prevention requirements.However,the mechanisms of interaction between natural granular flow and rigid barrier deflector...Rigid barrier deflectors can effectively prevent overspilling landslides,and can satisfy disaster prevention requirements.However,the mechanisms of interaction between natural granular flow and rigid barrier deflectors require further investigation.To date,few studies have investigated the impact of deflectors on controlling viscous debris flows for geological disaster prevention.To investigate the effect of rigid barrier deflectors on impact mechanisms,a numerical model using the smoothed particle hydrodynamics(SPH)method with the Herschel–Bulkley model is proposed to simulate the interaction between natural viscous flow and single/dual barriers with and without deflectors.This model was validated using laboratory flume test data from the literature.Then,the model was used to investigate the influence of the deflector angle and multi-barrier arrangements.The optimal configuration of multi-barriers was analyzed with consideration to the barrier height and distance between the barriers,because these metrics have a significant impact on the viscous flow pile-up,run-up,and overflow mechanisms.The investigation considered the energy dissipation process,retention efficiency,and dead-zone formation.Compared with bare barriers with similar geometric characteristics and spatial distribution,rigid barriers with deflectors exhibit superior effectiveness in preventing the overflow and overspilling of viscous debris flow.Recommendations for the rational design of deflectors and the optimal arrangement of multi-barriers are provided to mitigate geological disasters.展开更多
The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In th...The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.展开更多
Aiming to mitigate the aerodynamic lift force imbalance between pantograph strips,which exacerbates wear and affects the current collection performance of the pantograph-catenary system,a study has been conducted to s...Aiming to mitigate the aerodynamic lift force imbalance between pantograph strips,which exacerbates wear and affects the current collection performance of the pantograph-catenary system,a study has been conducted to support the beam deflector optimization using a combination of experimental measurements and computational fluid dynamics(CFD)simulations.The results demonstrate that the size,position,and installation orientation of the wind deflectors significantly influence the amount of force compensation.They also indicate that the front strip deflectors should be installed downwards and the rear strip deflectors upwards,thereby forming a“π”shape.Moreover,the lift force compensation provided by the wind deflectors increases with the size of the deflector.Alternative wind compensation strategies,such as control circuits,are also discussed,putting emphasis on the pros and cons of various pantograph types and wind compensation approaches.展开更多
In view of the complicated structure of the deflector-jet mechanism,a mathematical model based on the turbulent jet flow theory in the deflector-jet amplifier is proposed.Considering the energy transformation and mome...In view of the complicated structure of the deflector-jet mechanism,a mathematical model based on the turbulent jet flow theory in the deflector-jet amplifier is proposed.Considering the energy transformation and momentum variation,an equation of the flow velocity distribution at the key fluid region is established to describe the morphological changes of the fluid when it passes through the deflector and jets into the receiver.Moreover,the process is segmented into four stages.According to the research results,the oil enters the deflector and impinges with the side wall.Then one part of the oil＇s flow velocity decreases and a high pressure zone is formed by the oil accumulation,the other part of the oil reverses out of the deflector along the side wall.Prior to entering the receiver,the flow is a kind of plane impinging jet.Virtually,the working pressure of the receiver is generated by the impact force,while the high speed fluid flows out of the receiver and forms a violent vortex,which generates negative pressure and causes the oil to be gasified.Compared with the numerical simulation results,the turbulent jet model that can effectively describe the characteristics of the deflector-jet mechanism is accurate.In addition,the calculation results of the prestage pressure characteristic have been verified by experiments.展开更多
Inspired by the fact that bogies and bottom equipment generally contribute a great deal of aerodynamic drag to high-speed trains,this paper puts forward a simple method of mounting some small deflectors before and/or ...Inspired by the fact that bogies and bottom equipment generally contribute a great deal of aerodynamic drag to high-speed trains,this paper puts forward a simple method of mounting some small deflectors before and/or after the bogie cabins to optimize the underbody flow and reduce the aerodynamic drag of high-speed trains.The flow fields of the high-speed train models with and without bottom deflectors are numerically studied by the IDDES method.The effectiveness and further mechanism of the bottom deflectors on aerodynamic drag reduction are analyzed.It is demonstrated that the bottom deflectors could guide the underbody flow to the ground and prevent it from hitting on the bogies and bottom equipment of the train,resulting in a significant aerodynamic drag reduction effect.Moreover,the effects of different mounting locations of bottom deflectors on drag reduction are discussed as well,and an optimal mounting configuration with a drag reduction effect of up to about 12%is finally obtained.Nevertheless,the mounted deflector is also proved capable of significantly reducing the interference range of the underbody flow and reducing the slipstream of the train,which possesses a higher guarantee for the safety of railway workers and passengers waiting on the platforms.This work provides a new idea for aerodynamic drag reduction of high-speed trains,and is of great significance in energy conservation and consumption reduction.展开更多
The process of the gas jet from aircraft engines impacting a jet blast deflector is not only a complex fluid–solid coupling problem that is not easy to compute, but also a safety issue that seriously interferes with ...The process of the gas jet from aircraft engines impacting a jet blast deflector is not only a complex fluid–solid coupling problem that is not easy to compute, but also a safety issue that seriously interferes with flight deck envi?ronment. The computational fluid dynamics(CFD) method is used to simulate numerically the impact e ect of gas jet from aircraft engines on a jet blast deflector by using the Reynolds?averaged Navier?Stokes(RANS) equations and turbulence models. First of all, during the pre?processing of numerical computation, a sub?domains hybrid meshing scheme is adopted to reduce mesh number and improve mesh quality. Then, four di erent turbulence models includ?ing shear?stress transport(SST) k-w, standard k-w, standard k-ε and Reynolds stress model(RSM) are used to compare and verify the correctness of numerical methods for gas jet from a single aircraft engine. The predicted values are in good agreement with the experimental data, and the distribution and regularity of shock wave, velocity, pressure and temperature of a single aircraft engine are got. The results show that SST k?w turbulence model is more suitable for the numerical simulation of compressible viscous gas jet with high prediction accuracy. Finally, the impact e ect of gas jet from two aircraft engines on a jet blast deflector is analyzed based on the above numerical method, not only the flow parameters of gas jet and the interaction regularity between gas jet and the jet blast deflector are got, but also the thermal shock properties and dynamic impact characteristics of gas jet impacting the jet blast deflector are got. So the dangerous activity area of crew and equipments on the flight deck can be predicted qualitatively and quantitatively. The proposed research explores out a correct numerical method for the fluid–solid interaction during the impact process of supersonic gas jet, which provides an e ective technical support for design, thermal ablation and structural damage analysis of a new jet blast deflector.展开更多
In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the...In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.展开更多
This paper studies the four-engine liquid rocket flow field during the launching phase.Using threedimensional compressible Navier-Stokes equations and two-equation realizable k-epsilon turbulence model,an impact model...This paper studies the four-engine liquid rocket flow field during the launching phase.Using threedimensional compressible Navier-Stokes equations and two-equation realizable k-epsilon turbulence model,an impact model is established and flow fields of plume impinging on the two different shapes of flame deflectors,including wedge-shaped flame deflector and cone-shaped flame deflector,are calculated.The finite-rate chemical kinetics is used to track chemical reactions.The simulation results show that afterburning mainly occurs in the mixed layer.And the region of peak pressure occurs directly under the rocket nozzle,which is the result of the direct impact of exhaust plume.Compared with the wedgeshaped flame deflector,the cone-shaped flame deflector has great performance on guiding exhaust gas.The wedge-shaped and cone-shaped flame deflectors guide the supersonic exhaust plume away from the impingement point with two directions and circumferential direction,respectively.The maximum pressure and temperature on the wedge-shaped flame deflector surface are 37.2%and 9.9%higher than those for the cone-shaped flame deflector.The results provide engineering guidance and theoretical significance for design in flame deflector of the launch platforms.展开更多
Beam deflectors are important optical elements which can control the propagation direction of the beam in free space.However,with the development of miniaturization of the optical systems,conventional reflector-based ...Beam deflectors are important optical elements which can control the propagation direction of the beam in free space.However,with the development of miniaturization of the optical systems,conventional reflector-based mechanical beam deflectors confront a huge challenge due to their large sizes and incompatibility to the device integration.Here we propose an all-dielectric flat metasurface beam deflector which is composed of a single layer array of TiO_2 nanoantennas resting on a fused-silica substrate.Numerical simulations are performed to demonstrate that the proposed deflectors are able to efficiently deflect the incident beam for different angles with transmission efficiency higher than 80%at visible frequencies.This ultrathin all-dielectric metasurface deflector may have great potential applications in integrated optics.展开更多
The woven textile sandwich composite（WTSC） is a promising lightweight composite.In bending,two competing core shearing failure modes reduce the strength;deflection induced by the core shearing deformation reduces th...The woven textile sandwich composite（WTSC） is a promising lightweight composite.In bending,two competing core shearing failure modes reduce the strength;deflection induced by the core shearing deformation reduces the flexural rigidity.To replace a solid composite laminate,the span of WTSC panel must be greater than a critical value,which was deduced on the condition that the load capacity and flexural rigidity of the WTSC panel are equal to those of the composite laminate.Three WTSC panels were tested in bending,so that the failure modes were observed,and the critical spans were determined.Using the alternative design method,the WTSC based wind deflector with reduced weight has been fabricated and mounted on the CRH（China Railway High-speed）.展开更多
The cooling process of cooling water is veryimportant in power generation industry.The performanceof cooling towers has a great effect on security,stabilityand economy of power plants.The energy savingproblems of the ...The cooling process of cooling water is veryimportant in power generation industry.The performanceof cooling towers has a great effect on security,stabilityand economy of power plants.The energy savingproblems of the cooling tower have always beenneglected previously.With the aim of energy saving inthe power plants nowadays,improving the coolingefficiency of the cooling tower has important andpractical significance.展开更多
A new flow field mathematical model is proposed to describe accurately the flow field structure and calculate the static characteristics of the pilot stage in a deflector jet servo valve(DJSV). The flow field is divid...A new flow field mathematical model is proposed to describe accurately the flow field structure and calculate the static characteristics of the pilot stage in a deflector jet servo valve(DJSV). The flow field is divided into five regions, a 3D turbulent jet is adopted to describe the free jet region, and a velocity distribution expression of the jet is proposed. The jet entrainment model is put forward in the pressure recovery region to describe the coupling relationship between the pressure in the receiving chamber and the jet flow. The static characteristics, including pressure-flow characteristics, pressure characteristics,and flow characteristics of the pilot stage are obtained. The flow field structure and the static characteristics are verified by finite element analysis(FEA) and experiment, respectively, and the mathematical model results are in good agreement with the experimental and simulation results.展开更多
We developed high-speed time-domain (TD) en face optical coherence tomography (OCT) system using KTN optical beam deflector. The KTN optical beam deflector operates at a high repetition rate of 200 kHz with a fairly l...We developed high-speed time-domain (TD) en face optical coherence tomography (OCT) system using KTN optical beam deflector. The KTN optical beam deflector operates at a high repetition rate of 200 kHz with a fairly large beam deflection angle. We proposed a high-speed en face OCT system that used a KTN optical deflector as the sample beam scanning. In the experiment, we obtained en face OCT images of human fingerprint with a frame rate of 800 fps, which is the fastest speed obtained by a TD-OCT imaging. Furthermore, a 3D-OCT image was also obtained at 0.2 s (=5 volumes/s) by our imaging system.展开更多
In order to obtain uniform exposure in variably shaped electron beam lithography,the beam current density and edge resolution on the target must not change for different spotshapes and sizes.The key to the goal is the...In order to obtain uniform exposure in variably shaped electron beam lithography,the beam current density and edge resolution on the target must not change for different spotshapes and sizes.The key to the goal is the appropriate design of shaping deflectors.A linearand rotation compensation approach is presented.Values of linear and rotation compensationfactors versus the distances between electron source image and centers of deflectors are measuredon an experimental electron beam column with variable spot shaping.The experimental resultsare in good agreement with the calculated ones.展开更多
Analytical expressions are given for computing the magnetic potential and charac-teristic functions produced by the non-radial deflectors.These expressions are useful for designingthe defiectors such as those used in ...Analytical expressions are given for computing the magnetic potential and charac-teristic functions produced by the non-radial deflectors.These expressions are useful for designingthe defiectors such as those used in the color picture tubes and the electron beam lithographysystem.The computing results are in agreement with the measured values.展开更多
When the spacecraft flies much faster than the sound speed (~1200 km/h), the airflow disturbances deflected forward from the spacecraft cannot get away from the spacecraft and form a shock wave in front of it. Shock w...When the spacecraft flies much faster than the sound speed (~1200 km/h), the airflow disturbances deflected forward from the spacecraft cannot get away from the spacecraft and form a shock wave in front of it. Shock waves have been a detriment for the development of supersonic aircrafts, which have to overcome high wave drag and surface heating from additional friction. Shock wave also produces sonic booms. The noise issue raises environmental concerns, which have precluded routine supersonic flight over land. Therefore, mitigation of shock wave is essential to advance the development of supersonic aircrafts. A plasma mitigation technique is studied. A theory is presented to show that shock wave structure can be modified via flow deflection. Symmetrical deflection evades the need of exchanging the transverse momentum between the flow and the deflector. The analysis shows that the plasma generated in front of the model can effectively deflect the incoming flow. A non-thermal air plasma, generated by on-board 60 Hz periodic electric arc discharge in front of a wind tunnel model, was applied as a plasma deflector for shock wave mitigation technique. The experiment was conducted in a Mach 2.5 wind tunnel. The results show that the air plasma was generated symmetrically in front of the wind tunnel model. With increasing discharge intensity, the plasma deflector transforms the shock from a welldefined attached shock into a highly curved shock structure with increasing standoff distance from the model;this curved shock has increased shock angle and also appears in increasingly diffused form. In the decay of the discharge intensity, the shock front is first transformed back to a well-defined curve shock, which moves downstream to become a perturbed oblique shock;the baseline shock front then reappears as the discharge is reduced to low level again. The experimental observations confirm the theory. The steady of the incoming flow during the discharge cycle is manifested by the repeat of the baseline shock front.展开更多
The purpose of the present study was to establish a passive flow control method for a rectangular jet using two types of deflectors installed symmetrically inside a nozzle. This deflector in a rectangular nozzle gener...The purpose of the present study was to establish a passive flow control method for a rectangular jet using two types of deflectors installed symmetrically inside a nozzle. This deflector in a rectangular nozzle generates the rectangular coaxial jets. The effect of the slant angle of the deflectors on the flow characteristics and the spread of the rectangular jet was investigated experimentally and by large-eddy simulation. The experiment and the numerical simulation were carried out at a Reynolds number of 9000. The rectangular jet with no deflectors generates a vortex ring from the nozzle exit. The vortex ring collapses in the downstream region and the outline of the jet changes from rectangular to diamond-shaped as a result of the axis-switching phenomenon. The rectangular jet with divergent and convergent deflectors shows particularly noticeable changes in the flow characteristics and vortical structures, as compared to the case with no deflectors. In the case of the rectangular jet with divergent deflectors (slant angle of <i style="font-family:" font-size:13.3333px;white-space:normal;"="">α</i><span style="font-family:" font-size:13.3333px;white-space:normal;"=""> = 6<span style="white-space:nowrap;">°</span>), minor axis spread is promoted more than major axis spread, and axis switching occurs closer to the nozzle exit than that in the case of no deflectors. The outline of the jet also changes from lateral rectangular to vertical rectangular as a result of axis switching. On the other hand, in the case of a rectangular jet with convergent deflectors (</span><i style="font-family:" font-size:13.3333px;white-space:normal;"="">α</i><span style="font-family:" font-size:13.3333px;white-space:normal;"=""> = -6<span style="white-space:nowrap;">°</span>), minor axis spread is suppressed more than major axis spread, and axis switching occurs farther from the nozzle exit than that in the case with no deflectors. The outline of the jet does not change until the downstream region. Therefore, the spread and the axis-switching location for the rectangular jet can be controlled by the deflectors inside the rectangular nozzle.</span>展开更多
X-ray free-electron lasers(FELs)are cutting-edge research instruments employed in multiple scientific fields capable of analyzing matter with unprecedented time and spatial resolutions.Timeresolved measurements of ele...X-ray free-electron lasers(FELs)are cutting-edge research instruments employed in multiple scientific fields capable of analyzing matter with unprecedented time and spatial resolutions.Timeresolved measurements of electron and photon beams are essential in X-ray FELs.Radiofrequency(RF)transverse deflecting structures(TDSs)with a fixed streaking direction are standard diagnostics to measure the temporal properties of the electron beams.If placed after the undulator of the FEL facility,TDSs can also be employed to reconstruct the power profile of the FEL pulses.We present measurements of an X-band RF TDS system with variable polarization with a resolution below one femtosecond.We show FEL power profile measurements with associated root mean square pulse durations as short as 300 attoseconds.The measurements have been carried out at Athos,the soft X-ray beamline of SwissFEL.Measurements with variable polarization and attosecond resolution are essential to characterize and optimize the electron beams in all its dimensions for all types of X-ray FEL experiments,in particular for ultrafast X-ray applications.展开更多
A novel electro-optic deflector based on a quadratic electro-optical potassium lithium tantalate niobate(KLTN)crystal operating slightly above the ferroelectric phase transition is presented.The new deflection scheme ...A novel electro-optic deflector based on a quadratic electro-optical potassium lithium tantalate niobate(KLTN)crystal operating slightly above the ferroelectric phase transition is presented.The new deflection scheme was based on the electric field gradient generation along the vertical axis caused by the trapezoidal geometry of the crystal.A deflection angle of 6.5 mrad was attained for a low voltage of 680 V.The deflector was used as an electro-optic modulator for implementing active Q-switching in a thulium-doped yttrium lithium fluoride(Tm:YLF)laser(1880 nm).The laser was operated at three different repetition rates of 0.4,0.5 and 0.7 kHz,and reached high energies per pulse up to 6.9 mJ.展开更多
文摘Smart materials,especially shape memory composites and 4D printing materials,are widely used in aerospace.Deflectors are essential equipment in wind tunnel construction.Classical deflectors are made of metal materials and have a relatively high structural weight.The deflector made of smart material has the advantage of being lighter in weight compared to classical structure,and it could change the bending angle of the deflector structure under external excitation.In this study,the corresponding mechanical property test and finite element simulation of the smart material are carried out,and the deflector made of smart material is further studied and analyzed.Maxwell viscoelasticity model for the material is established,and relevant parameters are obtained through stress relaxation test fitting.According to relevant parameters and literature,finite element simulation of intelligent deflector structure is carried out.The pressure loss coefficient,airflow deflection angle,and velocity uniformity are studied.The numerical model of the minimum pressure loss coefficient is established with reference to the relevant data,and the formula for calculating the optimal upwind radius of the deflector is obtained.Combined with the numerical simulation results of the flow deflection angle and velocity uniformity of the flow field,it provides a reference for the selection of the size of the deflector.
基金supported by the National Natural Science Foundation of China(Grant Nos.42120104008 and 42207198).
文摘Rigid barrier deflectors can effectively prevent overspilling landslides,and can satisfy disaster prevention requirements.However,the mechanisms of interaction between natural granular flow and rigid barrier deflectors require further investigation.To date,few studies have investigated the impact of deflectors on controlling viscous debris flows for geological disaster prevention.To investigate the effect of rigid barrier deflectors on impact mechanisms,a numerical model using the smoothed particle hydrodynamics(SPH)method with the Herschel–Bulkley model is proposed to simulate the interaction between natural viscous flow and single/dual barriers with and without deflectors.This model was validated using laboratory flume test data from the literature.Then,the model was used to investigate the influence of the deflector angle and multi-barrier arrangements.The optimal configuration of multi-barriers was analyzed with consideration to the barrier height and distance between the barriers,because these metrics have a significant impact on the viscous flow pile-up,run-up,and overflow mechanisms.The investigation considered the energy dissipation process,retention efficiency,and dead-zone formation.Compared with bare barriers with similar geometric characteristics and spatial distribution,rigid barriers with deflectors exhibit superior effectiveness in preventing the overflow and overspilling of viscous debris flow.Recommendations for the rational design of deflectors and the optimal arrangement of multi-barriers are provided to mitigate geological disasters.
基金Project(2020YFA0710901)supported by the National Key Research and Development Program of ChinaProject(2023JJ30643)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(12372204)supported by the National Natural Science Foundation of ChinaProject(2022ZZTS0725)supported by the Self-exploration and Innovation Project for Postgraduates of Central South University,China。
文摘The complex structure of the bottom of a high-speed train is an important source of train aerodynamic drag.Thus,improving the bottom structure is of great significance to reduce the aerodynamic drag of the train.In this study,computational fluid dynamics(CFD)based on three-dimensional steady incompressible Reynolds-average Naiver-Stokes(RANS)equations and Realizable k-εturbulence model were utilized for numerical simulations.Inspired by the concept of streamlined design and the idea of bottom flow field control,this study iteratively designed the bogies in a streamlined shape and combined them with the bottom deflectors to investigate the joint drag reduction mechanism.Three models,i.e.,single-bogie model,simplified train model,and eight-car high-speed train model,were created and their aerodynamic characteristics were analyzed.The results show that the single-bogie model with streamlined design shows a noticeable drag reduction,whose power bogie and trailer bogie experience 13.92%and 7.63%drag reduction,respectively.The range of positive pressure area on the bogie is reduced.The aerodynamic drag can be further reduced to 15.01%by installing both the streamlined bogie and the deflector on the simplified train model.When the streamlined bogies and deflectors are used on the eight-car model together,the total drag reduction rate reaches 2.90%.Therefore,the proposed aerodynamic kit for the high-speed train bottom is capable to improve the flow structure around the bogie regions,reduce the bottom flow velocity,and narrow the scope of the train’s influence on the surrounding environment,achieving the appreciable reduction of aerodynamic drag.This paper can provide a new idea for the drag reduction of high-speed trains.
文摘Aiming to mitigate the aerodynamic lift force imbalance between pantograph strips,which exacerbates wear and affects the current collection performance of the pantograph-catenary system,a study has been conducted to support the beam deflector optimization using a combination of experimental measurements and computational fluid dynamics(CFD)simulations.The results demonstrate that the size,position,and installation orientation of the wind deflectors significantly influence the amount of force compensation.They also indicate that the front strip deflectors should be installed downwards and the rear strip deflectors upwards,thereby forming a“π”shape.Moreover,the lift force compensation provided by the wind deflectors increases with the size of the deflector.Alternative wind compensation strategies,such as control circuits,are also discussed,putting emphasis on the pros and cons of various pantograph types and wind compensation approaches.
基金Project supported by the International Science and Technology Cooperation Program of China(Grant No.2012DFG71490)
文摘In view of the complicated structure of the deflector-jet mechanism,a mathematical model based on the turbulent jet flow theory in the deflector-jet amplifier is proposed.Considering the energy transformation and momentum variation,an equation of the flow velocity distribution at the key fluid region is established to describe the morphological changes of the fluid when it passes through the deflector and jets into the receiver.Moreover,the process is segmented into four stages.According to the research results,the oil enters the deflector and impinges with the side wall.Then one part of the oil＇s flow velocity decreases and a high pressure zone is formed by the oil accumulation,the other part of the oil reverses out of the deflector along the side wall.Prior to entering the receiver,the flow is a kind of plane impinging jet.Virtually,the working pressure of the receiver is generated by the impact force,while the high speed fluid flows out of the receiver and forms a violent vortex,which generates negative pressure and causes the oil to be gasified.Compared with the numerical simulation results,the turbulent jet model that can effectively describe the characteristics of the deflector-jet mechanism is accurate.In addition,the calculation results of the prestage pressure characteristic have been verified by experiments.
基金supported by the National Key Research&Development Projects(Grant No.2017YFB0202801)the Strategic Priority Research Program of the Chinese Academy of Sciences(class B)(Grant No.XDB22020000)Research project of Chinese Academy of Sciences(Grant No.XXH13506-204).
文摘Inspired by the fact that bogies and bottom equipment generally contribute a great deal of aerodynamic drag to high-speed trains,this paper puts forward a simple method of mounting some small deflectors before and/or after the bogie cabins to optimize the underbody flow and reduce the aerodynamic drag of high-speed trains.The flow fields of the high-speed train models with and without bottom deflectors are numerically studied by the IDDES method.The effectiveness and further mechanism of the bottom deflectors on aerodynamic drag reduction are analyzed.It is demonstrated that the bottom deflectors could guide the underbody flow to the ground and prevent it from hitting on the bogies and bottom equipment of the train,resulting in a significant aerodynamic drag reduction effect.Moreover,the effects of different mounting locations of bottom deflectors on drag reduction are discussed as well,and an optimal mounting configuration with a drag reduction effect of up to about 12%is finally obtained.Nevertheless,the mounted deflector is also proved capable of significantly reducing the interference range of the underbody flow and reducing the slipstream of the train,which possesses a higher guarantee for the safety of railway workers and passengers waiting on the platforms.This work provides a new idea for aerodynamic drag reduction of high-speed trains,and is of great significance in energy conservation and consumption reduction.
基金Supported by National Natural Science Foundation of China(Grant No.51505491)Shandong Provincial Natural Science Foundation of China(Grant No.ZR2014EEP019)
文摘The process of the gas jet from aircraft engines impacting a jet blast deflector is not only a complex fluid–solid coupling problem that is not easy to compute, but also a safety issue that seriously interferes with flight deck envi?ronment. The computational fluid dynamics(CFD) method is used to simulate numerically the impact e ect of gas jet from aircraft engines on a jet blast deflector by using the Reynolds?averaged Navier?Stokes(RANS) equations and turbulence models. First of all, during the pre?processing of numerical computation, a sub?domains hybrid meshing scheme is adopted to reduce mesh number and improve mesh quality. Then, four di erent turbulence models includ?ing shear?stress transport(SST) k-w, standard k-w, standard k-ε and Reynolds stress model(RSM) are used to compare and verify the correctness of numerical methods for gas jet from a single aircraft engine. The predicted values are in good agreement with the experimental data, and the distribution and regularity of shock wave, velocity, pressure and temperature of a single aircraft engine are got. The results show that SST k?w turbulence model is more suitable for the numerical simulation of compressible viscous gas jet with high prediction accuracy. Finally, the impact e ect of gas jet from two aircraft engines on a jet blast deflector is analyzed based on the above numerical method, not only the flow parameters of gas jet and the interaction regularity between gas jet and the jet blast deflector are got, but also the thermal shock properties and dynamic impact characteristics of gas jet impacting the jet blast deflector are got. So the dangerous activity area of crew and equipments on the flight deck can be predicted qualitatively and quantitatively. The proposed research explores out a correct numerical method for the fluid–solid interaction during the impact process of supersonic gas jet, which provides an e ective technical support for design, thermal ablation and structural damage analysis of a new jet blast deflector.
基金supported by the National Key Technology R&D Program(No.2013BAD13B03)the Key R&D Project from Science and Technology Department of Zhejiang Province(Nos.2018C02026,2018C02040)+1 种基金the National Natural Science Foundation of China(No.31072246)the Fundamental Research Funds for the Central Universities(No.201564020)
文摘In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.
文摘This paper studies the four-engine liquid rocket flow field during the launching phase.Using threedimensional compressible Navier-Stokes equations and two-equation realizable k-epsilon turbulence model,an impact model is established and flow fields of plume impinging on the two different shapes of flame deflectors,including wedge-shaped flame deflector and cone-shaped flame deflector,are calculated.The finite-rate chemical kinetics is used to track chemical reactions.The simulation results show that afterburning mainly occurs in the mixed layer.And the region of peak pressure occurs directly under the rocket nozzle,which is the result of the direct impact of exhaust plume.Compared with the wedgeshaped flame deflector,the cone-shaped flame deflector has great performance on guiding exhaust gas.The wedge-shaped and cone-shaped flame deflectors guide the supersonic exhaust plume away from the impingement point with two directions and circumferential direction,respectively.The maximum pressure and temperature on the wedge-shaped flame deflector surface are 37.2%and 9.9%higher than those for the cone-shaped flame deflector.The results provide engineering guidance and theoretical significance for design in flame deflector of the launch platforms.
基金supported in part by the National Natural Science Foundation of China under Grant (61575092)support from the Thousand Talents Program for Young Professionals,Collaborative Innovations Center of Advanced Microstructures
文摘Beam deflectors are important optical elements which can control the propagation direction of the beam in free space.However,with the development of miniaturization of the optical systems,conventional reflector-based mechanical beam deflectors confront a huge challenge due to their large sizes and incompatibility to the device integration.Here we propose an all-dielectric flat metasurface beam deflector which is composed of a single layer array of TiO_2 nanoantennas resting on a fused-silica substrate.Numerical simulations are performed to demonstrate that the proposed deflectors are able to efficiently deflect the incident beam for different angles with transmission efficiency higher than 80%at visible frequencies.This ultrathin all-dielectric metasurface deflector may have great potential applications in integrated optics.
基金Project supported by the National Natural Science Foundation of China(Nos.11172089 and 11372095)the State Key Laboratory of Mechanics and Control of Mechanical Structures(Nos.MCMS-0212G01 and MCMS-0215G01)
文摘The woven textile sandwich composite（WTSC） is a promising lightweight composite.In bending,two competing core shearing failure modes reduce the strength;deflection induced by the core shearing deformation reduces the flexural rigidity.To replace a solid composite laminate,the span of WTSC panel must be greater than a critical value,which was deduced on the condition that the load capacity and flexural rigidity of the WTSC panel are equal to those of the composite laminate.Three WTSC panels were tested in bending,so that the failure modes were observed,and the critical spans were determined.Using the alternative design method,the WTSC based wind deflector with reduced weight has been fabricated and mounted on the CRH（China Railway High-speed）.
文摘The cooling process of cooling water is veryimportant in power generation industry.The performanceof cooling towers has a great effect on security,stabilityand economy of power plants.The energy savingproblems of the cooling tower have always beenneglected previously.With the aim of energy saving inthe power plants nowadays,improving the coolingefficiency of the cooling tower has important andpractical significance.
基金supported by the National Natural Science Foundation of China (Nos. 51775383 and 52175059)。
文摘A new flow field mathematical model is proposed to describe accurately the flow field structure and calculate the static characteristics of the pilot stage in a deflector jet servo valve(DJSV). The flow field is divided into five regions, a 3D turbulent jet is adopted to describe the free jet region, and a velocity distribution expression of the jet is proposed. The jet entrainment model is put forward in the pressure recovery region to describe the coupling relationship between the pressure in the receiving chamber and the jet flow. The static characteristics, including pressure-flow characteristics, pressure characteristics,and flow characteristics of the pilot stage are obtained. The flow field structure and the static characteristics are verified by finite element analysis(FEA) and experiment, respectively, and the mathematical model results are in good agreement with the experimental and simulation results.
文摘We developed high-speed time-domain (TD) en face optical coherence tomography (OCT) system using KTN optical beam deflector. The KTN optical beam deflector operates at a high repetition rate of 200 kHz with a fairly large beam deflection angle. We proposed a high-speed en face OCT system that used a KTN optical deflector as the sample beam scanning. In the experiment, we obtained en face OCT images of human fingerprint with a frame rate of 800 fps, which is the fastest speed obtained by a TD-OCT imaging. Furthermore, a 3D-OCT image was also obtained at 0.2 s (=5 volumes/s) by our imaging system.
文摘In order to obtain uniform exposure in variably shaped electron beam lithography,the beam current density and edge resolution on the target must not change for different spotshapes and sizes.The key to the goal is the appropriate design of shaping deflectors.A linearand rotation compensation approach is presented.Values of linear and rotation compensationfactors versus the distances between electron source image and centers of deflectors are measuredon an experimental electron beam column with variable spot shaping.The experimental resultsare in good agreement with the calculated ones.
文摘Analytical expressions are given for computing the magnetic potential and charac-teristic functions produced by the non-radial deflectors.These expressions are useful for designingthe defiectors such as those used in the color picture tubes and the electron beam lithographysystem.The computing results are in agreement with the measured values.
文摘When the spacecraft flies much faster than the sound speed (~1200 km/h), the airflow disturbances deflected forward from the spacecraft cannot get away from the spacecraft and form a shock wave in front of it. Shock waves have been a detriment for the development of supersonic aircrafts, which have to overcome high wave drag and surface heating from additional friction. Shock wave also produces sonic booms. The noise issue raises environmental concerns, which have precluded routine supersonic flight over land. Therefore, mitigation of shock wave is essential to advance the development of supersonic aircrafts. A plasma mitigation technique is studied. A theory is presented to show that shock wave structure can be modified via flow deflection. Symmetrical deflection evades the need of exchanging the transverse momentum between the flow and the deflector. The analysis shows that the plasma generated in front of the model can effectively deflect the incoming flow. A non-thermal air plasma, generated by on-board 60 Hz periodic electric arc discharge in front of a wind tunnel model, was applied as a plasma deflector for shock wave mitigation technique. The experiment was conducted in a Mach 2.5 wind tunnel. The results show that the air plasma was generated symmetrically in front of the wind tunnel model. With increasing discharge intensity, the plasma deflector transforms the shock from a welldefined attached shock into a highly curved shock structure with increasing standoff distance from the model;this curved shock has increased shock angle and also appears in increasingly diffused form. In the decay of the discharge intensity, the shock front is first transformed back to a well-defined curve shock, which moves downstream to become a perturbed oblique shock;the baseline shock front then reappears as the discharge is reduced to low level again. The experimental observations confirm the theory. The steady of the incoming flow during the discharge cycle is manifested by the repeat of the baseline shock front.
文摘The purpose of the present study was to establish a passive flow control method for a rectangular jet using two types of deflectors installed symmetrically inside a nozzle. This deflector in a rectangular nozzle generates the rectangular coaxial jets. The effect of the slant angle of the deflectors on the flow characteristics and the spread of the rectangular jet was investigated experimentally and by large-eddy simulation. The experiment and the numerical simulation were carried out at a Reynolds number of 9000. The rectangular jet with no deflectors generates a vortex ring from the nozzle exit. The vortex ring collapses in the downstream region and the outline of the jet changes from rectangular to diamond-shaped as a result of the axis-switching phenomenon. The rectangular jet with divergent and convergent deflectors shows particularly noticeable changes in the flow characteristics and vortical structures, as compared to the case with no deflectors. In the case of the rectangular jet with divergent deflectors (slant angle of <i style="font-family:" font-size:13.3333px;white-space:normal;"="">α</i><span style="font-family:" font-size:13.3333px;white-space:normal;"=""> = 6<span style="white-space:nowrap;">°</span>), minor axis spread is promoted more than major axis spread, and axis switching occurs closer to the nozzle exit than that in the case of no deflectors. The outline of the jet also changes from lateral rectangular to vertical rectangular as a result of axis switching. On the other hand, in the case of a rectangular jet with convergent deflectors (</span><i style="font-family:" font-size:13.3333px;white-space:normal;"="">α</i><span style="font-family:" font-size:13.3333px;white-space:normal;"=""> = -6<span style="white-space:nowrap;">°</span>), minor axis spread is suppressed more than major axis spread, and axis switching occurs farther from the nozzle exit than that in the case with no deflectors. The outline of the jet does not change until the downstream region. Therefore, the spread and the axis-switching location for the rectangular jet can be controlled by the deflectors inside the rectangular nozzle.</span>
文摘X-ray free-electron lasers(FELs)are cutting-edge research instruments employed in multiple scientific fields capable of analyzing matter with unprecedented time and spatial resolutions.Timeresolved measurements of electron and photon beams are essential in X-ray FELs.Radiofrequency(RF)transverse deflecting structures(TDSs)with a fixed streaking direction are standard diagnostics to measure the temporal properties of the electron beams.If placed after the undulator of the FEL facility,TDSs can also be employed to reconstruct the power profile of the FEL pulses.We present measurements of an X-band RF TDS system with variable polarization with a resolution below one femtosecond.We show FEL power profile measurements with associated root mean square pulse durations as short as 300 attoseconds.The measurements have been carried out at Athos,the soft X-ray beamline of SwissFEL.Measurements with variable polarization and attosecond resolution are essential to characterize and optimize the electron beams in all its dimensions for all types of X-ray FEL experiments,in particular for ultrafast X-ray applications.
基金supported by the Israel Ministry of Science,Technology and Space,Grant No.88428。
文摘A novel electro-optic deflector based on a quadratic electro-optical potassium lithium tantalate niobate(KLTN)crystal operating slightly above the ferroelectric phase transition is presented.The new deflection scheme was based on the electric field gradient generation along the vertical axis caused by the trapezoidal geometry of the crystal.A deflection angle of 6.5 mrad was attained for a low voltage of 680 V.The deflector was used as an electro-optic modulator for implementing active Q-switching in a thulium-doped yttrium lithium fluoride(Tm:YLF)laser(1880 nm).The laser was operated at three different repetition rates of 0.4,0.5 and 0.7 kHz,and reached high energies per pulse up to 6.9 mJ.
