Railway noise barriers are an essential piece of infrastructure for reducing noise propagation.However,these barriers experience aerodynamic loads generated by high-speed trains,leading to dynamic effects that may com...Railway noise barriers are an essential piece of infrastructure for reducing noise propagation.However,these barriers experience aerodynamic loads generated by high-speed trains,leading to dynamic effects that may compromise their fatigue capacity.The most common structural design for railway noise barriers consists of vertical configurations of posts and panels.However,there have been few dynamic analyses of steel post/wood panel noise barriers under train-induced aerodynamic loads.This study used dynamic finite element analysis to assess the dynamic behavior of such noise barriers.Analysis of a 40-m-long noise barrier model and a triangular simplified load model,the latter of which effectively represented the detailed aerodynamic load,were first used to establish the model and input of the moving load during dynamic simulation.Then,the effects of different parameters on the dynamic response of the noise barrier were evaluated,including the damping ratio,the profile of the steel post,the span length of the panel,the barrier height,and the train speed.Gray relational analysis indicated that barrier height exhibited the highest correlations with the dynamic responses,followed by train speed,post profile,span length,and damping ratio.A reduction in the natural frequency and an increase in the train speed result in a higher peak response and more pronounced fluctuations between the nose and tail waves.The dynamic amplification factor(DAF)was found to be related to both the natural frequency and train speed.A model was proposed showing that the DAF significantly increases as the square of the natural frequency decreases and the cube of the train speed rises.展开更多
Evacuated tube transportation(ETT)offers a promising high-speed transport solution,but trains operating at supersonic speeds within a sealed tube can induce complex aerodynamic phenomena that impact safety and reliabi...Evacuated tube transportation(ETT)offers a promising high-speed transport solution,but trains operating at supersonic speeds within a sealed tube can induce complex aerodynamic phenomena that impact safety and reliability.This study utilized the Reynolds-averaged Navier-Stokes(RANS)shear stress transport k-ω(SST k-ω)turbulence model for steady-state simulations and the improved delayed detached eddy simulation(IDDES)SST k-ωmodel for unsteady state simulations,both coupled with the advection upstream splitting method(AUSM).Four tunnel cross-sectional areas(49 m^(2),64 m^(2),81 m^(2),and 100 m^(2))with corresponding blockage ratios(β)(0.253,0.192,0.150,0.121)were analyzed to explore shock wave formation and its dependence on blockage ratios,along with surface pressure distribution and aerodynamic loading.Results show that higher blockage ratios increase shock wave intensity,while larger tunnel areas reduce this intensity,improving flow structure and wake effects.Moreover,as the blockage ratio decreases,the total drag coefficient of the entire train decreases linearly.When the blockage ratio decreases from 0.253 to 0.121,the total drag coefficient of the entire train decreases by 46.2%,with the head carriage and tail carriage drag coefficients decreasing by 23.3%and 32.7%,respectively,while the drag coefficient of the middle carriage remains nearly unchanged.The percentage of the total drag coefficient contributed by the head carriage decreases from 51.1%to 40.9%,while the percentage for the tail carriage increases from 47.0%to 56.6%.These findings enhance understanding of ETT fluid dynamics and performance.展开更多
The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study.A mechanism is suggested to explain the change of hunting behavior due to actions of aerod...The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study.A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads：the aerodynamic loads can change the position of vehicle system（consequently the contact relations）,the wheel/rail normal contact forces,the gravitational restoring forces/moments and the creep forces/moments.A mathematical model for hunting stability incorporating such influences was developed.A computer program capable of incorporating the effects of aerodynamic loads based on the model was written,and the critical speeds were calculated using this program.The dependences of linear and nonlinear critical speeds on suspension parameters considering aerodynamic loads were analyzed by using the orthogonal test method,the results were also compared with the situations without aerodynamic loads.It is shown that the most dominant factors a ff ecting linear and nonlinear critical speeds are different whether the aerodynamic loads considered or not.The damping of yaw damper is the most dominant influencing factor for linear critical speeds,while the damping of lateral damper is most dominant for nonlinear ones.When the influences of aerodynamic loads are considered,the linear critical speeds decrease with the rise of cross wind velocity,whereas it is not the case for the nonlinear critical speeds.The variation trends of critical speeds with suspension parameters can be significantly changed by aerodynamic loads.Combined actions of aerodynamic loads and suspension parameters also a ff ect the critical speeds.The effects of such joint action are more obvious for nonlinear critical speeds.展开更多
The 2-dimensional unsteady aerodynamic forces,in the context of both a thin airfoil where theory of potential flow is always applicable and a bluff bridge-deck section where separated flow is typically induced,are inv...The 2-dimensional unsteady aerodynamic forces,in the context of both a thin airfoil where theory of potential flow is always applicable and a bluff bridge-deck section where separated flow is typically induced,are investigated from a point of view of whether or not they conform to the principle of linear superposition in situations of various structural motions and wind gusts.It is shown that some basic preconditions that lead to the linear superposability of the unsteady aerodynamic forces in cases of thin airfoil sections are no longer valid for a bluff section.Theoretical models of bridge aerodynamics such as the one related to flutter-buffeting analysis and those concerning aerodynamic admittance(AA)functions,however,necessitate implicitly this superposability.The contradiction revealed in this work may throw light on the perplexing problem of AA functions pertaining to the description of buffeting loads of bridge decks.Some existing theoretical AA models derived from flutter derivatives according to interrelations valid only for thin airfoil theories,which have been employed rather extensively in bridge aerodynamics,are demonstrated to be illogical.Finally,with full understanding of the preconditions of the applicability of linear superposability of the unsteady aerodynamic forces,suggestions in regard to experiment-based AA functions are presented.展开更多
An implicit upwind finite volume solver for the Euler equations using the improved flux - splitting method is established and used to calculate the transonic flow past the airfoils with heaving, pitching oscillations ...An implicit upwind finite volume solver for the Euler equations using the improved flux - splitting method is established and used to calculate the transonic flow past the airfoils with heaving, pitching oscillations and the control surface. Results are given for the NACA64A - 10 airfoil which is in harmonic heaving and pitching oscillation and with the control surface in the transonic flow field. Some computational results are compared with the experiment data and the good agreements are shown in the paper.展开更多
In this paper,we propose an finite element approach based on classical plate theory to investigate the dynamic stability of a layered composite plate subject to nonlinear aerodynamic load.This study considers the infl...In this paper,we propose an finite element approach based on classical plate theory to investigate the dynamic stability of a layered composite plate subject to nonlinear aerodynamic load.This study considers the influence of temperature,nonlinear geometry,and nonlinear aerodynamic load on composite plate structures simultaneously.Specifically,the present work conduct comparison the results of the critical pressure value between the nonlinear aerodynamic load and the linear aerodynamic load,thereby pointing out some necessary cases which must consider the nonlinearity of aerodynamic load for calculating the aerospace structures.We determine the critical pressure value and vibrational amplitude response of the plate by means of calculation.The outcomes of our calculations can be useful in designing and repairing body shells and wings of aircraft equipment.展开更多
The design idea of tracking-differentiator and the nonlinear PID controllerare introduced, the applicable algorithm and its real result for distributed aerodynamicsloading control system are discussed, and the constru...The design idea of tracking-differentiator and the nonlinear PID controllerare introduced, the applicable algorithm and its real result for distributed aerodynamicsloading control system are discussed, and the construction of the test & contro1 system arealso presented. The application shows that the nonlinear PID algorithm has the advan-tages of high reliability, short run time and strong stability.展开更多
Large Eddy Simulations are carried out to analyze flow past flat plate in different configurations and inclinations.A thin flat plate is considered at three inclination angles(α=30°,60°and 90°)and thre...Large Eddy Simulations are carried out to analyze flow past flat plate in different configurations and inclinations.A thin flat plate is considered at three inclination angles(α=30°,60°and 90°)and three aspect ratios(AR=0.5,2 and 5).The Reynolds number based on the free stream velocity and chord length of the plate at different inclination angles varies between 75,000 to 150,000.An increase in the inclination angle while the aspect ratio(span to chord)is constant results in higher drag and lower lift on the plate.Increasing the aspect ratio at a constant inclination angle increases the mean aerodynamic loading except for theα=30°and AR=0.5 case where the mean forces are larger than the other aspect ratios for this specific inclination angle.The small aspect ratio suppresses and blocks the separation of the flow from the top and bottom edges causing larger aerodynamic forces relative to AR=2,5.Visualization of the flow structures shows the tip vortices have a significant role in controlling the shedding vortices from the top and bottom edges.Atα=30°and AR=0.5,the two tip vortcies control and suppress the flow separation from the top and bottom edges.A stable wake was found for this case with no fluctuation.As the aspect ratio increases,the influence of the tip vortices on flow separation from the top and bottom edges reduces.As a result,larger fluctuations were found for cases with higher aspect ratios.展开更多
The influence of train height on aerodynamic characteristics of high-speed train(HST)is significant in crosswind environments.This study employed the improved delayed detached eddy simulation(IDDES)turbulence model to...The influence of train height on aerodynamic characteristics of high-speed train(HST)is significant in crosswind environments.This study employed the improved delayed detached eddy simulation(IDDES)turbulence model to analyze the aerodynamic characteristics of trains with three different heights under a crosswind of 20 m/s.The numerical model was validated through comparison with wind tunnel experimental data.A comprehensive analysis was conducted on the characteristics of the flow field around trains,surface pressure distribution,and aerodynamic loads for trains with different heights.Results indicate that the side force coefficient increased by up to 61.54%with an increase in train height from 3.89 to 4.19 m.Compared with the 3.89 m case,the roll moment coefficient on the head,middle,and tail cars for 4.19 m cases increased by 18.11%,24.78%and 34.23%,respectively.The increase in train height widens the impact width of the leading car’s front vortex on the leeward side and intensifies the helical shedding and coupling interactions of two vortices in the wake,leading to an increase in the intensity and extent of wake flow in both vertical and longitudinal directions.Additionally,the increase in height shifted the flow separation point on the leeward side,moving vortices farther from the train,expanding the back-flow region,and intensifying Reynolds stress and turbulent fluctuations on the leeward side,which adversely impacted train stability and safety.The research findings can provide a reference for the design of train configurations and the assessment of dynamic performance in crosswind environments.展开更多
The structural safety of high-speed trains is significantly endangered by increasing operating speeds.The objective of this research was to investigate the evolution of the flow field in trains passing through a tunne...The structural safety of high-speed trains is significantly endangered by increasing operating speeds.The objective of this research was to investigate the evolution of the flow field in trains passing through a tunnel while there is a strong crosswind at the tunnel entrance and exit.Moreover,the effect of aerodynamic pressure waves on structural strength was analyzed to evaluate the safety of the carbody.In this study,we selected the improved delayed detached-eddy simulation(IDDES)method as a turbulence model.The mechanism of interaction among the train,tunnel,and crosswind was evaluated through a complex computational fluid dynamics(CFD)model,simulating high-speed trains moving through tunnels at various crosswind speeds.Additionally,the dynamic stress response of the carbody was calculated using a sequential coupling approach,where integral aerodynamic forces were applied as substitutes for direct CFD pressure loads.We assessed the effect of aerodynamic loads on the dynamic stresses of the carbody at different crosswind velocities(0,10,15,and 20 m/s).The results indicate that crosswinds exert a substantial influence on the fluid structure surrounding the train.Consequently,the aerodynamic forces contribute significantly to potential damage to the carbody,posing increased safety risks for high-speed trains.展开更多
Owing to the advantages of wire-driven parallel manipulator, a new wire-driven parallel suspension system for airplane model in low-speed wind tunnel is constructed, and the methods to measure and calculate the aerody...Owing to the advantages of wire-driven parallel manipulator, a new wire-driven parallel suspension system for airplane model in low-speed wind tunnel is constructed, and the methods to measure and calculate the aerodynamic parameters of the airplane model are studied. In detail, a static model of the wire-driven parallel suspension is analyzed, a mathematical model for describ- ing the aerodynamic loads exerted on the scale model is constructed and a calculation method for obtaining the aerodynamic parameters of the model by measuring the tension of wires is presented. Moreover, the measurement system for wire tension and its corresponding data acquisition system are designed and built. Thereafter, the wire-driven parallel suspension system is placed in an open return circuit low-speed wind tunnel for wind tunnel tests to acquire data of each wire tension when the airplane model is at different attitudes and different wind speeds. A group of curves about the parameters for aerodynamic load exerted on the airplane model are obtained at different wind speeds after the acquired data are analyzed. The research results validate the feasibility of using a wire-driven parallel manipulator as the suspension system for low-speed wind ttmnel tests.展开更多
An iterative and full-coupled rotor/fuselage aerodynamic interaction analytical method is developed based upon the rotor free-wake model and the 3-D fuselage panel model. A close vortex/ surface interaction model usin...An iterative and full-coupled rotor/fuselage aerodynamic interaction analytical method is developed based upon the rotor free-wake model and the 3-D fuselage panel model. A close vortex/ surface interaction model using the Analytical/Numerical Matching (ANM) was adopted in the method in order to simulate effectively the unsteady close interaction between the rotor tip-vortex and fuselage surface. By the analytical method, the unsteady and steady pressure distribution on the fuselage surface, and the unsteady lift and pitching moment of the fuselage in a rotor interaction environment were calculated for different advance ratios. It is shown that the unsteady aerodynamic loads of the fuselage due to the rotor interaction have the same periodic characteristics as the rotor. The comparisons between the present close vortex/surface interaction model and a previous model, which simply excludes vortex filaments inside the fuselage, were also made and the advantages of the former over the latter were demonstrated in improving unsteady close interaction calculations.展开更多
Aiming to maximize the aerodynamic performance of the Distributed Electric Propulsion(DEP)aircraft,a hybrid design framework which focuses on the aerodynamic performance of the propeller/wing integration has been deve...Aiming to maximize the aerodynamic performance of the Distributed Electric Propulsion(DEP)aircraft,a hybrid design framework which focuses on the aerodynamic performance of the propeller/wing integration has been developed and validated numerically.Variable-fidelity modelling for propeller aerodynamics has been used to achieve computational efficiency with reasonable accuracy.By optimizing the aerodynamic loading distributions on the tractor propeller disk,the induced slipstream is redistributed into a form that is beneficial for the wing downstream,based on which the propeller blade geometry is generated through a rapid inversed design procedure.As compared with the Minimum Induced Loss(MIL)propeller at a specified thrust level,significant improvements of both the lift-to-drag ratio of the wing and the propeller/wing integrated aerodynamic efficiency is achieved,which shows great promise to deliver aerodynamic benefits for the wing within the propeller slipstream without any additional devices.展开更多
To investigate the distinct properties of the helicopter rotors during circling flight,the aerodynamic and dynamic models for the main rotor are established considering the trim conditions and the flight parameters of...To investigate the distinct properties of the helicopter rotors during circling flight,the aerodynamic and dynamic models for the main rotor are established considering the trim conditions and the flight parameters of helicopters.The free wake method is introduced to compute the unsteady aerodynamic loads of the rotor characterized by distortions of rotor wakes,and the modal superposition method is used to predict the overall structural loads of the rotor.The effectiveness of the aerodynamic and the structural methods is verified by comparison with the experimental results,whereby the influences of circling direction,radius,and velocity are evaluated in both aerodynamic and dynamic aspects.The results demonstrate that the circling condition makes a great difference to the performance of rotor vortex,as well as the unsteady aerodynamic loads.With the decrease of the circling radius or the increment of the circling velocity,the thrust of the main rotor increases apparently to balance the inertial force.Meanwhile,the harmonics of aerodynamic loads in rotor disc change severely and an evident aerodynamic load shock appears at high-order components,which further causes a shift-of-peak-phase bending moment in the flap dimension.Moreover,the advancing side of blade experiences second blade/vortex interaction,whose intensity has a distinct enhancement as the circling radius decreases with the motion of vortexes.展开更多
The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force bala...The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.展开更多
The interaction effect of rotor wake on fuselage of helicopter was investigated with experimental method. The results from experiment have proved that for the drag of fuselage the effect of rotor airflow is closely in...The interaction effect of rotor wake on fuselage of helicopter was investigated with experimental method. The results from experiment have proved that for the drag of fuselage the effect of rotor airflow is closely in connection with both the flight speed and the collective pitch of blades, while for the thrust and pitch moment of fuselage the collective pitch angle of blades plays more important role. A simple and effective computing method about aerodynamic interaction can be derived from the measured data. In order to implement the experiment, a fuselage model, a special sensor, the measurement and data acquisition and processing system were designed and manufactured according to the special requirements of this research project, thereby a good base was built up for carrying out experiments successfully with high quality.展开更多
Distributed Propulsion Wing(DPW)technology offers significant advantages in terms of flight energy savings,but the strong aerodynamic coupling between the propulsive internal flow and aerodynamic external flow brings ...Distributed Propulsion Wing(DPW)technology offers significant advantages in terms of flight energy savings,but the strong aerodynamic coupling between the propulsive internal flow and aerodynamic external flow brings significant design challenges.As the primary DPW profile design is of great significance,this paper proposes a hybrid method to solve the inverse problem mainly based on the formula relationship between the required aerodynamic loads and the profile shape,which is more direct and instructive compared with traditional parametric iterative methods.The aerodynamic characteristics are described by the circulation distribution in the Fourier series form,then the mean camber line of the profile is solved through the re-derived airfoil theory considering disk's influence.Further CFD correction methods are also proposed.To validate the effectiveness and feasibility of the proposed hybrid inverse method,several DPW profile design tests are then conducted.Finally,the relationship between 2D and realistic 3D unit shape is also researched.The results show that the proposed inverse design method has great accuracy and convergence speed in the design tests,and shows good robustness against changes of the design parameters.The 2D profile shape and the actual 3D shape of DPW unit can establish an aerodynamic-propulsion equivalent relationship based on the same internal mass fluxes.展开更多
The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift f...The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift force and overturning moment with different wind speeds and wall heights were calculated. According to the principle of static moment balance of vehicles, the overturning coefficients of trains with different wind speeds and wall heights were obtained. Based on the influence of wind speed and wall height on the aerodynamic performance and the overturning stability of trains, a method of determination of the load balance ranges for the train operation safety was proposed, which made the overturning coefficient have nearly closed interval. A min(|A1|+|A2|), s.t. |A1|→|A2|(A1 refers to the downwind overturning coefficient and A2 refers to the upwind overturning coefficient)was found. This minimum value helps to lower the wall height as much as possible, and meanwhile, guarantees the operation safety of various types of trains under strong wind. This method has been used for the construction and improvement of the windbreak walls along the Lanzhou–Xinjiang railway(from Lanzhou to Urumqi, China).展开更多
This article presents a new mathematical model for helicopter comprehensive analysis with the features of flexibility and mathematical simplicity. The model synthesizes the rigid fuselage motion model with 6 degrees o...This article presents a new mathematical model for helicopter comprehensive analysis with the features of flexibility and mathematical simplicity. The model synthesizes the rigid fuselage motion model with 6 degrees of freedom,coupled flap-lag-torsion elastic rotor blade motion model,unsteady aerodynamics model with dynamic stall and high order generalized dynamic wake model. A new blade structural operator with implicit form is formulated,and the components of the blade structure model are independent of each other so that it is convenient to change or handle any component of blade structure without changing the others. What is more,the entire model is developed in a strict state-space form to simplify the comprehensive analysis. Finally,the UH-60 helicopter is taken as an example to predict the blade natural characteristics,the trim characteristics including controls and fuselage attitudes as well as the airloads at blade section under the flight conditions of high speed with moderate thrust and high thrust with moderate speed. The results are compared with UH-60 flight test data and those predicted by two well-known comprehensive codes. The validity of the model presented in this article is verified.展开更多
基金financially supported by the Swedish Transport Administration(Trafikverket)through the“Excellence Area 4”and FOI-BBT program(Grant Nos.BBT-2019-022 and BBT-TRV 2024/132497).
文摘Railway noise barriers are an essential piece of infrastructure for reducing noise propagation.However,these barriers experience aerodynamic loads generated by high-speed trains,leading to dynamic effects that may compromise their fatigue capacity.The most common structural design for railway noise barriers consists of vertical configurations of posts and panels.However,there have been few dynamic analyses of steel post/wood panel noise barriers under train-induced aerodynamic loads.This study used dynamic finite element analysis to assess the dynamic behavior of such noise barriers.Analysis of a 40-m-long noise barrier model and a triangular simplified load model,the latter of which effectively represented the detailed aerodynamic load,were first used to establish the model and input of the moving load during dynamic simulation.Then,the effects of different parameters on the dynamic response of the noise barrier were evaluated,including the damping ratio,the profile of the steel post,the span length of the panel,the barrier height,and the train speed.Gray relational analysis indicated that barrier height exhibited the highest correlations with the dynamic responses,followed by train speed,post profile,span length,and damping ratio.A reduction in the natural frequency and an increase in the train speed result in a higher peak response and more pronounced fluctuations between the nose and tail waves.The dynamic amplification factor(DAF)was found to be related to both the natural frequency and train speed.A model was proposed showing that the DAF significantly increases as the square of the natural frequency decreases and the cube of the train speed rises.
基金Project(JZ202201)supported by the Key Project of Basic and Applied Basic Research of Jiangmen,ChinaProject(2021WGALH15)supported by the Hong Kong and Macao Joint Research and Development Fund of Wuyi University,China+2 种基金Project(S202411349091)supported by the University Students'Innovation and Entrepreneurship Project of Guangdong,ChinaProject(52202426)supported by the National Natural Science Foundation of ChinaProjects(15205723,15226424)supported by the Research Grants Council(RGC)of the Hong Kong Special Administrative Region,China。
文摘Evacuated tube transportation(ETT)offers a promising high-speed transport solution,but trains operating at supersonic speeds within a sealed tube can induce complex aerodynamic phenomena that impact safety and reliability.This study utilized the Reynolds-averaged Navier-Stokes(RANS)shear stress transport k-ω(SST k-ω)turbulence model for steady-state simulations and the improved delayed detached eddy simulation(IDDES)SST k-ωmodel for unsteady state simulations,both coupled with the advection upstream splitting method(AUSM).Four tunnel cross-sectional areas(49 m^(2),64 m^(2),81 m^(2),and 100 m^(2))with corresponding blockage ratios(β)(0.253,0.192,0.150,0.121)were analyzed to explore shock wave formation and its dependence on blockage ratios,along with surface pressure distribution and aerodynamic loading.Results show that higher blockage ratios increase shock wave intensity,while larger tunnel areas reduce this intensity,improving flow structure and wake effects.Moreover,as the blockage ratio decreases,the total drag coefficient of the entire train decreases linearly.When the blockage ratio decreases from 0.253 to 0.121,the total drag coefficient of the entire train decreases by 46.2%,with the head carriage and tail carriage drag coefficients decreasing by 23.3%and 32.7%,respectively,while the drag coefficient of the middle carriage remains nearly unchanged.The percentage of the total drag coefficient contributed by the head carriage decreases from 51.1%to 40.9%,while the percentage for the tail carriage increases from 47.0%to 56.6%.These findings enhance understanding of ETT fluid dynamics and performance.
基金supported by the National Basic Research Program(973 Program)of China(2011CB711100 and 2014CB046801)the National Natural Science Foundation of China(11072246 and51490673)the Knowledge Innovation Program of Chinese Academy of Sciences(KJCX2-EW-L01)
文摘The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study.A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads：the aerodynamic loads can change the position of vehicle system（consequently the contact relations）,the wheel/rail normal contact forces,the gravitational restoring forces/moments and the creep forces/moments.A mathematical model for hunting stability incorporating such influences was developed.A computer program capable of incorporating the effects of aerodynamic loads based on the model was written,and the critical speeds were calculated using this program.The dependences of linear and nonlinear critical speeds on suspension parameters considering aerodynamic loads were analyzed by using the orthogonal test method,the results were also compared with the situations without aerodynamic loads.It is shown that the most dominant factors a ff ecting linear and nonlinear critical speeds are different whether the aerodynamic loads considered or not.The damping of yaw damper is the most dominant influencing factor for linear critical speeds,while the damping of lateral damper is most dominant for nonlinear ones.When the influences of aerodynamic loads are considered,the linear critical speeds decrease with the rise of cross wind velocity,whereas it is not the case for the nonlinear critical speeds.The variation trends of critical speeds with suspension parameters can be significantly changed by aerodynamic loads.Combined actions of aerodynamic loads and suspension parameters also a ff ect the critical speeds.The effects of such joint action are more obvious for nonlinear critical speeds.
基金Projects(51178182,90915002)supported by the National Natural Science Foundation of ChinaProject(SLDRCE10-MB-03)supported by the Open Project of the State Key Laboratory of Disaster Reduction in Civil Engineering,China
文摘The 2-dimensional unsteady aerodynamic forces,in the context of both a thin airfoil where theory of potential flow is always applicable and a bluff bridge-deck section where separated flow is typically induced,are investigated from a point of view of whether or not they conform to the principle of linear superposition in situations of various structural motions and wind gusts.It is shown that some basic preconditions that lead to the linear superposability of the unsteady aerodynamic forces in cases of thin airfoil sections are no longer valid for a bluff section.Theoretical models of bridge aerodynamics such as the one related to flutter-buffeting analysis and those concerning aerodynamic admittance(AA)functions,however,necessitate implicitly this superposability.The contradiction revealed in this work may throw light on the perplexing problem of AA functions pertaining to the description of buffeting loads of bridge decks.Some existing theoretical AA models derived from flutter derivatives according to interrelations valid only for thin airfoil theories,which have been employed rather extensively in bridge aerodynamics,are demonstrated to be illogical.Finally,with full understanding of the preconditions of the applicability of linear superposability of the unsteady aerodynamic forces,suggestions in regard to experiment-based AA functions are presented.
文摘An implicit upwind finite volume solver for the Euler equations using the improved flux - splitting method is established and used to calculate the transonic flow past the airfoils with heaving, pitching oscillations and the control surface. Results are given for the NACA64A - 10 airfoil which is in harmonic heaving and pitching oscillation and with the control surface in the transonic flow field. Some computational results are compared with the experiment data and the good agreements are shown in the paper.
文摘In this paper,we propose an finite element approach based on classical plate theory to investigate the dynamic stability of a layered composite plate subject to nonlinear aerodynamic load.This study considers the influence of temperature,nonlinear geometry,and nonlinear aerodynamic load on composite plate structures simultaneously.Specifically,the present work conduct comparison the results of the critical pressure value between the nonlinear aerodynamic load and the linear aerodynamic load,thereby pointing out some necessary cases which must consider the nonlinearity of aerodynamic load for calculating the aerospace structures.We determine the critical pressure value and vibrational amplitude response of the plate by means of calculation.The outcomes of our calculations can be useful in designing and repairing body shells and wings of aircraft equipment.
文摘The design idea of tracking-differentiator and the nonlinear PID controllerare introduced, the applicable algorithm and its real result for distributed aerodynamicsloading control system are discussed, and the construction of the test & contro1 system arealso presented. The application shows that the nonlinear PID algorithm has the advan-tages of high reliability, short run time and strong stability.
基金the Natural Sciences and Engineering Research Council of Canada(NSERC)through the Postdoctoral Fellowship(PDF)program.
文摘Large Eddy Simulations are carried out to analyze flow past flat plate in different configurations and inclinations.A thin flat plate is considered at three inclination angles(α=30°,60°and 90°)and three aspect ratios(AR=0.5,2 and 5).The Reynolds number based on the free stream velocity and chord length of the plate at different inclination angles varies between 75,000 to 150,000.An increase in the inclination angle while the aspect ratio(span to chord)is constant results in higher drag and lower lift on the plate.Increasing the aspect ratio at a constant inclination angle increases the mean aerodynamic loading except for theα=30°and AR=0.5 case where the mean forces are larger than the other aspect ratios for this specific inclination angle.The small aspect ratio suppresses and blocks the separation of the flow from the top and bottom edges causing larger aerodynamic forces relative to AR=2,5.Visualization of the flow structures shows the tip vortices have a significant role in controlling the shedding vortices from the top and bottom edges.Atα=30°and AR=0.5,the two tip vortcies control and suppress the flow separation from the top and bottom edges.A stable wake was found for this case with no fluctuation.As the aspect ratio increases,the influence of the tip vortices on flow separation from the top and bottom edges reduces.As a result,larger fluctuations were found for cases with higher aspect ratios.
基金Project(2020YFA0710903)supported by the National Key R&D Program of ChinaProject(2024JK2037)supported by the Key Research and Development Program of Hunan Province,China+1 种基金Project(52402458)supported by the National Natural Science Foundation of ChinaProjects(2025ZZTS0703,2025ZZTS0209)supported by the Fundamental Research Funds for the Central Universities,China。
文摘The influence of train height on aerodynamic characteristics of high-speed train(HST)is significant in crosswind environments.This study employed the improved delayed detached eddy simulation(IDDES)turbulence model to analyze the aerodynamic characteristics of trains with three different heights under a crosswind of 20 m/s.The numerical model was validated through comparison with wind tunnel experimental data.A comprehensive analysis was conducted on the characteristics of the flow field around trains,surface pressure distribution,and aerodynamic loads for trains with different heights.Results indicate that the side force coefficient increased by up to 61.54%with an increase in train height from 3.89 to 4.19 m.Compared with the 3.89 m case,the roll moment coefficient on the head,middle,and tail cars for 4.19 m cases increased by 18.11%,24.78%and 34.23%,respectively.The increase in train height widens the impact width of the leading car’s front vortex on the leeward side and intensifies the helical shedding and coupling interactions of two vortices in the wake,leading to an increase in the intensity and extent of wake flow in both vertical and longitudinal directions.Additionally,the increase in height shifted the flow separation point on the leeward side,moving vortices farther from the train,expanding the back-flow region,and intensifying Reynolds stress and turbulent fluctuations on the leeward side,which adversely impacted train stability and safety.The research findings can provide a reference for the design of train configurations and the assessment of dynamic performance in crosswind environments.
基金supported by the National Natural Science Foundation of China(No.52375160)the Natural Science Foundation of Hebei Province(No.2024105064),China.
文摘The structural safety of high-speed trains is significantly endangered by increasing operating speeds.The objective of this research was to investigate the evolution of the flow field in trains passing through a tunnel while there is a strong crosswind at the tunnel entrance and exit.Moreover,the effect of aerodynamic pressure waves on structural strength was analyzed to evaluate the safety of the carbody.In this study,we selected the improved delayed detached-eddy simulation(IDDES)method as a turbulence model.The mechanism of interaction among the train,tunnel,and crosswind was evaluated through a complex computational fluid dynamics(CFD)model,simulating high-speed trains moving through tunnels at various crosswind speeds.Additionally,the dynamic stress response of the carbody was calculated using a sequential coupling approach,where integral aerodynamic forces were applied as substitutes for direct CFD pressure loads.We assessed the effect of aerodynamic loads on the dynamic stresses of the carbody at different crosswind velocities(0,10,15,and 20 m/s).The results indicate that crosswinds exert a substantial influence on the fluid structure surrounding the train.Consequently,the aerodynamic forces contribute significantly to potential damage to the carbody,posing increased safety risks for high-speed trains.
基金National Natural Science Foundation of China (50475099)
文摘Owing to the advantages of wire-driven parallel manipulator, a new wire-driven parallel suspension system for airplane model in low-speed wind tunnel is constructed, and the methods to measure and calculate the aerodynamic parameters of the airplane model are studied. In detail, a static model of the wire-driven parallel suspension is analyzed, a mathematical model for describ- ing the aerodynamic loads exerted on the scale model is constructed and a calculation method for obtaining the aerodynamic parameters of the model by measuring the tension of wires is presented. Moreover, the measurement system for wire tension and its corresponding data acquisition system are designed and built. Thereafter, the wire-driven parallel suspension system is placed in an open return circuit low-speed wind tunnel for wind tunnel tests to acquire data of each wire tension when the airplane model is at different attitudes and different wind speeds. A group of curves about the parameters for aerodynamic load exerted on the airplane model are obtained at different wind speeds after the acquired data are analyzed. The research results validate the feasibility of using a wire-driven parallel manipulator as the suspension system for low-speed wind ttmnel tests.
文摘An iterative and full-coupled rotor/fuselage aerodynamic interaction analytical method is developed based upon the rotor free-wake model and the 3-D fuselage panel model. A close vortex/ surface interaction model using the Analytical/Numerical Matching (ANM) was adopted in the method in order to simulate effectively the unsteady close interaction between the rotor tip-vortex and fuselage surface. By the analytical method, the unsteady and steady pressure distribution on the fuselage surface, and the unsteady lift and pitching moment of the fuselage in a rotor interaction environment were calculated for different advance ratios. It is shown that the unsteady aerodynamic loads of the fuselage due to the rotor interaction have the same periodic characteristics as the rotor. The comparisons between the present close vortex/surface interaction model and a previous model, which simply excludes vortex filaments inside the fuselage, were also made and the advantages of the former over the latter were demonstrated in improving unsteady close interaction calculations.
基金supported by the Key Research and Development Program of Shaanxi Province of China(No.2018ZDCXL-GY-03-04)。
文摘Aiming to maximize the aerodynamic performance of the Distributed Electric Propulsion(DEP)aircraft,a hybrid design framework which focuses on the aerodynamic performance of the propeller/wing integration has been developed and validated numerically.Variable-fidelity modelling for propeller aerodynamics has been used to achieve computational efficiency with reasonable accuracy.By optimizing the aerodynamic loading distributions on the tractor propeller disk,the induced slipstream is redistributed into a form that is beneficial for the wing downstream,based on which the propeller blade geometry is generated through a rapid inversed design procedure.As compared with the Minimum Induced Loss(MIL)propeller at a specified thrust level,significant improvements of both the lift-to-drag ratio of the wing and the propeller/wing integrated aerodynamic efficiency is achieved,which shows great promise to deliver aerodynamic benefits for the wing within the propeller slipstream without any additional devices.
基金supported by the National Natural Science Foundation of China(Nos.12102186,12032012)the Natural Science Foundation of Jiangsu Province,China(No.BK20200433)+2 种基金the Laboratory Foundation of China(No.61422202201)the Young Elite Scientists Sponsorship Program by CAST,China(No.2022QNRC001)the Priority Academic Program Development of Jiangsu Higher Education Institutions,China。
文摘To investigate the distinct properties of the helicopter rotors during circling flight,the aerodynamic and dynamic models for the main rotor are established considering the trim conditions and the flight parameters of helicopters.The free wake method is introduced to compute the unsteady aerodynamic loads of the rotor characterized by distortions of rotor wakes,and the modal superposition method is used to predict the overall structural loads of the rotor.The effectiveness of the aerodynamic and the structural methods is verified by comparison with the experimental results,whereby the influences of circling direction,radius,and velocity are evaluated in both aerodynamic and dynamic aspects.The results demonstrate that the circling condition makes a great difference to the performance of rotor vortex,as well as the unsteady aerodynamic loads.With the decrease of the circling radius or the increment of the circling velocity,the thrust of the main rotor increases apparently to balance the inertial force.Meanwhile,the harmonics of aerodynamic loads in rotor disc change severely and an evident aerodynamic load shock appears at high-order components,which further causes a shift-of-peak-phase bending moment in the flap dimension.Moreover,the advancing side of blade experiences second blade/vortex interaction,whose intensity has a distinct enhancement as the circling radius decreases with the motion of vortexes.
基金supported by the National Natural Science Foundation of China(11072142)Shanghai Program for Innovative Research Team in Universities
文摘The tip vortices and aerodynamics of a NACA0012 wing in the vicinity of the ground were studied in a wind tunnel.The wing tip vortex structures and lift/drag forces were measured by a seven-hole probe and a force balance,respectively.The evolution of the flow structures and aerodynamics with a ground height were analyzed.The vorticity of tip vortices was found to reduce with the decreasing of the ground height,and the position of vortex-core moved gradually to the outboard of the wing tip.Therefore,the down-wash flow induced by the tip vortices was weakened. However,vortex breakdown occurred as the wing lowered to the ground.From the experimental results of aerodynamics,the maximum lift-to-drag ratio was observed when the angle of attack was 2.5°and the ground clearance was 0.2.
基金the National Defence Science and Technology in Advancethe National Laboratory of Rotorcraft Aeromechanics
文摘The interaction effect of rotor wake on fuselage of helicopter was investigated with experimental method. The results from experiment have proved that for the drag of fuselage the effect of rotor airflow is closely in connection with both the flight speed and the collective pitch of blades, while for the thrust and pitch moment of fuselage the collective pitch angle of blades plays more important role. A simple and effective computing method about aerodynamic interaction can be derived from the measured data. In order to implement the experiment, a fuselage model, a special sensor, the measurement and data acquisition and processing system were designed and manufactured according to the special requirements of this research project, thereby a good base was built up for carrying out experiments successfully with high quality.
文摘Distributed Propulsion Wing(DPW)technology offers significant advantages in terms of flight energy savings,but the strong aerodynamic coupling between the propulsive internal flow and aerodynamic external flow brings significant design challenges.As the primary DPW profile design is of great significance,this paper proposes a hybrid method to solve the inverse problem mainly based on the formula relationship between the required aerodynamic loads and the profile shape,which is more direct and instructive compared with traditional parametric iterative methods.The aerodynamic characteristics are described by the circulation distribution in the Fourier series form,then the mean camber line of the profile is solved through the re-derived airfoil theory considering disk's influence.Further CFD correction methods are also proposed.To validate the effectiveness and feasibility of the proposed hybrid inverse method,several DPW profile design tests are then conducted.Finally,the relationship between 2D and realistic 3D unit shape is also researched.The results show that the proposed inverse design method has great accuracy and convergence speed in the design tests,and shows good robustness against changes of the design parameters.The 2D profile shape and the actual 3D shape of DPW unit can establish an aerodynamic-propulsion equivalent relationship based on the same internal mass fluxes.
基金Project(U1334203) supported by the National Natural Science Foundation of China
文摘The aerodynamic performances of a passenger car and a box car with different heights of windbreak walls under strong wind were studied using the numerical simulations, and the changes of aerodynamic side force, lift force and overturning moment with different wind speeds and wall heights were calculated. According to the principle of static moment balance of vehicles, the overturning coefficients of trains with different wind speeds and wall heights were obtained. Based on the influence of wind speed and wall height on the aerodynamic performance and the overturning stability of trains, a method of determination of the load balance ranges for the train operation safety was proposed, which made the overturning coefficient have nearly closed interval. A min(|A1|+|A2|), s.t. |A1|→|A2|(A1 refers to the downwind overturning coefficient and A2 refers to the upwind overturning coefficient)was found. This minimum value helps to lower the wall height as much as possible, and meanwhile, guarantees the operation safety of various types of trains under strong wind. This method has been used for the construction and improvement of the windbreak walls along the Lanzhou–Xinjiang railway(from Lanzhou to Urumqi, China).
文摘This article presents a new mathematical model for helicopter comprehensive analysis with the features of flexibility and mathematical simplicity. The model synthesizes the rigid fuselage motion model with 6 degrees of freedom,coupled flap-lag-torsion elastic rotor blade motion model,unsteady aerodynamics model with dynamic stall and high order generalized dynamic wake model. A new blade structural operator with implicit form is formulated,and the components of the blade structure model are independent of each other so that it is convenient to change or handle any component of blade structure without changing the others. What is more,the entire model is developed in a strict state-space form to simplify the comprehensive analysis. Finally,the UH-60 helicopter is taken as an example to predict the blade natural characteristics,the trim characteristics including controls and fuselage attitudes as well as the airloads at blade section under the flight conditions of high speed with moderate thrust and high thrust with moderate speed. The results are compared with UH-60 flight test data and those predicted by two well-known comprehensive codes. The validity of the model presented in this article is verified.
