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 DOI: 10.1177/0954409712471620published online 3 January 2013

2014 228: 260 originallyProceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid TransitZuo Jianyong, Wu Mengling, Tian Chun, Xi Ying, Luo Zhuojun and Chen Zhongkai

Aerodynamic braking device for high-speed trains: Design, simulation and experiment  

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Original Article

Aerodynamic braking device forhigh-speed trains: Design, simulationand experiment

Zuo Jianyong1, Wu Mengling1, Tian Chun1, Xi Ying2,Luo Zhuojun1 and Chen Zhongkai1

Abstract

This paper proposes the design of an aerodynamic braking device for a high-speed train. The design is based on the

parameters of the high-speed train and the working principles of airplane wings. The proposed device is a unidirectional

opening model driven by hydraulics. The prototype uses hard-wired signals to transmit braking commands on eight

levels. The important characteristics of the device include a synchronous action and a fault-oriented security design. Its

functions include service braking, gradual braking, emergency braking and self-checking. Simulation results show that

deceleration in the high-speed zone between 250 and 500 km/h can be improved by between 8 and 60%. When the train

runs at 500 km/h, the braking deceleration rate can be improved by 0.12 m/s2. The simulation results are found to agree

with wind tunnel test results. The braking characteristics are also investigated using a test bed, which mimics the

aerodynamic load exerted on the prototype when the train is running between 0 and 550 km/h. It is clearly demonstrated

that the proposed principle of the aerodynamic braking system is feasible and its design scheme is reasonable. The

aerodynamic braking device can survive a 50,000 N aerodynamic load, and the time taken to achieve the maximum

braking capacity, which is the time taken to take the brake panel from its closed position of �5� to the maximum angle of

75�, is less than 3 s. The proposed prototype therefore offers an important step in the design of practical systems.

Keywords

High-speed trains, aerodynamic braking, numerical simulation, prototype design, test

Date received: 22 April 2012; accepted: 19 September 2012

Introduction

Modern high-speed trains can reach running speeds ofup to 300 km/h and there are reports that a test trainwith an operating speed of up to 500 km/h has beenbuilt in China. These increased running speeds meanthat braking-related issues are receiving increasingattention. If the speed of a train increases from 300to 350 km/h, its kinetic energy increases by 40%, andtherefore the braking capacity also needs to beincreased by 40%.

The braking methods used in high-speed trains canbe classified into two types: adhesion braking andnon-adhesion braking. In adhesion braking, the cre-ated force is limited by the maximum force betweenthe wheelset and the rail; however, this limitationdoes not exist in non-adhesion braking. Currently,adhesion braking methods are commonly used onhigh-speed trains. As an example, service braking isperformed using a regenerative brake and disc brakeand is a kind of adhesion braking, and emergency

braking is performed entirely using a disc brakedriven by compressed air. Since the adhesion coeffi-cient decreases as the running speed of the trainincreases, the braking force produced using the adhe-sion braking method is limited. Therefore, non-adhe-sion braking approaches such as eddy currentbraking, electromagnetic rail braking and aero-dynamic braking are of considerable interest as tech-niques to deal with the problem of effective braking athigh speeds.

1Railway and Urban Rail Traffic Academy, Tongji University, People’s

Republic of China2School of Mechanical Engineering, Tongji University, People’s Republic

of China

Corresponding author:

Zuo Jianyong, Railway and Urban Rail Traffic Academy, Tongji University,

Shanghai 200092, People’s Republic of China.

Email: zuojy@tongji.edu.cn

Proc IMechE Part F:

J Rail and Rapid Transit

2014, Vol. 228(3) 260–270

! IMechE 2012

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It has been reported that some European countries,as well as Japan, have already started researching newtypes of braking and safety technologies. Germanyhas applied non-adhesion eddy current braking on itsInter City Express trains. Japan has built several aero-dynamic brake prototypes. Figure 1(a) shows aero-dynamic braking devices mounted on the MLU002NMiyazaki maglev test train and Figure 1(b) shows theaerodynamic braking devices mounted on ShinkansenFastech 360S and Fastech 360Z high-speed trains.Both of these trains have passed aerodynamic brakingtests at running speeds of up to 400 km/h. The resultsobtained for the Fastech 360S train showed that thebraking distance at an initial speed of 360 km/h withaerodynamic braking was almost the same as that at aninitial speed of 275 km/h without aerodynamic brak-ing. The mechanical structure and aerodynamic brak-ing performance of the aerodynamic braking deviceson the Shinkansen Fastech 360S and Fastech 360Z testtrains have been extensively investigated.1–3 Accordingto these studies, it is necessary to apply non-adhesionbraking under an emergency situation, in order tocompensate for the deficiencies of adhesion brakingat high speeds. This ensures safe and reliable brakingof high-speed trains under emergency situations.

The present paper describes a new aerodynamicbrake prototype that has been trialed on ChinaRailway’s high-speed test train.

Principles and features of aerodynamicbraking

In order to enhance the running resistance of a high-speed train when braking, aerodynamic brakingincreases the surface area of the brake panel so as toincrease the windward area of the entire train.Aerodynamic braking transfers the kinetic energy ofthe train by making use of friction between the run-ning brake panel and the ambient air; it is then dis-sipated into the surrounding atmosphere.4–6

Figure 2 gives an illustration of the operating prin-ciple of a kind of aerodynamic braking. When theaerodynamic braking device is operating, the brakepanel blocks the wind in front of it. As a result, anegative pressure zone forms behind it. The pressuredifference between the two sides of the brake panelprovides the aerodynamic resistance for braking.This aerodynamic braking force is proportional tothe square of the relative speed between the trainand the ambient air. The higher the running speedof the train, the more efficient the aerodynamic brak-ing method.

Aerodynamic braking has several advantages overnon-adhesion braking methods.

1. It stretches the brake panel to enhance aero-dynamic resistance when braking. Since aero-dynamic resistance is proportional to the squareof the relative velocity, aerodynamic braking per-forms efficiently at high speed, and can be used tocompensate for the deficiencies of adhesionbraking.

2. Aerodynamic braking uses the relative speedbetween the natural wind and the vehicle. Unlikeother braking methods, such as disc braking andelectrical braking, aerodynamic braking has a rela-tively simple control scheme. Also, the panel pro-vides a vertical force that is very useful in

Figure 1. Aerodynamic braking devices on (a) the MLU002N Miyazaki maglev test train and (b) on the Shinkansen Fastech 360S and

Fastech 360Z high-speed trains.

running direction

wind direction

positive pressure zone

negative pressure zone

……

Figure 2. Operating principle of aerodynamic braking.

Jianyong et al. 261

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improving the contact between wheelset and rail.Aerodynamic braking needs little energy to driveit. Moreover, noise emission by aerodynamicbraking can be reduced by shape design and opti-mization of the structure of the brake panel.

3. Compared with electromagnetic rail braking andeddy current braking, an aerodynamic brakingdevice will usually be mounted on top of the vehicleand can be flexibly designed and allocated.Different schemes can be carried out accordingto the interfaces of a specific train, which can min-imize alterations to the train. On the other hand,electromagnetic rail braking and eddy currentbraking require the structure of a bogie to beredesigned before installation and add extra loadto the primary suspension which affects wheelsetquality.

4. An aerodynamic braking device generates lowlevels of abrasion compared with disc braking.Compared with electromagnetic rail braking, theamount of generated frictional heat is much lower,and it quickly dissipates into the ambient air.Thus, aerodynamic braking has relatively highreliability and low maintenance costs.

Prototype schemes of the aerodynamicbraking device

Components of the aerodynamic braking prototype

Figure 3 shows a schematic diagram of the opening ofthe brake panel chosen for our prototype. This is aunidirectional opening scheme, which means that thebrake panel is only allowed to incline in one direction.The reason we chose this unidirectional schemeinstead of a bidirectional scheme was to simplify themechanical structure while at the same time maintain-ing sufficient mechanical strength. Moreover, in orderto ensure a streamlined shape of the entire train andimprove aerodynamic efficiency, a flow deflector wasadded around the brake panel.

This aerodynamic braking device has the followingfeatures.

1. A modular design method is employed for theseprototypes, so the device can be installed on eachcar of a train or on selected cars only, asconvenient.

2. A unidirectional opening scheme is used, whichsaves mounting space on the car roof as a resultof the simple mechanical structure of this scheme.

3. By applying appropriate layout schemes such as asymmetric distribution along the train, the proto-types can provide braking force regardless ofwhether the train is moving forward or backwardby using different panels in different displacementdirections.

The aerodynamic braking prototype, which isshown in Figure 4(a), has three main parts: thebrake panel device on the car roof, the hydraulicactuating device and the electronic control device.The electronic control unit contains several sub-mod-ules including the aerodynamic braking control unit(ABCU)7–8, hydraulic control unit (HCU)9–10, self-check module, fault diagnosis module and emergencymodule. These sub-modules are discussed in detail inthe rest of this section. Figure 4(b) shows the aero-dynamic braking prototype mounted on a test train.

The brake panel device changes the stretch lengthof the hydraulic cylinders to drive the brake panel tothe required angle in order to comply with the brakinglevel commands issued by the electronic controldevice. The hydraulic actuating device uses hydraulicvalves to control the oil flow used to drive the hydrauliccylinders.11–12 The electronic control device has severalcritical functions, including controlling the motions ofthe brake panel, monitoring the operating conditionsof the brake panel device and the hydraulic actuatingdevice, and exchanging information between aero-dynamic braking prototypes in different vehicles. Thehydraulic actuating device and the electronic controldevice are assembled in the same cabinet.13

Figure 5 shows a block diagram of the control logicof the control software in the prototype. The brakingcommands are sent to cars M2, M3 and M5 usingwires. Each aerodynamic braking device exchanges

Figure 3. Opening scheme of the brake panel.

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information via an RS485. After the braking com-mands are decoded in the ABCU mounted on everycar, the ABCUs control their corresponding HCU,which controls the movement of the brake panel.The self-check modules are used to check the workingconditions of the entire system when the system is inservice. The fault diagnosis modules are used as real-time monitors to detect faults and to send the detectedfaults to the ABCU. An emergency circuit is alsoinstalled. When an emergency situation occurs, theclosed loop is opened, which triggers the emergencymodules. Then, the emergency modules close thebrake panels.

Features of the aerodynamic braking prototype

Material selection for the brake panel. Considering thecomplicated working conditions, in which the brakepanel has to bear aerodynamic loads, impacts, corro-sion and so on, together with the cost of the material,a composite material type with a sandwich structurewas chosen. Its central part is made of foam and theother two sides are made of a fiber-reinforced com-posite material. This kind of material has excellent

processing properties, anti-fatigue properties andthermal stability. It also helps to lower the weight ofthe entire device. The brake panel of this prototypeweighs only 60 kg, and it meets the bird impactrequirements of the UIC-651 standard.

The hydraulic device. The effective stroke of the hydrau-lic cylinders is about 200mm. The time taken toachieve the maximum braking capacity, which is thetime taken to move the brake panel from the closedposition (�5�) to the maximum angle of 75�, is lessthan 3 s. When a fault occurs, for example, low oillevel, over pressure, leakage and so on, the hydraulicactuating device detects the problem and sends analarm signal. The device also has a secure functionagainst severe failures without electricity: in cases ofemergency, such as loss of electricity, the brake panelcan be closed and driven by a manual pump.14–15

The electronic control device. The main functions of theelectronic control device are as follows:

(a) to produce and transmit braking signals and con-trol the movement of the brake panel;

Figure 5. Block diagram of the control logic of the prototypes.

Figure 4. Aerodynamic braking prototype.

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(b) to supply electricity for the hydraulic actuatingdevice and control the hydraulic pump;

(c) to acquire displacement and pressure signals ofthe hydraulic cylinders so as to control themotions of the brake panel;

(d) to close the brake panel in case of emergency;(e) to monitor working conditions of the brake panel

with a camera;(f) to self-check, store data, provide a real-time dis-

play, and record and warn about faults.

Control mode of the aerodynamic braking prototype. Theaerodynamic braking prototypes use wires and theRS485 to transmit braking commands and otherinformation. One of cars M2, M3 or M5 is chosenas the central control unit. It can monitor and storethe information of other prototypes, such as brakingcommands, failure state, angle of brake panel and thestate of the hydraulic unit. The braking commandshave eight levels and are transmitted by three wires.

Fault diagnosis. If faults appear during self-checking ornormal operation, a programmable logic controller(PLC) in the electronic control device runs a faultdiagnosis procedure to close the brake panel. At thesame time, the PLC sends the fault information to theABCU, which displays the failure state of the entireprototype. Before restarting a failed prototype, allfaults should be cancelled and the failure state ofthis prototype should be reset.

Human–machine interface. The aerodynamic brakingprototype is equipped with a human–machine inter-face, which helps to check the failure state, display theopening angle of the brake panel and the brakingresistance of a prototype, and display videos of thepanel’s working conditions. The human–machineinterface consists of three sub-interfaces, which auser can conveniently switch between.

Numerical simulation and wind tunneltest

Computational fluid dynamics (CFD) software wasused to simulate the working conditions of high-speed trains installed with aerodynamic brakingdevices. The simulation results were analyzed in com-parison with wind tunnel test results so that the brak-ing efficiency of the prototype and the flow fieldconditions around the train could be checked.

The simulation calculation area had a length of800m, width of 52.5m and height of 100m; thetrack space was 5m, and the ground clearancebetween the train and the ground was 0.2m. Ourstudy used the ICEM CFD software to obtain a struc-tured mesh and adopted an O-grid structure to meshthe vehicle and the brake panel. The O-grid was usedto divide a block around the train’s surface so as to

adapt to the shape of the geometry profile and obtaina good-quality mesh. The number of meshes for asingle train with the brake panel was approximately6,500,000 and that without the brake panel wasapproximately 5,500,000. The Reynolds number wasabout 3.46� 107, which was calculated using theequation

Re ¼ �vD=� ð1Þ

where Re is the Reynolds number, � is the density ofair (1.293 kg/m3), v is the velocity (500 km/h), D is thebasic length (3.45m) and � is the dynamic viscosity ofair (17.9� 10�6Pa�s).

For near wall treatment, the fine mesh around thewall and the standard k-! model, which is a low-Reynolds-number model, were used to directly solvethe near wall flow. The cell growth aspect ratio adja-cent to the walls was taken to have a value of 1.2.

Numerical simulation

We built a six-car train model on which we mountedaerodynamic braking prototypes. The aim was tocheck the braking efficiency of the prototypes underdifferent working conditions, including different run-ning speeds and different opening angles of the panels.Figure 6 shows the pressure coefficient contour of atrain with the three brake panels opened to 75� at arunning speed of 500 km/h. The pressure coefficientvalues were calculated using the equation

Cp ¼ ð p1 � p2Þ=ð0:5�v2Þ ð2Þ

where Cp is the pressure coefficient, p1 is the staticpressure of the calculated point, p2 and v are thestatic pressure and velocity of the reference point,respectively, and � is the density of air.

From Figure 6, it can be seen that the pressure onthe front face of the panels is considerably higher thanthose on the other surfaces.

Figure 7 shows the braking force simulation resultsof the aerodynamic braking devices. The total brakingforce consists of two parts: the force of the flow deflec-tors and the force of the brake panels. The layout ofthe flow deflector and the brake panel was shown inFigure 3. Since compressibility effects can affect theaccuracy of the simulation results at higher speeds,which have relatively high Mach numbers, the airwas treated as being compressible in cases where therunning speed was greater than 300 km/h. The brak-ing forces of the panels and the flow deflectors whenthe brake panels were opened to 0�, 45� and 75� areshown in Figure 7(a), (b) and (c), respectively. Thefollowing conclusions were drawn from the obtainedresults.

1. The braking forces produced both by the panelsand the flow deflectors are proportional to the

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Figure 7. Numerical simulation results of braking force: (a) braking force with brake panels at 0�; (b) braking force with brake panels

at 45�; and (c) braking force with brake panels at 75�.

Figure 6. Pressure coefficient contour of the train with panels opened to 75� at a speed of 500 km/h.

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square of the running speed of the train when thebrake panels are opened to a specified angle.

2. When the brake panels are inclined, the brakingforce of the brake panels increases at a faster ratethan that of the flow deflectors.

3. When the brake panels are opened to 75� and thetrain runs at 500 km/h, the combined brakingforce of the brake panels and the flow deflectorsreaches approximately 42,000N. Therefore, if theaxle load of the train is 15 t, the deceleration rateof the train can be increased by approximately0.12m/s2.

Figure 8 is a graph of aerodynamic braking effi-ciency based on the numerical simulation results.The black curve represents the maximum decelerationthe Chinese Railway’s high-speed train can createusing the adhesion braking method at various runningspeeds. It is clear that the deceleration attained by thetrain declines rapidly as the running speed increases.The maximum deceleration is only 0.22m/s2 at aspeed of 500 km/h. Since aerodynamic braking is akind of non-adhesion braking, the low levels of decel-eration at higher speeds can be supplemented byapplying aerodynamic braking. The red curve in thefigure shows the maximum deceleration of the trainwhen it is equipped with the proposed aerodynamicbraking prototype. The maximum deceleration valuesare noticeably improved in the high-speed zone inwhich aerodynamic braking is applied. In the high-speed zone between 250 and 500 km/h, the maximumdeceleration values are improved by between 8 and60%. Thus, aerodynamic braking is an efficient wayto compensate the insufficient deceleration level

created solely using adhesion braking methods athigh speeds.

Wind tunnel test

In order to mimic the working conditions of a realtrain, a wind tunnel test model with the same size asthe prototype was built. The Aerodynamic and Aero-acoustic Wind Tunnel (AAWT) at the ShanghaiAutomotive Wind Tunnel Center was used. The max-imum wind speed that can be obtained in the AAWTis 250 km/h, and the background noise is lower than61 dBA at 160 km/h. The nozzle area is up to 27 m2,and AAWT test vehicles range from normal-sizedautomobiles to railway vehicle models.

The wind tunnel test shown in Figure 9 validatedthe efficiency of aerodynamic braking. Tests underworking conditions with different opening angles (0–75�) at different wind speeds were performed. Results

Figure 8. Braking efficiency of aerodynamic braking.

Figure 9. Photograph of the wind tunnel test model.

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of the tests were analyzed in comparison with theresults of the numerical simulation.

Figure 10 shows the test and simulation results at a250 km/h test wind speed. The simulation results canbe seen to agree with the wind tunnel test results.When the opening angle of the brake panels isbetween 0� and 75�, the maximum percentage differ-ence between the test and simulation results is about17%, which occurs at the opening angle of 0�. Thepercentage difference between the test and simulationresults is within �8% when the opening angle isbetween 10� and 75�. Thus, the feasibility of thenumerical simulation method is validated by thesemeasurements.

Testing the aerodynamic brakingprototype

Service braking test

The aerodynamic braking prototype has eight brakinglevels, related to the eight opening angles. It can easilyswitch between braking levels. Moreover, the brakepanel of this prototype can be locked to the corres-ponding angle of a given braking level, which carriesout the function of service braking. The time thebrake panel takes to open from �5� to 75� shouldbe no more than 3 s.

Figure 11 is a sketch of the opening angle of thebrake panel during a service braking test. It took lessthan 3 s for the brake panel to move from �5� to 75�.

Aerodynamic load test

The AAWT wind tunnel used in the test has a topwind speed of only 250 km/h. However, this was

acceptable since the main purpose of the windtunnel test was to verify the braking force value andair flow distribution and compare these data withthose of the numerical simulations. Since the max-imum speed of the aerodynamic braking devices wasdesigned to be 500 km/h it is necessary to design a testbed that can simulate the aerodynamic load at550 km/h.

Configuration and working principle of the aerodynamic load

test bed. Figure 12 shows the aerodynamic load testbed used to test the aerodynamic braking prototype.It consists of several parts, including a wind gener-ator, an air passage, an air-passage controller and aplatform to mount the prototype. The wind generatorwas used to generate high-speed wind, inside the gen-erator there is a motor driving a fan whose rotating

Figure 10. Comparison of test and simulation results.

75

65

55

45

35

25

15

–50 3 6 9 12 15

Ope

ning

ang

le in

deg

rees

θ[º

]

Time in seconds t [s]

Figure 11. Opening angle during a gradual braking test.

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speed is changeable. The air passage was used to guidethe wind to the brake panel. The air-passage control-ler is located inside the air passage and was used tochange the cross-sectional area of the air passage so asto change the wind pressure and flux. The workingprinciple of the aerodynamic load test bed was usedto simulate the wind pressure on the brake panel whena train is running at 500 km/h, as we were unable toreach this level in the AAWT wind tunnel. Becausethe brake panel was very close to the outlet of the airpassage and the gap between them was small, wecould achieve the wind pressure for a train runningat 500 km/h with a considerably lower wind speed

than 500 km/h. Based on this working principle, theaerodynamic load test bed was able to simulate theequivalent aerodynamic load of train running speedsfrom 0 to 550 km/h.

Relationship between the support force of hydraulic cylinders

and wind loads. The test results were acquired usingtwo pressure sensors mounted at the bottom ofthe hydraulic cylinders. The mounting position ofthe pressure sensors is shown in Figure 13. Beforewe describe the test results, the relationship betweenthe support force and the wind loads should beexplained. Figure 13 shows a side view of the structure

Figure 13. Relationship between the support force and the wind loads.

Figure 12. Aerodynamic load test bed.

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of the aerodynamic braking device. The three jointsare labeled A, B and C, respectively. The equivalentpoint of action of the aerodynamic loads is labeled asD. The A and B joints are fixed to the chassis of thedevice, and the C joint is moveable. The opening angleof the brake panel can be controlled by varying thelength of the cylinders.

Based on the setup shown in Figure 13, the rela-tionship between the support force and the wind loadscan be given as follows

F¼

Fx 90cos�þ360sin�ð Þ

�Fy 360cos�þ90sin�ð Þ

� �

742:676sin cos�1742:6762�L2�152:5972� �

2�742:676�L2

� �� �

ð3Þ

where F is the support force of the cylinders, Fx andFy are the components of the equivalent aerodynamicforce and L is the length of the hydraulic cylinders,which is equal to the distance between B and C.

Aerodynamic load test results. The aerodynamic load testbed was able to simulate the aerodynamic loadexerted on the prototype when the train was runningat speeds between 0 and 550 km/h. Functioning of theprototype was verified with aerodynamic loads wereexerted on it. Figure 14 shows some of the test resultsof the aerodynamic load test. These results indicatethat for an inclined brake panel at a given windspeed, the support force of the hydraulic cylindersmeasured by the two pressure sensors increased lin-early. The maximum support force was about14,000N when the panel opened to 75� at the windspeed of 500 km/h. This support force is equivalent toan aerodynamic wind load of 41,500N. The support

force values at a wind speed of 250 km/h are approxi-mately one-fourth those at a wind speed of 500 km/h.The test results verify the results of the numericalsimulation. According to the aerodynamic load test,the prototype can endure approximately 50,000N ofaerodynamic load, which is equal to the aerodynamicload created at a running speed of 550 km/h.

Conclusions

Aerodynamic braking is increasingly drawingattention from researchers since it is a clean andnon-adhesion braking method. An aerodynamic brak-ing prototype has been designed based on the param-eters of high-speed trains and the working principlesof airplane wings. The prototype is a unidirectionalopening model and is driven by a hydraulic system.The aerodynamic braking prototype consists of abrake panel device, a hydraulic actuating device andan electronic control device. It has successfully carriedout several functions, including service braking, real-time monitoring, data storage, and fault detecting andhandling.

The numerical simulation results indicate thatbraking efficiency in a high-speed zone can be consid-erably improved using the aerodynamic brakingprototypes mounted on a train. Deceleration in thehigh-speed zone between 250 and 500 km/h could beimproved by between 8 and 60%, thus corroboratingthe efficiency of aerodynamic braking. The numericalsimulation results agree with the wind tunnel testresults.

In order to verify the performance of the aero-dynamic braking prototype, a test bed was built tosimulate real wind loads created between 0 and550 km/h. The bench test results confirm that the

Figure 14. Results of wind load test.

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functions of the aerodynamic braking prototype weresuccessfully carried out under intense aerodynamicloads. The main findings can be summarized asfollows.

1. The time to taken to achieve the maximum brak-ing capacity of the prototype, which is the timetaken to open the brake panel from the closedposition (�5�) to the maximum angle of 75�, isless than 3 s.

2. The maximum support force measured at thejoints of the hydraulic cylinders is about14,000N when the panel is opened to 75� at awind speed of 500 km/h. This support force isequivalent to an aerodynamic load of 41,500N.

3. The support force of the hydraulic cylinders isproportional to the square of the wind load,which was generated by the test bed.

4. The prototype was able to endure approximately50,000N of aerodynamic load, which meets thedesign requirement of enduring an aerodynamicload at 550 km/h wind speed.

Currently, the prototype is mounted on a Chinesehigh-speed test train. The next step is to carry outonline tests so as to thoroughly evaluate the perform-ance of the aerodynamic braking devices.

Funding

This project is supported by National Natural ScienceFoundation of China (grant 61004077), and Fundamental

Research Funds for the Central Universities. (grant2860219022).

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