Aerodynamics HSR02

7/31/2019 Aerodynamics HSR02

1/46

Progress in Aerospace Sciences 38 (2002) 469514

Aerodynamics of high-speed railway train

Raghu S. Raghunathana, H.-D. Kimb,*, T. Setoguchic

aSchool of Aeronautical Engineering, The Queens University of Belfast, David Keir Building, Stranmillis Road, Belfast BT9 5AG,

Northern Ireland, UKbSchool of Mechanical Engineering, Andong National University, 388, Songchun-dong, Andong 760-749, South Korea

cDepartment of Mechanical Engineering, Saga University, 1, Honjo, Saga 840-8502, Japan

Abstract

Railway train aerodynamic problems are closely associated with the flows occurring around train. Much effort to

speed up the train system has to date been paid on the improvement of electric motor power rather than understanding

the flow around the train. This has led to larger energy losses and performance deterioration of the train system, since

the flows around train are more disturbed due to turbulence of the increased speed of the train, and consequently the

flow energies are converted to aerodynamic drag, noise and vibrations. With the speed-up of train, many engineering

problems which have been neglected at low train speeds, are being raised with regard to aerodynamic noise and

vibrations, impulse forces occurring as two trains intersect each other, impulse wave at the exit of tunnel, ear discomfort

of passengers inside train, etc. These are of major limitation factors to the speed-up of train system. The present review

addresses the state of the art on the aerodynamic and aeroacoustic problems of high-speed railway train and highlights

proper control strategies to alleviate undesirable aerodynamic problems of high-speed railway train system.

r 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Train aerodynamics; Impulse noise; Train tunnel; Compressible flow; Unsteady flow; Aerodynamic drag

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471

2. Speed-up tendency of train . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471

2.1. Requirement for the speed-up of train . . . . . . . . . . . . . . . . . . . . . . . . . . 471

2.2. Transportation energy efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

2.3. Limiting factors to the speed-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474

3. Aerodynamic problems of railway train . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474

4. Aerodynamic forces on railway train . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475

4.1. Aerodynamic drag of train . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475

4.2. Estimation of aerodynamic drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476

4.3. Comparison of the drags on different trains . . . . . . . . . . . . . . . . . . . . . . . 477

4.4. Pressure drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478

4.5. Friction drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

5. Aerodynamic shape of railway train . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

*Corresponding author. Tel.: +82-54-820-5622; fax: +82-54-823-5495.

E-mail address:[email protected] (H.-D. Kim).

0376-0421/02/$ - see front matterr 2002 Elsevier Science Ltd. All rights reserved.

PII: S 0 3 7 6 - 0 4 2 1 ( 0 2 ) 0 0 0 2 9 - 5


2/46

Nomenclature

a speed of sound or constant

A cross-sectional area of tunnel

A0 cross-sectional area of train

Ao Fourier transformb constant

c speed of sound or constant

Cd aerodynamic drag coefficient

Cds aerodynamic drag coefficient of short model

train

Cdl aerodynamic drag coefficient of long model

train

Cdp pressure drag coefficient

d hydraulic diameter of tunnel

d0 hydraulic diameter of train

D total drag

DM mechanical drag

DA aerodynamic drag

Ds aerodynamic drag of short model train

E energy

f frictional force on train

F frictional force on tunnel wall

h height of train

Hp horse power

I sound intensity

J Bassel function

c train length

m mass flow per unit time per unit volume

Mt train Mach number

M mass flow per unit timep static pressure

Dp0 pressure difference

P pressure of impulse wave

Per reference sound pressure

Pr Prandtl number

r radial distance

R cross-sectional area ratio of train to tunnel

Re Reynolds number

S Struve function

t time

u flow velocity

u0

flow velocity between train and tunnel wallU speed of train

V speed of train

Wp payload

W weight of train

x axial distance of tunnel

Greek letters

a angle of attack

g ratio of specific heats

r density

l friction factor of tunnel wall

l0

friction factor of train

l0m friction factor of model train

j energy dissipation

f blockage ratio or velocity potential

n kinetic viscosity coefficient

k wave number

Sub/superscripts

0 atmospheric state

1 state just before train fore-body

2 state just behind train fore-body

d drag force

H hydraulic diameter

l long model trainmax peak or maximum value

M pitching moment

in inside tunnel

out outside tunnel

s short model train or stagnation state

^ moving coordinate system

5.1. Wind tunnel test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482

5.2. Train-induced flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483

5.3. Aerodynamic forces due to trains passing each other . . . . . . . . . . . . . . . . . . 485

5.4. Cross-wind effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

6. Aeroacoustic problems of railway train . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

6.1. Aerodynamic noise due to train . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

6.2. Wind tunnel test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489

6.3. Reduction of aerodynamic noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490

7. Vibration of railway train . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491

8. Aerodynamics of railway train/tunnel systems . . . . . . . . . . . . . . . . . . . . . . . . . 491

8.1. Aerodynamic analysis of train/tunnel systems . . . . . . . . . . . . . . . . . . . . . . 491

8.2. Pressure wave due to the train entering into tunnel . . . . . . . . . . . . . . . . . . . 493

8.3. Pressure variation and aerodynamic drag inside tunnel . . . . . . . . . . . . . . . . . 493

8.4. Pressure variation inside train . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

R.S. Raghunathan et al. / Progress in Aerospace Sciences 38 (2002) 469514470


3/46

1. Introduction

During the past 60 decades, a great deal of attentionhas been concentrated on the development of airplanes.

Fluid dynamics, structural mechanics and automatic

control engineering have made large contributions to the

present aerospace technologies. Of them, fluid dynamics

mainly dealing with aerodynamic drag has played the

most important role in the development of airplanes and

flight vehicles.

Relatively, there have been only a few studies of the

full train system. This has been attributed to the fact

that train has run at very low speeds along a fixed track,

compared with airplanes. Thus, aerodynamic problems

on the train system could not have attracted much

attention from fluid dynamists. Recently, the train speed

exceeded over 300 km/h, being nearly comparable with

the past airplane speeds. Furthermore, the train system

is playing much more roles in transport than the

airplane. Systematic work is needed in the development

of the train system.

Aerodynamic and aeroacoustic problems accompa-

nied by the speed-up of train system are, at present,

receiving a considerable attention as practical engineer-

ing issues that should be urgently resolved. With the

speed-up of train, many engineering problems which

have been reasonably neglected at low speeds, are being

raised with regard to aerodynamic noise and vibrations,impulse forces occurring as two trains intersect each

other, impulse wave at the exit of tunnel, ear discomfort

of passengers inside train, etc. These are of major

limiting factors to the speed-up of the train system.

Such aerodynamic problems mentioned above are

closely associated with the flows occurring around the

railway train. However, much effort to speed up the

train system has been paid, to date, on the improvement

of electric motor power rather than understanding the

flow physics around the train and thereby finding a

proper control method. This has led to larger energy

losses and performance deterioration of the train, since

the flows around train are more disturbed due to

turbulence of the increased speed; consequently, the

flow energies are being converted to aerodynamic drag,noise and vibrations.

Now, many countries are operating the high-speed

railway trains, such as German Inter City Express (ICE),

Japanese Shinkansen and French Train de Grande

Vitesse (TGV); moreover, some countries like South

Korea and China are trying to construct the high-speed

railway train. Systematic work is highly needed to

understand the aerodynamics of high-speed railway

train, and to improve the existing conventional railway

trains and to develop a new generation of high-speed

train (HST) system.

This article deals with the aerodynamic phenomena

with regard to the high-speed railway trains, with a view

to understand practical engineering problems of the

present high-speed railway trains and with an emphasis

on proper control methods for the aerodynamic

problems.

2. Speed-up tendency of train

2.1. Requirement for the speed-up of train

Since 1960s, the speed-up of transportation vehicles

has been made with the timely requirements for a safeand bulk volume of transportation. This has led to the

advent of a large tanker, a high-speed railway train, a

jumbo jet, and a supersonic transportation (SST)

vehicle. The speed-up of transportation engine always

leads to the shortness of an economic distance asso-

ciated with the shortness of timedistance, resulting in

an increased value of time. The speed of a transportation

vehicle should be determined from the point of view of

the energy efficiency of the transportation.

Fig. 1 shows Bouladons criterion for the speed of a

transportation vehicle [1], in which the speed required

for a transportation vehicle is given by a function of

9. Impulse wave at the exit of tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496

9.1. State-of-the-art of impulse wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498

9.2. Theory of impulse wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498

9.3. Slab and ballast track tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500

9.4. Short and long tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502

9.5. Control methodologies of impulse wave . . . . . . . . . . . . . . . . . . . . . . . . . 503

9.5.1. Train body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5039.5.2. Tunnel entrance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504

9.5.3. Inside tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506

9.5.4. Tunnel exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508

10. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512

R.S. Raghunathan et al. / Progress in Aerospace Sciences 38 (2002) 469514 471


4/46

distance. The solid line indicates the required speed

according to the transportation distance, showing a

general tendency that the longer the transportation

distance, the higher the speed required. This line also

indicates an increased gradient with time, thus leading to

more increasing requirement for the speed-up of a

transportation vehicle. An ideal speed required for

transportation vehicle in the 21st century is also

indicated as the thick solid line. The present realizable

speed to meet the speed-up requirement for a transpor-

tation vehicle is also indicated in Fig. 1.

There are several regions between the distancespeed

curves of each transportation and the solid line, which

are, at present, not able to meet the requirement for the

speed of transportation. Region 1 indicates too long

distance for walking, but too short distance for driving.

Region 2 is between train and airplane. Region 3

indicates the speed lack of subsonic airplane for inter-

continental transportation. Region 4 indicates too long

a distance for boat on sea, but too short a distance for

airplane. To meet the speeds required for each region,

new-generation traffic system, high-speed railway train,

SST, and speedboat are under development, respec-

tively.

2.2. Transportation energy efficiency

In general, energy efficiency of a transportation

vehicle can be estimated based upon the fuel consump-

tion used. In the case of cargo transport, the energy Enecessary to carry unit weight per unit distance is

expressed as [2]

E consumed energykcal

transport capacityton transport distancekm:

1

In the case of passenger transport, Eq. (1) is changed to

E consumed energykcal

personone person transport distancekm: 2

Meanwhile, the efficiency of a transportation engine can

be obtained from the economic aspects of the fuel used:

economic efficiency of fuel

lower calorific value of fuel kcal=g

consumption rate of fuel g=hp h

horse power hp time hpayload ton distance km

: 3

For a given lower calorific value and consumption

rate of fuel, Eq. (3) reduces to

economic efficiency of fuel

phorse power time

payload distance

horse power

payload speed

Hp

Wp V: 4

The economic efficiency of fuel used can be an index

indicating the transportation energy, and is, thus,expressed by an inverse of the transportation efficiency:

transport efficiencypWp V

Hp

W V

Hp

Wp

W; 5

where W is the total payload, V the speed, and Hp the

horse power.

Using the equations above, Fig. 2 shows a comparison

between the transportation energies necessary to carry

one person up to 1 km [2]. For three different types of

vehicles, i.e., train, bus and car, the number on the right

side indicates the transportation energy relative to the

train, in which the transportation energy of the train is

10

100

1000

10.1 10 100 1000 100001

SST

6000km

13000km

1

2

4

3

Speed(km

/h)

Distance (km)

Automobile

Seoul-Pusan

Train

High-speed train (Shinkansen)

Jet-plane

Supersonic plane

Super-high speed train

New traffic system

Walking

Intercontinent

Ship

Ideal s

peed in

the 2

1thcentur

y

Ideal

speed

inthe

prese

nttim

e

Sea

Maximumdistance

Fig. 1. Relationship between speed and distance required for transportation vehicle.



5/46

assumed to be 100 kcal. It is found that the transporta-

tion energy of a car amounts to 6 times that of a train.

From the economic point of view of the fuel used,

Fig. 3 shows a comparison between each transportation

engine [3]. The solid line indicates the well-knownKarmanGabriellis limiting line (KG line). The KG

line increases with the speed of transportation vehicle. It

is noted that the economic efficiency of the fuel used in

transportation engine is improved as the transportation

vehicle approaches the KG line. Each transportation

vehicle has different speed ranges. For instance, the boat

is in the range below 50 km/h, the ground vehicles are in

between 50 and 200 km/h, the airplane in between 500

and 800 km/h.

These speed ranges can be classified, depending on

whether the vehicle is driven by the buoyancy force, the

reaction force, or the lift force. The KG line indicates the

lower limits of each speed range. For the range of the

buoyancy force support, the energy consumption in low-

speed ranges is comparatively low. However, with the

speed-up of the boat, the transportation efficiency

becomes remarkably low due to the increased wavedrag on the boat. For instance, the value of P=WpVincreases up to several hundred times as the boat speed

increases from about 15 knot (28.7 km/h) to 30 knot

(55.6 km/h), resulting in an extremely low transportation

efficiency. Therefore, a hydrofoil boat or a hovercraft of

the lift force support can be one of the alternatives for

higher speeds.

For the range of the reaction force support, the value

of P=WpV is low in the mid of the speed ranges. Forthe speeds over this range, a high-speed railway train is

recommended. In this case, the value of P=WpV is on

an extended line for the existing conventional train

100kcal

172kcal

593kcal

Train

Bus

Automobile

Fig. 2. Energies necessary to carry one person up to 1 km.

0.001

0.002

0.003

0.0050.004

0.01

0.02

0.030.040.05

0.1

0.2

0.3

0.40.5

1.0

2

3

10 20 30 50 100 200 300 500 1000 2 000

TGVICE

Shinkansen

MAGREV

SST

B737

B727

B707

B767B747SR

Karman-Gabrielli

HC

YS11F27

0.001

0.002

0.003

0.004

0.01

0.02

0.030.040.05

0.1

0.2

0.40.5

1.0

0.005

0.3

3

1

2

Speed(km/h)

New

estship

Large

tanker

Liner

Container

Warship

Small boat

Destroyer

Cruiser

HB

Helicopter

BusTruck

Turboprop

Jet plane

Jet plane(next generation)

Buoyancysupport

Reaction forcesupport Lift support

Buoyancy support

Lift support

Reaction force

support

P/W

V(kW

h/tonkm)

p

P/W

V(PSh/tonkm)

p

Automobile

Fig. 3. Comparison of each transportation.



6/46

system. Further extension of this line approaches the

Magnetic levitation (Maglev) train system. For the

range of the lift force support, the value ofP=WpV is,in general, dependent on the lift-drag ratio, being

independent of the speed of the transportation vehicle.

2.3. Limiting factors to the speed-up

In general, the transportation vehicle connecting from

city to city is required to meet the following conditions:

high-speed transportation, bulk volume transportation,

safe and comfortable transportation with less air

pollution and noise, highly reliable transportation with

low cost and maintenance, etc. The high-speed railway

train can be one of the alternatives to meet these

requirements.

Since 1940s, many countries have tried to speed-up

the conventional train system. Fig. 4 shows the progress

of the speed-up of train [4]. SymbolJ refers to the TGVin France,& the ICE in Germany,K the Shinkansen in

Japan and the HST in UK. It is found that in over a

half century, the train speed has increased more than

two fold.

Major limiting factors to the speed-up of train result

from many different sources. Technical factors are

associated with train/rail systems, while geographical

factors are related to the tunnel system. For instance, in

Japan, the portion of the tunnel to the total railway line

amounts to about 60%, while in France it is at most

several per cent. Fig. 5 shows the technical limiting

factors to the speed-up of train and associated factors.

These factors are mainly associated with the train body,

the track line, the electric devices around the track, etc.

For instance, the train speed along a curved track is

limited by the traveling performance, passengers

comfort and safety, which are again associated with

the train body and track line. Thus, to be able to

increase the maximum speed of trains, it is necessary to

take account of these limiting factors.

3. Aerodynamic problems of railway train

For the purpose of development of a faster and moresafe train system with lower air pollution and noise,

many researchers are paying much attention on the

aerodynamics of high-speed railway train. These works

have attention to the development of new-generation

train body, rail and tunnel systems. The aerodynamic

phenomena with regard to high-speed railway train are

strongly dependent on the train speed. Thus, the

aerodynamic problems become more important as the

train speed increases.

In general, the train aerodynamics are related to

aerodynamic drag, pressure variations inside train,

train-induced flows, cross-wind effects, ground effects,

pressure waves inside tunnel, impulse waves at the exitof tunnel, noise and vibration, etc. The aerodynamic

drag is dependent on the cross-sectional area of train

body, train length, shape of train fore- and after-bodies,

surface roughness of train body, and geographical

conditions around the traveling train. The train-induced

flows can influence passengers on the platform and is

also associated with the cross-sectional area of train

body, train length, shape of train fore- and after-bodies,

surface roughness of train body, etc.

The pressure variations, occurring as two trains

intersecting each other, are related to passengers

comfort and safe traveling of train. These are dependent

1935 1945 1955 1965 1975 1985 1995100

200

300

400

500

DCEL

Inter City Express(ICE)

Train de Grande Vitesse(TGV)

Shinkansen

High Speed Train(HST)

205

186km

215

243

331

256

253

286

318

380

319

317

345

406.9

336

325.7

EL

EL

482.4

515.3

ICEModelShinkansen

TGV

TGV

TGV-A

TGV-A

ICE

ICE

Speed(km

/h)

Year

DC : diesel locomotiveEL : electric locomotive

Fig. 4. Progress of railway train.

Speed type

Maximum speedBrake

performace

Power

Brake system

Body

Track

Tunnel

Electric lines

Electric facilities

Signalcommunication

Travel equipment

Train

Railroad

Electricity

Environmentalproblem

Passengercomfort

Controlperformance

Pantograph

performance

Travelingperformance

Retrogressionperformance

Adjustablevelocity

HardwareLimiting factors

Foundation Elementsof Railway system

Speed oncurved track

Speed onbranched track

Fig. 5. Factors limiting the speed-up and related factors.



7/46

on the shape of train fore- and after-bodies, train width,

and the distance between track lines. The cross-wind can

also influence the safe traveling of the train, relating to

train height and perimeter, bridge system, etc.

The impulse wave at the exit of tunnel influences the

surrounding area around the train track and is

dependent on the cross-sectional area of train body,

the cross-sectional area of tunnel, the shape of train

fore- and after-bodies, the tunnel length, the kind of

track, etc. The pressure variations influence the struc-

tural strength of the train body, passengers comfort,

and are associated with the cross-sectional area of the

train body, cross-sectional area of tunnel, train length,

tunnel length, etc. Table 1 lists these major aerodynamic

problems of HST and associated factors. All of these

aerodynamic problems are closely related to the train

shape, which is required to produce aerodynamically

good characteristics.

4. Aerodynamic forces on railway train

4.1. Aerodynamic drag of train

The aerodynamic characteristics of HST are quite

different from those of airplane. There are many

characteristic features in the aerodynamics of the high-

speed railway train, in the points that the train length is,

in general, very long, compared with the equivalent

diameter of it, the train runs close to adjacent structures,

passes through a confined tunnel, and intersecting with

each other, the train runs along a fixed railway track,

always interacting with ground, and the train can be

influenced by cross-winds. Thus, the aerodynamics,

which has been applied to airplane, may not be of help

for a detailed understanding of the HST aerodynamics.

In general, a desirable train system should be

aerodynamically stable and have low aerodynamic

forces. These aerodynamic characteristics are closely

associated with the aerodynamic drag of the running

train. The aerodynamic drag on the traveling train is

largely divided into mechanical and aerodynamic ones.

Of both, the aerodynamic drag can influence the energy

consumption of train. Thus, detailed understanding on

the aerodynamic drag and its precise evaluation are of

practical importance.

It has been well known that the aerodynamic drag is

proportional to the square of speed, while the mechan-

ical drag is proportional to the speed. Compared with

the mechanical drag, the portion of the aerodynamic

drag becomes larger as the train speed increases. Thus,

reduction of the aerodynamic drag on high-speed

railway train is one of the essential issues for the

development of the desirable train system.

In the open air without any cross-wind effects, the

total drag on the traveling train can be expressed by a

sum of the aerodynamic and mechanical ones [5]:

D DM DA a bVW cV2; 6

where DA and DM are the aerodynamic and mechanicaldrags, respectively, a; b and c are the constants to bedetermined by the experiment, V the train speed and Wthe train weight. In Eq. (6), the mechanical drag, being

proportional to the train weight, includes the sliding

drag between rails and train wheels, and the rotating

drag of the wheels.

The measurement of the total drag on train and its

precise prediction are not straightforward. The total

drag can be obtained by using a deceleration speed of

train or the consumed electric power, as will be

described later. Fig. 6 shows a typical example of the

measured total drag on train [5]. All of the data

Table 1

Aerodynamic problems and their related matters

Aerodynamic problems Related matters

1 Aerodynamic drag of train Maximum speed, energy consumption

2 Aerodynamic characteristics of train due to cross-winds Safety in strong cross-winds

3 Aerodynamic force due to passing-by of two trains Running stability,Quality of comfort for passengers

4 Winds induced by train Safety for passengers on platforms,

Safety for maintenance workers

5 Pressure variations in tunnels Quality of comfort for passengers,

(Ear discomfort)

Airtightness of vehicle,

Stress upon vehicle,

Ventilating system of vehicle

6 Micro-pressure waves radiating from tunnel exit Environmental problems near tunnel exit

7 Ventilation and heat transfer in underground station and tunnel Quality of comfort for passengers,

Prevention of disaster (fire)

8 Aerodynamic noise Environmental problems



8/46

indicated refer to a given train with the same weight and

length, and these collapse onto a single line, given by acurve fit, D 12:484 0:04915 0:001654V2:

In order to reasonably estimate the total drag on the

trains with variable weight and length, it is necessary to

divide it into the mechanical and aerodynamic drags.

For instance, the least-squares method can be used to

correlate the data, and consequently the term propor-

tional to the square of speed can be considered as the

aerodynamic drag. However, it is quite difficult to

reasonably extract the aerodynamic drag from the total

drag, since it can contain natural wind effects, and

additionally, it can depend on the methods of how to get

the second-order polynomials for the correlation as well.

4.2. Estimation of aerodynamic drag

Unlike the aerodynamics of airplane, the train runs

along a fixed track, strongly interacting with surround-

ing structures, ground, tunnel, platform, etc. Especially,

the presence of an intersecting train makes the analysis

of the train aerodynamics extremely difficult.

In order to speed up the train, it is necessary that the

electric motor power increases or the aerodynamic drag

reduces. Compared with the open air traveling, the

aerodynamic drag can considerably increase as the trainpasses through a tunnel [6]. This is because the train-

induced flows do work to increase the pressure by

interacting with the tunnel walls. A pantograph system

may produce the aerodynamic drag corresponding to

that caused by one train. In particular, the structures

underneath the train may produce more drag.

In the open air traveling, the aerodynamic drag on

train can be divided into two contributions; one is

dependent on train length and the other is independent

of it. The drag independent of the train length is the

pressure drag caused by the fore- and after-bodies of

train. It is not easy to estimate the drag dependent on

the train length. This is because the friction drag on the

train body should involve all kinds of the drags

occurring in the connecting parts between trains,

photographs, the structures under the train, etc.

In this case, the aerodynamic drag can be expressed

as [7]

D 1

2rA0V2 Cdp

l0

d0c

; 7

where V is the train speed, r the density of air, A0 the

cross-sectional area of train, Cdp the coefficient of the

pressure drag caused by the fore- and after-bodies of

train, d0 the hydraulic diameter of train, l the train

length, and l0 the hydraulic friction coefficient caused by

the connecting parts between trains, photographs, the

structures under the train, etc.

In general, a wind tunnel test for measuring the

aerodynamic drag on train, which is quite long

compared with the equivalent diameter, is highlydifficult. The use of a small model for the train wind

tunnel test causes several problems associated with lower

Reynolds numbers. In addition, ground effects on the

aerodynamic drag should be considered in the wind

tunnel test.

In Eq. (7) Cdp can be obtained by wind tunnel

experiment. Using the real train entering into the tunnel,

Hara [8] reported that l0 could be obtained by the

pressure rise on the train body, when it enters into

tunnel. A train entering into the tunnel compresses the

atmospheric air ahead of the train and the resulting

compression waves will propagate nearly at the speed of

sound towards the exit of the tunnel.

Meanwhile, the air displaced by the train entering into

the tunnel will discharge back from the entrance of

tunnel. In this case, the air flow should overcome the

frictional drag on the train body and tunnel walls,

resulting in a pressure gradient. Due to this fact, the

pressure on the train body will increase as the train

proceeds into the tunnel, as schematically shown

in Fig. 7.

The compression waves propagating along tunnel will

discharge from the exit of the tunnel, consequently

forming an impulse wave, as will be described later. At

the same instant as the compression waves discharge

0

50

100

150

200

0 50 100 150 200 250 300

D=12.484+0.04915V+0.001654V2

Sinkansen 100series

Speed (km/h)

Travelingd

rag(N)

Fig. 6. Traveling drag on Shinkansen (series 100).

x

U

po

p2(A-A')

v2f

F

po(A-A')

32

Fig. 7. Flow model for friction coefficient.



9/46

from the exit of the tunnel, expansion waves will be

formed to meet the mass conservation law, and then

propagate back from the exit of the tunnel towards the

entrance of tunnel. In Haras analysis, it is assumed that

the expansion waves do not interact with the train body

inside tunnel and the after-body of the train is still in the

open air.

In Fig. 7, the momentum equation can be applied to

the control volume between the cross-sections 2 and 3,

as below

p2 p0A A0 f0 F 0; 8

where p2 is the pressure on the train body, p0 the

atmospheric pressure, A the cross-sectional area of

tunnel, A0 the cross-sectional area of train, f the

frictional force on train body, and F the frictional force

on tunnel walls. Eq. (8) can be changed to [8]

p2 p01 R 12rV2c Rl

0

d0c v2

V

2l

dv2V

2

; 9

where R is the ratio of cross-sectional areas of train to

tunnel, l the distance from the entrance of tunnel to

train, l the hydraulic friction coefficient on tunnel walls,

l0 the hydraulic friction coefficient on the train body, d

the hydraulic diameter of tunnel, d0 the hydraulic

diameter of train, V the train speed and v2 the air flow

velocity occurring between train and tunnel walls. For a

known value ofv2=V; the hydraulic friction coefficient l0

on the train body can be obtained by measuring the

pressure rise (p2 p0).

4.3. Comparison of the drags on different trains

The aerodynamic drag measurement results [9], which

were conducted using a wind tunnel test in France, are

summarized in Table 2, where each of the contributions

of the train body (TGV), the connecting part between

trains and the structures under the train on the

aerodynamic drag are indicated. The wind tunnel test

was carried out at a train speed of 260km/h under

standard atmospheric conditions. The total drag is also

presented on the right side of Table 2.

Of the total drag, the aerodynamic drag only on the

train body is about 80%, the aerodynamic drag due to

the pantograph system and other devices over the train

is 17%, the rest drag of 3% is due to the mechanical

drag caused by the brake system, etc. From the

measured data above, the total traveling drag D on

train is given by D A BV CV2; where theconstants A and B are experimentally given by 250

and 3.256, respectively. Note that these values are 5%and 17.1% of the aerodynamic drag on only the train

body, respectively.

Figs. 8 and 9 present the aerodynamic drag on the

Germany ICE [9]. The type of the ICE, its cross-

sectional area and aerodynamic drag are also indicated

in Fig. 8. For example, the train of type a has a cross-

sectional area of 14.61 m2 and is assumed that its

aerodynamic drag is 100%. For the trains of different

types and cross-sectional areas, relative aerodynamic

drag is given based on the train of type a. In the case of

the train of type k, the cross-sectional area of the train is

11.39 m

2

and the aerodynamic drag relative to the type a

Table 2

Wind tunnel experiment for the traveling drag on TGV

Components of traveling drag Drag coefficient (151C,

1013 mbar)

Total drag

Drag in 260 km/h Power in

260km/h (kW)

N/(km/h)2 (%) N (%)

Aerodynamic component Drag of train 0.04595 80 3106 62.5 2243

Equipments on train

roof

0.00965 17 652 13.1 471

Total aerodynamic

components

0.05560 97 3758 75.6 2714

Disk brake 0.00170 3 115 2.3 83

Total 0.05730 100 3873 77.9 2797

Rolling drag (train

407ton)

BV 3:256V 847 17.1 612

A 250 250 5.0 181

Total drag D A BV CV2 4970 100.0 3590



10/46

is 78%. In Fig. 8, note that the trains of different cross-

sectional areas have a train body mount system and a

skirt system to smooth the structures underneath the

train.

For the trains shown in Fig. 8, each portion of the

contributions of the fore- and after-bodies of train, the

connecting part between trains, the train wall surfaces,

the pantograph system, etc. to the total aerodynamic

drag is given in Fig. 9 [9]. In the case of type a, it is

found that the aerodynamic drag caused in the

connecting part between trains is about 4%, the surfacefriction drag 23%, the fore- and after-bodies 8%, the

pantograph system 7%, and the underneath structures

of train 58%. For type f; the total aerodynamic drag isabout 50% of that of type a; and each of the portions isquite different from that of type a. For reference, all

these data refer to the same train length (200 m).

In the case of Japanese Shinkansen, the 0 series have

been known as l0 0:018; and Cdp 0:2 [10,11]. Anempirical equation to predict the aerodynamic drag on

the traveling train is given by the following equation:

D 1:2 0:022VW 0:013 0:00029 cV2; 10

where D is the total drag (kgf), V the train speed (km/h),

W the total weight of train (ton), and l the train length

(m). The term that is proportional to the square of speed

is the aerodynamic drag. For l 400 m, corresponding

to the length of 16 trains, about 90% of the aerodynamic

drag is attributed to the friction drag on the middle part

of the train. Of the Japanese Shinkansen, series 100 has a

semi-body mount system for the underneath structures,

and series 200 has an underneath coverage to prevent

snow accumulation on the train body. Table 3 lists some

major parameters influencing on the aerodynamic

drag [10,11]. It is found that smoothing the under-

neath structures of train by using the body mount

system or the skirt system reduces the hydraulic friction

coefficient.

4.4. Pressure drag

Of the aerodynamic drag components, the pressure

drag comes from the pressures on the fore- and after-

bodies of train, and, in the case with a double deck in

train series, it stems from the pressures due to the abrupt

change in the cross-sectional area of the train. Assuming

that the coefficient of the pressure drag is Cdp and in the

case of a double deck, it is Cdpd; a wind tunnel test [12]has been carried out to investigate the pressure drag. In

the experiment, each of the models for the fore- and

after-bodies of train and the middle part of train has

been manufactured. Depending on the length of the

middle part of the model, the model train experiment of

different lengths could be done.

For a train model with a short length, the coefficient

of the aerodynamic drag can be written as

Cds Ds

1

2rU2A0

; 11

15

10

5

0a b c e f

4%

23%

8%

7%

58%

2%

35%

10%

9%

44% 44%

5%

11%

40%

52%

14%

7%

27%

61%

15%

2%

22%

Type

Cross-sectionalarea(m2)

Surfacefriction

Pantograph

Head & tailof train

Underneathstructures

Connectingparts

Fig. 9. Aerodynamic drag components of ICE.

a

b

c

d

e

f

14.61 100%

11.39 78%

10.14 69%

8.70 60%

7.80 53%

7.10 49%

Type Cross-sectionalarea (m )2

Drag(%)

Moving direction

(m2)

Fig. 8. Aerodynamic drag on ICE (the hatching area is the

device to smooth the structures underneath train).



11/46

where Cds is the coefficient of the aerodynamic drag for

the short train model, Ds the aerodynamic drag, A0 the

cross-sectional area of the model train, U the wind

velocity, and r the density. Furthermore, the coefficient

of the aerodynamic drag can be divided into two

components: one depending on the length of the model

train and the other independent of the length of the

model train, as

Cds Cdp l0m

cs

d0; 12

where Cdp is the coefficient of the pressure drag on the

fore- and after-bodies of the model train, l0m thecoefficient of the hydraulic friction on the model train,

ls the length of the model train, and d0 the hydraulic

diameter of the model train.

Meanwhile, for a long model train, the coefficient of

the aerodynamic drag is similarly given

Cdl Cdp l0m

cl

d0; 13

where ll is the length of the longer model train. From

Eqs. (12) and (13), the coefficient of the pressure drag

Cdp can be obtained by

Cdp Cdscl Cdlcs

cl cs: 14

In reality, the coefficient l0m of the hydraulic friction

on the model train can be significantly different from

that of real train, as will be described later.

4.5. Friction drag

Of the aerodynamic drag components, the estimation

of the friction drag is more complicated, compared with

that of the pressure drag. The friction drag comes from

the train walls, the pantograph system, the connecting

part between trains, other devices on train roof, etc.

As described previously, the friction coefficient can be

obtained by the pressure rise on the train body entering

into tunnel.

Fig. 10 shows the experimental data of the stagnation

pressure and the pressure rise on the train, which enters

into tunnel [8,10], where a refers to the state just after the

fore-body of the train enters into tunnel, b just after the

after-body of the train enter into tunnel, and c refers to

the instant that the compression waves occurring when

the train fore-body enters into tunnel are reflected back

from the exit of tunnel as the expansion waves. In order

to estimate the hydraulic friction coefficient of a train,

we can use the pressure rise from the instant a to b:Fig. 11 represents the pressure distributions measured

on the train body for the time range between a and b

[8,10]. For the sake of simplicity, the fore-body of the

train is assumed to be x 0; where x is the distance fromthe entrance of tunnel to the fore-body of the train. It is

found that the pressure increases nearly linearly. How-

ever, in reality, the pressure near the fore-body of the

train may deviate from the linear distribution due to the

fore-body effects. In this case, we can eliminate the fore-

body effects to precisely estimate the friction coefficient,

as schematically shown in Fig. 12, where the compression

waves due to the train fore-body entering into tunnel donot yet reach at the exit of the tunnel.

For the flowfield shown in Fig. 12, we can again

assume that the flow is one-dimensional. Neglecting the

viscous forces on the flows between the train fore-body

and the compression waves, the isentropic relation and

the simple wave theory can be written as

p1

rg1

p0

rg0

; 15

2

g 1 ffiffiffiffiffiffiffigp1

r1r u1 2

g 1 ffiffiffiffiffiffiffiffigp0

r0;r 16

Table 3

Parameters associated with aerodynamic drag (Shinkansen)

Series Cross-sectional

area A0 (m2)

Hydraulic

diameter d0 (m)

Friction

coefficient of

train side body

(l0)

Pressure drag

coefficient Cdp

Train 0 12.6 3.54 0.017 0.20

200 13.3 3.64 0.016 0.20

100 12.6 3.54 0.016 0.15

Tunnel Line Cross-sectional

area A (m2)

Hydraulic

diameter d (m)

Friction coefficient of tunnel wall (l)

Tokaido 60.5 7.8 0.02

Sanyo 63.4 8.1 0.02

Tohoku

Joetsu



12/46

where p is the pressure, u the velocity, r the density, g the

ratio of specific heats of air, and subscript 0 and 1

denote the states just before the compression waves and

just before the train fore-body, respectively. In addition,

the flow properties just before and after the train fore-

body can be obtained by the equation systems of mass

a

b

c

1kPa

1.0sec

U

p

Train

Tunnel

Time(t)

Pressure distribution for the steady flow inside tunnel

Pressure on the side body of the 1st train

Pressure on the side body of the 2nd train

Stagnation pressure on the lst train

Time(t)

Pressure

Pressure on the side body of the 4th train

Pressure on the side body of the 6th train

Fig. 10. Pressure rise due to the train entering into tunnel (U 220 km/h, and Shinkansen series 100).

3.0

2.0

1.0

0.0

400 300 200 100 0

Train speed, U=216km/hSlab track

Tunnelentrance

Pressureriseonthesidebodyoftrain(kPa)

Trainhead

Distance from tunnel entrance to train head, X(m)

Tunnelentrance

Tunnelentrance

Tunnelentrance

Tunnelentrance

Tunnelentrance

Fig. 11. Pressure distributions on the side body of train.



13/46


14/46

5. Aerodynamic shape of railway train

5.1. Wind tunnel test

Detailed configuration of the fore- and after-bodies of

train can significantly influence the aerodynamic char-

acteristics. An example of typical wind tunnel test using

model trains is shown in Fig. 15, where the experiments

yield 16 different kinds of the fore- and after-bodies ofmodel trains [14,15]. The fore-body of the model train is

the same shape as the after-body. The configuration of

the model train is characterized by number 1, 2, 3 and 4,

and the characters A, B, C and D. For the sake of

simplicity, here we define the numbers as train series and

the characters as train types.

In addition, the number refers to the length of the

change in cross-sectional area of the model train. For

instance, the length of the change in the cross-sectional

area of the model train becomes longer with the number;

for further details, series 1, 2, 3 and 4 have the lengths of

the change in the cross-sectional area of the model train

0.5 times, 1 time, 2 times, and 4 times the model width,

respectively. It is assumed that the length of the change

in the cross-sectional area for the A type of series 1 is

zero.

Meanwhile, the model configurations of the A and B

types are nearly two-dimensional, but those of the C and

D types are nearly three-dimensional. For further

details, see Fig. 15. In real high-speed railway trains,

the ICE is close to A or B type, but the Shinkansen(Series 100) close to C or D type.

These systematic train models were tested in a

subsonic wind tunnel, which is schematically shown in

Fig. 16 [14,15], where the fore- and after-bodies are

installed onto the wind tunnel test section to measure the

aerodynamic forces on them. The fore- and after-bodies

of the train model are always combined with the middle

part and the dummy fore- and after-bodies, thus

forming a full model train. Fig. 17 shows the effects

of the fore-body configuration on the aerodynamic

drag [14,15], where the middle part and dummy after-

body are fixed. Fig. 18 presents the influences of the

50 150 250 350 4500.0

0.02

0.04

Distance from tunnel entrance to train head, X(m)

Hydraulicfrictionalcoefficientontrain(

)'

Fig. 14. Relationship between l0 and X (Shinkansen 0 series).

1-A

1-B

1-C

1-D

2-A 3-A 4-A

2-B 3-B 4-B

2-C 3-C 4-C

2-D 3-D 4-D

Fig. 15. Model train configuration.



15/46

after-body configuration on the aerodynamic drag[14,15], where the middle part and dummy fore-body

are fixed. Note that the length of the fore-body is

normalized by the width of the train model.

For series 1 of a comparatively short fore-body, the

aerodynamic drag on types B and C is nearly the same,

and their Cd values are relatively low, compared with

types A and D. It is found that the fore-body of type A

has the highest Cd value. For a given type of the train

model, it is interesting to note that the aerodynamic drag

does not change for L=W values larger than 1.0.It seems that the after-body effects on the aerody-

namic drag are more sensitive to L=W; compared with

those of the fore-body. For a given type of the modeltrain, series 4 has the lowest Cd value. In the case of the

same series of the model train, the aerodynamic drag on

type D is the lowest. The fore- and after-bodies effects

on the aerodynamic drags are associated with flow

separations, which can influence the train-induced flows,

as will be described next.

5.2. Train-induced flows

The winds induced by a traveling HST can affect

passengers at platform and the structures around the

railway lines. Thus, estimation of the train-induced flows

1500

385

800

415

131332400613

13.5

300

103

50m/s

347141

347131

(a) Aerodynamic drag measurement of train head

1500

385

800

415

131332 400 613

13.5

300

103

50m/s

347

(b) Aerodynamic drag measurement of train tail

HeadMiddle

Tail(dummy)

Exit of wind-tunnel

Head(dummy)Middle Tail

Pitot tube

Exit of wind-tunnel

Pitot tube

Pitot tube

Balance meterBalance meter

Fig. 16. Test rig for aerodynamic drag on train.

:1-A,2-A,3-A,4-A:1-B,2-B,3-B,4-B

:1-C,2-C,3-C,4-C

:1-D,2-D,3-D,4-D

0.0 1.0 2.0 3.0 4.00.0

0.2

0.8

0.4

0.6

3-C type Middle(dummy)

Head

Dragcoefficient(C)D

L / W

Fig. 17. Effect of L=W on aerodynamic drag.

:1-A,2-A,3-A,4-A

:1-B,2-B,3-B,4-B:1-C,2-C,3-C,4-C

:1-D,2-D,3-D,4-D

0.0 1.0 2.0 3.0 4.00.0

0.2

0.8

0.4

0.6

3-C type Middle Tail

(dummy)

L / W

Dragcoefficient(C)D

Fig. 18. Effect ofL=W on aerodynamic drag.



16/46

should be included in a structural design of the platform

and surrounding facilities around the railway lines. For

a given speed of train, the train-induced flows are

strongly dependent on the fore-body configuration, and

train length. In particular, the train-induced flows candiffer, depending on whether the fore-body shape is two-

or three-dimensional.

Fig. 19 shows an example of the experimental test rig

for the train-induced flows [14,15]. In order to simulate

the train-induced flows occurring at a platform, a model

platform is placed on one side of the model train, in

which a hot-wire system is installed at a height of 1.20 m

from the ground surface, and the train-induced flows at

a certain distance away from the model train is

measured. The train-induced flow data are presented,

subtracted the wind tunnel air velocity from the

measured velocities.

The train-induced flows due to the fore-body are like a

source flow, while those due to the after-body are like a

sink flow. This phenomenon is more striking for two-

dimensional shapes rather than three-dimensional ones.

The effects of the fore- and after-bodies on the train-induced flows are shown in Fig. 20 [14,15]. It is found

that the train-induced flows become small with an

increase in L=W: For a given series, types A and Bproduce lower train-induced flows, compared with types

C and D. Note that types C and D are close to three-

dimensional shapes. In types A and B, a more train-

induced flows will pass over the model train roof, while

in types C and D, the flow that spills over the model

train can be of the same magnitude as it passes beside

the train.

For series 13, the train-induced flows produced in

type D are larger than those in type C. This is attributed

30m/s

(a) Measurement of train head

(b) Measurement of train tail

(c) Train and platform

158

50

112

70

30m/s

Pitot tube Pressure measurement

Head Middle

(dummy)

Model platform

Exit of wind-tunnel

Model platform

MiddleTail

Pressure measurement

(dummy)

Exit of wind-tunnel

Ground plate

Measuring point of pressure

Model platform

Fig. 19. Test rig for train-induced flow measurements.



17/46


18/46


19/46

produced when the after-bodies of the model train pass

each other is lower than that created when the fore-

bodies of the model train pass each other. The length of

the after-body somewhat affects the negative peak

pressures, but it does not influence the positive peak

pressure. It is, thus, concluded that the model trains

which are close to the two-dimensional shape produces

the positive and negative peak pressures less than those

of the three-dimensional shape.

In the open air, the pressure variations on the side

bodies of real trains passing each other are shown in

Fig. 25 [5], where two cases are compared with each

other; The speed V of one train is zero while the speed U

of the other train is 260 km/h, traveling towards the

right side, as shown in Fig. 25(a). In Fig. 25(c), the speed

V of one train is 210 km/h, while the speed U of the

other train is 260km/h. The pressure variations aremeasured on the middle part of each train.

It is found that the positivenegative pressure varia-

tion like a pulse wave is produced as the fore-bodies of

real trains pass each other, while the negativepositive

pressure variation is created as the after-bodies pass

each other. These pressure variations on the side body of

trains are strongly dependent on the detailed shape of

the fore- and after-bodies and the speed of each train,

and can cause the yawing motions of the traveling trains.

It is known that the peak pressures produced by the

trains passing each other is proportional to the square of

the speed of trains and the timewidth of the peak

pressures is proportional to an inverse of the sum of the

speeds of each train. Here it should be noted that in

the open air, the pressures, produced opposite side to the

trains passing each other, nearly remain constant at

atmospheric pressure without any appreciable fluctua-

tions, as shown in Fig. 25(b).

p(kPa)

0

0.5

1.0

-0.5

-1.0

U=260km/h, V=210km/h

0.5s0.0s 1.0s 1.5s

U=260km/h, V=0km/h

0

0.5

1.0

-0.5

-1.0

p(kPa)

0.5s0.0s 1.0s 1.5s 2.0s 2.5s

0

0.5

U

V A

B

(c)

(b)

(a)

Passing train head Passing train tail

Pressure fluctuation

Pressure fluctuation (opposite side of the train)

Pressure fluctuation

Time(sec)

Time(sec)

Fig. 25. Pressure variations occurring when two trains pass each other.

1500

2500

187

12112693333

1390

39

333

Dummy Dummy

Measuring trains

Rail

Bridge

Rotating end plate

Rotating end plate

End plate End plateThreecomponentforcemeter

Fig. 26. Test rig for cross-winds.



20/46

5.4. Cross-wind effects

The cross-wind effects on the traveling train can

closely be associated with the traveling safety. The cross-

winds can be more seriously influence when the train

runs over a bridge [1618]. Fig. 26 shows the typical

example of a 1/30 model test to investigate the three-component forces on the train running over a bridge

[19]. The wind tunnel has a dimension of 1.5 m 2.5 m.

In tests, the wind speed and its angle of attack are

changed, the resulting Reynolds number being in the

range of 6 1048 104. Table 4 summarizes the results

of the wind tunnel tests for the coefficients of drag (Cd),

lift (Cl) and pitching moment (CM), compared with a

computational prediction [19].

For the wind speed of 10m/s, the coefficients of

drag (Cd), lift (Cl) and pitching moment (CM) are,

respectively, 1.4, 0.2 and 0.2 as the train runs in

the open air, while these are, respectively, 1.7, 0.6, and

0.3 as the train travels over the bridge. It is believed

that the drag and lift coefficients on the train become

much higher when it travels over the bridge. The

computations of the three-component forces only

qualitatively predict the measured aerodynamic forces

on the train.

6. Aeroacoustic problems of railway train

6.1. Aerodynamic noise due to train

For the assessment of aerodynamic noises producedby a traveling train in the open air, it can be often

convenient to classify the noise sources. In addition to

the aerodynamic noises due to the flows around the

traveling train, there are many different noises which are

caused by train wheels, structures around track,

pantograph system, etc. In order to reduce these noises,

it is required to know how extent is each contribution to

the noises. In general, aerodynamic noises are strongly

dependent on the train speed U [2022], being approxi-

mately proportional to U62U8: Thus, the noise allevia-tion is of more practical importance when the train

speed increases.

Fig. 27 shows the aerodynamic noises produced by a

traveling train in the open air [2325]. It can be found

that the aerodynamic noises due to the traveling train

are largely generated by the fore-body of the train, the

connection part between trains, and the panto-

graph system. In practice, the pantograph system is

composed of many bars with small diameters, which can

play a musical instrument to create the aerodynamic

noises. The pantograph system creates a number of

vortices behind it. A pantograph cover can be used to

reduce the aerodynamics noises generated by the

pantograph system [24,25], but it can be of an additional

1 2 3 4 5 6 7 8 9 10 11 12

10dB

1.0s

(a) Typical noise level of high-speed train

(b) Outlook of high-speed train

U=235km/h

Time(t)

Soundpressurelevel(d

B)

Downward pantographUpward pantograph

Pantograph Pantograph cover

Air conditioning unit

High-voltage cable connector

Fig. 27. Aerodynamic noise level of HST.

Table 4

Comparison of wind tunnel experiment and computational results

Train Train+bridge

Experiment Computation Experiment Computation

Drag coefficient Cd 1.4 1.4 1.7 1.7Lift coefficient Cl 0.2 0.2 0.6 0.2

Pitching moment CM 0.2 0.3

Reynolds number Re 56,000 5000 84,000 5000



21/46

aerodynamic drag and can be a source of additional

noise as well. There may be a big separation region

downstream of the pantograph cover, and consequently

it can cause the train body to vibrate, consequently

influencing the traveling safety of train and passengers

comfort.

The fore-body of a train is one of the noise sources. Inusual, there are a lot of roughness on the fore-body

surface. The aerodynamic noises are strongly dependent

on the detailed configuration of the surface roughness

and the entire shape of train fore-body as well. These

geometrical configurations are associated with the wind

speed along them and separation.

Fig. 28 shows a typical example of the aerodynamic

noise measurement at a location of 25 m away from

a traveling train [24,25], where the peak frequency

components generated by the fore-body of train are

presented. It is found that the aerodynamic noises are

largely composed of high-frequency components. From

the point of view of the aerodynamic noises, it is

desirable that the fore-body configuration of train

should have a long nose to reduce aerodynamic noises.

6.2. Wind tunnel test

The aerodynamic noises are almost always associated

with the aerodynamic drag. Reducing the aerodynamic

noises should be done without increasing the aerody-

namic drag. In addition to the aerodynamic noises

generated by the fore-body of train, the connection part

between trains has lots of component structures such as

ventilation system, pantograph system, etc. Of them, a

majority part of noises are generated by the pantograph

system.Fig. 29 shows a typical measurement example of the

aerodynamic noises which are caused by the pantograph

system [24,25], where the pantograph system and

microphone array are schematically illustrated. The

locations of the microphone are indicated by M1M7.

The wind tunnel used has a test dimension of

3.0m 5.0m, and its maximum wind speed and the

turbulence intensity are estimated by 270km/h and

0.2%, respectively.

In general, the aerodynamic noises generated by the

pantograph system have some directivity towards the

flow direction, normal to the direction of the panto-graph length. Thus, the measurement locations M7 and

M3, which are, respectively, just over and beside the

pantograph, are employed to assess the aerodynamic

200 500 1000 2000 5000

10dB

U=270km/h

U=230km/h

Shinkansen (100 series)

1/3 Octave band frequency (Hz)

Soundpressurelevel(dB)

Fig. 28. Aerodynamic noise due to train head.

4000mm

1160mm

5435mm

1000mm

2000mm

5160m

m

5000mm

4000mm

1000mm

2000mm

M1

M2

M3

M4

M5

M6

M7

M2,4,6

M1,3,5

M7

Exit of wind-tunnel Side view Front view

Fig. 29. Test rig for aerodynamic noise measurement.



22/46

noises, as shown in Fig. 30. The wind speed is changed

between 100 and 260 km/h. It is found that the sound

pressure level (SPL) of the aerodynamic noises is closely

related to the wind speed, and the aerodynamic noises

generated by the pantograph system are composed of

large amplitude components of a wide band frequency.

This is because the pantograph system is very compli-

cated and thereby, the noises being caused by many

different sources. For instance, the pantograph system is

composed of many bars of different diameters. Thus, the

different characteristic lengths to the aerodynamicnoises can be responsible for the wide band frequency.

6.3. Reduction of aerodynamic noise

In order to reduce the aerodynamic noises produced

by a traveling train, the fore-body configuration of train

is needed to be of the long nose with a smooth surface,

and the middle part of train to be designed without any

sizable roughness. An aerodynamically well-designed

shape of train can have such a noise level as low as in the

boundary layer shear flows. In practice, there is a limit in

making the strain surface aerodynamically smooth.

Fig. 31 presents a measurement example of the

aerodynamic noises which are generated by a two-

dimensional body, like the cross-sectional area of the

pantograph system [24,25]. A circular cylinder with a

diameter of 50 mm (see Fig. 31(a)) and a square cylinder

with the same equivalent diameter (see Fig. 31(b)) are

employed as the aerodynamic noise sources. The windspeed is 200 km/h. The noise measurement is done at a

location beside the cylindrical body. In order to

investigate the surface roughness effects, the cylindrical

body is coated with a sponge, a carpet, and a thick cloth,

respectively. It is found that the SPL of the aerodynamic

noises in the square cylinder is higher than that

produced in the circular cylinder. For the circular

cylinder, it seems that coating the body surface some-

what reduces the aerodynamic noises.

In the case of the square cylinder, the peak SPL and

its peak frequency for the cylinder with an equivalent

diameter of 100 mm are higher than those for thecylinder of an equivalent diameter of 50mm. In

addition, coating the cylinder surface reduces the

aerodynamic noise level.

63 125 250 500 1000 2000 4000 800050

60

70

80

90

110

100

50

60

70

80

90

110

100

63 125 250 500 1000 2000 4000 8000

100km/h

150km/h

260km/h

200km/h

100km/h

150km/h260km/h

200km/h

1/3Octavebandsound

pressurelevel(dB)

Central frequency (Hz)

(a) M3

1/3Octavebandsoundpressurelevel(dB)


(b) M5

Fig. 30. Aerodynamic noise due to pantograph system.

63 125 250 500 1000 2000 4000 800050

60

70

80

90

110

100

63 125 250 500 1000 2000 4000 800050

60

70

80

90

110

100

(a) Circular cylinder

(b) Square cylinder

U=200km/h

U=200km/h1/3Octavebandsoundpressurelevel(dB)




: Wind tunnel noise level

: No coating

: Sponge coating

: Carpet coating

: Thick cloth coating

: Wind tunnel noise level

: No coating: Sponge coating: Carpet coating: Thick cloth coating

Fig. 31. Aerodynamic noise in flows over circular and square

cylinders.



23/46

Fig. 32 shows the effects of the shape of the cross-

sectional area of the cylindrical body on the aerody-

namic noises [24,25]. Several shapes of the cross-

sectional area of pantograph are investigated for the

purpose of design of the pantograph system. The overallSPL seems to be the lowest in the cylindrical body like

an elliptic shape. Fig. 33 presents the measurement

example of the aerodynamic noises generated by several

streamlined bodies [24,25]. It is found that the stream-

lined body B has a peak frequency at 500 Hz, but the

body C, a peak frequency at 3.15kHz. These peak

frequencies are due to the trailing edge vortices of the

streamlined bodies.

Compared with the overall SPLs generated in the

previous square and circular cylinders, for the stream-

lined bodies the overall SPLs are significantly lower. It

is, thus, believed that the aerodynamic noises can be

reduced if the pantograph system is designed as a

streamlined body.

7. Vibration of railway train

A considerable amount of the lateral vibration of atrain can be often found when the train travels at high

speeds in the open air. Such a lateral vibration becomes

more significant near the trail of the train or in the train

equipped with the pantograph system [2628]. The

lateral vibration of the train can be an important factor

to the traveling performance. The Karman vortices

downstream of the train can be responsible for the

lateral vibration. The vertical flows are closely asso-

ciated with the train length and detailed configuration of

the after-body of train. For long trains, some structural

vibrations occurring in the leading coach can be one of

the reasons for the trailing coach to appreciably vibrate.The study on the lateral vibration of train has not been

sufficient in the past.

8. Aerodynamics of railway train/tunnel systems

8.1. Aerodynamic analysis of train/tunnel systems

The aerodynamic problems occurring when train travels

at high speed in tunnel are more complicated and serious,

compared with the open air traveling. The aerodynamic

drag and noises on the train are strongly dependent on the

pressure waves in the tunnel. The aerodynamic drag on a

train traveling in a tunnel can significantly increase,

compared with that in the open air [6,29,30].

When a HST enters a tunnel, a compression wave is

formed ahead of the train which propagates along the

tunnel at a nearly sonic speed. A part of the compression

wave is reflected back from the exit of the tunnel as an

expansion wave. A complex wave interaction occurs

inside the tunnel due to successive reflections of the

pressure waves at the exit and entry to the tunnel. These

pressure waves cause large pressure transients resulting

in fluctuating loads on the train causing discomfort to

passengers. It is necessary to predict these pressuretransients to design trains and tunnels, and to improve

the passenger comfort.

Further, a part of the compression wave leaving the

tunnel exit gives rise to an impulse noise, as will be

described later. Such an impulse noise was not an

important issue in the past when the speed of trains was

not so high. But in recent years, with the increase in the

speed of trains the noise and vibration due to impulse

waves have become a new type of environmental noise

problem. According to some measurements conducted

near the exit of the tunnel, the noise is known to be of

low frequency of short duration, and its magnitude

50

60

70

80

90

100

110

63 125 250 500 1000 2000 4000 8000

U=200km/h

a) b)

c) d)

: a)

: b)

: c)

: d)

:



Cross section

Wind-tunnel noise level

Fig. 32. Aerodynamic noise in flows over several cylinders.

40

50

60

70

80

90

100

63 125 250 500 1000 2000 4000 8000

U=200km/h


1/3Octav

ebandsoundpressurelevel(dB) : Cross section a)

: Cross section b)

: Cross section c): Wind-tunnel noise level

a)

b)

c)

Fig. 33. Aerodynamic noise in flows over streamlined bodies.



24/46

being approximately proportional to V3 (where V is

train velocity). Moreover the impulse noise is closely

related to the detailed characteristics of the compression

waves inside the tunnel [3135].

Here, let us focus on the aerodynamics of the train

traveling inside tunnel. In nature, the aerodynamics of

train/tunnel systems is governed by a three-dimensional,unsteady, turbulent, compressible flow. Very frequently,

this method requires an extremely time-consuming work

of high cost and much effort to solve the governing

equations as well. It is more helpful to deal with the

aerodynamics of train/tunnel systems with several

reasonable assumptions.

We here describe a simple analytical approach to

understand such complicated aerodynamic problems

occurring inside tunnel. Assume that the cross-sectional

areas of train and tunnel are constant, and their equivalent

diameters are much larger than tunnel length, and train

speed V is very low compared with the speed of soundcorresponding to the atmospheric conditions, and the

propagation speed of pressure wave is the same as the

speed of sound. Under these assumptions, it is reasonable

to prescribe that the continuity equation involves variable

density of air but the compressibility effect is not

considered in the momentum and energy equations.

Assuming that u is the air velocity, and p the pressure,

the continuity equation is written as [36]

a2qu

qx

1

r

qp

qt g 1j 23

and the momentum equation is given by

qu

qt

1

r

qp

gx f; 24

where a is the speed of sound, the density r is assumed

to be constant, x the distance along tunnel, t the time, g

the ratio of specific heats (g 1:4) and f and j are thefrictional force and energy dissipation, respectively, as

given in Eqs. (25) and (26). For the sake of simplicity,

here we divide the flows into three regions: ahead of

train, behind train, and in train. For the regions ahead

of and behind train, the frictional forces are generated

on tunnel walls:

f l2d

ujuj; 25

j l

2djuj3: 26

For the region in train, the frictional forces stem from

both train body and tunnel wall surfaces. Thus, the

frictional force and energy dissipation can be expressed as

f l

2d

1

1 Ru0ju0j

l0

2d01

1 Ru0 Vju0 Vj; 27

j l

2d

1

1 R

ju0j3 l0

2d0

R

1 R

ju0 Vj3; 28

where d and d0 are, respectively, the hydraulic diameters

of tunnel and train, and l and l0 the friction coefficients of

tunnel wall and train body surfaces, respectively, R the

ratio of the cross-sectional areas of train to tunnel, and u0

the flow velocity occurring between train and tunnel.

The compatibility conditions should be used to

connect the flowfields in the three regions. Using thecoordinate system moving with train, the conservation

laws of mass and energy are given by

1 Ru0 V u V; 29

p0 1

2ru0 V2 p

1

2ru V2 p0; 30

where p0 is the stagnation pressure on the fore-body of

train. In general, a wake flow is formed behind the trail

of train; but far away from it, the flow can be regarded

to be uniform across tunnel cross-sectional area. For the

region closed by the trail of train and the uniform flow

area, the conservation laws of mass and momentum areexpressed as

u V 1 Ru0 V; 31

p ru V2 p01 Rru0 V2

Cdp R1

2ru0 V2; 32

where Cdp is the coefficient of the pressure drag on train

in the open air. At the entrance and exit of tunnel, it is

assumed that the flow discharges at atmospheric

pressure and when the flow comes into tunnel, it is also

assumed that the pressure reduces as much as thedynamic pressure. At the entrance and exit of tunnel, the

boundary conditions can be given by

tunnel entrance p

1

2ru2; uX0;

0; uo0;

8

Aerodynamics HSR02

Documents

Transcript of Aerodynamics HSR02