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Building and Environment 37 (2002) 11391152

www.elsevier.com/locate/buildenv

Numerical simulation for optimizing the design of subwayenvironmental control system

Ming-Tsun Ke , Tsung-Che Cheng, Wen-Por Wang

Department of Air Conditioning and Refrigeration, National Taipei University of Technology, No. 1, Sec 3, Chung-Hsiao E. Rd., Taipei 106, Taiwan

Received 31 July 2001; received in revised form 7 November 2001; accepted 16 November 2001

Abstract

Subway Environmental Simulation Program (SES) was used to combine with the commercial computational uid dynamics (CFD)software to explore the inuence of various operating situations to the subway environment of Taipei Rapid Transit System in the present

study. The results show that the under platform exhaust (UPE) has a substantial inuence on the temperature and the cross-sectional area

of the ventilation shaft has quite more eect on the ventilation volume than length. The pressure distribution caused by the piston eect

and its eect on the platform screen door was also discussed and compared. ? 2002 Published by Elsevier Science Ltd.

Keywords: Computational uid dynamics; Under platform exhaust; Piston eect

1. Introduction

This paper mainly focuses on numerical simulation anal-

ysis for the environmental control system of the subwaystation area and the underground tunnel area between sta-

tions. The construction of the tunnel ventilation system is

one of the important environmental control systems aiming

at controlling the temperature inside the tunnel so that the

auxiliary system equipment of the train and the electrical

equipment in the tunnel can operate properly under accept-

able working temperature, and when emergency re occurs,

it can eectively control the direction of the spread of the

smoke and discharge the smoke out of the tunnel. On the

other hand, the ventilation shafts being installed on both

ends of the station can slow down the pressure wave in the

station platform and the inuence of the thermal load of thetunnel in the station area.

The application of SES program [1] is very popular in the

rapid transit systems of many cities in the world. The related

conceptual design of the subway can be resolved by the

thermal load analysis of the SES program and the selection

of equipment. Although there are many research reports on

the rapid transit system by using the SES program, yet the

design conditions and the weather conditions are dierent

Corresponding author. Tel.: +886-2-27712171; fax: +886-2-

27314919.

E-mail address: [email protected] (M.-T. Ke).

from those in Taiwan. There are not too many researches

that are related to the piston eect; therefore it is necessary

to use the numerical results of the SES program to combine

with the detailed simulation of the three-dimensional CFDsimulation for further studies on this subject as the reference

for the future planning of the tunnel ventilation and the

environmental control system.

2. Design conditions and theoretical model

The subway route under investigation is the Hsin Chuan

route of the Taipei Rapid Transit System. The SES soft-

ware was used to combine with the commercial CFD

package software PHOENICS (Parabolic, Hyperbolic or

Elliptic Numerical Integration Code Series) to establish

the three-dimensional numerical analysis model to proceedwith the detailed physical phenomenon simulation analysis

for the tunnel environmental control system.

2.1. Design conditions and design guidelines

According to the Taipei Rapid Transit System Planning

Handbook, the related design conditions for the environ-

mental control system are described as follows.

A.External temperature conditions

The rush hours of the Taipei Rapid Transit System are

08:00 and 17:00, and the temperature for the rush hours

0360-1323/02/$ - see front matter? 2002 Published by Elsevier Science Ltd.

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


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1140 M.-T. Ke et al./ Building and Environment 37 (2002) 11391152

Nomenclature

AA Hsin Chuan station

BB Fu Jen University station

CC Tan Feng station

DD Hui Lung stationA net cross-sectional area of tunnel (m2)

Av cross-sectional area of ventilation shaft (m2)

C proportional constant, = 0:48

Cm ow split parameter

Cp driving pressure coecient

Cps head loss through a ventilation shaft

CHi entrance loss, = 1 for a T-junction ventilation

shaft

CHC coupling loss between the tunnel and the venti-

lation shaft

Dh hydraulic diameter (m)

E eciency of UPE

f friction factorf modied friction factor

F energy head added (m2=s2)

g gravitional acceleration (m=s2

)

hf frictional energy head loss, =(fL=D)(V2=2)

(m2=s2)

hfr minor head loss, =KV2=2 (m2=s2)

k turbulent kinetic energy, (m2=s2)

K loss coecient

Ki parameter, = 0:965

Ko parameter, = 0:9 for square tunnels

L length (m)P static pressure (Pa)

Q ventilation rate (m3=s)

Qv ventilation rate in ventilation shaft (m3=s)

R(ui) residuam vector

R0 reference base vector

Re Reynolds number

T air temperature (

C)

u velocity in x direction (m=s)

v velocity in y direction (m=s)

V air velocity (m=s)

Vv air velocity in ventilation shaft (m=s)

w velocity in zdirection (m=s)

Z elevation head (m)

Greek symbol

dissipation rate of turbulent kinetic energy,

(m2=s3)

a absolute roughness factor

air density (kg=m3

)

Table 1

Design weather conditions

Summer (17:00) Winter (17:00)

Dry-bulb temperature 32.2

C 9.7

C

Wet-bulb temperature 26.0

C 7.6

C

Atmospheric pressure 1013 mbar 1013 mbar

in the afternoon is higher, therefore 17:00 is taken to be

the design hour, and the external temperature conditions are

illustrated in Table 1.

B.The design conditions of the tunnel area

The air dry-bulb temperature in the tunnel should be keptbelow 37

C during normal operation, and should be below

43

C at conjested condition.

C.Tunnel area

The tunnel area for this research is from the cross-over

track downstream the Hsin Chuan station (AA station) to

the tunnel area of the Huei Lung station (DD station), and

the range is described as below:

(a) Hsin Chuan Station to Fu Jen University Station (BB

station) (up and down tracks),

(b) Fu Jen University Station to Tan Feng Station (CC sta-

tion) (up and down tracks),

Table 2

Tunnel dimensions

AABB BBCC CCDD Lay-up

Tunnel Tunnel Tunnel track

Length (m) 1370 1227 1416 About 600

Inclination (%) 0:3=0:53 0:3=0:36 0:47=0:3 3=3

Remark A cross-over A cross-over

near AA side near DD side

(c) Tan Feng Station to Huei Lung Station (DD station)

(up and down tracks),

(d) Extended to the reception track and the departure track

of the lay-up track of the tunnel.Tunnel sections are primarily bored tunnels except that

cross-over tracks and lay-up tracks are cut and cover

tunnels, and the geometric dimensions are shown in

Table 2.

D.The tunnel area of the cross-over track and the tunnel

portal of the lay-up track

There is a cross-over track in the CC Station to DD Sta-

tion proximate to the DD station, and behind the DD sta-

tion there is a lay-up track being extended to the ground

level to the maintenance and repair plant. The up and down

tracks are linked together by the cross-over track, making


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M.-T. Ke et al./ Building and Environment 37 (2002) 11391152 1141

Table 3

Dimensions of stations

Fu Jen Univ. Tan Feng Hui Lung

Station Station Station

Length of station area (m) 194 153 277.2

Height of concourse (m) 4.15 4.15 4.15

Height of track area (m) 6.21 6.21 6.21Width of track area (m) 16.55 16.55 17.55

Length of platform area (m) 141 141 141

Width of platform area (m) 8.7 8.7 8.9

the airow in one track to ow to another track and thus

reducing the piston eect. Therefore, jet fan should be in-

stalled to guide the airow. However, since there is a lay-up

track tunnel extending to the ground level, the hot air in the

tunnel can be exhausted, or outside air can also be induced

too.

E.Ventilation shaft

According to the design requirements, ventilation open-ings are installed on both sides of the station, which con-

nect with the environmental control system plantrooms

and the natural outdoors air, and it includes three indepen-

dent shafts: exhaust shaft, intake shaft, and pressure relief

shaft.

F.Station area geometry

The concourses and the island type platforms of Fu Jen

University station, Tan Feng station and Hui Long Station

are all located in cut and covered boxes. Platform-screen

doors are installed between the platform and the track

area. Each side of the platform is supposed to be lined

with a train with six cars and each car has four doors.

The station is a two-oor underground building verti-

cally connected by a concourse and the platform track-

layer. The dimension of the station area is generalized in

Table 3.

G.UPE

In present research there are platform-screen doors that

separate the track from the platform. There is quite small

148713681758

AA station DD stationCC stationBB station

PORTAL

0.3 %

-0.3 %0.53 %-0.3 %

0.36 %

0.47 %

AIR FLOW

DIRECTION

Unit: m

Fig. 1. Schematic plot of the tunnel ventilation system between stations.

amount of air owing between the platform and the tunnel

since the gap between the train and the platform-screen door

is only 10 cm wide. The installation of screen doors serves

to prevent heat in the tunnel and in the train from getting

into the platform area and reduce the cooling load of air

conditioning in the concourse and platform layer. However,

temperature in the tunnel of the track area will rise sincethere is no air conditioning to cool down the air. Therefore,

the heat in the tunnel along the track has to be expelled

by UPE. The denition for the eciency E of UPE is as

follows:

E=Heat expelled by UPE

Heat released by train = CQ: (1)

As proven by the result of the experiment, the proportional

constantCin Eq. (1) is 0.48 when the eciencyEis under

65% whereas there is no experimental data to refer to ifEis

greater than 65%. However, as known through the eciency

curve in theory, the eciency will not exceed 80% no matter

how the discharge capacity is.

2.2. Theoretical model

The present research rst used the SES to perform the

analysis for the underground tunnel ventilation system and

obtained the important operational data, and then these data

were used as the boundary conditions to proceed with the

3D CFD simulation to give us detailed and useful numerical

results. Fig. 1 shows the layout of the ventilation system

in the tunnel between each station, and Fig. 2 is the local

detailed 3D layout of the station area.

2.2.1. One-dimensional analysis model

The installation of ventilation shaft will have an impact

on the visual landscape and the surrounding environment

because of the prominent vertical construction and the occu-

pation of valuable land so that the design for the ventilation

shaft may need to be changed. It results in the originally

planned ventilation requirement. Therefore, we must study

the inuence of the length and the cross-sectional area of the


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Fig. 2. Local detail layout of present underground station.

ventilation shaft on the piston eect in advance as a basis

for future reference.

Bernoullis equation can be used for the analysis of

present subway ventilation system.

gZ1+P1

+

V212

+F= gZ2+P2

2+

V222

+ hf+ hfm: (2)

In the subway ventilation system, if the height of the

ventilation shaft remains unchanged, and only the length

and the cross-sectional area are considered, it will only in-

uence hf and hfm, and the relation between the friction

loss and the cross-sectional area and length is describedbelow.

hf= f L

Dh

V2

2 ; (3)

hfm= KV2

2 : (4)

To study the inuence of the ventilation shaft to the piston

eect, we need to know about the airow distribution in the

tunnel and the ventilation shaft. We can deduce the following

according to [2,3].

The ow split parameter for the airow passes throughthe ventilation shaft and inside the tunnel is dened

as

Cm=AvVv

AV =

Airow volume inside ventilation shaft

Airow volume inside tunnel :

(5)

The ow split parameter when air ows into the ventila-

tion openings is dened as

Cmi= KiAv

A

Cp

Cps: (6)

The ow split parameter when air ows out from the

ventilation openings is

Cmo= KoAv

A

Cp+ 1 CHi

Cps CHC; (7)

whereCHCcan be neglected whenCps1.

The foregoing ow split parameters are only suitable for

the tunnel that only has one ventilation shaft. However, we

can know about the relation between the airow and the area

and resistance coecient of the ventilation shaft. When the

cross-sectional area or the length of the ventilation shaft ischanged, we assume the airow caused by the piston eect

in front of the ventilation shaft is the same (that is Q2= Q1,

Cp2 =Cp1 ), and there is change in airow distribution

only in the ventilation shaft and at its downstream, and it is

known as the change of ow split parameter. Let the original

ow split parameter be Cm1 , and the ow split parameter

after changing the cross-sectional area and the length of

the ventilation shaft be Cm2 , then the relation of the airow

volume is shown below.

Qv2

Qv1=

Av2

Av1K+ f1L1=Dh1

K+ f2L2=Dh2; (8)

where the friction factor f can be calculated by the

Altshul-Tsal equation [4]:

f = 0:11

a

Dh+

68

Re

0:25

if f 0:018: f= f

if f 0:018: f= 0 :85f + 0:0028

(9)

withRe = 66:4 103DhV.


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Table 4

Relaxation factors set in present study

Variable P u v w k T

Relaxation factor 0.3 104 104 104 0.3 0.3 0.1

2.2.2. Three-dimensional CFD model

A full-size three-dimensional model is developed accord-

ing to the actual size of the station and the tunnel area in

Cartesian coordinate. The ow is regarded as incompress-

ible, transient and turbulent. The boundary conditions are as

follows.

(a) The boundary of all kinds of solids in the model does

not consider the surface roughness and no-slip boundary

conditions are set.

(b) The boundary conditions at both sides of station and

those of the ventilation outlets all take the results

of SES simulation as in [5]. There are two tunnelventilation fans (TVFs) at each ends of the station.

The supply air volume of each TVF is 25 m3=s with

static pressure 1:2 kPa. The suction speed of UPE

is 3:48 m=s.

The turbulence model used in the numerical model is the

widely used standardk model. The relaxation factors setin the course of iteration are shown in Table 4. Except the

linear mode used in the pressure term, the rest terms all use

the false time-step mode.

PHOENICS applies the residual vector R (ui) to check

convergence. Right after each process of iteration, the preset

eective convergence criteria must be checked at once, inorder to decide whether iteration should be continued. This

preset convergence criteria is as follows:

||R(ui)||

||R0|| 6 101: (10)

3. Result and discussion

3.1. Normal operation mode

If the ventilation openings are located at the appropri-

ate positions, the natural ventilation can be accomplishedby the piston eect caused by the moving train in the

subway tunnel. There is no need to turn on the fans in

order to save the energy cost. Therefore, the train should

be able to introduce sucient air to cool down the heat

generated by the train. It must be very careful in the

planning, evaluation, and calculation for the layout of the

ventilation openings and the size of their cross-sectional

areas, and they should be conrmed with the SES

simulation.

UPE is a slot of 0:25 m wide and 1 m long on both sides

of the platform, each side has a total of 46 evenly dis-

tributed slots to capture the heat generated from the train.

There are exhaust duct under the platform and each of

the both ends has an exhaust shaft. Each exhaust shaft on

each end has two sets of fans to simultaneously proceed

with the exhaust of hot air on the same side of the both

ends.

There is platform-screen doors installed in the station plat-

form according to the present research, therefore the airowat the passenger area of the platform and that at the track area

does not have direct convection. When the train arrives a sta-

tion, and the platform-screen door opens, only small amount

of air ows in because the gap between the platform-screen

door and the carriage door is small, and hence the convection

can be ignored. Only the heat conduction generated by tem-

perature dierence inside and outside the platform-screen

door needs to be taken into consideration. The heat of such

conduction was taken into consideration in the estimation of

cooling load at the passenger area of the station and in the

SES simulation. The simulation time is peak hour of 17:00

in the afternoon, and there is a train for every 120 s, and the

train stops at a station for 25 s. The simulation duration is of

14; 400 s, and then takes the average data of the last 3600 s.

The results with various operating conditions are shown

below.

Normal operation mode with no UPE system. The SES

simulation results show that the temperature at the tunnel

area reaches up to 46:6

C and the temperature at the station

area reaches up to 48:8

C.

Normal operation mode with UPE system (suction air-

ow rate is30 m3=s). The results show that the temperature

drops signicantly, but the temperature in the tunnel area

and the tunnel adjacent to the tracks of the station area is

still as high as 3839

C, which exceeds the required designtemperature of 37

C.

Normal operation mode with UPE system (suction air

ow rate is 40 m3=s). The suction airow rate of UPE of

each track in the station area at the BB and CC stations is

40 m3=s, and at the DD stations and others is still 30 m3=s.

The simulation results show that the temperature at the tun-

nel area has dropped below 37

C, and the average temper-

ature next to the tracks in the station area also drops below

37

C.

The above simulations show that when the station area

does not have the UPE system, the temperature will rise to

49

C approximately. When the operation is performed inan environment with the temperature higher than 45

C, the

performance of the electrical equipment, air conditioning

system and auxiliary equipment of the train itself in the

tunnel will drop to below 50%. When the temperature of the

environment further rises over 55

C, they will not be able to

operate. Therefore, it is necessary to install the UPE system

to prevent the operation eciency of system equipment in

the tunnel from being seriously inuenced by the extreme

environment.

Since there is a crossover on the up track departing

from the AA station, when the suction airow rate of UPE

is 30 m3=s for each side of the platform the piston eect


6/14


Distance from AA Station (m)

DryBulbTemper

ature(C)

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Distance from AA Station (m)

0 500 1000 1500 2000 2500 3000 3500 4000 4500

29

30

31

32

33

34

35

36

37

38

39

40BB/CC/DD UPE=15 m3 /s, Headway=120 sec.

BB/CC UPE=20 m3 /s, DD UPE=15 m3 /s, Headway=120 sec.

BB/CC/DD UPE=15 m3 /s, Headway=120 sec.

BB/CC UPE=20 m3 /s, DD UPE=15 m3 /s, Headway=120 sec.

BB Station

BB Station CC Station DD Station

CC Station DD Station

DryBulbTemperature(oC)

29

30

31

32

33

34

35

36

37

38

39

40

(a)

(b)

Fig. 3. Temperature distributions in up track and down track tunnels.

cannot function as expected. In the down track the DD

station is the terminal station and has no entrance or exit

passing through the ground surface. When the train departs

the DD station, it will immediately meet the cross-over and

reduce the function of the piston eect. Although there is a

signicant drop in the air temperature in the tunnel, yet it

still does not meet with the design requirement. More partic-

ularly, the temperature reaches up to about 39

C on the track

in the BB station and the CC station. Since the piston eect

cannot accomplish the expected result, only reinforcing the

performance of UPE system can be considered. Therefore,

suction airow rate at the BB and the CC stations will rise

to 40 m3=s on each side of the platform and still keeps at

30 m3=s for the DD station. The comparison of the simu-

lation results is shown in Fig. 3. The average temperatures

in dierent location according to the present conditions are

shown in Table 5. The simulation results show that the av-

erage temperature of the air next to the track in the tunnel

Table 5

Average temperature in tunnel and station areas (UPE suction rates:

BB=CC stations= 40 m3=s, DD station= UPE30 m3=s)

Tunnel area Up track (

C) Down track (

C)

AABB 36.4 35.1

BBCC 36.5 35.5CCDD 35.8 35.2

DDPortal 31.7 30.6

Station area

BB 36.9 35.6

CC 36.4 35.7

DD 34.2 30.5

and the station area is below 37

C. Therefore, it is recom-

mended to increase the suction airow rate of UPE system

at the BB and CC stations to 40 m 3=s on each side of the

platform.


7/14


3.2. The inuence of the cross-sectional area and length

of the ventilation shaft on the piston eect

Studying and understanding the inuence of the

cross-sectional area and the length of the ventilation tun-

nel to the piston eect serves as the reference basis for

the design change and reduces the impact on surroundingenvironment and the visual landscape in the future.

In the present research, the cross-sectional area and the

length of the upstream and downstream ventilation shafts in

the BB station are separately changed, and the case analy-

ses by comparing the results with the theoretical values are

shown below.

3.2.1. Eect of the cross-sectional area of the ventilation

shaft

The cross-sectional area of the ventilation tunnel at the

BB station is set to 15, 20, 25, and 30 m 2, and the length is

maintained at 60 m to investigate its impact. All of the UPEsystems are closed to avoid inuences to the analysis of the

piston eect.

The simulation results are shown in Fig. 4. When the

cross-sectional area of the ventilation shaft is doubled, the

airow rate in it will increase by 1.4 times, and the theoret-

ical value of the ow should also be doubled. It is because

the theoretical result only takes one ventilation shaft into

consideration and there is no inuence from any other, but

the SES simulation accounts the inuence of all ventilation

Cross-Sectional Area of Ventilation Shaft (m2)

Volume

Flow

rateinVentilationShaft(m3/s)

15 20 25 303

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Downstream BB Station, ExhaustDownstream BB Station, IntakeUpstream BB Station, ExhaustUpstream BB Station, IntakeTheoretical Value

Fig. 5. Eect of the length of ventilation shaft on the airow rate (cross-sectional area = 20 m 2).

Cross-Sectional Area of Ventilation Shaft (m2)

VolumeFlowrateinVentilationShaft(m3/s)

15 20 25 30

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Downstream BB Station, ExhaustDownstream BB Station, Intake

Upstream BB Station, Exhaust

Upstream BB Station, Intake

Theoretical Value

Fig. 4. Eect of the cross-sectional area of ventilation shaft on the airowrate (length = 60 m).

shafts. Therefore, there is a dierence in the results, and the

SES simulation is used as the basis for the analysis.

3.2.2. Eect of the length of the ventilation shaft

The length of the ventilation shaft at the BB station

is separately changed to 40, 60, 80, and 100 m, and the


8/14


Fig. 6. Coupling eect of the cross-sectional area and length of ventilation shaft on the airow rate.

Tunnel Distance (m)

TemperatureinTunnel(oC)

500 100030

32

34

36

38

40

42

44

46

48

5020 km/hr

40 km/hr60 km/hr

80 km/hr

BB Station CC Station

Fig. 7. Temperature distributions in tunnel under various train speeds.

cross-sectional area remains at 20 m2, and all of the UPE

systems are closed to avoid any inuence to the analysis of

the piston eect.


length of the ventilation shaft is increased to 2.5 times, the

airow rate at the downstream of the ventilation shaft at


9/14


Fig. 8. Pressure and velocity distributions when the train entering the station area under various speeds.

the BB station is reduced to 0.75 0.85 times, and that at the

upstream of BB station is reduced to about 0.95 times. Since

the inuence at the upstream ventilation shaft is smaller

than that at the downstream due to the change of length,

theoretically the change in airow rate due to the change in

length is very small and is about 1%.

3.2.3. Coupling eect of the cross-sectional area and the

length of the ventilation shaft

The design specication basically regulates the cross-

sectional area of the ventilation shaft that cannot be greater

than 20 m2, and the length should not exceed 60 m, but

sometimes the length of the ventilation shaft has to be in-

creased due to the problem of limiting land and the position

of the exit of the ventilation opening has to be changed.

Therefore, when the original design with an area of 20 m2

and length of 60 m is changed to the lengths of 80 and

100 m, the cross-sectional area should be increased ac-

cording to the simulation to obtain the same air exhaust

volume.


length of the upstream and downstream ventilation shafts at

the BB station are increased to 80 m, the cross-sectional area

should be enlarged to 22:5 m2 to accomplish the originally

designed total intake and exhaust air volume (at 20 m2

, and60 m) caused by the piston eect. When the length of the

ventilation shaft is increased to 100 m, the cross-sectional

area should be enlarged to 25 m2.

3.3. The inuence of train velocities on environment

temperature in the tunnel and track areas

Dierent piston eects caused by dierent train velocities

will inuence the induction and exhaust of the airow in the

ventilation shaft, and further impact the thermal exchange

of the hot air in the tunnel with the external air and hence


10/14


Fig. 9. Pressure and velocity distributions when the train passing through the ventilation shaft under various speeds.

aects the temperature distribution in the tunnel. The heat

in the tunnel is generated from the equipment such as lights,

indicating lights, and electric equipments, and the major

source comes from the train due to its acceleration heat,

braking heat, and the heat discharged from air-conditioning

equipment and its accessory equipment.

The SES program is used to separately simulate dierentpiston eects caused by dierent train velocities (20, 40, 60,

and 80 km=h) passing through the tunnel for the analysis of

temperature distribution, assuming the length of the tunnel,

the length, dimension and position of the ventilation shaft,

and the train schedule interval are constant.

The simulation results are shown in Fig. 7. The simulation

results show that when the train velocity is in the range of

4060 km=h, the temperature in the tunnel is lower. When

the velocity is at 20 km=h, it has more cars in the tunnel due

to the slow speed and causes a drastic rise in temperature

due to the weak piston eect. When the train velocity is

at 80 km=h, although there is a better piston eect, yet the

larger heat released from the high speed of the train causes

the air temperature in the tunnel higher than those at the

velocities of 40 and 60 km=h.

3.4. The inuence of train velocities on pressure

distribution in the station area

Due to the safety and economic considerations, all stations

in the Hsin Chuan route will be designed to install platform

screen doors. However, the addition of screen doors easily

causes the piston eect when the train arrives the station.

A large pressure at the train head will be produced, and the

thickness of the glass and the anti-pressure capability of the

platform screen door must be taken into consideration.

To simulate the situations of the train passing the station,

the actual dimensions of the station and tunnel are consid-

ered as detailed as possible into the numerical model. Both

sides of the model are tunnels, and the length at the end of


11/14


Fig. 10. Pressure and velocity distributions upon the train arriving the platform screen door area under various speeds.

the entrance to the tunnel is 171 m, and the length at the

end of the exit of the tunnel is 150 m. The total length of

the station is 198 m, wherein the platform screen door area

is 141 m, the height of the station is 5 :31 m, and they are

of the actual size. The 46 UPE slots under the platform are

simplied into 5, but the total opening area and the suction

air volume remain unchanged. In the mean time, in order

to simplify the model, and since the station is symmetrical

sideway, only the track on one side is considered for the

CFD simulation in order to reduce the CPU time.

The by-pass and the ventilation shafts are taken into con-

sideration, and they are put into the model for simulation.

A 29:5 m 3:2 m 141 m block represents the train of theTaipei Rapid Transit System. A theoretical reference value

can be derived by the calculation according to the design data

[2]. When the train is traveling at the velocity of 80 km=h,

the length of the tunnel is 1400 m, and the blockage ratio is

42.5%, the pressure dierence generated by the train head

is 1132 Pa. 3D CFD simulation results are shown in Fig. 8

when the train entering the platform area and traveling at the

velocity of 80, 65, and 55 km=h, respectively. The contour

diagram represents the pressure, and the vector diagram rep-

resents the velocity. Fig. 9 shows the pressure and velocity

distributions of the train passing the ventilation shaft with

dierent velocities. Fig. 10 shows the pressure and veloc-

ity distributions of the train just entering into the platform

screen door area. Fig. 11 shows the pressure and velocity

distributions when the pressure generated by the head of the

train reaches the maximum.

The maximum pressure at 80 km=h is 1727 Pa, as can

be seen from these gures and the head of the train gener-

ates the maximum pressure of 1119 Pa at 65 km=h. Further-

more, Fig. 12 shows the pressure and velocity distributions

of the train just departing from the platform screen door

area at dierent velocities, and it shows the pressure and ve-

locity distributions at each location. When the train passes


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Fig. 11. Pressure and velocity distributions when the pressure on the train head reaches maximum under various speeds.

through the platform at dierent velocities, the maximum

pressure caused by the trains displacement is shown in Fig.

13. When the train enters the platform area from the circular

tunnel, the maximum pressure generated by the train head

starts to drop, and it is because the eects of the by-pass

and the ventilation shafts. After the train passes the by-passand the ventilation shafts, the pressure starts to accumulate.

When the velocity of the train is 80 km =h, the maximum

pressure of 1727 Pa of the entire simulation process approx-

imately occurs at the second car of the train when it enters

the platform screen door area, and the pressure will progres-

sively decrease thereafter. When the velocity of the train is

65 km=h, the maximum pressure generated by the train head

is up to 1119 Pa, and at the velocity of 55 km =h, the maxi-

mum pressure is 782 Pa.

When the train passes through the platform screen door

area, the maximum pressure occurs at the position near the

train head, since the cross-sectional area of the station is

descending when it enters the platform screen door area,

and the pressure obviously starts increasing. Meanwhile, it

can be observed that only when the train passes through the

neighborhood of the by-pass and the ventilation shafts, it has

signicant pressure releasing eect. After the train passing

by-pass and the ventilation shafts, it has no eect on therelease of pressure.

4. Conclusions

This study combines the SES program and the CFD soft-

ware PHOENICS for detailed simulation and analysis of

subways environmental control system as a reference for

design. The conclusions of the analysis of the present re-

search are described below:

The temperature change in tunnel under dierent piston

eects and train velocities. When the velocity of the train


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Fig. 12. Pressure and velocity distributions when the train head leaving the station area under various speeds.

is at 4060 km=h, the air temperature in the tunnel is lower

than that at the velocity of 80 km=h by 12

C, and when the

velocity is at low speed of 20 km=h, the temperature will

rise due to the weak piston eect.

The inuence of cross-sectional area and length of the

ventilation shaft on the piston eect. If the height of the

exit of the ventilation shaft and the minor head loss remains

unchanged, the increase in length of the ventilation shaft will

increase the friction. When the length is increased from 40

to 100 m, the airow rate will decrease by 1525%. Theincrease in cross-sectional area of the ventilation shaft will

signicantly reduce the friction resistance and the resistance

due to the reduction in velocity. When the cross-sectional

area is increased from 15 to 30 m2, the airow rate will be

increased by about 40%. When the length of the ventilation

shaft is increased to 80 m, the cross-sectional area has to be

increased to 22:5 m2 in order to maintain the original piston

eect. If the length of the ventilation shaft is increased to

100 m, the cross-sectional area has to be increased to 25 m 2.

The inuence to the platform-screen door when the train

passes through the station.The CFD simulation result of the

maximum pressure when the train that passes through the

platform screen door with a velocity of 80 km=h is 1727 Pa,

which is higher than the result of 1132 Pa obtained from

the empirical correlation, which is a simplied model with

less parameters. The value diers from the simulation results

obtained by the PHOENICS by approximately 30%.

The CFD simulation results show that when the train is

traveling at 80 km=h, the train head generates the maximum

pressure of 1727 Pa, which approximately occurs at the sec-

ond car of the train when it enters the platform-screen door

area. When the velocity slows down to 65 and 55 km=h,

the maximum pressures are decreased to 1119 and 782 Pa,

respectively, which also occurs at the second car of the

train when it enters the platform-screen door area. The

foregoing results recommend a speed of less than 55 km =h

when the train passes through the platform without a

stop.


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Position (m)

Pressure(Pa)

10 20 30 40 50 60 700

200

400

600

800

1000

1200

1400

1600

1800

2000Speed= 80 km/hrSpeed= 60 km/hrSpeed= 55 km/hr

Fig. 13. Pressure distribution along distance when the train head arriving the station area under various speeds.

The pressure generated by the train head can only be re-

leased when the train is passing through the by-pass and the

ventilation shafts. After the train passes through the by-pass

and the ventilation shafts, the pressure starts to increase

quickly.

References

[1] Subway environmental design handbook, vol. II, Subway

environmental simulation computer program, Version 4, Part 1, Users

manual. DOT of USA, 1997.

[2] Subway environmental design handbook, vol. I, Principles and

applications. DOT of USA, 1975.

[3] ASHRAE applications handbook. ASHRAE, 1999 [Chapter 28].

[4] Tsal RJ, Adler MS. Evaluation of numerical methods for ductwork

and pipeline optimization. ASHRAE Transactions 1987;93(1):1734.

[5] Cheng TC. Simulations of ventilation and smoke system for subway

tunnel. MS thesis, National Taipei University of Technology, Taiwan,

2000.

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