EFFECTS OF CROSSWIND ON THE DRAG OF MEDIUM SPEED TRAINS

Abstract

Aerodynamic research on medium-speed trains is trying to map the flow of fluid around trains. The train model testing is conducted to study Cd values experimentally using a closed-loop wind tunnel at the Balai Besar Teknologi Aerodinamika, Aeroelastika, dan Aeroakustika. In addition to the experimental method, the computational method can be used to validate the experimental results, map the fluid flow around the train model, and calculate Cd values. The computational results of Cd obtained using ANSYS are compared against Cd values from wind tunnel tests. Further analysis using the ANSYS program with variations in the yaw angle can predict crosswind effects on the train model. It is found that vortices are formed around the train body, and modifying the head shape and adding fairing increases Cd values.

Full text

V13 N2
eISSN 2477-6041 artikel 10, pp. 407 – 415, 2022
Corresponding Author: sheila.tobing@ui.ac.id
DOI: https://doi.org/10.21776/jrm.v13i2.1011
Received on: August 2021
Accepted on: May 2022
407
David Prayoga
Paramaputera
Student
Atma Jaya Catholic University of
Indonesia
Department of Mechanical Engineering
Email: d.prayoga.p@gmail.com
Sheila Tobing
Lecturer
Atma Jaya Catholic University of
Indonesia
Department of Mechanical Engineering
Email: sheila.tobing@atmajaya.ac.id
Lecturer
Universitas Indonesia
Faculty of Engineering
Email: sheila.tobing@ui.ac.id
Matza Gusto Andika
Researcher
Badan Pengkajian dan Penerapan
Teknologi
Balai Besar Teknologi Aerodinamika,
Aeroelastika, dan Aeroakustika
Email: matza.gusto@bppt.go.id
EFFECTS OF CROSSWIND ON
THE DRAG OF MEDIUM SPEED
TRAINS
Aerodynamic research on medium-speed trains is trying to map
the flow of fluid around trains. The train model testing is con-
ducted to study Cd values experimentally using a closed-loop wind
tunnel at the Balai Besar Teknologi Aerodinamika, Aeroelastika,
dan Aeroakustika. In addition to the experimental method, the
computational method can be used to validate the experimental
results, map the fluid flow around the train model, and calculate
Cd values. The computational results of Cd obtained using ANSYS
are compared against Cd values from wind tunnel tests. Further
analysis using the ANSYS program with variations in the yaw an-
gle can predict crosswind effects on the train model. It is found
that vortices are formed around the train body, and modifying the
head shape and adding fairing increases Cd values.
Keywords: Wind Tunnel, ANSYS, Medium Speed Train, Finite
Volume Method, Crosswind
1. INTRODUCTION
The development of the medium speed train by PT INKA in collaboration with the Badan Pengkajian dan
Penerapan Teknologi, Balai Besar Teknologi Aerodinamika, Aeroelastika, dan Aeroakustika (BPPT BBTA3),
Puspitek Serpong requires several considerations before application in real life, including research on the
aerodynamics experienced by the train body in its cruise speed and the phenomenon of crosswinds. For
example, aircraft development requires a streamlined body design or current split. In contrast, land vehicles
operating above ground require consideration of the length-to-diameter ratio, the effect of crosswinds, and
body shape with optimal drag coefficient values before the production process is carried out [1].
In this research, the analysis is carried out to determine how the yaw angle affects the Cd value on the
medium speed train model and how much drag occurs in the BPPT medium speed train model and one modified
head train model with the addition of a fairing. The purpose of this research is to determine the impact of
changes in yaw angle on drag on two train models, the BPPT medium speed train or Model 2, and the modified
head train with the addition of a fairing. The results of this study can provide an understanding of the effects
of the design of a medium-speed train has on drag. In addition, the results of this study can provide insight into
the impact of adding a fairing to protect the bogie component and determine the impact of changes in the shape
of the head of the train to drag coefficient (Cd). This research also studied the visualization of airflow contours
due to the crosswind phenomenon that occurs at various yaw angles.
Drag is a force that works in the opposite direction to the motion of an object [2]. Two components that
play a role in the formation of total drag are induced drag and parasitic drag. Induced drag is the drag force of
an object that is formed due to lift. Induced drag can only arise from three-dimensional flow; therefore, only
skin friction, waves, and pressure drag occur in the case of airfoils. Parasitic drag is generated by the shape of
objects (form) and surface friction. Parasitic drag is divided into several types, namely skin frictions drag, wave
drag, and pressure drag. Skin friction drag is caused by the viscous force on the surface of the object. Wave
drag is caused by the compressive force on the object's surface due to supersonic flow or shock waves [3].
Pressure drag is caused by compressive force due to the formation of a boundary layer on the object's surface.
When the boundary layer begins to thicken, or in exceptional cases, a boundary layer separation is formed, the
pressure drag can increase [3].
A crosswind is a phenomenon where the wind blows against the direction of the train at a certain angle.
Crosswind can also cause instability of the train model due to the aerodynamic force of the airflow acting on
the surrounding surface of the train [4]. Crosswind is investigated by increasing the aerodynamic forces, which

David Prayoga Paramaputera, Sheila Tobing, Matza Gusto Andika; Rekayasa Mesin, v. 13, n. 2, pp. 407 – 415, 2022.
408
can affect the safety of train operation. As many as 29 accidents involving the crosswinds phenomenon have
been recorded in Japan since 1872 [4]. The stability of the crosswind effect received much attention from
researchers to prevent accidents. Railway infrastructure with embankments on the tracks and a high distance
from the ground surface is prone to wind blowing.
On the other hand, the study of the aerodynamics of trains under the influence of the crosswind with the
help of various types of numerical simulations and wind tunnels is equally essential. Previous researchers
investigated the flow structure around a simplified ICE 2 carriage model for yaw angles 35⁰ and 90⁰ [4].
Others investigated the aerodynamic performance around a simplified high-speed train model using the LES
method. He found that the flow separation appeared laterally at the tip near the nose of the carriage leading to
the creation of two vortices starting from the nose of the carriage [5]. Gawthorpe (1994) studied the effect of
yaw angle under 45° on a simplified train model, and the results of his research resulted in a mapping of airflow
around the train body [6].
1.1 Nomenclature
Cd
Drag Coefficient
𝛽
Yaw Angle
𝑉0
Velocity
CDb
Wind tunnel drag coefficient
2. METHODOLOGY
The validation method used is Computational Fluid Dynamics (CFD) simulation using ANSYS Fluent. The
addition of a fairing to the train has the purpose of providing safety to the bogie. Besides, the addition of the
fairing also functions to reduce form drag [7]. This chapter describes the test steps carried out for the validation
case and the parameters used in this research (Figure 1).
3. EXPERIMENTAL DATA
Through the tests carried out, it can be seen that the Cd values of the Head 2 model are smaller than the Cd
values of the Head 1 model through a comparison of the Cd value at each yaw angle (Table 1 and Table 2).
This high Cd of the Head 1 model can be caused by a less aerodynamic design or the addition of a cowcatcher
to the Head 1 model, thus increasing the Cd value [8]. The flat front glass design on the Head 1 model can also
add to the drag value because the shape is not aerodynamic. However, there is an advantage that the flat shape
of the Head 1 carriage glass design does not cause visual distortion as produced in the curved glass on the Head
2 model, as shown in Figure 2.
Table 1: Aerodynamic forces of the Head 1 model measured in the wind tunnel.
V0
Yaw Angle (𝛽)
CDb of Head 1
44.22
-44.99
1.0266
44.1
-29.99
1.6244
44.03
-20.03
1.5408
44.01
-9.93
1.3733
44.03
-0.01
0.9904
44.05
9.99
1.323
44.06
20.07
1.533
44.07
29.97
1.5595
44.18
44.97
1.086

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Table 2: Aerodynamic forces of the Head 2 model measured in the wind tunnel.
V0
Yaw Angle (𝛽)
CDb of Head 2
44.06
-44.99
0.7142
44.07
-30.01
1.3123
44.05
-20.01
1.3516
44.03
-9.93
1.2085
44.03
0.01
0.84
44
9.99
1.1651
44.1
20.03
1.3547
44
29.98
1.2734
43.99
45.01
0.7646
4. COMPUTING METHODS (CFD)
The CFD analysis is carried out on the experimental model Head 2 and a modified model of the Head 2 with
modifications in a fairing and a change in the head shape, as shown in Table 3 and Table 4. The setup and error
targets of the validation cases are shown in Table 5.
Table 3: Comparison between two models.
NO.
TRAIN DESIGN
MODEL NAME
1
Base model
(Head 2)
2
The model with Fairing and
Head Modification
(Modified Head 2)
Table 4: Comparison between two models.
NO.
TRAIN DESIGN
MODEL NAME
1
Head 2
2
Modified Head 2

David Prayoga Paramaputera, Sheila Tobing, Matza Gusto Andika; Rekayasa Mesin, v. 13, n. 2, pp. 407 – 415, 2022.
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Figure 1: Methodology flow chart.

David Prayoga Paramaputera, Sheila Tobing, Matza Gusto Andika; Rekayasa Mesin, v. 13, n. 2, pp. 407 – 415, 2022.
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Figure 2: Head comparison of the two experimental models.
Table 5: The setup and error target of the validation cases.
FIXED
VARIABLES
INDEPENDENT
VARIABLES
INDEPENDENT
VARIABLES VALUE
MODEL
NAME
VALIDATION
METHOD
OBJECTIVE
Velocity:
44 m/s
Angles
0o;
+10o;
+20o;
+30o;
+45o;
Head 2
Comparison with
the experimental
method
Error Value
⪯15%
5. RESULT AND DISCUSSION
5.1 Case Study
This case study investigates the crosswind effects on the
Cd
of the train models. The train model is made based
on technical drawings, and a predetermined scale is tested in the wind tunnel. The wind speed is kept constant
at a speed of 44 m/s or equivalent to Re = 8,478,651.685 and with variations in the yaw angle of −45 °, −30 °,
−20 °, −10 °, 0 °, + 10 °, + 20 °, + 30 °, + 45 °. Dimensional analysis has been fulfilled by comparing the two
models using the same Reynolds number, namely 8,478,651.685 at a speed of 44 m/s and the dimensions of
the train model in the wind tunnel and the train model in the ANSYS CFD are the same.
The air velocity contours in the experimental tests are depicted through the laying of wool tufts which
function to see the airflow around the model train. During the simulation, the same thing can be done but using
pathlines [9]. The airflow pathlines that exist at various angles show the same results as wool tufts in the
experiments, and this is shown by several comparative figures such as at the yaw angle of 20°, where the flow
that occurs around the joints between the carriages has the same pattern as presented in Table 6.
Table 6: Comparison between the flow patterns observed in experiments and simulations.
ANGLE
EXPERIMENTAL
SIMULATION
0o
10o
Head 2
Head 1

David Prayoga Paramaputera, Sheila Tobing, Matza Gusto Andika; Rekayasa Mesin, v. 13, n. 2, pp. 407 – 415, 2022.
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20o
30o
45o
5.2 Validation of Model 2
The differences between the simulation and the wind tunnel results of the Head 2 model show that the maxi-
mum error value is below 10%. Through the comparison of Cd values, it can be seen that the Cd value is not
constant even though it is at the same yaw angle (Table 7) [10]. For example, at an angle of -10° and +10°, a
difference in Cd values of 1.2068 and 1.1644, respectively, is observed. This can be caused by the airflow
velocity that is not constant in value, namely 44 m/s, as shown in the airflow velocity data (V0).
Table 7: Cd data comparison of experiment results and simulation results for Model 2.
WIND TUNNEL MODEL HEAD 2
MODEL HEAD 2 ANSYS SIMULATION
NO.
β
V0
Cd
V0
Cd
Error
1
-45
44.05
0.7005
44
0.72
2.70833 %
2
-30
43.99
1.3128
44
1.302
0.82949 %
3
-20
44.03
1.3437
44
1.321
1.71840 %
4
-10
44.06
1.2068
44
1.202
0.39933 %
5
0
44.01
0.8313
44
0.761
9.23784 %
6
10
44.03
1.1644
44
1.202
3.12812 %
7
20
44
1.3468
44
1.321
1.95307 %
8
30
44
1.2685
44
1.302
2.57296 %
9
45
44.07
0.7664
44
0.72
6.44444 %
The impact of the change in yaw angle or the orientation of the wind is the emergence of vortices and
wakes from the flow around the train [11]. At a change in the angle from 0° to 10° (Figure 3), it can be seen
that an increase in the total Cd value is a result of a significant increase in viscous / friction drag. The increase
in total Cd from an angle of 10 ° to 20 ° is due to increased pressure drag [12]. From an angle of 20° to 30°,
there is a slight decrease in total Cd due to a combination of reduced pressure and viscous drag. However, from
30° to 45°, there is a decrease in Cd due to a significant drop in viscous / skin friction drag.

David Prayoga Paramaputera, Sheila Tobing, Matza Gusto Andika; Rekayasa Mesin, v. 13, n. 2, pp. 407 – 415, 2022.
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Figure 3: Cd value comparison between the wind tunnel tests and simulations of Model 2.
Figure 4: Cd value comparison between the wind tunnel tests of the Head 2 model and the simulation results of
the Modified Head 2 model.
Table 8: Cd data of the wind tunnel tests of the Head 2 model and the simulation results of the Modified Head 2
model.
HEAD 2 WIND TUNNEL
MODIFIED HEAD 2 ANSYS SIMULATION
Num.
β
V0
Cd
V0
Cd
Cd INCREASE
PERCENTAGE
1
-45
44.05
0.7005
44
1.72
59.27326 %
2
-30
43.99
1.3128
44
1.978
33.62993 %
3
-20
44.03
1.3437
44
1.825
26.3726 %
4
-10
44.06
1.2068
44
1.586
23.90921 %
5
0
44.01
0.8313
44
1.228
32.30456 %
6
10
44.03
1.1644
44
1.586
26.5826 %
7
20
44
1.3468
44
1.825
26.20274 %
8
30
44
1.2685
44
1.978
35.86957 %
9
45
44.07
0.7664
44
1.72
55.44186 %
Figure 4 shows the simulation results for the Modified Head 2 with the addition of a fairing and the
change in the shape of the train head to the Head 2 model. The increase in the values of Cd due to these

David Prayoga Paramaputera, Sheila Tobing, Matza Gusto Andika; Rekayasa Mesin, v. 13, n. 2, pp. 407 – 415, 2022.
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modifications is caused by form drag which results in an increase and decrease in the curve [13]. The percent-
age difference in the value of Cd of the Modified Head 2 to the basic model or the Head 2 model also increases
due to form drag [14]. Table 8 shows the Cd values of the wind tunnel test of the Head 2 and the simulation
data of the Modified Head 2 model, and it can be seen that the impact of the head change and the addition of
the fairing cause a significant change in the Cd values.
Table 9: Table of Pressure Drag Coefficient, Viscous Drag Coefficient, and Total Drag Coefficient.
MODEL HEAD 2
NO.
ANGLE
PRESSURE
VISCOUS
TOTAL DRAG
COEFFICIENT
1
0o
0.5839
0.1771
0.761
2
10o
0.677
0.525
1.202
3
20o
0.823
0.498
1.321
4
30o
0.712
0.59
1.302
5
45o
0.6242
0.0958
0.72
The changes in yaw angle or the orientation of the wind cause different vortices and wakes to appear
around the train. At a change in the angle of 0 ° to 10 ° showed in Table 9, it can be seen that an increase in the
total Cd value is a result of a significant increase in viscous / friction drag [15]. The increase in total Cd from
an angle of 10° to 20° is due to increased pressure drag. From an angle of 20° to 30°, there is a slight decrease
in total Cd due to a combination of reduced pressure and increased viscous drag. From 30° to 45°, there is a
fall in Cd due to a significant decrease in viscous / skin friction drag.
6. CONCLUSION
Based on the research and testing that are carried out both in wind tunnels and through CFD simulations,
several conclusions are withdrawn, including:
1. Drag generally increases from a yaw angle of 0° to 30°. Drag force is dominated by pressure drag.
2. Drag decreases from an angle of 30° to 45°. The decrease in drag is caused by a significant decrease in
viscous / skin friction drag.
3. The medium-speed train model that experiences the least drag is the BPPT Head 2 model.
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