Journal of Engineering Aerodynamics Comparative …iet-journals.org/archive/2015/june_vol_5_no_6/9523961428922326.pdfAerodynamics Comparative Analysis of Cargo Truck Tricycles

International Journal of Engineering and Technology Volume 5 No. 6, June, 2015

ISSN: 2049-3444 © 2015– IJET Publications UK. All rights reserved. 375

Aerodynamics Comparative Analysis of Cargo Truck Tricycles

Agarana David1, Ekuase Austin2, Odomagah Emmanuel Saturday2, Olah Samuel2, Dania David E1. 1Department of Research and Development, 2 Department of Manufacturing and Production

National Engineering Design Development Institute, Nnewi, Anambra State, Nigeria.

ABSTRACT

The study of drag and lift coefficients as well as pressure distribution on the surface of a road vehicle is mainly done by the analysis

of their aerodynamics. In this work, an aerodynamic comparative study is done on three different shapes of cargo truck tricycles,

with the major difference being their frontal shapes. CAD models of the cargo truck tricycles were created using Creo Element/Pro

5.0 Software. The Computational Fluid Dynamics (CFD) simulation was done using Solidworks software. An external flow analysis

was carried out for speeds of 40kmph, 60kmph, 80kmph, 100kmph and 120 kmph. The value of coefficient of lift to coefficient of

drag ratio is plotted against speeds and compared. Pressure and velocity distribution were analyzed for each body shape in relation to

fluid flow, drag and lift force. A model with good economic value is the best choice. Model 3 possesses the best aerodynamic

features of the three models created.

Keywords: Aerodynamics, Downforce, Drag, Lift.

INTRODUCTION

1.1 Motivation

Tricycle (locally called “kekenapep”) is now a very famous

mode of transportation, especially for short distance journeys

on the Nigerian roads. The sales and usage have enjoyed

quite a steady increase especially since many state

governments in Nigeria had placed different ban conditions

on motorcycle usage[1]. Tricycle in Nigeria has become a

household name, coming in different shapes and purposes.

The cargo tricycle is one of such; it could serve several

purposes but basically to transport goods and materials.

Therefore, the design of a cargo tricycle with good economic

value, especially in terms of safety and maintenance became a

step in the right direction. One way to achieve this is to

increase the stability and reduce the power consumption of

the tricycle as detailed in Lajos work [2].Therefore,

optimization of the aerodynamic lift can stabilize the tricycle

while its power consumption reduction can be achieved by

aerodynamic drag reduction[2].

Lift and drag are mechanical forces generated on the surface

of an object as itinteractswith a fluid [3].

According to Weigel [4]drag is an aerodynamic force that

opposes a vehicle’s motion through the air, caused by

interaction and contact of a solid body with a fluid. Unlike

other resistive forces, such as dry friction, which are

independent of velocity, drag forces depend on velocity. Drag

depends on the density of the air,the square of the velocity,

the size and shape of the body and a variable known as the

drag coefficient. The drag force of a vehicle is represented as;

D = 0.5ρV2ACd ……………………………………….(1)

where;

D = drag force

ρ = air density (the density of air at 250 C is 1.184kgm-3)(the

engineering toolbox)[5].

V = speed of the vehicle

Cd = coefficient of drag

A = cross-sectional area of the object (measured in a plane

perpendicular to its motion).

Benson [6] suggested that the reference area to be used for

computing the drag of a vehicle should be the frontal area

which is perpendicular to the flow direction of the fluid.

Yong and Chang [7], explained that important in road vehicle

design is the concept of aerodynamic lift, where pressure

differences lift the vehicle and reduce its downward normal

force, thereby jeopardizing stability and traction at high

speeds. In very simple terms, the flow over a vehicle's body is

lower in pressure than that underneath due to the vehicle's

shape and the longer path of travel over the vehicle top,

thereby producing an upward, destabilizing force to the

vehicle.

Lift is a component of force that is perpendicular to the

direction of flow of the air stream. In automobile design,

Giwaand Obiajulu[8], describes lift as an undesirable

phenomenon as it reduces traction, resulting to an unbalanced

design, as sliding of the tires may occur. The lift force of a

vehicle represented below;

L = 0.5ρV2ACl……………………………………………(2)

International Journal of Engineering and Technology (IJET) – Volume 5 No. 6, June, 2015


where;

L = lift force

ρ = air density (the density of air at 250 C is 1.184kgm-3)(the

engineering toolbox) [5]

V = speed of the vehicle

Cl = coefficient of lift

A = cross-sectional area of the object (measured in a plane

perpendicular to its motion).

Prasad [9] considered road vehicle as a bluff body. Bluff

bodies are characterized by a large region of separated flow, a

direct consequence of which is that they suffer from large

values of the drag coefficient. Although automotive

manufacturer have designed and produced a more streamlined

outer shape[reference,(who told you??)] car as a road vehicle

still carry the effect of a bluff body in aerodynamics test. The

drag value has been reduced significantly for passenger car

but it still not anywhere reaching the Cd for a formula one car

or jet-shaped vehicle. Studies on aerodynamics of road

vehicle benefits directly toward decreasing the fuel

consumption, which result from the end purpose to reduce the

drag coefficient. It has been one of the main concerns of

automotive research centers for decades. Muyl [10]showed

that 40% of drag coefficient depends on the external shape

with most of the effect comes from the rear geometry.

Execution of good aerodynamic design under stylistic

constraints requires an extensive understanding of the flow

phenomena and, especially, how the aerodynamics are

influenced by changes in body shape, Guilmineau,

[11].Vehicle aerodynamics includes three interacting flow

fields:

- Flow past vehicle body

- Flow past vehicle components (wheels, heat exchanger,

brakes, windshield),

- Flow in passenger compartment

The optimizing of aerodynamic features in a vehicle has the

objective of improving the flows around the vehicle and

consequently resulting to the following objectives;

- Reduction of fuel consumption

- More favorable comfort characteristics (mud deposition on

body, noise, ventilating and cooling of passenger

compartment)

-Improvement of driving characteristics (stability, handling,

traffic safety) evaluation, Lajos[2].

A road vehicle’s shape is primarily determined by functional,

economic and aesthetic arguments. The aerodynamic

characteristics are not usually,generated intentionally; they

are the consequences of, but not the reason for, the

shape. These "other than aerodynamic" considerations place

severe constraints on vehicle aero-dynamicists. Depending

on the specific purpose of each type of vehicle, the

objectives of aerodynamics differ widely. While low drag

is desirable for all road vehicles, other aerodynamic

properties are also significant. Hucho& Sovran [12], affirms

that though negative lift is decisive for the cornering

capability of race cars, but is of no importance for

trucks. The objective of this paper is to analyze the

aerodynamic performance of three different cargo tricycle

models and to identify the one with the best aerodynamic

performance.

1.2 Literature Review

Cooper [13] stated that for a typical truck, some of the

maneuvering room for aerodynamics would be closing the

gap between the cabin and the bucket (figure 5) and also

adding a well-streamlined tractor.

University of Maryland [14,15,16] made a serious effort to

improve truck fuel consumption by studying the

aerodynamics of tractors and trailers. Figure 1 shows a

progressive modification put into the modelling of a tractor-

trailer truck. With the exception of the full-height skirts and

streamlined tail, all the modifications could be implemented.

Even the seemingly impractical changes can be utilized in a

less extreme fashion. It is clearly shown from the graph in

figure 2 how this adjustments and modifications drastically

reduced the drag force.



Figure 1: Trail mobile study (Tractor-trailer models modifications. Source: University of Maryland Aerodynamic Development)

Figure 2: Graph of drag coefficient against Yaw angle. (source:University of Maryland Aerodynamic Development)

To determine the outcome of the effect of aerodynamics

features on a vehicle, a computational fluid dynamics (CFD)

is perform to mimic a real life condition and results like

coefficients of drag, lift and pressure distribution etc.

provides the platform to judge if a design is aerodynamically

okay or not. The importance of aerodynamics to several type

vehicle bodies model needs a development of drag and lift

estimation to know how much the vehicle performance on the

road against air resistance beside to improve the stability,

reducing noise and fuel consumption.

We have performed previous studies on Vehicle body shape

and Dynamic stability Analysis for three wheelers vehicle

[17, 18], hence aerodynamic Analysis of Cargo–type tricycle

will be studied in this research work.

2. METHODOLOGY

Different shapes of tricycles were modeled using Creo

Element/Pro 5.0 Software. The CFD simulation was done

using Solidworks flow simulations software.

2.1 Methodology flow chart

The flowchart below in Figure 7 outlines the steps before the

lift and drag forces of the tricycle is obtained.

Figure 3: Flow Chart of CFD Analysis



2.2 Cad modeling

From general understanding of road vehicle aerodynamics, to

reduce the aerodynamic drag, two key points need to be

achieved. First is to decrease the high static pressure in the

front body of the car. Second is to recover the static pressure

in the rear body of the car. Three different CAD models were

created for comparism, with the major difference being their

frontals and constrains such as the height and width. Other

parameters to achieve a good aerodynamic feature were

considered. Such as different slight angles of the frontals,

streamlined cabin shape, smooth surfaces, closing up the gap

between the cabin and the bucket (figure 5), tapering of

roofing shape etc. The three created models are shown in

figure 4 below.

Figure 4: CAD Modelled Tricycles

2.3 Computational fluid dynamics (CFD)

The model is analyzed using Computational Fluid Dynamics

(CFD) to get a credible result. The analysis is external flow

with targeted speeds of 40kmph, 60kmph, 80kmph, 100kmph

and 120kmph. The value of lift and drag coefficients are

plotted and compared. To find the efficiency of the body

shape a pressure coefficient was analyzed to see how it relates

to drag and lift. An overall velocity distribution is also

targeted to visualize the fluid flow.The condition and

parameter of this CFD study is as follows:

Figure 5: Closed up gap between the cabin and the bucket



Table 1: Conditions and Parameter of the CFD

Parameters Conditions

1 Vehicle speeds 40kmph, 60kmph, 80kmph, 100kmph and 120 kmph

2 Analysis type External

3 Fluid type Gas (air)

4 Flow Type Laminar and Turbulent

5 Pressure 101325 Pa

6 Temperature 293.2 K

7 Turbulence intensity 0.1%

8 Result resolution 4

9 Computational Domain shown in figure 6

10 Goals global goals (force (X) and force (Y) as drag and lift respectively)

11 Used software Solidworks flow simulation 2012

12 CPU time (4 cpu)- (HP G62 – POWER 2.4GHz)

Figure 6: Computational Domain/boundary setting.

Table 2: Computational domain

Views Dimensions

Right 2.44m

Left -1.08m

Top 1.30m

Bottom -0.581m

Front 0.79m

Back -0.79m



2.4 Tricycle Frontal Area Computation

Model 1 Model 2 Model 3

Figure 7: Frontal areas of the 3 model

Table 3: Frontal areas

Model 1 Model 2 Model 3

Area A = length x breath

1647.13 x 1274.79

2099744.8527

= 2.10m2


2050.66 x 1286.99

2639178.9134mm2

= 2.64m2


2073.51 x 1273.17

2639930.7267

= 2.64 m2

3. RESULT

The specifications set up for the analysis is maintained for the

three models.

3.1 Data collection/calculations

Table 3, 4 and 5 are tables generated from the flow

simulations made from the three different models. It shows

the different simulations done at various speeds,and their

corresponding drag and lift force. It also shows the

coefficient of lift Cl and the coefficient of drag Cd which were

calculated from the equations below;

Cl = 𝐿

0.5𝜌𝐴𝑉2

………………………………………………………….(3)

Cd = 𝐷

0.5𝜌𝐴𝑉2

………………………………………………………..(4)

Table 4: Model 1 data outcome

s/

n

Lift

(N)

Drag

(N)

Speed(km

ph)

Cl

Cd Cl/Cd

1 139.8

3

368.3

5

40 0.7261

54

1.9128

86

0.3796

12

2 314.2

2

828.3

4

60 0.7209

00

1.9004

22

0.3793

37

3 559.0

1

1471.

19

80 0.7257

52

1.9100

17

0.3799

71

4 870.8

5

2295.

91

100 0.7209

88

1.9008

14

0.3793

05

5 1252.

74

3299.

53

120 0.7228

48

1.9038

73

0.3796

72

6 1688.

78

4461.

49

140 0.7140

82

1.8864

93

0.3785

24




s/

n

Lift

(N)

Drag

(N)

Speed(kmph

) Cl Cd Cl/Cd

1 -23.6 148.7 40 -

0.1540

7

0.97078

7

-

0.1587

1

2 -53.9 334.9 60 -

0.1554

6 0.96592

-

0.1609

4

3 -95.6 595.4 80 -

0.1560

3

0.97176

6

-

0.1605

6

4 -

149.

1

930.8 100 -

0.1551

8

0.96878

1

-

0.1601

8

5 -

214.

0

1339.

4

120 -

0.1552

3

0.97158

5

-

0.1597

7

6 -

291.

5

1820.

5

140 -

0.1549

5

0.96772

2

-

0.1601

2


s/

n

Lift

(N)

Drag

(N)

Speed(kmp

h) Cl Cd Cl/Cd

1 34.56 99.81 40 0.1794

74

0.5183

25

0.3462

58

2 78.42 225.44 60 0.1799

15

0.5172

17

0.3478

53

3 138.4

1

399.03 80 0.1796

95

0.5180

53

0.3468

66

4 224.3

0

625.76 100 0.1857

01

0.5180

75

0.3584

44

5 307.8

6

897.98 120 0.1776

39

0.5181

46

0.3428

36

6 419.8

4

1225.0

8

140 0.1775

25

0.5180

12

0.3427

04

3.2 Data analysis

Graphs were plotted from the data above to show the

behavior of drag and lift forces, coefficient of drag and

coefficient of lift to drag ratio at different speeds for the three

models. Figure 8, shows that model 3 has the lowest range of

drag force, followed closely by model 2 and model 1 has the

highest range of drag force comparatively. While from figure

9, it was observed that model 1 has the highest lift, model 2

has a negative lift also known as downforce, and model 3

falls in between i.e. not having a high lift compare to model 1

and also not having a downforce as model 2.

Figure 10 shows that the drag coefficients (Cd) at different

speeds for each of the models were constant, though model 1

has the highest value of Cd, compare to the other models and

model 3 has the lowest Cd. Again the values of coefficient of

lift to coefficient of drag (Cl/Cd) were the same at different

speed for the 3 models. Model 1 has the highest Cl/Cd value,

next to model 3 then model 2 has the lowest Cl/Cd value.

Figure 8: Graph of Drag (N) against Velocity (Km/h), for the three models.



Figure 9: Graph of Lift (N) against Velocity (Km/h), for the three models

Figure 10: Cd against Speed

Figure11: Cl/Cd against Speed



4. DISCUSSION

4.1 Pressure distribution

The pressure distributions of the three models are shown in the figure 11 below.

Model 1

(a)

Model 2

(b)

Model 3

(c)

Figure 10: Pressure distribution on the three models

Early separation point favors downforce

More pressure below than above. More lift is observed



Figure 10 (a); shows model 1 having a differential pressure.

The lift force is normally generated due to the difference in

pressure between the upper region and the lower region of the

vehicle.With a lower pressure at the upper region, this model

will experienced more lift; consequently becomes unstable.

Also model 1 has the highest drag amongst the 3 model

which indicates high fuel consumption. Though model 2

experience a low drag compare to model 1 which makes it

preferable indicating less fuel consumption, it experiences a

downforce as shown in figure 10 (b). The downforce is

generated by clogging (circulating airflow) on top of the

vehicle which indicates an early separation point (fig.

10b).The separation point is very close to the leading edge,

therefore the net suction on the top of the model will decrease

and a decrease in lift will occur, in this case resulting to

downforce. Downforce increases the weight of the vehicle

which consequently increases the drag. Figure 10 (c) shows

the pressure distribution on model 3’s side view. The pressure

pattern shows that a relatively low pressure is experienced at

both the upper and lower region, having approximately the

same value. Therefore, there is no much pressure differential

perpendicular to the relative wind; hence, the model will

produce a very low lift. Also model 3 experienced the lowest

range of drag force. Hence model 3 will consume less fuel

and it’s more stable than the rest models.

4. CONCLUSION

We have employed the use of Computer aided Design

approach to model three different cargo tricycles for

aerodynamic analysis. Computational Fluid Dynamic (CFD)

software was used to simulate a near real life condition,

mimicking a full-scale wind tunnel. Models were imported

into this environment and similar environmental condition

was maintained for them with different speed values.

The methodology developed was applied to study the

aerodynamic effects on the three models created. A plausible

conclusion is that model 3 possesses the best aerodynamic

features of the three models created. The model 3 will require

the lowest power and consume less fuel as a result of the

lowest drag experienced by it. It experiences the lowest drag

force leading to the lowest power consumption which also

means lowest fuel consumption. It also showed an

appropriate lift force – a lift force value not too high resulting

to an unstable condition or a negative lift (downforce)

resulting in more power consumed.

Model 3 has the best aerodynamic characteristics of the three

cargo truck tricycle models. It is safer, consume less fuel

therefore possesses good economic value.

A better economic value could even be achieved by further

optimizing the cargo truck tricycle. We will recommend the

truck could be fitted with a contemporary aerodynamics

package consisting of a cab-roof fairing and side extenders.

To this baseline the following could be added:

1. Tractor skirts and front trailer skirts back to the trailer

wheels

2. Beveled base panels (simple boat tail)

3. Additional rear skirts behind the trailer wheels

4. A gap seal between tractor and trailer

5. A filler block to completely close and fair the gap

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Documents

Journal of Engineering Aerodynamics Comparative …iet-journals.org/archive/2015/june_vol_5_no_6/9523961428922326.pdfAerodynamics Comparative Analysis of Cargo Truck Tricycles