FINAL SUBMISSION project - Copy (1)

Department of Aeronautical and Automobile Engineering MIT, Manipal
External Aerodynamic analysis of HCVs
using simulation & wind tunnel techniques
By
Amit Jain (080934122)
Under the guidance of
Mr. Laxmikant G. Keni
Assistant Professor
Dept.of Aeronautical &
Automobile Engineering
MIT, Manipal

CONTENTS
• Introduction
• Literature review
• Summary
• Problem definition
• Objective
• Methodology
• future work
• References

INTRODUCTION
• The rapidly increasing fuel prices and the regulation of green
house gases to control global warming have given tremendous
pressure on the design engineers to enhance the current
designs of automobile using minimal changes in the shapes.
• To fulfill the above requirements, design engineers have been
using the concepts of aerodynamics to enhance the efficiency of
automobiles.
• Aerodynamics is used by design engineers for cooling engines,
improving the performance of the vehicle, enhancing the comfort
of the rider, stabilizing the car in external wind conditions and
also increasing the visibility of the rider.

Spectrum of task for vehicle
aerodynamics

PERFORMANCE FACTOR
Fuel consumption is a function of power required at the wheels and
overall engine-accessories-driveline efficiency.
Factors that affect fuel consumption at steady speeds over level
terrain are:
(a) Power Output-Engine-Accessory- Driveline System:
• Basic engine characteristics; fuel consumption vs. RPM and
BHP.
• Overall transmission and drive axle gear ratios.
• Power train loss; frictional losses in overall gear reduction
system.
• Power losses due to fan, alternator, air-conditioning, power
steering, and any other engine-driven accessories.

(b) Power Required - Vehicle and Tires
The horsepower required for a vehicle to sustain a given
speed is a function of the vehicle’s total drag. The greater
the drag, the more horsepower is required. The total
vehicle drag can be broken into two main components;
aerodynamic drag and tire drag. Factors affecting these
components are:
• Aerodynamic – Vehicle speed
• Vehicle Frontal area
• Vehicle Shape
• Tire – Vehicle Gross Weight
• Tire Rolling Resistance

 Both aerodynamic drag and tire drag are influenced by vehicle speed. It is
important, though, to note that speed has a much greater affect on
aerodynamic drag than on tire drag. Figure 1.

Gains in fuel economy can be made by either optimizing or reducing some
of the factors affecting drag.
The shape of the vehicle uses about 3 % of fuel to overcome the resistance in
urban driving, while it takes 11% of fuel for the highway driving. This
considerable high value of fuel usage in highway driving attracts several
design engineers to enhance the aerodynamics of the vehicle using minimal
design changes.

LITERATURE REVIEW
Dr. Ilhan Bayraktar, Old Dominion University :
His project focuses on analyzing ground vehicle aerodynamics and understanding
complex wake flow behind vehicle bodies.
His study shows that most of the drag force takes place due to the
separation of the flow at the back of the vehicle.
His Computational studies show that about 80% of total drag is from pressure
drag, and the rest is from friction. The maximum pressure difference is observed
at the back surface of the truck, where complex flow phenomena, such as
separation, reattachment and vortices are found.

Jaswanth Chowdary U, Tata Consultancy Services Pvt. Ltd. :
Vortex-Generators used over the Audi R8 car model, for drag reduction. For the
research work, a 1:18 model was taken and analyzed in a wind tunnel.
Vortex Generators (VG) placed directly above B-Pillar of the test model whose
frontal area is 8.25X10-3 m² and with dimensions 262*90*75 mm3.
The Drag is reduced with the VG placed at 45 degrees and 90 degrees
considerably due to the increase in the flow velocity at the trailing edge which led
to the delay in the flow separation. The separation caused by the VG induces a
turbulence in the flow thereby reducing the vortex formation.
Results show that drag is reduced but the variation not being gradual may pose
problems with drive handling. The instabilities may increase Lift force or vortices in
the flow and the Yaw moment on the car which is undesirable. Thus the optimum
inclination (it varies from model to model) for the present model is 45 degrees as
relatively low drag is enacted .

Xu Wei-gang, Wen Gui-jin, China National Heavy Duty Truck Group Co. Ltd :
Computational Fluid Dynamics (CFD) simulation for two types of heavy commercial
vehicle (one with aerodynamic drag reduction devices and the other without) is
performed to investigate their aerodynamic characteristics.
Through the analysis of airflow and pressure distribution on the full vehicle surface,
the drag reduction mechanism and the influence of these drag reduction devices
on commercial vehicle’s aerodynamic characteristics are discussed.
Result shows that by adding aerodynamic drag reduction devices such as wind
deflector and dome, the aerodynamic drag coefficient of heavy commercial vehicle
significantly reduces 10%.

SUMMARY
From the literature survey it is observed that:
• About 80% of total drag is from pressure drag, and the rest is from friction.
• Drag can be reduced by placing the vortex generators over the vehicle
surface, which can further help increasing the speed of the vehicle. But this
technology is in nascent stage in automotive field.
• There is a increase in fuel efficiency, by simply changing the shape of the
vehicle. Actually by using the add on such as Wind deflector, modifications at
the back of the trailer, etc.

PROBLEM DEFINITION
External Aerodynamic flow analysis of
HCVs using simulation & wind tunnel
techniques & implementation of
various techniques to reduce drag,
improve fuel efficiency and vehicle
performance.

OBJECTIVE
The main objective of this project was to study the
coefficient of drag of Heavy commercial vehicle
while using the different shape and height of wind
deflectors.

METHODOLOGY
The main steps involved are:
1. Generation of 3D solid models by using CATIA V5 R19.
2. analysis of the flow and drag force patterns of the models by using ANSYS-
CFX software.
3. Comparison of results obtain.
4. Validation of simulation results will be done by sub sonic wind tunnel
testing.

1. Generation of 3D solid models by using CATIA V5 R19.
• Blue print is obtained from the website.
• Rough dimensions are taken such as height, width, wheel base and length of
the vehicle.
• Left side view of the model is generated by using drafting software (CATIA V5
R19).
• Coordinates are obtained from this left side view in order to obtain fine
geometry.
• From these coordinates 3d models are generated, by giving fine dimensions in
the product design module of CATIA V5 R19.

1. Normal model dimensions which resembles to EICHER truck

2. Model with wind deflector (dimensions)

1.Normal 3D model without any drag reduction attachments.

2. 3D model with curve shaped wind deflector.

3. 3D model with triangular shaped wind deflector

Generation of the meshed model
The IGS file of the model is imported into ANSYS Workbench. Here the body
of (vehicle) was subtracted from the body of the channel to leave the region of
interest for CFD simulation. The CFD simulation involves meshing, setting the
initial conditions, solution and post processing the result.
4. Vehicle geometry after import, in ANSYS CFX
• Geometry Creation

5. Generation of box (channel) around the vehicle body
In this project, the length of the computational field is approximately fourteen
times of the vehicle lengths. The inlet is 4 times of the vehicle lengths far
from ahead of the vehicle and outlet is 9 times of the vehicle lengths far from
the container’s back. The height and the width of the computational field are
5 times of the vehicle heights and 7 times of the vehicle widths respectively.
Ground clearance is 30 mm.

6. Channel after the subtraction of vehicle body.

• Meshing
Six regions are defined in the model, one each for the four walls of the channel, inlet, and outlet. A
separate region is created for the body, for visualization purposes and setting mesh controls. To create a
fine mesh around the surface of the body, face spacing was created to concentrate nodes and elements
in this region. To create a layer of thin prismatic elements around the body surface inflation was used.
The values of parameters of facing spacing and inflation are:

7. Selection of inflated boundary
To create a layer of thin prismatic elements around the body surface
inflation was used.

After values of the above parameter are set as mentioned in the figure the surface
mesh and then the volume mesh was generated.
Surface mesh of the body Surface mesh of side of the channel

• Setting the boundary and initial conditions for flow simulation
The flow simulation and analysis for the model was done using general purpose fluid
dynamics program, ANSYS CFX V12.0. A flow domain is defined for running the simulation in
ANSYS CFX Pre. The flow in the domain is expected to be turbulent and the Shear Stress
Transport Turbulence model is used with automatic wall function treatment because of its
highly accurate assessment of flow separation. Here we are modeling a compressible flow to
calculate density variation thus a realistic value of reference pressure must be specified
because many properties of the fluid are calculated on the basis of absolute pressure (static
pressure plus reference pressure).
Table 1 Parameters of the fluid domain
Air at 25o
C
Morphology Continuous Fluid
Buoyancy Model Non Buoyant
Domain Motion Stationary
Heat Transfer Isothermal
Fluid Temperature 298 K
Turbulence Model Shear Stress Transport

Table 2 Boundary conditions for the inlet and outlet
BOUNDARY TYPE (INLET)
Flow regime Subsonic
Normal speed 15ms-1
(for all models)
Turbulence Option Medium Intensity and Eddy Viscosity Ratio
Mass And Momentum Normal Speed
BOUNDARY TYPE (OUTLET)
Flow Regime Subsonic
Mass and Momentum Option Static Pressure
Relative Pressure 0 Pascal
Channel after defining the computational field

Table 3 Solver control parameters
Maximum Iterations 100
Fluid Time Scale Physical Timescale
Physical Timescale 0.2 seconds (for speed of 15ms-1
)
Convergence Criteria (residual Target) 1e-05
The boundary conditions for the top and side walls of the channels is set as “free slip” and “adiabatic wall”
but that for the bottom wall is set as “no slip” and “adiabatic wall” as it simulates the ground effect. The
boundary condition for the body in the channel is also set as “wall” and “no slip”. Then the initial values of
the X, Y and Z components of fluid velocity are specified. In this model the values of X and Z components
are 0 as the direction of the fluid flow is along positive Y axis. Then the solver control is defined.
Physical timescale provides sufficient relaxation for the equation non-linarites so that a converged
steady state solution is obtained. It can be approximated as the Dynamic Time of the flow. It is
nothing but the time taken by a point in the flow to pass through the fluid domain.

The above procedure for analysis is followed in all the models with different configurations.
Table 4 Curve shaped wind deflector height data
Curve shaped wind deflector height (from the ground) Frontal area
(96,140), (15,160), (50,155) 160 mm 0.02 m2
(96,140), (15,165), (50,160) 165 mm 0.02 m2
(96,140), (15,170), (50,165) 170 mm 0.02 m2
(96,140), (15,175), (50,170) 175 mm 0.020331m2
(96,140), (15,180), (50,175) 180 mm 0.021006m2
Figure 3.15 Creation of CAD model of truck with curve shaped wind deflector (96,140),
(15,180), (50,175) 180 mm (Height)

Table 5 Triangular shaped wind deflector height data
Triangular shaped wind deflector height (from the ground) Frontal area
(96,140), (15,160) 160 mm 0.02 m2
(96,140), (15,165) 165 mm 0.02 m2
(96,140), (15,170) 170 mm 0.02 m2
(96,140), (15,175) 175 mm 0.020331m2
(96,140), (15,180) 180 mm 0.021006m2
Figure 3.16 Creation of CAD model of truck with curve shaped wind deflector (96,140),
(15,180) 180 mm (height

160 mm 160 mm
165 mm 165 mm
170 mm 170 mm
175 mm 175 mm
200 mm 200 mm
Figure 3.17 Different configurations of truck with curve & triangular shaped wind deflector
(with varying height)

All the above models were tested with the same procedure in ANSYS CFX at 15 m/s and
results were obtained.
Equations used:

• Wind tunnel testing
In this methodology we will discuss
1. The modelling of scaled HCV models.
i. HCV without wind deflector
ii. HCV truck with curve wind deflector
iii. HCV truck with triangular wind deflector
2. Calibration of sub sonic wind tunnel.
3. Smoke flow visualisation technique for all the three models.
4. Surface pressure distribution over a bluff body (HCV models)

• Model specifications
Fig 3.18 specification for HCV without wind deflector

Fig 3.19 specification for HCV with curved wind deflector

• Modeling of scaled model
1. Modeling
The modelling of the three HCV models was done in CATIA V5 R19 in scaled dimension of
1:20 which was used as a blue print for the preparation of the models to be used in
experimental analysis.
2. Construction of models
 MATERIALS USED
1. Plaster of paris
2. Aluminium sheet
3. Engineering drawing board
4. Sand paper
5. Aluminium foil
6. Black tape
7. Duct tape
8. Pressure tubes (dia 0.6mm )
9. Connecting tubes (dia 0.8mm)
10. pins
• Tools used
The following tools were used during the preparation of the
scaled HCV models
1. Bosch drilling machine
2. 4 mm drill bit
3. Hammer
4. Metal sheet cutter
5. Pliers
6. Scissors
7. Mallet

Fig.3.20 Outline sketch of model drawn on aluminium foil
• Preparation of the models
 Preparation of the models
1. An engineering drawing board was taken and aluminium foil was wrapped over it to
facilitate the drawing of the scaled outline of the HCV model which was to be
prepared.
2. The outline sketch was drawn on the aluminium foil using marker pen .all the
important coordinates were marked using pins and joined by lines to get the outline.

Fig 3.21. Aluminium sheet in desired curved shape with members joined by black tape.
3. The aluminium sheet was then cut according to the dimensions of the model using a
metal sheet cutter. The height, width and length were all take into consideration while
cutting the sheet.
4. The metal sheet was placed in such a way that the side of the scaled model would be
the base of the model.
5. Parts of the metal sheet were joined using black tape/duct tape.
6. The frontal parts like the wind shield, front grille, bumper, wind deflector which were
to be given curved shape were created using a mallet which was used to get the
desired shape from the aluminium sheet.

Fig 3.22 The slurry solidifying inside the mould of desired shape
7. The central line of the sheet was marked starting from the front bumper to the wind
deflector’s topmost part.
8. Points were marked at equal distances and on important points where pressure
difference was to be measured.

9. A Bosch drilling machine with 4mm drill bit was then used to drill holes at these points through which the receiving part
of the pressure tube was to be placed.
10. A hole was made at the base of the model from where the rear end of all the ten pressure tubes would come out. This
end would be connected to the manometer for taking the readings.
11. The curved shaped sheet was then placed on the marked coordinates and wound around pins which were used to
denote important coordinates.
12. This sheet was then placed firmly on the aluminum foil by the help of black tape which was wound all around the
circumference of the base and this was done to make the mould leak proof and stable so as to hold the plaster of paris
mixture.
13. The pressure tubes were then placed in their respective positions and were numbered from 1 to 10.
14. Plaster of paris was then taken and mixed with water to form a slurry of ideal properties which would set into solid in
around six hours.
15. The slurry was stirred constantly to keep the mixture uniform and not form unwanted mounds.
16. Carefully the slurry was poured into the aluminum sheet mould and the mould was filled by plaster of paris till the
marked height.
17. The exposed region of the mould was given finishing using sand paper and smooth surface finish was given using
lime.
18. The slurry was left to solidify for around 6 hours without any disturbance.
19. The slurry solidified and took the shape of the mould desirably.

FINISHED SCALED MODELS
1. HCV without wind deflector
Fig 3.23 Front view (pressure ports visible at the front)

2. HCV with wind deflector
Fig 3.25 Side view

3. HCV with triangular wind deflector

Fig 3.30 Pressure tubes coming out of the base of the model

 Calibration of subsonic wind tunnel:
A calibration chart was prepared which gave us the mean speed at the working
section in terms of the reading of the upstream pressure tapping.
 EQUIPMENTS USED
1. Sub sonic wind tunnel
2. Multi tube manometer
3. Pitot static tube
Fig.3.32 Multi tube manometer

Fig.3.33 Smoke generator apparatus

Fig.3.33 Pressure tubes connection for manometer readings.

RESULT ANALYSIS
This section includes the aerodynamic (numerically as well as
experimentally) analysis that was done on HCV under three different design
configurations but under same environmental conditions. In all the above
mentioned cases, air velocity of 15m/s at the inlet and relative pressure
zero at the outlet is applied. Three different models of HCV’s are used
throughout the analysis i.e. Basic HCV model, HCV model with curve
shaped wind deflector and HCV model with triangular shaped wind
deflector. After validating, the numerical analyses of these models with
experimental analysis, we further study the effect of shape and height of the
wind deflectors. The results in all the cases are compiled in the form of
screenshots of the ANSYS CFX window.
i. Numerical analysis
ii. Experimental analysis

i. Numerical analysis
1. Screenshots for, air velocity =15m/s (Model 1)
Fig 4.1 Streamline flow over the HCV base model

2. Screenshots for the HCV with curve shaped wind deflector model case, air velocity 15m/s.
Fig 4.2 streamline flow around HCV with curve shaped wind deflector (Model 2)

3. Screenshots for the HCV with triangular shaped wind deflector model case, air velocity
15m/s.
Fig 4.3. streamline flow around HCV with triangular shaped wind deflector (Model 3)

Airflow distribution analysis
Airflow field around the model and flow separation as well as tail vortex on
the model can be observed by airflow distribution. Different front airflow
separations lead to different tail vortex in the rear of the container.
According to W. Hucho, the elimination of the tail vortex can reduced the
drag. The smaller the trail vortex is, the smaller the vehicle's aerodynamic
drag. As model 2 & 3 have a smaller vortex, so they have smaller
aerodynamic drag coefficient than that of model 1.

Fig 4.4 Pressure contour around the HCV base model.

Fig 4.5Pressure contour around the HCV with curve shaped wind deflector (height = 170mm)

Fig 4.6 Pressure contour around the HCV with triangular shaped wind deflector

Fig 4.7 Pressure over the HCV with curve shaped wind deflector (height = 170mm)

Fig 4.8 Pressure over the HCV with curve shaped wind deflector (height = 170mm)

Pressure distribution analysis
The distribution of pressure around the vehicle is mainly affected by air
velocity around the vehicle. Vortex generated by airflow separation evidently
changes the distribution of pressure. Giving a definite external shape, the
reduction of vertex generated by airflow separation is the major way to
reduce the aerodynamic drag. The above figures show that both on model 1,
model 2 and model 3, pressure on front grill and the bottom of windshield
glass is high, while on the front top of the cab is low. On front of the
container, there is an especially high pressure area on model 1.

Fig 4.9 velocity contour around the HCV base model

Fig 4.10 velocity contours around HCV with curve shaped wind deflector (height =170mm)

Fig 4.11 Velocity contours around the HCV with triangular shaped wind deflector.
From above figures, we can see that model 1 has the
highest vortex generation at back of its container which is
the main cause of high coefficient of drag. Cd =0.6971

1. HCV base model case (Model 1)
force_y()@body = 1.91361 [N] (drag force) Cd = 0.6971
force_z()@body = -0.334936 [N] (lift force)
force_x()@body = -0.0101962 [N] (side force)
2. HCV with curve shaped wind deflector case (Model 2)
force_y()@body = 1.6998 [N]
force_z()@body = -0.511125 [N] Cd = 0.6192
force_x()@body = 0.0170118 [N]
3. HCV with triangular shaped wind deflector model case (Model 3)
force_y()@body = 1.67544 [N]
force_z()@body = -0.465912 [N] Cd = 0.6103
force_x()@body = -0.0213523 [N]
Simulation Results

ii. Experimental analysis
In this analysis we will
1. Calibrate the sub sonic wind tunnel with necessary tabulation and calculation
2. Analyse the smoke flow visualisation of the three bluff bodies.
3. Calculate the surface pressure distribution over the bluff bodies and calculate
their coefficient of drag.

1. CALIBRATION OF SUB SONIC WIND TUNNEL
Table 6-Table of measurements
Serial no.
Rpm
Initial
manometer
reading(mm)
Final
manometer
reading(mm)
H(mm)
Velocity
(m/sec)
1
60 16 17 1 2.55
2 100 16 18 2 3.62
3 200 16 21 5 5.72
4 300 16 25 9 7.67
5 400 16 37 21 11.73
6 500 16 50 34 14.92
7 600 16 65 49 17.91
8 700 16 85 69 21.26
9 800 16 108 92 24.55
10 900 16 135 119 27.92
11 1000 16 165 149 31.24

SAMPLE CALCULATIONS-
Reading no. 1, rpm= 60,
Initial reading=16 mm
Final reading =17 mm
Difference in reading H= 17-16=1mm
Therefore V=3.62
V=3.62
V=2.55 m/sec
Using the above formula for our experimental use we require 15 m/sec which comes out to be
520 rpm
Fig.4.12 Wind tunnel running at 520 rpm or 15 m/sec

• Analysis of smoke flow visualizations of bluff bodies
FIG 4.13 Streamlined flow over the body
We observed streamlined flow over the body which was at a distance from the body and there
was visible low pressure over the cabin which increased the drag and hence by the use of
wind deflector this effect has to be reduced.

Fig.4.14 Streamlined flow over HCV with curved wind deflector
We observed streamlined flow over the body which was at a distance from the body and
because of the wind deflector there was no low pressure region and the flow was streamlined
throughout hence reducing drag and giving favourable outcome.

Fig.4.15 Streamlined flow over hcv with triangular wind deflector
Here also we observed streamlined flow over the body which was at a distance from the body
and because of the wind deflector there was no low pressure region and the flow was
streamlined throughout hence reducing drag and giving favourable outcome

• Calculating the surface pressure distribution over the bluff bodies and calculating
their coefficient of drag.
The drag coefficient (commonly denoted as: cd, cx or cw) is a dimensionless quantity that is
used to quantify the drag or resistance of an object in a fluid environment such as air or
water. It is used in the drag equation-
Where:
Is the drag force, which is by definition the force component in the direction of
the flow velocity
Is the mass density of the fluid which is air (1.1 kg/m3)
Is the speed of the object relative to the fluid (which is 15 m/s for our analysis)
Is the reference area
Here =P.A
Where P=static pressure
& A is the projected area

Since our bluff body has a frontal area in the shape of a rectangle the projected and reference
area both are same and cancel out in the numerator and denominator.
P the static pressure is the mean of the static pressures at all the ten station ports.
From the change in height of the working fluid in the manometer we can calculate the static
pressure change using the following formula
Where
 -density of working fluid i.e ethyl alcohol which is 800 kg/m3
h- Change in height of working fluid
A compressible fluid at rest is governed by the statics equation,
Where z is the height above an arbitrary datum, and g is the gravity acceleration constant
(9.81 m/s2
). This equation describes the pressure profile of the atmosphere, for example.
For an incompressible fluid, the statics equation simplifies to,

HCV WITHOUT WIND DEFLECTOR-CALCULATING ITS SURFACE PRESSURE
DISTRIBUTION AND COEFFICIENT OF DRAG
Table 7 Pressure at various pressure points
Serial no. Port no.
Initial height
h1(mm)
Final height
h2 (mm)
Difference in
height
h2- h1(mm)
P
Static
pressure(in
Pa)
1 1 30 39 9 70.63
2 2 30 42 14 109.87
3 3 30 51 21 164.8
4 4 30 49 19 149.11
5 5 30 52 22 172.65
6 6 30 47 18 141.26
7 7 30 40 14 109.87
8 8 30 35 5 39.24
9 9 30 24 -6 -47.08
10 10 30 26 -4 -31.39

Now the mean static pressure is calculated by taking the sum of P1-10 and dividing it by the
total number of observations i.e. 10.
Therefore mean pressure comes out to be
(70.63+109.87+164.8+149.11+172.65141.26+109.87+39.24-47.08-31.39)/10=87.59 Pa
Now using the formula
Here =1.1 kg/m3
V=15 m/s
Therefore Cd=87.59×2/(15)2
×1.1
Hence Cd=0.7078

HCV WITH CURVED WIND DEFLECTOR-CALCULATING ITS SURFACE
PRESSURE DISTRIBUTION AND COEFFICIENT OF DRAG
Table 8 Pressure at various pressure points
Serial no. Port no.
Initial height
h1(mm)
Final height
h2 (mm)
Difference in
height
h2- h1(mm)
P
Static
pressure(in
Pa)
1 1 30 39 9 70.63
2 2 30 42 12 94.17
3 3 30 52 22 172.23
4 4 30 51 21 164.80
5 5 30 51 21 164.80
6 6 30 48 18 141.26
7 7 30 39 9 70.63
8 8 30 26 -4 -31.39
9 9 30 25 -5 -39.24
10 10 30 24 -6 -47.08

total number of observations i.e 10.
Therefore mean pressure comes out to be =78.88 Pa
Here =1.1 kg/m3
V=15 m/s
×1.1
Hence Cd=0.6213

HCV WITH TRIANGULAR WIND DEFLECTOR-CALCULATING ITS SURFACE
PRESSURE DISTRIBUTION AND COEFFICIENT OF DRAG
Table 9 pressure at various pressure points
Serial no. Port no.
Initial height
h1(mm)
Final height
h2 (mm)
Difference in
height
h2- h1(mm)
P
Static
pressure(in
Pa)
1 1 30 39 9 70.63
2 2 30 42 12 94.17
3 3 30 52 22 172.56
4 4 30 50 20 156.96
5 5 30 52 22 172.56
6 6 30 49 19 149.11
7 7 30 39 9 70.63
8 8 30 25 -5 -39.24
9 9 30 25 -5 -39.24
10 10 30 24 -6 -47.08

total number of observations i.e. 10.
Therefore mean pressure comes out to be =76.11 Pa
Here =1.1 kg/m3
V=15 m/s
×1.1
Hence Cd=0.6145

Validation and comparison
Table 10 Comparison table
Model Numerical Experimental Difference
1. Base model Cd= 0.69713 Cd= 0.7078 0.01067
2.With Curve shaped wind deflector Cd= 0.61923 Cd= 0.6213 2.07e-3
3.With triangular shaped wind deflector Cd= 0.6103 Cd= 0.6145 4.2e-3
Wind tunnel test and CFD results are compared to demonstrate the correlation of the
two methods. The scale of the wind tunnel test model is 1:20. Test was performed at
Low speed wind tunnel. Table shows the comparison between simulation result and
test result. We can see that the simulation result has better correlation with that of the
test.
The streamline flows over the vehicle body during wind tunnel testing are similar to
that in simulations.

After validating above three models, we modified the base model into ten different models
depending upon the height and shape of the wind deflector and tested in ANSYS CFX. Data and
results have been given below.
Table 11 Data table
Curve shaped wind deflector height (from the ground) Frontal area & Cd value
(96,140), (15,160), (50,155) 160 mm 0.02 m2 Cd= 0.66732
(96,140), (15,165), (50,160) 165 mm 0.02 m2 Cd= 0.604539
(96,140), (15,170), (50,165) 170 mm 0.02 m2 Cd= 0.619234
(96,140), (15,175), (50,170) 175 mm 0.020331m2 Cd= 0.65437
(96,140), (15,180), (50,175) 180 mm 0.021006m2 Cd= 0.64469
Triangular shaped wind deflector height
(from the ground)
Frontal area & Cd value
(96,140), (15,160) 160 mm 0.02 m2 Cd= 0.64566
(96,140), (15,165) 165 mm 0.02 m2 Cd= 0.6173
(96,140), (15,170) 170 mm 0.02 m2 Cd= 0.6103
(96,140), (15,175) 175 mm 0.020331m2 Cd= 0.77549
(96,140), (15,180) 180 mm 0.021006m2 Cd= 0.650441

In the above result, we can see that lowest coefficient of drag lies in between 165
to 170 mm height (which is less than the height of the container i.e. 170 mm). It
also shows that curve shaped wind deflector is more effective than that of
triangular shaped. Vortex generation in this range of height was very less
compare to others. Hence, less drag will act over the vehicle.

Conclusions
By performing a series of CFD simulations, we have investigated the drag
reduction mechanism of commercial vehicle. By adding aerodynamic drag
reduction devices such as wind deflector and dome, the aerodynamic drag
coefficient of heavy commercial vehicle significantly reduces 10%. The
comparison of CFD result with wind tunnel test result reveals the same
trends of the aerodynamic characteristics.
Airflow analysis demonstrates that the wind deflector can reduce drag
successfully and the dome should be improved to match well with the
container. So there is still space to improve the aerodynamic characteristics
of heavy commercial vehicles by further optimization or increase the
aerodynamic drag reduction devices
From the above results we conclude that shape and height of the wind
deflector have great effect on fuel economy of the vehicle. By optimising the
size and shape of the wind deflector, we can increase the fuel efficiency of
the HCV’s. As well as we can cut down the cost of production of wind
deflectors by finding the minimum Cd at the lowest possible height.

Significance of the results obtained
• No significant previous projects have worked on the shape and size of the
wind deflectors.
• The speed taken, during the whole analysis was by considering the Indian
road conditions i.e. 15 m/s.
• Pressure distribution obtained was in the similar range when compared to
actual models.
• Streamline flow over the vehicle bodies were mostly the same as in ANSYS
CFX.

Future scope of work
• This project took into consideration the height and shape of the wind
deflector for analysis purposes hence leaving room for future study on
the effect of wind deflectors with different angular positions.
• Future research on drag reduction techniques can also take into the
implementation of air ducts at the leading edge & vortex generators at
the trailing edge.
• There is also scope of getting further insight caused by after body
modifications and trying them at different angles & shape.
• Further we can use FLUENT, GAMBIT, HYPERMESH etc. various other
software can be used for analysis. For modeling purpose PRO-E,
UNIGRAPHICS, SOLIDWORKS can be used.
• Future work can also be done on models which have been made by the
process of Rapid prototyping and 3 D printing.

REFERENCES
Journal / Conference Papers
[1] Rose McCallen Fred Browand Anthony Leonard,“Progress in Reducing
Aerodynamic Drag for Higher Efficiency of Heavy Duty Trucks Class 7-8 ” ,
SAE TECHNICAL PAPER SERIES: 1999-01-2238
[2] Jason M Ortega Kambiz Salari, “An Experimental Study of Drag Reduction
Devices for a Trailer Underbody and Base”, AIAA-2004-2252 V5
[3] Bonnet C. Fritz H., “External Truck Aerodynamics”
DominionUniversity,Norfolk,VA,USA,2009-03-4104
Reference / Hand Books
[1] Aerodynamics of road vehicles, Wolf-heinrich, SAE International , ISBN- 0-
7680-0029-7
[2] ANSYS CFX reference manual.
Web
[1] NASA Dryden research; www.nasa.gov
[2]SAE International www.sae.org
[3] Lawrence Livermore national laboratory; www.llnm.org
[4]Norfolk state university; www.norfolk.edu

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