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

8. Volume mesh of 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


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

Therefore Cd=78.88×2/(15)2×1.1

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


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

Therefore Cd=76.11×2/(15)2×1.1

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

THANK YOU

final submission project - copy (1)

Documents