[SEM]_Final Report [v6]

8/19/2019 [SEM]_Final Report [v6]

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DESIGN

OF AN AERODYNAMIC

SHELL ECO-MARATHON

VEHICLE BODY

Alessandra Miras FernandezHAN Facul! "# Au"$"i%e En&ineerin&

1


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AC'NO(LEDGEMENTS

As an international student in exchange for a year at the HAN University of AppliedSciences, it is my pleasure to present this technical report as a demonstration of my

achievements during my stay in this school. However, more important than to

notice what I could accomplish is to notice that nothing would have een possile

without the help and advice of many special people.

!herefore, I would li"e to than" #r. $oortman for his guidance as my student

counsellor, #r. Horn for following closely my %ourney the whole year, helping me

several times and always showing me "indness and patience &specially patience'(,

and #r. )wart for his valuale classes and always clever advisory during the

developing of this pro%ect.

I would also li"e to than" the always friendly and helpful memers of the HAN

Hydromotive team, who received me in their group as an all*time memer since the

+rst day, for ma"ing themselves availale to answer all my uestions, for trying

their est to ma"e me comfortale all the time, and for allowing me to e part of a

great experience with them during the Shell -co*marathon -urope /10 in

otterdam.

#y heartfelt than"s goes to my friends and fellow students 2uintin 3et and 4elle 5en

6laauwen, who made this pro%ect possile y helping me in the critical times and

sharing their "nowledge with me in the "indest way. A special than"s to my fellow

international students #atheus Alves and 7arolina 6ai, for all the support, incentiveand productive deates during this pro%ect.

8enerally, I would li"e to than" all the sta9 wor"ing for the HAN, for the U:A67, and

for the Science ;ithout 6orders program, for giving me this ama


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)REFACE

!he Shell -co*#arathon is an annual competition held around the world, sponsoredand promoted y Shell, that emraces the challenges raised y energy use in the

personal transportation sector as it reuires of its participants to e on the edge of

innovation to uild vehicles capale of achieving the highest possile fuel e=ciency.

!he event>s history stretches ac" over seventy years? starting as a simple

scientists> et, now it is the environment for o=cial world records.

See"ing to e part of this history, the faculty of automotive engineering of the

Hogeschool van Arnhem en Ni%megen founded the HAN Hydromotive? a highly

motivated team, with professors and students wor"ing together to develop and

research on hydrogen fuel cells and compete with a hydrogen vehicle in the Uran*

concept class of the Shell -co*#arathon.

Along the years, di9erent vehicles have een designed and uilt y the HAN

Automotive students in the team. @ne outstanding model is the Arval Inspire II,

which further than eing rd place in the Shell -co #arathon -urope /1B,

overcame the challenge of eing road legal. !o have a license plate is a great

achievement, specially performing so well during the competition, ut it also rings

the downside of "eeping the vehicle from performing its most as security items end

up compromising the lightweight and aerodynamic ody design.

As the challenge of eing road legal and also in the top of most fuel e=cient

vehicles in its class is achieved, the team now wants to uild a new car for thefuture Shell -co*#arathon years. :ree of the oligation of eing road legal, this

vehicle will e developed thin"ing only on the highest possile performance for fuel

e=ciency.

!he focus of this pro%ect then is to design the new vehicle>s ody thin"ing only on its

aerodynamic performance. 3arameters as frontal area and drag coe=cient will e

compared to the existing vehicle and other concepts to enhance the improvement

achieved.

A more aerodynamic ody reCects in less fuel consumption as it lowers the forces

opposing to the vehicle>s movement. !he tractive force supplied y the engine is

employed in overcoming these forces, which include the aerodynamic drag.

!herefore, less drag reuires less power. Aerodynamic forces can contriute up to

near B/D of the total reuired power in normal driving conditions.

!his pro%ect, when completed, will give other students the opportunity to wor" on

the vehicle>s ody y validating the design through wind tunnel testing of a scale

model, evaluating the forces acting on the ody through +nite element analysis,


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choosing its materials and productions methods and also integrating the vehicle>s

ody to other vehicle>s systems.

B


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TABLE OF CONTENTS

Ac"nowledgements....................................................................................................3reface.......................................................................................................................

!ale of contents........................................................................................................ B

Introduction................................................................................................................ E

1 Fiterature eview.................................................................................................G

1.1 6asic Cuid mechanics....................................................................................G

1. 8eneral principles of aerodynamics...............................................................

1. $ehicle aerodynamics..................................................................................1/

1..1 Aerodynamic drag.................................................................................111.. 5rag area...............................................................................................1

1.B Aerodynamics and fuel consumption...........................................................1

6ody Structure...................................................................................................1B

.1 5e+ning the vehicle architecture.................................................................1B

. 5e+ning the target parameters...................................................................10

. 5esign constraints.......................................................................................1E

.B !he topological model..................................................................................1G

6ody 5esign.......................................................................................................1

.1 3reliminary 5esign J Hard 3oints.................................................................1

. Shape design J A few concepts....................................................................1

. :low simulations..........................................................................................1

..1 !ools......................................................................................................1

.. Settings.................................................................................................

.. esults...................................................................................................

.B !he optimum ody shape............................................................................E

B 6ody 5etailing....................................................................................................

B.1 Simulations settings.....................................................................................

B. Nose shape..................................................................................................1

B. Surface roughness and s"in friction.............................................................

B.B !railing*edge thic"ness................................................................................

B.0 4unctions and interference drag...................................................................G

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B.E 8round clearance and camer.....................................................................

B.G #irrors..........................................................................................................B/

B. @penings and gaps......................................................................................B/

B. ;heel fairings and Coor...............................................................................B

0 :inal 6ody...........................................................................................................B0

E Successful real world examples.........................................................................B

G :uture steps.......................................................................................................0/

7onclusion..........................................................................................................0/

eferences................................................................................................................01

Appendices...............................................................................................................0

A. Fist of symols and useful relationships......................................................0

6. Shell -co*marathon -urope /10 J Uran 7lass rules..................................0

7. 3lan of approach..........................................................................................05. Simulation reports........................................................................................0

-. 7ontact information.....................................................................................0

E


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INTROD*CTION

Along the years, di9erent hydrogen*powered vehicles have een designed and uilt y theHAN Automotive students in the HAN Hydromotive team to compete in the Uran 7oncept

class of the Shell -co*marathon. !he Uran 7oncept class reuires that the vehicle shows,

esides e=ciency, an architecture that loo" as much as possile as a real*world vehicle.

!he previous uilt and current model, Arval Inspire II, conuered the rd place in the Shell

-co #arathon -urope /1B while overcoming the challenge of eing road legal, achieving its

goals. -ven though its performance is remar"ale, eing road legal rings the downside of

"eeping the vehicle from performing its most as meeting the authorities reuirements

compromise the lightweight and aerodynamic ody design.

!he team now has a new goal? to uild a new car for the future Shell -co*#arathon years,

free of the oligation of eing road legal, with the highest possile performance for fuel

e=ciency.

In this new goal the vehicle aerodynamics is a driven part, as a streamlined ody reCects in

less fuel consumption y lowering the forces opposing to the vehicle>s movement. !he

power reuired from the engine is employed in overcoming these forces, therefore, less

aerodynamic drag reuires less power from the engine, which is reCected in the lower fuel

consumption.

Having this relation into account, this pro%ect is settled to design a new vehicle>s ody that

attends the reuirements for low aerodynamic drag. ;hat factors are inCuencing the ody>s

drag and therefore how its shape should e are uestions that this pro%ect wants to answer.

!his report will show the design process and choices for the new vehicle>s ody thin"ing onlyon its aerodynamic performance and it is uild up as the following?

7hapter 1 gives an overview of aerodynamics asics, searching the driven parameters to

have a well streamlined ody. 7hapter determines the vehicle>s topology y de+ning its

targets characteristics and design constraints. !he topological model is the asis for the

development of di9erent ody concepts.

7hapter presents a few concepts that arise from the vehicle asic architecture and their

performance according to Cow simulation. In this chapter the optimum ody shape can e

found. 7hapter B shows how the optimum ody shape is detailed until the +nal ody is

completed. In this chapter features as interference drag, mirrors, internal Cow, windows and

driving staility are studied.

7hapter 0 presents the +nal model of the vehicle>s ody and its aerodynamic performance

according to Cow simulations. Here an overview of the +nal model can e found. In 7hapter

E parameters as frontal area, wetted area and drag coe=cient will e compared to the

existing vehicle and other concepts to ualify the improvement achieved.

7hapter G shows the possiilities for future wor"s on the vehicle>s ody as validating the

design through wind tunnel testing of a scale model, evaluating the forces acting on the

G


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ody through +nite element analysis, choosing its materials and productions methods and

also integrating the vehicle>s ody to other vehicle>s systems.

7hapter is the +nal chapter and contains the conclusion of the pro%ect. :ollowing this

chapter, the Shell -co*marathon rules, a list of symols and relations used in the presented

calculations and some literature topics can e found in annex. Also, contact information is

availale in annex 5 for any uestions or further explanation.

+ LITERAT*RE REVIE(

!his chapter introduces the fundamentals relevant to the ody design of a fuel

e=cient vehicle. As estate efore, the aerodynamic features of the vehicle>s ody

interfere in its fuel consumption, this chapter is dedicated to demonstrate how.

A deep lesson on the su%ect would reuire a lot more than a mere chapter to e

given. !his chapter>s goal is %ust to give the common reader a context on the

matters that will e read further in this report, therefore ma"ing it more accessile

to a wider range of audiences.

+,+BASIC FL*ID MECHANICS

“A fuid is a substance, as a liquid or gas, that is capable o fowing and that

changes its shape at a steady rate when acted upon by a orce tending to change

its shape.”

&5ictionary.com, n.d.(

According to the de+nition aove, the dynamics of a Cuid sustance can e

explained as y the forces acting on it, determining not only its tra%ectory, ut also

its velocity and ehaviour. !he following +gures show how a given Cuid ehaves

according to this rule.


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Figure 1: Flow behaviour under dierent pressure gradients due to compression

and epansion!

Figure 2: Flow behaviour under dierent pressure gradients due to geometry!

Flow separation infuenced by type o boundary layer!


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Figure 3: "etail on transition and separation!

:igures 1, and also show a very important characteristic of a Cuid, the oundary

layer. 5escried y the 8erman physicist and aerodynamics pioneer Fudwig 3randtlin 1/B, the oundary layer explains the Cuid ehaviour as inCuenced y its own

viscosity in a thin Cow region near surfaces, ringing reconciliation etween

experimental and theoretical discrepancies.

+,GENERAL )RINCI)LES OF AERODYNAMICS

KAerodynamics is the way air moves around things. !he rules of aerodynamics

explain how an airplane is ale to Cy. Anything that moves through air reacts to

aerodynamics. A roc"et lasting o9 the launch pad and a "ite in the s"y react to

aerodynamics. Aerodynamics even acts on cars, since air Cows around cars.L

&Nasa.gov, n.d.(

As read aove, aerodynamics is concerned aout the interaction of a Cuid &as air(

with a solid &as a car( when either one or the other is in motion. It measures the

interference caused y the geometry inserted on the originally free Cow.

!his measurements are made in terms of weight, lift, thrust and drag. Mef 1

1/


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Figure 4: Forces acting on a body due to fuid interaction!

@n a conventional system, weight and lift are the forces acting on the ody y

pulling it down or pushing it up and drag and thrust oppose each other y pulling

the ody ac" or pushing it forward. An additional term very used in vehicleaerodynamics is KdownforceL, which is nothing ut negative lift force &pushing the

ody down(.

;eight is a force related to the mass of the ody, and therefore we can say y now

that it>s not an aerodynamic concern unless we aim to move the ody up or down.

!hin"ing on a forwardOac"ward orientation, weight is important when it comes to

the rolling resistance &friction etween a ody and a wall, as a car and the road(

which will not e discussed in great detail in this wor".

!hrust can e generated y an enormous variety of sources, from roc"ets to

hydrogen fuel cells. It does a9ect the aerodynamics as Cuids interact with odies indi9erent ways depending on their speed, which is predicted y the dimensionless

constant eynold>s Numer. Mef. 1

Fift and drag are geometry depending, since the geometry of the ody will alter the

pressure +eld around itself and determine how the Cuid ehaves during their

interaction.

Figure 5: #ressure $eld around an

airoil!

Figure 6: Flow stream around an airoil!

%it generation!

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+,.VEHICLE AERODYNAMICS

A vehicle, as anything else on -arth, can e understood as a ody immersed in

Cuid. In this case, the considered Cuid is air.

!o minimis natural toconclude that given vehicle should distur as minimum as possile the Cuid in its

surrounds. !he role of aerodynamics is therefore to shape this vehicle in a KCow

friendlyL way.

Figure 7: #ressure $eld around an airoil

positioned at dierent angles relative to

the main fow direction!

Figure 8: Flow stream around an airoil

positioned at dierent angles relative to

the main fow direction!

!he most important aerodynamic force for a land vehicle moving forward is the

aerodynamic drag. Secondarily, liftOdownforce has its role in driving staility y

"eeping the vehicle from moving upwards or deviating from its desired tra%ectory

due to inertial forces. 5ownforce contriutions are only ene+cial aove certainspeeds. Special attention should e paid to the Coor or elly pan shape of the

vehicle since the proximity with the ground ma"es this area under the vehicle to

ehave as a $enturi tue Mef. and . !his phenomena is also "nown as road

e9ect and can e counteracted with design measures explained in detail further in

this wor".

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+,.,+ Aer"d!na$ic dra&

:or a land vehicle on cruise condition, aerodynamic drag is typically the dominating

retarding force along with the rolling resistance due to tires or earings. !his force is

composed y four components? the pressure drag, the viscous friction, the induced

drag and the interference drag. Mef. and

F d=C d × ρ ×V

2

× Aref

2

F d : total dragforce C d:dragcoefficient ρ : fluid density V : flowspeed

A ref :referencearea

Equation 1: "rag orce!!

!he pressure drag is commonly the dominant term on the composition of

aerodynamic drag and it>s due to the Kvacuum e9ectL on the rear of the vehicle

caused y the detachment of the air from the surface of the trailing edge,

generating vortices that consume energy and also a void that literally suc"s the

vehicle ac"wards. !his feature has a strong relation with the ody>s frontal area.

Mef. and

!he viscous friction is the term referring to the e9ects of the oundary layer, as the

shearing of the Cuid tangentially to the vehicle>s surface &s"in friction( and the

pressure drag cause y the impossiility of full pressure restoration at the rear of

the vehicle due to the existence of a oundary layer with thic"ness. Mef. and In

a very well streamlined ody, i.e. a ody with no Cow separation, the viscous

friction is the dominant term of the aerodynamic drag. !his feature is strongly

related to the ody>s wetted surface area.

Induced drag is the e9ect caused y components of liftOdownforce, created due to

the pressure di9erential on the geometry. !his e9ect gains special importance in

land vehicles as it relates to ground e9ect, an additional force generated y the

proximity of the ody with the ground that will e analysed in more detail further in

this wor". !he last component of the aerodynamic drag is the interference drag. !he

interference drag is resultant from the Cow ehaviour around %unctions and holes,

as in a ody made of two or more shapes assemled together. !he interference

drag is in nature pressure drag and can e as much as half of a vehicle total drag.

Mef. and

1


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!o design a vehicle with a great aerodynamic performance, the aerodynamic drag

should e minimi


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@n a land vehicle moving constantly forward, the rolling resistance of the tires and

the aerodynamic drag are the only two forces opposing its movement. According to

literature, this relation evolves with the cruise speed of the vehicle, as shown in the

+gure ellow.

Figure 9: Aerodynamic drag evolution with driving speed!

In the scope of the Shell -co*marathon, the cruise speed of the vehicle will e

maintained around / "mOh, which assigns to aerodynamic drag around D of the

power reuired of the vehicle to move forward. Mef. B

Since the teams is provided with special tires to minimi


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BODY STR*CT*RE

!his chapter shows how the "nowledge acuired from literature is rought togetherwith the Shell -co*marathon rules in order to achieve a asic model of the new

vehicle>s ody. 5i9erent existent concepts have een studied during this phase of

the development to ring inspiration and also a etter understanding of the real

application of some rules as design constraints.

,+DEFINING THE VEHICLE ARCHITECT*RE

!he vehicle architecture is de+ned as a group of ma%or decisions aout how the

vehicle should e that are made during early stages of the pro%ect to avoid

foridden or unrealistic solutions and set, along with the goals, the priority areas

where most e9ort should e employed. 6esides controlling pro%ect resources, a

asic and strict vehicle architecture is also useful to give the designer a more

concrete vision of design possiilities y serving as input for the initial designing

cycles. It also controls the progression towards the target +gures, verifying if they

are reachale andOor eing reached.

!he concern of this wor" is to design a vehicle>s ody with low aerodynamic drag to

compete in the uran*concept class of the Shell -co*marathon, accordingly some

design +gures as drive wheels, ra"e wheels, and numer of axles are of low

concern for the given goal and will not e developed in this report. However, the

+gures numer of wheels, trac" width, steer wheels, wheelase, and ground

clearance are of importance and developed as follows.

Nu$0er "# 12eels3 KUran 7oncept vehicles must have exactly four wheels,

which under normal running conditions must e all in continuous contact with the

road. A +fth wheel for any purpose is foridden.L Mef. 1

Trac4 1id23 K!he trac" width must e at least 1// cm for the front axle and / cm

for the rear axle, measured etween the midpoints where the tires touch the

ground.L Mef. 1A larger trac" width increases the roll*over resistance of the

vehicle. @n the other hand, it can also increase the frontal area of the vehicle. As

the goal of this wor" is to design the vehicle>s ody around its aerodynamicperformance, minimi


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trac" width will e "ept shorter than the front trac" width and also at the minimum

allowed.

Seer 12eels3 !he Shell -co*marathon rules determine that only front wheel*

steering is allowed for prototype class vehicles. However, it ma"es no mention to

uran class vehicles leaving this choice to the designer. !here are plenty of up and

downsides of di9erent steering systems, and as explained aove, the aerodynamic

performance is considered priority over other factors. -ven so, some oservance

must e "ept to avoid excessive increase in complexity andOor weight in the future

stages of development of the vehicle.

!he ma%or +gure is that a steer wheel inside the vehicle reuires room to turn

without touching the vehicle>s ody. !he vehicle must comply with a minimum

turning radius, which implies in turning angles for each wheel. !urning the wheel y

a given angle will increase the room ta"en y it inside the vehiclePs ody and

therefore ma"e it wider.

!he Shell -co*marathon rules determine that K!he turning radius must e less thanE m. !he turning radius is the distance etween the center of the circle and the

external wheel of the vehicle. !he external wheel of the vehicle must e ale to

follow a /Q arc of E m radius in oth directions.L Mef. 1. !o comply with this rule,

the necessary turning angle of each wheel needs to e calculated. !hese

calculations are inCuenced y the chosen steering system.

A four*wheel steering system decrease the necessary turning radius at low speeds

and can e used to improve driving staility in high speeds or manoeuvraility in

tight spaces. However, it increases the frontal area of the vehicle whilst turning and

reuire room at the ac" of the vehicle, which is not availale due to the

aerodynamic considerations that suggest a gradual decrease of cross section area

towards the tail. A two*wheel steering system will e used instead.

Steer wheels located at the front increase frontal area while steer wheels located at

the rear reuire space not availale in the vehicle. Some literature search shows

that the con+guration with rear steer wheels also has some prolems in maintaining

the correct heading and steering staility. Accounting all the aove mentioned

reasons, a frontal two wheel*steering system is chosen as the est availale option.

As a result of this choice, oth scenarios in with all wheels or only the rear wheels

are contained inside the vehicle>s ody are possile. !he increase in frontal area

given y having the front wheels contained in the vehicle>s ody is determined ythe minimum needed turning angle. @n the other hand, the drag of an exposed

wheel system is di=cult to model analytically, ut literature presents relevant

empirical data that shows unneglectale contriution to the total drag Mef . 6oth

options will e analysed further in this wor", eing preferale to "eep a model with

all wheels contained inside the vehicle>s ody.

1G


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Gr"und-clearance3 !he ground*clearance is a critical component of the vehicle

architecture since it>s one of the measures that can e adopted to counteract the

downforce generated y the road e9ect. Fiterature research shows the development

of downforce related to di9erent ground clearances, giving a curve in which a

minimum ground clearance can e found for di9erent airfoil shapes and si


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,.DESIGN CONSTRAINTS

!wo ma%or sources are ta"en into consideration for design constraints in this wor"?

race regulations and aerodynamics.

:rom the race regulations all minimum and maximum sis ody are provided. !he vehicle must e in compliance with all Shell

-co*marathon rules. :or a detailed reading please go to Appendix 6.

:rom aerodynamics the vehicle>s ody should e shaped in order to distur as

minimum as possile the Cow around itself. It should not generate lift or downforce

as well as "eep the aerodynamic drag the lowest. Starting from s"etch can e a

di=cult tas" for the designer since the possiilities are in+nite. However, the

literature o9ers a great amount of reliale data to guide the s"etch of initial shapes

and therefore have a reduced numer of design cycles. A summing up of these data

can e found in the next section of this chapter.

Special attention is now given to the steer wheels since, as speci+ed efore, they

reuire room to turn without touching the vehicle>s ody and thus are also a source

of design constraints. !he following calculations show the iggest turning angle

reuired to follow the minimum turning radius speci+ed y the Shell -co*marathon

rules for the steering con+guration chosen in section .1 of this chapter.

Figure 10: 'alculated required turning angle!

,/THE TO)OLOGICAL MODEL

In this section a summari


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!his document>s purpose is to condensate the long literature review into a uic"

consultation source to guide the designer during early design cycles and to enhance

the ody>s target parameters. As the highly iterative design cycles evolve, this list

is updated to guide the next cycle andOor answer identi+ed uestions.

• :irst target 7d? T /.10 &Arval Inspire II(R

• Ideal target 7d? prox. /./G0 &3A7 II * prototype(R

• :irst target Af? T /.Bm &Arval Inspire II(R

• Ideal target Af? T /.0m &3A7 II * prototype(R

• Initial trailing edge angle? V1/W*1WR XVWR

• Initial camer? 0DR

• Sis ody. All s"etches will e made around this topological model. Ananatomically correct human +gure is included to give a perspective of how the real

pilot would +t in the car.

Figure 11: (opological model!

/


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. BODY DESIGN

.,+)RELIMINARY DESIGN 5 HARD )OINTS

6ased on the information o9ered y the vehicle>s topological model, free*hand

s"etches and clay models of di9erent possile solutions were made. !hese

representations help the designer to evaluate the complexity of the shapes and

their feasiility. As mentioned efore, time is the most valuale resource in this

wor". !he correct notion of what solutions are worth employing further e9ort on

development is not only helpful ut mandatory.

Figure 12: )and s*etch! Figure 13: )and s*etch!

Figure 14: )and s*etch! Figure 15: )and s*etch!

1


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!he following sections present in more detail the development of some of the

shapes seem aove.

.,SHA)E DESIGN 5 A FE( CONCE)TS

A shape design is the result of several progressive steps. @nce the preliminary

shape is estalished, consecutive model iterations ased on that design are

developed and tested using 7:5 analysis. !he results of the simulations are ta"en

into consideration in the suseuent iterations to support or modify the shape until

an optimum ody shape is considered achieved. !he criteria used to de+ne what is

an optimum asic shape are explained in detail in section .B of this chapter.

!he translation of the preliminary design phase into the 7A5 application is showed

in the next paragraphs.

S2a6e +

Shape 1 is inspired on the low eynold numers airfoil S/G. It contains

modi+cations on the early third to achieve smaller cross section area at the tailing

edge at the same time the minimum height reuired for the driver>s compartment

and the maximum length of the vehicle are respected. !he torpedo shape is

modi+ed into a shouldered ody in order to reduce the frontal area. !he transition at

the shoulder line is meant to e as smooth as possile to minimi


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Figure 16: +hape dierent views and measurements!

S2a6e

Shape is composed of two di9erent odies acting together as a vehicle, in the

same way a motorcycle with a side pod would do, for example. 5i9erently from

Shape 1, Shape is not symmetrical. However it does follow the same shouldering

techniue to reduce frontal area. !he Kside podL ody covers the wheels and

contains little space for voluminous loads. !he KmainL ody meets the Shell -co*

marathon reuired dimensions for oth driver>s and load>s compartments. !his

model has a great advantage over others in terms of frontal area. @n the other

hand, viscous drag and interference drag are expected to e igger as we now have

more wetted area and a very li"ely $enturi tue e9ect etween the odies. !his

design also does not have optimi


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Figure 17: +hape - dierent views and measurements!

S2a6e .

Shape is inspired on a fellow competitor of the Shell*-co marathon. !he 4apanese

prototype class car attending y the name of :ancy 7arol shows a non*conventional

solution for surfacing and also good results. Mef 10 !his concept has eentranslated to the uran*concept class rules, resulting in the model seen elow.

B


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Figure 18: +hape dierent views and measurements!

.,.FLO( SIM*LATIONS

.,.,+ T""ls

KS@FI5;@YS :low Simulation is a class of 7:5 &7omputational :luid 5ynamics(

analysis software &called 7oncurrent 7:5( that is fully emedded in the mechanical

design environment, for all general engineering applications.L

&I$AN@$, /1B(

!he choice on the 7:5 software was made ased on a few factors. !he +rst factor is

that Solidwor"s :low Simulation was used in the development of the Arval Inspire II.

Using the same solver would eliminate an extra layer of inconsistency whencomparing oth models.

!he second factor is that Solidwor"s :low Simulation is already emed in the 7A5

tool used for the development of the models, which guarantees that no

inconsistencies due to compatiility issues when importing and meshing the

geometry will occur.

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!he +nal factor is that Solidwor"s :low Simulation provides, for the needed typed of

simulation, a satisfactory precision level with lower computational time, lower

computational resources and easy user*friendly interface. Mef 1

K5ue to the use of a 7artesian*ased mesh coupled with some engineering

techniues and methods implemented in S@FI5;@YS :low Simulation, numerical

calculations reach acceptale accuracy on far coarser meshes when compared with

traditional 7:5 codes. 5ue to this fact, users can ma"e calculations of Cuid Cow and

heat transfer for very complex 5 cases with relatively modest computational

resources.L

&I$AN@$, /1B(

As the Cow conditions to e simulated don>t reuire any advanced oundary

condition, the simplicity of Solidwor"s :low Simulations proves not to e a road*

loc".

.,., Sein&s

!he settings report for all simulations can e found in Appendix 7.

It is worth noticing that in this phase of the design the ualitative Cow analysis is

more meaningful than uantitative results. As a conseuence of short

computational time eing preferred over great precision, no e9ort was employed on

detailed meshing manually. !he computational domain was de+ned ased on the

geometry si


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Figure 19: +hape fow simulation results.


G


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Figure 21: +hape - fow simulation results.

Figures 22 and 23: +hape - fow simulation results.


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Figure 26: (he pressure generated by the nose shape infuences on fow

detachment and wa*e length.

.,/THE O)TIM*M BODY SHA)E

!ime is de+ned as the most valuale resource in this wor". !o avoid spending this

resource in activities that ring little added value to the +nal vehicle>s ody, a

procedure of developing and optimi


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#odel :rontal Area Surface Area :low AttachmentShape 1 /.G m G.G m 8oodShape /. m 11.11 m 8oodShape 1./1 m .G m 3oor

Table 1: +ummary!

!he +rst and main goal is to minimi


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In this stage, simulations are held with a computational domain si


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• !he mesh total si


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Figure 31: /e$ned meshing detail!



/,NOSE SHA)E

!he shear forces are greater at the nose section and therefore, the nose shape is

critical to ensure that laminar Cow is achieved on the elly*pan and the top of the

vehicle. Faminar Cow is desirale since the friction created y turulent Cow can e

1/ times greater than the friction created y laminar Cow, minimi


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and !he ody contour should e gentle and its surface should e smooth and

seamless to help providing gentle acceleration of the oundary layer in this region.

However, at vehicle>s height pea" the oundary layer should e forced into

turulent Cow to ensure greater length without separation due to adverse pressure

gradients. !urulent Cow is not only much less li"ely to su9er separation, as +gure

B shows, ut can also e used to improve cooling as it transfers energy in all

directions &therefore hot components are advisale to e placed near this region of

the vehicle(. Mef and

Figure 34: %et 0 %aminar boundary layer! /ight 0 (urbulent boundary layer!

0


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Figure 35: Front view! (urned wheels in color!

Figure 36: +ide view!

E


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Figure 37: (op view!

!he +gures aove show how the nose shape evolved from the asic shape to ma"e

air Cow easier. 7hanges include smoothing and rounding the contours and the

transition to the ellypan.

/,.S*RFACE RO*GHNESS AND S'IN FRICTION

Surface smoothness is a su%ect of maximum attention since it can provide or

destroy the possiility of running a laminar Cow on roughly the +rst third of the

vehicle or provide separation on the remaining length.

!he ody seam should e located where laminar Cow is not sought or at the

stagnation line where no oundary layer has yet developed. 8aps from wind shields

and doors should e sealed without creating KstepsL or KumpsL for the air Cowing

on them. Additionally, signal lights and stic"ers should e incorporated to the

vehicle>s ody, as for example covering decals with a layer of clear*coat. Mef

:urther suggestions are given in the next susections.

/,/TRAILING-EDGE THIC'NESS

A thin trailing*edge results in smaller wa"e area, which is great for restoring the

pressure at the end of the vehicle and thus reduce pressure drag.

!here are some di9erent techniues in use to determine the maximum thic"ness of

the trailing*edge for given ody si


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y approximating the maximum trailing edge thic"ness y several times smaller

than the thic"ness of the oundary layer at the trailing edge Mef and .

All di9erent approaches result in milimetrical results that, although reasonale, are

hard to achieve in within the competition rules for the si


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angle. !his allows the vehicle to e shorter if necessary with less impact in wa"e

area. @n the other hand, it changes the camering of the vehicle, which may create

induced drag. #ore details on this matter are given further in the next susections.

Figure 39: 1asic tail!

Figure 40: "etailed tail!

Figure 41: 1asic tail and its vorticity!


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Figure 42: "etailed tail and its vorticity!

Figure 43: 1asic tail and wa*e!

Figure 44: "etailed tail and wa*e!

B/


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/,78*NCTIONS AND INTERFERENCE DRAG

!he drag of a ody is minimis compartment should have at least cm of height,while the whole vehicle should e etween 1//cm and 1/cm. Mef. 1

!he vehicle>s elly pan &or Coor( along with the ground create a tunnel*li"e structurethat restrains the Cow according to its shape and sis principleone can infer that if the local speed increases, than the local pressure has todecrease. !his pressure di9erence on the top and ottom of the vehicle create asuction e9ect towards the ground, or negative lift, also "nown as downforce. Mef ,, G

B1


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As one may conclude, ground clearance is an important feature since it inCuencesthe amount, or even presence, of induced drag. Induced drag is not desirale in thiswor", neither in the form of lift or downforce, since it is produced at an energyexpense to create the vorticity necessary for its maintenance. Mef and

!he next +gure shows how a ody in free air ehaves di9erently when close to the

ground. In the case of a symmetrical ody that generates no lift in free air, whenput closer to the ground downforce can e oserved. A simple solution to that iscamering the ody. A camered ody produces lift in free air, ut no induced dragat all when close to the ground.

Figure 45: 3ect o ground proimity and cambering on induced drag!

Fiterature provides us with a rigorous investigation of camered ground vehicles

guiding the development of streamlined odies in the proximity of the ground. Mef. !he alance etween camering and ground clearance is given y simulationresults, with an initial guess oriented y literature as it can e seen in thereuirements list presented in chapter .

!his su%ect rings ac" the trailing edge design to highlight, once the tail shapee9ectively modi+es the camer of the ody. It can e seen in +gure ZZ that somedownforce is generated y the vehicle at /W yaw and /W pitch.

B


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Figure 46: 3ect o trailing edge attitude on lit generation!

Figure 47: 3ample o the eect o trailing edge according to simulations!

Some vehicles adopt igger ground clearances to decrease the tric"y induced drage9ect. Naturally, igger ground clearances ring igger frontal and surface areas

since a igger portion of the wheels is not integrated anymore in the main*ody. !his reuires further development on wheel fairings and therefore also increases %unction drag.

As always, it is a matter of alance to choose what approach is the est for thevehicle under development. In this wor", the results show that even though someinduced drag can e oserved, the gain in reduction of pressure drag outweigh thee9ect. !hus, the design choices up to now are maintained.

/,:MIRRORS

!he competition rules state that the driver must have access to a direct arc of visiility ahead and to /Q on each side of the longitudinal axis of the vehiclewithout aid of any optical &or electronic( devices such as mirrors, prisms, periscopes,etc. Also, the vehicle must e euipped with a rear*view mirror on each side of thevehicle, each with a minimum surface area of 0 cm[ &0cm x 0cm(, to provideindirect view of E/cm high poles spread out every /Q in a Bm radius half*circlearound the vehicle. !his mirrors cannot e replaced y electronic devices. Mef 1

B


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!o attend these rules without adding appendages to the vehicle, the proposedsolution is to "eep the wind shield as ig as necessary to "eep the mirrors inside thedriver>s compartment. As visiility studies are "u "# 2e sc"6e of this wor", thewindshield design is yet to e developed and must e calculated ta"ing into accountthe compliance of visiility rules with inside mirrors to e produced.

!here are availale examples of teams using this same solution as it can e seen inreferences Mef. , B and 1/.

/,;O)ENINGS AND GA)S

No detailed study related to windshield, wheel system, ventilation and door gapshas een conducted. However, some advisory for the production is provided asfollows.

8aps, umps, and internal Cow greatly increase the drag of a vehicle, maximum

attention must e paid on the design of these features.

Venilai"n and inernal


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a NA7A duct has to e sit ingest the oundary layer or trip it

prematurelyR• -xisting gaps &such wheel*wells( can e also used oth for inlet and outletR

!he Shell -co*marathon has designated gaps in the rules for providing the driver>scompartment and the fuel cell>s compartment with ventilation. Mef. 1

(ind s2ield and d""r

!he following +gure shows how grooves can trip the laminar oundary layer intoturulent oundary layer.

Figure 48: 3ect o bumps or grooves on the boundary layer!

!he solution for this "ind of prolem around windshields and windows is very simpleand can e achieved y ma"ing rounded neat and thin sealing. Around doors

however, the prolem is more complicated since the driver has to e ale of comingout of the vehicle without help and within small time*window in case of any accidentMef. 1. @ne possile solution for it is sealing the door gap with clay. At the sametime that it +lls the groove up and smooth the surface, it has no strength to endureforce applied on the door in order to open it, therefore not harming the driver>sscape.

B0


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Figure 49: 3ect o bumps or grooves on the drag coe2cient!

(2eel s!se$

!he drag from the wheel system is formed y the following factors Mef. ?

• !he exposed portion of the wheelR

• !he wheel*steer cut*out in the elly panR

• !he wheel fairingR

• !he wheel well &housing that isolates the wheel form the cain(R

• ;indage losses due to spinning wheelR

An extended literature review was done on the su%ect and the following decisionswere made.

In this wor" the wheel wells and steer cut*outs are developed ut a fully sealed

system is considered. !his solution can e oserved in the 1 ;orld Solar

7hallenge champion car>s system Mref solar? integrating a rotating thin ely pan

plate that acts sealing the hourglass cut.

Fiterature suggests that a cover of around E/D of the wheels is appropriate to

minimi


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No optimum wheel fairing was found during the development of this wor" and

therefore not addedR !he following +gures show how the adding of wheel fairings

conCicted with the main ody geometry increasing the vortices generation under

the vehicle and therefore its drag. !here>s room for improvement as appropriated

wheel fairings can still e researched and added.

Figure 50: 4+peed5 3ample o the eect o non6optimum wheel airings! 7pper8

without airings! %ower8 with airings! 1igger vortices can be observed with a non6

optimum wheel airing infuence.

BG


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Figure 51: 49orticity5 3ample o the eect o non6optimum wheel airings! 7pper8

without airings! %ower8 with airings! )igher vorticity can be seen or longer lengths

with a non6optimum wheel airing infuence.

!he air under the Coor encounters the wheel in an angle, disturing the Cow after

that point. !he pressure di9erential created y the rotating wheel system might aswell distur the Cow under the vehicle increasing its induced drag. !he naturalconclusion from these prolems is that the vehicle>s Coor &or elly pan( can yet eimproved according to the wheel fairing developed and the windage e9ect.

B


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Figure 52: 3ample o the eect o non6optimum wheel airings! 7pper8 without

airings! %ower8 with airings! :o signi$cant improvement can be credited to the

non6optimum wheel airing that ;usti$es it increase in riction and intererence

drag..

B


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7 FINAL BODY

A summed up presentation of the +nal ody achieved during this wor", regarding all

the information given eforehand, is given elow.

Figure 53: (op view!

Figure 54: Front view!

0/


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Figure 55: +ide view!

Figure 56:


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Figure 57: 1elly pan detail!


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Figure 60: +imulation results!



0


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!he results show that a total force of /,>N is achieved and therefore, according

the euation 1, the drag coe=cient of the vehicle is Cd ? >,+. Since the main

source of drag is the pressure drag, the reference area used in the calculations is

the frontal area and measures >,:=$. !he surface area is 1/.E m,

!he drag area, used to compare the vehicle to others in a meaningful way, is Cd @

A ? >,>=7.$

9 S*CCESSF*L REAL (ORLD EAM)LES

In this chapter, a rief uantitative comparison etween the results of this wor" and other

"nown models is provided. Mef. B, , , 1/

M"del Cd Are# Dra& area CdA

Ar%al Insi6ire II /.1E /.0 /.1Ci!8"ule /.11* /.* /./G*)ac II /./G0* /.0B* /./1*

Ne1 $"del /.1/ /.G /./0

: F*T*RE STE)S

!he completion of this wor" opens several opportunities for other students willing to wor" on

the development of the vehicle. 6esides the already mentioned topics, during this wor"

some other issues concerning aerodynamics were noticed, as listed?

• 5evelopment of windshield and doors through visiility and scape testsR

• 5evelopment of the ventilation system along with the vehicle>s interior designR

• 5evelopment of the wheel well sealing and optimum wheel fairingsR

• Integration of components such as lights, mirrors and stic"ers to the main ody as

suggested in this wor"R

As the reader might notice, this report contains some orientation aout all these su%ects as

they were considered y the designer even if not detailed studied or developed.

; CONCL*SION

!his wor" was developed trying to answer the uestion? )ow a +hell 3co6marathon 7rban

'oncept class car=s body should be to achieve its maimum aerodynamic perormance>

Along the months of its completion, a full main*ody asic design was achieved, followed y

a re+ned, detailed main*ody which is the main +nal product of this wor".

0B


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!he success of the achieved design can e measure as its estimated generated drag is lower

than the designs> used y the team and also its close competitors, however wind*tunnel test

validation is necessary for ensure the results.

!he +nal 7d otained for this model is >,+> and the +nal drag area is >,>=7$ . !his

means a 9,7 i$6r"%e$en "%er 2e curren %e2icle $"del and a .1D improvement

over its closer competitor.

!he model is still open to modi+cations to etter accommodate any changes that might e

necessary due to production choices or rules alterations.

00


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REFERENCES

M1 S2ell Ec"-$ara2"n >+7 Ocial Rules C2a6er +

M !A#AI, 8oroR

T2e Leadin& Ed&e3 Aer"d!na$ic desi&n "# ulra-srea$lined land %e2icles

IS6N /*GE*/E/*/

M HU7H@, ;olf*HeinrichR

Aer"d!na$ics "# R"ad Ve2icles3 Fr"$ ++->+

M 6UI4S!-N, #i"eR

Ver0eerin& %an de aer"d!na$isc2e ei&ensc2a66en aan de Ar%al Ins6ire II

M1/ http?OOwww.cci*rest.frO+lesO5ossierpresse7ity4oule.pdf

M11 AHA#A5R A6@*S-I-R 8A\FA5R

Mes2 "6i$izai"n #"r &r"und %e2icle aer"d!na$ics

4aguar*Fand over, 7oventry Univerisity, UYR /1/R

M1 I$AN@$R !-6UNSYIYHR 3FA!@N@$I7HR

Validai"n Me2"d"l"&! #"r M"dern CAD-E$0edded CFD C"de3 #r"$

Funda$enal Tess " Indusrial Benc2$ar4s

#entor 8raphics 7orporation, 5assault SystemsR ussiaR /1BRM1 https?OOwww.grc.nasa.govOwwwO"*1OairplaneOga.html

M1B http?OOwww.shell.comOgloalOenvironment*societyOecomarathon.html

M10 http?OOwww.fc*design.%pOfancycarolOtecO1]carG.htm

M1E 6@;AN5, :.R

Reducin& Aer"d!na$ic Dra& and Fuel C"nsu$6i"n

0E

http://www.cci-brest.fr/files/DossierpresseCityJoule.pdfhttps://www.grc.nasa.gov/www/k-12/airplane/bga.htmlhttp://www.shell.com/global/environment-society/ecomarathon.htmlhttp://www.fc-design.jp/fancycarol/tec/1_car97.htmhttp://www.cci-brest.fr/files/DossierpresseCityJoule.pdfhttps://www.grc.nasa.gov/www/k-12/airplane/bga.htmlhttp://www.shell.com/global/environment-society/ecomarathon.htmlhttp://www.fc-design.jp/fancycarol/tec/1_car97.htm


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University of South 7aliforniaR USAR /11R

M1G http?OOthetiredigest.michelin.comOmichelin*ultimate*energy*tire

A))ENDICES

A, LIST OF FIG*RES

B, SHELL ECO-MARATHON E*RO)E >+7 5 *RBAN CLASS R*LES

C, )LAN OF A))ROACH

D, SIM*LATION RE)ORTS
http://thetiredigest.michelin.com/michelin-ultimate-energy-tirehttp://thetiredigest.michelin.com/michelin-ultimate-energy-tire

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[SEM]_Final Report [v6]

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