DESIGN AND SIMULATE AN AERODYNAMIC URABNCONCEPT CAR BODY FOR THE SHELL ECO-MARATHON WITH LESS COEFFICIENT OF DRAG
A Thesis Proposal Presented to the School of Mechanical and Manufacturing Engineering Mapua Institute of Technology
In Partial Fulfillment Fulfillment of the Requirements for the Degree of Bachelor of Science in Mechanical Engineering
By: Da Silva, Elisario M. 2009108764 Diwa II, Jose S. 2009151238 Pimentel, Marc Desie D. 2010100349
December 2014
TABLE OF CONTENTS
LIST OF FIGURES FIGURES ................................................. ..................................................... .......................................................... ..... i LIST OF TABLES ................................................... ..................................................... ......................................................... .... ii ACKNOWLEDGEM ACKNOWLEDGEMENT ENT .............................................................................................. . iii ABSTRACT ABSTRACT ..................................................... ........................................................................................................... ................................................................. ........... iv CHAPTER CHAPTER 1 INTRODUCTION INTRODUCTION .............................................. ........................................2 1.1 Background of the Study ................................................ ........................................2 1.2 Statement Statement of the Problem ............................................... ........................................3 1.3 Objectives Objectives of the Study .............................................................................. .............3 1.3.1 General Objective Objective ................................................... ........................................3 1.3.2 Specific Objectives.................................................. ........................................4 1.4 Significance of the Study................................................. ........................................4 1.5 Scope and Limitations ...................................................... .............................................................................................4 .......................................4 1.5.1 Vehicle Design ................................................. ................................................5 1.3.1 Dimensions Dimensions ......................................................................................... .............5 1.3.1 Time Constraint Constraint ....................................................... ..............................................................................................5 .......................................5 CHAPTER CHAPTER 2 REVIEW OF RELATED RELATED LITERATURE LITERATURE ...............................................6 2.1 Review of Related Studies ............................................... ........................................6 2.1.1 Computational Study of Flow Around a Car body (Z. Zheng 2009) .........6 2.1.2 Design and Construction of the Urban-concept Car Exterior for Shell Ecomarathon marathon Asia 2011 (M. Bernabe et. al, 2011) ..................................7 2.1.3 Simulation and analysis of drag and lift coefficient between Sedan and Hatcback Hatcback car (Salleh 2009) .................................................... .............7 2.2 Review of Related Literature Literature .................................................................... .............8 2.2.1 Vehicle Forces ................................................. ................................................8 2.2.1.1 Lift ............................................... ..................................................... ..........................................................8 .....8 2.2.1.2 Drag ............................................. ..................................................... ..........................................................8 .....8 2.2.1.3 Downforce ...................................................... .............................................................................................8 .......................................8 2.2.2 Aerodynamic Aerodynamic ................................................... ................................................9 2.2.2.1 Dynamic Pressure Pressure ................................................................................9 .......................................................... ......................9
TABLE OF CONTENTS
LIST OF FIGURES FIGURES ................................................. ..................................................... .......................................................... ..... i LIST OF TABLES ................................................... ..................................................... ......................................................... .... ii ACKNOWLEDGEM ACKNOWLEDGEMENT ENT .............................................................................................. . iii ABSTRACT ABSTRACT ..................................................... ........................................................................................................... ................................................................. ........... iv CHAPTER CHAPTER 1 INTRODUCTION INTRODUCTION .............................................. ........................................2 1.1 Background of the Study ................................................ ........................................2 1.2 Statement Statement of the Problem ............................................... ........................................3 1.3 Objectives Objectives of the Study .............................................................................. .............3 1.3.1 General Objective Objective ................................................... ........................................3 1.3.2 Specific Objectives.................................................. ........................................4 1.4 Significance of the Study................................................. ........................................4 1.5 Scope and Limitations ...................................................... .............................................................................................4 .......................................4 1.5.1 Vehicle Design ................................................. ................................................5 1.3.1 Dimensions Dimensions ......................................................................................... .............5 1.3.1 Time Constraint Constraint ....................................................... ..............................................................................................5 .......................................5 CHAPTER CHAPTER 2 REVIEW OF RELATED RELATED LITERATURE LITERATURE ...............................................6 2.1 Review of Related Studies ............................................... ........................................6 2.1.1 Computational Study of Flow Around a Car body (Z. Zheng 2009) .........6 2.1.2 Design and Construction of the Urban-concept Car Exterior for Shell Ecomarathon marathon Asia 2011 (M. Bernabe et. al, 2011) ..................................7 2.1.3 Simulation and analysis of drag and lift coefficient between Sedan and Hatcback Hatcback car (Salleh 2009) .................................................... .............7 2.2 Review of Related Literature Literature .................................................................... .............8 2.2.1 Vehicle Forces ................................................. ................................................8 2.2.1.1 Lift ............................................... ..................................................... ..........................................................8 .....8 2.2.1.2 Drag ............................................. ..................................................... ..........................................................8 .....8 2.2.1.3 Downforce ...................................................... .............................................................................................8 .......................................8 2.2.2 Aerodynamic Aerodynamic ................................................... ................................................9 2.2.2.1 Dynamic Pressure Pressure ................................................................................9 .......................................................... ......................9
2.2.2.2 Center of Pressure................................................................. Pressure................................................................. ...............9 2.2.1.3 Flow Similarity Similarity ...................................................... ...................................................................................10 .............................10 2.2.1.4 Reynolds Number........................................................... Number...............................................................................10 ....................10 2.2.3 Types of Flow .................................................. ..............................................11 2.2.3.1 Continuum Flow............................................................. Flow.................................................................................11 ....................11 2.2.3.2 Free Molecular Molecular Flow ...................................................... ..........................................................................11 ....................11 2.2.3.3 Low Density Flow.................................................. .............................11 2.2.3.4 Viscous Flow ................................................. ......................................11 2.2.3.5 Inviscid Flow.......................................................................................12 2.2.3.6 Incompressible Incompressible Flow ...................................................... ..........................................................................12 ....................12 2.2.3.7 Compressible Flow ................................................ .............................12 2.2.3.8 Subsonic Flow............................................... ......................................13 CHAPTER CHAPTER 3 THEORETICAL THEORETICAL BACKGROUND BACKGROUND ....................................................... ........................................................14 .14 3.1 Shell Eco-marathon Eco-marathon Rules 2013 ..................................... ......................................14 3.2 Aerodynamics Aerodynamics .................................................................. ......................................14 3.2.1 Bernoulli’s Principle.....................................................................................14 Principle .....................................................................................14 3.2.1.1 3.2.1.1 Bernoulli’s Equation ...................................................... ..........................................................................15 ....................15 3.2.2 Front Pressure Pressure ..............................................................................................17 ......................................................... .....................................17 3.2.3 Drag Force.....................................................................................................18 Force .....................................................................................................18 3.2.4 Coefficient Coefficient of Drag .......................................................................................19 ................................................. ......................................19 3.2.1 Down Force ..................................................... ...................................................................................................20 ..............................................20 3.3 Energy Losses due to Aerodynamic Resistance Resistance ................................................. .22 3.4 Power Required for Rolling Resistance.................................................... ...............................................................23 ...........23 3.5 Energy Saved Due to Weight Reduction Reduction .............................................................24 3.6 Resistance Due to Inertia ................................................ ......................................24 3.7 Wind Speed in Manila ...................................................... ...........................................................................................25 .....................................25 CHAPTER CHAPTER 4 METHODOLOGY METHODOLOGY ...................................................... ...................................................................................26 .............................26 4.1 Considering the Parameters Parameters .................................................... .................................................................................27 .............................27 4.1.1 Shell Eco-marathon Eco-marathon Asia Rules 2013 ............................................... ...........27 4.1.2 Theoretical Consideration ...........................................................................27 4.1.3 Exterior Body Design of the previous entry “Habagat” ...........................27
4.2 Design of the Exterior Body ............................................................. ....................28 4.2.1 TVR TUSCAN ................................................ ..............................................28 4.2.2 3D Design using Computer Software............................................... ...........29 4.3 Simulation of Aerodynamic Characteristics .......................................................30 4.3.1 Simulation of Exterior Body of Haribon ................................................... .30 4.3.2 Aerodynamic Characteristics Comparison ................................................31 CHAPTER 5 DISCUSSION AND ANALYSIS OF RESULTS ...................................33 5.1 Results.....................................................................................................................33 5.1.1 Data of Drag Force and Coefficient of Drag were calculated using the Autodesk Flow Design Simulation Software . ......................................................33 5.2 Discussion .............................................. .................................................................34 CHAPTER 6 CONCLUSION AND RECOMMENDATION......................................36 6.1 Conclusion ............................................. .................................................................36 6.2 Recommendation ...................................................................................................37 Appendices .............................................. ..........................................................................38 Appendix A. Gannt Chart ................................................. ..............................................38 Appendix B. Expenses ................................................................................. ....................38 Appendix C. CAD of Exterior Body of Haribon ................................................ ...........39 Appendix D. CAD of Exterior Body of Habagat ................................................ ...........43 Appendix E. Dimensions of Exterior Body of Habagat................................................47 Appendix F. Dimensions of Exterior Body of Haribon ................................................49 Appendix G. Computations of Wind Speed ..................................................................51 Appendix H. Simulation of Exterior Body of Habagat using Autodesk Flow Design ................................................. ........................................................53 Appendix I. Simulation of Exterior Body of Haribon using Autodesk Flow Design ................................................. ........................................................55 Appendix J. Step by step method using Autodesk Flow Design ..................................57 Appendix K. Shell Eco-marathon Asia Rules 2013.......................................................61 Appendix L. Computation of Percent Difference of Frontal Area..............................63 Appendix M. Shell Eco-marathon Asia 2014 ................................................................64 Appendix N. Sponsors ................................................................................. ....................66
Bibliography ................................................................................................. ....................70
LIST OF FIGURES
Figure 2-1 Effect of the wind angle to the drag and lift coefficient ..........................6 Figure 2-2 Center Pressure (Anderson 2001) .......................................................... ...9 Figure 2-3 Example of Flow Similarity (Anderson 2001) ........................................10 Figure 2-4 Division of Flow (Anderson 2001) ...........................................................12 Figure 2-5 Subsonic Flow (Anderson 2001) ..............................................................13 Figure 3-1 Bernoulli’s Principle .................................................................................16 Figure 3-2 Bernoulli’s Principle on wing with Air as fluid ......................................13 Figure 3-3 Drag Force generated by motion and air flow .......................................18 Figure 3-4 Various shapes with coefficient of drag ................................................. .20 Figure 3-5 Down force on an automobile .............................................. ....................21 Figure 3-6 Rolling resistance on automobile tire......................................................23 Figure 3-7 Wind Speed graph in Manila for the month of February .....................25 Figure 4-1 Process Flowchart of the study ................................................................26 Figure 4-2 HABAGAT .................................................. ..............................................28 Figure 4-3 TVR TUSCAN ..........................................................................................28 Figure 4-4 Haribon CAD using Autodesk Inventor ................................................ .29 Figure 4-5 Flow Simulation of Haribon using Autodesk Flow Design ...................30 Figure 4-6 Habagat CAD using Autodesk Inventor ................................................ .31 Figure 4-7 Flow simulation of Habagat using Autodesk Flow Design....................32
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LIST OF TABLES
Table 5-1 Aerodynamic Characteristics of Habagat................................................33 Table 5-2 Aerodynamic Characteristics of Haribon ................................................34
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ACKNOWLEDGEMENT This thesis is the end of our journey in obtaining our BS degree in Mechanical Engineering. We have not travelled alone in this journey. The contributions of many different people, in their different ways, have made this study possible. Foremost, we would like to extend our appreciation and thank God for the wisdom and perseverance that He has bestowed upon us throughout this study. Moreover, we would like to grab this opportunity to express our gratitude to everyone who supported us throughout this journey. We are thankful for their aspiring guidance, invaluably constructive criticism and indeed friendly advice during the study. We are sincerely thankful to them for sharing their truthful and illuminating views on a number of issues related to this thesis project. We would like to express our sincere gratitude to our advisor Prof. Sherwin S. Magon for the continues support in this research, for his patience, motivations and immense knowledge. This work would have not been possible without his guidance, support and encouragement. Under his guidance we overcame many difficulties and learned a lot. Besides our advisor, we would also like to thank our panels; Engr. Igmedio Isla, Engr. Jaime Honra and Engr. Hans Felix Bosshard for their helpful criticisms, insightful comments and valuable suggestions. Last but not the least, we would like to thank our families especially our parents for supporting us spiritually throughout our lifes.
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ABSTRACT
The Shell Eco-marathon is an annual competition wherein teams from different universities design and construct vehicles with the aim to travel the furthest distance with least amount of energy. Detailed design must be employed in order to have an ideal model in fabrication of vehicle parts. In this study, the grouped designed and simulated a vehicle body to be used by an urbanconcept vehicle. The group employed engineering software namely Inventor and Flow Design. The vehicle body is designed using Inventor. Flow Design is used to simulate the aerodynamic characteristic of the design in comparison with the d esign of the old vehicle Habagat . Using different wind speeds, the vehicle design, named Haribon, resulted to a coefficient of drag of 0.3.
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CHAPTER 1 INTRODUCTION This is a study to design and simulate an aerodynamic urbanconcept exterior body for Shell Eco- Marathon Asia 2013 to attain low coefficient of drag and help the vehicle attain less fuel consumption. This chapter discusses the background, statement of the problem, objectives, significance and scope and limitations of the study. 1.1 Background of the study
The Royal Dutch Shell sponsors an annual competition about the future of transportation and mobility titled Shell Eco-marathon. It is a worldwide competition wherein students are challenged to design, build and drive the most energy-efficient car. The competition is focused on maximizing a vehicle’s mileage with a given amount of fuel rather than achieving high speeds. The winner of the competition would be the vehicle that could travel the most distance given one liter of fuel. This is the third time that the Mapúa Institute of Technology School of Mechanical and Manufacturing Engineering will be competing for the challenge under the urbanconcept category. Urbanconcept is a prototype car that contains all the features of today’s commercially available cars. The institute’s first urbanconcept entry in 2011 was named “Habagat”. Due to some constraints and difficulties, it was unable to finish the race.
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1.2 Statement of the Problem
In 2011, Habagat, the Eco-Car of MIT was heavy. The vehicle body was made of fiber glass material. The factors that affected the 2011 Eco-Car were the excessive tubes that were used as support mounting for the vehicle body, the wide frontal area, and the heavy body cover. With this study, the design and performance of the vehicle car body may be improved by analyzing the factors that affect the aerodynamics. The challenge with this study is to be able to design and construct a vehicle body that would have less drag than commercial vehicles in accordance to the existing competition rules to be able to help achieve better fuel economy. 1.3 Objectives of the Study
The goal of the Shell Eco-marathon competition is to challenge students in building the world’s most fuel efficient vehicle. Eco-cars should consume less of fuel as possible over some distance. This study aims to satisfy the following general and specific objectives as shown below: 1.3.1 General Objective
The study aimed to design and simulate an aerodynamic vehicle body for the Mapúa’s eco-car urbanconcept entry to help the car to attain less drag coefficient and determine its aerodynamic performance.
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1.3.2 Specific Objectives 1.3.2.1 Design an exterior body for an urbanconcept car that is compliant with
the rules of Shell Eco-Marathon 2013. 1.3.2.2 Minimize the frontal area of the eco-car Haribon, it should be less than
that of Habagat. 1.3.2.3 Use of Computer Aided Design software in developing the design of the
vehicle. 1.3.2.4 Simulate and compare the previous vehicle Habagat to the new design
Haribon in terms of coefficient of drag. 1.4 Significance of the Study
The significance of this aerodynamic study can be used as reference for anyone who wishes to participate in the Shell Eco-marathon Challenge or any competition that holds the same goals and nature. The techniques and principles in this study can also be used as reference for any individual who will study aerodynamic effects on automotive vehicles and the like. 1.5 Scope and Limitations
The study only covers the design of the vehicle body and the simulation of its aerodynamic performance. The limitations are due to the rules and regulations given by the Shell Eco-marathon Asia 2014 and the time-constraint to design the vehicle.
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1.5.1 Vehicle Design (Article 25, page 13)
b) Aerodynamic appendages, which adjust or are prone to changing shape due to wind whilst the vehicle is in motion, are forbidden. 1.5.2 Dimensions (Article 45, page 20)
a) The total vehicle height must be between 100 cm and 130 cm. b) The total body width, excluding rear view mirrors, must be between 120 cm and 130 cm. c) The total vehicle length must be between 220 cm and 350 cm. d) The track width must be at least 100 cm for the front axle and 80 cm for the rear axle, measured between the midpoints where the tyres touch the ground. e) The wheelbase must be at least 120 cm. f) The Driver’s compartment must have a minimum height of 88 cm and a minimum width of 70 cm at the Driver’s shoulders. g) The ground clearance must be at least 10 cm. h) The maximum vehicle weight (excluding the Driver) is 205 kg. 1.5.3 Time-constraint
This study is limited since the organizers of the Shell Eco-marathon competition require the teams to finish and submit the designs in less than half a year.
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CHAPTER 2 REVIEW OF RELATED LITERATURE The presentation of both thesis and journal articles in this part shows to expound further how aerodynamic concepts can significantly affect the output of a vehicle. 2.1 Review of Related Studies
The presentation of both thesis and journal articles in this part shows to expound further how aerodynamic concepts can significantly affect the output of a vehicle. 2.1.1 Computational Study of Flow Around a Car body ( Z. Zheng 2009).
Z.Zheng made a study about the flow around a car body with different relative angle wind to car axis, varying it from 0 to 30 ° as shown in figure 2-1. The scale of the automobile he uses is 435 mm x 168 mm x 148 mm (length x width x height) with 360,000 mesh size. In this study, the drag and lift coefficients are used in order to compare the different effects of the front window angle on the performance of the vehicle.
F Figure 2-1. Effect of the wind angle to the drag and lift coefficient (Zheng 2009)
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2.1.2 Design and Construction of the Urban-concept Car Exterior for Shell Ecomarathon Asia 2011 (M. Bernabe et. al, 2011)
Previous vehicle entry of Mapúa for Shell Eco-Marathon Asia urbanconcept car made a research about its exterior body. The researcher design and fabricate the exterior body of an urbanconcept that compete in Malaysia on 2011. The design of the exterior body has average coefficient of drag of 9.7. Tear drop shape of an exterior body was highly recommended by the researchers since it only has 0.05 coefficient of drag.
2.1.2 Simulation and analysis of drag and lift coefficient between Sedan and Hatcback car (Salleh 2009)
The thesis showed difference coefficients barriers and lift coefficients for two basic design types of sedan and hatchback cars. Process simulation and analysis for 14 both the model design was conducted with computer-aided drawing software and analyzed using COSMOS Floworks software. Restriction coefficient and lift coefficient for the hatchback design is lower than the sedan design. With this observation, the hatchback design becomes more efficient and its aerodynamic value increases.
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2.2 Related Literature
This section discussed related literature regarding aerodynamic. 2.2.1 Vehicle Forces
There are four main forces that affect the aerodynamics of a vehicle. 2.2.1.1 Lift
Lift is a force perpendicular to the velocity flow of air. Lift opposed the weight of a vehicle. (Anderson 2001) Lift helps heavy vehicle to consume less energy by decreasing the force due to weight. 2.2.1.2 Drag
Drag is a force parallel to the velocity flow of air. It also opposed the motion of vehicle through air. (Anderson 2001) Drag is generated through interaction of the vehicle to a form of liquid or gas. 2.2.1.3 Downforce
Downforce is a force perpendicular to the velocity flow of air. Downforce is generated because of gravitational attraction of the vehicle to earth. (Anderson 2001)
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2.2.2 Aerodynamics
The dynamic of gases, especially atmospheric interactions with moving objects. (Anderson 2001) 2.2.2.1 Dynamic Pressure
Dynamic pressure is a property of moving gas. It is also used in the lift coefficient and drag coefficient theory. Dynamic pressure is directly proportional to density and velocity which have a unit of pressure. (Anderson 2001). 2.2.2.2 Center of Pressure
Center of pressure is located where the resultant of a distributed load effectively acts on the body. Center of pressure is just like center of gravity where center of gravity is located on a body due to weight while center of pressure is located on a body due to pressure. When moment is applied to the center of pressure the acting distributed load will be equal to zero. (Anderson 2001)
Figure 2-2 Center Pressure (Source: Fundamentals of Aerodynamics 2001) 9
2.2.2.3 Flow Similarity
In flow similarity two different parameters are considered, two different bodies and flow fields but these parameters must be dynamically similar. The streamline pattern must be geometrical, force of coefficient must be the same, and dimensionless coefficients must be the same if plotted in nondimensional coordinates. Flow similarity is commonly applied to wind tunnels and computer simulation. (Anderson 2001)
Figure 2-3 Example of Flow Similarity (Source: Fundamentals of Ae rodynamics 2001) 2.2.2.3.1 Reynolds Number
Reynolds number is important in Flow similarity, since in flow similarity the two different bodies that will be compared must have the same Reynolds number. Reynolds number is also equal to the ratio inertial force and viscous force. (Anderson 2001) 10
2.2.2.4 Types of Flow
In Aerodynamics there are different kinds of flow that is being considered. 2.2.2.4.1 Continuum Flow
Continuum flow exist when the body surface experience frequent molecules impact and the body cannot distinguish the individual collision. In continuum flow the fluid is treated as a continuous flow. Continuum flow is the most common flow that is being used in aerodynamics application. (Anderson 2001) 2.2.2.4.2 Free Molecular Flow
Free molecular flow is opposite of continuum flow where the impact of the molecules to the body surface is infrequent because the molecules is spaced. In free molecular flow the body can distinguish each molecular impact. (Anderson 2001) 2.2.2.4.3 Low Density Flow
Low density flow is a flow which can experience both characteristics of free molecular flow and continuum flow. 2.2.2.4.4 Viscous Flow
Viscous flow is a flow which exhibit effects of a transport phenomenon. Transport phenomenon is a phenomena of mass diffusion, viscosity and thermal conduction which occur when the mass,
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momentum and energy are transported from one location to another fluid. (Anderson 2001) 2.2.2.4.5 Inviscid Flow
Inviscid Flow is opposite of viscous flow which do not exhibit effects of transport phenomenon. (Anderson 2001)
Figure 2-4 Division of a flow. (Fundamentals of Aerodynamics 2001)
2.2.2.4.6 Incompressible Flow
Incompressible flow is a flow where density is constant. (Anderson 2001) 2.2.2.4.7 Compressible Flow
Compressible flow is a flow where density is variable. (Anderson 2001)
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2.2.2.4.8 Subsonic Flow
Subsonic flow is a flow where the Mach number of the flow field is less than 1. The streamlines of subsonic flow is smooth. Subsonic flow has a rule of thumb, where rule of thumb stated that Mach number of a body must be less than 0.8 (Anderson 2001)
Figure 2-5 Subsonic Flow (Fundamentals of Aerodynamics)
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CHAPTER 3 THEORETICAL CONSIDERATION This chapter focuses on the concepts involved in an aerodynamic design for a vehicle exterior body. The vehicle body plays an important role in increasing the efficiency of a vehicle since it is in primary contact with the air flow. The parameters that are set by Shell EcoMarathon Challenge in the design of the vehicle exterior body are also discussed in this chapter. 3.1 Shell Eco-marathon Official Rules
The primary consideration in the design of the vehicle exterior body should comply with the rules and regulations of the Shell Eco-Marathon (SEM). There are set of specifications for the vehicle dimensions and safety issues that should be followed. 3.2 Aerodynamics
The aerodynamics is one of the important parameters in the design and development of automobile. Under road conditions, an automobile’s performance is affected by air resistance. When a car is in motion, air flow in opposite direction and in some cases it flows across the vehicle. Therefore, to be able to overcome this resisting flow of air, a car should be driven with greater amount of power to move forward. 3.2.1 Bernoulli’s Principle
The basic principle in consideration for aerodynamic design is the Bernoulli’s principle. This theory states that as the fluid velocity increase, the pressure exerted by that fluid decreases, various flows can be examined using this theory. The Bernoulli’s
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equation will be used in the calculation of fluid flow. Also, the Bernoulli’s principle came from Thermodynamics. 3.2.1.1 Bernoulli’s Equation
Energy Balance, Assuming zero friction loss From Energy Balance: Energy In = Energy Out
(Eq. 3.1)
+ ++ = + + +
(Eq. 3.2)
( + + + = + + + )
+ + +
+ + = ϒ
= + + +
++
+ + =
ϒ
++
(Eq. 3.3) (Eq. 3.4) (Eq. 3.5) (Eq. 3.6)
Note: Force (F) is equal to the product of Pressure (P) and Area (A). There is also not change in temperature (ΔT=0) Equation 3.5 and 3.6 are called Bernoulli’s equation. Either of the two equations can be used to calculate problems in fluid dynamics. The second law of thermodynamics states that “when energy is transferred, that energy cannot be conserved and some energy must be reduced to some lower value”. From the second law of thermodynamics, the Bernoulli’s equation (Eq. 3.5) is modified in consideration of friction losses (ℎ ).
+ + = ϒ
++ +ℎ ϒ
(Eq. 3.7)
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Rearranging to show pressure difference, Eq. 3.7 yields: − ϒ
=
−
+ℎ
(Eq. 3.8)
Fig. 3-1 Bernoulli’s Principle (Source: cdxtexbook)
Fig. 3-2 Bernoulli’s Principle on wing with Air as fluid (source: uafedu)
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From the law of mass conservation and continuity equation, mass does not change with respect to position, nor is it affected by pressure, temperature or motion.
=
(Eq. 3.9)
=
(Eq. 3.10)
=
(Eq. 3.11)
Q=
(Eq. 3.12)
Note: Fluid is assured incompressible From Eq. 3.10 the density was cancelled due to the same material:
=
(Eq. 3.13)
3.2.2 Front Pressure
Front pressure is caused by the compressed air molecules acting against the direction of motion of a vehicle. As a vehicle is moves forward, the air attempts to flow over the vehicle but the front part of the vehicle counters with the air. Since the vehicle front part exerts force on the resisting air, the air molecules is compressed by counter force. These compressed air molecules are high-pressure and push the vehicle toward low pressure zones which are the bottom, top and sides of a vehicle. The equation governing front pressure is as follows:
=
(Eq. 3.14)
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Where:
= Frontal Pressure = Drag Force = Frontal Area 3.2.3 Drag Force
Drag Force is a type of force that is relevant to motion. This force is generated by interaction between a solid body and a fluid. There are two requirements to generate drag. First, the body should be in contact with the fluid to generate drag. Since drag force is acting between a body and fluid, no fluid means zero drag. Second, there should be a difference in velocity between the body and the fluid.
Fig. 3-3 Drag Force generated by motion and air flow (source: Bright Hub Engineering)
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=
(Eq. 3.15)
Where:
=
(kinetic or dynamic contribution to pressure)
3.2.4 Coefficient of Drag
The coefficient of Drag is a dimensionless number that is used to quantify Aerodynamic Drag on a vehicle body as it moves over some fluid. Low drag coefficient would mean that the vehicle can pass through a fluid with relatively low resistance. This is the rational on why automotive and aircraft engineers experience on various shapes and designs to effectively lower the air resistance to maximize performance. The area of drag is one factor to determine the aerodynamic efficiency of a body. In the design a vehicle, the total shape of the exterior body is considered such as the front and cross-sectional areas. The shape of an object has a very great effect on the amount of drag (NASA). The computation for co efficient of drag is as follows:
=
(Eq. 3.16)
Where:
= Drag Force ρ = Mass density of the fluid
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v = Speed of the object relative to the fluid
= Frontal Area
Fig. 3-4 Various shapes with coefficient of drag (Source: NASA) 3.2.5 Down Force
Down force is a downward type of force produced due to aerodynamic factors. There are two things about down force. First is the benefit, it provides additional contact between the vehicle tires and the road by means of pushing the vehicle downward. Second is that, excessive down force can lead to larger power requirement to drive the vehicle, thus translating to more fuel consumption. Down force value
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depends on the function of the vehicle under design. The equation below shows the formula for down force: F = 0.5* * * ρ *
(Eq. 3.17)
Where:
= Total Area of a vehicle = Coefficient of Drag Ρ = Density of air depending on temperature and altitude
= Speed of the car
Fig. 3-5 Down force on an automobile
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3.3 Energy Losses due to Aerodynamic Resistance
The air contains kinetic energy, which is energy transferred as it comes contact with another body. This energy from the air, is opposed to the wind direction, and therefore leads to energy drain for the vehicle. The energy loss is computed by:
= KE
=
=
= [( )( )()( )]
(Eq. 3.18)
(Eq. 3.19)
(Eq. 3.20)
(Eq. 3.21)
Where:
= Energy absorbed that cause energy loss and drag KE = Kinetic Energy in the air transferred in the v ehicle
= Mass of air v = Velocity of the air relative to the vehicle
= Frontal Area of the vehicle D = Distance travelled by the vehicle
= Coefficient of Drag
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3.4 Power Required for Rolling Resistance
Rolling resistance pertains to the energy lost when the tire is rolling along its path. The reason for this energy loss due to rolling resistance is the time deformation due to continuous use. The equation provided below shows the power requirement for rolling resistance.
= mgv
(Eq. 3.22)
Where:
= Power needed to overcome rolling resistance = Rolling coefficient of the tires m = Mass of the body g = Gravitational Acceleration v = Velocity of the car
Fig. 3-6 Rolling resistance on automobile tire (Source: Engineering toolbox and BMW) 23
3.5 Energy Saved due to weight reduction
Power is defined as the required energy to move q Newton (N). Body at a velocity of 1m/s. In SI units, power is expressed in watt (W). The relationship of power to weight and velocity is given by the equation:
= mgv
(Eq. 3.23)
Where:
= Power save due to reduction of weight m = Mass of the Body g = Gravitational Acceleration v = Velocity of the Car 3.6 Resistance due to Inertia
Inertia resistance is defined by Mass and Inertia. Inertia is difficulty to change the momentum of a body. The relationship of momentum, mass and velocity is given by: Momentum (p) = Mass (m) x Velocity (v)
(Eq. 3.24)
Also, From Newton’s Law of motion mass (m) can be derived from: Force (F) = Mass (m) x Acceleration (a)
(Eq. 3.25)
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3.7 Wind Speed in Manila
The wind speed in Manila from the month of February may vary from 0m/s to 8m/s and the maximum wind speed recorded was 17m/s. At the beginning of the month the wind speed vary from 3m/s to 7m/s while at the end of the month the wind speed vary from 4m/s to 8m/s.
Figure 3-7 Wind Speed graph in Manila for the month of February (Source: https://weatherspark.com/averages/33313/2/Metro-Manila-Philippines)
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CHAPTER 4 METHODOLOGY This chapter discussed the methods and procedures of designing and fabricating the exterior body of urbantype vehicle entry of Mapúa Institute of Technology for Shell Eco-Marathon Asia 2013. This chapter also discussed the different software used to help the researcher to conduct the study. The process flowchart of the study is in figure 4-1:
Considering the Parameters
Design of the Exterior Body by Computer Software
Simulation of Aerodynamic Characteristic through Computer Software
Figure 4-1 Process Flowchart of the study.
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4.1 Considering the Parameters
The design of the exterior body of vehicle for 2013 was based on different parameters. 4.1.1 Shell Eco-Marathon Asia 2013 Rules
The Shell Eco-Marathon Rules for 2013 was the basis of the design of the exterior body. There are limitations and recommendations made by the organizers regarding the exterior body. Refer to Appendix K for the rules. 4.1.2 Theoretical Consideration
The researcher used the Aerodynamic principles in Chapter 3 as a basis in designing the exterior body. The shape recommended by NASA was also considered to attain low coefficient of drag that affect the vehicle performance. Coefficient of drag can affect the energy needed by a vehicle to run; low coefficient of drag will give lower energy needed since the air flowing through the vehicle will flows smoothly to the body. 4.1.3 Exterior Body Design of the previous entry “Habagat”
Habagat is the first entry of Team Cardinals for the Shell Eco Marathon Asia urban type category. The exterior body design of Habagat was reviewed for its positive and negative aspects. Habagat’s negative side is its frontal area because it captures more air, since it is wide. The exterior body is heavy and the under chassis is not fully covered. These parameters help the researchers in designing the new exterior body of the urbanconcept vehicle. 27
Figure 4-2 HABAGAT 4.2 Design of the exterior body 4.2.1 TVR TUSCAN
The design of the exterior body of the urbanconcept vehicle for 2013 is based from TVR TUSCAN. TVR TUSCAN was selected because of the shape of its body. Its body has low coefficient of drag which can help the performance of the car. The design of TVR TUSCAN was also considered since the curviness of the body perfectly fits to the design of the chassis.
Figure 4-3 TVR TUSCAN (Source: http://betterparts.org/tvr/tvr-tuscan.html)
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4.2.2 3D Design using Computer Software
Considering the aerodynamic principle, rules and the basis design TVR TUSCAN the researchers came up with the final dimensions refer to appendix. The researcher uses Autodesk Inventor for making a 3D sketch of Haribon. Autodesk Inventor is a program that enables you to make a 3D sketch with a desired material and run a stress analysis test. Finalizing the shape, dimensions and aesthetics of the exterior body is shown in figure 4-3.
Figure 4-4 Haribon CAD using Autodesk Inventor
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4.3 Simulation of Aerodynamic Characteristics
The exterior body will be simulated in a computer software to determine its aerodynamic characteristics and compare to the exterior body of Habagat. 4.3.1 Simulation of exterior body of Haribon
After sketching the exterior body of Haribon in Autodesk Inventor the material selected was considered and input to the sketch. The exterior body is simulated in Autodesk flow design to determine the aerodynamic characteristics. Autodesk flow design is a program developed by Autodesk especially for flow analysis. Autodesk flow design can determine the coefficient of drag and drag force; speed wind can also change from 0 to 100 m/s. The model used was imported from Autodesk Inventor, any CAD program can also be import, orientation of the model can also be change, and different view of the wind is also available.
Figure 4-5 Flow Simulation of Haribon using Autod esk Flow Design 30
4.3.2 Aerodynamic Characteristics Comparison
The aerodynamic characteristics of exterior body of Haribon were compared to Habagat. The exterior body of Habagat was also 3D Sketch; since the actual exterior body of Habagat is not available the researcher based the dimensions of the sketch in the thesis of previous team. The sketch was also simulated through Autodesk flow design for its aerodynamic characteristics.
Figure 4-6 Habagat CAD using Autodesk Inventor
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Figure 4-7 Flow simulation of Habagat using Autodesk Flow Design
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Chapter 5 DISCUSSION AND ANALYSIS OF RESULTS This chapter shows the results of the simulation and d iscusses the effect of the results to the vehicle body. 5.1 Results 5.1.1 Data of Drag Force and Coefficient of Drag were calculated using the Autodesk Flow Design Simulation Software.
Habagat Trial
Wind Speed
Coefficient of
Drag Force
Highest Front
(m/s)
Drag
(N)
pressure (Pa)
1
7.22
0.47
14.130
26.512
2
10.56
0.47
30.359
60.388
3
13.89
0.47
51.602
104.778
Table 5-1 Aerodynamic Characteristics of Habagat
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Haribon Trial
Wind Speed
Coefficient of
Drag Force
Highest Front
(m/s)
Drag
(N)
Pressure (Pa)
1
7.22
0.31
0.074
11.374
2
10.56
0.30
0.155
22.357
3
13.89
0.30
0.272
39.983
Table 5-2 Aerodynamic Characteristics of Haribon 5.2 Discussion
Three (3) trials were made to acquire data for the simulation of the two (2) models Haribon and Habagat. The data used in calculating the coefficient of drag and drag force were based on the actual dimensions of the vehicle. Appendix H and I shows the actual dimensions of both vehicles, Haribon and Habagat. The assumption for the simulation is that air is still and that the vehicle speed is used as the wind speed. Vehicle speed was calculated based on overall distance travelled over time to finish the race track. The vehicle speed of 26kph is the minimum speed, 38kph is the median speed and 50kph is the maximum speed. These figures of speed were based on the SEM 2014 race track and vehicle max speed. The track spans 1.2km and the competition requires 10laps per trial which translates to overall travel distance of 12km with a time limit of 29 minutes per trial. Appendix G shows the computation for the vehicle speed. 34
CAD software is used in determining the vehicle total frontal area and Flow Design is utilized to calculate the drag forced given the wind speed. Highest front pressure is calculated as well. The coefficient of drag is determined by the shape of the design. Drag force is affected mainly by velocity. Increasing velocity yields higher value for drag force and higher value for frontal pressure.
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Chapter 6 CONCLUSION AND RECOMMENDATION This chapter presents the conclusion of the study and recommendations future improvement of studies that will be conducted. 6.1 Conclusion
To be able to compete, the Shell Eco-marathon 2013 rules and regulations should be considered. The parameters in the design and the final dimensions are shown on appendix K. Frontal area should be reduced if one is to reduce the value of drag coefficient. The new urbanconcept body for Haribon, has less frontal area as compared to Habagat. The reduction in front area is 10.59%. Computation for reduction in area is shown in appendix L. The shape of an object affects the numerical value of the coefficient of drag. The frontal area of the vehicle body is the reference in the simulation of the coefficient of drag. Minimizing frontal area is the key in reducing drag coefficient. The computed coefficient of drag via simulation is less compared to commercial cars since its size is minimized and the body is streamlined. Drag force, meanwhile is also reduced with minimized frontal area of the design. Although drag coefficient is determined by an object’s shape, drag force can still change
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depending on the numerical value of the velocity. From the data results, it is clear that increasing velocity would yield increasing value for the drag force.
6.2 Recommendation
Detailed designing and accurate molding of the vehicle body is a must since the shape of an object greatly affects the coefficient of drag. The design should be conceptualized based on existing aerodynamic models such as current trend on car shapes streamlining. A software simulation is a must in designing the vehicle body so that the team can cut in determining the optimum shape of the vehicle. Simulation gives the advantage of skipping construction of prototypes and can give the team more time on fabrication. Time is limited for the team to produce a vehicle for the Shell Eco-marathon competition; design phase should be immediately started as soon as a new team is formed so that design details can thoroughly checked and more time can be provided on fabrication phase. The fabrication of the vehicle body should also consider light-weight materials since it also affects vehicle performance. Rules and Regulations of the Shell Eco-marathon competition should always be taken into account in the design and fabrication of the vehicle body. Besides the above given, teamwork and sharing of ideas gives best result in the design and construction of a good vehicle.
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APPENDICES Appendix A. Gannt Chart
Appendix B. Expenses
Description Fabrication of Mold Fabrication of Exterior Body Total Expenses
Price P 90,000 P 90,000 P 180,000
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Appendix C. CAD of exterior body of Haribon
ISOMETRIC FRONT RIGHT VIEW
ISOMETRIC FRONT LEFT VIEW
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ISOMETRIC REAR LEFT VIEW
ISOMETRIC REAR RIGHT VIEW
40
FRONT VIEW
TOP VIEW
41
SIDE VIEW
REAR VIEW
42
Appendix D. CAD of exterior body of Habagat
ISOMETRIC FRONT RIGHT VIEW
ISOMETRIC FRONT LEFT VIEW
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ISOMETRIC REAR LEFT VIEW
ISOMETRIC REAR RIGHT VIEW
44
FRONT VIEW
TOP VIEW
45
SIDE VIEW
REAR VIEW
46
Appendix E. Dimensions of Exterior Body of Habagat Units: inches (in)
SIDE VIEW
FRONT VIEW 47
TOP VIEW
48
Appendix F. Dimensions of Exterior Body of Haribon Units: millimeter (mm)
FRONT VIEW
SIDE VIEW
49
TOP VIEW
50
Appendix G. Computations for Wind Speed
Shell Eco-marathon Asia 2014 Manila Track
Stop time = 2 sec (at least); say 5 sec stop time per lap. Total stop time, tstop-total = 5 sec x 10 laps = 50 sec; say 1 min per trial Total time to finish, ttotal = 29 min (includes stopping time) Max time for car to finish at track, t max = 29min – 1 min = 28 min
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=
max
1000 1 = 25.71ℎ; 26ℎ = 1ℎ 28 60 12
= 50ℎ
=
50ℎ 26ℎ 2
= 38ℎ
Assumption for simulation: Air is still, V car = Vwind
− = 26
1000 1ℎ = 7.22 / ℎ 1 3600
− = 38
1000 1ℎ = 10.56 / ℎ 1 3600
− = 50
1000 1ℎ = 13.89 / ℎ 1 3600
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Appendix H. Simulation of Exterior Body of Habagat using Autodesk Flow Design
Trial 1 Speed 7.22 m/s
Trial 2 Speed 10.56 m/s
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Trial 3 Speed 13.89 m/s
The Streamline Air Flow for the simulation of Habagat
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Appendix I. Simulation of Exterior Body of Haribon using Autodesk Flow Design
Trial 1 Speed 7.22 m/s
Trial 2 Speed 10.56 m/s
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Trial 3 Speed 13.89 m/s
The Streamline Air Flow for the simulation of Haribon
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Appendix J. Step by step method using Autodesk Flow Design
Autodesk Flow Design
Import CAD File, in this study the researcher import locally a CAD file 57
The file imported is saved as a STL; STL is the neutral file format of CAD
On the toggle bar you can edit the XYZ orientation of the model
58
Since the Air Flow is from Left side to right, fix the desired position of the model.
On the toggle bar you can edit the wind speed from 0-100 m/s
59
Different characteristics of the flow lines can be edit on the flow lines settings located at the toggle bar.
Click the drag plot on the toggle bar to view the drag graph
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Appendix K. Shell Eco-marathon Asia Rules 2013
Chapter 1 Article 25 of Shell Eco-marathon Asia Rules 2013 (Vehicle Design)
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Chapter 1 Article 45 of Shell Eco-marathon Asia Rules 2013 (Dimensions)
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Appendix L. Computation of Percent Difference of Frontal Area
% Difference =
− +
% Difference =
.−. .+.
= 10.59%
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Appendix M. Shell Eco-Marathon 2014
Haribon Passed the Technical and Safety Inspection
Haribon Before the Run 64
Team Cardicals 2014 Urbanconcept Haribon
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Appendix N. Sponsors
Amameco Industries Resources Corp.
Autodesk
BES Technical Works & Services, Inc.
Blanco Race Engineering
BOSCH
CALCO Industries Incorporated
Decal Republic
ELEWELD
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Ian Carlo Rice Dealer
SHELL
SolidWorks
TIARA
Malabon Diesel
SMART
SUN Cellular
TRIMEKSTAL Industrial Supply INC.
TOYOTA 67
