High Downforce Aerodynamics for Motorsports - Repository - North

141 Pages·2011·3.17 MB·English

Abstract
PAKKAM, SRIRAM SARANATHY. High Downforce Aerodynamics for Motorsports. (Under the di-
rection of Dr. Ashok Gopalarathnam).
Using a combination of inverse airfoil design techniques, rapid interactive analysis methods, detailed
computational fluid dynamics (CFD) and wind tunnel testing, this paper aims to provide a better
understanding of aft loading as a design direction for high downforce airfoils for race car rear wing
applications while ensuring performance sustainability across a wide angle-of-attack operating range.
This design philosophy was possible because, unlike with aircraft applications, there are no pitching
moment constraints for race car wings. Both single-element and two-element airfoils were considered in
this study.
The work was carried out in two parts. In the first part, the high downforce design methodology
was explored. The first step in the design process was the use of an inverse design method (PROFOIL),
which was used to generate candidate airfoil shapes. The inverse design method uses Newton iterations
to converge on the desired solution based on various imposed constraints. In this study, in addition to
standard airfoil parameter specifications such as thickness, camber, and pitching moment, additional
constraints on trailing edge bluntness (as mandated by most motorsport governing bodies) and leading
edgeradiuswereusedinthedesign. Basedonthespecifiedconstraints,theinversedesigncodegenerates
airfoil shapes to match the specified invicsid velocity profile. In order to evaluate the candidate airfoils
quickly and efficiently, the XFOIL (single element) and MSES (multi element) codes were used in the
secondsteptoprovideviscouspredictionsfortheairfoilsdesignedusingPROFOIL.Thesecodesallowed
for rapid analysis of the airfoils at several angles of attack, Reynolds numbers, and for several flap
configurations. Wind tunnel testing and CFD simulations were used as a final step to corroborate the
resultsoftheoptimizedairfoilshape. Surfacepressuredistribution,forceandmomentdata,andoil-flow
visualization photographs from wind tunnel tests conducted in the NCSU subsonic wind tunnel were
used to provide comparisons with XFOIL/MSES and the CFD predictions. The results show that aft
loading on an airfoil is conducive to high downforce requirements and is a favorable design direction
when considering airfoils for race car wing applications. Comparisons have been made with airfoils
representative of the high lift design philosophies of Dr. Liebeck, Dr. Wortmann and Dr. Selig. As
a case study, a high-lift multi-element airfoil configuration developed for the NCSU Formula SAE race
car will be used. For this airfoil, XFOIL / MSES, CFD, and wind tunnel results for single and multi
elementairfoilswillbepresented. Theresultsconfirmtheimportanceofaftloadingasadesigndirection
in maximizing the performance. While the research will focus on the wing and airfoil aerodynamics for
the NCSU Formula SAE car, the results and discussion will be applicable to a variety of race vehicles
with wings. Due to the reduced vehicle speeds encountered in a formula SAE competition (as compared
to other professional motorsports), the bulk of the analysis and testing was performed at low Reynolds
numbers ranging from 300,000 to 600,000 to provide a realistic estimate of the feasible aerodynamic
gains at the relevant cornering speeds. The results confirm the importance of aft loading in maximizing
doenforce performance.
The second part details the development of a lap simulation code that analytically generates and
usesracinglinesforthespecifiedtrackgeometry. Theprimarypurposeofthesimulationforthecurrent
research was to enable further comparisons between the high downforce airfoil developed using inverse
design and other existing high lift designs. An analytical method for generating racing lines for a
wide variety of corners has been proposed and used in the simulation to enable better aerodynamic
comparisons and analysis, as opposed to using constant radius and steady-state cornering models. The
racing-line physics is coupled with the code’s ability to simulate trail braking to provide a vehicle model
that successfully maneuvers the edges of the traction envelope and thus maintains limit performance.
Sincelimitperformanceandlimithandlingaretheracingobjectives,aerodynamicevaluationsneedtobe
conductedattheseoperatingconditionstoeffectivelyrepresentdesignrequirementsandmimicexpected
conditions more closely. The results of the lap simulations confirm the importance of including racing-
linephysicsandtrailbrakinginevaluatingtheinfluenceofaerodynamicdownforce. Acomparisonofthe
calculated lap times for the different airfoils brings out the benefits of designing airfoils with aft loading
and a wide angle-of-attack range over which high downforce is achieved.
(cid:13)c Copyright2011bySriram Saranathy Pakkam
AllRightsReserved
HighDownforceAerodynamicsforMotorsports
by
Sriram Saranathy Pakkam
A thesissubmittedto theGraduateFaculty of
NorthCarolinaStateUniversity
in partialfulfillmentofthe
requirementsfortheDegreeof
MasterofScience
AerospaceEngineering
Raleigh, NorthCarolina
2011
APPROVED BY:
Dr. Jack Edwards Dr. EricKlang
AdvisoryCommitteeMember AdvisoryCommitteeMember
Dr. Robert White Dr. AshokGopalarathnam
AdvisoryCommitteeMinorRep. ChairofAdvisoryCommittee
Biography
Sriram Saranathy Pakkam was born on 4 August 1987 in Hyderabad, India. He completed
his schooling at the Bishops School, Pune and his secondary schooling from Loyola Junior
College,Pune. HeattendedtheUniversityofPune,locatedinPune,India,forhisundergraduate
studies and earned a Bachelor of Engineering (B.E) in Mechanical Engineering degree in May
2009. Sriram has had an immense passion for automobiles and racing for a very long time
and this keen interest was further accentuated during his undergraduate studies. He had the
opportunity to work for the Engine Development Lab (EDL) at the Automotive Research
Association of India (ARAI) on a one year engineering project as part of his undergraduate
requirements. He had the opportunity to be a part of a racing team which won techinical
collegiate events that had participation from hundreds of teams from across Asia. These and
his passion for racing events such as Formula 1, Le Mans, NASCAR, etc. led him to seek work
dealing with the technical aspects of motorsports. In Fall 2009, Sriram enrolled as a graduate
studenttowardsadegreeinAerospaceEngineeringatNorthCarolinaStateUniversity, Raleigh,
NC. His research interest in race car aerodynamics led him to Dr. Ashok Gopalarathnam, who
has been his advisor since the end of Fall 2009.
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Acknowledgements
I would like to thank my advisor, Dr. Ashok Gopalarathnam, whose help and guidance
played an elemental role in the successful completion of this thesis. I am also grateful to Dr.
Jack Edwards, Dr. Eric Klang and Dr. Robert White for consenting to be on my advisory
committee.
There are a large number of people without whose timely assistance, most of the following
research would have been a mere shadow of its current state. Since this effort was not backed
by funding from any organizations, it was fuelled by the charitable dispositions of the various
people who chipped in at the right times and helped resuscitate aspects of the research that
sorely needed it. I would like to thank the following people for their direct assistance with the
research:
James Dean of the Design School cut out various airfoil sections from scrap renshape and
wood using the CNC router in the Design School workshop. Without these pieces, wind
tunnel testing just could not have been done. Fineline Prototyping provided two pressure
tapped central sections for wind tunnel testing. These components were rapid prototyped
using stereolithography and each component cost close to $1000. I am extremely grateful to
the people at Fineline, Eric Utley in particular, for letting me have two such components at no
charge. Realising a design from the computational world to the real world would not have been
possiblewithoutthesetwomajorcontributions. IwouldalsoliketothankAndrewMisenheimer
for his help with the solid modelling.
For testing the multi-element airfoil in the wind tunnel, rapid prototyped flap-element
sectionswereneededandDr. OlaHarryson,oftheIndustrialandSystemsEngineeringDepartment
here at State, rapid prototyped these sections using equipment and material from his own lab
supplies.
I would also like to thank the team at Corvid, especially Greg McGowan, for his help with
setting up the C.F.D runs and showing me the intricacies of gridding. Without Greg’s help, the
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C.F.D in this effort would have been nothing more than colorful plots backed by horrid grids
and erroneous numbers. Thanks also to Patrick Keistler for his help with the grid.
Finally, Noah McKay of Richard Childress Racing has been a major source of inspiration
and help in various aspects. I would like to thank him for all his guidance relating to race car
aerodynamics and the essential techinical pointers with regard to the nuances and aerodynamic
trickery prevalent in various classes of motorsports. He has been extremely generous in having
me over at full scale wind tunnel tests, every session of which was a massive learning experience
thelikesofwhichcannotberealizedinclassrooms. Also,Iwouldliketothankhimforpermitting
me the use of the composites facility at Richard Childress Racing in order to fabricate carbon
fiber wings for the NCSU Formula SAE race car. The guys at the shop, Toby and Carroll in
particular, turned out wings crafted so masterfully that it pains me to even consider making
mounting holes on its beautifully finished surface. Again, all the expensive carbon fiber, facility
usage and expertise came with no charge.
The above mentioned people have been instrumental to this research in terms of their direct
contributions, either in terms of material or expertise. I am extremely grateful to them for all
their help.
I thank my labmates Joe, Kela, Balu and Wolfgang Mozart for their support as well fun
times in the lab. I would also like to thank my friends and roommates in Raleigh who made the
stay an enjoyable one: Cobra, Pox, Unkillman, Mogaji, Gultesh, BD, Baljeet, Ponda, Bullesh,
Graaginder, Kundesh. Thanks in particular to Gangesh and Bhujang for the amazing jam
sessions and studio recording sessions.
Special thanks to Zepp. I’d like to thank to my parents, for everything.
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Table of Contents
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 High Downforce Wing and Airfoil Design in Motorsports . . . . . . . . . . . . . 1
1.2 Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Outline of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Chapter 2 High Downforce Airfoil Design Methodology . . . . . . . . . 7
2.1 High Downforce Design Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1 Existing High-Lift Design Methodologies . . . . . . . . . . . . . . . . . . . 7
2.1.2 Considerations for an Effective High Downforce Philosophy . . . . . . . . 13
2.2 Design Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.1 Background on Inverse Design . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.2 Brief Description of the PROFOIL Inverse Design Code . . . . . . . . . . 23
2.2.3 Design Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Chapter 3 Single-Element Airfoil Results . . . . . . . . . . . . . . . . 29
3.1 Resulting Airfoil Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Computational Results for Base Airfoil . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2.1 Base Airfoil Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2.2 Performance Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2.3 LSB Based Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.3 Blunt Trailing Edge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
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3.4 Wind Tunnel Testing of the MSHD airfoil with 0.5% Trailing Edge Gap . . . . . 50
3.4.1 N.C.S.U Subsonic Wind Tunnel . . . . . . . . . . . . . . . . . . . . . . . 50
3.4.2 Airfoil model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.4.3 Wind Tunnel Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4.4 Clean-Airfoil Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.4.5 Tripped Airfoil Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
3.4.6 Flow Visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Chapter 4 Multi-element Setup and Results . . . . . . . . . . . . . . . 76
4.1 Multi-element Airfoil Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.2 Wind Tunnel Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.2.1 Multi-Element Airfoil Model . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.2.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.3 C.F.D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.3.1 The Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.3.2 Numerical Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.4 Carbon-Fiber Wings for use on the Wolfpack Formula SAE Racecar . . . . . . . 87
4.4.1 Wing Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4.4.2 Fabrication of the Wings. . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Chapter 5 Simulation of Race Car Performance with Aerodynamics . . . 91
5.1 Aerodynamic Influences on Race Car Performance . . . . . . . . . . . . . . . . . 91
5.1.1 The Racing Objective: Maximization of the Traction Envelope . . . . . . 93
5.2 Lap Simulation Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.3 Lap Simulation with Racing Line . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
5.3.1 Vehicle Model and Parameters . . . . . . . . . . . . . . . . . . . . . . . . 99
5.3.2 Racing Line Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
5.3.3 Braking Interpolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.3.4 Functioning of the Racing-Line Simulation Code . . . . . . . . . . . . . . 105
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5.4 Results from Racing Line Simulation . . . . . . . . . . . . . . . . . . . . . . . . . 107
Chapter 6 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . 114
6.1 Summary of Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
6.1.1 High Downforce Design Philosophy . . . . . . . . . . . . . . . . . . . . . . 115
6.1.2 Lap Simulation Code with Aerodynamic Considerations . . . . . . . . . . 116
6.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
6.2.1 Wind Tunnel Corrections for the MSHD Multi-element Airfoil Results . . 117
6.2.2 Aerodynamics Package on the NCSU Wolfpack Formula SAE Race Car . 119
6.2.3 Enhancements for the Racing Line Simulation Code . . . . . . . . . . . . 119
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
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