Race Car Aerodynamics GDPMSc Race Car Aerodynamics

Z. Chen, B. Dufour, C. Elliott, F. Harrold, C. Jacques, N. McDowell and R. van der Meer

2

Introduction Good aerodynamic design reduces lap

time Improve the aerodynamics of a hill-climb

car model CFD enables analysis of different

concepts at low cost

3

Overview Aims & Objectives Methodology CFD Methodology Design Baseline Car Design upgrades Resulting Car Discussion Conclusion

4

Aim & Objectives The aim of this project is “to accurately determine and improve

the aerodynamic performance of a hill climb car model using CFD”

First semester objectives were:– Determining the regulations and general performance levels

of hill climb race cars.– Gaining a clear understanding of the devices used to add

aerodynamic performance to a race car.– Setting up a valid CFD simulation of a baseline race car model

to accurately determine its aerodynamic performance.

5

Aim & Objectives Second semester objectives were:– Making alterations to the model to improve aerodynamic

performance.– Quantifying the impact of these alterations using CFD.– Optimising the alterations and ensuring they result in a

holistic design.

6

Methodology

7

CAD Corrections Baseline CAD was unsuitable. Modifications made:

– Realignment of Rear Wing– Realignment of Sidepods– The addition of relationships between respective parts– CFD Preparation– Changing of the axis system to ensure usability later on

8

Boundary ConditionsBoundary Conditions

Car Surface No Slip Wall

Inlet Velocity Inlet

Outlet Pressure Outlet

Engine Intake Pressure Outlet

Sidepod Intake Pressure Outlet

Ground Moving Wall

Symmetry Plane Symmetry

Top and Side Walls No Slip Wall

9

Physics SettingsPhysics Settings

Inlet VelocityGround Tangential Velocity  

Front Wheel Wall Rotation  Rear Wheel Wall Rotation  

10

Domain

Cross section:Based on the RJ Mitchell wind tunnel

Length:Roughly 3 car lengths upstream and 5 car lengths downstream

11

SolverSolver Parameter Value

Space Three DimensionalTime Steady

Material GasFlow Segregated

Equation of State Constant DensityViscous Regime Turbulent

Reynolds Averaged Turbulence K-EpsilonRelaxation Scheme Gauss Seidel

Turbulent Specification Intensity and Viscosity RatioTurbulent Viscosity Ratio 10

12

Mesh SettingsMesh Parameter Value

Base Size 1.0mMaximum Cell Size 0.25m

Maximum Core/Prism Layer Transition Ratio 2Prism Layers 8

Prism Layer Stretching 1.05Prism Layer Thickness 0.01m

Surface Curvature 180 points per circleSurface Growth Rate 1.3

Minimum Surface Size 0.001mMaximum Surface Size 0.5mTemplate Gowth Rate Very Slow

Wrapper Feature Angle 30 degWrapper Scale Factor 25%

13

Domain and Mesh IndependenceDomain Length

(m) CL CD Efficiency

17 -2.025 0.805 2.515

18 -1.989 0.837 2.376

0.0E+00 2.0E+06 4.0E+06 6.0E+06 8.0E+06 1.0E+07 1.2E+07 1.4E+07 1.6E+07-2.10

-2.05

-2.00

-1.95

-1.90

-1.85

-1.80

-1.75

-1.70

-1.65Baseline Mesh Independency Study

Number of Cells

CL

• Mesh independence tested by varying base size between 0.7-5m

• Mesh found to be stable for most runs

• Domain independence showed small changes through lengthening

• Minimal changes

14

Y-Plus• Below 30 in regions of stagnation and separation• Average 50

15

Design Methodology

16

Objective Increase lift coefficient value above

4 Keep drag coefficient value below

1.2 Increase efficiency Drivable aerodynamic balance (39%

to 44% front)

17

HardpointsThe following were considered unchangeable: Mass flow into the sidepod and engine air intake (within 5% of

baseline) Shape of the wheels Wheelbase of the vehicle Shape and position of driver

18

Member AllocationPerson

Area of Car Group Tasks

Barret Sidepod Communication and Organization

Chen Engine Cover and Nose Cone

CAD Assembly

Craig Front Wing CAD Assembly, Third Iteration Simulation, Report Proof Reading

Cyril Underbody Full Car Data Processing, First Iteration Simulation, Second Iteration Simulation

Francis Rear Wing and Exhaust

Baseline Simulation Setup and Runs, First Iteration CAD Assembly, Interim Presentation Assembly, Third Iteration Simulation, Report Proof Reading

Nicky Front Wing CAD Corrections, Baseline Simulation Setup and Runs, Third Iteration Simulations

Robbin Underbody Assembly of Report, Second Iteration Simulation, Third Iteration Simulation, Project Planning and Supervision

19

Baseline Results

20

Lift, Drag, Efficiency & Balance

Car (Unit) CL CD Efficiency % Front BalanceBaseline -2.02 0.805 2.52 24.4

Frontal area: 0.08022687m² Downforce and drag are both low Balance is too far rearward

21

Components breakdown

-20.00% -10.00% 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00%

35.74%

55.58%

10.48%

-9.81%

-9.36%

17.37%

Components CL breakdownUnderbody

Sidepods

Wheels

Body/Nose

Rear Wing

Front Wing

In terms of downforce: Rear wing is the part producing

most of the downforce Unbalance between front and rear

wing Underbody is only producing 17% Sidepods is high, nearly 10%

In terms of drag: Wheels are producing most of the

drag The other source is the rear wing Rest is about 7-10%

Front wing

Rear wing

Sidepods

Wheels

Body/Nose

Underbody

0.00% 10.00% 20.00% 30.00% 40.00% 50.00%

7.43%

22.69%

7.14%

44.66%

9.60%

8.49%

Components CD breakdown

22

Pressure Coefficient Top view

– High pressure visible on the rear wing pressure side

– Low pressure on the side pod inlet Side view

– Low pressure on the outer side of both rear and front tyres

Bottom view– Pressure on the underbody is close to zero– High pressure on the diffuser inlet

23

Pressure Coefficient Front view– High pressure region on the nose

cone, inner side of the front tyres and bottom of the sidepod inlet

Rear view– Separation developing on the diffuser

24

First Design Iteration Upgrades

25

Front Wing – 2D Optimisation 2D Analysis of Baseline Wing

Selection of suitable aerofoil profile

2D Optimisation of New Wing – Angles, Slot Gaps, Overlaps

Wing Version

Cl Cd Efficiency

Baseline 2D -2.888 0.649 4.449Final 2D -4.389 0.236 18.5930 5 10 15 20 25 30 35 40 45

0.020.030.040.050.060.070.080.09

0.1Wake Velocity Profiles

Baseline Wing

2D Final Wing Geome-try

Velocity, m/s

Posit

ion,

m

26

Front Wing – 2D OptimisationBaseline Wing Geometry

Iteration 1 Wing Geometry

27

Front Wing – Width Study This study was focused

primarily around efficiency of the full car

Optimal reviewing the data points lies between 80-87.5% width

70% 75% 80% 85% 90% 95% 100%2.732.742.752.762.772.782.79

2.82.812.822.832.84

Wing Width Study, Efficiency

Wing Width, % of Total width allowed

Efficie

ncy,

L/D

28

Front Wing Iteration 1Endplate Refinement: Addition of Footplate Turning Vane for optimised

flow Sweep angles tested to

reduce separation but channel underfloor flow

29

Sidepod

1-SP-IT1-CS1-A 1-SP-IT1-CS1-B 1-SP-IT1-CS1-C

1-SP-IT1-CS1-DCar 1 Sidepod

30

Engine Cover

Geometry:

Removed sharp corner

Made it longer

Made it smoother

31

Engine Cover

Model Overall CL Rear Wing CL Efficiency

Baseline -2.030 -1.1276 2.523

Iteration 1 -2.213 -1.2633 2.620

CFD results:Improve the rear wing performance

32

Underfloor Diffuser shape changed to an aerofoil shape: S1223 Venturi channels included into the underfloor design

and tucked inwards. Diffuser is extended from 159 to 423mm behind the

rear wheels and widened as closest as possible to the rear tyres.

Two different exit heights tested: 150mm and 170mm.

Flat plates installed on the side of the diffuser. Inlet shape was also modified.

33

Underfloor Significant increase in downforce Moderate increase in drag The 170mm exit height has proven to be the best Less separation visible on the diffuser Recirculation region removed from the inlet

Total

Fwing

Rwing

Sidep

odWheel

s

Body

& Nose

Underb

ody

-0.10.20.50.81.11.41.7

22.32.62.9

CL Breakdown Comparison

Baseline car Design 2 : 150mm Design 2 : 170mm

CL

Total

Fwing

Rwing

Sidep

odWhe

els

Body

& Nose

Underb

ody

-0.050.050.150.250.350.450.550.650.750.85

CD Breakdown Comparison

Baseline car Design 2 : 150mmDesign 2 : 170mm

CD

34

Rear Wing Changed all aerofoil profiles to Selig-1223. Rotated first element to -5 degrees AoA. Beam wing lowered by 60mm. Beam wing and diffuser interaction led to

removal of beam wing.

Baseline First Iteration

35

First Iteration Car

36

First Iteration Full Car Geometry

37

Lift, Drag, Balance & Efficiency

Model CL CDAerodynamic

Efficiency% Front Balance

Baseline -2.02 0.805 2.52 24.4

First Iteration -3.07 0.925 3.31 31.2

52% increase in downforce production. 15% increase in drag production. 31% increase in efficiency. 7% increase in balance towards the front

of the car.

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Component Breakdown

Total Fwing Rwing Sidepod Wheels Body & Nose

Underbody-0.3

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

Component Lift Coefficient Breakdown

Baseline car First Iteration

CL

Total Fwing Rwing Sidepod Wheels Body & Nose

Underbody0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Component Drag Coefficient Breakdown

Baseline car First Iteration

CD

39

Pressure Coefficient Against Baseline

40

Second Design Iteration Upgrades

41

Front WingRide height of wing analysis with respect to full car downforce:

Balance moves rearwards with increasing ride height

Optimal coefficient of lift at approximately 18mm ride height

16 17 18 19 20 21 22 23 24 253.023.033.043.053.063.073.083.09

Coefficient of Lift vs Ride height

Ride height, mm

Coeffi

cient

of L

ift

16 17 18 19 20 21 22 23 24 2564%66%68%70%72%74%

Balance vs Ride height

Ride height, mm

Bala

nce

Rear

ward

s %

42

Front WingTest of Different Concepts Cut-out Wing Bridge Wing Shallow Angle of Attack Wing Bargeboard EndplatesCarried Forwards Cut-out Front Wing

Description CL CD Balance % Rearward

Efficiency

Baseline Setup 3.086 0.925 69.186 3.336Bridge Wing 2.973 0.927 69.441 3.208

Shallow Angle 2.905 0.939 85.525 3.095Experimental

cut-out3.093 0.948 74.351 3.262

Bargeboard 2.528 0.919 78.074 2.749

43

Front WingCascade Addition: Fourth and Fifth Element 2D X and Y

optimisations Span length of cascade

0 20 40 60 80 100 120 140 160 180 2004.1

4.2

4.3

4.4

4.5

4.6

4.7

16.216.416.616.81717.217.417.617.81818.2Coefficient of Lift against X Position

Coeffi-cient of Lift CL

Effi-ciency

X Direction distance (mm)

Coeffi

cient

of L

ift

Efficie

ncy

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 801.5

1.752

2.252.5

2.753

3.253.5

3.754

4.254.5

4.75

5791113

151719

Coefficient of Lift against Y Position

Coefficient of Lift CL

Efficiency

Y Direction distance (mm)Co

efficie

nt o

f Lift

Efficie

ncy

44

Sidepod

Part NumberInlet Area

(mm^2)

Mass Flow

(Kg/S)CL CD Efficiency

2-SP-IT2-CS1-F 5880 0.1409 -3.314 1.005 3.295

2-SP-IT2-CS2-A 6011 0.1540 -3.410 1.003 3.3982-SP-IT2-CS1-F

2-SP-IT2-CS2-A

45

Nose Cone Made the nose higher to

help diffuser

Connected the nose and splitter curve

Reduced the effect on the trailing edge of the front wing

CFD results:Runs Overall CL Overall CD Front Wing

CL

Rear Wing CL

Diffuser CL Efficiency

Iteration 1 -2.98 0.93 -1.07 -1.14 -1.30 3.20Iteration 2 -3.15 0.95 -1.16 -1.14 -1.39 3.33

46

Underfloor Modifications were brought to an “idealised car”

Run Diffuser CL

Diffuser CD

Overall CL Overall CD Efficiency

First Iteration Car

-1.31 0.145 -3.07 0.925 3.31

Idealised Car -1.41 0.164 -2.68 0.937 2.86

47

Underfloor

Different area ratios were tested

Lower pressure appearing on the diffuser

Throat

Exit Ratio to ground

clearance

DiffuserCL

DiffuserCD

Overall

CL

Overall

CD

Efficiency

15 170 6.34 -1.41 0.164 -2.68 0.937 2.8620 170 5.41 -1.55 0.164 -2.93 0.942 3.1120 190 6.00 -1.74 0.176 -3.09 0.953 3.2520 210 6.59 -1.85 0.189 -3.17 0.965 3.2820 230 7.18 -1.90 0.198 -3.26 0.994 3.2820 250 7.76 -1.87 0.204 -3.07 0.993 3.1025 265 7.15 -1.90 0.209 -3.18 1.02 3.13

48

Underfloor Illegal skirts tested

Upward skirts tried

Runs DiffuserCL

DiffuserCD

Overall

CL

Overall

CD

Efficiency

Throat 20mm (T20) Exit 230mm (E230)

-1.90 0.198 -3.28 0.994 3.28

T20 E230 with illegal skirts -2.36 0.205 -3.67 0.967 3.79T20 E230 with upward skirts -1.95 0.200 -3.20 0.975 3.28

49

Underfloor Area ratio optimized from 7.18 to 7.47 New side pod included in the design Flat plates added behind the rear wheels

Runs DiffuserCL

DiffuserCD

Overall

CL

Overall

CD

Efficiency

T20 E230 with upward skirts

-1.95 0.200 -3.20 0.975 3.28

T20 E220 with upward skirts

-1.92 0.197 -3.17 0.963 3.29

T20 E240 with upward skirts

-1.96 0.205 -3.22 0.983 3.28

T20 E240 with upward skirts and iteration 2 side

pod

-1.94 0.204 -3.40 1.01 3.36

T20 E240 with upward skirts, iteration 2 side pod

and rear flat plates

-2.00 0.208 -3.46 1.01 3.42

50

Rear Wing Slot gap and Overlap Optimisation Remodelled mounts Redesigned endplates Rear wing positioning optimisation

First iteration Second Iteration

Model CL CD Efficiency

Revised Iteration 1 -2.871 0.970 2.960

Iteration 1 with New RW -3.092 0.935 3.307

51

Second Iteration Car

52

Second Iteration Car

53

Lift, Drag, Balance & EfficiencyModel CL CD

Aerodynamic Efficiency

% Front Balance

Baseline -2.02 0.805 2.52 24.4

First Iteration -3.07 0.925 3.31 31.2

Second Iteration -3.47 1.010 3.42 34.3

• 11.5% increase in downforce production• 8.4% increase in drag production• 3.2% increase in efficiency• 3.1% increase in balance towards the front of the car

54

Component Breakdown

Full car Front Wing

Rear Wing Sidepods Wheels Body/Nose Un-der-body

-0.3

0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3

3.3

Component Lift Coefficient Breakdown

Iteration 1 Iteration 2

CL

Full car Front Wing

Rear Wing

Sidepods Wheels Body/Nose

Un-der-body

-0.05

0.05

0.15

0.25

0.35

0.45

0.55

0.65

0.75

0.85

0.95

1.05

Component Drag Coefficient Breakdown

Iteration 1 Iteration 2CD

55

Pressure Coefficient

56

Third Design Iteration Upgrades

57

Front Wing Movement of wheels outboard of the car Introduction of Strakes Re-introduction of the middle of the wing

Carried Forward: Re-introduction of the middle of the wing

58

Front Wing

Vortex Channel Configuration CL CD

Wide Main, Original Cascade -3.47603 1.010946

Original Main, Original Cascade -3.57881 1.011578

Original Main, Narrow Cascade -3.60611 1.011733

Capturing Vortices: Optimum width for mainplane

elements Optimum width for cascade

elements Vortex Generator design and

test

59

Sidepod

3-SP-IT1-CS1-A

3-SP-IT2-CS1-C

3-SP-IT3-CS1-A

Case Description

Part Number

Inlet Area (mm^2)

Mass Flow (Kg/S)

Area CL ∆CL CD ∆CD

3-SP-IT3-CS1-A 5062 0.1240 0.0874 -3.6618 -0.2521 0.9735 -0.030 3.761

60

Third Iteration-Nose Cone Improved the front wing performance by

pressing the front nose down Improved the flow around the trailing

edge of the front wing by making the middle nose higher

Moved the balance towards Was not carried forward

CFD results:

Runs Overall CL

Overall CD

Efficiency

Front Wing CL

Diffuser CL

% Front Balance

Iteration 2 -3.461 1.012 3.419 -0.960 -1.940 34.3Iteration 3 -3.434 1.003 3.424 -1.010 -1.824 39.4

61

Underfloor Vortex generators and fins

Zoom in on both devices

Runs Diffuser CL

Diffuser CD

Overall CL

Overall CD

Efficiency

Second Iteration Car -2.00 0.208 -3.46 1.01 3.42

Vortex Generators -2.02 0.208 -3.48 1.01 3.45Fins -2.02 0.209 -3.48 1.01 3.45

62

Underfloor Barge boards

Turning Vane

Runs Diffuser CL

Diffuser CD

Overall CL

Overall CD

Efficiency

Second Iteration Car -2.00 0.208 -3.46 1.01 3.42

Barge Boards -1.98 0.217 -3.45 1.01 3.42Single Turning

Vane -2.07 0.214 -3.52 1.01 3.50

Underfloor Double turning vanes

Double steeper vanes

Double steepest vanes

Runs DiffuserCL

DiffuserCD

Overall

CL

Overall

CD

Efficiency

Second Iteration Car -2.00 0.208 -3.46 1.01 3.42

Barge Boards -1.98 0.217 -3.45 1.01 3.42

Single Turning Vane -2.07 0.214 -3.52 1.01 3.50

Double Turning Vanes

-2.07 0.216 -3.54 1.01 3.51

Steeper Double -2.06 0.218 -3.52 1.01 3.51

Steepest Double -2.03 0.222 -3.49 1.01 3.46

63

64

Underfloor Gurney flap

Wing element

Runs DiffuserCL

DiffuserCD

Overall

CL

Overall

CD

Efficiency

Second Iteration Car -2.00 0.208 -3.46 1.01 3.42

Gurney Flap added -2.30 0.303 -3.68 1.07 3.45Wing element

added -2.41 0.368 -3.76 1.12 3.35

65

Underfloor Testing the Gurney Flap on the Final car at

different speed 30m/s

Runs Velocity m/s Diffuser CL Diffuser CD

Overall CL

Overall CD

Efficiency

Third Iteration Car 30 -2.84 0.422 -4.48 1.14 3.93Gurney Flap

added 30 -3.86 0.899 -5.43 1.52 3.57

Third Iteration Car 150 -2.62 0.247 -4.60 1.02 4.52Gurney Flap

added 150 -2.90 0.348 -4.80 1.08 4.45

150m/s

66

Exhaust Reimplementation Rear Wing improvements were limited through diffuser developments Exhaust reimplementation was deemed to add a larger performance gain Exhaust added to engine cover Exit speed calculated at 109.62m/s Tested over a range of exit angles

Second Iteration Third Iteration

CL CD

Exhaust Setting Full Car Rear Wing Diffuser Full Car Rear wing Diffuser

No Exhaust -3.832 -1.022 -2.389 0.989 0.240 0.260

Optimised -4.597 -1.112 -3.093 1.133 0.244 0.461

67

Third Iteration Car

68

Third Iteration Car

69

Lift, Drag, Balance and Efficiency

Model CL CD

Aerodynamic Efficiency % Front Balance

Baseline -2.02 0.805 2.52 24.4

First Iteration -3.07 0.925 3.31 31.2

Second Iteration -3.47 1.010 3.42 34.3

Third Iteration -4.48 1.142 3.93 32.1

22.5% increase in downforce production 3.7% increase in drag production 13.0% increase in efficiency 2.2% reduction in front balance

70

Component Breakdown

Full car Front Wing Rear Wing Sidepods Wheels Body/Nose Underbody-0.5-0.20.10.40.71.01.31.61.92.22.52.83.13.43.74.04.34.6

Coefficient of Lift Breakdown Comparison

Iteration 3 Iteration 2

CL

Full car Front Wing Rear Wing Sidepods Wheels Body/Nose Underbody-0.050.050.150.250.350.450.550.650.750.850.951.051.15

Coefficient of Drag Breakdown Comparison

Iteration 3 Iteration 2

CD

71

Component Breakdown

Full c

ar

Front

Wing

Rear

Wing

Sidep

ods

Wheels

Body

/Nose

Underb

ody

-0.50.00.51.01.52.02.53.03.54.04.5

Coefficient of Lift Breakdown Comparison

Iteration 3 Iteration 3: 150m/s

CL

Full car Front Wing Rear Wing Sidepods Wheels Body/Nose Underbody-0.050.050.150.250.350.450.550.650.750.850.951.051.15

Coefficient of Drag Breakdown Comparison

Iteration 3 Iteration 3: 150m/s

CD

72

Pressure Coefficient

73

Discussion

74

Reynolds Scaling EffectsVelocity

(m/s)CL CD Balance

% FrontBalance% Rear

Efficiency

30 -4.4823 1.1416 0.3206 0.6793 -3.926160 -4.4228 1.0458 0.4365 0.5634 -4.229090 -4.4683 1.0256 0.4543 0.5456 -4.3568

120 -4.4710 1.0141 0.4628 0.5371 -4.4088150 -4.6042 1.0185 0.4629 0.5370 -4.5203

Significant rearward balance at 30 m/s ≈ 23 mph full-car

Balance shifts forward as speed increases• Inertial forces dominate so

reduced separation• Exhaust effect diminishes

Balance is 46% forward at 150m/s ≈ 117 mph full-car

Efficiency increases at higher Reynolds number

20 40 60 80 100 120 140 1600

0.050.1

0.150.2

0.250.3

0.350.4

0.450.5

Velocity against Front Balance

Velocity (m/s)%

Fron

t Bal

ance

75

CFD Accuracy Baseline car model• Extensive verification• Validation against force coefficients• No comparison of flow field with experiment

Design alterations• Carried over settings of baseline car• Potential inaccuracy for radical geometry changes• Ideally verify and validate further

Design FeasibilityThere are some feasibility concerns as this is a purely aerodynamic investigation: The rear wing mounts and the underbody are sticking out far rearward The wing-shaped diffuser results in high engine positioning The lack of suspension results in no attachment of the wheels to the car

chassis The limited space for the driver in the final nose design

76

77

Further Design Optimisations Front Wing:

• Angles of attack• Aerofoil shape• Further analysis into inwash wings• Bargeboard Endplates

Sidepod• Optimize airflow from wheel cover to rear wing• Vortex generators

78

Further Design Optimisations

Rear wing• Teamwork with engine cover and diffuser• Beam wing• Channelling of the turbulent air emanating from the wheels• Addition of cut-outs to the endplate

Diffuser• Gurney• Bargeboard ahead the diffuser• An automated optimisation on the top surface

79

Conclusion Baseline model simulated in CFD

• Extensive verification• Validation against force coefficients

Design improvements made• 3 design iterations were performed• Coefficient of Lift value increased to 4.48• Coefficient of Drag value kept relatively low at 1.14

Further work to be done• Verify and validate CFD of final design• Further optimise design and address feasibility concerns