Aerodynamics Reduction

8/12/2019 Aerodynamics Reduction

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By Kang Qin, Pung

Project Supervisor: Eastwick, Carol


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Outline

1. Introduction

2. Development

2.1 Pre-processing2.2 Solving

2.3 Post-processing

3. Result4. Recommendation and Conclusion


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1. Introduction

Primary concern:

Increasing of fuel price

Reduce resistant forces exerted on vehicle.


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1.1 Aerodynamic Resistant

Mainly contributed by pressure drag

Cdis very depending on shape of body.

=1

2

2

U


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1.4 Objectives

To create a baseline model LGV by CAD

Meshing and simulation.

Reduce drag force.

Modifications add on.

Cab roof

Rear-end Flap 10 degrees of inward angle

20 degrees of inward angle

30 degrees of inward angle


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30 InwardAngle

Cab Roof

Design 1

Cab Roof

Design 2

20 Inward

Angle

10 Inward

Angle


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2. Development

Pre-processing

CAD model.

Define boundaries. Meshing.

Solving

Setting and start simulation.

Post-processing

Analysis of quantitative results.


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2.1 Pre-ProcessingCAD Model (1)

Tractor 2.350m long

2.000m wide

1.933m height

Trailer 4.200m long

2.000m wide 2.650m height

Projected Area 5.2m2


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2.1 Pre-ProcessingCAD Model (2)

All dimensions shown in mm10~20H5H

5~10H

Testing Domain


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2.1 Pre-Processing - Meshing

Z1 Z2 Z3 Z4 Z5Z6

Z7

Z8

Z9

Zone Mesh Size, mm

Z1 60

Z2 69

Z3 83Z4 104

Z5 135

Z6 182

Z7 254

Z8 369Z9 553

Growth rate: increase by 0.05 @ eachlayer.

More precise and accurate result to becaptured in critical zones (Z1 Z4).

Reduce number of cells in far stream.


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2.2 Solving (1)

Pressure-based

Solver

2D steady state case. 2D transient case.

k turbulence model

RNG model

Standard wall function

Assume no heat transfer


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2.2 Solving (2)

Constant inlet speed at 60km/h (16.67m/s)

Zer0 pressure gauge at outlet

Solution method Coupled Solver

First order scheme*

Second order scheme*

Convergence Criterion

Continuity ~ 1e-6

*PS: results from both schemes will be compared


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2.3 Post-ProcessingFirst Order

Scheme (1)

Pressure Contour

-1.21e2 ~ -1.48e2 Pa


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Scheme (2)

Velocity Vector


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Scheme (3)

Backflow


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Scheme (4)

1. Underbody 0.00 5.30

2. Engine Shield 35.79 0.07

3. Front End Tractor 115.46 0.27

4. Front End Trailer 77.19 0.00

5. Windshield 117.91 0.41

6. Rear Trailer 351.41 0.00

7. Top Tractor 0.00 -0.03

8. Top Traciler 0.00 -0.04Total Force 697.77 5.98

Pressure

Force, N

Viscous

Force, NPart

Viscous force contributes very little in total, thus, it canbe eliminated.

1

23

4

56

78


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2.3 Post-ProcessingSecond Order

Scheme

400.00

450.00

500.00

550.00

600.00

650.00

700.00

750.00

0 50 100 150 200 250

Force,

N

Element Size in Core Region, mm

Total Force vs Mesh Size

First Order

Scheme

Second Order

Scheme


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3. Result

First round simulation:

Single modification add on baseline model.

Second round simulation: Combine best two individual result.


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3.1 Result of First Cab Roof Design (1)

Pressure contour

CAD model

-5.94e1 ~ -9.59e1 Pa


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3.1 Result of First Cab Roof Design (2)

Backflow

Velocity


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3.2 Result Comparison

Baseline 697.77 -

Cab Roof 1 231.42 66.83

Cab Roof 2 227.31 67.42

30 Inward Flap 704.64 -0.98

20 Inward Flap 704.81 -1.01

10 Inward Flap 698.72 -0.14

Pressure

Force, NReduction, %

Feature A

Feature B


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3.3 Optimal Result (1)

CAD model

Pressurecontour

-5.78e1 ~

-9.32e1 Pa


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Velocity

Backflow


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1. Underbody 36.52

2. Engine Shield 21.97

3. Front Tractor 85.61

4. Windshield 90.58

5. Rear Trailer 157.19

6. Cab Roof -233.04

7. Top Trailer 14.47

Total Force 173.29

Pressure

Force, NPart


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3.4 Transient Solver

Flow is unsteady with time.

Dynamic simulation where integrating in

time. More reality than steady case (time averaged)

Step size = 0.0001s

Number of time steps = 60,000 Simulate until t = 6s.


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3.4 Transient SolverBaseline Model (1)

Time: 2nd

second to 6th

second


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0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1600.00

1800.00

2000.00

0.0

01

0s

0.0

02

0s

0.0

03

0s

0.0

04

0s

0.0

05

0s

0.1

11

0s

0.2

11

0s

0.3

11

0s

0.4

11

0s

0.5

11

0s

0.6

10

0s

0.7

10

0s

0.8

10

0s

0.9

10

0s

1.0

00

0s

1.2

00

0s

1.4

00

0s

1.6

00

0s

1.8

00

0s

2.0

00

0s

2.2

00

0s

2.4

00

0s

2.6

00

0s

2.8

00

0s

3.0

00

0s

3.2

00

0s

3.4

00

0s

3.6

00

0s

3.8

00

0s

4.0

00

0s

4.5

00

0s

5.0

00

0s

5.5

00

0s

6.0

00

0s

Total Force, N

Total Force, NAverage Force

685.12N

3.4 Transient SolverResult of Baseline

Model (2)


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3.4 Transient Solver - Comparison

Underbody 0.00 0.00

Engine Shield 35.79 29.69

Front Tractor 115.46 125.55

Front Trailer 77.19 73.17

Windshield 117.91 104.21Rear Trailer 351.42 352.17

Top Tractor 0.00 0.00

Top Trailer 0.00 0.00

Total Force 697.77 684.79

Transient Case,

NPartSteady in Time

Case, N

Discrepancy, % 1.90


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3.4 Transient SolverOptimal Model (1)

Time: beginning to 6th

second


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0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

0.1

00

0s

0.2

00

0s

0.3

00

0s

0.4

00

0s

0.5

00

0s

0.6

00

0s

0.7

00

0s

0.8

00

0s

0.9

00

0s

1.0

00

0s

1.2

00

0s

1.4

00

0s

1.6

00

0s

1.8

00

0s

2.0

00

0s

2.2

00

0s

2.4

00

0s

2.6

00

0s

2.8

00

0s

3.0

00

0s

3.2

00

0s

3.4

00

0s

3.6

00

0s

3.8

00

0s

4.0

00

0s

4.2

00

0s

4.4

00

0s

4.6

00

0s

4.8

00

0s

5.0

00

0s

5.2

00

0s

5.4

00

0s

5.6

00

0s

5.8

00

0s

6.0

00

0s

Total Force, N

Total Force, N

Average Force

249.89N

3.4 Transient SolverOptimal Model (2)

Require more number of time steps to achieve steady stateresult


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3.4 Transient Solver - Comparison

Underbody 36.52 12.52

Engine Shield 21.97 21.42

Front Tractor 85.61 93.92

Windshield 90.58 100.88

Rear Trailer 157.19 195.87

Cab Roof -233.04 -189.10

Top Trailer 14.47 13.85

Total Force, N 173.29 249.34

Steady in Time

Case, N

Transient Case,

NPart

Discrepancy, % 30.50


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4. Recommendation and Conclusion

Educational package only allows cell elementsbelow 512k for 3D simulation.

Second order scheme provide more precise

result. Transient simulation describes the nature of flow

behaviour in reality rather than time averaged.

Cab roof feature reduces significant drag force.

Flaps increase drag. When combination featuresis considered it reduces further.

Reduce fuel consumption significantly.


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THANKYOU

Q & A

for your attention!


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-6.00

-4.00

-2.00

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

X-Velocity,

m/s

Ratio of Rear Region

Wake Region Analysis

Baseline Model

Cab Roof Design 1

Cab Roof Design 2

30 degrees Inward Flap

20 degrees Inward Flap

10 degree Inward Flap

Optimal Model

Reduced~49%

Steady State Result

Velocity field 1 7m above the ground

Aerodynamics Reduction

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