Tractor-Trailer Drag Reduction Study Christopher Frasson and Team B.S.E. Aerospace Engineering, Minor Mathematics

University of Michigan

Overview

•  Introduction •  Problem •  Task •  Solution

• Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • Wind Tunnel • Results • Conclusion

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Problem

• Aerodynamically imperfect tractor-trailer design • Over 60% engine power used to overcome drag • Optimized for towing power •  Not fuel efficiency

•  5.5 – 6.5 mpg

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Task

• NorthStar Commercial – Project Sponsor •  Real estate company in Grand Rapids, MI

•  Scott Nowakowski - Direct Contact • Reduce coefficient of drag experienced by tractor-

trailer

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Solution

• Air Channeling Devices (ACDs) •  Redirect airflow to reduce drag

• Design using CAD and test with CFD • Build and test multiple ACDs • Determine which combination of ACDs gives

greatest improvement in drag

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Overview

•  Introduction • Air Channeling Devices (ACDs) •  Front Flaps •  Rear Flaps •  Side Skirts

• Computational Fluid Dynamics (CFD) • Wind Tunnel • Results • Conclusion

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Air Channeling Devices (ACDs)

•  Front Flaps • Rear Flaps •  Side Skirts

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Side Skirt

Front Flaps Rear Flaps

Front Flaps

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Front Flaps Cont.

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To back of tractor-trailer

Rear Flaps

• Keep flow attached to back end • Reduce vortex drag

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Rear Flaps Cont.

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Rear Flaps Cont.

𝐹↓𝐷 =.5𝐶↓𝐷 𝜌𝐴𝑣↑2 

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Side Skirts

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Side Skirts Cont.

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Overview

•  Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) •  CFD Simulation •  CFD Results

• Wind Tunnel • Results • Conclusion

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CFD Simulation

•  1:10 scale CAD model (Siemens NX 8) • Only tested rear flaps and side skirts •  Computing power and time limitations •  Meshing issues

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CFD Simulation Cont.

• Michigan’s High Performance Computing Cluster • Unstructured Tetrahedral Mesh

(ANSA) •  ~15 million cells

• K-omega SST turbulence model (FLUENT 14.5) •  Best boundary layer resolution

•  60 mph free stream velocity •  1500 iterations

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CFD Results

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Without ACDs With ACDs

Overview

•  Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • Wind Tunnel Testing

•  Facilities •  Equipment •  Calibration •  Testing Methodology •  Criteria Rationale •  Testing •  Assumptions

• Results • Conclusion

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Facilities

• University of Michigan’s 5’ x 7’ Low Turbulence Subsonic Wind Tunnel • Aerospace Machine

Shop •  Construction

• Wind Tunnel Building •  Assembly

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Equipment

•  1:10 scale tractor-trailer model • Ground Plane • Wind Tunnel Load Cell •  Lift, Drag, Side Force, Roll Pitch, Yaw

• Wind Tunnel Data Acquisition Software

21  5 ft 2.125 in 10.125 in

1 ft 2.5 in

Calibration

•  Load Cell •  Hanging weights

• Data Acquisition Software •  Coefficient of Drag (CD)

•  𝐶↓𝐷 = 𝐹↓𝐷 /.5𝜌𝐴𝑣↑2  

•  Values within 1%

•  Used tunnel values

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𝐹↓𝐷 =  Drag  Force  𝜌=𝐴𝑖𝑟  𝐷𝑒𝑛𝑠𝑖𝑡𝑦  

𝐴=𝐶𝑟𝑜𝑠𝑠  𝑆𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙  𝐴𝑟𝑒𝑎  𝑣=𝐹𝑙𝑜𝑤  𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦  

Testing Methodology

• Reynolds Number matching •  𝑅𝑒= 𝜌𝑣𝐿/𝜇 

•  𝑅𝑒↓𝐴 = 𝜌𝑣↓𝐴 𝐿↓𝐴 /𝜇  •  𝑅𝑒↓𝐸 = 𝜌𝑣↓𝐸 𝐿↓𝐸 /𝜇  • ⇒𝑅𝑒↓𝐸 /𝑅𝑒↓𝐴  = 𝜌𝑣↓𝐸 𝐿↓𝐸 /𝜇 /𝜌𝑣↓𝐴 𝐿↓𝐴 /𝜇  ⇒1= 𝑣↓𝐸 𝐿↓𝐸 /𝑣↓𝐴 𝐿↓𝐴   • ⇒𝑣↓𝐴 = 𝑣↓𝐸 /10 

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Testing Methodology Cont.

•  Simulate Highway Speeds - ~650mph wind tunnel •  Not possible

• Tested at 70, 80, 90 mph •  7-10 mph for actual truck

• Trends of CD as a function of Re •  If CD constant as Re increases •  Then results represent full scale model

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Criteria Rationale

•  Effectiveness •  At least 2% reduction in coefficient of drag

•  Feasibility •  Easily attached/detached ACDs from vehicle •  ACDs do not limit tractor-trailer functionality

•  Profitability •  Reduce fuel cost by 5% or more

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Testing

•  Five Configurations •  No ACDs - Baseline •  Rear Flaps •  Side Skirts •  All ACDs •  Front and Rear Flaps

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Assumptions

• CAD and actual truck model were identical •  Truck •  ACDs

• Models represent real tractor-trailers •  Missing undercarriage components •  Missing suspension •  Stationary wheels

•  Perfect conditions •  No sideslip condition or crosswind

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Overview

•  Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • Wind Tunnel • Results •  Effectiveness •  Feasibility •  Profitability •  Best Configuration •  Improvements

• Conclusion 28  

Results

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Average CD 95% Accuracy Lower Limit Upper Limit

Baseline .8482 ±.0038 .8444 .8520

Side Skirts Only

.8697 ±.0048 .8649 .8745

Rear Flaps Only

.7733 ±.0184 .7549 .7917

Front and Rear Flaps

.7289 ±.0021 .7268 .7310

All ACDs .7819 ±.0047 .7772 .7866

Results Cont.

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Effectiveness

• At least 2% reduction in coefficient of drag •  Baseline: - •  Side Skirts: 2.53% increase in CD •  Rear Flaps: 8.83% decrease •  Front and Rear Flaps: 14.1% decrease •  All ACDs: 7.82% decrease

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%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒= | 𝐶↓𝐷−𝐴𝐶𝐷 − 𝐶↓𝐷−𝐵𝑎𝑠𝑒 |/𝐶↓𝐷−𝐵𝑎𝑠𝑒    

Effectiveness Cont.

•  Side skirts fail •  Manufacturing mistake •  Flutter

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Feasibility

•  Easily attached/detached ACDs and ACDs do not hinder functionality •  Front Flaps: Failed •  Rear Flaps: Failed •  Side Skirts: Passed

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Profitability

• Reduce fuel costs by 5% or more

• 100,000 miles per year • 6 miles per gallon • $3.81 per gallon of diesel • Baseline - $63,500 per year

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Profitability Cont. •  2:1 correspondence between coefficient of drag

reduction and fuel economy improvement •  Baseline: - •  Side Skirts: 1.27% decrease in fuel efficiency •  Rear Flaps: 4.42% increase •  Front and Rear Flaps: 7.05% increase •  All ACDs: 3.39% increase

• Apply to 6 mpg baseline

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Profitability Cont.

•  Side Skirts: 1.04% increase in fuel cost • Rear Flaps: 4.23% decrease •  Front and Rear Flaps: 6.59% decrease • All ACDs: 3.28% decrease

• Only front and rear flap combination passed

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%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒= | 𝐹𝑢𝑒𝑙𝐶𝑜𝑠𝑡↓𝐴𝐶𝐷 − 𝐹𝑢𝑒𝑙𝐶𝑜𝑠𝑡↓𝐵𝑎𝑠𝑒 |/𝐹𝑢𝑒𝑙𝐶𝑜𝑠𝑡↓𝐵𝑎𝑠𝑒    

Best Configuration

•  Front and Rear Flaps •  14.1% reduction in coefficient of drag •  6.59% decrease in fuel cost • $4182 savings •  6.42 mpg • Recommendation

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Improvements

• New side skirt design • New rear flap design •  Different angles •  Only top and bottom or sides

•  Front and rear flap maneuverability • Take more data • Test in larger wind tunnel

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Overview

•  Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • Wind Tunnel • Results • Conclusion •  Current Technology •  References

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Conclusion

• Reduce drag on tractor-trailer by adding ACDs • Tested three unique ACDs •  CFD •  Wind Tunnel

• Recommend front and rear flaps •  Significantly reduce drag •  Increase fuel economy •  Further testing will yield better results

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Current Technology

• ATDynamics TrailerTail •  5.5% increase in fuel economy •  6 mpg => 6.33 mpg •  Our rear flap, 6.27 mpg

• Cummins-Peterbilt SuperTruck •  10.7 mpg

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References

• ATDynamics.com •  Fundamentals of Aerodynamics – John D. Anderson •  Images.google.com •  Introduction to the Aerodynamics of Flight, NASA

SP-367, 1975 •  Peterbilt.com •  Simple and Low-Cost Aerodynamic Drag Reduction

Devices for Tractor-Trailer Trucks – Richard M. Wood and Steven X. S. Bauer

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Questions

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Thanks To

• Team Members •  Steven Dowding •  Orion Haro •  Anton Havrylyuk •  Charlie Jamieson

• University of Michigan •  Use of 5’ x 7’ wind tunnel

•  Sponsor •  NorthStar Commercial

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