Download - Tractor Trailer Drag Reduction Study
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
2
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
3
Task
• NorthStar Commercial – Project Sponsor • Real estate company in Grand Rapids, MI
• Scott Nowakowski - Direct Contact • Reduce coefficient of drag experienced by tractor-
trailer
4
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
5
Overview
• Introduction • Air Channeling Devices (ACDs) • Front Flaps • Rear Flaps • Side Skirts
• Computational Fluid Dynamics (CFD) • Wind Tunnel • Results • Conclusion
6
Air Channeling Devices (ACDs)
• Front Flaps • Rear Flaps • Side Skirts
7
Side Skirt
Front Flaps Rear Flaps
Overview
• Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • CFD Simulation • CFD Results
• Wind Tunnel • Results • Conclusion
15
CFD Simulation
• 1:10 scale CAD model (Siemens NX 8) • Only tested rear flaps and side skirts • Computing power and time limitations • Meshing issues
16
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
17
Overview
• Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • Wind Tunnel Testing
• Facilities • Equipment • Calibration • Testing Methodology • Criteria Rationale • Testing • Assumptions
• Results • Conclusion
19
Facilities
• University of Michigan’s 5’ x 7’ Low Turbulence Subsonic Wind Tunnel • Aerospace Machine
Shop • Construction
• Wind Tunnel Building • Assembly
20
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
22
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
23
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
24
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
25
Testing
• Five Configurations • No ACDs - Baseline • Rear Flaps • Side Skirts • All ACDs • Front and Rear Flaps
26
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
27
Overview
• Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • Wind Tunnel • Results • Effectiveness • Feasibility • Profitability • Best Configuration • Improvements
• Conclusion 28
Results
29
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
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
31
%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒= | 𝐶↓𝐷−𝐴𝐶𝐷 − 𝐶↓𝐷−𝐵𝑎𝑠𝑒 |/𝐶↓𝐷−𝐵𝑎𝑠𝑒
Feasibility
• Easily attached/detached ACDs and ACDs do not hinder functionality • Front Flaps: Failed • Rear Flaps: Failed • Side Skirts: Passed
33
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
34
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
35
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
36
%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
37
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
38
Overview
• Introduction • Air Channeling Devices (ACDs) • Computational Fluid Dynamics (CFD) • Wind Tunnel • Results • Conclusion • Current Technology • References
39
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
40
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
41
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
42