10 browand 10_11_trans
- 1. Reducing Aerodynamic Drag and Fuel Consumption Fred Browand Aerospace and Mechanical Engineering Viterbi School of Engineering University of Southern California for Global Climate and Energy Project Workshop on Advanced Transportation October 10-11, Stanford University
- 2. Reducing Aerodynamic Drag and Fuel Consumption Year 2002 statistics for combination trucks (tractor-trailers) on nation’s highways * 2.2 million trucks registered 138.6 billion miles on nation’s highways, 3-4% increase/yr 26.5 billion gallons diesel fuel consumed, 4-5% increase/yr 5.2 mpg, or 19.1 gallons/100 miles ~ 2.47 million barrels/day ** ~ 12-13% of total US petroleum usage (19.7×106 bbls/day) * from DOT, FHA, Highway Statistics, 2002, and US DOT Transportation Energy Data Book Edition 24. **26.5/(365×.7×42)
- 3. Level Highway Speed, MPH Horsepower Contributions to power consumption from drag and rolling resistance for a typical class-8 tractor trailer Power required to over- come aerodynamic drag is the greater contribution at highway speeds Reducing Aerodynamic Drag and Fuel Consumption
- 4. Most of the drag (90%, or more) results from pressure differences Airflow higher pressure lower pressure body Skin friction ( ) 2 2/1 USCD D ρ××= drag coefficient, dependent upon shape cross-sectional area dynamic pressure Net pressure force Reducing Aerodynamic Drag and Fuel Consumption
- 5. AuxPURRUDPower +×+×= PowerbsfcFCnConsumptioFuel ×=≡ )( ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ ∆ + ∆ + ∆ ×= ∆ = ∆ U U S S C C P P FC FC D D 3 η Relationship between changes in drag and changes in fuel consumption property of the driving cycle η ≈ 0.5-0.7 for a car or truck at highway speeds Make changes in shape to improve aerodynamics make the car/truck cross-section smaller reduce highway speeds—very effective! Reducing Aerodynamic Drag and Fuel Consumption
- 6. Reducing Aerodynamic Drag and Fuel Consumption Improved fuel economy from close-following
- 7. At large spacing, close-following results in drag saving (fuel saving) for the trail vehicle… …because the trail vehicle experiences a diminished dynamic pressure in the wake. The two vehicles collectively have less drag than the two in isolation. This can be regarded as a decrease in drag coefficient. It is well understood. Reducing Aerodynamic Drag and Fuel Consumption
- 8. At sufficiently close spacing—less than one vehicle length in the case of a car, or one vehicle height in the case of a truck—the interaction is stronger. Pressure is higher in the “cavity” than would be experienced by a vehicle in isolation. The drag of each vehicle is less than the corresponding drag in isolation. Both vehicles save fuel in the “strong interaction” regime. Reducing Aerodynamic Drag and Fuel Consumption
- 9. Reducing Aerodynamic Drag and Fuel Consumption Wind tunnel tests Two van-shaped vehicles, drag ratio versus spacing
- 10. Reducing Aerodynamic Drag and Fuel Consumption Measuring fuel consumption directly using instantaneous outputs from engine map. Three Buick LeSabres under computer control, traveling in HOV lanes I-15, San Diego. PATH Program, UC Berkeley, California DOT
- 11. 1 2 3 4 5 6 7 0.8 0.85 0.9 0.95 1 1.05 Forward Vehicles Interior Vehicles Trail Vehicles Reliability estimate, one standard deviation Reducing Aerodynamic Drag and Fuel Consumption Results from test. Average fuel consumption saving for three-vehicles at 0.8 car length spacing is ≈ 6-7%.
- 12. Reducing Aerodynamic Drag and Fuel Consumption The site at Crows Landing
- 13. Reducing Aerodynamic Drag and Fuel Consumption Two century-class Freightliner trucks under computer control at 4-meter spacing. Single truck: southbound (red) northbound (blue)
- 14. 3.2 liters/100 km 1.36 gal/100 mi Two class-8 trucks close-following Reducing Aerodynamic Drag and Fuel Consumption
- 15. Reducing Aerodynamic Drag and Fuel Consumption Improved fuel economy from other shape changes The DOE effort to reduce truck aerodynamic drag* The DOE Energy Efficiency and Renewable Energy, Office of FreedomCAR & Vehicle Technologies, supports a collaborative effort of 9 organizations: LLNL, SNL, ANL,NASA Ames, USC, Caltech, UTC, Auburn, GTRI *see, for example, The Aerodynamics of Heavy Vehicles: Trucks, Buses, and Trains, eds., R.McCallen, F.Browand, J.Ross, Lecture Notes in Applied and Computational Mechanics, Springer-Verlag, 2004
- 16. No aero shield Huge radiator Many corners Protruding lamps, tanks, pipes, etc. Reducing Aerodynamic Drag and Fuel Consumption Early 1990’s
- 17. Built-in aero shield Small radiator Rounded corners Recessed lamps, tanks, etc. Reducing Aerodynamic Drag and Fuel Consumption Model year 2000
- 18. Gap Wheels & underbody Trailer base cab extenders splitter plate skirts underbody wedge boat-tail plates flaps Areas of possible improvement Reducing Aerodynamic Drag and Fuel Consumption
- 19. Reducing Aerodynamic Drag and Fuel Consumption Skirts: Wind tunnel model, full scale conditions, Re = 5×106 ∆CD ≈ 0.05 Wedge: Wind tunnel model, Re = 3×105 ∆CD ≈ 0.01 Wheels & underbody DOE’s Effort to Reduce Truck Aerodynamic Drag through Joint Experiments and Computations Leading to Intelligent Design, R. McCallen et al., Proc. of the 2005 SAE Commercial Vehicle Engineering Conference, Chicago, Illinois, Nov. 1-3, 2005
- 20. Reducing Aerodynamic Drag and Fuel Consumption Trailer base Base flaps: Wind tunnel model, full scale conditions, Re = 5×106 ∆CD ≈ 0.08 DOE’s Effort to Reduce Truck Aerodynamic Drag through Joint Experiments and Computations Leading to Intelligent Design, R. McCallen et al., Proc. of the 2005 SAE Commercial Vehicle Engineering Conference, Chicago, Illinois, Nov. 1-3, 2005
- 21. Reducing Aerodynamic Drag and Fuel Consumption Computational Simulation of Tractor-Trailer Gap Flow with Drag-Reducing Aerodynamic Devices, P. Castellucci & K. Salari, Proc. Of the 2005 SAE Commercial Vehicle Engineering Conference, Chicago, Illinois, Nov. 1-3, 2005 Gap Cab extenders or trailer splitter plate RANS computation Re = 3×105 ∆CD ≈ 0.01- 0.03
- 22. Reducing Aerodynamic Drag and Fuel Consumption The summary of improvements
- 23. Reducing Aerodynamic Drag and Fuel Consumption Add–ons: Base flaps, skirts, gap control, ∆CD ≈ 0.13-0.15 For CD ≈ 0.6, ∆CD/CD ≈ 0.22, implies ∆FC/FC ≈ 11% Close-following: Field tests demonstrate ∆FC ≈ 1.36 gal/100 mi ∆FC/FC ≈ 7% Add–ons plus close following may not be additive gains! Probably a portion is, ∆FC/FC ≈ 15% If fully implemented, would result in reduction in current usage of 0.37 Mbbls/d = 135 Mbbls/yr, and a reduction of 60 Mtonnes CO2 released.
- 24. Reducing Aerodynamic Drag and Fuel Consumption Hastening the adoption of improvements
- 25. Reducing Aerodynamic Drag and Fuel Consumption Incentives for adoption of add-ons by trucking companies onaddofCostCapital misavedfuelofCost Incentive − = )000,250( For base-flaps & skirts CC = $1800 Incentive ≈ 2.5×($ per gal diesel) At $3.00 /gal, the saving would be 7.5×cost of add on, or $13,500 For base flaps, skirts & close-follow CC = $4800 Incentive ≈ 1.5×($ per gal diesel) At $3.00 /gal, the saving would be 4.5×cost of add on, or $21,600
- 26. Reducing Aerodynamic Drag and Fuel Consumption Encourage research in CFD National Labs have the computing capabilities Universities have expertise in new code development University support particularly needed Computational Simulation of Tractor-Trailer Gap Flow with Drag-Reducing Aerodynamic Devices, P. Castellucci & K. Salari, Proc. Of the 2005 SAE Commercial Vehicle Engineering Conference, Chicago, Illinois, Nov. 1-3, 2005
- 27. Reducing Aerodynamic Drag and Fuel Consumption Encourage field test experiments Trucking companies are besieged with ideas for fuel saving add-ons Type II SAE sanctioned tests take place, but usually results are not made public Close-following geometries have not been explored systematically Need field tests under controlled conditions (such as Crows Landing) to isolate the most promising technology