improving vehicle aerodynamics for better
DESCRIPTION
good book!TRANSCRIPT
Passenger vehicles Commercial vehicles
Trains
Improving vehicle aerodynamics for better energy efficiency
Siniša Krajnović
Applied Mechanics, Vehicle Aerodynamics Laboratory, Chalmers
Aerodynamic drag
High pressure Net aerodynamic force Low pressure
2
21 UACD D ρ××=
Drag coefficient Depends on shape
Area of cross-section Dynamic pressure
Skin friction drag
Flow
Aerodynamic drag consumes between 35%- 65 % of energy at higway speeds
• Different between North America and Europe
Mccallan, 2002
Ways of reducing fuel consumption by reducing aerodynamic drag
• Reducing speed is very efficient
• Aerodynamic shape optimization • Flow Control • Platooning
∆+
∆+
∆=
∆U
USS
CC
ptionFuelConsumptionFuelConsum
D
D 3η
Property of driving cycle, 7.05.0 −≈η
Change in shape Reduce vehicle cross-section
Reduce speed (factor of 3)
Drag decrease by 9 %
Potential for improvement (trains) (Source Orellano and Sperling, 2009)
• The potential to reduce the drag of regional trains is around 20-25%. This drag would lead to energy reductions of 6-8%.
Typical drag distribution.
Potential for improvement.
There is no improvement without understanding of the flow physics
Originally, the styling modell with the back angle of 45 degrees. The drag coefficient was 0.40. Reduction of slant angle to 30 deg. lead to a sudden 10 % increase in drag.
Improvement of the vehicle’s design using shape optimization
Mesh Generation Optimization Mesh Deformation
ORIGINAL DESIGN GEOMETRY MODIFICATION
CFD Simulation
Original
Optimized
Passive flow control using impinging devices
• Passive flow control devices are simple to use but cannot addapt to flow condition.
Position of separation
Influence of the flow control on the flow over the slant and in the near wake
Natural flow Controled flow
Drag reduction of 10 %
Flow control of trailing vortices on A-pillar
Natural flow
Suction Krajnovic et al., Int. Journal of Flow Contro 2011
The geometry of the cube (a), the computational domain (b) .
(a)
(b)
Flow control using moving surface boundary layer control (Han and Krajnovic, Turbulence, Flow and Combustion, 2013.)
Experimental results show drag reduction up to 35%. (Modi 1992)
The time-averaged streamlines for non-rotating case (a) and rotating case (b) in the case of 300 yaw angle, top view in the middle plane of the cube.
(a)
(b)
Improvement by flow control Passive flow control
Bombardier Contessa (Öresundståget) used for regional traffic in Sweden. Bad aerodynamic shaping
Corner nozzles on the rear, change flow and reduce drag up to 15% → ~ 5% fuel savings for a truck. [1] M. Tsai, “Study of using corner nozzles to reduce the drag of a truck”
Research question: Can we apply similar types of nozzles on Öresundståget to reduce the drag and? We investigate by simulating the flow around a simplified model of the train. Complex flow simulation to do accurately.
Improvement by flow control (Passive flow control)
Another strategy is to place an cavity at the base of the train. On a real train a mechanical construction must be designed so that the cavity can be folded when the train changes direction. J. Östh and S. Krajnović. “Simulations of flow around a simplified train model with a drag reducing device using Partially Averaged Navier-Stokes”. Conference on Modelling Fluid Flow (CMFF’12), The 15th International Conference on Fluid Flow Technologies. Budapest, Hungary, 4-7 September, 2012
Drag reduction ~10%
On road tests shows fuel savings of around 10% on tractor-trailers Over-the-Road Tests of Sealed Aft Cavities on Tractor Trailers, K. Grover and K. D. Visse, SAE 2006
Improvement by flow control -Active flow control
The idea
The experiment The explanation
Natural flow
Controled flow
Active and passive flow control (El-Alti M., Kjellgren P. and Davidson L.)
Prototype, 5% fuel reduction on road test comparing AFC to NO AFC on
the same configuration.
Cooperation with VOLVO 3P and SKAB
5/17/2013
Improvement of energy efficiency of regional and freight trains
•Large potential for improvement of energy efficiency. •Many existing trains with poor aerodynamic performance. •Little knowledge about these flows.
Regional trains Freight trains
Where are we and what more is needed to achive the enviremental goals?
• Research about flow control techniques is promising. Research is ongoing in the road sector but much can be done in the rail transports too.
• Commercial vehicles and trains are systems and improvement of
aerodynamic properties requires the control on the entire system.
• It is important to keep in mind the whole picture.
• New technologies and areas of research • Education is important.
Experimental results show drag reduction up to 35%. (Modi 1992)