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)