In many trains the bogie area is uncovered up to the height of the wheel. In order to minimise drag in high speed trains, the bogie areas may be covered with smooth and streamlined surfaces.

Technical details and design requirements

The greatest reduction in drag can be expected for bogie fairings fitted flush to the external contour of the train. However, this generally requires inside frame bogies. In the case of bogies with outboard journal frames, bellied bogie fairings have to be chosen. From an aerodynamic point of view, the latter need to be designed very carefully to avoid flow separation.

Fairings have to be designed in an optimised way both for aerodynamics and for cost-effective maintenance.

The fairing geometry has to respect a number of requirements which depend on the respective train design and infrastructure: For example for the ETR 500 the fairings had to respect the gauge limits and to avoid interference between bogie and car elements such as yaw dampers, doors, etc. In addition, openings on the fairings were necessary to allow, for instance, the view on brake indicators.

As a result, it is usually not possible to exploit the aerodynamic reduction potential up to 100 %. For newly designed stock, there are obviously less restrictions than for retrofitting measures.

Fields of application

• Main-line and high-speed trains
• There is a similar measure discussed for freight trains which is however mainly aimed at noise reduction and therefore not considered here.

Manufacturer:

Manufacturers of railway vehicles. The bogie fairings for the Italian ETR 500 were manufactured by AnsaldoBreda.

• Noise reduction
• Energy efficiency (Future high speed trains with increased speed will generate a strong rise in the energy costs of operations through increased air drag.)

Maintenance

For maintenance purposes an easy access to the bogies is required. Bogie fairings obviously make access more difficult, but this problem can be minimised by intelligent construction.

About 40% of air resistance is owed to bogies and wheels. They are therefore among the most promising areas for reducing running resistance of high-speed vehicles. The bogie fairings reduce air drag by eliminating flow separations at unshielded bogies and by shielding bogie components that would otherwise protrude into the rapid airflow along train sides. Due to the increased surface area using bogie fairings, frictional drag will be slightly greater. Since the form or pressure drag as predominating drag fraction is diminished, fitting a vehicle with bogie fairings will produce a significant reduction in drag as a whole.

Results of the ETR 500 test series

The full scale test series performed on the Italian ETR 500 with fairings revealed reductions in running resistance of approximately 10 % compared to the standard configuration without fairings. This figure refers to a speed range of 100 to 300 km/h and the train configuration planned to operate on the Italy – France routes, consisting of 2 locomotives and 8 trailer cars and which has a total length of 249.7 m. Reduced scale tests on a 1:7.5 model of ETR 500 using different fairing geometries indicate that the drag reduction could be further increased if the fairing design was aimed for the aerodynamic optimisation and not only for the retrofitting on the existing bogies.

Conclusion

A reduction potential of approximately 10% is confirmed by studies performed in the 1930s as well as Japanese experience from today’s Shinkansen 300X research train. In today’s high-speed trains running resistance accounts for over 60% of the energy consumption. This share will rise even more as further increases in speed are achieved. Bogie fairings therefore offer an overall energy efficiency potential of 6% per vehicle (and even more in the future).

Noise reduction

The DB, SNCF, FS joint research project aims at reducing noise emission originating from the bogie by 2 dB(A). It is not known whether this goal was achieved with the experimental bogie fairings tested in Italy.