What do they know?

Impacts of aerodynamic noise on noise mitigation efficiency, part 2

Readers of my blog Are you taking this seriously? (posted 27 Nov 2012) will recall that HS2 Ltd thinks that the “significance” of aerodynamic noise is “often overstated” and any fears that we may about its impacts are due to “misunderstandings”.

One thing that I have done to prepare me for writing my blogs is a great deal of background reading, and I thought that some quotes that I have found might serve to enlighten us about what the rest of the world seems to think about this issue.

Japan:

“The pantograph installed on a train roof is one of the major sources of aerodynamic noise in high speed trains” – Aerodynamic Noise Reduction in Pantographs by Shape-smoothing of the Panhead and Its Support and by Use of Porous Material in Surface Coverings, Ikeda, M., Mitsumoji, T., Sueki, T., Takaishi, T., Quarterly Report of Railway Technical Research Institute (Japan Railways), Vol. 51, No. 4, Nov. 2010 (here).

“The acoustic energy of aerodynamic noise is proportional to a train’s speed by a power of 6 to 8, which is higher than for other kinds of noises such as rolling noise and structure-borne noise. Accordingly, as operational train speed increases, aerodynamic noise becomes the predominant source of high speed trackside noise. In the case of Shinkansen trains, aerodynamic noise becomes dominant when velocity exceeds approximately 200km/h.” – Aerodynamic Noise Reduction, op cit.

USA:

“In general, aerodynamic noise has lower peak frequencies than that of wheel-rail noise, which means that a barrier is less effective at attenuating aerodynamic noise. In addition, aerodynamic noise sources tend to be located higher up on the train than wheel-rail noise sources. As a result, a noise barrier high enough to shield aerodynamic noise will be relatively expensive compared to a barrier for controlling wheel-rail noise, because it must extend 15 ft or more above the top of rail. For operating speeds up to approximately 160 mph, a barrier high enough to shield wheel-rail and other lower carbody sound sources would normally provide sufficient sound attenuation.” – High-Speed Ground Transportation Noise and Vibration Impact Assessment, section 2.3.4 on pp. 2-15 and 2-16, U. S. Department of Transportation Federal Railroad Administration, Final Report September 2012 (here).

“A relatively low barrier will not shield sound sources located high above the guideway, since such sources would protrude above the top of the barrier. This noise includes noise from propulsion sources, such as cooling fans, as well as aerodynamic noise generated at the upper part of the train.” – High-Speed Ground Transportation Noise, op cit, section 4.2.7 on pp. 4-18 to 4-20.

Germany:

“… it can be deduced that the reducing effect of sound insulation walls is significantly higher for freight trains compared to high speed ICE trains. This effect can essentially be put down to the reduced effect on high positioned noise sources as aerodynamically caused noises by the pantographs.” – The new German prediction model for railway noise ‘Schall 03 2006’ – Potentials of the new calculation method for noise mitigation of planned rail traffic, Moehler, U., Liepert, M., Kurze, U. J., Onnich, H., Noise and Vibration Mitigation for Rail Transportation Systems, Proceedings of the 9th International Conference on Railway Noise, Munich 4-8 September 2007, Volume 99, 2008, pp. 186-192 (here).

France:

“At higher running speeds, the energy of aerodynamic noise sources located on the roof of the train increases and the barrier height is not sufficient.” – Experimental Study of Noise Barriers for High Speed Trains, summary on p. 495, Belingard, P., Poisson, F., Bellaj, S., Noise and Vibration Mitigation for Rail Transportation Systems, Proceedings of the 10th International Workshop on Railway Noise, Nagahama Japan 18-22 October 2010, Volume 118 2011 (not available for download).

UK (surprisingly from HS2 Ltd):

“As current high speed trains exceed 300km/h, aerodynamic noise around the bogie areas, at coach connections and around the pantographs (including where they connect to the train), increases. Because these sources are higher up the coach body, and therefore higher above the rails, a barrier will be less effective in reducing the noise from these sources than in reducing rolling noise.” – Noise Source Height of High Speed Trains for the Appraisal of Sustainability, attachment to HS2 Ltd response to FOI request 11/327, 5th December 2011 (here).

UK (from acoustics consultants that advised on HS1):

“The contribution of elevated sources to overall train noise levels is a key component in the determination of overall acoustic barrier performance, which is dependent on the geometric relationship between individual sources, receiver and the barrier apex. Significant reductions in sources of noise at low height such as wheel rail rolling noise will not therefore be reflected in the net reduction of overall train noise levels where the contribution of other higher sources to train passby noise levels is significant.” – 51m Response to HS2 Consultation: Appendix 18 Acoustics Review, paragraph 4.6.3 on p. 11, Southdowns Environmental Consultants Ltd, June 2011 (here).

Quite a chorus, you might think, and one to which, perhaps, HS2 Ltd should be listening. Still, HS2 Ltd knows best, doesn’t it.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: