19th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2-7 SEPTEMBER 2007

HIGH SPEED TRAINS EXTERNAL NOISE: RECENT RESULTS IN THE TGV CASE

Gautier, Pierre-Etienne1; Poisson, Franck1 ; Létourneaux, Fabien 2 1 SNCF, Innovation and Research Department, 45 rue de Londres,F75379 Paris cedex08, France; [email protected] ;[email protected] 2 SNCF, Agence d’Essai Ferroviaire, 21 Av S ; Allende 94407 Vitry /Seine cedex, France ; [email protected]

ABSTRACT For the past 15 years, a number of high speed tests were carried out for the TGV, in which various acoustical measurements have been done, either in dedicated programs (Deufrako Cooperations K and K2, 350 kph measurement campaign a few years ago on TGV Duplex, and more recently 360 kph test on TGV Reseau), or at the occasions of the recent very high speed campaigns. The processing of results involves estimating the characteristics of sources (rolling noise, aerodynamic noise) with different methods. After a review of the different results in terms of global noise, source identification as applied to the TGV case, is presented. The models that use the characteristics of the source to predict the pass-by noise are also developed.

INTRODUCTION Noise from high speed trains is a sensitive issue, as high speed train lines are built either in densely populated areas, or conversely in zones where the pre existing noise was very low. High interest was then given, as soon as the 1990’s, to the measurement of pass-by noise from high speed trains, and especially in France to the TGV case, with emphasis on the evolution with running speed. At the same time, interest was also given to noise source identification on the trains with the help of acoustic arrays method, in order to reduce, whenever possible, the most prominent sources on the train. More recently, with the idea of interoperability of railway traffic throughout Europe, train pass-by noise was considered as an “interoperability parameter” and thence limited in the high speed trains (then conventional) Technical Specification for Interoperability (TSI) for trains. The idea was to limit train pass- by noise for all trains in Europe in order not to jeopardize the quality of the protections (noise barriers) installed by Member States to protect the dwellings. In order to establish these TSI limits for high speed trains, a comprehensive series of tests were carried out, including TGV’s. Even more recently, measurements at higher speeds were carried out on operational series of TGV’s (double decker Duplex type at 350 kph, then Reseau at 360 kph). After a review of the global pass-by measurements results for TGV’s, as compared to other high speed trains, the paper will focus on source identifications results , also with a review of the different results obtained. The use of these results in “global “ models for train pass-by will then be addressed, as well as these models capabilities in predicting global noise reduction from the reduction on isolated components in the trains.

GLOBAL LEVEL MEASUREMENTS A number of global level measurements were carried out since the 1990’s at speeds up to 350 kph. Among them the DEUFRAKO K [1] and K2 projects [2]. The tests mentioned here will concern only commercial configuration of the train for tests. In tests like the world records, the composition was smaller in terms of trailer cars thus being not representative of operation. Then, a few years ago, tests at 350 kph were carried out with a double-decker TGV Duplex, including global measurements and acoustic array measurement for source identification. Meanwhile, in the framework of interoperability, tests had been carried out until 320 kph on different types of trains TGV and Duplex, AVE in Spain, ICE [3]. Whenever possible, i.e. apart from the AVE tests which were carried out in Spain, the different trains were analysed on the same sites, respectively in France, , and Belgium, the tracks being, except for the Belgian case, compliant with the TSI specifications in terms of roughness and track decay rates [4]. Recently, in 2006, tests up to 360 kph were carried out on two commercial single deck

trainsets of the TGV Réseau type. The track on the measuring site was nearly compliant with the TSI specifications. All the results are presented in table 1.

Table I.- Pass-by noise of high speed trains in Europe

Pass-by noise Test site Train speed (kph) values measured at 25m in dB(A) TSI+ tracks 250 300 320 350 except Belgium TGV Thalys Belgium 88.5 92 93 France 85.5 90 92 Germany 85.5 TGV Duplex France 87 91 92 95 TGV Atlantique France 90.5 94.7 TGV Réseau France 89 91.5 94 (330kph) 97 ICE3 France 87.5 90 91.5 Germany 85.5 89 92 AVE Spain 86 90 91 ETR480 Italy 90.5 ETR500 Italy 88 90.5 TSI limits TSI+ - 92 94 -

A general remark following the analysis of the above results is that the external noise from the different series of TGV’s is very close from each other, ranging around 1.5 dB(A) form one type to another, when analyses on the same track are taken into account. Moreover, different series of trains from different countries (TGV, ICE, ETR…) show very close values on the same measurement site, identical values for 300 kph and above, and up to 2 dB(A) at 250 kph. It then can be asserted that, on specified track, the noise from different series of TGV as well as different types of high speed trains is very close.

Influence of the state of the wheels. During the TGV-Réseau campaign at 360 kph, pass-by noise was recorded at different stages of the measurement campaign. It appeared that following track works at a few defined dates during the test campaign, some ballast dust might have been run over by the wheels, the roughness of which significantly increased on the days following track works. The measured noise values were then increased by 1.5 to 2.5 dB(A) after each track work episode, and the influence of the increase of the measured pass-by level can be noticed throughout the whole investigated speed range : 250 to 360 kph (see table 2). It can also be inferred from the latter observation that the transition speed between rolling noise and aerodynamic noise for the TGV Réseau is higher than often previously claimed, when is had been said to lie around or under 300kph. Following that hypothesis, the influence of rolling noise created by the wheel roughness on noise up to 360 kph would not have been so significant: for the TGV Réseau case, the upper values of measured pass-by noise (for corrupted wheel state) went up to 97 dB(A), whereas values measured on the TGV Duplex in a former campaign were not higher than 94 dB(A) at 350 kph. These observations also still confirm in this case the applicability of the “30 logV” regression rule, which was shown in [5].

Table 2.- Influence of the wheel surface quality on pass-by noise (TGV Réseau)

Pass-by noise Train speed (kph) values measured at 25m in dB(A) 250 300 330 TGV Réseau 89 91.5 94 TGV Réseau 93 95.5 97 “bad wheels”

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19th INTERNATIONAL CONGRESS ON ACOUSTICS – ICA2007MADRID

SOURCE MODELS Deufrako Campaigns Many of the measurement campaigns were, as soon as the DEUFRAKO K and K2 campaigns accompanied by acoustic array measurements. The acoustic array measurements in DEUFRAKO K project was further analysed by INRETS, where a first estimation of the level of the sources was attempted, by summing the acoustical energy received on a zone surrounding the assumed position for the source.

Table 3.- Estimation of the level of the sources of a TGV A (DEUFRAKO project) [1]

Level at 5m 100 kph 200 kph 300 kph 350 kph DB(A) Wheels, coach 82.4 89.7 97.2 98.1 Wheels, forward 82.9 89.4 102.5 100.4 Wheels, rear 81.7 89.6 102.7 98 power car 82.1 91.3 103.5 104.3 Cooling fan, 78.9 87.9 101.3 104 front Cooling fan, 78.3 79.6 102.1 100.5 rear Front window / 77.9 88.5 102.2 104.9 Roof Intercar gap 81.7 87.1 92 98.1 (aero) 76.8 78.6 90.1 93.3

Later in DEUFRAKO K2 some monopole fitting to the array results was attempted. Unfortunately, in order to prove the method, a loudspeaker was carried out by the train. It appeared that the loudspeaker source was not retrieved by the SDM method in a way that the exploitation of the method on other sources less precisely located on the train could be reliably done.

TGV Duplex tests at 350kph and TGV Réseau at 360 kph The tests carried out with TGV Duplex at 350 kph also involved acoustic array measurements. An example of the obtained results is given in figure 1.

Figure 1. - example of a TGV Duplex noise maps obtained with an antenna of microphones Above : third octave band 500 Hz / Below : third octave band 4000 Hz

For processing the TGV Duplex results at 350 kph, a different method was developed [5], where sources contents in third octaves band could be estimated. A summary of the results is given in figure 2.

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19th INTERNATIONAL CONGRESS ON ACOUSTICS – ICA2007MADRID

Figure 2.- example of source power identification on TGV Duplex running at 350 kph (SPL of the most energetic third octave band of the source)

For the processing of the tests at 360kph, the process carried out for the TGV Duplex was also applied. The comparison of table 3 and figure 2 leads to the following conclusions : - At 200 kph, the rolling noise is an important source but the noise radiated by the area located around the first bogie (bogie and windscreen) is in the same order, - At 300 kph, the area around the first bogie is the main source but the noise radiated by the cooling and the pantograph can not be neglected, - At 350 kph, the area located around the first bogie and the pantograph radiates much more. These data are currently used as input of a pass-by noise simulation software (see MAT2S and VAMPASS presented in the following paragraph) to assess the contribution of each source to global pass-by noise. The most radiating source is not always the main source in terms of contribution to the pass-by noise due to the number of sources, their location, their spectra, … An example of result is presented in [6] for a simulation carried out with MAT2S.

GLOBAL MODELS FOR SIMULATION As soon as sources estimation were available, different models for train pass-by simulations were developed. It should be emphasized that these models were NOT aiming at predicting the train pass-by noise in longer distances, but rather to be able, through parametric studies, to determine the most efficient options to reduce the pass-by noise. Although the first attempt to derive such a model in the DEUFRAKO K project, the real availability of aerodynamic sources for TGV came with the DEUFRAKO K2 project, with the MAT2S model.

The MAT2S model The MAT2S model was developed within the frame of DEUFRAKO K2 [2]. A train is defined as a combination of cars/wagons. Each one is defined by a group of noise sources identified either from acoustic array measurements or from real well known position. Noise sources can also be included in the intercar gap. Each noise source is defined by : - a third octave band spectrum 1m far from the source, at a reference speed, - some pure tones 1m far from the source, at a reference speed, - the horizontal directivity, monopole, dipole or defined by the user, - the vertical directivity, monopole, dipole or defined by the user, - a speed exponent a to extrapolate the level of the spectrum according to the speed. After calculation (30s), the software provides three types of results : - third octave band spectrum of the pass-by every 125ms,

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19th INTERNATIONAL CONGRESS ON ACOUSTICS – ICA2007MADRID

- time history of the pass by, - equivalent sound pressure level in dB(A). A parametric study was carried out for the TGV–Réseau case, where it appeared that the number of sources could be significantly reduced. The total number of source on the train was reduced from 50 to 30, without significant loss of precision in the pass-by level. The sources are summarised in table 4.

Table 4.- Noise sources defined in MAT2S software

Front power car Coaches Rear power car First bogie (aerodynamic) Louvers Pantograph Second bogie (aerodynamic) Bogie (aerodynamic) Last bogie (aerodynamic) Windscreen Wheels Wheels Pantograph cavity Intercar gap Wheels

Such a model can be used to conduct parametric studies to reduce the pass-by noise of a train in given operating conditions. An example is given in [6], where the noise reduction of a TGV running at 350 kph is discussed. The combination of noise reduction solutions shows that : - the maximum noise reduction achieved is between 4 and 5 dB(A) at 350kph when traction equipment, aerodynamic and rolling noise sources are reduced, - the reduction of only the aerodynamic noise sources is not sufficient to obtain a significant pass by noise reduction (<2 dB(A)), - the reduction of the rolling noise combined with the reduction of the aerodynamic noise of the first bogie is the most efficient solution, close to the reduction achieved by acting on all the sources. This parametric study provides the main guidelines to follow to efficiently reduce the pass-by noise of high speed trains up to 350 kph. The future model Within the frame of the EU Silence project, the development of a new model called VAMPASS is in progress [7]. The main objective of the new approach is to calculate the sound sample corresponding to the pass-by in addition to the third octave band and narrow band spectra, the time history of the pass by noise and the equivalent sound pressure level in dB(A). Then, parametric studies carried out to reduce the pass-by noise of a train can be combined with experiment in laboratory to assess the annoyance of the pass-by conducting listening tests. The definition of the noise sources is of the same type as in MAT2S. Source spectra are split into broad band noise and pure tones. The calculation is carried out in the time-frequency plane and transformed in the time domain by a single inverse fast Fourier transform. Then, the time calculation remains small enough to conduct parametric studies (less than 1mn for a complete Diesel train). The validation of the software (noise indicators and sound samples) is still in progress. A first parametric study has been conducted to define the best way to reduce the pass-by noise of a Diesel multiple unit train [8]. Application to TGV will follow.

Conclusion The measurements carried out during the last 15 years show that the global pass–by noise levels of the high speed trains (TGV, ICE and ETR) in Europe are quite homogeneous. As the rolling noise and the aerodynamic noise are the main sources at commercial speeds, the reduction of the global noise must be a combination of actions on all prominent sources. In order to practically carry out such a reduction an accurate definition of the noise sources is needed along with a prediction tool of the global noise by a model using these data as input. Such models are available and new developments will soon enable the sound synthesis that will make it possible to hear both current situation and anticipated progress.

References [1] German-French cooperation, Annex K – Final Report. December 1994. [2] German-French cooperation, Annex K – Final Report. December 1999. [3] P.Fodiman & C.J.C Jones, Noise emission measurement campaign for high speed interoperability in Europe : the NOEMIE Project – first results towards an improved definition of reference tracks. Proceedings of CFA/DAGA joint congress , Strasbourg, march 2004.

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[4] Technical specification for interoperability relating to the rolling stock subsystem of the trans European high-speed rail system, 30/05/2002, official journal of the EC (12/09/2002). [5] C. Mellet, F. Létourneaux, F. Poisson, C. Talotte, « High Speed Train emission : Last investigation for the aerodynamic / rolling noise contribution”, IWRN, 2004. [6] F. Poisson, P-E. Gautier, A. Fortain, F. Margiocchi, “Pass-by noise reduction at 350 kph : a parametric study”, WCRR Montreal, 2006. [7] S. Molla, E. Bongini, P-E. Gautier, D. Habault, P.O Mattei, F. Poisson, “Prediction and audio synthesis of vehicle noise in urban area”, ICA, 2007. [8] F. Poisson, P-E. Gautier, “The reduction of railway noise in the European integrated project Silence”, ICA Madrid, 2007.

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19th INTERNATIONAL CONGRESS ON ACOUSTICS – ICA2007MADRID