Prediction of high-speed train noise on Swedish tracks Xuetao Zhang SP Technical Research Institute of Sweden Research SP Technical Energy Technology SP Report 2010:75 2 Prediction of high-speed train noise on Swedish tracks Xuetao Zhang Abstract Aiming at applying the Nord2000 propagation model to predict high speed train noise in Sweden, the noise emission data of X2 trains has been studied. By using the Imagine source model for rolling noise (i.e. the roughness-transfer-function method), it becomes possible to empirically estimate the aerodynamic noise based on the collected inclusive noise emission data. The sound power level per meter train has been determined for each noise type/component (i.e. the rail/track and wheel radiation and the aerodynamic noise) and for the speed range of interest (150-300 km/h). The calculation method is described and the horizontal directivity for each noise type/component is provided. Key words: X2 train noise, high speed train noise, aerodynamic noise, pantograph noise, aero-noise around bogie area, sound power level, horizontal directivity, roughness and transfer function SP Sveriges Tekniska Forskningsinstitut SP Technical Research Institute of Sweden SP Report 2010:75 ISBN 978-91-86622-18-3 ISSN 0284-5172 Borås 2010 4 Contents Abstract 3 Contents 4 Preface 5 Summary 6 1 Introduction 7 2 X2 train noise and the model prediction 8 3 Method to determine input data 16 3.1 Rolling noise 16 3.2 Aerodynamic noise 16 4 Input data for prediction of X2 train noise 18 4.1 Estimation of X2 train pantograph noise 18 4.2 Revised model prediction of X2 train noise 20 4.3 Input data 26 5 Discussion 32 Reference 33 Annex A Methods to determine the sound power level of a traffic noise source 34 A.1 Determination of L from the L of a train pass by 34 WA Aeq,Tp A.2 To determine LWA from the SEL of a train pass by 39 A.3 To calculate the LpF max of a train pass by 39 Annex B The horizontal directivity of railway noise 41 B.1 Directivity function 41 B.2 Normalization 42 Annex C Input data for higher speeds 44 5 Preface This project is founded by the Swedish Transport Administration (Trafikverket), with the contract nr TRV 2010/57212. Dr. Hans Jonasson provides his valuable comments. The cover picture is provided by Bombardier. All the above supports are gratefully acknowledged. Borås 2010-09-30 Xuetao Zhang 6 Summary The Imagine model has successfully been applied on Swedish X2 trains to predict rolling noise. By subtracting this predicted rolling noise contribution from the collected total noise emission data, it becomes possible to estimate the contribution of the aerodynamic noise from the bogie areas as well as from the pantograph(s). Thus, a complete model of the noise emission of X2 trains at high speed was elaborated capable of predicting the overall noise level in one-third octave frequency bands of interest within the speed range 150-300 km/h. The model assumes certain roughness levels and transfer functions but it can later be used to incorporate new values on these parameters. 7 1 Introduction In this project, the input data, the sound power level per meter of the X2 train type, will be worked out. The relevant methods will also be described. In traffic noise engineering, the quantities of sound pressure level ( L p ), (for a certain time interval T) the equivalent (continuous) sound pressure level ( Leq, T ), the sound exposure level (SEL), the maximum sound pressure level using time-weighting F ( L pF max ) and the corresponding sound power level ( LW ) are frequently used. The first four quantities can be measured directly, whereas the sound power level can in principle be derived from one of these measured quantities. As proposed by the European Harmonoise project, the sound power level is to be used in describing the noise emission of rail bound vehicles. Therefore, the method to determine the sound power level using one of the measured quantities is described in Annex A. In Annex B, the relevant horizontal directivity is provided. Moreover, in the model calculations, the sound propagation is handled using the Nord2000 propagation model, which was proved during the European Harmonoise project to be accurate, in particular for cases little affected by meteorological conditions. Aiming at estimating noise impact from high speed trains on Swedish tracks, the noise emission data of X2 trains was studied as shown in section 2. The measured SEL data of X2 trains presented in SP Rapport 1994:25, the SEL values predicted by using the Nord2000 source model and by using the Imagine source model are compared. Based on the positive results shown in section 2, the way to work out the input data was then proposed in section 3 and the input data was given in section 4. Some detailed discussion was presented in section 5. 8 2 X2 train noise and the model prediction Presently, the X2 train is, together with the Arlanda Express X3 train, the existing high speed train type in Sweden, which can reach 200 km/h. In the near future, the Gröna Tåg (Green Train), developed based on the Regina train type, is expected to achieve a top service speed of 250 km/h [1]. In this section, SEL values of the noise emission data of X2 trains have been studied. SEL values of X2 trains are calculated using the method shown in Annex A. The different input data, the sound power level per meter of the train type, for a given speed and on a track equipped with BV50 rail, for the Imagine source model (based on the description of roughness and transfer function) and for the Nord2000 source model (based on the measured data presented in SP Rapport 1994:25), have been tested respectively. The resulted SEL values were presented in Fig. 1(a) and 1(b). For single values of the A-weighted SEL levels, the Imagine-source-model results show the speed dependence of 20,9*log10(v), compared with 24*log10(v) showing by the Nord2000-source-model results. (The corresponding speed exponent of the sound power level is then 30,9 for the Imagine results and 34 for the Nord2000 results.) The Imagine-source-model results are for the rolling noise only, whereas the Nord2000-source-model results are for the inclusive noise emission. Except for low and middle frequencies where noise types other than rolling noise have a strong influence, the Imagine-source-model results are in general about 0,5-1 dB higher than the Nord2000-source-model results (Fig. 3). This small difference is not critical and can easily be explained by the difference between the real and assumed roughness levels. Moreover, as in the Nord2000-source-model the contribution of the aerodynamic noise is included, then the resulted SEL values are of a speed dependence higher than that when considering rolling noise only. In Fig. 2, the collected SEL data presented in SP Rapport 1994:25 [2] are shown. Comparing Fig. 1(a) and Fig. 2, it is clear that the Imagine source model correctly describes the shift of the peak level of rolling noise in frequency domain when train speed varies. This feature is important when working in spectrum for estimating aero-noise contribution. Since rolling noise is not important below about 500 Hz, it is obvious that other noise types need to properly be dealt with in order to have a good noise prediction not only in the single value of the total A-weighted noise exposure level but also in its spectrum components. For high speed trains, the low-frequency noise components are mainly contributed by aerodynamic noise. In Fig. 3, the predicted SEL values by using the two source models were compared with the collected SEL data of the noise emission from X2 trains. It can be seen that, the Imagine source model and the Nord2000 source model agree well for rolling noise. Moreover, it seems that aerodynamic noise is important up to 500 Hz below 200 km/h, whereas it will also influence 1 kHz or even higher when above 200 km/h. 9 SEL for X2 trains, predicted by the Imagine model 100 90 80 70 60 dB 50 100 km/h (92,7 dBA) 150 km/h (96,6 dBA) 40 200 km/h (99,6 dBA) 250 km/h (101,8 dBA) 30 300 km/h (103,4 dBA) 350 km/h (104,4 dBA) 20 400 km/h (105,3 dBA) 2 3 4 10 10 10 Frequence (Hz) (a) SEL for X2 trains, predicted by the Nord2000 model 100 90 80 70 60 dB 50 100 km/h (92,1 dBA) 150 km/h (95,9 dBA) 40 200 km/h (98,8 dBA) 250 km/h (101,3 dBA) 30 300 km/h (103,3 dBA) 350 km/h (105,2 dBA) 20 400 km/h (106,8 dBA) 2 3 4 10 10 10 Frequence (Hz) (b) Fig. 1. The SEL values (the A-weighting is included) of the noise emission from X2 trains at representative speeds, in one-third octave bands of 25-10000 Hz, predicted (a) by using the Imagine source model (rolling noise only) and (b) by using the Nord2000 source model (including all noise types). 10 SEL data for X2 trains, SP Rapport 1994:25 95 90 85 70 km/h (90,1 dB) 130 km/h (95,4 dB) 80 140 km/h (94,7 dB) 160 km/h (97,2 dB) 170 km/h (97,6 dB) 75 180 km/h (98,8 dB) 190 km/h (98,2 dB) 200 km/h (98,4 dB) 70 2 3 10 10 Frequence (Hz) (a) SEL data for X2 trains, SP Rapport 1994:25 95 90 85 80 210 km/h (98,9 dB) 220 km/h (98,6 dB) 230 km/h (100,2 dB) 240 km/h (99,3 dB) 75 250 km/h (101,1 dB) 260 km/h (102,2 dB) 270 km/h (103,2 dB) 70 2 3 10 10 Frequence (Hz) (b) Fig.