At speeds above 300–350 km/h, the main source of noise from trains is the aerodynamic noise caused by the air flow over the train structure. The sound level increases with train speed at a rate of between 60 and 80 times the logarithm of the speed so that, as speeds increase further, the noise increases dramatically. The main aerodynamic noise is produced by the air flow passing over the pantograph, the train nose, the bogie region and cavities such as the pantograph recess and the inter-coach gap. Experimental and numerical methods for studying aerodynamic noise are reviewed including the use of microphone arrays, wind tunnels, computational fluid dynamics and semi-empirical methods. Potential mitigation measures that can control aerodynamic noise are also reviewed.

Recent developments in the prediction and control of aerodynamic noise from high-speed trains

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Theory Of Vortex Sound

Stochastic analysis model for vehicle-track coupled systems subject to earthquakes and track random irregularities

Component-based model to predict aerodynamic noise from high-speed train pantographs

Excessive vibrations of railway vehicles induced by dynamic impact loadings have a significant impact on train operating safety and stability; however, due to the complexity and diversity of railway lines and service environment, they are extremely difficult to eliminate. A comprehensive overview of recent studies on the impact vibration behavior of railway vehicles was given in this paper. First, the sources of impact excitations were categorized in terms of wheel-rail contact irregularity, aerodynamic loads, and longitudinal impulses by train traction/braking. Then the main research approaches of vehicle impact vibration were briefly introduced in theoretical, experimental, and simulation aspects. Also, the impact vibration response characteristics of railway vehicles were categorized and examined in detail to various impact excitation sources. Finally, some attempts of using the railway vehicle vibration to detect track defects and the possible mitigation measures were outlined.

Impact vibration behavior of railway vehicles: a state-of-the-art overview

Aerodynamic noise becomes a significant noise source at speeds normally reached by high-speed trains. The train bogies are identified as important sources of aerodynamic noise. Due to the difficulty to assess this noise source carrying out field tests, wind tunnel tests offer many advantages. Tests were performed in the large-scale low-noise anechoic wind tunnel at Maibara, Japan, using a 1/7 scale train car and bogie model for a range of flow speeds between 50, 76, 89 and 100 m/s. The dependence of the aerodynamic noise from the bogie region on different factors has been studied for different bogie configurations and inflow conditions representing different positions of the bogie along the train. The speed dependence and the noise directivity have also been assessed. The results show the particular importance of the components exposed to the free flow, whereas those shielded within the bogie cavity are shown to radiate much less noise.

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Anechoic wind tunnel tests on high-speed train bogie aerodynamic noise

Experiments to simulate the flow induced vibration and noise radiation from a car window are described. Two cases are considered: flow over a backwards-facing step and flow over a half-cylinder placed on a flat plate. Thefirst configuration represents the flow separation and subsequent re-attachment into a turbulent boundary layer generated by the A-pillar of a car. The second configuration is representative of the turbulent flow over a side window produced by a car wing mirror. Measurements were carried out in an open jet anechoic wind tunnel at the ISVR, where a very low noise flow of up to 40 m/s can be achieved. Wall pressure fluctuations were measured using a streamwise array of microphones, from which the Power Spectral Density, coherence and cross-correlation of the pressure fluctuations were obtained. It was also possible carry out a spatial Fourier transform to give the wavenumber-frequency spectra of the wall pressure fluctuations. The vibrational response of the test panel was measured on a grid of points and noise radiation was measured using sound intensity mapping and a fixed microphone in the acoustic farfield.

Validation tests for flow induced excitation and noise radiation from a car window

Scanning measurement techniques allow reducing significantly the number of sensors required to characterize time-stationary sound fields. Therefore, it is possible to produce sound maps by combining the signal acquired while moving a transducer with its tracking information. Structural vibrations can be measured acoustically by using a particle velocity sensor or Microflown since particle velocity is proportional to surface displacement under specific conditions. Moreover, relative phase information can be acquired by adding an additional static reference sensor. Combining particle velocity with relative phase information across the structure gives a very powerful visualization technique for studying operational deflection shapes (ODS). In this paper a theoretical basis of the measurement principle is presented along with a experimental example. In addition, a discussion focused on the advantages and disadvantages of the particle velocity based scanning method is given.

/pdf/measuring-operational-deflection-shapes-with-a-scanning-p-u-3uhjghjyep.pdf

Eduardo Latorre Iglesias

Papers

Recent developments in the prediction and control of aerodynamic noise from high-speed trains

Anechoic wind tunnel tests on high-speed train bogie aerodynamic noise

Validation tests for flow induced excitation and noise radiation from a car window

Measuring operational deflection shapes with a scanning P-U probe

Wind tunnel tests on the noise radiated by cylinders with different cross-sections