Aerodynamic noise of urban rail vehicles: sources, frequency distribution and control
Aerodynamic noise is produced by the interaction of airflow and structure. It is an important part of urban rail vehicle noise and grows with speed.
Where the noise comes from
The main source is the relative motion between vehicle and air; at high speed in particular, turbulent zones form at the nose and sides and produce a lot of aerodynamic noise. Onboard fans, air outlets and similar equipment also make aerodynamic noise when running.
Frequency distribution
The frequency range is wide, from 50 Hz at the low end to 5 kHz at the high end. Noise from vehicle–air relative motion lies mainly in the mid-to-high band, with frequency tied to speed and shape; noise from onboard equipment lies mainly in the low-to-mid band, with frequency tied to how the equipment runs.
Control approach
For noise from vehicle–air relative motion, an effective strategy is to optimise the vehicle shape and shrink turbulent zones; sound-absorbing material can also be fitted at the nose and sides. For noise from onboard equipment, improve the equipment design to lower running noise, or fit sound-absorbing material around the equipment.