What are the main sources and mechanisms of aerodynamic noise in high-speed trains?

1 What is aerodynamic noise?

Aerodynamic noise is the sound generated by the interaction of air flow and solid surfaces, such as the train body, the pantograph, the bogies, and the track. It can be divided into two types: surface noise and wake noise. Surface noise is caused by the pressure fluctuations on the surface of the train due to the turbulent boundary layer and the separation of the flow. Wake noise is caused by the vortex shedding and the instability of the wake behind the train.

2 How does aerodynamic noise vary with speed?

The intensity and frequency of aerodynamic noise depend on the speed of the train and the shape of the train components. As the speed increases, the Reynolds number and the Mach number increase, which means that the flow becomes more turbulent and compressible. This leads to higher levels of surface noise and wake noise. The frequency of aerodynamic noise also shifts to higher values as the speed increases, due to the Doppler effect and the convective amplification.

3 What are the main sources of surface noise?

The main sources of surface noise in high-speed trains are the pantograph, the bogies, and the carbody. The pantograph is the device that connects the train to the overhead catenary system, and it is exposed to high wind loads and vibrations. The bogies are the assemblies that support the wheels and the suspension system, and they are also subject to aerodynamic forces and excitation. The carbody is the outer shell of the train, and it has various features that can generate noise, such as windows, doors, gaps, edges, and corrugations.

4 What are the main sources of wake noise?

The main sources of wake noise in high-speed trains are the nose, the tail, and the inter-car gaps. The nose is the front part of the train, and it is responsible for creating a pressure wave that propagates along the track and interacts with the tunnel entrances and exits. The tail is the rear part of the train, and it is where the flow separates and forms a wake with vortices and shear layers. The inter-car gaps are the spaces between the cars, and they can cause periodic fluctuations of pressure and velocity in the wake.

5 How can aerodynamic noise be reduced or controlled?

There are several methods to reduce or control aerodynamic noise in high-speed trains, such as design optimization, passive control, and active control. Design optimization involves modifying the shape and size of the train components to minimize the noise generation and propagation. Passive control involves adding devices or materials to the train surface or the track to disrupt or absorb the noise, such as fairings, spoilers, porous materials, or barriers. Active control involves using sensors and actuators to generate counteracting sound waves or forces to cancel or mitigate the noise, such as active pantographs, active bogies, or active noise cancellation systems.

6 Here’s what else to consider

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