Effect of cavity flow on high speed train pantograph aerodynamic noise

For high-speed trains the aerodynamic noise sources become important for speeds above about 300 km/h. The pantograph is mounted on the train roof, often in a shallow cavity. Because of its elevated position it is an important source of noise from high-speed trains, especially in the presence of noise barriers which shield sources that are lower on the train. In this paper, the flow features and noise sources of a high-speed train pantograph and its recess are numerically investigated at a speed of 300 km/h (Mach number 0.24). The geometry of the pantograph recess is simplified as a 'closed' rectangular cavity and two pantographs (one opened and one retracted) are included that are based on a DSA 350 pantograph. To resolve the details of the turbulent flow structures and hence enable accurate noise predictions, the Improved Delayed Detached-Eddy (IDDES) model is used to model the flow field. The Ffowcs-Williams & Hawkings aeroacoustics model is employed for far-field acoustic calculations. In comparison with the same cavity without pantographs, the flow around the cavity shows slightly different characteristics when the pantographs are placed in the cavity. The wake region in the downstream region of the cavity is slightly reduced due to interaction between cavity flow and pantographs. This can affect the noise emission from this region. This study indicates that the main noise sources are from the raised pantograph, and the panhead of the retracted pantograph as shear layers impinge on them. The cavity trailing edge also generates significant levels of noise. The far-field noise is found to be broadband. The directivity of the noise radiated from pantographs and cavity is also obtained