Unsteady aerodynamics of high speed train pantograph cavity flow control for noise reduction

Flow induced noise increase significantly with speed, consequently noise reduction has become an important consideration for high-speed train designs. However, reducing noise from a train pantograph is more challenging because of the difficulty to shield it using rail side acoustic barriers. The flow behavior around a high-speed pantograph arm and train roof at a 1/10 scale is investigated using computational fluid dynamics. The geometries of the roof and the pantograph arm are simplified as a square shallow cavity and a straight cylinder, respectively. To resolve the details of the turbulent flow structures and hence enable accurate noise predictions, the improved delayed detached-eddy simulation is used in near-field modelling and Ffowcs-Williams & Hawkings aeroacoustics model is employed for far-field acoustic calculation. In this work, the influence of geometrical alteration at the cavity leading edge is considered. The results show that the recirculation vortices, which generate highly turbulent flow, decrease with increasing cavity leading edge roundness, and this reduces wall pressure fluctuations, which is a major noise source, on the cavity and cylinder surfaces. Furthermore, aerodynamics performance, such as drag, is improved. Finally, the effect of the arm positions is studied. No significant effect was found for overall sound pressure level, but tonal noise levels from the cylinder was reduced. A reduction of interaction between the lower part of the cylinder surface and cavity shear layers was detected, and it is believed that the reduction of interaction reduces the peak noise levels