Coherence and reduced order analyses of flow field and aerodynamic noise for full-scale high-speed trains pantograph

• The simulation of full-scale pantograph is verified by tandem square cylinders. • Far-field noise radiated from pan-head presents several peak frequencies. • Coherence analysis is used to understand the source of the peak frequencies. • The vortex shedding patterns are distinguished through reduced-order analysis. Unsteady flow field and far-field noise generated by full-scale high-speed trains pantograph were predicted by large eddy simulation and FW-H equation, and analyzed by coherence and reduced-order analyses. The agreement between simulation and test of tandem square cylinder at close Reynolds number of 1.8 × 10 5 indirectly validates the numerical method of full-scale pantograph. For the full-scale pantograph running at the speed of 300 km/h, the total sound pressure level radiated to the standard far-field receiver is 81.2 dB. The far-field noise radiated by the pan-head is more significant than that of the support rod and base frame, and the peak noise occurs at the frequencies of 252 Hz and 353 Hz. The coherence analysis shows that the peak noise frequency of 252 Hz generates near the knuckle of the pan-head and the upper arm, and that of 353 Hz generates in the middle position of the pan-head’s three rods, where there is a complete vortex shedding structure with positive and negative phase distribution. The reduced-order analysis shows that the first and second order modes containing the most energy represent the spatial vortex shedding around the pan-head. A typical wake flow with the frequency of 353 Hz is shed behind the pantograph rods, while an alternating vortex with the frequency of 252 Hz is shed on both sides of the rods.