Generation Mechanism And Control Study Of Low-Frequency Aerodynamic Noise At Inter-Coach Space Of High-Speed Train

The speed-up of trains has brought great convenience to people’s travel,but it has also caused disturbing noise problems.When the train is running at high speeds,the aerodynamic noise at the inter-coach spaces is regarded as one of the main noise sources.And with the increase of speed of trains,the interior noise becomes more serious,exacerbating the negative impact.There exists intense low-frequency noise at the inter-coach space of non-fully enclosed windshields of a certain type of high-speed train running at 350 km/h speed on an artery in China.In response to this problem,a combination of on-board measurement and numerical simulation is adopted to analyze the generation mechanism of dominant frequency of the noise based on the theory of cavity flow-induced noise in this thesis.It also explores the corresponding control methods after clarifying the generation mechanism.The main work and conclusions are as follows.Firstly,on-board measurement is conducted at the interior and exterior areas of intercoach space of a certain type of high-speed train running at 350 km/h.The results show that the noise inside and outside the car is mainly characterized by significant low frequency,and the noise amplitude of them at 37.0 Hz is over 14 d B and 17 d B higher than those at other frequencies,respectively.In order to analyze the mechanism of near-field low-frequency noise at the inter-coach space,a review of the research on cavity flow-induced noise at home and abroad is drawn,which mainly includes cavity flow self-sustained oscillation and cavity flowinduced resonance noise.According to the mechanism of flow-induced noise,a preliminary analysis of the generation mechanism of low-frequency noise at the inter-coach space of the high-speed train is carried out,and it is preliminarily judged that the dominant frequency is mostly caused by the periodic vortex shedding from the upstream of the lower openings of the outer windshield at the inter-coach space,and the "Helmholtz Cavity” shaped by the inner and outer windshield.Secondly,the accuracy of the numerical simulation method is verified.For the sake of further verifying the judgement in the preliminary analysis,a near-field aerodynamic noise prediction models for inter-coach spaces of different high-speed trains are established,based on the compressible large eddy simulation method.Numerical simulation is performed on the original model with two vehicles and the space at the speed of 350 km/h.The results show that there is a dominant frequency of 38.1 Hz,which is in good agreement with the on-board measurement results.At the same time,the study on the influence of operating speeds and different openings confirms the preliminary conclusion.Finally,after clarifying the generation mechanism of near-field low-frequency aerodynamic noise at the inter-coach space,the numerical simulation of changing the key parameters(space distance L and cavity volume V)as well as installing passive devices(spoilers)near the openings is carried out in order to control the peak frequency and amplitude.The results suggest that changing the cavity volume V to control the specific frequency is more significant,and adding a spoiler at the lower opening has a significant noise suppression effect on the peak amplitude(reduction of 5 d B),which may be related to reducing the magnitude of the vortex excitation force.This thesis mainly studies the problems of the low-frequency aerodynamic noise at the inter-coach space of the high-speed train,and could provide reference to the further study on similar cavity flow-induced problems in high-speed trains.