Numerical computation and improvement of aerodynamic radiation noises of pantographs

Abstract

This paper studied the aerodynamic characteristics of cylinder and pantograph based on large eddy simulation and the acoustic boundary element method, compared sound pressure levels of different observation points and adopted measures to reduce radiation noises. Pressure distributions on the upper and lower surfaces of the cylinder were symmetrical, and radiation noises were basically the same too. Sound pressure level in the front of the cylinder was more than that on the upper and lower surfaces of the cylinder. Sound pressure level at the back of the cylinder was the maximum. With the increase of the computational time, shedding vortexes gradually developed backwards, and the influence area was bigger. The radius of radiation sound field of the cylinder was obviously reduced after applying porous materials. Additionally, contours for noise were highly symmetrical in the whole analyzed frequency band. At 2000 Hz, the cylinder presented the obvious characteristics of dipole noise source. The aerodynamic drag and lift of pantographs through numerical computation were similar to experimental results and increased with the increase of flow velocity, which showed that the computational model for the aerodynamic characteristics of pantographs in this paper was effective. Pressure was large in the area close to the pantograph head, in the connection position between upper and lower pull rods and near the base. Long dragged airflow was formed at the pantograph head, upper and lower pull rods and at the back of the base, which had a serious influence on the distribution of aerodynamic noises of pantographs. Obvious shedding vortexes were formed in the area far away from the pantograph rather than near the pantograph. The density and strength of shedding vortexes were not large. Sound pressure levels of observation points which had the same distance from the center of pantograph base were basically the same in change trend, value and peak frequency. However, the sound pressure level of observation points around the pantograph head was obviously greater than that of other observation points when the analyzed frequency was over 1000 Hz. Radiation noises in the connection position between upper and lower pull rods were greater than that of other observation points. With the increase of the analyzed frequency, the dispersive-ness of aerodynamic noises of pantographs was increasingly obvious. The radiation noise of pantographs was mainly spread along the inclined plane of 45°. When a layer of porous materials was covered on the surface of pantographs, the influence area of radiation noises was obviously reduced. In addition, the sound pressure level of radiation noises was improved.