Noise from Train Cooling Fans

This thesis concerns a study undertaken on a railway vehicle cooling fan system. Several design modifications were proposed and tested in the laboratory in order to evaluate different noise control measures. The most effective noise control measure involving combining lots of different measures gave 7 dB(A) noise reduction. Furthermore a modification by replacing the axial fan by a radial fan can even reduce the radiated sound power by 10 dB(A). The transfer functions were also examined for a dipole source to acoustic pressure in the far field to evaluate the acoustic loading created by the cooling fan enclosure. One fan was taken out from the complete unit and mounted between two acoustic test chambers to measure the effect of various parameters on the acoustic source strength (power) under controlled conditions. To predict accurate data of radiated sound power for comparison with the experimental work, two models have been developed: one model using the Farassat formula for a rotating dipole and the other model based on a 3D acoustic-vortex model. The heat exchangers in the cooling unit can have a significant effect on sound emitted from a cooling fan. An acoustic model based on so called equivalent fluid model for an anisotropic medium was derived to evaluate the sound transmission and the absorption through a parallel plate type of heat exchanger