Mehanizmi generiranja buke kod ventilatora za hlađenje motora s unutamjim izgaranjem
Abstract
Among all engine auxiliary units a cooling fan is the noisiest. There are two mechanisms that generate the overall noise of the fan: the rotational and non-rotational one. These mechanisms depend on the fans geometry and operation conditions. The rotational noise is characterized by a broadband noise and superimposed discrete frequency tones. The superimposed tones are linked with the blade passage frequency and its higher harmonics. In heavily loaded conditions (at the lower flow rate) non-rotational noise is found to be prevailing. The non-rotational noise spectrum has a peak at frequency that is not related to the rotational speed or blade passage frequency. Rotational noise is mainly the consequence of the fluctuating forces on the rotor blades and is provoked by the interaction of the rotor blades with the nearby stationary objects. Non-rotational noise is caused by: a) laminar boundary layer vortex shedding, b) blade interaction with the tip clearance vortex and c) blade stall. The goal of this paper is highlight all these noise generating mechanisms caused by axial fans in IC engines cooling applications.
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