3) centrifugal outlet due to the presence of the volute or the presence of the fan-shaped fan rear guide leaves produced by the presence of interference noise, discrete noise with discrete spectral characteristics, the fundamental frequency (i = 1 corresponding to the frequency) the strongest noise , Higher harmonics are decreasing.
2) Rotational frequency noise generated by blades in non-smooth or asymmetric enclosures.
(1) intake air interference due to the presence of the front vane or metal mesh.
Machine discrete noise (rotating noise): the rotation of the impeller. Especially in high-speed, low load conditions, this noise is particularly prominent. Discrete noise is due to the asymmetry between the blade structure and the blade design test rotation formed by the formation of the circumferential flow of the interaction caused by uneven noise, is generally considered to have the following
