Centrifugal fans are actually a positive displacement compressor, including a pair of vertically meshing relative to the high-speed rotation of the rotating gas. Centrifugal fan runs, the main noise of aerodynamic noise (ie, airflow noise). Transmission gear noise, motor noise and pressure control valve noise until the part, the highest intensity, the greatest impact is the aerodynamic noise. Periodic exhaust noise includes centrifugal fan impeller rotation periodically caused by pressure fluctuations caused by eddy current noise and lead to air vortex centrifugal fan impeller on the interface when divided into two parts. The main force of the exhaust and the rotation speed of the impeller, fan exhaust flow and pressure and other factors, the noise spectrum is often low frequency, and accompanied by a certain noise peak. And the eddy current noise depends on the fan blade shape, the flow velocity of the mobile phase and the flow pattern of the main body, and the high frequency noise usually produces a continuous spectrum.

Under certain conditions of operation, high intensity noise from the fan inlet, outlet pipe, casing and other areas of radiation. In actual use conditions, the exhaust port is often connected with the gas pipeline and closed. Therefore, the intake noise is the strongest, the interference of the environment is the most serious. As a result, the noise level of the "one" file in the fan outlet is as high as 105 to 135 dB, and the noise level of the "C" file is about 110 to 140 dB.

Fans not only have high noise intensity, but also have complex and continuous frequency components. In order to quantitatively describe the energy distribution over the entire frequency range of the noise, the noise measurement with the noise spectrum analysis octave filter tests eight octaves of the frequency of 800 Hz to 63 Hz, the noise spectrum characteristic curve is obtained by the sound source, Ie the octave sound pressure level at this frequency relationship curve. Noise spectrum characteristics:

First, the noise spectrum is wide, which is the main component of the wide frequency range and high noise, low frequency noise, when the pressure is low, the load is small, usually at a lower frequency of 125 Hz peak frequency; when running to the rated pressure condition , At a frequency of 500 Hz, a new noise peak will appear. This shows that the centrifugal fan of the work pressure increases, medium and high frequency noise will increase significantly. The noise intensity and the static pressure of the fan and fan are working on the size of the spectral characteristics, but also with the centrifugal fan flow, there is a great relationship between the speed. As the flow increases, the noise increases, and when the speed is doubled, the fan noise can be increased by about 5 to 10 dB, especially to improve the high frequency of noise is more important.