Centrifugal fan, in some sense, is a positive displacement compressor. It is mainly through a pair of vertical meshing waist shaped impeller for relatively high speed rotation movement, so as to achieve the gas transmission. The working principle of the compressor is similar to that of the compressor.
When the centrifugal fan is in operation, there will be different types of noise. Among them, aerodynamic noise is the main part. In addition, there are transmission gear noise, motor noise and pressure control valve noise and so on. When the impeller of the centrifugal fan rotates, the noise caused by eddy current noise caused by periodic pressure fluctuation belongs to periodic exhaust noise, when it is in the centrifugal fan impeller interface two parts.
For centrifugal fans, the main force of exhaust is influenced by impeller rotating speed, fan exhaust flow rate and pressure. So the noise is often low medium frequency and with a certain noise peak . The vortex noise of centrifugal fan depends on the shape of fan blade, the main pattern of flow velocity and flow rate of the mobile phase belongs to high frequency noise.
Under certain conditions, high intensity noise will be radiated from the inlet, outlet pipe, casing and other areas of the centrifugal fan. Under the actual conditions, because the exhaust is often connected and closed with the gas pipeline, so the intake noise is the most intense, and the environmental interference is also the most serious.
It has been proved by test that the noise in the middle and high frequency will increase obviously with the increase of the working pressure of the centrifugal fan. But along with the increase of flow rate, the noise increase. When the speed is doubled, the noise of the fan can be increased by about 5-10 DB. This is more meaningful for studying the high frequency noise of centrifugal fans.