Fan noise awareness and some solutions

Update:13-08-2019
Summary:

We all know that there are many reasons for the noise g […]

We all know that there are many reasons for the noise generated by the fan. Only when we find the cause of the noise can we solve the problem. The problem is that the fan is actually a volumetric compressor. It is rotated by a pair of waist-shaped impellers that are vertically meshed with each other. gas. When the wind turbine is running, the noise generated mainly includes the dynamic noise of the air (ie, the airflow noise). The transmission gear noise, the motor noise and the pressure of the pressure regulating valve are the parts, among which the highest strength and the most influential are the aerodynamic noise.

 

It includes the periodic exhaust noise generated by the pressure pulsation caused by the periodic outward exhaust when the fan impeller rotates, and the eddy current noise caused by the gas vortex splitting at the fan impeller interface. The intensity of the exhaust gas is mainly related to the rotational speed of the impeller, the flow rate of the exhaust of the fan and the static pressure. The noise spectrum is often low-intermediate and accompanied by a certain noise peak. The eddy current noise depends on the shape of the fan impeller. The flow rate and flow state of the airflow relative to the body generally produce high frequency noise of continuous spectrum.

 

When operating under certain working conditions, high-intensity noise is radiated from the inlet, exhaust, casing and piping of the fan. Under actual use conditions, the exhaust port of the fan is often closed to the gas pipeline. Therefore, the noise radiated from the air inlet is the strongest, and the interference to the environment is also the most serious. According to the actual measurement, the noise emitted from the fan port can be about 105~135 decibels in the "A" file, and the noise level in the "C" file is about 110~140 decibels.

 

The fan is not only very noisy, but also has a complex and continuous frequency component. In order to quantitatively describe the distribution of its noise energy over the entire audio range, in the noise measurement, the octave filter is often used to perform spectrum analysis on the noise in eight octave bands from 63 Hz to 800 Hz to obtain sound. The noise spectrum characteristic curve of the source, that is, the relationship between the octave sound pressure level and the current frequency. Its noise spectrum curve features:

 

Fan control measures
In addition to considering the wind noise, the noise reduction of the fan should be paid attention to according to the site conditions.
Due to the large noise generated by the axial fan, the fan noise also increases with the increase of air volume and wind pressure. There are several ways to solve the fan noise problem:

 

1) The noise of the casing and the motor can be solved by installing an acoustic enclosure. The fan is placed in an independent fan sound insulation room, and the sound absorption and sound insulation are processed in the fan room.

2) Install a muffler outside the fan exhaust vent and built-in muffler inserts to reduce noise when passing through a specially constructed muffler. The muffler is an effective measure to reduce the radiation of the inlet and exhaust ports of the aerodynamic device or to transmit noise along the pipe.

3) Use anechoic louvers as much as possible on the ground floor louvers.

4) The fan is suspended by a damper spring hanger damper.