Mechanical operation will inevitably produce loud noise, and centrifugal fans are no exception, especially the larger the size of the centrifugal fan, the greater the noise it emits, and the damage to some parts is often accompanied by some special noises , Under normal circumstances, where is the noise of the centrifugal fan mainly? What is the cause?
1)The main places where the centrifugal fan emits noise
1. Impeller and volute part
When the impeller rotates, a circumferential uneven airflow will be formed. The interaction between this airflow and the volute will cause cyclone noise. The main parts that emit noise are the volute, the blades and the volute tongue. The more uneven this airflow, the louder the noise from these parts.
2. Transmission parts
The vibration of the bearing, belt transmission mechanism and various parts of the centrifugal fan during transmission will generate vibration noise. When the fan is running, the mechanical movement generated by these transmission parts is often accompanied by friction and vibration, and friction and vibration will directly lead to air vibration. , and then form noise. In addition, these mechanical vibrations and airflow collisions will also cause vibration of the casing and pipes, resulting in noise.
3. Fan power source
The power source of centrifugal fans is mainly electric motors, and even some fans will use speed-increasing machines or transmission mechanisms. When they are running, they will also produce various mechanical noises, airflow noises, etc., like centrifugal fans. noise, and as the power of the motor gets bigger, so does the electromagnetic noise.
2)Reasons for the centrifugal fan to produce aerodynamic noise
The noise source of the centrifugal fan body is mainly the aerodynamic noise generated when the airflow enters and discharges. It is divided into two types: rotating noise and eddy current noise. The reasons for the two kinds of noise are different:
1. Rotational noise
When the impeller of the centrifugal fan rotates, at the outlet of the blade, there will be uneven airflow speed and pressure along the circumferential direction. This uneven airflow will rush to the volute before it can be leveled, and then formed on the volute. A pressure pulsation, which becomes a source of noise. At the same time, due to the existence of the volute tongue, this pressure pulsation will in turn affect the rotation of the impeller over time, so the airflow on the blade will also have this pulsation over time, making the blade a second noise source.
2. Eddy current noise
Eddy current noise becomes turbulent noise, which is due to the formation of a turbulent boundary layer on the object surface when the object flows around, and the trailing edge noise and blade tip noise caused by pressure pulsation on the object surface caused by its separation. The main reasons for this noise are:< br />
(1) Due to the turbulent boundary layer formed by the moving airflow on the surface of the object, the noise generated by the turbulent pressure pulsation of the airflow in the boundary layer acts on the surface of the object. The thicker the turbulent boundary layer develops, the stronger the noise is.
(2) The shedding of the trailing edge vortex of the blade will cause the pulsation of lift and generate noise. When the vortex leaving the trailing edge of the blade is hit by obstacles behind (such as support rods, vanes, etc.), the noise will be greater.
(3) Noise caused by blade force pulsation caused by the turbulence of the incoming flow.
(4) Vortex noise caused by air leakage in the blade clearance.