Axial flow fan from China The total noise level is proportional to the sixth power of the blade speed. According to the analysis, the noise source of Axial flow fan from China is basically of dipole nature. It can be further deduced that the noise is caused by the blade acting on the upper pulsation force of the air flowing through the Axial flow fan from China. It can be considered that there are two discrete frequency noise sources for the fan, one is the propeller-type noise caused by the pressure field with the rotor blade movement, and the other is the blade pulsation noise caused by aerodynamic interference. The distance between the moving and stationary blades of the fan is an important factor in the interference noise.

When this distance is small, both potential flow and wake changes have an effect, and it is also possible for the blade to act as a sound barrier, enhancing the acoustic radiation generated by lift pulsations on blades adjacent to the blade row. This effect depends on the ratio of the wavelength of the sound wave associated with the lift pulsation to the size of the blade acting as a barrier. In the frequency range where this ratio is greater than 2, the change in radiation intensity due to this effect is most pronounced. Therefore, the effect will be stronger when a noise radiating blade has the same number of blades upstream and downstream, and each blade in the two rows of blades meets a rotor blade at the same time to form a sound barrier on both sides of the source.
When the distance between the moving and stationary blades increases, the effect of the potential flow interference decreases much faster than the effect of the change of the wake velocity, and the effect of the blades as a sound barrier also decreases with the increase of the distance. It can be seen that at least three parameters affect the magnitude of the interference noise: the blade shape of the velocity field waveform (that is, the blade load), the distance between the blade rows, and the blade radiation area as a sound source. Very small spacing can have two acoustic effects. If the force pulsation created by the interference field of the vane on the moving vane makes the moving vane a sound source, and the vane is a sound barrier.
The above is a brief introduction to the noise analysis knowledge of Axial flow fan from China.