Axial fans and centrifugal fans are commonly used, and they also face some issues during operation. Similar to axial fans, noise is generated during their use. What are the reasons for the noise?

The blades of an axial fan are thin, with excessive forward sweep and a shifted center of gravity from the root section of the blade. The centrifugal force caused by high speed and the instability of the incoming airflow lead to changes in the blade’s lift, which can cause blade vibration. Additionally, due to fluid-structure interaction, blade vibration can result in premature fatigue damage, reducing the fan’s efficiency and generating significant aerodynamic noise.

The impeller’s modal vibration pattern is typically composed of four different axial vibrations of the blades. The cause is often that the stiffness of the forward-swept blades is much smaller than that of the hub, meaning the blades are “soft” while the hub is “hard.” The low-frequency vibration mode mainly involves the overall twisting of the blades, while the high-frequency vibration is primarily the bending wave of the blades. In terms of noise impact, the first six vibration modes have a significant effect. Due to their large impact on the airflow field, the blade’s inlet angle changes, ultimately causing fluctuations in the lift on the blade surface. In the most severe cases, this leads to vibrations that generate a large amount of aerodynamic noise, significantly reducing efficiency.

Understanding the causes of noise generated by axial fans, it’s important to pay attention to reducing noise during operation.