The noise level of a centrifugal fan square at different speeds is influenced by multiple factors, and its variation is closely related to aerodynamic noise, mechanical vibration, and structural resonance. Speed, as a core parameter, directly determines the airflow motion state inside the fan and the dynamic characteristics of mechanical components, thus affecting the noise spectrum distribution and sound pressure level intensity.
When the centrifugal fan square is in the low-speed range, the airflow velocity is low, and the friction and impact between the impeller and the air are relatively mild, with vortex noise dominating the aerodynamic noise. At this time, the vortex energy formed on the back of the blades due to airflow separation is small, and the radiated noise is mainly low-frequency, resulting in a low sound pressure level. Simultaneously, the vibration amplitude of mechanical components is small at low speeds, and the mechanical noise from bearings, transmission gears, and other parts is also at a low level, resulting in an overall noise characteristic of wide frequency and low intensity.
As the speed increases, the airflow velocity increases significantly, and the periodic pressure fluctuations generated by the impeller rotation intensify, gradually highlighting the rotational noise component in the aerodynamic noise. The frequency of rotational noise is directly related to the impeller speed and the number of blades, and its fundamental frequency and harmonic components form obvious peaks in the noise spectrum. Simultaneously, the boundary layer separation phenomenon formed by high-speed airflow on the blade surface intensifies, increasing the energy of eddy noise and raising the proportion of high-frequency components. At this point, the overall intensity of aerodynamic noise significantly increases, becoming the dominant noise source. Mechanically, the vibration of bearings and transmission components increases with rotational speed, potentially triggering resonance and further amplifying the noise.
When the centrifugal fan square reaches its design limit or operates under overload, the airflow enters a turbulent state, further broadening the spectrum of aerodynamic noise, with mid-to-high frequency components dominating. At this time, the airflow pulsation pressure at the impeller outlet reaches its peak, intensifying its interaction with structures such as the volute and volute tongue, generating strong aerodynamic noise. Mechanically, the high-speed rotating impeller may cause rotor dynamic imbalance, leading to severe vibration and accelerated wear of bearings, gears, and other components. The mechanical and aerodynamic noises superimpose, forming a sharp and piercing noise characteristic. Furthermore, at high speeds, the vibration frequencies of various fan components may approach the structural natural frequencies, triggering resonance and causing noise energy to be released in a concentrated frequency band, forming a significant noise peak.
The structural characteristics of the centrifugal fan square have a significant modulating effect on noise levels at different rotational speeds. The geometry of the volute, the clearance of the volute tongue, and its tilt angle directly affect the pressure distribution of the airflow at the outlet. A well-designed structure can reduce airflow separation and vortex generation, thus lowering vortex noise. The number, shape, and installation angle of the impeller blades determine the frequency characteristics and sound pressure level of rotational noise; optimized design can reduce noise peaks in specific frequency bands. Furthermore, the stiffness and damping characteristics of the fan casing affect the transmission and attenuation of vibration energy. Using high-damping materials or adding structural reinforcing ribs can effectively suppress resonance and reduce noise radiation efficiency.
To control the noise level of a centrifugal fan square at different speeds, a comprehensive approach is needed, encompassing aerodynamic design, mechanical optimization, and structural noise reduction. In terms of aerodynamic design, techniques such as swept blades and unequal-pitched blade arrangements can be used to disrupt the periodic pulsation of airflow and reduce rotational noise; optimizing the volute tongue clearance and tilt angle reduces vortex noise generation. In terms of mechanical optimization, high-precision bearings and low-noise transmission gears should be selected, and rotor dynamic balancing should be strengthened to avoid mechanical noise caused by high-speed vibration. In terms of structural noise reduction, sound-absorbing materials are used to wrap the fan casing, and silencers are installed at the air inlet and outlet to block the noise propagation path. Finite element analysis is used to optimize structural stiffness and prevent resonance.
The noise level of the centrifugal fan square exhibits dynamic changes at different speeds, and its intensity and spectral distribution are influenced by aerodynamic noise, mechanical vibration, and structural resonance. Through targeted design optimization and noise reduction measures, noise levels at different speeds can be effectively controlled, meeting the stringent noise control requirements of various application scenarios.
