Optimizing the airflow channel of a centrifugal fan square is crucial for reducing operating noise, and its design must balance airflow smoothness and acoustic characteristics. Turbulence generated within the channel due to friction, eddies, or sudden pressure changes is the primary source of noise; therefore, optimization requires coordinated improvements across multiple dimensions, including channel shape, airflow guidance structure, surface treatment, and silencing devices.
A smooth transition in channel shape is fundamental to reducing airflow resistance. Abrupt expansion or contraction of the centrifugal fan square's inlet and outlet can trigger airflow separation and eddies, significantly increasing noise. The design should employ a gradual transition structure, such as replacing a square inlet with a rounded rectangle or ellipse, allowing the airflow to gradually adapt to changes in channel cross-sectional area and reducing impact losses. Simultaneously, right-angle bends should be avoided within the duct; rounded transitions or designs with large radii of curvature guide airflow along a smooth path, preventing turbulence caused by sudden changes in direction.
A well-designed airflow guidance system can significantly improve airflow uniformity. Installing a baffle at the inlet of a centrifugal fan square can evenly distribute the incoming airflow to all areas of the impeller, reducing eddies and vibrations caused by uneven flow. The shape of the baffle needs to be optimized according to the impeller rotation direction and airflow velocity, for example, using a forward-swept or backward-swept design, to allow the airflow to adapt to the impeller inlet angle in advance, reducing inlet impact noise. Furthermore, installing a flow divider or rectifier inside the duct can further refine the airflow distribution and avoid turbulent noise caused by excessively high local flow velocities.
Surface roughness has a significant impact on airflow friction noise. Burrs, welds, or unevenness on the inner wall of the centrifugal fan square's duct will increase friction between the airflow and the wall, generating high-frequency noise. Therefore, the inner wall of the duct needs to be polished or coated with a low-friction coefficient coating, such as PTFE or a ceramic coating, to reduce airflow resistance. For metal ducts, laser welding or argon arc welding can be used to ensure smooth and even welds. For non-metallic ducts, materials with high surface hardness and wear resistance must be selected to prevent surface peeling and additional noise after long-term operation.
Targeted installation of silencers is crucial for reducing aerodynamic noise. The inlet and outlet noise of a centrifugal fan square is primarily mid-to-high frequency, which can be suppressed using resistive silencers. Resistive silencers convert sound energy into heat energy through porous sound-absorbing materials (such as glass wool or mineral wool), thereby reducing noise propagation. The silencer type should be selected based on the fan flow rate and noise frequency during the design phase. For example, plate silencers are suitable for high-frequency noise, while honeycomb silencers are more effective for mid-frequency noise. Furthermore, incorporating guide vanes inside the silencer can prevent airflow from directly impacting the sound-absorbing material, ensuring noise reduction while minimizing pressure loss.
Improved volute structure can significantly reduce rotational noise. If the gap between the impeller outlet and the volute in a centrifugal fan square is too small or its shape is unreasonable, it can cause periodic airflow impacts on the volute, generating high-frequency pulse noise. Optimization can employ an inclined volute design, where the edge of the volute forms an angle with the impeller's rotation direction, reducing the area affected by in-phase pulsating aerodynamic forces and thus lowering radiated noise. Simultaneously, appropriately increasing the radius of the volute's tip can mitigate the direct impact of airflow on the volute, further suppressing vortex noise.
Improving the matching between the impeller and the duct requires starting with aerodynamic design. The shape, number, and installation angle of the centrifugal fan square impeller blades must be precisely matched to the duct dimensions to avoid vortices caused by excessively narrow or wide airflow channels. For example, using a swept-back twisted blade design can reduce the impeller inlet velocity and increase the deceleration degree, reducing airflow separation caused by excessively rapid duct expansion; while appropriately tilting the outlet blades forward can guide the airflow out smoothly, preventing the formation of vortex embryos. Furthermore, numerical simulation (CFD) analysis of the flow field between the impeller and the duct can predict noise hotspots in advance, providing a basis for structural optimization.
The optimization of the airflow channel in a centrifugal fan square aims to reduce turbulence, minimize friction, and suppress resonance. This is achieved through a comprehensive approach, including smooth shape transitions, optimized flow guide configurations, surface treatments, installation of silencers, improvements to the volute structure, and impeller matching optimization. These optimizations not only enhance the fan's operational stability but also extend its lifespan, meeting the low-noise environment requirements of both industrial and residential applications.
