How can the noise generated by air‑suspended blowers be addressed?

I. Introduction: Why Should Air‑Suspended Fans Still Be Subject to Noise Considerations?

Air‑suspended blowers achieve contactless rotor operation through air‑bearing technology, eliminating the mechanical friction noise typical of conventional Roots blowers; at a distance of 1 meter during normal operation… Noise Typically, noise levels are kept between 75 and 80 dB, representing a reduction of 20 to 40 dB compared with conventional Roots blowers (100–112 dB). However, in practical engineering applications, the noise issues associated with air‑suspension blowers have not been entirely eliminated: aerodynamic noise, structure-borne vibration transmission, duct resonance, and surge‑induced whining under abnormal operating conditions persist. Particularly in scenarios involving multiple units operating in parallel or near residential areas, noise control remains a significant engineering challenge.

This paper systematically presents solutions for mitigating noise in air‑suspension blowers, examining four key dimensions: analysis of noise source mechanisms, control at the source, interruption of the propagation path, and AI‑based intelligent noise reduction.

II. Noise Source Mechanism: Clarifying the Origin of the “Noise”

The noise of an air‑suspension blower is primarily composed of the following three categories:

Aerodynamic noise (accounts for the largest share)

• Impeller rotational noise: The blades periodically cut through the air, generating discrete-frequency rotational noise—namely, the “blade passing frequency” and its harmonics.
• Turbulent noise: Flow separation and vortex formation within the impeller passages generate broadband, random noise.
• Intake and exhaust pulsation noise: Pulsations in the airflow arise at the inlet and outlet due to abrupt pressure changes, becoming particularly pronounced under variable operating conditions.

Structural Vibration Noise

• Vibration of the motor housing radiates noise into the air.
• Rigid connections such as bases and piping create “acoustic bridges,” transmitting vibrations into the building structure.

Abnormal operating condition noise

• Surge: When the system resistance is mismatched with the fan’s performance characteristics, the airflow undergoes periodic oscillations, generating low-frequency roaring noises.
• Air intake filter clogging: causes uneven air intake, unbalanced impeller forces, and a significant increase in noise.

Diagnostic techniques: High-frequency, sharp sounds typically indicate bearing abnormalities or turbulence; low-frequency pulsating sounds suggest surge or pipe resonance; and periodic knocking noises point to loose transmission components.

III. Source-Side Control: From “Symptomatic Treatment” to “Root-Cause Resolution”

Aerodynamic Optimization Design of the Impeller

This is the core approach to fundamentally reducing aerodynamic noise:

• Three-dimensional impeller design: By leveraging computational fluid dynamics (CFD) simulations to optimize blade curvature, inlet and outlet angles, and flow passage geometry, the airflow is maintained in attached flow within the impeller, thereby minimizing flow separation and vortex formation.
• Biomimetic blade design: Drawing inspiration from the serrated edge structure of owl feathers, a sawtooth‑like profile is incorporated at the blade tip, effectively suppressing tip vortices and reducing aerodynamic separation noise by approximately 3–5 dB.
• Aircraft aluminum alloy volute: The volute is manufactured using high-strength, lightweight materials and incorporates topology optimization—such as honeycomb structures and rib‑reinforced designs—to enhance structural stiffness and suppress resonance, thereby reducing mechanical vibration noise by 5–10 dB.

Acoustic flow guide device

Installing acoustically designed guide vanes or diffusers at the inlet and outlet of the fan can ensure a smooth, uniform airflow transition, reduce flow separation and vortex‑induced noise, and lower aerodynamic disturbance noise by approximately 5–10 dB, with particularly pronounced effects on high‑frequency noise.

Parameter Optimization of Magnetic and Air Bearings

By adjusting the bearing control parameters—stiffness and damping—we can avoid the system’s resonant frequencies and reduce noise generated by bearing vibrations. Dynamic tuning should be performed in conjunction with the fan’s actual operating conditions to achieve noise reduction without compromising bearing stability.

IV. Blocking Transmission Pathways: Systems Engineering Thinking

Whole-machine soundproof enclosure solution

This is currently the most widely used noise-reduction method in engineering practice:

Key Design Considerations:

• Rubber sealing strips are used at the seams of the enclosure to prevent sound leakage (sound-leakage points can reduce the overall noise‑reduction performance by more than 10 dB).
• The observation window is made of double-layer insulated tempered glass, with a sound insulation rating of 30–40 dB.
• Install a resistive silencer at the air inlet and outlet (with a length of ≥1 m) to ensure that noise is attenuated by 15–20 dB as the airflow passes through.
• The temperature rise inside the enclosure is kept within 10°C; if necessary, a low-noise axial fan can be installed to assist with heat dissipation.

Noise Reduction in Piping Systems

• Impedance-combined silencer: The resistive section attenuates high-frequency noise, while the reactive sections (expansion chambers and resonant cavities) reduce mid- and low-frequency noise; the overall sound reduction can reach 15–30 dB.
• Pipe sound‑insulation wrapping: an inner layer of 30–50 mm acoustic foam, topped by an outer layer of 1–2 mm sound‑proofing felt; additional flow‑deflecting vanes are installed at bends and valves to reduce eddy‑current noise.
• Flexible connection: The inlet and outlet pipelines shall be connected using silicone hoses or metal corrugated hoses with a length of ≥300 mm to prevent rigid vibration transmission.
• Elastic hangers: Install vibration‑isolating supports at intervals of 1.5 to 2 meters, and provide a minimum 50 mm gap at pipe penetrations through walls, which shall be filled with elastic sealing material.

Acoustic Renovation of the Server Room

• Wall sound absorption: Install a metal perforated panel with a perforation rate of ≥20% together with 50–100 mm of sound-absorbing cotton; the mid‑ to high‑frequency sound absorption coefficient can reach 0.6–0.8.
• Floating floor: 50 mm rubber vibration-isolating pad + 100–150 mm reinforced concrete layer, reducing low-frequency vibration noise by 15–20 dB.
• Reverberation Time Control: Use acoustic absorbers to keep the machine room’s reverberation time within 1.5 to 2.0 seconds.

V. AI Empowerment: Cutting-Edge Technologies for Intelligent Noise Reduction

Active Noise Cancellation (ANC) system

Drawing on the principles of consumer‑grade noise‑cancelling headphones, a microphone array is deployed inside the sound enclosure or at critical locations within the machine room to capture noise signals. A controller then generates, in real time, anti‑phase counter‑waves, which are emitted through speakers to cancel out the original noise. This technology is particularly effective against low‑frequency, narrowband noise—such as rotational speed frequencies and their harmonics—reducing noise at specific frequencies by 10 to 15 dB.

AI-Adaptive Noise Control

Compared with the fixed-parameter control of traditional ANC, an AI‑driven adaptive noise‑cancellation system can:

• Real-time spectral analysis: Using deep learning algorithms, the operating noise of wind turbines is decomposed into its spectral components in real time, enabling identification of the dominant noise sources and their origins.
• Dynamic parameter optimization: Automatically adjusts the ANC system’s anti-phase parameters in response to operating condition changes—such as load fluctuations and speed variations—to maintain optimal noise cancellation.
• Predictive Maintenance: By integrating vibration sensor data and leveraging machine learning models, this approach predicts abnormal conditions such as bearing wear and impeller fouling, providing early warnings before noise levels deteriorate.

Variable-Speed Intelligent Control and Multi-Machine Coordination

• Variable-speed control: Soft start and smooth speed adjustment are achieved via a variable-frequency drive, avoiding operation within resonance‑induced speed ranges; under light load, noise levels can be reduced by approximately 5–8 dB.
• Multi-fan collaborative noise reduction: When multiple fans operate in parallel, the AI control system coordinates their start‑stop sequences and speed phases to prevent noise interference, reducing the overall noise level of the fan array by 3–5 dB.

Acoustic Simulation and Digital Twin

By coupling computational fluid dynamics (CFD) with acoustic finite element analysis (FEA), it is possible to predict fan noise distribution during the design phase and perform targeted optimization of structural parameters such as impeller curvature and volute geometry. Combined with digital twin technology, this approach enables simulation of noise behavior under various operating conditions in a virtual environment, significantly reducing post‑design retrofitting costs.

Acoustic Metamaterials (Cutting-Edge Research Area)

Recent research indicates that applying acoustic metamaterials to wind turbine noise reduction can achieve anomalous refraction and absorption of specific-frequency sound waves through artificially engineered subwavelength structures. Experimental results show that, without compromising airflow velocity, acoustic metamaterial structures can reduce aerodynamic noise by approximately 4.9 dB, demonstrating significant potential for noise control in wind turbines.

VI. Overall Noise Reduction Performance and Implementation Recommendations

Comparison of Typical Noise Reduction Performance

Implementation Recommendations

1. Diagnosis before remediation: Use a sound level meter to measure noise levels at each measurement point and generate spectrum plots, thereby identifying the primary noise components and their frequency distribution and avoiding one-size-fits-all mitigation approaches.
2. Source‑level prioritization: By addressing noise at its source—such as impeller design and bearing parameters—the approach delivers the most lasting results without compromising equipment performance.
3. Balancing heat dissipation and maintenance: The soundproof enclosure shall be equipped with a removable access door (≥800 mm × 1200 mm) to enable regular monitoring of the internal temperature, ensuring that the motor’s temperature rise remains within the permissible limits.
4. Introducing AI‑powered monitoring: Deploying an intelligent surveillance system to enable real-time noise monitoring, anomaly alerts, and adaptive control, shifting from reactive mitigation to proactive management.

VII. Conclusion

Noise control for air‑suspended blowers has evolved from the traditional passive approach of “adding sound enclosures and wrapping with sound‑absorbing cotton” to a multi‑layered systems engineering that integrates source‑level optimization, propagation‑path mitigation, and AI‑driven intelligent control. As cutting‑edge technologies such as acoustic metamaterials, digital twins, and adaptive active noise cancellation continue to mature, future blower noise reduction will advance toward greater intelligence, higher precision, and lower costs—enabling industrial equipment to operate efficiently while truly coexisting harmoniously with the environment.