Avoiding resonance between the modal frequency and the excitation frequency of a closed impeller pneumatic component requires a systematic solution encompassing multiple dimensions, including design, materials, manufacturing, and operation and maintenance. The key approach is to adjust the impeller's natural frequency or alter the excitation force characteristics to keep the frequency difference between the two frequencies above a safe threshold, thereby preventing destructive vibration caused by energy coupling.
During the design phase, modal analysis is required to optimize the impeller's structural parameters. The closed impeller's natural frequency is determined by the material's elastic modulus, geometric dimensions, and boundary conditions, with the blade's bending and torsional vibration modes being key control targets. For example, adjusting the blade thickness distribution or the cover-side curvature can alter the stiffness matrix, thereby increasing the natural frequency. For rotating impellers, centrifugal forces significantly increase the dynamic frequency. Therefore, dynamic frequency coefficient corrections must be incorporated into static frequency calculations to ensure that the modal frequency remains above the excitation frequency even at high rotation speeds. Furthermore, using coprime numbers to design the number of impeller and stator blades can disperse the energy of the closed impeller's pass-through frequency, preventing the periodic excitation force from being concentrated in a specific mode.
Material selection and surface treatment have a decisive influence on damping characteristics. Internal material resistance is the core mechanism for dissipating vibration energy. Non-metallic or composite materials exhibit significantly higher attenuation rates than metals, but this requires a trade-off between fatigue strength and fracture toughness. For metal impellers, applying hard coatings such as tungsten carbide not only improves wear resistance but also enhances gas damping by increasing surface roughness, further attenuating high-frequency vibrations. The vibration damping structure at the blade root connection is also crucial. Active pins, bosses, or dovetail grooves can dissipate energy through dry friction. Blade bosses are the mainstream choice for long blades in high-flow compressors due to their excellent vibration damping and simple manufacturing process.
Manufacturing accuracy and assembly processes directly impact the actual modal parameters of the impeller. Blade manufacturing errors or improper installation can reduce blade root connection rigidity, resulting in a decrease in natural frequency. For example, the presence of a root gap can extend vibration to the rim, increasing the mass involved in vibration and thus reducing the natural frequency. Therefore, strict control of blade manufacturing tolerances is crucial, and dynamic balancing is required to calibrate the impeller mass distribution to avoid additional excitation forces caused by unbalanced mass. During assembly, ensure the equipment is well secured to minimize vibration propagation paths. Damping materials or vibration absorbers should be used to isolate external vibration sources.
Dynamic monitoring and parameter adjustment during operation and maintenance are the final line of defense against resonance. Accelerometers placed at key locations on the closed impeller can collect vibration signals in real time, extract frequency domain features, and use the admittance circle method to identify modal frequencies and vibration modes. When the modal frequency approaches the excitation frequency, the excitation force frequency can be adjusted by adjusting the equipment's operating speed or modifying airflow parameters (such as pressure and velocity distribution). For equipment operating under variable speed conditions, a resonant speed map should be established to ensure that the operating speed stays within a certain range of the resonance zone. Regular inspections should be conducted for blade fatigue damage, and worn parts should be replaced promptly to maintain modal parameter stability.
Resonance avoidance in closed impellers of pneumatic components is essentially a dynamic management of frequency safety margins. From modal optimization in the design phase to real-time monitoring during operation, every step must be focused on reducing vibration energy coupling efficiency. Through collaborative innovation in structure, materials, and processes, a comprehensive vibration safety protection system covering the entire lifecycle should be established.
