220V AC Cooling Fan impeller modal

"220V AC Cooling Fan" impeller modal vibration form mainly by four blades week to various combinations of vibration, resulting mainly for this reason is forward-swept blade stiffness is much smaller than the hub stiffness that blade "soft", and the hub of "hard "; leaf blade low frequency vibration modes mainly dominated overall torsional pendulum, but mainly in the high-frequency wave-based blade bending. From the impact of "220V AC Cooling Fan" think big in terms of noise before the sixth-order mode effects, because of its place as a result of the flow field has a greater impact, resulting in a change in the angle of attack of the blades into the air, thus forming the blade surface fluctuations in the lift, the most serious cases will have galloping, have a greater aerodynamic noise and great efficiency. Understand the reasons "220V AC Cooling Fan" axial fan noise generation. I believe we can use the process of attention.