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The cause of the cooling fan rotating stall is analysed

by:TOCH     2021-01-27
The working principle of the cooling fan is implemented according to the energy conversion, namely: the electrical energy to electromagnetic energy, mechanical energy to kinetic energy. The circuit principle generally divided into a variety of forms, the circuit is different, the performance of the cooling fan will have difference.

to prevent cooling fan fault cause unnecessary loss of accident, and will be modified by design. Thus get rid of the criticism to fundamentally to changes in the nature.

the formation of a cooling fan rotating stall, a cooling fan impeller structure and size are designed according to the rated air volume, when a cooling fan when he worked in a normal air volume, the direction of the gas into the impeller and blade air import installation Angle is consistent, gas can smoothly enter the impeller, when the gas flow in the impeller is less than the rated flow, the radial velocity of gas into the impeller is reduced, the direction of the relative velocity of gas flow into the impeller Angle is reduced, and therefore is not consistent with blade inlet installation Angle. Cooling fan blade in the process of machining and installation, for various reasons make the blade can't be exactly the same shape and installation Angle. Therefore, when the operation condition change and make the direction of flow deviation occurs, in each blade inlet Angle of attack is impossible to exactly the same. If a leaf inlet attack Angle reaches the critical value, the first on the blade stall occurs, not all blade stall occurred at the same time, this kind of phenomenon continues, the stall caused by blockage area along with the impeller rotating in opposite directions, namely so-called 'rotating stall' phenomenon. Cooling fan into the unstable running condition area, within the impeller will produce one to a number of rotating stall area. Leaves each after a stall zone is an exciting force, which can make the blade to produce resonance. At this time, the dynamic stress of blade increase, may cause of blade fracture, so from the perspective of the absolute reference frame of impeller outside, stall area or along the impeller rotation direction, causing mechanism of rotating stall, rotating stall in impeller pressure fluctuation of the excitation rotor abnormal vibration exciting force, the size of the exciting force related to the size of the gas molecular weight, they are proportional to the relationship, the larger the molecular weight, the greater the exciting force.

the rotor frequency of rotating stall: when a cooling fan running, is the direction of the impeller with the direction of the rotor is consistent, the direction of flow when an exception occurs, the abnormal vibration of the rotor. So this is also the cause of a cooling fan rotating stall.
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