The reason of the cooling fan rotating stall.

The working principle of the cooling fan is implemented according to the energy conversion, namely: the electrical energy → electromagnetic energy→mechanical energy → 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.

In order to avoid cooling fan is break down by accident and cause unnecessary loss, 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 is working in a normal air volume, the direction of the gas into the impeller shoud be accordance with blade air import installation Angle , gas can smoothly enter into 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 will accurs stall on this blade,will not stall for all blade at the same time, this kind of phenomenon continues,blockage area caused by stalling will be proceed along with the opposite directions of impeller rotating, 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. Each time when blade via a stall zone will Under the effect of an exciting vibration 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, pressure surge happend in impeller when rotating stall is the exciting force to motivate rotor occurs abnormal vibration,the size of the exciting force related to the size of the gas molecular weight, they are proportional, the larger of molecular weight, the greater of exciting force.

Frequency of rotor rotating stall: when a cooling fan running regular, the direction of the impeller is consistent with the direction of the rotor, when flow direction when occurs exception, rotor will abnormal vibration, so this is also the cause of a cooling fan rotating stall.