When the fan is in normal condition, the angle of attack is very small (the direction of the air flow is opposite to that of the leaf blade). The airflow keeps the flow line around the wing blade. When the airflow and the blade inlet form a positive angle,
The blades of the fan are in the process of processing and installation, and for various reasons the blades can not have exactly the same shape and mounting angle.
The more the horn is greater than the critical value, the more serious the stall phenomenon, the greater the flow resistance of the fluid, so that the leaf barrier, while the fan pressure also will be rapidly reduced.
That is, α> 0, and the positive angle of attack exceeds a certain critical value, the flow condition on the back of the blade begins to deteriorate, the boundary layer is destroyed, and the eddy current area appears at the rear end of the blade, the so-called "stall" phenomenon.
Therefore, when the operating conditions change the flow direction of the deviation, the impulses in the various leaves can not be exactly the same.
