Diagonal fan

A diagonal fan, comprising:

• a frame comprising an inlet, an outlet, an accommodation space and a guiding wall, wherein the inlet and the outlet are disposed at two opposite sides of the frame, respectively, and in fluid communication with each other through the accommodation space;
• and
• an impeller accommodated within the accommodation space of the frame and comprising a hub, a cylindrical part, a conical section shell and a plurality of blades, wherein the cylindrical part is configured to accommodate a rotor,
• wherein the cylindrical part comprises a plurality of protrusion portions and a plurality of indentation portions disposed on an inner surface thereof, and the plurality of protrusion portions are abutted against an outer surface of a magnetic shell of the rotor.