Centrifugal fan

1. A centrifugal fan comprising:

an impeller;

an upper casing that is disposed above the impeller;

a lower casing that is disposed below the impeller;

an outlet port that is provided between the upper casing and the lower casing and from which an air suctioned by rotation of the impeller is discharged,

wherein the upper casing is provided with a flange that protrudes in an outer radial direction of the impeller from an outer circumferential edge of the upper casing,

wherein the flange partially covers the outlet port when viewed from a direction perpendicular to a rotation axis of the impeller, and

wherein the flange is provided with a plurality of protruding streaks that protrude in a direction along the rotation axis of the impeller from a surface of the flange facing the lower casing.

2. The centrifugal fan according to claim 1 ,

wherein the flange is formed by integral molding with the upper casing.

3. The centrifugal fan according to claim 1 ,

wherein lengths of the protruding streaks in the radial direction of the impeller are set in accordance with a length of the flange protruding from the outer circumferential edge of the lower casing at positions at which the protruding streaks are provided.

4. The centrifugal fan according to claim 1 ,

wherein the impeller is provided with a hub, a plurality of blades, and an annular shroud,

wherein the blades extend in a direction along the rotation axis of the impeller from the annular shroud and is connected to the hub on an inner circumference side of the blades, and

wherein the annular shroud is accommodated in a recessed portion that is formed to be concave upward in the upper casing.

5. The centrifugal fan according to claim 1 ,

wherein a length, in a direction along the rotation axis of the impeller, of a part of the outlet port which is not covered with the flange when viewed from the direction perpendicular to the rotation axis is set to be less than 5.6 mm.

6. The centrifugal fan according to claim 1 ,

wherein the lower casing is formed to have a substantially square shape when viewed from a bottom side.

7. The centrifugal fan according to claim 1 ,

wherein the upper casing and the lower casing are attached with each other to configure a combined casing that accommodates the impeller, and

wherein the combined casing is formed to have a rectangular parallelepiped shape as a whole except for the flange.

8. The centrifugal fan according to claim 1 ,

wherein the flange has a part extending outward from the upper casing in an arced shape.

9. The centrifugal fan according to claim 1 ,

wherein the flange has a part extending downward and partially covering the outlet port.

10. The centrifugal fan according to claim 1 ,

wherein the flange is formed as a member separated from the upper casing and is attached to the upper casing.