Reversible flow fan

1. A reversible flow fan comprising:

an impeller that includes blade portions; and

a set of curved portions disposed on surfaces on either one of rear or front edge sides of each of the blade portions in a rotation direction of the impeller, wherein

each of the curved portions is convexly curved from a center of the impeller toward directions of outer peripheral portions of the blade portions in airflow directions during a rotation of the impeller,

the curved portion has an inflection point as a position where a curvature of the curved portion varies,

the inflection point is positioned on a position apart from the center of the impeller by 70% to 90% of a length from the center of the impeller to the outer peripheral portion of the blade portion,

an inclined angle of the curved portion in a direction of the impeller center with respect to the inflection point is in a range of −5° to +5°, and

an inclined angle of the curved portion in a direction of the outer peripheral portion of the impeller with respect to the inflection point is in a range of +15° to +30°.

2. The reversible flow fan according to claim 1 , wherein

each of the curved portions is disposed on surfaces on the rear edge sides of the blade portions in the rotation direction of the impeller.

3. The reversible flow fan according to claim 1 , wherein

each of the curved portions is disposed on surfaces on the front edge sides of the blade portions in the rotation direction of the impeller.

4. The reversible flow fan according to claim 3 , further comprising:

rear-edge curved portions disposed on surfaces on rear edge sides of the blade portions in the rotation direction of the impeller, wherein

the rear-edge curved portions are convexly curved from the center of the impeller toward the directions of outer peripheral portions of the blade portions in the airflow directions during the reverse rotation of the impeller.