Turbofan

A turbofan comprising:

• a shroud which has a suction inlet that is configured to suction air;
• a main plate which is located on a side of the shroud in an axial direction of a rotational axis;
• and
• a plurality of blades which are located between the shroud and the main plate and are arranged one after another around the rotational axis, wherein:
• each of the plurality of blades has:
• a thick wall portion which has a plate thickness that is relatively large, wherein the thick wall portion is located adjacent to a leading edge of the blade;
• a thin wall portion which has a plate thickness that is smaller than the plate thickness of the thick wall portion, wherein the thin wall portion is located on a side of the thick wall portion where a trailing edge of the blade is placed;
• and
• a stepped portion which is formed between the thick wall portion and the thin wall portion, wherein a plate thickness of the stepped portion is progressively decreased toward a positive pressure surface of the blade in a direction that is directed from the thick wall portion toward the thin wall portion;
• in a cross-section of each of the plurality of blades that is perpendicular to the rotational axis, a first curved surface forms a negative pressure surface of the thick wall portion and is arcuate, and a second curved surface forms a negative pressure surface of the thin wall portion and is arcuate while the second curved surface is located on a side of the first curved surface where the positive pressure surface of the blade is placed, and a negative pressure surface of the stepped portion connects between the first curved surface and the second curved surface;
• the leading edge of each of the plurality of blades is located on a radially inner side of an inner diameter of the suction inlet of the shroud;
• and
• when a blade length of each of the plurality of blades is equally divided into three parts, the stepped portion is located only at a center part that is centered among the three parts.