| CPC F03D 3/061 (2013.01) [F03D 9/25 (2016.05)] | 9 Claims |
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1. A rotary blade provided rotatably about a rotation axis and configured to receive a fluid, the rotary blade comprising:
a front blade surface parallel to the rotation axis and curved so as to protrude frontward in a rotation direction; and
a rear blade surface located on a back side of the front blade surface, the rear blade surface being parallel to the rotation axis and curved so as to be concave frontward in the rotation direction, the rear blade surface having a smaller curve depth than the front blade surface, wherein
in a plan view perpendicular to the rotation axis, an end of the front blade surface on a side far from the rotation axis is defined as an outer end, and an end thereof on a side close to the rotation axis is defined as an inner end,
the front blade surface includes
a first curved surface forming a part far from the rotation axis and formed frontward in the rotation direction from the outer end, and
a second curved surface forming a part close to the rotation axis and formed rearward in the rotation direction from a side opposite to the outer end of the first curved surface, so as to connect to the inner end, a surface length of the second curved surface in the plan view being smaller than that of the first curved surface,
a recess is formed on the first curved surface,
a part of the first curved surface where the recess is not formed is defined as a main surface,
the recess includes a first inner surface forming a stepped portion facing rearward in the rotation direction, and a second inner surface formed rearward in the rotation direction from an end in a recessed direction of the first inner surface and connecting to the outer end or the main surface,
a plane obtained by extending a plane having the same curvature as a curvature of the main surface at a boundary portion between the main surface and the first inner surface toward the recess side from the boundary portion is defined as a virtual curved plane,
as seen in a cross-section perpendicular to the rotation axis, a slope angle of the first inner surface is defined as
an angle between an extended line obtained by extending a tangent of the main surface at the boundary portion between the main surface and the first inner surface outward from the boundary portion, and a tangent of the first inner surface at the boundary portion, or
an angle between a tangent of the virtual curved plane at a boundary portion between the virtual curved plane and the first inner surface, and a tangent of the first inner surface at the boundary portion,
as seen in the cross-section perpendicular to the rotation axis, a slope angle of the second inner surface is defined as
an angle between an extended line obtained by extending a tangent of the second inner surface at a boundary portion between the second inner surface and the main surface outward from the boundary portion, and a tangent of the main surface of the boundary portion, or
an angle between a tangent of the virtual curved plane at a boundary portion between the virtual curved plane and the second inner surface, and a tangent of the second inner surface at the boundary portion, and
the slope angle of the second inner surface is smaller than the slope angle of the first inner surface,
wherein as seen in a cross-section perpendicular to the rotation axis, an angle between the first inner surface and the second inner surface is an acute angle.
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