Centrifugal fan

Abstract

Each of blades of a centrifugal fan includes a primary wing section that has a trailing edge which is parallel to a central axis of rotation, a leading edge end section which is parallel to the central axis of rotation, and a thickness gradually growing thinner toward the trailing edge and the leading edge end section; and an auxiliary wing section that extends from the leading edge end section of the primary wing section toward the interior of the centrifugal fan. The auxiliary wing section has a length from the leading edge end section of the primary wing section to the leading edge of the auxiliary wing section that is greater at a side of a support section than at an intake side when viewed in a direction of the central axis of rotation, and a constant thickness across the entire area of the auxiliary wing section.

Claims

1. A centrifugal fan in which a rotation shaft is attached to a mounting section to rotate in a predetermined direction so that air taken in from a front of a support section is blown out radially, the centrifugal fan comprising: the support section having a circular shape viewed from the front; a plurality of blades arranged in an annular shape along an outer circumference of the support section; and the mounting section provided at a center of the support section, wherein each of the blades includes: a primary wing section that has a trailing edge which is parallel to a central axis of rotation of the rotation shaft, a leading edge end section which is parallel to the central axis of rotation, and a thickness gradually growing thinner toward the trailing edge and the leading edge end section; and an auxiliary wing section that extends from the leading edge end section of the primary wing section toward the interior of the centrifugal fan, and wherein the auxiliary wing section has a length from the leading edge end section of the primary wing section to a leading edge of the auxiliary wing section that is greater at a side of the support section than at an intake side when viewed in a direction of the central axis of rotation, and wherein the auxiliary wing section has a constant thickness across the entire area of the auxiliary wing section.

2. The centrifugal fan according to claim 1, wherein a pressure surface of the auxiliary wing section and a pressure surface of the primary wing section are smoothly connected to each other.

3. The centrifugal fan according to claim 2, wherein the auxiliary wing section extends in a tangential direction at a position of the leading edge end section on the pressure surface of the primary wing section.

4. The centrifugal fan according to claim 1, wherein the auxiliary wing section when viewed from the front is linearly formed from the leading edge end section of the primary wing section to the leading edge of the auxiliary wing section.

5. The centrifugal fan according to claim 1, wherein the leading edge of the auxiliary wing section when viewed from the side has a linear shape from the intake side in the direction of the central axis of rotation toward the side of the support section.

6. The centrifugal fan according to claim 5, wherein D1/D2 which is a ratio obtained by dividing an intake-side leading edge diameter D1 which is defined by the leading edge at the linear portion of each of the blades and is a diameter at the position of the intake side in the direction of the central axis of rotation by a trailing edge diameter D2 which is a diameter defined by the trailing edge of each of the blades satisfies the following relational equation (1), and D1/D2 which is a ratio obtained by dividing a support section-side leading edge diameter D1 which is defined by the leading edge at the linear portion of each of the blades and is a diameter at a position of the side of the support section in the direction of the central axis of rotation by the trailing edge diameter D2 satisfies the following relational equation (2):
0.75D1/D20.90(1) and
0.65D1/D20.75(2)

7. The centrifugal fan according to claim 1, wherein an angle formed by a tangent at the leading edge end section of an inscribed circle of the leading edge end section and a tangent at the leading edge end section of the pressure surface of the primary wing section is 65 or more and 75 or less, and an angle formed by a tangent at the trailing edge of a circumscribed circle of the trailing edge and a tangent at the trailing edge of the pressure surface of the primary wing section is 0 or more and 15 or less.

8. The centrifugal fan according to claim 1, wherein the leading edge of the auxiliary wing section when viewed from the side has a curved shape from the intake side in the direction of the central axis of rotation toward the support section.

9. The centrifugal fan according to claim 1, further comprising: an annular shroud configured to fix the trailing edges of the blades at tip sides of the blades.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a front view of a centrifugal fan A according to an embodiment of the present invention.

(2) FIG. 1B is a cross-sectional view taken along line X-X of FIG. 1A, showing a view of the centrifugal fan A.

(3) FIG. 2 is an enlarged view of a portion Y of FIG. 1A, showing a view of blades 2 of the centrifugal fan A.

(4) FIG. 3A is a characteristic diagram showing performance of the centrifugal fan A and a bar graph obtained by comparing noise and air blowing efficiency with those of the conventional fan.

(5) FIG. 3B is a characteristic diagram showing the performance of the centrifugal fan A and a graph showing an influence of a ratio (D1/D2) on noise and air blowing efficiency.

(6) FIG. 3C is a characteristic diagram showing the performance of the centrifugal fan A and a graph showing an influence of a ratio (D1/D2) on noise and air blowing efficiency.

(7) FIG. 3D is a characteristic diagram showing the performance of the centrifugal fan A and a graph showing an influence of an inlet angle on noise and air blowing efficiency.

(8) FIG. 3E is a characteristic diagram showing the performance of the centrifugal fan A and a graph showing an influence of an exit angle on noise and air blowing efficiency.

(9) FIG. 4 is a view showing a centrifugal fan B which is a modified example of the centrifugal fan A, showing a front view corresponding to FIG. 1A.

(10) FIG. 5 is a view showing another modified example of the centrifugal fan A, showing an enlarged cross-sectional view of a portion corresponding to a portion Z of FIG. 1B.

(11) FIG. 6 is a view showing yet another modified example of the aspect shown in FIG. 5, showing a partially enlarged view corresponding to a portion C of FIG. 5.

(12) FIG. 7 is a partial plan view of FIG. 6 taken along an arrow D-D of FIG. 5.

DESCRIPTION OF EMBODIMENTS

(13) Hereinafter, an embodiment of the present invention and modified examples thereof will be described with reference to the drawings.

(14) As shown in FIGS. 1A and 1B, a centrifugal fan A according to the embodiment is a rotating body having a substantially cylindrical appearance and configured to rotate about a central axis of rotation L (a central axis of a rotation shaft S of a motor (not shown)) counterclockwise. As indicated by an arrow R in FIG. 1A, the centrifugal fan A rotates counterclockwise to suction air F from above (an intake inlet) and radially discharge it in an outer circumferential direction (a direction substantially perpendicular to the central axis of rotation L).

(15) The centrifugal fan A includes a support section 1, a plurality of blades 2, a shroud 3, and a mounting section 4 as main constituent elements and is a resin molded product formed using a mold using, for example, polypropylene as a raw material.

(16) The support section 1 has a circular shape viewed from the front as shown in FIG. 1A and is a substantially conical shape (a dome shape) whose longitudinal cross-sectional shape gradually extends backward from above (the intake inlet) in the drawing from a center (the central axis of rotation L) toward an outer circumference as shown in FIG. 1B. As shown in FIG. 1B, the support section 1 of such a shape supports the plurality of blades 2 and guides the air F suctioned from above (the intake inlet) in an outer circumferential direction. In other words, when the centrifugal fan A rotates in an arrow R direction of FIG. 1A, the air F is taken in substantially in parallel with the central axis of rotation L, a flow direction of the air F is bent along an inclined surface (a guide surface 1a to be described below) of the support section 1, and the air is discharged outside of the centrifugal fan A in the outer circumferential direction as shown in FIG. 1B.

(17) An upper surface (a surface) configured to suction the air F in the support section 1 is the guide surface 1a configured to guide the air F. As shown in FIG. 1B, the guide surface 1a is a dome shape which gradually extends backward away from the central axis of rotation L (an angle of inclination is steep). On the other hand, a rear surface of the guide surface 1a of the support section 1 is a recessed surface.

(18) The blades 2 are provided at regular intervals along an outer circumference of the support section 1 when viewed from the front shown in FIG. 1A and are long elements extending in a direction in parallel with the central axis of rotation L when viewed in a cross section shown in FIG. 1B. In other words, the blades 2 are arranged in an annular shape at regular angular intervals at positions a constant distance away from the central axis of rotation L in a radial direction. The number of blades 2 is, for example, 41 in the embodiment shown in FIG. 1A.

(19) As shown in FIGS. 1A to 2, each of the blades 2 includes two portions, i.e., a primary wing section 2a and an auxiliary wing section 2b. The primary wing section 2a includes a trailing edge 2c which is parallel to the central axis of rotation L and a leading edge end section 2d which is similarly parallel to the central axis of rotation L.

(20) The primary wing section 2a has a thickness which gradually grows thinner toward the trailing edge 2c and the leading edge end section 2d and a shape which is gently curved as a whole to protrude in a direction opposite to a rotation direction. In other words, the primary wing section 2a has a front shape (a cross-sectional shape) where an intermediate part between the trailing edge 2c and the leading edge end section 2d which are parallel to each other gradually becomes thicker than the trailing edge 2c and the leading edge end section 2d as farther from the trailing edge 2c and the leading edge end section 2d.

(21) On the other hand, the auxiliary wing section 2b extends from the leading edge end section 2d of the primary wing section 2a toward the interior of the centrifugal fan A. In other words, the auxiliary wing section 2b is connected to the above-described leading edge end section 2d of the primary wing section 2a and extends in a tangential direction on a surface of a rotation direction side of the primary wing section 2a. To be more specific, the auxiliary wing section 2b linearly extends in the tangential direction at a position of the leading edge end section 2d on a pressure surface 2f which is the surface of the rotation direction side of the primary wing section 2a on a surface perpendicular to the central axis of rotation L as indicated by the dashed-dotted line in FIG. 2. Note that, in the primary wing section 2a, the above-described surface of the rotation direction side is a curved surface having constant curvature r as a whole.

(22) The auxiliary wing section 2b includes a leading edge 2e inclined with respect to the central axis of rotation L such that a downstream side (a lower side in FIG. 1B) of the air F is closer to the central axis of rotation L than an upstream side (an upper side in FIG. 1B) and has a thickness which is constant as a whole. In other words, the auxiliary wing section 2b has a length from the leading edge end section 2d of the primary wing section 2a to the leading edge 2e of the auxiliary wing section 2b that is greater at a side of the support section 1 than at an intake side and a constant thickness across the entire area of the auxiliary wing section 2b when viewed in a direction of the central axis of rotation L. To be more specific, the auxiliary wing section 2b has a shape in which a width w1 in a direction perpendicular to the central axis of rotation L (a radial direction) toward a suction direction of the air F (downward in the drawing) gradually spreads as shown in FIG. 1B. Note that the leading edge 2e has a linear shape as shown FIG. 1B.

(23) The surface of the rotation direction side of the primary wing section 2a and the auxiliary wing section 2b in each of the blades 2 is the pressure surface 2f whose pressure is greater than normal pressure when the centrifugal fan A rotates counterclockwise, while a surface opposite to the rotation direction is a suction surface 2g whose pressure is lower than the normal pressure. As shown in FIG. 2, the pressure surface 2f of the auxiliary wing section 2b and the pressure surface 2f of the primary wing section 2a are smoothly connected to each other. The auxiliary wing section 2b extends in the tangential direction at the position of the leading edge end section 2d on the pressure surface 2f of the primary wing section 2a. To be more specific, the auxiliary wing section 2b when viewed from the front is linearly formed from the leading edge end section 2d of the primary wing section 2a to the leading edge 2e of the auxiliary wing section 2b. The leading edge 2e of the auxiliary wing section 2b when viewed from the side as shown in FIG. 1B has a linear shape from the intake side in the direction of the central axis of rotation L toward the support section 1.

(24) As shown in FIG. 1B, an end of the primary wing section 2a of the intake side of the air F (the upper side in the drawing) in each of the blades 2 is a blade tip 2h perpendicular to the central axis of rotation L, while an end of the primary wing section 2a of a discharge side of the air F (the lower side in the drawing) is a blade rear end 2i similarly perpendicular to the central axis of rotation L.

(25) Each of the blades 2 including the primary wing section 2a and the auxiliary wing section 2b will be described in greater detail.

(26) First, a ratio (D1/D2) of a diameter defined by the leading edge 2e at a side of the blade tip 2h of each of the blades 2 (a tip leading edge diameter D1) and a diameter defined by the trailing edge 2c of each of the blades 2 (a trailing edge diameter D2) satisfies the following relational equation (3). In other words, D1/D2 which is a ratio obtained by dividing the intake-side leading edge diameter D1 which is defined by the leading edge 2e at a linear portion of each of the blades 2 and is a diameter at the position of the intake side in the direction of the central axis of rotation L by the trailing edge diameter D2 which is the diameter defined by the trailing edge 2c of each of the blades 2 satisfies the following relational equation (3). To be more specific, numerical values obtained by dividing a diameter at a position at which a distance dimension from the central axis of rotation L to the leading edge 2e is maximized (the tip leading edge diameter D1) by the diameter defined by the trailing edge 2c of the primary wing section 2a (the trailing edge diameter D2) are in a range of 0.75 to 0.90. Note that this range is more preferably 0.79 to 0.81 and most preferably 0.80.
0.75D1/D20.90(3)

(27) Also, D1/D2 which is a ratio obtained by dividing a support section-side leading edge diameter D1 which is defined by the leading edge 2e at the linear portion of each of the blades 2 and is a diameter at a position of the side of the support section 1 in the direction of the central axis of rotation L by the trailing edge diameter D2 satisfies the following relational equation (4). In other words, a ratio (D1/D2) of a diameter defined by the leading edge 2e at a side of the blade rear end 2i of each of the blades 2 (a rear end leading edge diameter D1) and the trailing edge diameter D2 satisfies the following relational equation (4). To be more specific, numerical values obtained by dividing a diameter at a position at which the distance dimension from the central axis of rotation L to the leading edge 2e is minimized (the tip leading edge diameter D1) by the trailing edge diameter D2 are in a range of 0.65 to 0.75. Note that this range is more preferably 0.69 to 0.72 and most preferably 0.71.
0.65D1/D20.75(4)

(28) Note that H/D2 which is a ratio obtained by dividing a length in parallel with the direction of the central axis of rotation L of each of the blades 2 (a wing length H) by the trailing edge diameter D2 is, for example, 0.4 to 0.5.

(29) As shown in FIG. 2, an angle formed by a tangent at the leading edge end section 2d of an inscribed circle of the leading edge end section 2d and a tangent at the above-described leading edge end section 2d of the surface of the rotation direction side of the primary wing section 2a, i.e., an inlet angle in each of the above-described blades 2 is an angle of 65 or more and 75 or less and more preferably 70. In other words, the inlet angle which is an angle formed by the inscribed circle coming into contact with the leading edge end section 2d with respect to the central axis of rotation L and the tangent at the position of the leading edge end section 2d of the pressure surface 2f of the primary wing section 2a is in a range of 65 to 75, and this range is more preferably 70.

(30) As shown in FIG. 2, an angle formed by a tangent at the trailing edge 2c of a circumscribed circle of the trailing edge 2c and a tangent at the trailing edge 2c of the surface of the rotation direction side of the primary wing section 2a, i.e., an exit angle in each of the above-described blades 2, is an angle of 0 or more and 15 or less, and more preferably 10. In other words, the exit angle which is an angle formed by the circumscribed circle of the trailing edge 2c and the tangent at the trailing edge 2c of the pressure surface 2f of the primary wing section 2a is in a range of 0 to 15, and this range is more preferably 10.

(31) As shown in FIG. 2, the trailing edge 2c has a pointed shape, i.e., a shape in which the pressure surface 2f comes into contact with the suction surface 2g at an acute angle when the centrifugal fan A is viewed from the front. On the other hand, the leading edge 2e is formed in a rounded shape, i.e., a shape in which the pressure surface 2f is connected to the suction surface 2g in a circular arc shape when the centrifugal fan A is viewed from the front as shown in FIG. 2.

(32) As shown in FIGS. 1A and 1B, a shroud 3 is connected to upper ends (tips) of the blades 2 arranged in the annular shape and has an annular shape that is slightly narrowed upward. The shroud 3 itself connects the upper ends (the tips) of the blades 2 to each other to reinforce a support state of the blades 2 connected to the support section 1 and define an inflow area (a flow path) of the air F flowing in from above in FIG. 1B. In other words, the shroud 3 has a shape in which the inflow area of the air F is slightly narrowed compared with a circular area defined by the trailing edge diameter D2. An upper end 3a of the shroud 3 is located above the blade tips 2h of the blades 2 as shown in FIG. 1B.

(33) The mounting section 4 is provided at the center of the support section 1 and is a portion for mounting the rotation shaft S of a driving apparatus (not shown) (e.g., a motor) configured to rotatably drive the centrifugal fan A. A mounting hole 4a used to insert the rotation shaft S is formed in the mounting section 4. The mounting section 4 protrudes upward from the upper end 3a of the shroud 3 as shown in FIG. 1B. In other words, the mounting section 4 protrudes upward from the blade tips 2h of the blades 2.

(34) Next, effects of the centrifugal fan A with such a constitution will be described in detail also with reference to FIGS. 3A to 3E.

(35) In the centrifugal fan A, the plurality of blades 2 arranged in the annular shape with a constant radius from the central axis of rotation L rotate counterclockwise so that the air F at the upper side in the drawing of the central axis of rotation L shown in FIG. 1B is suctioned and is blown out radially in the outer circumferential direction. In other words, the centrifugal fan A rotates about the central axis of rotation L so that the air at the upper side in the drawing is suctioned, a flow is formed, the air is fluidized, the air F passes through the inflow area (the flow path), the air is deflected, and the air is discharged in the outer circumferential direction.

(36) The centrifugal fan A of the embodiment includes the auxiliary wing section 2b of the shape in which the width of each of the blades 2 gradually spreads toward an opposite side (a lower side) to the suction direction of the air F in addition to the primary wing section 2a. In other words, in each of the blades 2 in the centrifugal fan A, a rear end side, i.e., a width of a discharge side of the air F (an extending width w2 from the leading edge 2e to the trailing edge 2c on the surface perpendicular to the central axis of rotation L), is gradually increased relative to a tip side, i.e., the intake side of the air F.

(37) According to the centrifugal fan A with the above constitution, for example, when an extending length of the blade tip 2h of each of the blades 2 is set to the same dimension as the conventional blade, the extending width w2 of each portion extending over the blade rear end 2i from the blade tip 2h of each of the blades 2 is gradually increased toward the blade rear end 2i compared with the conventional blade. As a result, as shown in FIG. 3A, operational sound (noise) occurring when the air F collides with the blade tips 2h of the blades 2 can be reduced by about 1 dB compared with the related art, and air blowing efficiency can be improved by about 2 to 3% compared with the related art. Note that one step on the vertical axis in the characteristic diagram of FIG. 3A indicates 1% with respect to air blowing efficiency (efficiency) and 1 dB with respect to operational sound (noise).

(38) According to the centrifugal fan A, since the tip leading edge diameter D1 and the rear end leading edge diameter D1 are set to satisfy the above-described relational expressions (3) and (4), improvement of air blowing efficiency and a decrease of operational sound can be optimized. Operational sound (noise) and air blowing efficiency exhibit a diametrical increase or decrease tendency with respect to the ratio (D1/D2) or the ratio (D1/D2) as shown in FIGS. 3B and 3C. In other words, the operational sound (noise) exhibits an increase or decrease tendency transferred from a decrease to an increase with respect to the ratio (D1/D2) or the ratio (D1/D2), but the air blowing efficiency exhibits an increase or decrease tendency transferred from an increase to a decrease with respect to the ratio (D1/D2) or the ratio (D1/D2).

(39) Therefore, the ratio (D1/D2) and the ratio (D1/D2) are set to ranges indicated by the relational equations (3) and (4), i.e., a relationship of the tip leading edge diameter D1 and the rear end leading edge diameter D1 are set to the ranges indicated by the relational equations (3) and (4) so that the air blowing efficiency can be improved to a greater level while the operational sound (noise) is suppressed to a lesser level as shown in FIGS. 3B and 3C. Note that one step on the vertical axes in the characteristic diagrams of FIGS. 3B and 3C indicates 1% with respect to maximum efficiency representing a ratio of air blowing efficiency to a predetermined reference value (the air blowing efficiency of a conventional product) and 1 dB with respect to minimum specific noise representing a ratio of operational sound (noise) to a predetermined reference value (the operational sound of a conventional product).

(40) According to the centrifugal fan A, the leading edge 2e of each of the blades 2 has an inclined linear shape. In other words, the extending width w2 from the leading edge 2e to the trailing edge 2c on the surface perpendicular to the central axis of rotation L is linearly increased. Thus, the operational sound can be effectively reduced compared with, for example, when the extending width w2 is increased stepwise. Note that a shape of the leading edge 2e configured to effectively reduce the operational sound is not limited to only a linear shape, but a constitution in which the leading edge 2e of the auxiliary wing section 2b when viewed from the side has a curved shape from the intake side in the direction of the central axis of rotation L toward the support section 1 can also be adopted. For example, as shown in FIG. 5, a leading edge 2e of a curved shape recessed gently in the suction direction of the air F can be adopted.

(41) According to the centrifugal fan A, since the inlet angle of each of the blades 2 is set to the angle of 65 or more and 75 or less, the maximum efficiency (the air blowing efficiency) can be improved to a greater level while the minimum specific noise (the operational sound) is suppressed to a lesser level as shown in FIG. 3D. Also, according to the centrifugal fan A, since the exit angle is set to the angle of 15 or less, the maximum efficiency (the air blowing efficiency) can be improved to a greater level while the minimum specific noise (the operational sound) is suppressed to a lesser level as shown in FIG. 3E.

(42) In other words, the inlet angle and the exit angle are set to the above-described ranges so that the occurrence of vortexes or the occurrence of separation of the air F from the surfaces of the blades 2 in the air F flowing between the blades 2 can be suppressed to the minimum. Thus, the noise caused by the vortexes or the separation of the air F from the blades 2 can be reduced. The energy loss caused by the vortexes or the separation of the air F from the blades 2 can also be suppressed to the minimum to improve the air blowing efficiency.

(43) Note that one step on the vertical axes in the characteristic diagrams of FIGS. 3D and 3E indicates 0.5% with respect to maximum efficiency representing a ratio of air blowing efficiency to a predetermined reference value and 0.5 dB with respect to minimum specific noise representing a ratio of operational sound (noise) to a predetermined reference value.

(44) Note that the present invention is not limited to only the embodiment, and for example, the following modified examples are considered.

(45) (1) The centrifugal fan A having the support section 1, the plurality of blades 2, the shroud 3, and the mounting section 4 as the main constituent elements has been described in the embodiment, but the present invention is not limited to only this constitution. Since the shape of the blades 2 have the long shapes extending in the direction which is parallel to the central axis of rotation L in the centrifugal fan A, the shroud 3 is provided at upper ends of the blades 2 to more firmly support the blades 2, but the shroud 3 can be omitted when the shapes of the blades 2 are different from those of the embodiment (e.g., when a length thereof is short).

(46) (2) The centrifugal fan A including the shroud 3 having a shape in which the inflow area of the air F is slightly narrowed compared with the circular area defined by the trailing edge diameter D2 has been described in the embodiment, but the present invention is not limited to only this constitution. For example, as shown in FIG. 4, a centrifugal fan B including an annular shroud 3 provided to connect trailing edges of the blades 2 at a blade tip side of the blades 2 may be adopted. The inflow area of the air is set to be substantially the same as the circular area defined by a trailing edge diameter in the shroud 3. In other words, recessions are provided at the upper portions of the blades 2 shown in FIG. 1B, and the annular shroud 3 that is narrowed to come into close contact with the recessions is integrally provided in the embodiment, but the blades 2 without the recessions are provided and the annular shroud 3 which is not narrowed is integrally provided to come into close contact with an upper outer circumferential side of the blades 2 in the modified example of FIG. 4.

(47) The centrifugal fan B including the shroud 3 is adopted to, for example, a relatively small centrifugal fan in which a ratio of a wing length and a trailing edge diameter of each of the blades 2 is set to a much larger value (e.g., 1 or more) than the above-described ratio (H/D2) of the centrifugal fan A.

(48) (3) The thickness of the auxiliary wing section 2b is set to a constant dimension across the entire area thereof in the embodiment and the modified examples, but is not limited to only this constitution. In addition, for example, a thickened reinforced section may be provided at a thickness of a root portion 2bx of the auxiliary wing section 2b as shown in FIGS. 6 and 7. In other words, the reinforced section in which the thickness of the root portion 2bx of the auxiliary wing section 2b which is a connected portion to the support section 1 is gradually increased to widen toward the end toward the guide surface 1a may be formed. When this reinforced section is provided at the root portion 2bx of the auxiliary wing section 2b, fixing strength of the blades 2 (2) to the support section 1 can be increased. Also, the mold used for injection molding of the centrifugal fan A (B) is easily manufactured, and it can also contribute to lower costs.

INDUSTRIAL APPLICABILITY

(49) According to the present invention, a centrifugal fan in which air blowing efficiency can be improved while an increase of operational sound is suppressed can be provided.

REFERENCE SIGNS LIST

(50) A, B Centrifugal fan 1 Support section 1a Guide surface 2 Blade 2a Primary wing section 2b Auxiliary wing section 2c Trailing edge 2d Leading edge end section 2e Leading edge 2f Pressure surface 2g Suction surface 2h Blade tips 2i Blade rear end 3 Shroud 4 Mounting section 4a Mounting hole D1 Tip leading edge diameter D1 Rear end leading edge diameter D2 Trailing edge diameter H Blade length L Central axis of rotation S Rotation shaft