BLADE FOR A LOW-NOISE INDUSTRIAL AXIAL FAN WITH TERMINAL MEMBER, INDUSTRIAL AXIAL FAN AND PROCESS FOR MANUFACTURING A BLADE OF AN INDUSTRIAL AXIAL FAN

Abstract

A blade for an industrial axial fan includes an extruded or pultruded airfoil, extending along a blade axis and having a leading edge, a trailing edge, a root side and a tip side, an intrados and an extrados. A terminal member is arranged to close the tip side and has a rounded front portion in a plan view at the leading edge and a rounded rear portion in a plan view between the front portion and the trailing edge.

Claims

1. A blade for an industrial axial fan comprising: an extruded or pultruded airfoil, extending along a blade axis and having a leading edge, a trailing edge, a root side, a tip side, an intrados and an extrados; and a terminal member arranged to close the tip side; wherein the terminal member has a rounded front portion in a plan view at the leading edge, and a rounded rear portion in a plan view between the front portion and the trailing edge.

2. The blade according to claim 1, wherein the terminal member has an outer face, an inner face opposite to the inner face and coupled to the airfoil and a maximum cord defined at the inner face.

3. The blade according to claim 2, wherein, in the radial direction, the front portion of the terminal member has a radial dimension ranging between 5% and 25% of the maximum cord.

4. The blade according to claim 2, wherein, in the tangential direction, the terminal member has a tangential dimension ranging between 3% and 25% of the maximum cord.

5. The blade according to claim 2, wherein the terminal member is tapered toward the outside in the direction of the blade axis.

6. The blade according to claim 5, wherein the terminal member has an intrados face, an extrados face, and a radially outer face and wherein the intrados face and the extrados face decline towards each other.

7. The blade according to claim 6, wherein the intrados face and the extrados face are connected to the radially outer face with respective rounded corners with respective bending radii ranging between 0.8% and 10% of the maximum cord.

8. The blade according to claim 7, wherein the terminal member has a radially inner face opposite the radially outer face and coupled to the airfoil and wherein the radially outer face has an area ranging between 40% and 80% of an area of the radially inner face.

9. The blade according to claim 2, wherein a maximum outer thickness of the terminal member to the outer face is at least 50% of a maximum inner thickness of the terminal member at the inner face.

10. The blade according to claim 1, comprising a rod, having a first end connected to the airfoil at an insertion point through the root side and a second end protruding from the airfoil for coupling to a hub; wherein the root side has a rounded contour with a concave stretch adjacent to the leading edge and a convex stretch adjacent to the trailing edge; wherein a root end of the leading edge protrudes with respect to the insertion point toward the second end of the rod in a direction parallel to the blade axis; and wherein the airfoil forms a lobe at a junction between the trailing edge and the root side and the lobe extends in the direction parallel to the blade axis toward the second end of the rod more than with respect to the root end of the leading edge.

11. The blade according to claim 1, wherein the trailing edge is rounded at least in a portion adjacent to the root side and joins the convex stretch of the root side without corners.

12. The blade according to claim 1, wherein the airfoil comprises a hollow first portion and a second portion (10b) in form of a lamina, wherein the first portion and the second portion extend adjacent to each other from the root side to the tip side and wherein the first portion defines the leading edge (11) and the second portion defines the trailing edge.

13. The blade according to claim 12, wherein at least in a region around a maximum cord point the trailing edge is bent toward the extrados.

14. Industrial axial fan comprising a hub rotatable about a rotation axis and a plurality of blades coupled to the hub, each blade comprising: an extruded or pultruded airfoil, extending along a blade axis and having a leading edge, a trailing edge, a root side, a tip side, an intrados and an extrados; and a terminal member arranged to close the tip side; wherein the terminal member has a rounded front portion in a plan view at the leading edge, and a rounded rear portion in a plan view between the front portion and the trailing edge.

15. The fan according to claim 14, wherein the rear portion of the terminal member has a bending radius coinciding with a maximum radius of the axial fan.

16. The fan according to claim 14, comprising a retaining ring and wherein the terminal member externally conforms to the retaining ring.

17. The axial fan according to claim 14, wherein the lobe of each blade overlaps, in a plan view, the root end of the leading edge of an immediately subsequent respective blade according to a rotation direction.

18. The axial fan according to claim 14, wherein the concave stretch of the root side of each blade is circular with a first radius equal to an outer radius of the hub and the convex stretch is circular with a second radius smaller than the first radius.

19. The axial fan according to claim 14, wherein in each blade the lobe extends parallel to the respective blade axis until the rotation axis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will now be described with reference to the accompanying drawings, illustrating some non-limiting embodiments thereof, in which:

[0059] FIG. 1 shows a simplified block diagram of an axial fan according to a first embodiment of the present invention;

[0060] FIG. 2 is a perspective view of the axial fan in FIG. 1;

[0061] FIG. 3 is a plan view from above of the axial fan in FIG. 1;

[0062] FIG. 4 is a plan view from above, enlarged, of a blade of the fan in FIG. 1;

[0063] FIG. 5 is a perspective view of the blade in FIG. 4;

[0064] FIG. 6 is a plan view from above of a blade of an industrial axial fan according to a different embodiment of the present invention;

[0065] FIG. 7 is a plan view from above of a blade of an industrial axial fan in accordance with an additional embodiment of the present invention;

[0066] FIG. 8 is a front view of an enlarged detail of the blade in FIG. 4;

[0067] FIG. 9 is a plan view from above of the detail in FIG. 8;

[0068] FIG. 10 is a side view of the detail in FIG. 8;

[0069] FIG. 11 is a first perspective view of the detail in FIG. 8;

[0070] FIG. 12 is a second perspective view of the detail in FIG. 8;

[0071] FIGS. 13-16 are graphics that show quantities relating to a blade according to the invention and a known blade;

[0072] FIG. 17 is a plan view from above of a blade of an industrial axial fan according to a different embodiment of the present invention;

[0073] FIGS. 18-20 show successive steps of a process for manufacturing a blade of an industrial axial fan in accordance with an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0074] The invention described below is especially adapted to the production of large axial fans, for example for heat exchangers used in natural gas liquefaction plants, refineries, or plants producing combined-cycle, turbine, or steam electricity.

[0075] With reference to FIG. 1, a fan assembly, indicated overall with the reference number 1, comprises an axial fan 2 driven by an electric motor 3.

[0076] The axial fan 2, which is represented in more detail in FIGS. 2 and 3, comprises a hub 4 connected to an electric motor 3 shaft, and multiple blades 5 that extend from the hub 4 basically in a radial direction. The hub 4 can swivel around a rotation axis R and has an outer radius r0 that, in the example illustrated, is defined by an anti-recirculation disk 6. Alternatively, the hub can be provided with a cover, like a cap or ogive, which define the outer radius.

[0077] The blades 5 are produced by extrusion or pultrusion, for example in aluminium, plastic, or fibreglass. The blades 5 are also connected to the hub 4 via respective rods 7. In one embodiment, the rods 7 can be oriented around respective longitudinal axes to enable the adjustment of a pitch of the blades 5 using a special adjuster 8 (FIG. 1). A retaining ring 9 is schematically illustrated in FIG. 3.

[0078] As also shown in FIGS. 4 and 5, each blade 5 comprises an airfoil 10, whether extruded or pultruded, extending along a blade axis A and having a leading edge 11, a trailing edge 12, a root side 13, and a tip side 14, an intrados 15 and an extrados 16. The airfoil 10 comprises a hollow first portion 10a and a second portion 10b in the form of a lamina, which extend longitudinally adjacent on the root side 13 to the tip side 14. The first portion 10a defines the leading edge 11, while the second portion 10b defines the trailing edge 12. On the root side 13, the first portion 10a of the airfoil 10 is closed by a mask 17. A terminal member 18 is arranged to close the tip side 14. A corresponding rod 7 has a first end connected to the airfoil 10 at an insertion point 20 through the root side 13 and a second end protruding from the airfoil 10 for coupling to a hub 4.

[0079] The leading edge 11 is rectilinear and parallel to the blade axis A.

[0080] In one embodiment, the trailing edge 12 is defined in the second portion 10b of the airfoil 10 between joints between the first portion 10a and the second portion 10b at the root side 13 and at the tip side 14. In other embodiments, in any case, the trailing edge may also comprise a stretch of the first portion of the airfoil (respectively 14 and 10a in FIG. 6); or the trailing edge may start in a stretch of the outline of the second portion not adjacent to the first portion (respectively 14, 10b, and 10a in FIG. 7).

[0081] In any case, the trailing edge 12 is rounded at least in a portion adjacent to the root side 13. In the embodiment in FIG. 4, the trailing edge 12 is rounded along its whole length. In embodiments not illustrated, in any case, a radially outer portion of the trailing edge 12 may be straight or have a bend. The trailing edge 12 preferably does not have any corners.

[0082] The root side 13 and the tip side 14 are opposite each other and extend from the leading edge 11 to the trailing edge 12 transversely to the blade axis A.

[0083] The root side 13 has a rounded contour with a concave stretch 13a adjacent to the leading edge and a convex stretch 13b adjacent to the trailing edge 12. The concave stretch 13a and the convex stretch 13b are joined together without corners, potentially with the interposition of a straight stretch. The insertion point 20 of the rod 7 is in the concave stretch 13a, for example, at a point of minimal distance from the tip side 14.

[0084] The concave stretch 13a is shaped so that a root end 11a of the leading edge 11 protrudes with respect to the insertion point 20 toward the end of the rod 7 connected to the hub 4 in a direction parallel to the blade axis A.

[0085] In one embodiment, the concave stretch 13a of the root side of each blade is circular with a first radius r1 equal to an outer radius of the hub 4, potentially with some play, and the convex stretch 13b is circular with a second radius r2 smaller than the first radius r1.

[0086] The trailing edge 12 joins the convex stretch 13b of the root side 13 without corners. In particular, at a joint between the trailing edge 12 and the root side 13, the airfoil 10 forms a rounded lobe 22 that extends in a direction parallel to the blade axis A towards the end of the rod 7 that is more connected to the hub 4 than to the root side 11a of the leading edge 11. More precisely, as shown in FIG. 3, the lobe 22 of each blade 5 overlaps, in plan, the root end 11a of the leading edge 11 of an immediately subsequent respective blade 5 according to a rotation direction ?, so as to protect against turbulence. In the embodiment illustrated here, in particular, the lobe 22 of each blade 5 extends parallel to the respective blade axis A to the rotation axis R.

[0087] The percentage of overlap between one blade and the other may depend on features such as the cord/width of the profile, the number of blades, and the size of the hub, and in some embodiments not shown, may be zero. In the cases in which geometrically the overlap, in plan, is greatly reduced or zero, a benefit in terms of noise reduction is, in any case, noted. In a region around a maximum cord point 25, the trailing edge 12 is bent towards the extrados 16 so as to accompany the exiting flow and reduce turbulence that could generate noise.

[0088] In each blade 5, the terminal member 18 is arranged to close the tip side 14 of the airfoil 10 and externally conforms with the retaining ring 9. A front portion 18f of the terminal member 18, near the leading edge 11, is rounded in plan, as shown in FIG. 9. In the radial direction, the front portion 18f of the terminal member 18 has a size DR ranging between 5% and 25% of a maximum cord CM of the terminal member 18 itself (FIGS. 9-12). In the tangential direction, perpendicular to the radial direction, the front portion 18f of the terminal member 18 has a tangential dimension DT ranging between 3% and 25% of the maximum cord CM.

[0089] A rear portion 18r of the terminal member 18, also rounded in a plan view, has a bending radius REXT, which in one embodiment is constant and basically coincides with the maximum radius of the axial fan 2. In other embodiments, however, the rear portion 18r of the terminal member 18 can have a variable bending radius, for example increasing in the direction from the leading edge 11 towards the trailing edge 12.

[0090] The front portion 18f is connected to the rear portion 18r at a connection point.

[0091] The terminal member 18 can also be tapered towards the outside in the direction of the blade axis A, as shown in FIG. 8. In practice, the terminal member has an intrados face 18a and an extrados face 18b, which decline towards each other and are joined at a (radially) outer face 18c with respective rounded corners, with respective bending angles RJ1, RJ2 ranging between 0.8% and 10% of the maximum cord CM. The outer face 18c has, thus, a smaller area than a (radially) inner face 18d of the terminal member 18 opposite and coupled to the airfoil 10. In one embodiment, for example, the area of the outer face 18c ranges between 40% and 80% of the area of the inner face 18d. The maximum cord CM is defined at the inner face 18d. In addition, a maximum outer thickness TE of the terminal member 18 at the outer face 18c is at least 50% of a maximum inner thickness TI of the terminal member 18 to the inner face 18d.

[0092] The terminal member, with the shape described, allows to obtain a substantial reduction in noise compared to known terminal members, without noticeably impacting performance. In particular, each of the elements described contributes, independently, to reducing the turbulence at the tip side 14 of the blade 5 and between the tip side 14 and the retaining ring 9, if present.

[0093] A similar advantage is obtained by using a terminal member with the features described in combination with extruded or pultruded blades of any kind, in particular different to the blades 5. For example, the graphics in FIGS. 13-16 refer to the comparison between blades of the type described in FIGS. 4-12 and equipped with a terminal member similar to that described (continuous line) and identical blades, with a conventional terminal member (dashed line). In particular, FIGS. 12 and 13 show, for different pitches (10?, 15?), that the static pressure (SP) and, respectively, the efficiency (?) do not significantly vary as the flow (Q) changes. FIGS. 14 (10? pitch) and 15 (15? pitch) show that the noise level (PWL) of the blade equipped with the terminal member 18 is less across the whole operation period.

[0094] FIG. 17 illustrates an extruded or pultruded blade 105, equipped with a terminal member 118 that has the features already described for the member 18. The blade 105, with and without the terminal member 118, is of the type used in the graphics in FIGS. 13-16. In particular, the blade 105 comprises an airfoil 110, whether extruded or pultruded, that has a leading edge 111, a trailing edge 112, a root side 113, and a tip side 114. The airfoil 110 comprises a hollow first portion 110a and a second portion 110b in the form of a lamina, which extend longitudinally adjacent on the root side 113 to the tip side 114. The first portion 110a defines the leading edge 111. The second portion 110b forms a flap, whose profile defines at least one section of the trailing edge 112 and, for example, may have a triangular or trapezoidal shape, potentially rounded. On the root side 13, the airfoil 110 is closed by a flat mask.

[0095] The terminal member 118 is arranged to close the tip side 114 and, as mentioned, has basically the same features as the terminal member 18 in FIGS. 8-12. In particular, in the terminal member 118: [0096] a rear portion has a first bending radius that basically coincides with the maximum radius of the axial fan; [0097] a front portion, near the leading edge 11, is rounded in a plan view and connects to the rear portion at a connection point; [0098] in the radial direction, the front portion has a size ranging between 5% and 25% of a maximum cord of the terminal member 118 itself; [0099] in the tangential direction, perpendicular to the radial direction, a tangential dimension ranges between 3% and 25% of the maximum cord; [0100] an intrados face and an extrados face decline towards each other and are joined at an outer face with respective rounded corners, with a respective bending radius ranging between 0.8% and 10% of the maximum cord; [0101] the outer face has a smaller area than the inner face coupled to the airfoil 10, for example the area of the outer face ranges between 40% and 80% of the area of the inner face; [0102] a maximum outer thickness at the outer face is at least 50% of a maximum inner thickness at the inner face.

[0103] The blades 5 may be manufactured with the process described below with reference to FIGS. 9-11.

[0104] Initially (FIG. 9), a section bar 50 is extruded (for example if manufactured in aluminium) or pultruded (if manufactured in fibreglass) along an axis A, which will then form the blade axis. The section bar 50 has the section of the airfoil 10 with an intrados 51 and an extrados 52. In addition, the section bar 50 comprises a hollow first portion 53 and a second portion 55 in the form of a lamina that extend adjacent to each other longitudinally.

[0105] The section bar 50 is cut transversely to the axis A (FIG. 10) so as to separate portions corresponding to each blade. In this step, the tip side 14 of each blade may already be defined.

[0106] The root side 13 is, in turn, cut to form the rounded contour 13 with the concave stretch 13a and the convex stretch 13b. In particular, the root side 13 is shaped so that the root end 11a of the leading edge 11 projects in relation to the direction opposite the tip side 14.

[0107] The second portion of the airfoil is then cut to form the trailing edge 12. In addition, the cut defines the lobe 22, which extends in the direction opposite the tip side 14 more than the root end 11a of the leading edge 11. The airfoils 10 of each blade are obtained thus (FIG. 11).

[0108] Finally, the rod 7 is inserted into the insertion point 18, fixed to the profile 10 via a connection system not shown, and the blade is completed with the mask 17 and the terminal member 18, to achieve the blade structure of FIGS. 4 and 5.

[0109] Lastly, it is clear that modifications may be made to the axial fan described herein, and variations produced thereof, without departing from the scope of the present invention, as described in the appended claims.

[0110] In particular, the diameter and number of the blades of the axial fan may vary in relation to what is described.

[0111] The connection between the blades and the hub may also differ from what is described. Among other things, the blades may be connected to the hub with a fixed pitch.

[0112] In addition, the blades may not have terminal members and/or brackets with an aerodynamic configuration, for example if not required for a specific application.