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

Abstract

A blade for an industrial axial fan includes an airfoil, extending along a blade axis and having a leading edge, a trailing edge, a root side, a tip side; and a rod, having a first end connected to the airfoil and a second end protruding from the airfoil for coupling to a hub. 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. 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. The airfoil forms a lobe that 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. The airfoil is extruded or pultruded and the leading edge is rectilinear and parallel to the blade axis.

Claims

1. A blade for an industrial axial fan comprising: an 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 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; 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; and wherein the airfoil is extruded or pultruded and wherein leading edge is rectilinear and parallel to the blade axis.

2. The blade according to claim 1, wherein the concave stretch and the convex stretch join each other without corners.

3. The blade according to claim 1, wherein the trailing edge is rounded at least in a portion adjacent to the root side.

4. The blade according to claim 1, wherein the trailing edge joins the convex stretch of the root side without corners.

5. The blade according to claim 1, wherein the airfoil comprises a hollow first portion and a second portion 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 and the second portion defines the trailing edge.

6. The blade according to claim 5, wherein at least in a region around a maximum cord point the trailing edge is bent toward the extrados.

7. The blade according to claim 1, comprising a terminal member arranged to close the tip side of the airfoil and tapered toward the outside in the direction of the blade axis.

8. The blade according to claim 7, wherein the terminal member has an inner face, coupled to the airfoil and having a first area, and an outer face, opposite to the inner face and having a second area smaller than the first area.

9. The blade according to claim 8, wherein the terminal member has an intrados face and an extrados face, joined to the outer face with respective rounded edges.

10. The blade according to claim 7, wherein the terminal member is rounded al leading edge in top view.

11. Industrial axial fan comprising a hub rotatable about a rotation axis and a plurality of blades coupled to the hub, each blade comprising: an 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 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; 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 lade axis toward the second end of the rod more than with respect to the root end of the leading edge; and wherein the airfoil is extruded or pultruded and wherein leading edge is rectilinear and parallel to the blade axis.

12. The axial fan according to claim 11, wherein, in top view, the lobe of each blade overlaps to the root end of the leading edge of an immediately subsequent respective blade according to a rotation direction.

13. The axial fan according to claim 11, 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.

14. The axial fan according to claim 11, wherein in each blade the lobe extends parallel to the respective blade axis until the rotation axis.

15. A process for manufacturing a blade of an industrial axial fan comprising: by extrusion or pultrusion, forming a section bar extending along an axis and having an airfoil section with a leading edge, an intrados and an extrados; cutting the section bar transversely to the axis so as to define a tip side and a root side having a rounded contour with a concave stretch adjacent to the leading edge and a convex stretch; and inserting a first end of a rod at an insertion point through the root side in the concave stretch; wherein cutting comprises shaping the root side so that 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 axis and so that the airfoil forms a lobe that extends in the direction parallel to the axis toward the second end of the rod more than the root end of the leading edge.

16. The process according to claim 15, wherein the section bar comprises a hollow first portion and a second portion in the form of a lamina, wherein the first portion and the second portion extend longitudinally adjacent to each other and wherein the first portion defines the leading edge.

17. The process according to claim 16, comprising forming, from the second portion of the section bar, a trailing edge rounded at least in a portion adjacent to the root side.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present invention will now be described with reference to the accompanying drawings, illustrating some non-limiting embodiments thereof, in which:

[0047] FIG. 1 shows a simplified block diagram of an axial fan according to a first embodiment of the present invention;

[0048] FIG. 2 is a perspective view of the axial fan in FIG. 1;

[0049] FIG. 3 is a plan view from above of the axial fan in FIG. 1;

[0050] FIG. 4 is a plan view from above, enlarged, of a blade of the fan in FIG. 1;

[0051] FIG. 5 is a perspective view of the blade in FIG. 4;

[0052] 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;

[0053] 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;

[0054] FIG. 8 is a front view of an enlarged detail of the blade in FIG. 4;

[0055] FIGS. 9-11 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

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] The leading edge 11 is rectilinear and parallel to the blade axis A.

[0062] 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).

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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) 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 a plan view, 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.

[0069] 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 a plan view, 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.

[0070] 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 of the terminal member 18, near the leading edge 11, is rounded in plan. The terminal member 18 is also 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 an outer face 18c with respective rounded corners. The outer face 18c has, thus, a smaller area than an inner face 18d of the terminal member 18 opposite and coupled to the airfoil 10.

[0071] The blades 5 may be manufactured with the process described below with reference to FIGS. 9-11.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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).

[0076] Finally, the rod 7 is inserted at 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.

[0077] 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.

[0078] In particular, the diameter and number of the blades of the axial fan may vary in relation to what is described.

[0079] 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.

[0080] 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.