Blade for industrial axial flow fan with wingtip lift attachment

Abstract

A blade for an industrial axial flow fan comprises an extruded or pultruded airfoil (10) having a leading edge (11), a trailing edge (12), a wingtip portion (14), an inner airfoil (15) and an outer airfoil (16). A wingtip lift appendage (20) is applied to the wingtip portion (14) of the airfoil (10) and protrudes beyond the trailing edge (12) to form an extension of the airfoil (10) in a downstream direction.

Description

[0001] Cross-reference to related applications

[0002] This patent application claims the priority of Italian Patent Application No. 102022000004106 filed on March 4, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to a blade for an industrial axial flow fan having a wing tip lift attachment. Background Art

[0004] As is known, an industrial axial flow fan generally comprises a hub and a plurality of blades extending from the hub substantially in a radial direction.

[0005] The wheel hub is rotatable about an axis and is connected to an electric motor for receiving rotational motion through a drive train.

[0006] The blade is provided with an airfoil portion so that a pressure difference is generated between the outer and inner airfoil surfaces of the blade due to the rotation applied by the motor. This pressure difference in turn generates an airflow in a direction substantially parallel to the axis of the hub.

[0007] The air flow rate set for axial motion depends on many factors, mainly on the rotational speed, the shape of the airfoil and the pitch angle of the blades.

[0008] As in many industries, also in the field of industrial fans, efficiency is becoming an increasingly important requirement and against the backdrop of increasingly stringent regulations.

[0009] Increasing the blade surface is not sufficient in itself to guarantee better efficiency and may even have an adverse effect on the pitch angle. In fact, the benefit of increased lift due to the increased angle of incidence may be offset by increased aerodynamic drag, which will result in greater power consumption.

[0010] In principle, this problem can be at least partially solved by modifying the shape of the blades to optimize the ratio between lift and aerodynamic drag. In principle, if a similar solution can be advantageously used for small and medium-sized fans, the blades of which are usually manufactured by molding, this solution will not be applicable to large-sized axial fans (usually having a diameter of not less than one meter). In fact, the blade manufacturing process for large-sized industrial fans is mainly based on extrusion and / or pultrusion technology, which is economically sustainable and provides products with satisfactory light weight and mechanical performance characteristics, while the use of molding technology is usually excluded mainly because of excessive costs. On the other hand, there are specific problems with extrusion and pultrusion technology because the available products cannot be freely formed. In fact, the products manufactured by extrusion and pultrusion of an extruder have a substantially uniform and straight hollow structure, which will not easily deform, bend or bend. As mentioned above, this problem is a common problem for large-sized industrial fans, while the blades of fans with smaller sizes can be manufactured using different and more flexible technologies (such as molding).

[0011] There is also a different problem, which is associated with fans of large dimensions, regardless of the manufacturing technology used for the blades. During the service life of the fan, flow demands may arise that are greater than those estimated during the design phase. To meet the greater flow demands, it may be necessary to redesign the fan and, in fact, replace it or at least its blades, which entails significant costs. In fact, modifying the pitch of the existing blades may not be enough. For example, increasing the pitch angle leads to a significant increase in aerodynamic drag and a corresponding increase in the required power, which the motor may not be able to provide. In any case, the interventions for modifying the pitch are relatively long and complex and, if they have to be carried out on different machines, entail considerable costs.

[0012] Obviously, this issue becomes more important the more fans are installed in a plant, such as in the condensers of a combined cycle power plant. Summary of the invention

[0013] The object of the present invention is therefore to provide a blade for an industrial axial fan and an industrial axial fan which make it possible to overcome or at least alleviate the limitations described and in particular make it possible to increase the efficiency.

[0014] According to the present invention, there is provided a blade for an industrial axial flow fan, comprising:

[0015] an airfoil portion having a leading edge, a trailing edge, a wingtip portion, an inner airfoil surface, and an outer airfoil surface; and

[0016] A wingtip lift attachment is applied to a wingtip portion of the airfoil and projects beyond the trailing edge to form an extension of the airfoil in a downstream direction.

[0017] In practice, the wingtip lift attachment is configured to extend the lifting surface of the airfoil under the limitation of the wingtip portion and provide an additional flow contribution. Thus, the wingtip lift attachment enables an advantageous increase in lift without significantly increasing aerodynamic drag, the wingtip lift attachment being limited to the end portion of the blade. In other words, the benefit in terms of lift compensates and exceeds the effect of greater drag and overall improves efficiency.

[0018] According to one aspect of the invention, the wingtip lift attachment is connected to the airfoil portion at a relative pitch angle relative to the airfoil portion.

[0019] The relative pitch angle may be advantageously selected to optimize the efficiency of the blades and / or to increase the achievable flow rate at the same energy consumption.

[0020] According to one aspect of the invention, the wingtip lift attachment is connected to the airfoil portion such that the relative pitch angle is adjustable.

[0021] Since the pitch angle can be adjusted, the configuration can be easily optimized by simple testing of the model and then reproduced on the blades of the same type of wind turbine and, if necessary, can be adapted to the overall configuration of the wind turbine (e.g. a wind turbine with a different number of blades). Furthermore, the configuration can be modified after installation if necessary.

[0022] According to one aspect of the invention, the wingtip lift attachment is hinged to the airfoil portion, wherein the hinge axis is oriented such that the relative pitch angle is modified due to a rotation of the wingtip lift attachment about the hinge axis.

[0023] According to one aspect of the invention, the blade comprises an adjustment device configured to adjust the relative pitch angle between the wingtip lift attachment and the airfoil portion.

[0024] The use of the adjustment device provided in particular makes it possible to select the configuration of the wingtip lift attachment not only in a simple and rapid manner, but also in a precise and easily reproducible manner.

[0025] According to one aspect of the invention, the blade comprises a connection structure rigidly fixed to the airfoil portion and configured to connect the wingtip lift attachment to the airfoil portion, and the wingtip lift attachment is hingedly connected to the connection structure.

[0026] According to one aspect of the invention, the adjustment device comprises: an adjustment member defining an operating position of the wingtip lift attachment relative to the connecting plate; and a counter screw fixing the wingtip lift attachment in the operating position defined by the adjustment screw.

[0027] According to one aspect of the invention, the adjustment device comprises a plurality of elastic elements which are assembled between a connecting plate and a wingtip lift attachment by means of adjusting screws, so that the tightening force of the adjusting screws determines the degree of compression of the elastic elements and the distance between the connecting plate and the wingtip lift attachment.

[0028] According to one aspect of the present invention, the blade includes a cover plate extending toward the wingtip lift attachment to connect the airfoil portion and the wingtip lift attachment without interruption.

[0029] The cover plate helps prevent flow turbulence and load losses (which could negatively affect efficiency).

[0030] According to one aspect of the invention, the cover plate is resilient and preloaded against the wingtip lift attachment so that the downstream edge of the cover plate is in contact with the wingtip lift attachment in every position of the wingtip lift attachment.

[0031] Due to the preload, the cover plate ensures a sufficiently regular surface for preventing eddy currents which are detrimental to efficiency, regardless of the adjustment of the relative pitch angle.

[0032] According to one aspect of the invention, the wingtip lift attachment is rigidly fixed to the airfoil portion.

[0033] According to one aspect of the invention, the wingtip lift attachment is provided with a radially outer wall and a radially inner wall extending perpendicularly to the wingtip lift attachment towards the outer airfoil surface and / or towards the inner airfoil surface.

[0034] The sidewalls of the wing tip lift attachment reduce the undesirable losses of air passing between the pressure side (inner airfoil) and the pressure relief side (outer airfoil) of the wing tip lift attachment. In fact, the flow between the pressure side and the pressure relief side does not increase the lift, but increases the drag of the blade and thus negatively affects the efficiency.

[0035] According to one aspect of the invention, the radially outer edge of the wingtip lift attachment is continuously aligned with the radially outer edge of the airfoil portion.

[0036] According to one aspect of the invention, the ratio between the dimension of the airfoil portion in the radial direction and the average dimension of the wingtip lift appendages in the radial direction is greater than four.

[0037] According to one aspect of the invention, a ratio between a chord of the airfoil at the wingtip portion and a dimension of the wingtip lift attachment in a tangential direction is between 1 and 4.

[0038] The size ratio between the airfoil portion and the wingtip lift attachment ensures that the overall efficiency of the blade is increased.

[0039] According to one aspect of the invention, the wingtip lift attachment comprises a lift panel.

[0040] According to one aspect of the invention, the wingtip lift attachment comprises a further airfoil portion.

[0041] According to one aspect of the invention, the airfoil is extruded or pultruded.

[0042] According to the present invention, there is also provided an industrial axial flow fan comprising a hub rotatable about a rotation axis and a plurality of blades as defined above connected to the hub. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The invention will now be described with reference to the accompanying drawings, which show some non-limiting exemplary embodiments of the invention, in which:

[0044] - Figure 1 It is a simplified block diagram of an axial flow fan;

[0045] - Figure 2 yes Figure 1 A top view of the axial flow fan in FIG.

[0046] - Figure 3 According to an embodiment of the present invention Figure 1 An enlarged top perspective view of the blades of the fan in FIG.

[0047] - Figure 4 yes Figure 3 A top plan view of the blade in FIG.

[0048] - Figure 5 It is along Figure 4 The trace plane VV in the Figure 3 A side view of a blade in FIG.

[0049] - Figure 6 About Figure 3 Schematic diagram of the amplitude of the blades in;

[0050] - Figure 7 yes Figure 3 an enlarged bottom perspective view of a portion of a blade in FIG.

[0051] - Figure 8 yes Figure 3 An enlarged side view of a detail of a blade in FIG.

[0052] - Fig. 9 is an enlarged side view of details of a blade of an axial flow fan according to various embodiments of the present invention;

[0053] - Fig.10 is a top perspective view of a blade of an axial flow fan according to another embodiment of the present invention;

[0054] - Fig.11is a top perspective view of a blade of an axial flow fan according to yet another embodiment of the present invention;

[0055] - Fig.12 yes Fig.11 A side view of a blade in FIG.

[0056] - Fig.13 is a side view of a blade of an axial flow fan according to yet another embodiment of the present invention;

[0057] - Fig.14 is a side view of a blade of an axial flow fan according to another embodiment of the present invention;

[0058] - Fig.15 and Fig.16 is a side view of a blade of an axial fan according to yet another embodiment of the present invention in a corresponding operating configuration; and

[0059] - Fig.17 Shown in Fig.16 Enlarged detail of the blade in the operating configuration. DETAILED DESCRIPTION

[0060] The invention described below is particularly suitable for manufacturing large-sized axial fans, which are usually not less than one meter in diameter. For example, the invention can be advantageously used to manufacture heat exchangers used in natural gas liquefaction plants, refineries, combined cycle power plants or steam turbine power plants.

[0061] refer to Figure 1 The fan assembly, generally indicated by reference numeral 1 , comprises an axial fan 2 actuated by an electric motor 3 .

[0062] exist Figure 2 The axial flow fan 2 shown in more detail in FIG. 1 includes a hub 4 connected to the shaft of the electric motor 3 and a plurality of blades 5 extending from the hub 4 in a radial direction.

[0063] The blades 5 are made of, for example, extruded or pultruded aluminum, plastic material or glass fiber reinforced plastic. 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 so that they can be controlled by a specially provided controller 8 ( Figure 1 ) to adjust the pitch angle of blade 5. Figure 2 A containment ring 9 is schematically shown in FIG.

[0064] Also like Figures 3 to 5, each blade 5 comprises an extruded or pultruded airfoil 10 having a leading edge 11, a trailing edge 12, a root portion 13, a wing tip portion 14, an inner wing surface 15 and an outer wing surface 16. In different embodiments not shown, the airfoil can be manufactured using different techniques, for example by molding. A flap 17 extends from the root portion along the trailing edge 12, and an end element 18 is arranged to close the wing tip portion 14. The flap 17 can be defined by a thin sheet portion extruded and cut together with the airfoil 10 or by an additional airfoil portion extruded separately and connected to the airfoil 10, so that a fluid passage can be formed between the airfoil 10 and the flap 17.

[0065] The blade 5 further comprises a wingtip lift attachment 20 applied to the wingtip portion of the airfoil 10 and protruding beyond the trailing edge 12 to form an extension of the airfoil 10 in the downstream direction; a connecting plate 22 ; a cover plate 23 ; and an adjusting device 25 .

[0066] The wing tip lift attachment 20 is defined by a flat or curved lift plate and is connected to the airfoil 10 ( Figure 6 ) is connected to the wingtip portion 14 of the airfoil 10 at a relative pitch angle (. The relative pitch angle ( may be defined as the (acute) angle between the chord C of the airfoil 10 in the wingtip portion 14 to which the wingtip lift attachment 20 is applied and the wingtip lift attachment 20.

[0067] The wing tip lift attachment 20 may have a generally quadrilateral shape, such as a rectangle or a trapezoid, with straight sides (such as in Figure 3 and Figure 4 For example, the radially outer side and the radially inner side may be curved. In addition, in one embodiment, the radially outer edge of the wingtip lift attachment 20 is continuously aligned with the radially outer edge of the airfoil portion 10.

[0068] The radial dimension L of the airfoil portion 10 is equal to the radial dimension L of the wing tip lift attachment 20 ( Figure 4 ) on the average size DR A The ratio between them is preferably greater than 4. Furthermore, the ratio between the chord C′ of the airfoil 10 at the wingtip portion 14 and the dimension DT of the wingtip lift attachment 20 in the tangential direction is preferably between 1 and 4.

[0069] The wingtip lift attachment 20 is connected to the airfoil 10 so that the relative pitch angle α can be adjusted. More precisely, a connecting plate 22 is rigidly connected to the wingtip portion 14 of the airfoil 10, in particular to the outer wing surface 16, for example by screws 26 or rivets or structural adhesive (not shown), and the wingtip lift attachment 20 is hinged to the connecting plate 22, wherein the hinge axis A is oriented so that the relative pitch angle (due to the rotation of the wingtip lift attachment 20 about the hinge axis A) is modified. For example, the hinge axis A can be substantially parallel to the leading edge 11 or parallel to the trailing edge 12. In an embodiment not shown, the connecting plate is also connected to the inner wing surface of the airfoil.

[0070] refer to Figure 7 The cover plate 23 extends from the connecting plate 22 towards the wingtip lift attachment 20 to close the gap 35 between the connecting plate 22 and the wingtip lift attachment 20 without interruption. The cover plate 23 is elastic and preloaded against the wingtip lift attachment 20 so that the downstream edge 23a of the cover plate is in contact with the wingtip lift attachment 20 in each position of the wingtip lift attachment 20 achieved by the adjustment device 25.

[0071] The adjustment device 25 is configured to adjust the relative pitch angle (θ) between the wingtip lift attachment 20 and the airfoil 10 and to fix the wingtip lift attachment 20 in an operating position. Figure 8 In the embodiment shown in FIG. 2 , the adjustment device 25 comprises an adjustment screw 27 and a counter screw 28. The adjustment screw 27 determines the relative pitch angle (and the operating position of the wingtip lift attachment 20 relative to the connecting plate 22), while the counter screw 28 is tightened to fix the wingtip lift attachment 20 in the operating position defined by the adjustment screw 27. The adjustment screw 27 may be replaced by another suitable adjustment member (e.g., a cam).

[0072] In different implementations ( Fig. 9 ), the adjustment device 25 comprises a plurality of elastic elements 30, such as discs, which are assembled between the connecting plate 22 and the wingtip lift attachment 20 by means of adjustment screws 31, so that the tightening force of the adjustment screws 31 determines the degree of compression of the elastic elements 30 and the distance between the connecting plate 22 and the wingtip lift attachment 20. Thereby, the relative pitch angle α is also determined. However, it should be understood that any adjustment device that allows the position of the wingtip lift attachment 20 relative to the connecting plate 22 to be modified in order to change the relative pitch angle α may be used.

[0073] according to Fig.10In the embodiment shown in FIG. 1 , in which parts identical to those already shown are denoted by the same reference numerals, a blade 105 for a large-sized axial fan has a wingtip lift attachment 120 defined by a lift plate rigidly fixed to the airfoil 10, for example to the outer wing surface 16. In this case, the radially inner edge of the lift plate is curved, for example parabolic or hyperbolic.

[0074] exist Figures 11 to 14 In the embodiment shown in FIG. 2 , the wing tip lift attachment (here indicated by 220) of the blade 205 is provided with a radially outer wall 222 and a radially inner wall 223. The walls 222, 223 may extend perpendicularly to the wing tip lift attachment 20 toward the inner airfoil 15 ( Fig.11 and Fig.12 ), both extend toward the outer wing surface 16 ( Fig.13 ) and in both directions ( Fig.14 ) extends. In addition, the walls 222, 223 can be used with adjustment devices, such as in Figures 3 to 9 In the case of the adjustable wing tip lift attachment 20, and as in Fig.10 The wingtip lift attachment 120 is fixed relative to the airfoil.

[0075] refer to Figures 15 to 17 In one embodiment, a blade 305 for a large-sized axial fan has a wingtip lift appendage 320 defined by another airfoil hinged to, for example, the inner airfoil surface 16. In this case, the upstream portion of the wingtip lift appendage 320 overlaps the trailing edge 12 and the downstream portion of the airfoil 10. An adjustment device, not shown here, allows the relative pitch angle between the airfoil 10 and the wingtip lift appendage 320 to be adjusted, for example between a first operating configuration in which a first end-of-travel portion 321 defined by the upstream edge of the wingtip lift appendage 320 is in contact with the inner airfoil surface 15 of the airfoil 10, and a second operating configuration in which a second end-of-travel portion 322 is in contact with the trailing edge 12 of the airfoil 10.

[0076] The cover plate 323 connects the wingtip lift attachment 320 to the inner airfoil 15 of the airfoil 10 to define a regular surface and prevent turbulence. The cover plate 323 is resilient and preloaded against the wingtip lift attachment 320 to maintain contact in all permissible operational configurations of the wingtip lift attachment 320.

[0077] In a different embodiment not shown, the wingtip lift attachment 320 may be connected to the airfoil 10 via a connection plate. More precisely, the connection plate is rigidly connected to the inner and / or outer surfaces 15, 16 of the airfoil 10 and the wingtip lift attachment 320 is hinged to the connection plate.

[0078] Finally, it is obvious that modifications and variations can be made to the axial fan described without departing from the scope of the invention as defined in the appended claims.

[0079] In particular, the connection plate may not be used or may be replaced by a bracket or by another connection structure suitable for connecting the wingtip lift attachment to the airfoil. The connection may ultimately be rigid or have an adjustable pitch angle according to design preferences. If the relative pitch angle is adjustable, the connection structure supports adjustment means for adjusting the relative pitch angle.

[0080] In all described embodiments, the wingtip lift attachment may be defined by a lift panel or an airfoil portion, depending on design preference.

[0081] The diameter and number of blades of an axial fan may vary relative to the blades described.

[0082] The connection between the blade and the hub may also be different from the connection described. In addition, the blade may be connected to the hub at a fixed pitch angle.

[0083] Furthermore, the blade may be provided without an end element, for example if an end element is not required for a particular application.

Claims

1. A blade for an industrial axial flow fan, comprising: An airfoil portion (10) having a leading edge (11), a trailing edge (12), a wingtip portion (14), an inner airfoil surface (15) and an outer airfoil surface (16); and A wingtip lift attachment (20; 120; 220; 320) is applied to the wingtip portion (14) of the airfoil (10) and projects beyond the trailing edge (12) to form an extension of the airfoil (10) in a downstream direction.

2. The blade according to claim 1, wherein: The wing tip lift attachment (20; 120; 220; 320) is connected to the airfoil (10) at a relative pitch angle (α) relative to the airfoil (10).

3. The blade according to claim 2, wherein: The wing tip lift attachment (20; 220; 320) is connected to the airfoil (10) so that the relative pitch angle (α) is adjustable.

4. The blade according to claim 3, wherein: The wingtip lift attachment (20) is hinged to the airfoil (10), wherein an articulation axis (A) is oriented such that the relative pitch angle (α) is modified due to a rotation of the wingtip lift attachment (20) about the articulation axis (A).

5. The blade according to claim 3 or 4, comprising an adjustment device (25) configured to adjust the relative pitch angle (α) between the wingtip lift attachment (20) and the airfoil portion (10).

6. The blade of claim 5, comprising a connection structure (22) rigidly fixed to the airfoil portion and configured to connect the wingtip lift attachment (20) to the airfoil portion (10), wherein: The wing tip lift attachment (20) is hinged to the connecting structure (22).

7. The blade according to claim 6, wherein: The adjustment device (25) comprises: an adjustment member (27) defining an operating position of the wingtip lift attachment (20) relative to the connection structure (22); and a counter screw (28) fixing the wingtip lift attachment (20) in the operating position defined by the adjustment member (27).

8. The blade according to claim 6, wherein: The adjustment device (25) comprises a plurality of elastic elements (30), which are assembled between the connection structure (22) and the wingtip lift attachment (20) via adjustment screws (31), so that the tightening force of the adjustment screws (31) determines the compression degree of the elastic elements (30) and the distance between the connection structure (22) and the wingtip lift attachment (20).

9. The blade according to any one of claims 5 to 8, comprising a cover plate (23; 323) extending towards the wingtip lift attachment (20; 320) to connect the airfoil (10) and the wingtip lift attachment (20; 320) without interruption.

10. The blade according to claim 8, wherein: The cover plate (23; 323) is resilient and preloaded against the wingtip lift attachment (20; 320) so that the downstream edge (23a) of the cover plate (23; 323) is in contact with the wingtip lift attachment (20; 320) in every position of the wingtip lift attachment (20; 320).

11. The blade according to claim 2, wherein: The wingtip lift attachment (120) is rigidly fixed to the airfoil portion (10).

12. A blade according to any one of the preceding claims, wherein: The wing tip lift attachment (220) is provided with a radial outer wall (222) and a radial inner wall (223), wherein the radial outer wall and the radial inner wall extend perpendicularly to the wing tip lift attachment (220) toward the outer wing surface (16) and / or toward the inner wing surface (15).

13. A blade according to any one of the preceding claims, wherein: The radially outer edge of the wingtip lift attachment (20) is continuously aligned with the radially outer edge of the airfoil portion (10).

14. A blade according to any one of the preceding claims, wherein: The ratio between the dimension (L) of the airfoil (10) in the radial direction and the average dimension (DA) of the wingtip lift attachment (20) in the radial direction is greater than 4.

15. A blade according to any one of the preceding claims, wherein: The ratio between the chord (C) of the airfoil (10) at the wingtip portion (14) and the dimension (DT) of the wingtip lift attachment (20) in the tangential direction is between 1 and 4.

16. A blade according to any one of the preceding claims, wherein: The wing tip lift attachment (20) comprises a lift panel.

17. The blade according to any one of claims 1 to 15, wherein: The wingtip lift attachment (320) includes another airfoil portion.

18. A blade according to any one of the preceding claims, wherein: The airfoil (10) is extruded or pultruded.

19. An industrial axial fan comprising a hub (4) rotatable about an axis of rotation (R) and a plurality of blades (5) according to any one of the preceding claims coupled to the hub (4).

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