Including a rotor with an auxiliary axial-flow fan and an axial-flow ventilator

Abstract

The present invention relates to a rotor (20) for an industrial large-diameter axial flow fan (22). The rotor according to the present invention comprises a hub (24) and n blades (26), wherein each rotor blade comprises an aerodynamic portion (30) and a root (28) for structurally connecting to the hub; the rotor according to the present invention further comprises a coaxial auxiliary axial flow fan (32), which auxiliary axial flow fan comprises n radially extending fan blades (34), and in an axial view, the fan is substantially included within a region P defined by the n radially inner ends of the aerodynamic portions of the rotor blades. The present invention further relates to an industrial large-diameter axial flow fan (22) comprising such a rotor.

Description

Field of the Invention

[0001] The present invention relates to the field of axial flow fans, and more particularly to large-diameter axial flow fans for industrial use. Background Art

[0002] As is well known, in the industrial field, axial flow fans are used to ensure sufficient air flow around special radiation surfaces in workshops where a large amount of heat needs to be dissipated.

[0003] An axial flow fan (e.g., an industrial axial flow fan) includes a central hub on which a plurality of blades are mounted. The hub defines an axis about which the blades rotate. Each blade generally includes a root and a so-called aerodynamic portion (i.e., the portion formed according to an airfoil). The root has a purely structural function of constraining the blade to the hub, while the aerodynamic portion has a function of interacting with air. As can be well understood by those skilled in the art, for different blade cross-sections, the tangential velocity is different. In fact, the tangential velocity of each blade portion is the product of the angular velocity (which is the same for all portions) and the radial distance from the axis of rotation (which increases as the distance from the axis of rotation increases).

[0004] Therefore, as is known to those skilled in the art, axial flow fan blades cannot operate in the same effective manner over their entire radial aperture. The tangential velocity of the innermost radial portion of the blade is generally considered too low to achieve an effective relative motion with respect to the air flow. Thus, the actual operation of the fan mainly depends on the outermost radial portion, which ensures almost all of the air flow generated by the axial flow fan.

[0005] The streamlines impinging on a single blade are theoretically circular arc segments whose centers coincide with the axis of rotation. However, this theoretical streamline path is actually only reflected in the central portion of the blade. In contrast, at the inner and outer radial ends of the blade, the streamlines change due to the so-called end effects, which will be briefly described below.

[0006] Along the middle portion of the blade, the high-pressure air region and the low-pressure air region are physically separated from each other due to the presence of the blade itself. At the ends of the blade, this separation no longer exists, and thus a natural air flow is generated that tends to move from the high-pressure region to the low-pressure region. Thereby, this generates end vortices that can significantly limit the efficiency of the fan. In addition, the end vortices that suck in the surrounding air cause the streamlines to change. These changes extend from the outer and inner ends towards the central portion of the blade, thereby affecting a large part of the entire radial extent of the blade. For this reason, in many known axial flow fans, most of the blades operate away from the optimal operating point represented by the theoretical streamline.

[0007] The end - effect problem is usually addressed with respect to the radially outer end because it is adjacent to the blade region that has the greatest effect on the overall aerodynamic operation of the blade as described above.

[0008] The initially proposed solution to counteract the influence of the outer - end vortices was to insert the ventilator into a duct, thereby confining it within a duct with a diameter slightly larger than the outer diameter of the ventilator itself. In the following text, this duct will be referred to as a shroud.

[0009] Due to the addition of the shroud, the size of the outer - end vortices is significantly reduced, thus reducing the amount of air moved by these vortices and the resulting drag. However, it is not only impossible to eliminate the distance between the outer end of the blade and the inner diameter of the shroud, but it is even not possible to reduce this distance beyond a certain limit.

[0010] Another solution, inspired by aeronautics, is to provide an auxiliary surface called a winglet at the outer end of each blade. The main function of the winglet is to form a wall that blocks the movement of air, thereby preventing the formation of end - vortices. In addition, depending on the shape adopted, the winglet also affects the residual end - vortices, i.e., optimizes the residual end - vortices to limit the formation of noise.

[0011] Another solution is described in the international patent application WO 2020 / 245674 of the same applicant. In the following text, this solution (hereinafter briefly referred to as the "annular base") will be briefly described, while the reader can refer to the same publication WO 2020 / 245674 for a more detailed description. According to this solution, the annular base is provided on the inner wall of the shroud, which extends circumferentially around the ventilator rotor and partially houses the outer ends of the blades. In particular, the annular base is open in the axial direction, and an axial baffle defined by the winglets mounted at the end of each blade extends therein. This special configuration forms a kind of maze that effectively blocks the movement of air around the outer ends of the blades. Therefore, the annular base has a considerable advantage in terms of the overall ventilator efficiency.

[0012] Regarding the radially inner end of the blade, it has been proposed to use a flat disk provided in the hub region in order to insert an obstacle that physically prevents air recirculation.

[0013] The patent document WO 2014 / 117288 describes a rotor for an axial - flow ventilator including an auxiliary centrifugal fan. The auxiliary centrifugal fan is coaxially mounted at the center of the rotor. In this solution, the auxiliary centrifugal fan generates a radially - outward air flow that impinges on the radially inner ends of the rotor blades in order to counteract the recirculation caused by the end - effect.

[0014] Although widely recognized, the above-known solutions are not without drawbacks. In fact, compared to the various solutions described above for solving the problem of the vortex at the outer radial end of the blade, there is no known solution for solving the vortex at the inner radial end to date. Perhaps the understanding of the aerodynamic effects in the inner radial region of the blade is relatively low, which has led designers to always believe that any intervention in this region cannot have any significant effect on the overall performance of the ventilator.

[0015] In addition, experimental activities have shown that adding a flat disc in the hub region does not mean any real benefit in terms of the efficiency of the ventilator.

[0016] Therefore, there is a need for an industrial axial-flow ventilator in which the performance of the inner radial region of the rotor is improved in terms of vortices.

[0017] Summary of the Invention and Objectives

[0018] Therefore, the objective of the present invention is to overcome the above-mentioned drawbacks of the prior art.

[0019] In particular, one task of the present invention is to provide an axial-flow ventilator with higher efficiency.

[0020] In addition, one task of the present invention is to provide an axial-flow ventilator that can generate higher pressure at the same speed compared to known types of ventilators.

[0021] In addition, one task of the present invention is to provide an axial-flow ventilator that can better limit the formation of tip vortices compared to known types of ventilators.

[0022] In addition, one task of the present invention is to provide an axial-flow ventilator that adjusts the streamline by making the streamline as similar as possible to the theoretically predicted streamline.

[0023] Finally, one task of the present invention is to provide a ducted axial-flow ventilator that not only introduces more advantages but also retains the advantages already achieved by known types of ventilators.

[0024] These and other objectives and tasks of the present invention are achieved by the rotor according to claim 1 and the ventilator according to claim 10. Other features are defined in the dependent claims. All the appended claims form an integral part of this specification.

[0025] According to a first aspect, the present invention relates to a rotor for an industrial large-diameter axial flow fan. The rotor includes a hub and n blades, and each rotor blade includes an aerodynamic portion and a root for structurally connecting to the hub. The rotor further includes an auxiliary axial flow fan, which includes n radially extending fan blades, and in an axial view, the auxiliary axial flow fan is substantially included within a region P defined by n radially inner ends of the aerodynamic portions of the blades of the rotor.

[0026] The presence of the auxiliary axial flow fan stabilizes the velocity and pressure ranges within the radial inner region of the rotor, enabling the rotor to operate better, thereby increasing the overall efficiency of the fan.

[0027] Preferably, in an axial view, the auxiliary axial flow fan 32 is inscribed within the region P. This feature achieves the best utilization of the scope of the region P without introducing interference between the auxiliary axial flow fan and the main rotor.

[0028] In some embodiments, the auxiliary axial flow fan includes a central portion, and n fan blades radially project from the central portion. In other embodiments, the auxiliary axial flow fan is obtained by directly attaching n fan blades to the rotor hub.

[0029] In some embodiments, the auxiliary axial flow fan is made as a single integral piece. In some embodiments, the fan blades of the auxiliary axial flow fan include a root for structurally connecting to the hub and an aerodynamic portion.

[0030] These different embodiments of the auxiliary axial flow fan and the corresponding fan blades allow the auxiliary axial flow fan to best adapt to different requirements.

[0031] Preferably, the radial extension of the fan blades of the auxiliary axial flow fan is between 60% and 75% of the radius of the auxiliary axial flow fan, and even more preferably between 65% and 70% of the radius of the auxiliary axial flow fan.

[0032] Preferably, the axial extension of the fan blades of the auxiliary axial flow fan is within 20% of the diameter of the auxiliary axial flow fan, and even more preferably between 5% and 15% of the diameter of the auxiliary axial flow fan.

[0033] Preferably, the thickness of each fan blade of the auxiliary axial flow fan is substantially uniform throughout the extension of the fan blade. Preferably, the thickness of the fan blades of the auxiliary axial flow fan is between 10% and 20% of the axial extension of the fan blades of the auxiliary axial flow fan.

[0034] According to the experiments conducted, these ratios of the auxiliary axial flow fan have achieved particularly positive results in improving the overall efficiency of the rotor.

[0035] In some embodiments of the rotor, at least one blade includes a winglet located at the radially outer end, wherein the winglet includes a baffle extending in the axial direction and the circumferential direction.

[0036] According to a second aspect, the present invention relates to an industrial ventilator including the rotor and a motor as described above.

[0037] In some embodiments, the ventilator further includes a duct surrounding the rotor. Preferably, the duct includes an annular base that extends circumferentially around the rotor and partially houses the outer ends of the rotor blades. Preferably, the annular base extends at least partially in the axial direction and partially houses the baffle defined by the blade winglet.

[0038] This ventilator configuration stabilizes the velocity and pressure ranges in the radially inner rotor region due to the auxiliary axial fan and stabilizes the velocity and pressure ranges in the radially outer rotor region due to the annular base that houses the baffle. Thus, the ventilator can operate in an optimal state, improving its overall efficiency.

[0039] Other features and advantages of the present invention will become more apparent from the description of the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention is described below in connection with certain examples provided by way of non-limiting examples and shown in the drawings. These drawings illustrate different aspects and embodiments of the present invention, and reference numerals that denote structures, components, materials, and / or similar elements shown in different drawings are denoted by similar reference numerals where appropriate. In addition, for clarity of illustration, certain reference numerals may not be repeated in all the drawings.

[0041] Figure 1 is an isometric view of an industrial axial ventilator according to the prior art;

[0042] Figure 2 is along Figure 1 a schematic cross-sectional view taken along line II-II of;

[0043] Figure 3 is an isometric view of an industrial axial ventilator according to an embodiment of the present invention;

[0044] Figure 4 is along Figure 3 a schematic cross-sectional view taken along line IV-IV of;

[0045] Figure 5 is an isometric view of a three-blade ventilator rotor according to an embodiment of the present invention;

[0046] Figure 6 is an isometric view of a three-blade ventilator rotor according to an embodiment of the present invention;

[0047] Figure 7 Is an axonometric view of a four - blade ventilator rotor according to an embodiment of the present invention;

[0048] Figure 8 Is a plan view of a three - blade auxiliary axial - flow fan for a rotor according to an embodiment of the present invention;

[0049] Figure 9 Is Figure 8 The axonometric view of the auxiliary axial - flow fan;

[0050] Figure 10 Is a plan view of a four - blade auxiliary axial - flow fan for a rotor according to an embodiment of the present invention;

[0051] Figure 11 Is Figure 10 The axonometric view of the auxiliary axial - flow fan;

[0052] Figure 12 Is similar to Figure 5 The plan view of the central details of the rotor in;

[0053] Figure 13 Is an exploded axonometric view of a component composed of a hub and an auxiliary axial - flow fan similar to the hub and the auxiliary axial - flow fan of the rotor in Figure 7 ;

[0054] Figure 14 Is Figure 13 The plan view of the component in;

[0055] Figure 15 Is a plan view of a five - blade ventilator rotor according to an embodiment of the present invention;

[0056] Figure 16 Is Figure 15 The enlarged view of the detail indicated by XVI in;

[0057] Figure 17 Is a plan view of a five - blade ventilator rotor according to another embodiment of the present invention;

[0058] Figure 18 Is Figure 17 The enlarged view of the detail indicated by XVIII in;

[0059] Figure 19 is an axonometric view of a four - blade auxiliary axial - flow fan for a rotor according to an embodiment of the present invention;

[0060] Figure 20 is an axonometric view of another four - blade auxiliary axial - flow fan for a rotor according to an embodiment of the present invention;

[0061] Figure 21 is a plan view of the central details of a rotor similar to the rotor in Figure 7 ; a plan view of the central details of a rotor similar to the rotor in

[0062] Figure 22.a and Figure 22.b are respectively a plan view of a separate and an auxiliary axial - flow fan blade mounted on a rotor blade according to an embodiment of the present invention;

[0063] Figure 23 is a plan view of the central details of a rotor according to an embodiment of the present invention, in which the theoretical flow lines and the actual flow lines are schematically highlighted;

[0064] Figure 24 shows a flow - pressure plan view, on which the characteristic curves of a ventilator according to the prior art and a ventilator according to the present invention are schematically shown; and

[0065] Figure 25 shows a flow - efficiency plan view, on which the characteristic curves of two ventilators according to the prior art and two ventilators according to the present invention are schematically shown. Detailed Description of the Invention

[0066] Although the present invention may have various modifications and alternative configurations, certain preferred embodiments are shown in the drawings and will be described in detail hereinafter. It must be understood in any case that the present invention is not intended to be limited to the specific embodiments shown, but is intended to cover all modifications and alternative and equivalent structures falling within the scope of the present invention as defined by the claims.

[0067] This specification elaborates in detail on the technical aspects and features specific to the present invention, while known aspects and technical features are only mentioned incidentally. In these aspects, the content described above in connection with the prior art is valid.

[0068] Unless otherwise specified, the use of "for example", "etc.", "or" means but is not limited to non - exclusive alternatives. Unless otherwise specified, the use of "comprising" and "including" means "including or including but not limited to".

[0069] The axial - flow ventilator of the present invention defines a rotation axis, with respect to which the terms "axial", "radial", "circumferential" and "tangential" are clearly defined. In addition, the axial - flow ventilator of the present invention is configured to generate an air flow, with respect to which the terms "upstream", "before", etc. and the relative terms "downstream", "after", etc. are uniquely defined.

[0070] One aspect of the invention relates to a small auxiliary axial fan intended to be mounted on the rotor of a large ventilator, which is known per se. To avoid any ambiguity, the fan of the invention will be referred to hereinafter as a fan, while the known large ventilator will be referred to hereinafter as a ventilator.

[0071] According to a first aspect, the present invention relates to a rotor 20 for an industrial large-diameter axial flow fan 22. The rotor 20 according to the present invention comprises a hub 24 and n blades 26, wherein each blade 26 of the rotor 20 comprises a root 28 for structural connection to the hub 24 and an aerodynamic portion 30; the rotor 20 according to the present invention further comprises a coaxial auxiliary axial flow fan 32, the auxiliary axial flow fan comprising n radially extending blades 34, which are substantially included in an area P defined by n radial inner ends of the aerodynamic portion 30 of the blades 26 of the rotor 20 in an axial view.

[0072] According to the embodiments in the figures, in axial or plan view, the radially inner ends of the aerodynamic portion 30 of the blade 26 are straight and tangentially oriented. Thus, in these embodiments, the area P defined by the n radially inner ends of the aerodynamic portion 30 is a polygonal area with n sides, each side being defined by the chord C, a portion thereof or an extension thereof. Thus, in these embodiments, the area P takes the form of a regular polygon with n sides. See in this respect Figure 12 , Figures 15 to 18 and Figure 21 According to other embodiments of the invention, in which the radially inner end of the aerodynamic portion 30 of the blade 26 presents a different shape, the region P presents a different shape. Generally speaking, the region P presents a regular shape that is centrally symmetrical and may be inscribed in a circle.

[0073] Here and below, a large diameter fan 22 means a fan 22 having a diameter greater than 80 cm (preferably greater than 150 cm). With regard to certain technical features to be described later, the distinction between so-called small fans (i.e., diameters less than about 5 m) and so-called large fans (i.e., diameters greater than about 5 m) will be mentioned in the case of the large diameter fans 22 to which the present invention relates.

[0074] The blade 26 of the rotor 20 has a structure known per se and includes a root 28 that performs a purely structural function and an aerodynamic portion 30 that performs an aerodynamic function of interacting with the air flow. The root 28 is for connecting the blade 26 to the hub 24 and is dimensioned such that it can effectively transfer stress from the hub 24 to the aerodynamic portion 30 and vice versa. The aerodynamic function of the blade 26 is performed only by the aerodynamic portion 30, which is shaped according to an airfoil. The aerodynamic portion 30 includes a radially inner end and a radially outer end and preferably includes winglets 36, which will be described further below.

[0075] The aerodynamic portion 30 of the blade 26 can be made of a metallic material (usually aluminum) or a composite material (usually glass fibers in an epoxy matrix), depending on the specific requirements. Preferably, the aerodynamic portion 30 is obtained from one or more semifinished products having a constant cross section, for example by extrusion (in the case where the aerodynamic portion is made of a metallic material) or pultrusion (in the case where the aerodynamic portion is made of a composite material).

[0076] According to some embodiments, the aerodynamic portion 30 has a fixed chord along the entire radial aperture from the radially inner end to the radially outer end. However, according to other embodiments, the blade 26 tapers outwards starting from a predetermined position (see Figures 1 to 6 ). In this case, the profile chord of the radially inner end is greater than the profile chord of the radially outer end. Hereinafter, unless otherwise specified, the term "chord" relating to the blade 26 shall be understood as the chord C of the radially inner end (see Figure 12 ). According to this embodiment, C can vary between 100 mm and 1000 mm, preferably between 150 mm and 800 mm.

[0077] The hub 24 (see specifically Figure 13 ) generally includes a central portion 38 that is preferably cylindrical, on which n attachments 40 are provided, which are configured to allow connection of the roots 28 of the blades 26. In some embodiments, the attachments 40 project radially from the central portion 38 of the hub 24 (for example see Figure 13 and Figure 14 ), while in other embodiments, the attachments 40 are integrated in the hub 24 (for example see FIGS. 19 and 20).

[0078] Preferably, the cooperation between each attachment 40 and the corresponding root 28 allows adjustment of the pitch angle θ (or angle of attack) of the blade 26, i.e.: it allows changing the orientation of each blade 26 about the corresponding radial axis for pitch variation. However, it should be noted that in almost all cases (especially in the case shown in the drawings), the rotor 20 of the present invention does not allow effective pitch variation during the operation of the ventilator 22. Here and hereinafter, pitch variation means the reconfiguration of the blade 26, which can only be carried out as a maintenance task performed by a technician when the ventilator 22 is stopped.

[0079] The rotor 20 defines a rotational axis R. In Figure 1 , Figure 3 and Figures 5 to 7 , the rotational axis R is oriented to indicate the general direction of the axial air flow generated by the ventilator 22. As already mentioned, the terms "before", "upstream", etc. and the relative terms "after", "downstream", etc. are uniquely defined according to the direction of the air flow.

[0080] As described above, the rotor 20 according to the present invention includes a coaxial auxiliary axial flow fan 32 (i.e.: mounted to share its geometric axis with the rotational axis R of the hub 24 of the rotor 20).

[0081] The auxiliary axial flow fan 32 includes a number n of fan blades 34 equal to the number n of the blades 26 of the rotor 20. For example, if the rotor 20 includes three blades 26, the auxiliary axial flow fan 32 includes three fan blades 34 (for example, see Figures 3 to 6 ); if the rotor 20 includes four blades 26, the auxiliary axial flow fan 32 includes four fan blades 34 (for example, see Figure 7 and Figure 21 ); if the rotor 20 includes five blades 26, the auxiliary axial flow fan 32 includes five fan blades 34 (for example, see Figures 15 to 18 ); and so on.

[0082] As described above, in the axial or planar view of the rotor 20 according to the present invention, the auxiliary axial flow fan 32 is substantially included within the region P defined by the n radial inner ends of the aerodynamic portions 30 of the blades 26 of the rotor 20. Preferably, in the same axial or planar view, the auxiliary axial flow fan 32 is completely included within the region P. Specifically, see Figure 12 and Figures 15 to 18 , the auxiliary axial flow fan 32 is inscribed within the region P, which means that the radially outer ends of the auxiliary axial flow fan 32 are located on the perimeter of the region P.

[0083] However, in the context of this discussion, the term "substantially included" has a broader meaning, which will be particularly combined with Figure 21To explain this in more detail. The term "substantially includes" means that the radially outer end of the auxiliary axial flow fan 32 can protrude from the region P by a distance f, where f is less than 5% of the diameter d of the auxiliary axial flow fan 32 itself.

[0084] According to some embodiments of the present invention (where the ventilator 22 is a so-called small ventilator (i.e., its diameter is approximately less than 5 meters)), in the axial view, the blades 34 of the auxiliary axial flow fan 32 have a sector shape with an aperture angle of β (see, for example, Figures 3 to 14 ). According to the following simple rule, the sum of the aperture angle β of each blade 34 of the auxiliary axial flow fan 32 and the angular distance γ between two adjacent blades 34 depends on the number of blades 34:

[0085] β + γ = 360° / n.

[0086] According to some embodiments, the aperture angle β of the blade 34 is equal to the angular distance γ between two adjacent blades 34:

[0087] β = γ.

[0088] Therefore, according to the above two relationships, the aperture angle of each fan blade 34 depends on the number of blades 34 according to a simple rule:

[0089] β = 360° / 2n.

[0090] For example, for the case of having three blades 34, the aperture angle β will be 60°, thus ensuring that the angle γ between the next two blades 34 is equal. For the case of having four blades 34, the aperture angle β will be 45°.

[0091] According to some embodiments, the auxiliary axial flow fan 32 includes a central portion 42 that is preferably cylindrical, and n blades 34 project radially from this central portion. Preferably, in the axial view, the characteristic dimension of the central portion 42 of the auxiliary axial flow fan 32 is equal to the corresponding characteristic dimension of the central portion 38 of the hub 24 of the rotor 20. In the embodiments of the drawings (where the central portions 38, 42 are both cylindrical), the characteristic dimension in the axial view can be the corresponding radius or diameter. In particular, the diameter of the central portion 42 of the auxiliary axial flow fan 32 is equal to the diameter of the central portion 38 of the hub 24 of the rotor 20 (see Figure 13 and Figure 14 ).

[0092] According to other embodiments, the auxiliary axial flow fan 32 is obtained by directly applying n blades 34 to the rotor 20. For example (see FIGS. 19 and 20), the auxiliary axial flow fan 32 can be obtained by directly attaching n blades 34 to the hub 24 of the rotor 20. Alternatively (see Figure 22.a and Figure 22.b), each blade 34 of the auxiliary axial fan 32 can be applied to the radially inner end of the aerodynamic portion 30 of the blade 26. For example, each blade 34 can be applied to a cover 29, which is typically used to enclose the radially inner end of the aerodynamic portion 30. According to these embodiments, the blades 34 can be manufactured as separate parts and then assembled to directly form the auxiliary axial fan 32 on the rotor 20.

[0093] As described above, the blades 34 of the auxiliary axial fan 32 extend in the radial direction; in other words, the blades 34 at least partially extend radially outward from the central portion 42 of the auxiliary axial fan 32 or from the central portion 38 of the hub 24.

[0094] Preferably, the radial extension B of the blades 34 of the auxiliary axial fan 32 (i.e., half of the difference between the diameter d of the auxiliary axial fan 32 and the diameter of the central portion 38 of the hub 24 or the diameter of the central portion 42 of the auxiliary axial fan 32, if any; see Figure 12 ) is between 60% and 75% of the radius d / 2 of the auxiliary axial fan 32, and even more preferably, B is between 65% and 70% of the radius d / 2 of the auxiliary axial fan 32.

[0095] According to some embodiments (such as the embodiments in Figures 8 to 11 ), the auxiliary axial fan 32 can be made as a single integral piece. This embodiment is generally preferably for rotors 20 that are relatively small relative to the scope of the present invention (e.g., rotors 20 with a diameter up to 5 meters). In these cases, in fact, the diameter d of the auxiliary axial fan 32 is comparable to the diameters of other small ventilators of known types (such as household desktop ventilators, or ventilators for the cooling circuits of heat engines in the automotive field or in air conditioner outdoor units). In other words, in these cases, with the knowledge already obtained by those skilled in the art, the diameter d of the auxiliary axial fan 32 can be small enough to enable it to be made as a single piece; the integral auxiliary axial fan 32 can be made, for example, by molding a metal plate, or by injection molding or by 3D printing a suitable polymer.

[0096] According to some embodiments (such as the embodiments in Figures 15 to 18 ), techniques similar to those used for the main rotor 20 can be employed to manufacture the auxiliary axial fan 32. In other words, the blades 34 of the auxiliary axial fan 32 can include a root portion 54 and an aerodynamic portion 56, and the root portion is used to structurally connect to the hub 24 or the central portion 42. This embodiment is generally preferably for the auxiliary axial fan 32 used for relatively large rotors 20 (e.g., rotors 20 with a diameter exceeding 5 meters). In these cases, the diameter d of the auxiliary axial fan 32 is large enough to enable the use of the construction techniques for the main rotor 20 itself.

[0097] Referring to the ventilator 22 with a reference diameter of about 5 meters, in the auxiliary axial-flow fan 32, the aperture angle β of each blade 34 is preferably equal to the angular distance γ relative to the adjacent blade 34. This special structure means that, in a plan view, except for the central part 42, the ratio of the solid to the void is about 1. In other words, the area occupied by the blades 34 is equal to the area occupied by the air between the blades 34, regardless of the number n of the blades 34. This feature is particularly obvious in Figure 8 and Figure 10 it.

[0098] In the case of an industrial ventilator, the ratio of the solid to the void is usually evaluated by a parameter called solidity. Generally, the solidity of the ventilator 22 is defined as follows:

[0099] Θ = n*c / D

[0100] where n is the number of blades 26 or blades 34;

[0101] c is the chord at the outer radial end; and

[0102] D is the diameter of the ventilator 22 (including the hub 24).

[0103] For the auxiliary axial-flow fan 32 of the ventilator 22 with a diameter within 5 meters according to the present invention, using the above classical formula, the obtained solidity is preferably included between 1 and 2.5, that is:

[0104] 1 ≤ Θ ≤ 2.5.

[0105] More specifically, for the auxiliary axial-flow fan 32 in Figure 8 and Figure 10 it has:

[0106] Θ = 1.4.

[0107] Preferably, the axial extension a of the blades 34 of the auxiliary axial-flow fan 32 is included within 20% of the diameter d of the auxiliary axial-flow fan 32 itself, and even more preferably, the axial extension a is included between 5% and 15% of the diameter d. Refer to Figure 13 and Figure 20. The axial extension a is hereinafter understood as the distance between two planes perpendicular to the rotation axis R, where the first plane includes the most upstream point of the blade 34, and the second plane includes the most downstream point of the blade 34. In the Figure 13 embodiment, the axial extension a of the blade 34 coincides with the axial extension of the central part 42 of the auxiliary axial-flow fan 32.

[0108] Preferably, the thickness t of the blade 34 is thinner relative to other dimensions of the blade 34 itself, such as Figure 9 , Figure 11 andFigure 13 As shown. Preferably, the thickness t of each blade 34 of the auxiliary axial flow fan 32 is substantially uniform throughout the range of the blade 34. Near the periphery of the blade 34 (i.e., near the leading edge and / or trailing edge and / or radially outer end of the blade 34), the thickness t may be reduced. In particular, the thickness t of the blade 34 of the auxiliary axial flow fan 32 preferably includes between 10% and 20% of the axial extension a of the auxiliary axial flow fan 32. These features of the thickness t can avoid the formation of eddy currents at the trailing edge of the blade 34. This enables each blade 34 to convey air in the preferred direction of the next blade 34 and without interference due to eddy current separation.

[0109] Research conducted by the applicant has shown the importance of the correct positioning of the auxiliary axial flow fan 32 relative to the rotor 20. Figure 12 A brief description of some of the preferred relationships between the quantities highlighted in

[0110] C(θ) is the projection of the chord of the aerodynamic portion 30 of the blade 26 (especially at the radially inner end) on the plane of rotation; this depends on the airfoil size and pitch angle θ selected for the aerodynamic portion 30.

[0111] B is the radial extension of the blade 34 of the auxiliary axial flow fan 32, that is: the difference between the radius d / 2 of the auxiliary axial flow fan 32 and the radius of the larger of the center portion 38 of the hub 24 and the center portion 42 (if any) of the auxiliary axial flow fan 32;

[0112] A is the minimum distance between the aerodynamic portion 30 of the blade 26 and the center portion 38 of the hub 24, or the sum of the radial extensions of the root 28 and the attachment 40 of the hub 24;

[0113] α is the angle between the radius along which A is measured and the leading edge of the blade 34 of the blade 26 immediately following the measurement of A;

[0114] Z is the distance along the chord C between the leading edge of the blade 26 and the point where A is measured;

[0115] X is the distance along the chord C between the trailing edge of the blade 26 and the point where the blade 34 reaches the aerodynamic portion 30 of the blade 26.

[0116] Preferably, the position of the auxiliary axial flow fan 32 relative to the rotor 20 is defined by the following equation:

[0117] X = C(θ) – B sin(α(θ)) - Z(θ)

[0118] wherein, when all components are scaled relative to the chord C, it becomes:

[0119] X / C = 1 - (B / C)sin(α) - Z / C = 1 - β(α) - δ

[0120] where δ = Z / C.

[0121] As the pitch angle θ increases, the position of the auxiliary axial flow fan 32 must be adjusted to avoid overlapping with the radially inner end of the aerodynamic portion 30 of the blade 26. Therefore, the geometric relationships involved can be defined as follows:

[0122] B cos(β) - (c - x)sin(θ) = 0

[0123] where B is the length of the fan blade 34 in the radial direction, C is the profile chord, and X is the distance from the trailing edge.

[0124] From the above equation with two unknowns, it can be found that X is a function of α. Therefore, α is derived as arcos(((C - X)sin(θ)) / B), and by inserting it into the above equation, the position of the auxiliary axial flow fan 32 can be found for each pitch angle θ.

[0125] Another degree of freedom for positioning the auxiliary axial flow fan 32 relative to the rotor 20 is the axial position. In fact, the auxiliary axial flow fan 32 can be arranged near the axial plane of the hub 24 (immediately downstream (e.g. Figure 5 in) or immediately upstream (e.g. Figure 6 in)), or it can be moved axially along the rotation axis R at a distance h.

[0126] For example, the distance h can be defined such that the radially outer end of the auxiliary axial flow fan 32 reaches near the radially inner end of the aerodynamic portion 30 of the blade 26 in the axial direction.

[0127] For example, there can be:

[0128] h = (C – Z)sin(θ).

[0129] Preferably, at least one blade 26 of the rotor 20 of the present invention includes a winglet 36 at its radially outer end. As is well known, the winglet 36 is a shaping device applied to the end of the blade 26 to improve its aerodynamic efficiency, thereby reducing the induced drag caused by tip vortices. The winglet 36 itself is known and preferably includes baffles 44 extending in the axial direction and the circumferential direction.

[0130] According to certain embodiments of the present invention, the rotor 20 of the present invention includes n blades 26 having a V-shaped geometry in a plan view. This solution is described in detail in the applicant's patent document WO 2017 / 085134 (not shown in the drawings). In particular, this V-shaped geometry of the blades 26, where the leading edge of the blades 26 is concave in a plan view, achieves a significant reduction in the noise generated by the fan 22.

[0131] According to a second aspect, the present invention relates to an axial fan 22 for industrial use, comprising a rotor 20 and a motor 46 as described above. Preferably, the fan 22 of the present invention includes an electric motor 46.

[0132] According to some embodiments of the present invention, the fan 22 of the present invention is a ducted fan, i.e.: it includes a duct 48 known per se surrounding the rotor 20 (see Figure 3 and Figure 4 ).

[0133] Preferably, the duct 48 includes an annular base 50 as described in the patent document WO 2020 / 245674. In particular, according to this solution, the inner wall of the duct 48 includes an annular base 50 that circumferentially extends around the rotor 20 of the fan 22 and partially houses the outer ends of the blades 26 of the rotor 20. Preferably, the annular base 50 at least partially extends in the axial direction and partially houses the baffle 44 defined by the winglets 36.

[0134] According to some embodiments, the fan 22 of the present invention includes a frame 52 configured to support the fan 22 under all operating conditions. In particular, the frame 52 is configured to firmly support the fan 22 at all rotational speeds in transient and steady states without experiencing uncontrolled vibrations.

[0135] According to some embodiments, the orientation of the fan 22 of the present invention is such that the axis of rotation R is vertical and points upward. In this case, the frame 52 and the motor 46 are preferably arranged upstream of the rotor 20 (i.e., below the rotor 20), and the frame 52 is firmly anchored in the workshop and thus typically anchored to the ground.

[0136] According to certain embodiments, the fan 22 of the present invention is part of a cooling system that includes a cooling module arranged immediately downstream of the fan 22, in which a coolant circulates. According to other embodiments, the fan 22 of the present invention is part of a ventilation or air flow system. In this case, there is typically a manifold downstream of the fan, from which one or more ducts branch off to supply the air flow generated by the fan 22 to a distribution network.

[0137] The experimental tests conducted by the applicant have shown that the efficiency of any type of ventilator 22 has been significantly improved after the introduction of the auxiliary axial-flow fan 32.

[0138] In each experimental test, the overall efficiency is calculated based on the ratio between the measured values of flow - pressure (downstream) and the power absorbed by the motor 46 upstream of the power inverter (upstream). Thus, in addition to the aerodynamic efficiency of the rotor 20, which is of most concern in this discussion, this overall efficiency also includes the electrical efficiency of the inverter, the electromechanical efficiency of the motor 46, and the effects of the mechanical efficiency of the coupling and transmission. Therefore, it should be noted that the overall efficiency measured in this way can be significantly reduced even by a single inefficient component, such as a poorly performing belt drive or inverter.

[0139] The experimental tests conducted by the applicant involve several different configurations of the ventilator 22. The various configurations of the ventilator 22 differ in the following aspects: the number of blades 26, the planar form of the blades 26, the pitch angle θ of the blades 26, the type of attachment 40 of the blades 26 to the hub 24, the presence or absence of a duct 48, the presence or absence of winglets 36, and whether it is within the duct 48 of the annular base 50 that partially houses the outer radial ends of the blades 26. For each specific configuration of the ventilator 22, as described above, the overall efficiency is calculated twice: the first time without the auxiliary axial-flow fan 32; the second time with the auxiliary axial-flow fan 32. Among the various known configurations, the efficiency of the ventilator 22 ranges between 41% and 46%, with an average of approximately 44%. In all the configurations considered, the addition of the auxiliary axial-flow fan 32 has significantly improved the efficiency. After adding the auxiliary axial-flow fan 32, the measured efficiency has increased by 1.9% to 6.5%, with an average increase of 3.46%. Although the increase in efficiency is quite significant, it can be well understood by those skilled in the art that the role of the auxiliary axial-flow fan 32 will be further enhanced by associating it solely with the aerodynamic components (i.e., omitting the measurement of the overall efficiency of all non-aerodynamic effects).

[0140] The applicant has also conducted experimental tests to determine the characteristic curves in the flow - pressure plane of the ventilator 22 according to the present invention (i.e., including the auxiliary axial-flow ventilator 32). Then, for each such ventilator 22, the characteristic curves are compared with those of an identical ventilator 22 (but without the auxiliary axial-flow fan 32). Figure 24 The average trend of these characteristic curves is shown qualitatively. In particular, the known type of ventilator 22 includes a common duct 48, and the corresponding auxiliary axial-flow fan 32 is added to this common duct to obtain the corresponding ventilator 22 of the present invention. In Figure 24It can be seen that the arrangement of the auxiliary axial fan 32 according to the present invention can achieve two remarkable advantages. First, the auxiliary axial fan 32 of the present invention allows the characteristic curve to move upward, which is the result achieved by increasing the pitch angle in a ventilator 22 of a known type. Second, since it allows the pitch to be reduced at the same flow rate, the auxiliary axial fan 32 of the present invention allows the stall region that appears in the left part of the characteristic curve of the prior art to be reduced or eliminated in some cases. By reducing or eliminating the stall, the ventilator 22 including the auxiliary axial fan 32 of the present invention can operate with higher efficiency.

[0141] According to the applicant's own research and the tests conducted, the applicant believes that the function of the auxiliary axial fan 32 does not lie in the air movement in the region of the hub 24, that is: in addition to the air flow generated by the main rotor 20, an additional air flow is increased. On the contrary, the applicant believes that the function of the auxiliary axial fan 32 is to stabilize the velocity and pressure fields in the radial inner region of the main rotor 20 (i.e., the region of the root 28 of the blade 26), so that the rotor 20 can work better and the overall efficiency can be improved. In other words, the presence of the auxiliary axial fan 32 significantly limits the radial extension of the disturbance caused by the (inner) end effect, so that the part of the blade 26 that works near the optimal point represented by the theoretical streamline extends in the radial direction. Figure 23 The influence of the auxiliary axial fan 32 on the air flow in the radial inner region of the rotor 20 is schematically shown in, where the dashed line represents a circumferential arc centered on the rotation axis R, and the arrow represents the streamline. From Figure 23 the schematic diagram, it can be seen that the auxiliary axial fan 32 is not intended to hinder the air recirculation in the radial inner region of the rotor 20, but is constructed to utilize this tendency of recirculation to stabilize the air flow.

[0142] An effect similar to that achieved by the auxiliary axial fan 32 in the rotor 20 of the present invention is also achieved by the annular base 50 described in the patent WO 2020 / 245674. In fact, it is noted that the annular base 50 that at least partially houses the ends of the blades 26 of the rotor 20 significantly limits the disturbance caused by the (outer) end effect, so that the part of the blade 26 that works near the optimal point represented by the theoretical streamline extends in the radial direction.

[0143] Specifically referring to the interaction between the auxiliary axial fan 32 of the present invention and the annular base 50 described in the patent document WO 2020 / 245674, the applicant conducted various experimental tests to determine the efficiency trend based on the flow rate when the structure of the ventilator 22 changes. In Figure 25 important curves are qualitatively shown, which schematically and understandably summarize the results of the entire experimental activity, which will be briefly described below.

[0144] In the initial phase of the experimental activity, a plurality of fans 22 of known types were identified, which differed from each other in one or more design parameters, such as the number of blades, diameter, profile type, pitch angle, etc. All the fans 22 considered in the experimental activity commonly employed winglets 36 and a duct 48, both of traditional types. Subsequently, for each type of fan 22, the following components were prepared and maintained:

[0145] - an auxiliary axial fan 32 according to the present invention; and

[0146] - an annular base 50 described in WO 2020 / 245674, i.e., a baffle 44 that is open in the axial direction and adapted to partially accommodate the winglets 36.

[0147] In the operating steps of the experimental activity, for each type of fan 22 in four different configurations of the same fan 22, curves showing the efficiency variation based on the flow rate were experimentally plotted:

[0148] - a basic configuration according to the prior art; in this basic configuration, the fan 22 includes only the winglets 36 and the duct 48.

[0149] - a first improved configuration according to the prior art; this configuration was obtained from the basic configuration by adding the annular base 50 described in WO 2020 / 245674.

[0150] - a second improved configuration according to the present invention; this configuration was obtained from the basic configuration by adding the auxiliary axial fan 32 of the present invention.

[0151] - a third improved configuration according to the present invention; this configuration was obtained from the basic configuration by adding the annular base 50 described in WO 2020 / 245674 and the auxiliary axial fan 32 of the present invention.

[0152] Figure 25 Four different curves are shown, schematically depicting the curves obtained for each of the above configurations, where:

[0153] - the curve related to the basic configuration (a part of the prior art) is a long-dashed virtual curve;

[0154] - the curve related to the first improved configuration (a part of the prior art) is a short-dashed virtual curve;

[0155] - the curve related to the second improved configuration (a part of the present invention) is a continuous single-dashed curve;

[0156] - the curve related to the third improved configuration (a part of the present invention) is a continuous double-dashed curve.

[0157] It can be noted that all the improved configurations have curves that are shifted upward relative to the basic configuration. This means that for the same air flow rate formed, the introduction of each improvement generally results in an increase in the efficiency of the ventilator 22. A different phenomenon that can be observed is the migration of the maximum efficiency point, although this phenomenon is not of concern in the present discussion.

[0158] A more interesting observation concerns the magnitude of the upward shift of the different curves. In particular, it can be noted that a significant improvement comparable to that achieved by only adding the annular base 50 (the first improved configuration) can be achieved by only adding the auxiliary axial fan 32 (the second improved configuration).

[0159] What is truly surprising is the combined effect of these two improvements. As can be clearly seen from Figure 25 the efficiency increase achieved by applying both improvements (the third improved configuration) is significantly greater than the sum of the efficiency increases achieved by applying these two improvements separately (i.e., first only the annular base 50 and then only the auxiliary axial fan 32). Based on the results of the research conducted, the applicant believes that the simultaneous presence of the annular base 50 and the auxiliary axial fan 32 in the third improved configuration can stabilize the velocity and pressure ranges in the radial inner region of the rotor 20 (thanks to the auxiliary axial fan 32) and the radial outer region of the rotor 20 (thanks to the annular base 50 of the baffle 44 that houses the winglets 36). Thus, the entire ventilator 22 can operate in an optimal state, improving its overall efficiency.

[0160] In view of the above, those skilled in the art can well understand how the presence of the two solutions in the same ventilator 22 enables a particularly preferred embodiment, in which the radial extension of the portion of the blade 26 that operates close to the optimal point represented by the theoretical streamline is maximized. It should be noted that in some cases, the overall improvement in the above performance can allow the use of a ventilator 22 according to the present invention, which has one less blade than a conventional ventilator 22 and is indispensable in a conventional ventilator 22; for example, in some cases, a three - blade ventilator 22 according to the present invention can ensure the performance of a four - blade ventilator 22 according to the prior art.

[0161] Furthermore, in some cases, the increase in the overall efficiency can allow the use of a motor with a smaller motor power on the ventilator 22 according to the present invention than that required to drive a conventional ventilator 22 with the same performance.

[0162] Those skilled in the art can well understand that these results can limit the investment and management costs of the ventilator 22. Those skilled in the art can well understand that the present invention overcomes the above - mentioned prominent disadvantages related to the prior art. In particular, the present invention provides an axial - flow ventilator 22 with higher efficiency.

[0163] In addition, the present invention provides an axial flow fan 22 which, compared with known types of fans, is capable of generating a higher pressure at the same speed.

[0164] In addition, the present invention provides an axial flow fan 22 which, compared with known types of fans, can better limit the formation of tip vortices.

[0165] In addition, the present invention provides an axial flow fan 22 which adjusts the flow lines by making the flow lines as close as possible to the theoretically conceived flow lines.

[0166] Finally, the present invention provides a ducted axial flow fan 22 which not only introduces more advantages but also retains the advantages already achieved by known types of fans.

[0167] In summary, all details can be replaced by other technically equivalent elements; features described in connection with a particular embodiment can also be applied to other embodiments; without departing from the scope of protection of the following claims, the materials employed, as well as the possible shapes and dimensions, can be any materials, shapes and dimensions according to specific implementation requirements.

Claims

1. A rotor (20) for an industrial large-diameter axial-flow fan (22), said rotor comprising a hub (24) and n blades (26), wherein each blade (26) of said rotor (20) comprises an aerodynamic portion (30) and a root (28) for structurally connecting to said hub (24), wherein said rotor (20) further comprises an auxiliary axial-flow fan (32), said auxiliary axial-flow fan (32) comprising n radially extending fan blades (34), and in an axial view, said auxiliary axial-flow fan is substantially included within a region P defined by the n radially inner ends of the aerodynamic portions (30) of the blades (26) of said rotor (20), wherein said auxiliary axial-flow fan (32) is disposed downstream or upstream of said hub (24), and wherein said auxiliary axial-flow fan (32) is fixedly mounted on said rotor (20).

2. The rotor (20) according to claim 1, wherein in an axial view, said auxiliary axial-flow fan (32) is inscribed within said region P.

3. The rotor (20) according to claim 1 or 2, wherein said auxiliary axial-flow fan (32) comprises a central portion (42), and said n fan blades (34) radially extend from said central portion (42).

4. The rotor (20) according to claim 1 or 2, wherein said auxiliary axial-flow fan (32) is obtained by directly applying n independent fan blades (34) on said rotor (20).

5. The rotor (20) according to claim 1 or 2, wherein the radial extension B of the fan blades (34) of said auxiliary axial-flow fan (32) is between 60% and 75% of the radius d / 2 of said auxiliary axial-flow fan (32).

6. The rotor (20) according to claim 5, wherein the radial extension B of the fan blades (34) of said auxiliary axial-flow fan (32) is between 65% and 70% of the radius d / 2 of said auxiliary axial-flow fan (32).

7. The rotor (20) according to claim 1 or 2, wherein the axial extension a of the fan blades (34) of said auxiliary axial-flow fan (32) is within 20% of the diameter d of said auxiliary axial-flow fan (32).

8. The rotor (20) according to claim 7, wherein the axial extension a of the fan blades (34) of said auxiliary axial-flow fan (32) is between 5% and 15% of the diameter d of said auxiliary axial-flow fan (32).

9. The rotor (20) according to claim 1 or 2, wherein the fan blades (34) of said auxiliary axial-flow fan (32) comprise a root (54) for structurally connecting to said hub (24) and an aerodynamic portion (56).

10. The rotor (20) according to claim 1 or 2, wherein said auxiliary axial-flow fan (32) is made as an integral unitary body.

11. The rotor (20) according to claim 1 or 2, wherein the thickness t of each fan blade (34) of said auxiliary axial-flow fan (32) is substantially uniform throughout the extension of said fan blade (34).

12. The rotor (20) according to claim 1 or 2, wherein the thickness t of the blades (34) of the auxiliary axial fan (32) is included between 10% and 20% of the axial extension a of the blades (34) of the auxiliary axial fan (32).

13. The rotor (20) according to claim 1 or 2, wherein at least one blade (26) includes a fin (36) located at the radially outer end, and wherein the fin (36) includes a baffle (44) extending in the axial direction and the circumferential direction.

14. An industrial ventilator (22), comprising a motor (46) and a rotor (20) according to any one of claims 1 to 13.

15. The industrial ventilator (22) according to claim 14, further comprising a duct (48) surrounding the rotor (20).

16. The industrial ventilator (22) according to claim 15, wherein the duct (48) includes an annular base (50) that extends circumferentially around the rotor (20) and partially houses the outer ends of the blades (26) of the rotor (20).

17. The industrial ventilator (22) according to claim 16, comprising the rotor (20) according to claim 13, and wherein the annular base (50) extends at least partially in the axial direction and partially houses the baffle (44) defined by the fin (36).

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