Axial fan comprising end plate at tip of blade

Abstract

The invention relates to an axial fan (20) comprising a cylindrical casing (22) in which: each blade (26) comprises an aerodynamic portion (30) extending radially outward and an end plate (32) at the outer end; the aerodynamic part is obtained from an extruded / pultruded profile and is defined as an airfoil in the cross section; the end plate extends in the axial direction and the circumferential direction and is provided with a cylindrical radial outer surface; when the end plates are properly disposed adjacent to the housing, they define a gap 34 having a uniform and constant thickness. Furthermore, the blade comprises a joint 36 between the aerodynamic portion and the end plate, where: the joint is structurally independent of the blade, the radially outer end of the aerodynamic portion being defined by a plane n; a radially outer end of the joint portion is continuously attached to the end plate; the radial inner end of the joint part is limited by a plane n; and a radially inner end of the joint is coupled and continuously connected to the aerodynamic portion and comprises means (40) for structural coupling with a radially outer end of the aerodynamic portion.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of axial fans, in particular to large diameter axial fans for industrial use. BACKGROUND

[0002] In the field of large diameter (i.e. having a diameter greater than 90 cm) axial fans 20 (see for example Figure 1 ) it is particularly widespread and popular to use extruded or pultruded profiles to manufacture the blades 26. In the following, the term "profile" refers to an elongated semi-finished product made by extrusion or pultrusion.

[0003] As is known, the extrusion process comprises forcing a ductile material (typically an aluminium alloy) through a die which reproduces the shape of the profile to be obtained. In the case of a profile for manufacturing the blades 26 of a fan 20, the outer shape is defined by an airfoil, while structural reinforcement partitions can be arranged inside the profile (see for example Figure 2 ). In order to simplify production, some airfoils having a particularly extended chord (for example greater than 40 cm) can be made of two or more complementary profiles which must then be joined together along the longitudinal direction. For example, a first profile can be made of the front part of the airfoil (the part defining the leading edge), while a second profile is made of the rear part of the airfoil (the part defining the trailing edge). This process allows to industrially produce profiles having a constant section with an indefinite a priori length along their longitudinal axis I.

[0004] Conceptually similar to extrusion is the pultrusion process, which is used in the field of long fibre composites. In this case, reinforcing fibres and a matrix in an unpolymerized state are pulled through a heated die which imparts the profile shape, while at the same time directing the polymerization of the matrix. Thus, at the outlet of the die we have a profile having a constant section and an indefinite a priori length. It should be noted that most of the fibres are as long as the profile itself and are arranged along their longitudinal axis I.

[0005] As briefly described above, both extrusion and pultrusion allow to manufacture profiles having a constant section and an indefinite a priori length. Moreover, both technologies guarantee a high quality of the outer surface of the profile, which is a particularly important characteristic in the field of fans 20 and aerodynamics. Despite this, both processes are characterized by a relatively low production cost. For all these analogies, in the following discussion the two processes and the resulting profiles will be considered as perfectly superimposable on each other, unless explicitly stated otherwise, provided that the extruded profiles are metallic (typically aluminium) while the pultruded profiles are made of composite material (typically epoxy matrix glass fibres).

[0006] The use of extruded / pultruded profiles has many advantages in terms of economy of production and flexibility of construction, which are well known in the field of industrial fans 20. In fact, the indefinite a priori length of the profiles allows them to be cut to size to obtain, depending on the case, blades 26 having an optimal length. This allows the designer to freely define the diameter of the fan 20. Conversely, the size of the blades 26 made by molding is directly defined by the size of the mold. Therefore, in this case, the designer can choose the diameter of the fan 20 only among the available sizes, or alternatively, must make a special mold, with a cost increase that is often unacceptable.

[0007] As is known, the airflow that collides against the ends of any aerodynamic surface, such as the blades 26 of the fan 20, during operation is particularly complex. This phenomenon involves both the radially inner end of the blade 26 and the radially outer end, also called tip, of the blade 26, with which the present invention is more directly connected.

[0008] Near the tip, the interruption of the blade 26 itself generates a displacement of the air from a high pressure area, which is normally created immediately downstream of the blade 26, towards a low pressure area, immediately upstream of the blade 26. This displacement increases the main airflow directed in both the circumferential and axial direction, generating the known tip vortex.

[0009] The use of extruded / pultruded profiles requires some precautions, also related to the aerodynamic phenomena that occur at the tip. Cutting the profile to the desired size exposes the internal cavity, making the interaction between the blade 26 and the vortex airflow present at the tip even more complex. In addition to the complexity of the local phenomena, which make the precise modeling of the fan 20 difficult, the most evident consequences at the macroscopic level are an increase in aerodynamic resistance, an increase in noise, and a reduction in the overall efficiency of the fan 20.

[0010] To this end, the so-called cap 31 is introduced, i.e. an element that reproduces exactly the shape of the airfoil used in the blade 26 and is shaped so as to be applied to the radially outer surface of the tip so as to cover the cavity of the profile and expose a continuous surface to the airflow (see in this regard Figure 2 ).

[0011] The introduction of the cap 31 also allows further advantages. Strictly speaking, the cut of the profile located at the tip should be curved, i.e. made along a cylindrical surface having a radius defined during the design phase of the fan 20. However, the cut operation that must be precisely followed on the extruded / pultruded profile is by no means trivial. To this end, in order to simplify the construction of the blade 26, the curved cap 31 is introduced (see Figure 3). The curved cover 31 allows straight cuts to be made on the profile, i.e. along a plane of cut and not along a cylindrical surface. The function of restoring the curvature of the ideal design cylinder is performed by the curved cover 31 itself. From Figure 3 a schematic plan view it can be understood that the cover 31 has a variable thickness and defines a (radially inner) flat surface coupled to the blade 26, and a (radially outer) curved surface following the ideal design curvature and, in the case of the ducted fan 20, approaching the casing 22. In this way, the structure of the blade 26 is further simplified.

[0012] Despite the evident lightening, the adoption of the curved cover 31 again presents the problem that the blade 26, previously made by molding, has already presented. The curvatures available in the catalog for the covers are in fact defined a priori, for example for some diameters most commonly used in industrial fans 20. In the case of diameters not available to the designer, the blade 26 can be easily made, while the corresponding cover 31 must be chosen on the basis of approximations, thus obtaining a suboptimal solution. In the case of a fan 20 ducted, i.e. in the case in which a cylindrical casing 22 is arranged around the fan 20, the adoption of a suboptimal solution can entail serious problems (see again Figure 1 ). In this case, the difference between the curvature of the cover 31 and the ideal (or design) curvature of the fan 20 becomes particularly evident due to the presence of the casing 22. In the example of Figure 3 , the tip of the blade 26 of the ducted fan 20 is represented in plan view, on which a cover 31 is mounted having a more pronounced curvature, i.e. a cover 31 intended for a fan 20 having a smaller diameter. As can be noted, the excessively pronounced curvature of the cover 31 means that the distance along the circumferential development of the tip between the casing 22 and the cover 31 itself is variable. This configuration of the gap 34 formed between the tip and the casing 22 can also generate negative interactions with the flow of air.

[0013] This problem can be solved by constructing a particular (i.e. customized) curved cover 31 shaped according to the correct design curvature. Although the production of a customized cover 31 is significantly simpler and cheaper than the production of an entire customized blade 26, this solution anyway implies a complexity and an undesirable increase in costs of production of the fan 20.

[0014] Still in the scope of the covers for the tips of the blades 26 made from extruded / pultruded profiles, it has recently been noted that considerable advantages are obtained by adding end plates 32 that exceed the shape of the airfoil and extend in the axial direction (and possibly in the circumferential direction). Such end plates allow, for example, to limit the extent of the tip vortex or to take advantage of the presence of the tip vortex and reduce the noise generated by the airflow at the tip. Other more specific advantages are related to the use of the end plates in combination with the casing 22. In this case, the end plate 32 (or at least its radially outer surface) must be shaped according to a cylindrical portion having a radius slightly smaller than that of the casing 22, with the difference between the radii being defined during the design phase. In particular, two partially conflicting requirements must be taken into account to define the distance. On the one hand, the smaller the distance, the greater the benefits of the interaction between the end plate 32 and the casing 22. On the other hand, it is necessary to avoid possible contacts or scratches between the end plate 32 and the casing 22 during the normal operation of the fan 20.

[0015] Even with the use of the end plate 32 at the tip, despite the interest, the desired results are not achieved. In fact, the end plate 32 is defined on the basis of the airfoil chosen for the blade 26 and possibly on the basis of the diameter of the casing 22. The other design parameters of the fan 20 described below are not taken into account in the definition of the end plate 32.

[0016] During the design phase, the same type of blade 26 can assume different angles of attack a, i.e. the blade 26 can be rotated around its longitudinal axis I to vary the forces generated in the interaction with the airflow. The end plate 32 follows the rotation of the blade 26 since it is integral with the blade 26. Figure 4 The tip of the blade 26 is shown in a view along the radial direction, with the respective end plate 32 and the casing 22 in the background. For the sake of clarity, in Figure 4 the cylindrical generatrix straight lines are highlighted on the cylinder of the casing 22 and on the cylinder of the end plate 32. As can be easily understood, the two cylinders are not perfectly coaxial, but are rotated with respect to each other.

[0017] Furthermore, during the design phase, the same type of blade 26 can adopt different pre-coning angles β, i.e. the blade 26 can be rotated around its base so as to exit the plane of rotation τ, i.e. the plane τ perpendicular to the rotation axis X (see Figure 5 ). Also in this case, the end plate 32 follows the blade 26. Figure 5 A front view of the blade 26 with the respective end plate 32 and the adjacent casing 22 is shown schematically. As can be easily understood, the end plate 32 is not perfectly parallel to the casing 22, but is inclined by an angle equal to the pre-coning angle β.

[0018] Finally, in the design phase, the entire blade 26 or a radially outer portion thereof can be rotated within its own plane of rotation T (forward or backward along the direction of rotation) by an angle called the swing angle γ (see Figure 6 Also in this case, the end plate 32 follows the blade 26. Figure 6 A plan view of the blade 26 with the respective end plate 32 and the adjacent casing 22 is schematically shown. As can be easily understood, the end plate 32 is not perfectly parallel and coaxial to the casing 22, but is tilted by an angle equal to the swing angle γ.

[0019] As is clear from the above description, each design parameter (i.e. the incidence angle a, the pre- cone angle β and the swing angle γ) implies a misalignment between the end plate 32 and the respective casing 22. Each misalignment implies a worsening of the aerodynamic phenomena occurring around the tip by introducing a variable distance between the end plate 32 and the casing 22.

[0020] Therefore, there is a need for an improved axial fan comprising an optimized end plate at the blade tip. SUMMARY

[0021] Therefore, it is an object of the present application to at least partially overcome the above-mentioned drawbacks related to the prior art.

[0022] In particular, it is a task of the present application to provide an axial fan which optimizes the geometry of the end plate at the blade tip.

[0023] Furthermore, it is a task of the present application to provide a ducted axial fan which optimizes the interaction between the end plate at the blade tip and the casing.

[0024] Moreover, it is a task of the present application to provide a method for increasing the efficiency of an existing axial fan.

[0025] Finally, it is a task of the present application to provide a method for implementing an improved axial fan comprising an optimized end plate at the blade tip.

[0026] These and other objects and tasks of the present application are achieved by an axial fan and a method according to the appended claims. Further features are identified in the dependent claims. All the appended claims form an integral part of the present disclosure.

[0027] According to a first aspect, the present application relates to an axial fan comprising a rotor rotatable about a rotation axis X and a cylindrical casing arranged around the rotor and coaxial to the rotor. In the fan of the present application:

[0028] - the rotor comprises a hub and a plurality of blades,

[0029] - each blade comprises a radially inner base portion constrained to the hub, an aerodynamic portion extending mainly radially outwards from the base portion, and an end plate at a radially outer end,

[0030] - the aerodynamic portion is obtained from an extruded / pultruded profile,

[0031] - the aerodynamic portion defines an airfoil in cross section,

[0032] - the end plate extends mainly in axial and circumferential directions,

[0033] - the end plate defines a radially inner surface and a radially outer surface, the radially outer surface being shaped according to a cylindrical surface portion, and

[0034] - when said end plate is correctly arranged adjacent to the casing, the radially outer surface co-defines with the casing a gap having a uniform and constant thickness.

[0035] The blade further comprises a junction portion positioned between said aerodynamic portion and said end plate, wherein:

[0036] - the junction portion is manufactured structurally independent from the aerodynamic portion of the blade;

[0037] - the radially outer end of the aerodynamic portion is defined by a plane p;

[0038] - the radially outer end of the junction portion is attached continuously to the radially inner surface of the end plate;

[0039] - the radially inner end of the junction portion is defined by the plane p;

[0040] - the radially inner end of the junction portion is coupled and connected continuously to the aerodynamic portion; and

[0041] - the radially inner end of the junction portion comprises means for structural coupling with the radially outer end of the aerodynamic portion.

[0042] The provision of the junction portion allows to perfectly link the aerodynamic portion of the blade to the end plate, whatever its orientation in space, the position of the end plate being firmly constrained by the casing so as to form a regular and uniform gap. In particular, manufacturing the junction portion as a structurally independent element allows great flexibility in the working operations, in particular cutting the junction portion along a spatial curve representing the intersection line between the blade and the radially inner surface of the end plate.

[0043] Preferably, the thickness of the gap comprised between the end plate and the casing is less than or equal to 0.005 times the diameter of said fan.

[0044] This distance between the shell and the end plate allows to optimize the aerodynamic performance of the tip of the blade while avoiding the risk of an unwanted contact between the end plate and the shell during the operation of the fan.

[0045] Preferably, during the assembly of the fan, the junction engages to the aerodynamic portion of the blade.

[0046] The engagement of the junction during the assembly of the fan guarantees a high manufacturing flexibility and improves the handling of the components from the production site of the fan to the final assembly site.

[0047] Preferably, the end plate is obtained by a radially innermost first panel and a radially outermost second panel which are juxtaposed to each other at least in the radial direction.

[0048] The provision of two panels makes it possible to improve the mechanical characteristics of the end plate while being able to obtain a high manufacturing flexibility.

[0049] According to some embodiments, the shell comprises an annular seat which extends circumferentially around the rotor and which is open in the axial direction. Advantageously, each end plate provided at the end of a blade is at least partially housed in the annular seat. Preferably, a baffle is provided on the junction, the baffle extending in the circumferential and axial directions, being radially inner with respect to the end plate and with respect to the annular seat.

[0050] Such embodiments take advantage of a solution developed by the same Applicant, which allows to obtain a labyrinthine seal between the blade and the shell. The seal prevents in a very effective manner the air from flowing around the tip of the blade. The presence of the baffle allows to further improve the effectiveness of the solution.

[0051] According to a second aspect, the present invention relates to an industrial cooling system comprising a fan as described above.

[0052] The use of a fan in an industrial cooling system allows to take advantage of the advantageous features of the present invention to the maximum.

[0053] According to a third aspect, the present invention relates to a method for retrofitting an existing axial fan comprising a hub rotatable around an axis of rotation X, a plurality of blades, and a cylindrical shell arranged around the hub and coaxial to the hub, wherein each blade comprises an aerodynamic portion obtained from an extruded profile having its own longitudinal axis I and having a cross section shaped according to an airfoil profile perpendicular to the longitudinal axis I. The method of the present invention first comprises a step of defining an end plate based on the diameter of the shell, and wherein the end plate:

[0054] - extends mainly in the axial and circumferential directions,

[0055] - defines a radially inner surface and a radially outer surface, the radially outer surface being shaped according to a cylindrical surface portion, and

[0056] - when the end plate is correctly arranged adjacent to the shell, the radially outer surface defines, jointly with the shell, a gap having a uniform and constant thickness.

[0057] The method further comprises the following steps:

[0058] - identifying an airfoil to be used for manufacturing the aerodynamic portion of the blade;

[0059] - identifying geometrical design parameters of the blade of the rotor, i.e.: angle of attack a, pre- cone angle β and flapping angle γ;

[0060] - defining a virtual blade having the above identified airfoil and geometrical design parameters and indefinite radial extension;

[0061] - when the end plate is correctly arranged adjacent to the shell, determining a spatial curve representing the intersection line of the virtual blade with the radially inner surface of the end plate;

[0062] - providing a joint having a radially inner end defining a support plane π and shaped to continuously couple and connect to a radially outer end of the pultruded profile of the blade;

[0063] - cutting the radially outer end of the joint along the intersecting spatial curve;

[0064] - constraining the radially outer end of the joint to the radially inner surface of the end plate;

[0065] - cutting the blade along the support plane π;

[0066] - constraining the radially inner end of the joint to the radially outer end of the aerodynamic portion of the blade after cutting; and

[0067] - repeating the above defined operations for each blade.

[0068] The method allows to apply the present invention to existing fans, thus achieving great benefits due to the costs limited to the change of the blade tip.

[0069] According to a fourth aspect, the present invention relates to a method for manufacturing, at first, an axial fan comprising a hub rotatable about an axis of rotation X, a plurality of blades and a cylindrical shell arranged around the hub and coaxial thereto. The method of the present invention comprises the following steps:

[0070] - defining a diameter of the shell,

[0071] - based on the diameter of the shell, defining an end plate, wherein the end plate:

[0072] - mainly extend in axial and circumferential directions,

[0073] - define a radially inner surface and a radially outer surface, the radially outer surface being shaped according to a cylindrical surface portion,

[0074] - when the end plate is correctly arranged adjacent to the casing, the radially outer surface jointly defines with the casing a gap having a uniform and constant thickness;

[0075] - selecting an airfoil for manufacturing the aerodynamic portion of the blade;

[0076] - providing an extruded / pultruded profile having the airfoil selected above and indefinite extension along its own longitudinal axis l perpendicular to the plane of the airfoil;

[0077] - providing a base at the radially inner end of the extruded or pultruded profile;

[0078] - defining geometrical design parameters of the blade of the rotor, i.e.: angle of attack a, pre- cone angle β and oscillation angle γ;

[0079] - defining a virtual blade having the airfoil selected above, the geometrical design parameters defined above and indefinite radial extension;

[0080] - when the end plate is correctly arranged adjacent to the casing, determining a spatial curve representing the intersection line of the virtual blade with the radially inner surface of the end plate;

[0081] - providing a joint having a radially inner end defining a support plane π and shaped to continuously couple and connect to the radially outer end of the extruded / pultruded profile of the blade;

[0082] - cutting the radially outer end of the joint along the intersecting spatial curve;

[0083] - constraining the radially outer end of the joint to the radially inner surface of the end plate;

[0084] - cutting the extruded / pultruded profile of the blade along the support plane π, thereby obtaining the aerodynamic portion;

[0085] - constraining the radially inner end of the joint to the radially outer end of the aerodynamic portion;

[0086] - constraining the base of the blade to the hub according to the geometrical design parameters;

[0087] - repeating the operations defined above for each blade.

[0088] This method allows to apply the present invention to completely new fans, thus maximizing all its advantages.

[0089] Preferably, in any of the above methods, at least some steps of the process are performed by means of a CAD / CAM type computer system.

[0090] Preferably, the step of cutting the radially outer end of the junction along the intersecting spatial curve is performed by means of a numerical control machine tool.

[0091] The use of a CAD / CAM type computer system, in particular a numerical control machine tool for cutting the junction along the intersecting spatial curve, allows to significantly simplify the implementation of the method of the present invention.

[0092] Further features and objects of the present invention will become more apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0093] The present invention is described hereinafter with reference to some examples provided by way of non-limiting illustration and shown in the accompanying drawings. The drawings show different aspects and embodiments of the present invention and, where appropriate, components, materials and / or similar elements in different drawings are denoted by like reference numerals. Furthermore, some references can not be repeated in all drawings for the sake of clarity.

[0094] Figure 1 is an axonometric view of a ducted axial fan for industrial use;

[0095] Figure 2 is an exploded axonometric view of the radially outer end of a blade of a fan according to the prior art;

[0096] Figure 3 is a schematic plan view of the radially outer end of a blade of a ducted fan according to the prior art;

[0097] Figure 4 is a schematic view of a blade of a ducted fan according to the prior art along a radial direction;

[0098] Figure 5 is a schematic front view of the radially outer end of a blade of a ducted fan according to the prior art;

[0099] Figure 6 is a schematic plan view of the radially outer end of a blade of a ducted fan according to the prior art;

[0100] Figure 7 is a schematic axonometric view showing a blade of a fan according to the present invention, in which some components of the fan have been deleted for the sake of clarity;

[0101] Figure 8 is a schematic plan view of the tip of a blade according to the present invention;

[0102] Figure 9 is a schematic plan view of the tip of a blade according to the present application;

[0103] Figure 10 is a schematic plan view of the tip of a blade according to the present application;

[0104] Figure 11.a is a schematic plan view of the tip of a blade being machined according to the present application;

[0105] Figure 11.b is a schematic front view of the tip of a blade being machined according to the present application;

[0106] Figure 12 and Figure 13 schematically illustrates two steps of the method according to the present application;

[0107] Figure 14 is a schematic isometric view of a semi-finished joint used in the method according to the present application;

[0108] Figure 15 is a schematic exploded front view of the tip of a blade according to the present application;

[0109] Figure 16 is a schematic plan view of the tip of Figure 15 ; is a schematic isometric view of the tip of ; and

[0110] Figure 17 is a schematic isometric view of the tip of Figure 15 ; and

[0111] Figure 18 is a schematic isometric view of the tip of a blade according to an embodiment of the present application;

[0112] Figure 19 is a view of a blade according to another embodiment of the present application similar to Figure 18 ; is a schematic front view of the tip of a blade according to another embodiment of the present application;

[0113] Figure 20 is a schematic front view of the tip of a blade according to another embodiment of the present application;

[0114] Figure 21 is a schematic plan view of the tip of a blade of Figure 20 ; is a schematic isometric view of the tip of a blade according to another blade of the present application; and

[0115] Figure 22 is a schematic isometric exploded view of the tip of another blade according to the present application; and

[0116] Figure 23 is a schematic plan view of the tip of a blade of Figure 22 . DETAILED DESCRIPTION

[0117] While the application is amenable to various modifications and alternative constructions, certain preferred embodiments have been shown in the drawings and will be described in detail below. It should be understood, however, that there is no intention to limit the application to the specific embodiments shown, but on the contrary, the application is intended to cover all modifications, alternatives, and equivalents falling within the scope of the application as defined by the claims.

[0118] The detailed description set forth below describes various aspects and technical features of the application. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, since various changes and modifications within the scope of the application should become apparent to those skilled in the art from this detailed description.

[0119] The use of the terms "for example," "e.g.," "or" and "such as" means "by way of example," "for example," and "such as" and not by way of limitation. The use of "including" and "including, but not limited to" means "including, but not limited to," and "including, but not limited to, and the like.

[0120] In the following discussion, the term "airfoil" generally indicates a shape per se known to those skilled in the art, suitable for interacting with a fluid flow to exchange forces. The shape used in the present application is generally intended to interact with air, and it is therefore also referred to as "airfoil", without thereby introducing any limitation to the interaction with gases other than air.

[0121] The term "airfoil" can have two slightly different meanings. The first meaning is virtual, indicating a curve drawn graphically on a plane or defined digitally for the study of the implementation of a real device. The second meaning is real, indicating a shape of a material that reproduces the virtual airfoil in cross section. If it is necessary to distinguish between the two meanings, the first can also be referred to as "virtual airfoil" and the second as "real airfoil".

[0122] Similarly to the term "airfoil", other terms indicating elements of the fan of the present application, such as "shell", "blade", "end plate", and the like, can also have two slightly different meanings. The first meaning is virtual, indicating a geometric or digital representation for the study and implementation of a real device. The second meaning is real, indicating a physical, material element. If it is necessary to distinguish between the two meanings, the first can also be indicated with the adjective "virtual" and the second with the adjective "real". In any case, the skilled person will not have difficulty in considering and evaluating the transition from the abstract or digital geometric field to the physical and real field.

[0123] In the following description, frequent reference is made to geometric concepts (parallel, perpendicular, coaxial, etc.) and geometric entities (plane, axis, cylinder, etc.). As the skilled person can well understand, such expressions are not to be understood in a purely geometric abstraction and perfect sense, but are to be interpreted in conjunction with the technical scope of the present invention and typical tolerances in the art.

[0124] The following discussion relates to an industrial axial fan, uniquely defining a rotation axis X, the terms "axial", "radial", "circumferential" and "tangential" being uniquely defined with respect to this rotation axis X.

[0125] In particular, the axial direction (sometimes denoted a in the figures) is the direction of any straight line parallel to the axis X; the radial direction (sometimes denoted r in the figures) is the direction of any half-straight line starting from the axis X and perpendicular to the axis X; the circumferential direction (sometimes denoted c in the figures) is the direction of any circumference centered on the axis X and lying on a plane perpendicular thereto; finally, the tangential direction (sometimes denoted t in the figures) is the direction of any straight line tangent to one of the circumferences just defined.

[0126] In the following description, frequent reference is made to a "longitudinal axis 1". Such longitudinal axis 1 is univocally defined for each profile, as it directly comes from the extrusion / pultrusion direction. Although the same longitudinal axis 1 is sometimes (inappropriately) referred to as the blade 26 or to its aerodynamic portion 30, the skilled person will not have any difficulty to correctly identify it based on the context.

[0127] According to a first aspect, the present invention relates to an axial fan 20 comprising a rotor rotatable about a rotation axis X and a cylindrical casing 22 arranged around the rotor and coaxial to the rotor. In the fan 20 of the present invention:

[0128] - the rotor comprises a hub 24 and a plurality of blades 26,

[0129] - each blade 26 comprises a base portion 28 constrained to a radially inner side of the hub 24, an aerodynamic portion 30 extending mainly radially outward from the base portion 28, and an end plate 32 at a radially outer end,

[0130] - the aerodynamic portion 30 is obtained from an extruded / pultruded profile,

[0131] - the aerodynamic portion 30 defines in cross section a wing profile,

[0132] - the end plate 32 extends mainly in axial and circumferential directions,

[0133] - the end plate 32 defines a radially inner surface and a radially outer surface, the radially outer surface being shaped according to a cylindrical surface portion,

[0134] - when said end plate 32 is correctly arranged adjacent to the casing 22, the radially outer surface defines, jointly with the casing 22, a gap 34 having a uniform and constant thickness,

[0135] and wherein the blade 26 further comprises a junction 36 positioned between said aerodynamic portion 30 and said end plate 32,

[0136] - said junction 36 is manufactured structurally independent of the aerodynamic portion 30 of the blade 26;

[0137] - the radially outer end of the aerodynamic portion 30 is defined by the plane p;

[0138] - the radially outer end of said junction 36 is continuously attached to the radially inner surface of the end plate 32;

[0139] - the radially inner end of said junction 36 is defined by the plane p;

[0140] - the radially inner end of said junction 36 is continuously coupled and connected to the aerodynamic portion 30; and

[0141] - the radially inner end of said junction 36 comprises means 40 for structural coupling with the radially outer end of the aerodynamic portion 30.

[0142] The fan 20 of the present application is described in greater detail below with reference to the attached drawings. The fan 20 of the present application is large in diameter, i.e. greater than 90 cm, preferably greater than 150 cm.

[0143] In the drawings, with the sole exception of Figure 1 for the sake of clarity, only one of the n blades 26 of the fan 20 is shown, and only partially the casing 22, so as not to hide other components that must be visible.

[0144] The base 28 is per se well known, having the sole structural function of connecting the blades 26 to the hub 24 and ensuring that they remain in the position defined during the design phase, in particular in terms of angle of attack a, precone angle b and wobble angle g, during the normal operation of the fan 20.

[0145] Preferably, the base portion 28 is constructed in such a way as to be pre- deformable in a predetermined manner, thus facilitating the main second order vibrations in the blades 26, which significantly limit the amount of translation of the tip in the axial direction with respect to the first order vibrations. A solution of this type is described in WO2017 / 063712, representative of the same applicant.

[0146] The aerodynamic portion 30 of the blade 26 is intended to interact with the air flow to the maximum extent in order to exchange forces and ultimately generate the air flow in the axial direction. The aerodynamic portion 30 thus performs both an aerodynamic function (generation of forces through interaction with the air flow) and a structural function (transmission and counteraction of the forces generated). The aerodynamic portion 30 is made from an extruded profile, shaped according to an airfoil profile.

[0147] Preferably, in manufacturing the aerodynamic portion 30 of the blade 26, a technique known per se, called profiling, is adopted, which allows to obtain a variation of the cross section of the extruded profile. Such a technique is applied to extruded profiles in which the back wall and the web join in a rear integral appendix 33 (see in particular Figure 2 and Figure 4 ). Such an integral appendix 33 extends rearward, generally with a rather marked curvature, up to the trailing edge. Profiling is briefly disclosed below with reference to Figure 1 which allows to obtain an extruded aerodynamic portion 30 with a variable airfoil profile along the longitudinal axis I.

[0148] In the blade 26 of Figure 17 and Figure 22 , the aerodynamic portion 30 extends radially with a constant cross section. Conversely, in the solution of Figure 1 , profiling has been adopted: the appendix 33 has been gradually reduced in the radially outer region of the aerodynamic portion 30. In Figure 1 , the portion of the appendix 33 that has been removed is shown in dashed line and is referred to as 33'. Profiling allows to obtain a higher aerodynamic efficiency, since along the blade 26, profiling gradually reduces the angle of attack a and the curvature of the airfoil profile in the radially outer region where the fluid flow reaches the highest speed.

[0149] The radially outer end of the aerodynamic portion 30 is defined by a plane p, i.e. the aerodynamic portion 30 is cut along a plane, preferably transversal to the longitudinal axis I of the blade 26.

[0150] According to some embodiments, for example those of Figure 8 and Figure 15 to Figure 17 , the end plate 32 is made from a simple flat layer of material, such as a sheet of metal or a thin composite plate, cut to size and bent according to a portion of the cylindrical surface that follows the casing 22 and maintains a uniform and constant distance therefrom. In this case, since the end plate 32 has a constant thickness, both the radially outer surface and the radially inner surface are cylindrical. These are the simplest embodiments of the end plate 32.

[0151] According to other embodiments, for example those of Figure 9According to an embodiment (for example, as illustrated in figure 1), the end plate 32 comprises ribs 38 arranged in the axial direction (i.e. along the generatrix of its cylinder). This embodiment, although not optimal aerodynamically, can significantly limit the radial deformation undergone by the axial end of the end plate 32. In fact, such deformation is mainly due to the centrifugal forces acting on the end plate 32 during the normal operation of the fan 20, which significantly increases with the growth of the axial extension of the end plate 32. In some cases, the benefits deriving from the axial extension of the end plate 32 can compensate for the drawbacks deriving from the presence of ribs 38 on the radial inner surface of the end plate 32.

[0152] Finally, according to other embodiments (for example, as illustrated in figure 2), the end plate 32 has a complex cross section, for example which in turn presents an airfoil profile. This embodiment is the most complex one, but allows to provide ribs 38 in the axial direction to limit the deformation generated by centrifugal forces, and at the same time to incorporate the ribs 38 in the thickness of the airfoil profile to eliminate aerodynamic disturbances. Figure 10

[0153] In view of the foregoing, it will be clear to the person skilled in the art that, while the radial outer surface of the end plate 32 is always a cylindrical surface, since it must closely follow the radial inner surface of the shell 22, the radial inner surface of the end plate 32 can present different shapes. In general, the radial inner surface of the end plate 32 will not be flat and therefore will not be directly connectable to the radial outer end of the aerodynamic portion 30 defined by the plane π.

[0154] The distance between the shell 22 and the end plate 32 (i.e. the uniform and constant thickness of the gap 34) must be defined during the design phase taking into account two partly contrasting requirements. On the one hand, the smaller the distance, the greater the benefits of the aerodynamic interaction between the end plate 32 and the shell 22. On the other hand, it must be avoided that, during the normal operation of the fan 20, there can be contact or scratching between the end plate 32 and the shell 22. Preferably, said distance is less than or equal to 0.005 times the fan diameter.

[0155] In the fan 20 of the present application, the blade 26 comprises a junction 36 positioned between the aerodynamic portion 30 and the end plate 32. The junction 36 is an element structurally independent of the aerodynamic portion 30 of the blade 26 and is preferably joined to the aerodynamic portion 30 of the blade 26 only during the assembly of the fan 20.

[0156] As mentioned above, the radial outer end of the junction 36 is configured to be continuously attached to the radial inner surface of the end plate 32. Below, a possible method for conforming the radial outer end of the junction 36 so that it is continuously attached to the radial inner surface of the end plate 32 is described. In this case, a semi-finished product of the junction 36 made therefrom is also described.

[0157] ​The radially inner end of the junction 36 is defined by the plane p, and this allows the radially inner end of the junction 36 to rest firmly against the radially outer end of the aerodynamic portion 30. Preferably, the radially inner end of the junction 36 is shaped according to the same airfoil as the aerodynamic portion 30. This enables the two portions to join and connect perfectly and continuously, guaranteeing the junction head excellent aerodynamic performance.

[0158] According to some embodiments, the junction 36 has a constant cross section along its extension in the radial direction between the aerodynamic portion 30 and the end plate 32. According to other embodiments (see, for example, Fig. 11), the junction 36 has a variable cross section along its extension in the radial direction; in the radial direction, from the aerodynamic portion 30 to the end plate 32, the junction 36 can have an increasing chord length (see Figure 11.a ) and / or the junction 36 can have an increasing thickness (see Figure 11.b ).

[0159] The variation of the cross section of the junction 36, either in chord and / or thickness, along its radial extension can cause a reduction in the noise generated by the fan 20 during its operation. In fact, as can be understood from Figure 11.a and 11.b , such variation of the cross section of the junction 36 allows the component of the air flow that travels in the radial direction along the blade 26 to be smoothly guided under the action of the centrifugal force, preventing such air flow from vertically impacting the end plate 32 and / or the casing 22.

[0160] In addition to defining a support plane intended to coincide with the plane p, the radially inner end of the junction 36 comprises means 40 for structural coupling with the radially outer end of the aerodynamic portion 30. By way of example, the structural coupling means 40 can comprise an internal protrusion intended to be inserted in the radial direction into a cavity defined by the extruded / pultruded profile of the aerodynamic portion 30 (see Figure 14 ). Such coupling means 40 allow the external shape of the airfoil to be maintained almost unchanged, thus minimizing the aerodynamic interference. In other embodiments, the structural coupling means 40 can comprise an external protrusion intended to partially overlap the extruded / pultruded profile of the aerodynamic portion 30. According to other embodiments, the coupling means 40 can comprise other solutions known in the art, such as screws, junction heads, glue or welding.

[0161] Thanks to the precision of the assembly, the use of the joint 36 of the application allows to obtain a particularly effective cooperation between the end plate 32 and the casing 22. This possibility can be exploited in a particularly advantageous manner by applying the application to the solution disclosed in the patent application WO 2020 / 245674 in the name of the same Applicant. According to such a known solution, the casing 22 comprises an annular seat 44 which extends circumferentially around the rotor of the fan 20. The annular seat 44 is open in the axial direction a; preferably, it is made by applying a converging smoothing surface 46 immediately upstream of the rotor inside the casing 22. Each end plate 32, provided at the end of a blade 26, extends in the axial direction a and in the circumferential direction c and is housed at least partially in the annular seat 44 of the casing 22. Such a solution is schematically shown in Figure 19 .

[0162] Figure 19 Embodiments of the application in which the end plate 32 is housed in the annular seat 44 can be further improved by adding a baffle 48 which extends in the circumferential direction c and in the axial direction a and is provided to the joint 36 radially inner with respect to the end plate 32 and with respect to the annular seat 44. In particular, the baffle 48 is provided to the joint 36 radially inner with respect to the converging smoothing surface 46. Embodiments of the application comprising the baffle 48 are schematically shown in Figure 20 and Figure 21 . As the person skilled in the art can understand from Figure 21 , the casing 22, the end plate 32, the edge of the converging smoothing surface 46 and the baffle 48 all extend on concentric cylindrical surfaces with a diameter which gradually decreases, in the order mentioned.

[0163] Figure 20 A front view of the end of the blade 26 comprising the end plate 32 and the baffle 48, both fixed to the joint 36, is schematically shown. As Figure 20 can be seen, a gap 34 is defined between the casing 22 and the end plate 32. Moreover, the converging smoothing surface 46 forms the annular seat 44 inside which the end plate 32 extends in the axial direction. Finally, the baffle 48 in turn abuts the converging smoothing surface 46, maintaining a predetermined distance, for example a distance similar to the thickness of the gap 34.

[0164] Preferably, as can be understood in the embodiments of Figure 20 , the baffle 48 extends in the axial direction only upstream of the rotor, i.e. downwards in Figure 20 , unlike the end plate 32 which extends in the axial direction both upstream and downstream of the rotor.

[0165] Figure 21 A front view of the end of the blade 26 comprising the end plate 32 and the baffle 48, both fixed to the joint 36, is schematically shown. As Figure 20a plan view of the tip of the blade 26. Such a blade 26 comprises an end plate 32 and a baffle 48, both fixed to the joint 36. As in Figure 20 Figure 21 between the shell 22 and the end plate 32. Moreover, the converging smooth surface 46 forms an annular seat 44 within which the end plate 32 is housed. Finally, the baffle 48 abuts the converging smooth surface 46, maintaining a predetermined distance.

[0166] In a manner known per se from patent application WO 2020 / 245674, the cooperation between the shell 22, the end plate 32 and the annular seat 44 defined by the converging smooth surface 46 defines a labyrinth seal. The fact that the end plate 32 enters the annular seat 44 in the axial direction defines an obstacle to the recirculation of air around the tip, since such recirculation requires the air itself to reverse direction twice.

[0167] The effect of such a labyrinth seal is further improved by the presence of the baffle 48, which is arranged radially inside with respect to the annular seat 44. The person skilled in the art can understand such a solution in particular from Figure 20 where the fixed elements (i.e. the shell 22 and the converging smooth surface 46) alternate with the rotating elements (i.e. the end plate 32 and the baffle 48), thus forming a particularly evident labyrinth. The tortuous path defined by the labyrinth represents an obstacle to the passage of air around the tip of the blade 26, since the air should repeatedly reverse its direction along such a path.

[0168] According to some embodiments, for example those of Figure 22 and Figure 23 The end plate 32 is made of at least two panels juxtaposed in the radial direction. In such a case, a first radially innermost panel 32' can consist of a sheet (for example of metal or composite material) simply cut to size. While a second radially outermost panel 32" can be curved according to the cylindrical surface portion of the shell 22. In this case, the first panel 32' defines the dimensions of the end plate 32 (in particular in the axial and circumferential directions), while the second panel 32" defines the curvature of the end plate 32, forcing the first panel 32' against the joint 36.

[0169] This embodiment allows small adjustments to the position of the end plate 32 during assembly, for example by rotating the first panel 32' with respect to the shell 22 in the range of a few degrees in order to correct any minor errors. To this end, the first panel 32' and the second panel 32" can rely on mounting screws 50 (see Figure 23 ​) and constrained to the junction 36. In this case, the second panel 32" (whose position with respect to the junction 36 is unique) can preferably comprise circular holes, each of which in turn uniquely defines the position of the associated mounting screw 50. Otherwise, the first panel 32' can preferably comprise elongated slots which, during assembly, allow the first panel 32' itself to have a smaller freedom of movement with respect to the junction 36 and to the casing 22.

[0170] Providing two panels 32' and 32" can also give the end plate 32 as a whole improved mechanical characteristics (for example counteracting centrifugal forces) which tend to move the free end of the end plate 32 radially outwards, i.e. furthest from the point of constraint (generally in the axial direction, but also in the circumferential direction). More specifically, the shape and material of which the second panel 32" is made can be defined so as to provide structural support to the first panel 32' counteracting the deformation thereof due to centrifugal forces.

[0171] In the case in which the end plate 32 is made by juxtaposing the two panels 32' and 32" in the radial direction, a gap 34 is included between the casing 22 and the radially outer surface of the second panel 32", said gap 34 being uniform and constant in thickness. Therefore, strictly speaking, the gap 34 uniform and constant in thickness has a smaller extension than the end plate 32 as a whole. However, in some embodiments, the thickness of the second panel 32" can be considered negligible with respect to the thickness of the gap 34, so that the thickness of the gap 34 can be considered uniform and constant throughout the extension between the casing 22 and the radially outer surface of the first panel 32'.

[0172] According to a second aspect, the present application relates to an industrial cooling system (not shown) comprising a fan 20 as described above.

[0173] The cooling system of the present application is generally a system for discharging heat generated by an industrial process. For example, the fan 20 can be included in a cooling tower intended for discharging heat generated by large HVAC systems (Heating Ventilation and Air Conditioning), by power plants, by oil refineries, by petrochemical plants, etc.

[0174] According to other aspects, the present application relates to a method for obtaining a fan 20 according to the foregoing.

[0175] The first method of the present application is intended to modify an existing duct fan 20 to improve its performance in the context of a retrofit intervention of the plant.

[0176] The existing axial fan 20 comprises a hub 24 rotatable about a rotation axis X, a plurality of blades 26, and a cylindrical casing 22 arranged around and coaxial to said hub 24, wherein each blade 26 comprises an aerodynamic portion 30 obtained from an extruded / pultruded profile having a self longitudinal axis I and having a cross section shaped according to an airfoil profile. The method of the present invention comprises the following steps:

[0177] - defining an end plate 32 (see Figure 12 ) based on the diameter of the casing 22, wherein said end plate 32:

[0178] - extends mainly in axial and circumferential directions,

[0179] - defines a radially inner surface and a radially outer surface, the radially outer surface being shaped according to a cylindrical surface portion,

[0180] - when said end plate 32 is correctly arranged adjacent to the casing 22, the radially outer surface defines, jointly with the casing 22, a gap 34 having a uniform and constant thickness;

[0181] - identifying an airfoil profile for manufacturing the aerodynamic portion 30 of the blade 26;

[0182] - identifying the geometric design parameters of the blade of the rotor 26, i.e.: angle of attack a, pre- angle of pitch β and angle of oscillation γ;

[0183] - defining a virtual blade 26' having the airfoil profile and the geometric design parameters identified above and indefinite radial extension;

[0184] - when said end plate 32 is correctly arranged adjacent to said casing 22, determining a space curve 42 representing the intersection line of said virtual blade 26' with the radially inner surface of said end plate 32 (see Figure 13 );

[0185] - providing a semi-finished joint 36 having a radially inner end defining a support plane π and shaped to continuously couple and connect to the radially outer end of the extruded / pultruded profile of said blade 26;

[0186] - cutting the radially outer end of the joint 36 along the intersecting space curve 42;

[0187] - constraining the radially outer end of the joint 36 to the radially inner surface of the end plate 32;

[0188] - cutting said blade 26 along said support plane π;

[0189] - constraining the radially inner end of the joint 36 to the radially outer end of the aerodynamic portion 30 of the cut blade 26;

[0190] - repeating the operations defined above for each blade 26.

[0191] As the skilled person can well understand, the method of the application can in theory be carried out entirely with manual equipment, without the aid of computer tools. However, this purely manual method would necessarily require the use of highly skilled labor and would not allow significant advantages in terms of economies of scale. It is therefore preferable that at least some steps of the method are carried out with the aid of a computer system of the CAD / CAM (Computer Aided Design / Computer Aided Manufacturing) type.

[0192] As mentioned above, in the present discussion the same terms (for example "end plate") can indifferently indicate a physical element in the real world (for example an aluminum sheet end plate) or a virtual representation thereof in the space of the descriptive geometry or a virtual representation in digital format (for example a CAD file representing the end plate). The skilled person will not find it difficult to correctly interpret the meaning of these terms according to the context and to transpose the considerations and evaluations from one range of meanings to another.

[0193] The step of identifying the airfoil can comprise a step of measuring the blade 26 of an existing fan 20; the measurement can be made graphically, for example manually, by drawing the airfoil on a drawing sheet. The manually drawn shape on the drawing sheet can then be acquired in digital format. Preferably, the measurement can be performed by three-dimensional scanning of the airfoil, for example with suitable laser technology known per se.

[0194] It is therefore preferable that in this step the virtual airfoil is generated in digital format, which allows at least some subsequent steps of the method to be carried out by computer.

[0195] The step of identifying the geometric design parameters of the blade 26 of the rotor (i.e. the angle of attack a, the pre- cone angle β and the angle of pitch γ) is certainly easy, since these parameters are macroscopically evident.

[0196] It is particularly advantageous that the steps of defining the virtually indefinite blade 26' and determining the space curve 42 (representing the intersection of said virtually indefinite blade 26' with the radially inner surface of the correctly positioned end plate 32) are carried out by computer. To carry out these operations manually, a deep understanding of stereometry and of perspective drawing and complex calculations are necessary.

[0197] On the other hand, by means of the computer, the end plate 32 and the virtual blade 26' are correctly positioned. In particular, the end plate 32 must be correctly positioned with respect to the casing 22 so that the two cylinders to which the radially inner surface of the casing 22 and the radially outer surface of the end plate 32 belong are coaxial. The obtained airfoil must be correctly arranged with respect to the axis X, in particular according to the identified geometric parameters.

[0198] Once the end plate 32 and the virtual blade 26' are correctly positioned, it is sufficient to virtually extrude the airfoil along the longitudinal axis I of the virtual blade 26' until the end plate 32 is crossed. In this case, if necessary, the end plate 32 can also be virtually moved in the axial direction and / or in the circumferential direction to obtain the best intersection with the virtual blade 26'.

[0199] Once the position of the end plate 32 and of the blade 26 has been defined, the CAD program easily obtains the intersection space curve 42 as the position of the points that simultaneously belong to the outer surface of the virtual blade 26' and to the radially inner surface of the end plate 32 (see Figure 13 ).

[0200] Once the intersection space curve 42 has been defined, it is necessary to provide a semi-finished joint 36 suitable for obtaining the desired joint 36 (see Figure 14 ). With reference to the correct orientation that it will assume inside the blade 26, the semi-finished joint 36 has a radially inner end and a predetermined radial extension. The radially inner end defines a support plane that, in use, is intended to coincide with the plane π defined by the radially outer end of the aerodynamic portion 30. The radially inner end of the semi-finished joint 36 comprises means for structural coupling with the radially outer end of the aerodynamic portion 30; such coupling means 40 have been described above.

[0201] The radial extension of the semi-finished joint 36 must be sufficiently extended so as to be able to contain all the possible configurations of the intersection space curve 42, which arise from different possible combinations of the geometric design parameters. At the same time, the radial extension of the semi-finished joint 36 must be sufficiently reduced to allow it to be loaded into a numerical control machine tool, for example a CNC machining center, to obtain the desired joint 36. By way of example, the radial extension of the semi-finished joint 36 can be comprised within 20 cm, preferably within 10 cm.

[0202] The joint 36 can be made of aluminum, for example by means of die casting, of polymer or of composite material, preferably with short fibers, for example by means of molding. According to some embodiments, the joint 36 can comprise the same extruded / pultruded profile segment as the one used to construct the aerodynamic portion 30 of the blade 26. In this case, the radially inner end must be cut so as to define the support plane π and the means 40 for structural coupling must be added.

[0203] Once the semi-finished joint 36 has been set, it must be cut along the intersection spatial curve 42. To this end, it is possible to use a manual device, although it is of course preferable to load the semi-finished joint 36 into a numerical control machine tool programmed and configured to perform a three-dimensional cut following the intersection spatial curve 42.

[0204] Once the cutting step is completed, the radially outer surface of the joint 36 is perfectly attached to the radially inner surface of the end plate 32. The joint 36 can therefore be made to rest on the end plate 32 and constrain the two components together. This constraining step is particularly easy thanks to the precision of the support obtained through the previous steps of the method.

[0205] As an example, in the case where both components are made of aluminum (for example, the end plate 32 is a rolled metal sheet and the joint 36 is a die-cast profile), the joining can be carried out by welding, for example by TIG (Tungsten Inert Gas) welding. While the welding can also be performed by a numerical control machine tool, the simplicity of the operation also allows it to be performed manually by following the support profile that curls between the two components along the intersection spatial curve 42.

[0206] Alternatively, in the case where both components are made of composite material (for example, the end plate 32 is a curved panel and the joint 36 is a molded piece), the joining can be carried out by, for example, gluing with epoxy. Even if the end plate 32 and the joint 36 are made of different materials, it is not difficult for a person skilled in the art to choose other constraining methods.

[0207] The blade 26, in particular the aerodynamic portion 30 thereof, must be cut along a support plane p, preferably perpendicular to the longitudinal axis I of the blade 26. The position of said plane p along the longitudinal axis I of the blade 26 is preferably calculated in a previous step, for example after the step of determining the intersection spatial curve 42. The support plane p is defined in such a way that, once the end plate 32 is constrained to the joint 36 and the joint 36 is constrained to the aerodynamic portion 30, the end plate 32 is correctly positioned with respect to the casing 22.

[0208] As a person skilled in the art can well understand, the above-described operations must be repeated for each blade 26 of the existing fan 20. Once all the blades 26 are completed, they can be assembled to the hub 24, thus obtaining a completely revamped fan 20 according to the present application.

[0209] The second method of the present application aims to make a duct fan 20 according to the present application from the outset, as part of a complete replacement of the fan 20 in an existing plant, or as part of the construction of a brand new plant. Therefore, this second method aims to make an axial fan 20 comprising a hub 24 rotatable about a rotation axis X, a plurality of blades 26 and a cylindrical shell 22 arranged around the hub 24 and coaxial thereto.

[0210] The second method of the present application comprises the following steps:

[0211] - defining the diameter of the shell 22,

[0212] - defining an end plate 32 based on the diameter of the shell 22, wherein the end plate 32:

[0213] - extends mainly in the axial direction and in the circumferential direction,

[0214] - defines a radially inner surface and a radially outer surface, the radially outer surface being shaped according to a cylindrical surface portion,

[0215] - when the end plate 32 is correctly arranged adjacent to the shell 22, the radially outer surface defines, jointly with the shell 22, a gap 34 having a uniform and constant thickness;

[0216] - selecting an airfoil for the aerodynamic portion 30 of the blade 26;

[0217] - providing an extruded / pultruded profile having the airfoil selected above and indefinite extension along its own longitudinal axis l perpendicular to the plane of the airfoil;

[0218] - providing a base 28 at the radially inner end of the extruded or pultruded profile;

[0219] - defining the geometric design parameters of the blade 26 of the rotor, i.e. the angle of attack a, the pre- coning angle β and the angle of oscillation γ;

[0220] - defining a virtual blade 26' having the airfoil selected above, the geometric design parameters defined above and indefinite radial extension;

[0221] - when the end plate 32 is correctly arranged adjacent to the shell 22, determining a spatial curve 42 representing the intersection line of the virtual blade 26' with the radially inner surface of the end plate 32;

[0222] - providing a joint 36 having a radially inner end defining a support plane π and shaped to continuously couple and connect to the radially outer end of the extruded / pultruded profile of the blade 26;

[0223] - cutting the radially outer end of the joint 36 along the intersection space curve 42;

[0224] - constraining the radially outer end of the joint 36 to the radially inner surface of the end plate 32;

[0225] - cutting the extruded / pultruded profile of the blade 26 along said support plane π, thus making the aerodynamic portion 30;

[0226] - constraining the radially inner end of the joint 36 to the radially outer end of the aerodynamic portion 30;

[0227] - constraining the base 28 of the blade 26 to the hub 24 according to said geometric design parameters;

[0228] - repeating the operations defined above for each blade 26.

[0229] As the skilled person can well understand, this second method is very similar to the first one, with the difference that the second method comprises several preliminary design phases of the fan 20. In the first method, such steps are not necessary, since the method itself aims at maintaining the fan 20 in an existing shape and only changes the end of the blade 26 by adding the end plate 32. In this second method, differently, from the beginning all the preliminary design phases are necessary, such as the definition of the diameter of the fan 20 and of the diameter of the casing 22, the selection of the airfoil of the blade 26, the definition of the geometric parameters, etc. Moreover, these phases are well known to the skilled person.

[0230] In view of the above, the skilled person can well understand how the present application overcomes the outstanding drawbacks associated with the prior art.

[0231] In particular, the provision of the joint 36 allows to cut along the intersection space curve 42 in a both precise and easy manner. This cut is in fact too complex to be performed manually and therefore requires the use of a numerical control machine. However, the aerodynamic portion of the blade 26 usually has dimensions incompatible with the working chamber of common CNC machines. On the other hand, the joint 36 has much smaller dimensions, which can be easily loaded into the working chamber of very common numerical control machines.

[0232] In particular, the present application provides an axial fan which optimizes the geometry of the end plate at the end of the blade.

[0233] Moreover, the present application provides a ducted axial fan which optimizes the interaction between the end plate at the end of the blade and the casing.

[0234] Furthermore, the present invention provides a method for improving the efficiency of an existing axial fan.

[0235] Finally, the present invention provides a method for implementing an improved axial fan comprising optimized end plates at the blade ends.

[0236] In general, all details can be replaced by other technically equivalent elements; characteristics described with reference to a specific embodiment can also be used in other embodiments; the materials used, as well as the possible shapes and dimensions, can be optional according to the requirements of the specific implementation, without departing from the scope of protection of the appended claims.

Claims

1. An axial fan (20) comprising a rotor rotatable about a rotation axis X and a cylindrical housing (22) arranged around and coaxial with the rotor, wherein: - The rotor includes a hub (24) and multiple blades (26). - Each blade (26) includes a radially inner base portion (28) constrained to the hub (24), an aerodynamic portion (30) extending outward primarily in the radial direction from the base portion (28), and an end plate (32) at the radially outer end. - The aerodynamic portion (30) is obtained from extruded / pultruded profiles, - The aerodynamic part (30) defines the airfoil in the cross-section, - The end plate (32) extends mainly in the axial and circumferential directions. - The end plate (32) defines a radial inner surface and a radial outer surface, the radial outer surface being shaped according to a cylindrical surface portion. - When the end plate (32) is properly arranged adjacent to the housing (22), the radial outer surface and the housing (22) together define a gap (34) having a uniform and constant thickness. Furthermore, the blade (26) further includes a joint (36) positioned between the aerodynamic part (30) and the end plate (32). - The joint (36) is manufactured as an aerodynamic part (30) that is structurally independent of the blade (26). - The radial outer end of the aerodynamic part (30) is defined by a plane π; - The radially outer end of the joint (36) is continuously attached to the radially inner surface of the end plate (32); - The radial inner end of the joint (36) is defined by the plane π; - The radially inner end of the joint (36) is continuously connected to and attached to the aerodynamic part (30); and - The radially inner end of the joint (36) includes a device (40) for structural connection with the radially outer end of the aerodynamic part (30).

2. The fan (20) according to claim 1, wherein, The thickness of the gap (34) between the end plate (32) and the housing (22) is less than or equal to 0.005 times the diameter of the fan.

3. The fan (20) according to claim 1 or 2, wherein, During the assembly of the fan (20), the joint (36) engages with the aerodynamic portion (30) of the blade (26).

4. The fan (20) according to one or more of the preceding claims, wherein, The end plate (32) is obtained at least by means of a first panel (32′) that is radially innermost and a second panel (32″) that is radially outermost and are placed side by side in the radial direction.

5. The fan (20) according to one or more of the preceding claims, wherein, The housing (22) includes an annular seat (44) that extends circumferentially around the rotor and is open in the axial direction a, wherein each end plate (32) disposed at the end of the blade (26) is at least partially accommodated in the annular seat (44).

6. The fan (20) according to the preceding claim, wherein, A baffle (48) is provided on the joint (36), the baffle (48) extending in the circumferential direction c and the axial direction a, and located radially inward relative to the end plate (32) and relative to the annular seat (44).

7. An industrial cooling system comprising a fan (20) according to one or more of the preceding claims.

8. A method for retrofitting an existing axial fan (20), the axial fan (20) comprising a hub (24) rotatable about a rotation axis X, a plurality of blades (26), and a cylindrical housing (22) arranged around and coaxial with the hub (24), wherein, Each blade (26) includes an aerodynamic portion (30) obtained from an extruded / pultruded profile having its own longitudinal axis l and a cross-section shaped according to an airfoil perpendicular to the longitudinal axis l, wherein the method includes the following steps: - Based on the diameter of the housing (22), an end plate (32) is defined, wherein the end plate (32): - Primarily extends in the axial and circumferential directions. - Defines a radial inner surface and a radial outer surface, the radial outer surface being shaped according to a cylindrical surface portion. - When the end plate (32) is properly arranged adjacent to the housing (22), the radial outer surface and the housing (22) together define a gap (34) having a uniform and constant thickness; - Identify the airfoil used in the manufacture of the aerodynamic portion (30) of the blade (26); - Identify the geometric design parameters of the blades of the rotor (26), namely: angle of attack α, pre-cone angle β and oscillation angle γ; - Define a virtual blade (26′), the virtual blade (26′) having the identified airfoil and the geometric design parameters and an indefinite radial extension; - When the end plate (32) is properly arranged adjacent to the housing (22), a space curve (42) is determined, which represents the intersection of the virtual blade (26′) and the radial inner surface of the end plate (32); - A joint (36) is provided, the joint (36) having a radially inner end that defines a support plane π and is shaped to be continuously connected and attached to the radially outer end of the extruded / pultruded profile of the blade (26); - Cut the radial outer end of the joint (36) along the intersecting spatial curve (42); - Constrain the radially outer end of the joint (36) to the radially inner surface of the end plate (32); - Cut the blade (26) along the supporting plane π. - Constrain the radial inner end of the joint (36) to the radial outer end of the aerodynamic portion (30) of the cut blade (26); - Repeat the operation specified above for each blade (26).

9. A method for manufacturing an axial fan (20), the axial fan (20) comprising a hub (24) rotatable about a rotation axis X, a plurality of blades (26), and a cylindrical housing (22) arranged around and coaxial with the hub (24), wherein, The method includes the following steps: - Define the diameter of the housing (22), - Based on the diameter of the housing (22), an end plate (32) is defined, wherein the end plate (32): - Primarily extends in the axial and circumferential directions. - Defines a radial inner surface and a radial outer surface, the radial outer surface being shaped according to a cylindrical surface portion. - When the end plate (32) is properly arranged adjacent to the housing (22), the radial outer surface and the housing (22) together define a gap (34) having a uniform and constant thickness; - Select the airfoil used to manufacture the aerodynamic part (30) of the blade (26); - Provide an extruded / pultruded profile having the airfoil selected above and an indefinite extension along its own longitudinal axis l perpendicular to the airfoil plane; - A base (28) is provided at the radial inner end of the extruded or pultruded profile; - Define the geometric design parameters of the blades of the rotor (26), namely: angle of attack α, pre-cone angle β and oscillation angle γ; - Define a virtual blade (26′) having the airfoil selected above, the geometric design parameters defined above, and an indefinite radial extension; - When the end plate (32) is properly arranged adjacent to the housing (22), a space curve (42) is determined, which represents the intersection of the virtual blade (26′) and the radial inner surface of the end plate (32); - A joint (36) is provided, the joint (36) having a radially inner end that defines a support plane π and is shaped to be continuously connected and attached to the radially outer end of the extruded / pultruded profile of the blade (26); - Cut the radial outer end of the joint (36) along the intersecting spatial curve (42); - Constrain the radially outer end of the joint (36) to the radially inner surface of the end plate (32); - The extruded / pultruded profile of the blade (26) is cut along the supporting plane π to obtain the aerodynamic part (30). - Constrain the radial inner end of the joint (36) to the radial outer end of the aerodynamic part (30); - Constrain the base (28) of the blade (26) to the hub (24) according to the geometric design parameters. - Repeat the operation specified above for each blade (26).

10. The method according to claim 8 or 9, wherein, At least some steps are performed with the help of CAD / CAM type computer systems.

11. The method according to any one of claims 8 to 10, wherein, The step of cutting the radial outer end of the joint (36) along the intersecting space curve (42) is performed by a CNC machine tool.

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