Airfoil and hydrodynamic surface comprising such airfoil

Abstract

The invention relates to an airfoil (40) comprising a leading front edge le, a trailing rear edge te, a midline ml and a thickness t. The airfoil further comprises: a forward portion (42) having a thickness that increases rearward from the leading edge up to a maximum thickness tmax; and a rear portion (44) having a thickness that increases forward from the trailing edge up to the maximum thickness. The airfoil further includes a middle portion (46) interposed between the forward portion and the aft portion, the middle portion (46) having a thickness constant and equal to a maximum thickness. Finally, the airfoil further comprises at least one forward part (48) and aft part (50) assembled. The front portion is defined by the front member and the rear portion is defined by the rear member. The invention also relates to an aerodynamic surface (54) comprising two airfoils according to the invention and to a method for defining such airfoils.

Description

Technical Field

[0001] The present invention relates to the field of fluid dynamic airfoils, in particular airfoils for realizing a fluid dynamic surface, that is, a surface intended to interact with a fluid flow (of air or liquid) for exchanging forces. Background Art

[0002] It is well known that the performance of a fluid dynamic surface depends largely on its geometrical characteristics, among which the shape of the adopted airfoil is particularly important.

[0003] Since the beginning of the 20th century, the realization and characteristics of fluid dynamic airfoils have received extensive attention in order to optimize their performance under various operating conditions. As an example, the scope of aerodynamic airfoils and their use in realizing aircraft wings is discussed below. This is actually one of the areas that has been explored more intensively in fluid dynamics research and has led to significant technological advances. However, it is well understood by those skilled in the art that the same discussion can be applied to other application areas of fluid dynamics, such as rotors, turbomachinery, surfaces of civil buildings exposed to wind, etc.

[0004] In known cases, a single airfoil 40 (e.g. Figure 1 The characteristics shown in Figure 1 are based on the purely theoretical assumption of an infinite span wing to eliminate end effects. This characteristic is essentially independent of the absolute dimensions of the airfoil, such as the actual measured values ​​of the chord cl and thickness t, but depends on other parameters, such as the ratio between the measured values, the distribution of the thickness t, any curvature, etc.

[0005] In contrast, the properties of an actual wing depend largely on geometric proportions, such as aspect ratio (i.e. the ratio of span to mean chord), taper (i.e. the decrease in chord from the wing root to the end of the half-wing), and so on.

[0006] Therefore, when designing a wing (and more generally a fluid dynamic surface), it is important to define not only the dimensionless geometry of the airfoil 40 to be employed, but also its actual dimensions. As a result, the same airfoil is often employed along the entire span of the wing, but scaled to accommodate the desired chord of the wing. This widespread and accepted practice is not without disadvantages.

[0007] In fact, this method of designing a wing is subject to some restrictions that may be too stringent in some cases. In particular, a reduction in the chord of the airfoil, for example towards the far end of the half-wing, necessarily leads to a proportional reduction in thickness. In other words, the designer is forced to reduce the thickness of the wing in order to maintain the proportions of the airfoil. Or, in fact, the designer changes the proportions of the airfoil and ends up with an airfoil of unknown characteristics.

[0008] Furthermore, a wing with a different chord cl and thickness t of the airfoil defines a rather complex three-dimensional surface, the industrial manufacture of which involves a lengthy and expensive process. Of course, in the manufacture of aircraft wings, this cost does not play a large role. On the contrary, in the manufacture of other types of equipment, it would be very useful if there were much cheaper methods of manufacturing aerodynamic surfaces.

[0009] For example, in the manufacture of blades for industrial axial fans, inexpensive manufacturing methods are well known. In fact, in this case, it is necessary to reduce the industrial costs of production as much as possible. Fig.13 A blade 56 of an axial fan of known type is depicted in a schematic plan view, shown together with its hub 60. The blade 56 comprises a root structure 62 and a fluid dynamic surface 54. The fluid dynamic surface 54 is intended to interact with the airflow, while the root structure 62 performs the purely mechanical function of connecting the fluid dynamic surface 54 to the hub 60 and correctly transmitting the forces exchanged between these two elements.

[0010] There are many methods for manufacturing the blade 56 of the fan, especially its fluid dynamic surface 54. One of the most efficient methods is to obtain the fluid dynamic surface 54 of the blade 56 by extrusion / pultrusion. The fluid dynamic surface 54 has a similar Figure 4 and Figure 5 The airfoil 40 (known per se) is shown.

[0011] Extrusion is an industrial process that essentially consists in forcing a ductile material by thrust through a die that reproduces the external shape of the workpiece to be obtained. In this way, it is possible to produce workpieces of constant cross section, whose extension along the extrusion direction (longitudinal direction ld) is not determined a priori. Extrusion can be used for metallic materials (especially aluminum, but also steel or titanium) and polymeric materials.

[0012] Pultrusion is an industrial process that essentially consists in forcing the components of a composite material (fibers and matrix) by means of traction through a die capable of reproducing the external shape of the workpiece to be obtained. The fibers are fed continuously and are arranged mainly in the direction of pultrusion, while the matrix polymerizes while passing through the die. In this way, it is possible to produce workpieces of constant cross-section, whose extension along the pultrusion direction (longitudinal direction ld) is not determined a priori. Pultrusion can be used for various types of composite materials (mainly glass fibers in an epoxy resin matrix).

[0013] Both processes are relatively inexpensive to manufacture. The typical molds used in both processes allow the production of workpieces of possibly complex cross-sections, in which very precisely machined outer surfaces can be combined with very rigid inner structures. In particular, for a fan blade 56, such an airfoil comprises a back wall and a ventral wall, between which one or more reinforcing ribs 68 are arranged (see Figure 4 and Figure 5 ).

[0014] However, although extrusion and pultrusion processes are widely accepted, they are not without disadvantages.

[0015] The first disadvantage is related to the maximum possible size of the extruded / pultruded product. Current technical limitations result in a maximum cross-sectional size of approximately 50 cm for an extruded / pultruded workpiece. Figure 4 The airfoil 40 obtained with two parts 48 and 50 (for example Figure 5 The airfoil in has partially overcome this limitation. In this way, under the condition of complicated production, the chord cl may be greater than 50cm, or even close to 100cm.

[0016] The second disadvantage is related to the fact that the cross section of the products obtained by extrusion / pultrusion is constant in the longitudinal direction ld. This characteristic significantly limits the potential for the application of these products in the field of fluid dynamics. In fact, in many fluid dynamic applications, the optimization of the performance of the hydrodynamic surface 54 requires a variation of the cross section along the main direction of development of the surface itself, usually the chord cl.

[0017] In this regard, as part of the production of blades 56 for industrial axial fans, a technique known as “trim” has been developed which allows obtaining variations in the cross-section of the extruded / pultruded airfoil 40, albeit rather limited ones. This technique employs an extruded / pultruded airfoil 40 of a known type in which the dorsal and ventral walls are joined at a single integral rear appendage 66 (see again Figure 4 and Figure 5 ). The one-piece rear appendage 66 extends rearwardly to the rear edge te, usually with a fairly pronounced curvature. Figure 13-16 Briefly describing “trimming”, known per se, “trimming” allows obtaining an extruded / pultruded hydrodynamic surface 54 with a variable airfoil 40 .

[0018] exist Fig.13 In the embodiment, the fluid dynamic surface 54 extends unchanged along the radial cross section, such as Fig.15 As shown. Fig.14In the technical solution of , "trimming" is adopted: in the radially outer area of ​​the fluid dynamic surface 54, the rear appendage 66 is gradually shortened. Then, in the radially inner area, the fluid dynamic surface 54 has a constant cross section, such as Fig.15 As shown, by gradually shortening the rear appendage 66, Fig.16 The "clipping" allows obtaining a higher aerodynamic efficiency because, along the blade 56, it gradually limits the angle of incidence and the curvature of the airfoil 40 in the radially outer zone where the fluid flow reaches the maximum velocity.

[0019] At present, "trimming" is the only technique that allows to change the chord cl and shape of the extruded / pultruded airfoil 40 to a limited extent. However, it is well understood by those skilled in the art that such changes are possible only within very strict limits. In particular, the chord cl of the airfoil 40 can be reduced but not increased. Furthermore, the chord cl can only be reduced to the extent allowed by the extension of the integrated rear appendage 66. Summary of the invention

[0020] It is therefore an object of the present invention to at least partially overcome the above-mentioned disadvantages highlighted with respect to the prior art.

[0021] In particular, the object of the present invention is to provide an airfoil whose extension in the chord direction can be freely varied in a simple and economical manner to adapt to different requirements.

[0022] Furthermore, the object of the present invention is to provide an airfoil which, despite being simple to manufacture, retains properties comparable to those of known airfoils.

[0023] Furthermore, it is an object of the present invention to provide a hydrodynamic surface whose proportions can be freely varied in a simple and economical manner to adapt to different requirements.

[0024] Finally, the object of the present invention is to provide a method for defining an airfoil in a simple and economical manner, which airfoil has an arbitrary chord in order to adapt to different requirements.

[0025] The above and other objects and tasks of the invention are achieved by an airfoil, a fluid dynamic surface and a method according to the appended claims. Further characteristics are defined in the dependent claims. All claims are an integral part of the present disclosure.

[0026] According to a first aspect, the invention relates to an airfoil, comprising a front leading edge le, a rear trailing edge te, a center line ml and a thickness t. The airfoil also comprises:

[0027] - anterior part, in which the thickness t increases from the front edge le toward the back along the midline ml to a maximum thickness t max ;as well as

[0028] - the posterior part, in which the thickness t increases along the midline ml from the posterior edge te to the front, until the maximum thickness t max .

[0029] The airfoil of the present invention further comprises a middle portion disposed between the front portion and the rear portion, wherein the thickness t in the middle portion is constant and equal to the maximum thickness t max .

[0030] The airfoil comprises at least one front part and a rear part assembled, wherein:

[0031] - the front portion is defined by a front member; and

[0032] - The rear portion is defined by a rear member.

[0033] Since the thickness t of the middle part is constant and the airfoil is obtained by assembling two different parts, it is easy to vary the extension of the airfoil in the chord direction.

[0034] Preferably, the front part and the rear part are obtained by extrusion / pultrusion.

[0035] The production of components by extrusion / pultrusion is particularly efficient in terms of the ratio between the quality of the workpiece obtained and the industrial costs of production.

[0036] Preferably, the middle portion is defined by the front component and / or by the rear component.

[0037] This results in a relatively simple airfoil consisting of only two parts.

[0038] In some embodiments, the airfoil further comprises a mid-section. Preferably, the mid-section is also obtained by extrusion / pultrusion.

[0039] The provision of a mid-section allows increasing the degrees of freedom in defining the airfoil and in particular allows increasing the possible maximum extension in the chord direction.

[0040] According to a second aspect, the invention relates to a hydrodynamic surface comprising two ends separated by a distance D and at least two airfoils according to the above description. The two airfoils have the same maximum thickness t max and midline ml of varying lengths.

[0041] The manufacture of such a hydrodynamic surface is extremely rapid and simple compared to that required for the manufacture of hydrodynamic surfaces of airfoils of known type having centre lines ml of different lengths.

[0042] Preferably, the front and rear parts of the two airfoils are identical, while the middle parts are different.

[0043] More preferably, the middle portion is perpendicular to the maximum thickness tmax The extension in the direction of changes continuously along at least a section between the two ends.

[0044] In some embodiments, the fluid dynamic surface is a half-airfoil. In other embodiments, the fluid dynamic surface is a blade of a rotor.

[0045] According to a third aspect, the present invention relates to a method for defining an airfoil. The method of the present invention comprises the following steps:

[0046] - providing a known airfoil having a front leading edge le, a rear trailing edge te, a center line ml and a thickness t;

[0047] - Determine the front part of the known airfoil (40), in which the thickness t increases from the leading edge le to the rear along the center line ml until the maximum thickness t max ;

[0048] - Determine the rear portion of the known airfoil (40) in which the thickness t increases along the center line ml from the trailing edge te to the front, until the maximum thickness t max ;

[0049] - Place the front and rear parts along the maximum thickness t max The direction is spaced perpendicular to the direction;

[0050] - inserting an intermediate portion between the front portion and the rear portion, the intermediate portion having a thickness equal to the maximum thickness t max of constant thickness.

[0051] The method of the invention allows to define in a simple and economical way an airfoil with an arbitrary chord to suit different requirements.

[0052] Other features and advantages of the present invention will become more apparent from the description of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will be described below with reference to some examples, which are used for illustrative and non-limiting purposes and are shown in the accompanying drawings. These drawings show different aspects and embodiments of the present invention, and the reference numerals representing structures, components, materials and / or similar elements in different drawings are represented by similar reference numerals when appropriate. In addition, for ease of description, some reference numerals may not be repeated in all drawings.

[0054] Figure 1 is a schematic diagram of a theoretical aerodynamic airfoil according to the prior art;

[0055] Figure 2 yes Figure 1 Schematic diagram of the airfoil divided into two parts;

[0056] Figure 3 is a schematic diagram of a theoretical aerodynamic airfoil according to the present invention;

[0057] Figure 4 is a cross-sectional view of an integrated aerodynamic airfoil according to the prior art;

[0058] Figure 5 is a cross-sectional view of a two-part aerodynamic airfoil according to the prior art;

[0059] Figure 6 is a cross-sectional view of a two-part aerodynamic airfoil according to the present invention;

[0060] Figure 7 is a cross-sectional view of a three-component aerodynamic airfoil according to the present invention;

[0061] Figure 8 is an axonometric schematic diagram of a three-component aerodynamic airfoil according to the present invention;

[0062] Fig. 9 is a cross-sectional view of a two-part aerodynamic airfoil according to the present invention;

[0063] Fig.10 is a cross-sectional view of a two-part aerodynamic airfoil according to the present invention;

[0064] Figures 11.a to 11.c It is possible through Figure 6 A cross-sectional view of an aerodynamic airfoil obtained from a component;

[0065] Figures 12.a to 12.f It is possible through Figure 7 A cross-sectional view of an aerodynamic airfoil obtained from a component;

[0066] Fig.13 is a plan view of a blade of an axial flow fan according to the prior art;

[0067] Fig.14 is a plan view of a blade of an axial flow fan according to the prior art;

[0068] Fig.15 is along Fig.13 or Fig.14 A cross-sectional view taken along any line XV-XV in ;

[0069] Fig.16 is along Fig.14 A cross-sectional view taken along line XVI-XVI of ;

[0070] Fig.17 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0071] Fig.18 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0072] Fig.19 is along Fig.17 or Fig.18 A cross-sectional view taken along any XIX-XIX line;

[0073] Fig. 20 is along Fig.17 or Fig.18 A cross-sectional view taken along any XX-XX line;

[0074] Fig.21 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0075] Fig. 22 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0076] Fig.23 is along Fig.21 A cross-sectional view taken along line XXIII-XXIII;

[0077] Fig.24 is along Fig.21 or Fig. 22 A cross-sectional view taken along any line XXIV-XXIV;

[0078] Fig.25 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0079] Fig.26 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0080] Fig. 27 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0081] Fig.28 is a schematic plan view of a blade of an axial flow fan according to the present invention;

[0082] Fig.29 is a schematic plan view of a half-wing according to the present invention;

[0083] Fig.30 is along Fig.29 A cross-sectional view taken along line XXX-XXX;

[0084] Fig.31 is along Fig.29 A cross-sectional view taken along line XXXI-XXXI of ;

[0085] Fig.32 is a schematic plan view of a half-wing according to the present invention;

[0086] Fig.33 is along Fig.32 A cross-sectional view taken along line XXXIII-XXXIII;

[0087] Fig.34 is along Fig.32 A cross-sectional view taken along line XXXIV-XXXIV of ; and

[0088] Fig.35 is a schematic diagram of the velocity field impinging on the blades of an industrial axial fan; and

[0089] Figure 36.a and 36.b The cross-sectional views of two aerodynamic airfoils, one in the prior art and one in accordance with the present invention, are respectively used for comparative experiments. DETAILED DESCRIPTION

[0090] Although the present invention is susceptible to various modifications and alternative structures, some preferred embodiments are shown in the drawings and described in detail below. In any case, it must be understood that the present invention is not intended to be limited to the specific embodiments shown in the drawings, but is intended to cover all modifications, substitutions and equivalent structures within the scope of the present invention defined in the claims.

[0091] This specification discusses the unique aspects and technical features of the present invention in detail, while the aspects and technical features known per se are only hinted at. In these aspects, the contents reported above with reference to the prior art are still valid.

[0092] Unless otherwise stated, the use of "such as", "etc", "or" means an unlimited, non-exclusive selection. Unless otherwise stated, the use of "include" and "including" means "including or including, but not limited to".

[0093] In the following discussion, the terms "airfoil" and "fluid dynamic airfoil" generally denote a shape, which is itself well known to those skilled in the art, which is suitable for interacting with a fluid flow to exchange forces. The term "airfoil" therefore has two slightly different meanings. The first meaning is theoretical and denotes a curve drawn graphically on a plane, which is used to study the implementation of a practical device. The second meaning is a practical meaning and denotes a cross-sectional shape that reproduces a theoretical airfoil. If it is necessary to distinguish between the two meanings, the former may also be referred to as a "theoretical airfoil" and the latter as a "practical airfoil".

[0094] The airfoil of the invention can be used to interact with different fluids, such as gases, in particular air, or liquids, in particular water. In the first case, the airfoil can be called an "aerodynamic airfoil", without thereby introducing restrictions on the interaction with gases other than air. In the second case, it can be called a "hydrodynamic airfoil", without thereby introducing restrictions on the interaction with liquids other than water.

[0095] The airfoil of the present invention is intended for use in the presence of a fluid flow, due to which the airfoil is able to perform its force-generating function. The direction of the flow defines the leading and trailing edges of the airfoil in a unique manner. The direction of the flow also defines the concepts of "forward", "front", etc. of the airfoil relative to "backward", "rear", etc.

[0096] In this discussion, common terms known to those skilled in the art are used to describe the geometric features of airfoils. Although the strict definition of these terms sometimes involves some complex issues, for those skilled in the art, these terms have very clear meanings. Figure 1 The airfoil includes a leading edge le and a trailing edge te, the leading edge le is located in the front and is rounded, and the trailing edge te is located in the rear and is pointed or sharp. The straight line segment connecting the leading edge and the trailing edge is called the chord cl. In addition to representing the chord cl, the term chord more generally represents the extension of the airfoil in the direction of the flow. Although this usage is not accurate, it has been widely accepted. In addition, the airfoil is characterized by a thickness t that varies along the chord. In particular, the thickness increases from the leading edge to the rear until it reaches a maximum value, then decreases and becomes zero again at the trailing edge.

[0097] For each airfoil, the median line ml can be defined as the position of each point located in the middle of the thickness, for example, as the position of the center of the inscribed circumference of the airfoil. Most airfoils, such as the one shown in the accompanying drawings, are used to generate a force that is always in the same direction as the direction of the fluid flow, for example Figure 1 In each of these cases, it is advantageous that the airfoil is asymmetric and that the centerline ml is curved and offset from the chord cl in the direction of the force to be generated. In an asymmetric airfoil, the dorsal (or suction side) and ventral (or pressure side) can be determined in a unique manner.

[0098] In the following discussion, thickness t is considered to be a function of, and measured perpendicular to, the centerline ml (rather than, for example, perpendicular to the chord as is other conventions).

[0099] In the following discussion, reference will be made to a hydrodynamic surface which can be considered as a series of airfoils juxtaposed to one another in a direction transverse to the airfoil itself. Each hydrodynamic surface comprises, in a manner known per se, a leading edge le consisting of a line defined by the point positions of the leading edges le of all the airfoils forming the hydrodynamic surface. Similarly, each hydrodynamic surface comprises, in a manner known per se, a trailing edge te consisting of a line defined by the point positions of the trailing edges te of all the airfoils forming the hydrodynamic surface.

[0100] The hydrodynamic surface typically has two ends separated by a distance D.

[0101] The airfoil of the present invention can be applied to various types of fluid dynamic surfaces. For example, the airfoil of the present invention can be applied to an aerodynamic surface, i.e., a surface for interacting with a flow of a gas (usually air, but not only air); or can be applied to a hydrodynamic surface, i.e., a surface for interacting with a flow of a liquid (usually water, but not only water).

[0102] Furthermore, some hydrodynamic surfaces may have a cantilever structure with structural restraints located only at one end (called the root end) and a free end (called the distal end). This type of hydrodynamic surface can be blades of rotors, half-wings and control and stabilizing surfaces of standard configuration aircraft, sails and rudders of ships, blades of turbomachinery, etc. Other hydrodynamic surfaces may have different structures in which the arrangement of structural restraints is different, such as the inner wing area of ​​a twin-fuselage or twin-tail-boom aircraft, the wing pieces of vehicles, some underwater load-bearing airfoils of ships, some deflectors of civil buildings exposed to the wind, etc.

[0103] In addition, the fluid dynamic surfaces can be used for different relative motions with respect to the fluid with which it must interact. For example, certain fluid dynamic surfaces of the present invention can be used for relative motions that are primarily translational, such as the wings (or semi-wings) of fixed-wing aircraft, control and stabilizing surfaces of aircraft, wing pieces of vehicles, sails of ships, underwater surfaces of ships (such as stabilizing fins or load-bearing airfoils), deflectors of civil buildings exposed to the wind, etc. Other fluid dynamic surfaces of the present invention can be used for relative motions that are primarily rotational, such as rotor blades of rotary-wing aircraft, rotor blades of industrial fans, propeller blades, turbomachinery blades (turbines or compressors), etc.

[0104] The fluid dynamic airfoils and surfaces of the present invention may be used in industrial axial flow fans. The axial flow fans of the present invention define an axis of rotation, and the terms "axial", "radial" and "tangential" are defined in a unique manner relative to the axis of rotation.

[0105] According to a first aspect, the invention relates to an airfoil 40, comprising a leading edge le, a trailing edge te, a center line ml and a thickness t, wherein the airfoil 40 further comprises:

[0106] - a front portion 42, wherein the thickness t increases from the front edge le toward the rear along the midline ml to a maximum thickness t max ;as well as

[0107] - a rear portion 44, in which the thickness t increases along the midline ml from the rear edge te forwardly to a maximum thickness t max ;

[0108] The airfoil 40 further includes a middle portion 46 disposed between the front portion 42 and the rear portion 44, wherein the thickness t is constant and equal to the maximum thickness t max ;

[0109] And wherein the airfoil 40 further comprises at least one assembled front component 48 and rear component 50, wherein

[0110] - the front portion 42 is defined by a front part 48; and

[0111] The rear portion 44 is defined by a rear part 50 .

[0112] Reference Figures 1 to 3 , what is discussed here is the theoretical airfoil, regardless of its actual implementation. Figure 1 The theoretical airfoil in itself is known, including the front leading edge le, the rear trailing edge te, the center line ml and the thickness t. The known theoretical airfoil 40 also includes:

[0113] - a front portion 42, wherein the thickness t increases from the front edge le toward the rear along the midline ml to a maximum thickness t max ;as well as

[0114] - a rear portion 44, in which the thickness t increases along the midline ml from the rear edge te forwardly to a maximum thickness t max .

[0115] Here, the front part 42 and the rear part 44 are also to be understood theoretically, ie as two parts of a curve which are plotted on a plane for research purposes.

[0116] Figure 2 Shows from Figure 1 The first conceptual step of obtaining the airfoil 40 according to the present invention begins with the known airfoil 40. Specifically, Figure 2 Shows something like Figure 1 The theoretical airfoil 40 in which the front portion 42 and the rear portion 44 have been conceptually determined, separated and moved away from each other. More specifically, the front portion 42 and the rear portion 44 have been moved along a plane perpendicular to the maximum thickness tmax Since the thickness is measured point by point in a direction perpendicular to the midline ml, the front portion 42 and the rear portion 44 are at the maximum thickness t max The points are moved away from each other along the direction of the line tangent to the midline ml. It should be noted that Figure 1 In the usual manner of drawing an airfoil 40 of the type shown, at the maximum thickness t max At the point where the tangent to the midline ml, the tangent to the back and the tangent to the abdomen are parallel to each other.

[0117] Figure 3 Shown by modifying Figure 1 An embodiment of the theoretical airfoil 40 of the present invention is obtained by using the airfoil 40 of the present invention. Specifically, relative to Figure 1 Airfoil 40, Figure 3 The airfoil 40 also includes a middle portion 46 disposed between the front portion 42 and the rear portion 44, wherein the thickness t is constant and equal to the maximum thickness t max As defined above, the middle portion 46 has a rectangular shape with two sides having lengths equal to the maximum thickness t max , the other two edges have arbitrary a priori lengths,

[0118] In a manner known per se, the airfoil 40 of the invention has a dorsal (or suction surface), a ventral (or pressure surface) and a median line ml. Preferably, the dorsal and / or ventral and / or median line ml are continuous (without discontinuities) and uniform (without steps, edges or sharp changes in direction). In particular, the middle portion 46 does not introduce any discontinuities in the surface of the dorsal, the surface of the ventral, and the median line ml.

[0119] The present invention also relates to the above Figure 3 Practical manufacturing of the described theoretical airfoil 40. Specifically, as desired above, the practical airfoil 40 according to the invention is obtained by assembling at least a front part 48 and a rear part 50, wherein:

[0120] - the front portion 42 is defined by a front part 48; and

[0121] The rear portion 44 is defined by a rear part 50 .

[0122] Preferably, the front part 48 and the rear part 50 are obtained by extrusion / pultrusion.

[0123] Those skilled in the art can well understand that the front component 48 and the rear component 50 here can be understood in a practical sense, that is, they are understood as two components produced from a material (such as aluminum or a composite material) and used to be assembled into the actual airfoil 40 .

[0124] According to the invention, the front part 48 and the rear part 50 can be obtained by extrusion or by pultrusion. Both processes are well known to those skilled in the art and have been briefly described with reference to the prior art.

[0125] As already mentioned, extrusion can be used mainly for metallic materials, but can also be used for polymeric materials. For the purposes of the present invention, it will be understood below that the workpiece obtained by extrusion is made of aluminum, since this is the material most used in the various fields of application of the present invention. However, as can be well understood by a person skilled in the art, nothing will change if the workpiece obtained by extrusion is made of other metals such as steel, titanium, magnesium or other alloys.

[0126] Similarly, pultrusion can be used for various types of composite materials. For the purposes of the present invention, it will be understood below that the workpiece obtained by pultrusion is made of glass fibers in an epoxy resin matrix, since this is the material most used in the various fields of application of the present invention. However, as will be well understood by a person skilled in the art, nothing will change if the workpiece obtained by pultrusion is made with other fibers (e.g. carbon fibers or polyaramid fibers) and / or other matrices (e.g. other thermosetting matrices such as polyester, acrylic, vinyl ester) or even thermoplastic matrices (e.g. PVC, polyurethane, polyethylene).

[0127] According to some embodiments, for example Figure 6 , Fig. 9 and Fig.10 In the embodiment of the invention, the middle portion 46 of the airfoil 40 is defined by the front part 48 and / or the rear part 50. In other words, the airfoil 40 has a constant thickness t max The middle portion 46 is defined by a rearward extension of the front component 48 and / or a forward extension of the rear component 50. The airfoil 40 of this embodiment does not require a middle component 52, thereby simplifying the manufacture of the airfoil 40 and limiting the associated costs, such as the costs incurred by providing an extrusion / pultrusion die.

[0128] According to some embodiments, for example Figure 7 or Figure 8 In the embodiments of the present invention, the airfoil 40 further comprises a middle member 52. According to these embodiments, the middle portion 46 of the airfoil 40 is at least partially defined by the middle member 52. In other words, the airfoil 40 has a constant thickness t max The middle portion 46 is defined by the middle component 52, but may also be defined in part by a possible rearward extension of the front component 48 and / or a possible forward extension of the rear component 50. The airfoil 40 of this embodiment allows a large variation in the chord cl.

[0129] According to some embodiments, for example Figure 7 or Figure 8 In the embodiment of FIG. 5 , the middle part 52 is obtained by extrusion / pultrusion in the same way as the front and rear parts 48 , 50 .

[0130] In other cases not shown but with Figure 8 In a similar embodiment, the middle part 52 can be obtained in different ways. For example, considering Figure 8 It will be readily appreciated that the middle member 52 may be omitted and replaced by two simple metal plates or polymer strips. This simpler solution may involve some problems with the overall stiffness of the airfoil 40, but those skilled in the art will certainly be able to solve these problems, for example by providing an extension of the root structure or another reinforcing structure inside the airfoil 40 itself.

[0131] According to a second aspect, the invention also relates to a hydrodynamic surface 54 comprising two ends separated by a distance D. The hydrodynamic surface 54 also comprises at least two airfoils 40 according to the invention, wherein the two airfoils 40 have the same maximum thickness t max and midline ml of varying lengths.

[0132] In other words, the hydrodynamic surface 54 of the present invention includes any variation in the chord cl of the airfoil 40 along its extension (or distance D) while maintaining a maximum thickness t max same.

[0133] In case the hydrodynamic surface 54 has a cantilever structure, it is possible to distinguish between a root end arranged close to the structural restraint and a free distal end.

[0134] For example, the cantilevered fluid dynamic surface 54 of the present invention may be a blade 56 of a rotor (see, e.g. Fig.17 , 18 , 21, 22 and 25 to 28) or a half wing 58 of an aircraft (see e.g. Fig.29 and 32 ). In the case of a blade 56, the root end is the radially inner end, which is connected to the hub 60 via a root structure 62, while the distal end is the radially outer end. In the case of a half-wing 58, the root end is the end that is structurally connected to the aircraft, while the distal end is the free end, also called the wing tip.

[0135] Preferably, in the above-mentioned fluid dynamic surface 54 , at least two airfoils 40 have the same front portion 42 and rear portion 44 and different middle portions 46 .

[0136] According to what has been said above, the invention also envisages that the fluid dynamic surface 54 comprises an abrupt change of the chord cl, for example abruptly transitioning from a first region with a constant airfoil 40 to a second region also with a constant airfoil 40 but with an airfoil 40 different from the first region. Thus, in this case, the same front portion 42 and rear portion 44 are connected to different middle portions 46 in two different regions of the aerodynamic surface. This type of abrupt change of the chord cl results in a step along the leading edge le and / or a step along the trailing edge te. This technical solution is rarely applied and is not shown in the accompanying drawings.

[0137] In some cases, the arrow-shaped half-wing 58 may be provided with a step along the leading edge 1e, in which case it may be desirable to adopt a solution known per se and referred to in aviation terminology as a dogtooth or notch. Both solutions create an abrupt discontinuity in the flow over the half-wing 58, thereby preventing unwanted airflow in the span direction of the half-wing 58.

[0138] Notwithstanding the above-mentioned special circumstances, the preferred embodiment of the fluid dynamic surface 54 of the present invention is that the middle portion 46 is perpendicular to the maximum thickness t max The extension in the direction of changes continuously along at least a section between the two ends.

[0139] In other words, a preferred embodiment of the hydrodynamic surface 54 of the present invention is that the chord cl varies continuously at least in sections along the distance D, for example Fig.17 , 18 , 21, 22 and 25-28 in the blade 56 and as Fig.29 and Fig.32 Half wing 58.

[0140] It can be noted that in these embodiments, the leading edge le and the trailing edge te are defined by continuous lines formed by straight line segments (which may also be dashed lines) on the plane, such as Fig.18 , 21 , blades 56 in 22, 26 and 28 and Fig.32 Half wing 58.

[0141] In the figures, the dashed arrows indicate the extrusion / pultrusion direction or longitudinal direction ld of the components 48, 50 and 52 of the airfoil 40 of the present invention. As can be well understood by a person skilled in the art, in the front component 48 and the rear component 50, the longitudinal direction ld is defined in a unique manner and can only be parallel to the leading edge le and the trailing edge te, respectively, without "trimming". In contrast, the longitudinal direction of the middle component 52 is not defined in a unique manner in a plan view, because they can be slightly rotated in their own plane without any external influence.

[0142] It can be seen that the longitudinal directions ld of the individual extruded / pultruded parts 48, 50, 52 included in the single fluid dynamic surface 54 of the present invention can be at an angle to each other. This possibility brings important degrees of freedom to the design and implementation of the fluid dynamic surface 54 including the extruded / pultruded airfoil 40. According to the prior art, in a fluid dynamic airfoil 40 composed of several extruded / pultruded parts 48, 50, the extruded / pultruded parts 48, 50 can only be assembled by arranging their respective longitudinal directions ld parallel to each other. According to the present invention, the different parts 48, 50, 52 can be arranged around a direction parallel to the maximum thickness t max In fact, according to the invention, the belly and the back of the middle part 52 are flat and parallel to each other, so these rotations do not introduce any discontinuity in the hydrodynamic surface 54.

[0143] The different parts 48, 50, 52 forming the airfoil 40 according to the invention can be connected together in a manner known per se. For example, the extruded / pultruded parts 48, 50, 52 can be connected by gluing, riveting, bolting, or by inserting connecting elements 64. Furthermore, the metal extruded parts 48, 50, 52 can also be connected by welding or brazing.

[0144] Some characteristics of the embodiment of the airfoil 40 of the invention shown by way of example in the accompanying drawings will be described below.

[0145] Figure 6 , Fig. 9 , Fig.10 and FIG. 11 show airfoils 40 according to the invention, these airfoils 40 comprising only two parts: a front part 48 and a rear part 50 .

[0146] Figure 6 The airfoil 40 is shown disassembled, while FIG11 shows some examples of how the airfoil 40 can be assembled. The airfoil 40 includes a rear appendage 66 with a large curvature, which indicates that it is an airfoil used to make a blade 56 for an industrial axial fan. Therefore, the airfoil 40 is shown with the back facing downward and the belly facing upward, because industrial fans are usually (although not necessarily) installed in such a way that an airflow is generated from the bottom to the top.

[0147] As one skilled in the art will note, Figure 11.b and Figure 11.c The characteristic feature of the present invention is clearly shown, namely that the thickness of the middle portion 46 is constant and equal to the maximum thickness t max In contrast, Figure 11.a The airfoil 40 in the embodiment is very similar to the airfoil 40 in the prior art. Figure 6The airfoil that can be obtained by the two components 48 and 50 has the one with the smallest chord.

[0148] As described above, in this type of airfoil 40 comprising two parts 48, 50, the middle portion 46 of constant thickness can be defined by a rearward extension of the front part 48 and / or a forward extension of the rear part 50. According to current technical limitations, Figure 6 The airfoil 40 of the present invention of FIG. 11 is similar to Figure 11.c A maximum chord cl of about 100 cm can be obtained in the construction.

[0149] As can be seen from the schematic diagram of Figure 11, a connecting element 64 is shown, in particular a tubular element with a quadrangular cross section. Although the connecting element 64 is not absolutely necessary, it helps to connect the two parts 48 and 50. In some special cases, the connecting element 64 can be an extension of the root structure 62 that binds the blade 56 to the hub 60.

[0150] Figure 7 12 shows a disassembled airfoil 40 according to the invention, which includes three parts: a front part 48, a rear part 50 and a middle part 52. In this case, the airfoil 40 also includes a rear appendage 66 with a large curvature, which indicates that it is an airfoil 40 used to manufacture a blade 56 for an industrial axial fan. Therefore, the airfoil 40 is shown with the back facing downward and the belly facing upward.

[0151] As can be seen by those skilled in the art, the front component 48 includes a rearward male interface, the rear component 50 includes a forward female interface, and the middle component 52 includes a rearward male interface and a forward female interface. The arrangement of these interfaces allows the components 48, 50, 52 to be easily connected, such as by gluing or riveting, without the need for a connecting element 64.

[0152] As will be well understood by those skilled in the art, in the airfoil 40 that can be obtained using these components 48, 50, 52, the use of Figure 7 and Figure 12.f The middle section 52 shown allows the manufacture of an airfoil 40 having a maximum chord. Figure 12.a The front part 48 is directly joined to the rear part 50 in this way, so that the airfoil 40 with the minimum chord is produced, which is very similar to the airfoil 40 in the prior art. Figure 12.b to Figure 12.e ), the middle part 52 must be cut to size so that it has the required extension in the direction of the center line ml. As can be well understood by those skilled in the art, it is preferred to cut the middle part 52 in the front, that is, in the part of the female interface, to retain the male interface for connection with the rear part 50. Figure 12.b to Figure 12.e The cutting will produce a new female interface, which is exactly the same as the original female interface and is suitable for connecting with the male interface of the front component 48. In the case where the cutting involves the location where the internal reinforcement element 68 is set, the female interface can be restored by simple milling.

[0153] According to current technical limitations, Figure 7 The maximum chord of the airfoil 40 of the present invention of FIG. 12 may be about 150 cm.

[0154] Figure 8 The airfoil 40 according to the invention is shown disassembled, and comprises three parts: a front part 48, a rear part 50 and a middle part 52. In this case, the airfoil 40 also comprises a rear appendage 66 with a high curvature, which indicates that it is an airfoil 40 for manufacturing a blade 56 for an industrial axial fan. Therefore, the airfoil 40 is shown with the back facing downwards and the belly facing upwards.

[0155] As can be seen by those skilled in the art, the front component 48 includes a male interface facing rearward, the rear component 50 includes a male interface facing forward, and the middle component 52 includes two female interfaces facing forward and backward. The arrangement of these interfaces allows the components 48, 50, 52 to be easily connected, for example, by gluing or riveting, without the need for a connecting element 64.

[0156] As will be well understood by those skilled in the art, in the airfoil 40 that can be obtained using these components 48, 50, 52, the use of Figure 8 The middle part 52 shown makes it possible to manufacture an airfoil 40 with a maximum chord. On the contrary, without the middle part 52 at all, that is, the front part 48 is directly connected to the rear part 50, so that an airfoil 40 with a minimum chord is manufactured, which is very similar to the airfoil 40 in the prior art. In this special case, the connection between the front part 48 and the rear part 50 requires the use of an external connecting element 64, at least for filling the step formed by the interface on the surface of the back and the abdomen. The connecting element 64 can be two simple metal sheets or polymer strips arranged along the longitudinal direction ld. When manufacturing an airfoil 40 with a medium chord length, the middle part 52 must be cut to size so that it has the required extension in the direction of the center line ml. As can be well understood by those skilled in the art, cutting the middle part 52 is not restricted because in any case it will produce a new female interface, which is the same as the original female interface and is suitable for connection with the male interfaces of the other two parts. As mentioned above, in the case of cutting involving the location where the internal reinforcing element 68 is set, the female interface can be restored by simple milling.

[0157] Figure 8The particular shape of the middle part 52 allows to obtain two middle parts 46, which may be identical to each other, for example by a cut similar to that shown in dashed lines. In particular, a cut along the median line obtains two rectangular middle parts 46, while a cut obliquely obtains two trapezoidal middle parts 46. In any case, each of the two middle parts 46 (whether rectangular or trapezoidal) comprises a female interface for connection with the corresponding front part 48 and rear part 50. As mentioned above, when the cut involves the site where the internal reinforcing element 68 is arranged, the female interface can be restored by simple milling. Figure 8 This particularity of the middle part 52 allows to obtain two hydrodynamic surfaces 54 using a single middle part 52, provided of course that the length of the front part 48 and / or the rear part 50 is correct. This makes it possible to utilize all the parts obtained by cutting the middle part 52 and greatly limits material scrap.

[0158] According to current technical limitations, Figure 8 The maximum chord of the airfoil 40 of the present invention may be about 150 cm.

[0159] Similar to Figure 8 The results for airfoil 40 can also be obtained using Fig. 9 The airfoil 40 is obtained in two composite parts, wherein the composite shape of the front part 40 and the rear part 50 allows to minimize the material scrap. In this case, in fact, as described above with respect to Figure 8 As described in the embodiment, the compound front component 40 can be cut along the longitudinal direction ld and along the direction inclined relative to the longitudinal direction ld, thereby obtaining two front components 48, which are rectangular or trapezoidal in the plane and can be identical to each other. Similarly, the compound rear component 50 can be cut along the longitudinal direction ld and along the direction inclined relative to the longitudinal direction ld, thereby obtaining two rear components 50, which are rectangular or trapezoidal in the plane and can be identical to each other.

[0160] Please note that the complex components 48, 50 (such as Fig. 9 The components in ( ) are particularly suitable for realizing two aerodynamic surfaces 54 that are mirror images of each other, such as two half wings of a single aircraft. In such a composite component 48, 50 with central symmetry, the cut inclined relative to the longitudinal direction ld actually forms two trapezoidal components that are mirror images of each other. In addition, other composite components 48, 50 (not shown) with axial symmetry are particularly suitable for realizing two aerodynamic surfaces 54 that are identical to each other, such as two blades of a single rotor. In such a composite component 48, 50 with axial symmetry, the cut inclined relative to the longitudinal direction ld actually produces two trapezoidal sections that are identical to each other.

[0161] As described above, the cutting of the composite part allows obtaining parts 48, 50, each of which comprises a similar Figure 6 The interface of the components 48 and 50 allows an assembly similar to that of FIG. 11. It should be noted that, among other things, Fig. 9 The airfoil parts 48, 50, once cut, are also connected with the airfoil parts 48, 50, such as Figure 6 The individual components 48, 50 are fully compatible as long as they have the same maximum thickness t max As mentioned above, if the cut involves the site where the internal reinforcing element 68 is provided, the female interface can be restored by simple milling. Fig. 9 This particularity of the technical solution allows to utilize all the parts obtained by cutting the front part 48 and the rear part 50 and greatly limits the material scrap.

[0162] In order to meet specific needs, the actual manufacture of the airfoil 40 according to the invention can also envisage the use of parts 48 , 50 and 52 of different lengths on the dorsal and ventral sides. Fig.10 An example of such an implementation is schematically shown in FIG. Fig.10 In the front part 48 of the embodiment, the wall defining the abdomen extends further rearward than the wall defining the back. Fig.10 In the rear part 50, the wall defining the back extends further forward than the wall defining the belly. During the manufacture of the airfoil 40, this particular solution can be obtained by providing the front part 48 and / or the rear part 50 by two cuts spaced apart along the center line ml.

[0163] Some particularities of the embodiment of the fluid dynamic surface 54 of the present invention shown by way of example in the accompanying drawings will now be described.

[0164] Fig.17 and 18 The plan view of two blades 56 of an industrial axial flow fan is schematically shown. The airfoil 40 used in the two blades 56 is the same as that described above. Figure 6 Similar to the airfoil 40 described in Figure 11. Both blades 56, although different from each other, show an increase in the chord cl towards the distal end (radially outer end). The increase in the chord in the radially outer area of ​​the blade 56 allows limiting the sound emissions generated during the operation of the fan in a manner known per se.

[0165] exist Fig.17In the blade 56, both the leading edge le and the trailing edge te are straight. The leading edge le is inclined forward relative to the radial direction, i.e., inclined in the direction of rotation of the blade 56. In contrast, the trailing edge te is parallel to the radial direction. As shown, the blade 56 comprises a single extension of the rear part 50 having a rectangular plan shape (therefore having a constant chord cl) and a single extension of the front part 48 having a trapezoidal plan shape (therefore having a variable chord cl along a distance D). The dotted arrows indicate the longitudinal directions ld of the respective parts 48, 50, which are inclined relative to each other.

[0166] exist Fig.18 In the blade 56, the trailing edge te is straight, while the leading edge le is defined by a broken line. The trailing edge te is parallel to the radial direction, while the leading edge le is parallel in the radially inner section and is inclined forward in the radially outer section. It can be seen that the blade 56 includes a single extension of the rear component 50 having a rectangular plan shape (and therefore having a constant chord cl). The blade 56 also includes a radially inner extension of the front component 48 having a substantially rectangular plan shape (and therefore having a constant chord cl) and a radially outer extension of the front component 48 having a trapezoidal plan shape (and therefore having a variable chord cl along a distance D). The dotted arrows indicate the longitudinal direction ld of each extension of the components 48 and 50. Preferably, the connection between the extensions of the two front components 48 is made along the bisector of the angle formed by their respective leading edges le.

[0167] Fig.21 and Fig. 22 The plan view of two blades 56 of an industrial axial flow fan is schematically shown. The airfoil 40 used in the two blades 56 is the same as that described above. Figure 6 Similar to the airfoil 40 described in FIG11 . The two blades 56 , although different from each other, both show an increase in the chord cl both towards the root end (radially inside) and towards the distal end (radially outside), the chord cl being smallest in the middle. According to a manner known per se, the increase in the chord cl in the radially inside region of the blade 56 improves the overall efficiency of the fan. The increase in the chord cl in the radially outside region of the blade 56 allows limiting the sound emissions generated during the operation of the fan in a manner known per se.

[0168] exist Fig.21In the blade 56, the trailing edge te is straight, while the leading edge le is defined by a broken line. The trailing edge te is parallel to the radial direction, while the leading edge le is inclined backward (i.e., opposite to the direction of rotation) on the radially inner section and inclined forward on the radially outer section. As can be seen, the blade 56 includes a single extension of the rear part 50 having a rectangular plan shape (and therefore having a constant chord cl). The blade 56 also includes two extensions of the front parts 48, one on the radial inner side and one on the radial outer side, both of which have a trapezoidal shape and therefore have a variable chord cl along the distance D. The chord cl of the blade 56 reaches a minimum at the connection between the extensions of the two front parts 48. The dotted arrows represent the longitudinal directions ld of the respective extensions of the parts 48 and 50. Preferably, the connection between the extensions of the two front parts 48 is carried out along the bisector of the angle formed by the respective leading edges le.

[0169] exist Fig. 22 In the blade 56 of the invention, the trailing edge te is straight, while the leading edge le is defined by a broken line. The trailing edge te is inclined forward, while the leading edge le is parallel to the radial direction on the radially inner section and inclined forward on the radially outer section. As can be seen, the blade 56 comprises a single extension of the rear part 50 having a trapezoidal plan shape (and therefore having a variable chord cl along the distance D). The blade 56 also comprises two extensions of the front part 48, one on the radial inner side, having a substantially rectangular plan shape, and therefore having a constant chord cl, and one on the radial outer side, having a trapezoidal plan shape, and therefore having a variable chord cl along the distance D. The chord cl of the blade 56 reaches a minimum near the connection between the extensions of the two front parts 48. The dashed arrows represent the longitudinal direction ld of each extension of the parts 48, 50. Preferably, the connection between the extensions of the two front parts 48 is carried out along the bisector of the angle formed by the respective leading edges le.

[0170] Figure 25 to Figure 28 Schematically shows the above-mentioned Figure 6 A plan view of other blades 56 of an industrial axial fan having a similar airfoil 40 as described in FIG. 11. These blades 56 represent the invention described above with reference to Figures 17 to 22 The blade 56 describes other possible implementations of the technical solution in different ways.

[0171] Please note that, for example, Fig.26 In the blade 56 of FIG. 5 , the progressive progression of the trailing edge te in the radially outer region can be obtained by "trimming" the rear appendage 66, or by a different orientation relative to the radial direction of the rear part 50 of the airfoil. These two technical solutions, although having the same planform, have different aerodynamic characteristics and therefore meet different requirements.

[0172] Fig.29 and Fig.32 The plan view of two half wings 58 of a fixed-wing aircraft is schematically shown. The airfoil 40 used in the two half wings 58 is the same as that described above. Figures 1 to 3 The two half-wings 58, although different from one another, both show a reduction in chord cl towards the distal end (wing tip). The reduction in chord cl in the distal region of the half-wing 58 improves the distribution of aerodynamic loads in a manner known per se by limiting the bending loads in the wing root region.

[0173] Although Fig.29 and Fig.32 The two half wings 58 may represent a very simplified technical solution for an aircraft, but they may also be effectively used for other aircraft, such as low-cost drones.

[0174] A third aspect of the invention relates to a method for defining an airfoil 40. The method of the invention comprises the following steps:

[0175] - providing a known wing 40 having a leading edge le, a trailing edge te, a center line ml and a thickness t;

[0176] - Determine the front portion 42 of the known airfoil 40, in which the thickness t increases from the leading edge le toward the rear along the center line ml to a maximum thickness t max ;

[0177] - Determine the rear portion 44 of the known airfoil 40, in which the thickness t increases along the center line ml from the trailing edge te forward to a maximum thickness t max ;

[0178] - the front portion 42 and the rear portion 44 are aligned with the maximum thickness t max The direction is spaced perpendicular to the direction;

[0179] - an intermediate portion 46 is inserted between the front portion 42 and the rear portion 44, the intermediate portion 46 having a maximum thickness equal to t max The constant thickness t;

[0180] - providing a front part 48 and a rear part 50 of the wing 40 , wherein the front portion 42 is defined by the front part 48 and the rear portion 44 is defined by the rear part 50 ; and

[0181] Assembling the front part 48 and the rear part 50 to obtain the wing 40 .

[0182] As those skilled in the art can well understand, the above method may involve both the definition of a theoretical airfoil 40 (eg, in the design phase) and the definition of an actual airfoil 40 (eg, in the actual manufacturing phase).

[0183] While remaining within the design limits, the method of the invention may be part of a more complex method for defining a fluid dynamic surface 54. In this case, the method may envisage defining at least two different airfoils 40, applying the above steps to each airfoil 40, wherein both airfoils 40 have the same maximum thickness t max and midline ml of varying lengths.

[0184] The hydrodynamic surface 54 will have two ends separated by a distance D. The method preferably comprises a step of defining the distance D, for example from the ratio of the centre lines ml of the two airfoils 40 .

[0185] Within the scope of practical manufacturing, the method of the invention also comprises a step of providing two or more parts 48, 50, 52 of the airfoil 40. Preferably, the parts 48, 50, 52 are obtained by extrusion / pultrusion.

[0186] For example, the method may envisage the steps of providing only the front part 48 and the rear part 50 of the airfoil 40, wherein:

[0187] - the front portion 42 is defined by a front part 48; and

[0188] The rear portion 44 is defined by a rear part 50 .

[0189] In this case, the mid-portion 46 of the airfoil 40 may be defined by a forward component 48 and / or an aft component 50 .

[0190] Alternatively, the method may envisage the steps of providing only the front part 48 , the rear part 50 and the middle part 52 of the airfoil 40 , wherein:

[0191] - the front portion 42 is defined by a front part 48;

[0192] - the rear portion 44 is defined by a rear part 50; and

[0193] The middle portion 46 is at least partially defined by a middle part 52 .

[0194] Other auxiliary steps of the method of the present invention can be deduced by a person skilled in the art based on the above description of the airfoil 40 and the fluid dynamic surface 54 of the present invention. In fact, based on the above description, it is not difficult for a person skilled in the art to infer the auxiliary steps of the method, which are necessary for determining the orientation of each component 48, 50, 52, connecting each component 48, 50, 52 together, etc.

[0195] Example

[0196] Reference Fig.3536, the following describes a comparison of the performance of two airfoils 40 with equal chord cl, one according to the prior art ( Figure 36.a ), another one according to the present invention ( Figure 36.b ). The performances considered in the comparison include lift (Lift), drag (Drag) and efficiency, which can be understood as the ratio between the two (Lift / Drag). The comparison involves applying the two airfoils 40 to the blades 56 of an industrial ducted axial fan and is performed by the owner using computational fluid dynamics (CFD) techniques. The two types of blades 56 were chosen to be simulated in a significantly stationary state of an industrial fan, testing different pitch angles.

[0197] Fig.35 The velocity field striking the fan blade 56 in a numerical simulation is schematically shown, assuming for comparison that one of the two airfoils 40 is struck at a time. Fig.35 An axial direction a (defined by the axis of rotation), a radial direction r (defined by a half-line originating from and perpendicular to the axis of rotation) and a tangential direction t (defined by a line normal to the radial direction and contained in a plane perpendicular to the axis of rotation) are shown.

[0198] Each part of the blade 56 is hit by the airflow, and the velocity of the airflow can be more easily considered if it is decomposed into two components described below. The first component is the tangential component Vt, which originates from the rotational motion of the blade 56. This tangential velocity Vt is proportional to the angular velocity of the blade 56 and the distance from the axis of rotation. This component is therefore assumed to have a triangular distribution, from a zero point at the axis of rotation to a maximum value at the distal end.

[0199] In the CFD simulation, it is assumed that the constant angular velocity of the blade 56 is equal to 660 rpm (revolutions per minute) and the maximum tangential velocity Vt at the distal end of the blade 56 is equal to 60 m / s. The second component of the velocity is the axial component Va, which is caused by the axial flow of the air due to the force generated by the fan itself. The distribution of the axial velocity Va is assumed to be the same as that obtained experimentally. Fig.35 . It can be seen that the distribution includes negative values ​​in the radially innermost region: this phenomenon is due to the recirculation that usually occurs in this region of the fan. The axial velocity Va reaches a maximum value about two-thirds of the way along the blade 56 and then returns to zero at the far end. In the simulation, the axial velocity Va is assumed to be constant over time, with a maximum value of 14 m / s.

[0200] Keeping these parameters constant, the CFD numerical simulations considered the two airfoils 40 at different pitch angles of 3°, 6°, 10.5° and 15°. The following table reports the results of the different simulations.

[0201]

[0202] Before the simulations were performed, the owner expected that the performance of the prior art airfoil 40 would be better than the airfoil 40 of the present invention in any case, because the airfoil 40 of the present invention has been greatly simplified in structure. Therefore, the purpose of the simulations was to evaluate the extent of the performance loss and, in turn, to evaluate the extent to which the simplified manufacture of the airfoil 40 could compensate for the performance loss.

[0203] Contrary to expectations, it can be seen from the table above that the performance difference between the two airfoils 40 is small, and in some cases, the airfoil 40 of the present invention even achieves the best performance. In particular, the airfoil 40 of the present invention shows better efficiency at smaller pitch angles (3° and 6°), and shows lower efficiency at larger pitch angles (10.5° and 15°), which is several percent lower.

[0204] To explain the results, the authors hypothesize that the flow is more likely to follow the airfoil 40 at lower pitch angles (3° and 6°), and that the shape of the airfoil 40 of the present invention results in better performance mainly due to the lower maximum thickness and thus lower form drag (see Figure 36.b On the other hand, at larger pitch angles (10.5° and 15°), the prior art airfoil 40 (see Figure 36.a )'s thicker, rounder shape will help flow along it more easily, especially on the back.

[0205] In view of the above, those skilled in the art can well appreciate how the present invention overcomes the shortcomings highlighted with respect to the prior art.

[0206] In particular, the invention provides an airfoil, the extension of which in the direction of the chord can be varied in a simple and economical manner to suit different requirements.

[0207] Furthermore, the invention provides an airfoil which, despite being simple to manufacture, still maintains performances comparable to or even better than known airfoils.

[0208] Furthermore, the invention provides a fluid dynamic surface, the proportions of which can be varied simply and economically to suit different requirements.

[0209] Finally, the invention provides a method for defining the airfoil 40 in a simple and economical manner, so as to adapt it to different requirements.

[0210] In short, all the details can be replaced by other technically equivalent elements; the features described with respect to a specific embodiment can also be used in other embodiments; without departing from the scope of protection of the following claims, the materials used and the accompanying shapes and sizes can be changed arbitrarily according to the needs of the specific implementation.

Claims

1. An airfoil (40) comprising a front leading edge le, a rear trailing edge te, a center line ml and a thickness t, wherein the airfoil (40) further comprises: - a front portion (42) in which the thickness t increases from the front edge le towards the rear along the midline ml to a maximum thickness t max ; as well as - a rear portion (44) in which the thickness t increases along the median line ml from the rear edge te forwardly to the maximum thickness t max ; The airfoil (40) further comprises a middle portion (46) disposed between the front portion (42) and the rear portion (44), wherein the thickness t in the middle portion (46) is constant and equal to the maximum thickness t max ; And wherein the airfoil (40) further comprises at least one front component (48) and a rear component (50) assembled, wherein: - said front portion (42) is defined by said front member (48); and - said rear portion (44) is defined by said rear part (50).

2. The airfoil (40) according to claim 1, wherein: The front part (48) and the rear part (50) are obtained by extrusion / pultrusion.

3. The airfoil (40) according to claim 1 or 2, wherein: The middle portion (46) is defined by the front component (48) and / or by the rear component (50).

4. The airfoil (40) according to one or more of the preceding claims, further comprising a mid-section (52).

5. The airfoil (40) according to claim 4, wherein: The middle part (52) is obtained by extrusion / pultrusion.

6. The airfoil (40) according to one or more of the preceding claims, further comprising a back and a belly, wherein the back and / or the belly and / or the center line ml is continuous and uniform.

7. A fluid dynamic surface (54) comprising two ends separated by a distance D and at least two airfoils (40) according to one or more of the preceding claims, wherein the two airfoils (40) have the same maximum thickness t max and midline ml of varying lengths.

8. The fluid dynamic surface (54) according to the preceding claim, wherein: The front portion (42) and the rear portion (44) of the two airfoils (40) are identical, but the middle portion (46) is different.

9. The fluid dynamic surface (54) according to claim 7 or 8, wherein: The middle portion (46) is perpendicular to the maximum thickness t max The extension in the direction of changes continuously along at least a section between the two ends.

10. The fluid dynamic surface (54) according to one or more of claims 7 to 9, wherein: The hydrodynamic surface (54) is a half-wing (58).

11. The fluid dynamic surface (54) according to one or more of claims 7 to 9, wherein: The fluid dynamic surface (54) is a blade (56) of a rotor.

12. A method for defining an airfoil (40), comprising the steps of: - providing a known airfoil (40) having a front leading edge le, a rear trailing edge te, a center line ml and a thickness t; - determining a front portion (42) of the known airfoil (40) in which the thickness t increases from the leading edge le toward the rear along the center line ml to a maximum thickness t max ; - determining a rear portion (44) of the known airfoil (40) in which the thickness t increases along the center line ml from the trailing edge te forwardly to the maximum thickness t max ; - the front portion (42) and the rear portion (44) are aligned with the maximum thickness t max The direction is spaced perpendicular to the direction; - an intermediate portion (46) is inserted between said front portion (42) and said rear portion (44), said intermediate portion (46) having a thickness equal to said maximum thickness t max Constant thickness of - providing a front part (48) and a rear part (50) of the airfoil (40), wherein the front portion (42) is defined by the front part (48) and the rear portion (44) is defined by the rear part (50); and - Assembling the front part (48) and the rear part (50) to obtain the airfoil (40).

13. A method according to the preceding claim, wherein: The front part (48) and the rear part (44) are obtained by extrusion / pultrusion.

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