阅读说明：本技术 具有后缘襟翼的轴流式风机 (Axial fan with trailing edge flap ) 是由 罗伯特·爱德华多·莫西维奇 于 2020-03-16 设计创作，主要内容包括：本发明涉及一种叶片组件(30),用于具有旋转轴线X的大尺寸轴流式风机(32)。本发明的叶片组件包括：-根部结构(34),其用于将叶片组件机械地连接至轮毂(36)；-叶片,其中叶片的至少一部分具有包括前部半翼型件(48)和后部襟翼(50)的复合翼型件(46),其中：-半翼型件用于通过根部结构相对于轮毂(36)以预定桨距角(α-(c))装配；-襟翼(50)安装在叶片上,使得襟翼能够被固定在介于相对于桨距角(α-(c))的最大偏转位置和最小偏转位置之间的位置；以及-在前部半翼型件和后部襟翼之间限定通道,该通道适于允许流体从复合翼型件的正面(v)流至背面(d)。本发明还涉及包括多个叶片的风机。(The invention relates to a blade assembly (30) for a large-size axial fan (32) having a rotation axis X. The blade assembly of the present invention comprises: -a root structure (34) for mechanically connecting the blade assembly to the hub (36); -a blade, wherein at least a part of the blade has a composite airfoil (46) comprising a front half-airfoil (48) and an aft flap (50), wherein: -half-airfoils for passing through a root structure at a predetermined pitch angle (α) with respect to a hub (36) c ) Assembling; -the flap (50) is mounted on the blade such that the flap can be fixed interposed with respect to the pitch angle (a) c ) A position between the maximum deflected position and the minimum deflected position; and-defining a passage between the front half-airfoil and the rear flap, the passage being adapted to allow a fluid to flow from the front face (v) to the rear face (d) of the composite airfoil.The invention also relates to a fan comprising a plurality of blades.)

1. A blade assembly (30) for a large size axial fan (32), the axial fan (32) having an axis of rotation X, the blade assembly (30) comprising:

-a root structure (34) for mechanically connecting the blade assembly (30) to a hub (36) of the axial fan (32);

-a blade (38), wherein at least a portion of the blade (38) has a composite airfoil (46), the composite airfoil (46) comprising a forward half-airfoil (48) and an aft flap (50), wherein:

-the half-airfoils (48) of the blades (38) being for passing through the root structure (34) with a predetermined pitch angle (a) with respect to the hub (36) of the axial fan (32)_c) Assembling;

-the flap (50) is mounted on the blade (38) such that the flap (50) can be fixed in place between the opposing surfacesAt the pitch angle (alpha)_c) A position between the maximum deflected position and the minimum deflected position; and

-defining a channel (54) between the front half-airfoil (48) and the rear flap (50), the channel (54) being adapted to allow a fluid to flow from a front face v to a rear face d of the composite airfoil (46).

2. The blade assembly (30) according to claim 1, wherein the portion of the blade (38) having the composite airfoil (46) is at least one radially inner portion (44), the radially inner portion (44) having a radial extension f, and a radially outer portion (40) of the blade (38) having a radial extension e.

3. A blade assembly (30) according to claim 2, wherein the blade (38) has a radial extension a, and wherein f is between 20% and 70% of a, preferably between 40% and 60% of a.

4. The blade assembly (30) according to claim 2 or 3, wherein between the radially inner portion (44) and the radially outer portion (40), one or more radially intermediate portions (62) are included, wherein each radially intermediate portion (62) has a composite airfoil (46).

5. A blade assembly (30) according to claim 4, wherein each portion (40, 44, 62) of the blade (38) has a radial extension substantially equal to each other.

6. The blade assembly (30) according to claim 4 or 5, wherein the airfoils (42, 46) of each portion (40, 44, 62) of the blade (38) have mutually substantially equal chords c in at least one respective section.

7. The blade assembly (30) according to one or more of the preceding claims, wherein, in use, the flap (50) is fixed with respect to the blade (38).

8. The blade assembly (30) according to one or more of the preceding claims, wherein said channels (54) are smooth and/or converge from said front face v to said rear face d.

9. The blade assembly (30) according to one or more of the preceding claims, wherein the blade (38) further comprises a wall (74) provided at a boundary between two adjacent radial portions, said wall (74) being adapted to close an opening formed between two adjacent flap portions (50) facing differently in a radial direction.

10. The blade assembly (30) according to one or more of the preceding claims, wherein said blade (38) further comprises a winglet (76) at the radial tip.

11. A rotor (56) for a large size axial fan (32), the rotor (56) comprising a plurality of blade assemblies (30) according to one or more of the preceding claims and a hub (36).

12. A large-size axial fan (32) comprising a rotor (56) according to the preceding claim and a motor (68) adapted to rotate the rotor (56) about a rotation axis X.

13. The axial fan (32) according to the preceding claim, further comprising a duct (70).

14. The axial fan (32) of claim 12 or 13, further comprising a frame (72), the frame (72) being adapted to securely hold the axial fan (32) in all operating conditions of the axial fan (32).

Technical Field

The present invention relates to a blade for an axial fan, in particular a blade for a large-size ducted axial fan for industrial use. By large-diameter axial fan is meant here and in the following an axial fan with a diameter D of more than 1 meter.

Background

In the industrial field, it is known to use large-diameter axial fans in systems that require dissipation of a large amount of heat, in order generally to ensure a sufficient flow of air around a specific radiant surface.

Axial fans for industrial use typically include a central hub defining an axis of rotation and on which a plurality of blades are mounted. Rotation of the hub rotates the blades and, as will be appreciated by those skilled in the art, imparts different tangential velocities to different sections of each blade. In practice, the tangential velocity of each blade segment is the product of the angular velocity (which is the same for all segments) and the radial distance from the axis of rotation (which increases when moving away from the axis of rotation).

As is known, the operational characteristics of a wind turbine are determined by a set of structural parameters, such as total rotor diameter, blade airfoil shape, blade pitch angle at the hub, number of blades, rotor speed, motor power, and the like.

For each fan configuration determined by fixed configuration parameters during planning, a characteristic curve is obtained on the flow-pressure side. An example of such a characteristic curve is qualitatively illustrated in the graph of fig. 5, where the dashed line represents the pair from α_c1Increase to alpha_c8Pitch angle alpha of_cDifferent characteristic curves were obtained. These characteristic curves are delimited above by the line marking the stall condition and below by the curve representing the dynamic pressure. The continuous curve of the thin strokes provides a representation of the efficiency epsilon of the fan. More specifically, each efficiency curve ε_nRepresenting different flow and pressure conditions but with the same efficiency. Furthermore, overall, the efficiency curve ε_nHas the same effect as the contour lines (or contour lines) in the topographical map, showing the overall efficiency trend as a function of flow and pressure. In the particular graph of FIG. 5, the efficiency is from ε₁Increase to epsilon₇。

Need to useEach particular industrial application of the fan defines a predetermined flow rate value at full speed under steady state conditions. Thus, for a fan, the operating point P at steady speed is defined by the point of the characteristic curve that ensures the required flow rate_f。

Axial fans of the known type are widely used because of their easy construction and operation, their relatively low cost and their ability to ensure a wide range of operating speeds.

However, these solutions, although widely appreciated, are not without drawbacks.

In fact, as known to those skilled in the art, the blades of an axial fan do not work effectively along their entire radial opening. The tangential velocity of the innermost section of the blade is usually too low to obtain an effective relative movement with respect to the air flow. Therefore, the actual operation of the fan is only entrusted with ensuring the outer section of almost the entire total air flow generated by the axial fan. Generally, to simplify the structure of the blade, the inner section is not even provided with airfoils, but is only intended to perform the mechanical role of supporting the outer section.

The diagram of figure 7 qualitatively shows the distribution of the air flow generated by the fan as a function of the radial distance from the rotation axis X. As can be observed, most of the flow is generated by the section near the radially outer end of each vane.

As can be appreciated by those skilled in the art, such a flow distribution makes the axial fan less efficient overall.

Moreover, as can be observed in fig. 5, the operating point P at full speed of a particular fan in a particular application_fNot always with the maximum efficiency point P epsilon of the fan itself_maxAnd (4) overlapping. In other words, the potential of the wind turbine is not fully exploited over almost the entire operating life of the wind turbine. This results in a significant portion of the energy being wasted for operating the fan.

Of course, by varying the design parameters of the fan, the characteristic curve can be modified so that the operating point P is made_fCloser to the point of maximum efficiency Pepsilon_max. However, each parameter is subject to external constraints that greatly limit the variationThe actual possibilities of conversion. In particular in fig. 5, for example at the same flow velocity, by pitching the angle α_cChange to alpha_c4And alpha_c3The efficiency epsilon can be slightly increased by the intermediate values in between. In this way, a slightly lower pressure and a slightly higher efficiency can be obtained at the same flow rate. However, the pitch angle α cannot be determined at all in reality_cCan be varied virtually at will. Moreover, as can be found by the person skilled in the art from the diagram of fig. 5, even by changing the pitch angle α_cThe efficiency that can be obtained anyway is still far from the point of maximum efficiency Pepsilon_max。

One of the most difficult parameters to change during planning is the blade airfoil for how to make a large diameter wind turbine. In fact, since the fan must have a low overall cost for the end user, the blade must be obtained by extrusion or extrusion starting from a very limited number of dies. Thus, the aerodynamic section of a blade made of an aluminium alloy or a fibre-reinforced composite material usually has a constant cross-section. Subsequently, the blades, which have been individually manufactured, are fitted on the hub in the number and pitch angle determined during planning.

This construction method makes large fans distinctly different from small and medium fans used in the automotive industry or for household ventilation, for example, small and medium fans used for cooling electronic equipment. For purposes of this discussion, a fan is considered large when it has a diameter D greater than 1 meter.

Small and medium-sized fans, precisely because of their small size and the large number of units for producing them, can be economically manufactured by techniques such as injection moulding. This production technique allows very economical construction of one-piece rotors with blades shaped according to even very complex shapes. For the large axial fans considered herein, these construction techniques cannot be used for various reasons. First, the large size of the fan does not allow injection molding of the integral rotor. In addition, the relatively small number of samples to be produced also prevents the use of injection moulding techniques for the construction of individual blades. Even if these technical and economic problems are overcome, the relationship between aerodynamic forces, mass forces and mechanical properties of blades of large dimensions prevents, in any case for structural purposes, the use of moulded plastics for the production of parts.

Disclosure of Invention

It is therefore an object of the present invention to overcome the previously highlighted drawbacks with respect to the prior art.

In particular, the task of the present invention is to provide a blade for an axial fan which allows to improve the overall efficiency of the fan.

Further, the task of the present invention is to provide a blade for an axial fan that allows the configuration to be changed to change the characteristic curve of the fan.

Such object and such task are achieved by a blade assembly for a wind turbine according to claim 1.

Drawings

For a better understanding of the present invention and to realize its advantages, some of its exemplary and non-limiting embodiments are described below with reference to the accompanying drawings, in which:

figure 1 is an axonometric view of a large-diameter axial fan according to the prior art;

figure 2 is a plan view of the blower of figure 1;

FIG. 3 is a cross-sectional view operating along the line III-III of FIG. 2;

FIG. 4 is a schematic view of an airfoil according to the prior art;

fig. 5 is a diagram qualitatively showing the characteristic curve, the point of maximum efficiency and the operating point of an axial fan according to the prior art;

fig. 6 is a diagram qualitatively illustrating the characteristic curve, the point of maximum efficiency and the operating point of an axial fan according to the invention;

fig. 7 is a diagram qualitatively illustrating the flow distribution as a function of the distance from the rotation axis for an axial fan according to the prior art;

fig. 8 is a diagram qualitatively illustrating the flow distribution as a function of the distance from the rotation axis for an axial fan according to the invention;

figure 9 is a schematic plan view of another blade assembly according to the present invention;

figure 10 is a cross-section according to line X-X of figure 9;

FIG. 11 is a view of the blade taken along the direction XI-XI in FIG. 9;

figure 12 is a cross-sectional view taken along line XII-XII of figure 9;

figure 13 is an isometric view of the blade of figure 9;

figure 14 is a schematic plan view of another blade assembly according to the present invention;

figure 15 is a schematic view of a section operating along the line XV-XV of figure 14;

figure 16 is a schematic view of a section operating along line XVI-XVI of figure 14;

figure 17 is a schematic view of a section operating along line XVII-XVII of figure 14;

figure 18a is an enlarged schematic view relating to a detail XVIII in figure 17;

figure 18b is an alternative schematic view relating to the details of XVIII in figure 17;

FIG. 19 is an enlarged schematic view relating to a detail of XIX in FIG. 17;

figure 20 is a schematic view of a detail similar to that of figures 18b and 19;

figures 21-24 are various isometric views of a blade assembly according to the invention.

Detailed Description

According to a first aspect, the present invention relates to a blade assembly 30 for a large-size axial fan 32 having a rotation axis X.

The blade assembly 30 of the present invention comprises:

a root structure 34 for mechanically connecting the blade assembly 30 to a hub 36 of the axial fan 32;

a blade 38, wherein at least a portion of the blade 38 has a composite airfoil (airfoil)46, the composite airfoil 46 comprising a front half-airfoil (semi-airfoil)48 and a rear flap (flap)50, wherein:

the half-airfoils 48 of the blades 38 are intended to be set at a predetermined pitch angle (α) with respect to the hub 36 of the axial fan 32 by means of the root structure 34_cAssembling;

flap 50 anMounted on blade 38 such that flap 50 may be fixed intermediate to pitch angle α_cA position between the maximum deflected position and the minimum deflected position; and

between the front half-airfoil 48 and the rear flap 50, a passage 54 is adapted to allow fluid to flow from the front face v to the rear face d of the composite airfoil 46.

In the context of this discussion, some terminology conventions have been adopted to make reading easier and more unobstructed. These term conventions refer to concepts well known in aerodynamics. Its use in this discussion remains intuitive, as from a geometric perspective, strict definitions may differ between different authors. Some terminology conventions are disclosed below with particular reference to fig. 4.

The term airfoil or aerodynamic foil refers to a foil that is specifically designed to ensure high efficiency of the generation of aerodynamic forces (i.e. from interaction with the fluid flow). In a known manner, an airfoil (e.g., the airfoil of fig. 4) has a rounded leading edge, which is surrounded by a fluid flow; in FIG. 4, an osculating circle approximating the airfoil leading edge is highlighted. In a manner also known, the airfoil has a sharp trailing edge from which the fluid flow exits. The leading edge is also considered to be the "forward" region of the airfoil, while the trailing edge is considered to be the "aft" region. The distance between the leading edge and the trailing edge is called the chord c. Furthermore, each individual airfoil may be characterized by a curvature, intuitively represented by the centerline lm of the airfoil.

Research has been conducted on airfoils primarily for their use in wings, in which airfoils are used to generate lift (i.e., an upwardly directed aerodynamic force). As such, the most common representative example of a vane is the vane of fig. 4, where the curvature of the vane has a concave shape facing downward. Referring to this representative example, the convex portion of the tab is the back surface d and the concave portion is the front surface v. However, it should be noted that in other applications, the airfoil may be used to generate forces that are directed in different directions, such as downward forces (i.e., downwardly directed aerodynamic forces). For example, in the application of fig. 1 and 3, the blades 38 of the axial fan 32 are mounted on the hub 36 such that the vanes are inverted relative to the vanes of fig. 4. Nevertheless, the following discussion holds on the most common terms described above, where the back surface d represents the convex portion of the tab, and the front surface v represents the concave or flat portion.

The distance between the back surface d and the front surface v defines the thickness t of the tab. Generally in an airfoil, as in the example of fig. 4, proceeding along the mid-line lm from the leading edge to the trailing edge, the thickness t of the airfoil increases rapidly, reaches a maximum within the leading half of the chord (generally between 1/4 and 1/3), then gradually decreases towards the trailing edge until the thickness is zero without any abrupt changes.

The axial fan 32 of the present invention clearly defines the axis of rotation X. With respect to this axis of rotation X, the geometrical concepts "axial", "radial" and "tangential" are defined.

As already mentioned above, here and hereinafter, the large diameter axial fan 32 is defined as an axial fan 32 having a diameter of more than 1 meter.

As mentioned above, the blades 38 themselves (which are designed to perform aerodynamic functions) are intended to be connected to the hub 36 of the axial fan 32 by means of a root structure 34 (which is designed to perform only mechanical functions). The blades 38 have a radial extension a, while the root structure 34 and the radius of the hub 36 of the axial fan 32 together have an overall radial extension b. For the purposes of this discussion, the distinction between the radial extension of the root structure 34 and the radial extension of the hub 36 is not important, as these elements are all performing only mechanical functions. The sum of a and b determines the radius R of the rotor 56, equal to half the diameter D of the rotor 56 of the axial fan 32. For this purpose, see in particular fig. 2 and 9.

According to some embodiments, the blade portion 38 with the composite airfoil 46 is at least a radially inner portion 44, while the radially outer portion 40 has a simple airfoil 42. The single airfoil 42, if present, is adapted to have a predetermined pitch angle α with respect to the hub 36_cAssembled, preferably, with the pitch angle α of the half-airfoil 48_cHas consistency. As can be appreciated by those skilled in the art, the pitch angle α applied to both the simple airfoil 42 and the half airfoil 48 is provided_cIs not easy. However, inStaying at the intuitive level, it is easy to understand what the respective pitch angles may be in order to obtain continuity between the half airfoils 48 and the possible simple airfoils 42. Figures 11 and 15-17 illustrate this concept explicitly.

Preferably, the simple airfoil 42 and the composite airfoil 46 have chord c and thickness distribution t that are substantially equal to each other. One possible embodiment of such a flap is described below.

According to certain embodiments, a radially outer portion 40 of the blade 38 with a simple airfoil 42 has a radial extension e, while a radially inner portion 44 of the blade 38 with a composite airfoil 46 has a radial extension f.

According to certain embodiments, f is between 20% and 70% of a, more preferably, f is between 40% and 60% of a.

In other embodiments of the invention, the respective portions of the blade have substantially equal radial extensions to each other. In particular, the radial extension e of the radially outer portion 40 is substantially equal to the radial extension f of the radially inner portion 44.

Moreover, the airfoils (single 42 or composite 46) of each portion 40 and 44 of the blade 38 have chords c that are substantially equal to each other, at least in one respective section. In particular, when considering the radially innermost section of the radially outer portion 40 of the blade 38, the chord of the composite airfoil 46 is substantially equal to the chord of the simple airfoil 42. For the radially outermost section, the tapering of the blade 38 of FIG. 9 results in a difference between chords c.

For purposes of this discussion, "substantially equal" means that the difference between the two measurements is less than 10% of the greater of the two measurements.

As can be seen from fig. 11 and 12, the simple airfoil 42 of the radially outer portion 40 of the blade 38 has all the typical characteristics of a common airfoil: it has a rounded leading edge, a sharp trailing edge and a conventionally distributed thickness. In particular, proceeding along the midline lm of the simple airfoil 42 from the leading edge to the trailing edge, the thickness t of the airfoil increases rapidly, reaches a maximum in the leading half of the chord, then gradually decreases towards the trailing edge until the thickness becomes zero without abrupt changes.

As can be seen in fig. 10 and 15-17, similar characteristics can be discerned in the airfoil of flap 50. Thus, the flap 50 is shaped as a conventional airfoil.

Instead, the forward half airfoils 48 preferably have different geometric characteristics. In particular, as can be seen in fig. 10 and 15-17, the half-airfoil 48 has a rounded leading edge, but a different thickness distribution along its centerline and a large trailing edge. In the half airfoil 48, proceeding along the midline from the leading edge to the trailing edge, the thickness t of the airfoil increases rapidly, reaches a maximum in the leading half of the chord, then tapers toward the trailing edge, and then undergoes a sharp decrease near the trailing edge. With respect to the sharp decrease in thickness t near the trailing edge, it should be noted that in the embodiment of fig. 10, the half airfoil maintains 50% of its maximum thickness up to more than 80% of its chord, preferably up to more than 85% of its chord (considering 0% leading edge and 100% trailing edge). In addition, the tip of the trailing edge moves to near the back face d of the half airfoil 48. In other words, the half-airfoil 48 of the radially inner portion 44 of the blade 38 is not particularly effective for generating aerodynamic forces when used alone, as the sharp reduction of the thickness t near the trailing edge involves significant fluid flow disturbances away from the half-airfoil 48. The flow disturbances tend to create turbulence that limits the efficiency of the fins.

However, in use of the present invention, the half-airfoils 48 are not separate, but are followed a short distance by flaps 50. In other words, the half-airfoil 48 and the flap 50 together comprise the composite airfoil 46 of the blade 38. From an aerodynamic perspective, the composite airfoil 46 is an organic unit that utilizes synergy between the half-airfoil 48 and the flap 50.

In particular, the flap 50 is mounted on the blade 38 such that the flap 50 is oriented as desired and fixed in a predetermined position. In other words, during assembly of the axial fan 32, the flap 50 may be deflected by a deflection angle α predetermined during the design step_fAnd (4) orientation. For example, the angle of deflection α of the flap 50_fMay be defined as the angle between the chord of the flap 50 and the chord of a simple airfoil 42, the simple airfoil 42 having a chord c and a chord c substantially equal to the composite airfoil 46 (see FIG. 10)The thickness distribution t. The possibility of orienting the flap 50 allows for an increase in the overall curvature of the composite airfoil 46. As known to those skilled in the art, within certain limits, the increase in curvature increases the lift coefficient of a given airfoil.

In the embodiment shown in fig. 10 and 11, the flap 50 is mounted on the blade 38 by a shaped plate 58, the shaped plate 58 comprising a slot 60 shaped like an arc of a circle and centered on the rotation point of the flap 50. The slot 60 extends to define a maximum deflection position and a minimum deflection position of the flap 50. During assembly of the axial fan 32, the flap 50 may be brought to a design deflected position and then secured to the contoured plate 58 to be securely held in place during the operational life of the axial fan 32.

According to other embodiments (not shown), the flap 50 is mounted on the blade 38 by a shaped plate 58 that uniquely defines the designed deflection position. Thereafter, once the flap is secured to the contoured plate 58, the flap automatically adopts the design deflection and securely maintains the design deflection throughout the operating life of the axial fan 32. That is, in use, the flap 50 is fixed relative to the blade 38.

Between the half airfoil 48 and the flap 50, a channel 54 is defined that is adapted to allow fluid to flow from the front v to the back d of the composite airfoil 46. Some possible embodiments of the channel 54 are depicted in fig. 18b, 19 and 20 and will be described in more detail below. Preferably, the channel 54 is defined by smooth walls, adapted not to interfere with the fluid flow it contains. The walls defining the channel 54 are located at the aft tip of the half airfoil 48 and the forward tip of the flap 50, respectively. As will be described in greater detail below, the walls are adapted to define channels 54 that are smooth and/or converge from the front face v to the back face d.

As can be appreciated by those skilled in the art, when the composite airfoil 46 is properly oriented in the fluid flow impinging thereon (which occurs during normal operation of the axial fan 32), a low pressure zone is created adjacent the back face d of the composite airfoil 46, while an overpressure zone is created adjacent the front face v of the composite airfoil 46. This pressure difference generates the required aerodynamic force in a manner known per se. Further, in the presence of the passages 54 connecting the front and back surfaces v, d of the composite airfoil 46, the pressure differential causes a certain amount of fluid to be drawn from the over-pressure zone to the passage of the low-pressure zone. This phenomenon is schematically depicted in fig. 10, where the thick arrows qualitatively represent the fluid flow pulses.

In passing from the front surface v to the rear surface d of the fin, the fluid flow acquires a certain amount of energy from the channel 54, which accelerates the fluid flow in the trailing direction. In this way, the flow from the passage 54 accelerates the flow that is already present on the back face d of the composite airfoil 46. This allows the flow attached to the composite airfoil 46 to be maintained even under conditions where a similar simple airfoil 42 is at risk of entering a stall condition. In other words, the presence of the passage 54 between the half airfoil 48 and the flap 50 allows the composite airfoil 46 to operate at high angles of attack without the risk of stall. The presence of the channels 54 in the radially inner portion 44 of the blade 38 is advantageous because in this region the flow conditions are particularly critical, and the action of the channels 54 allows to stabilize the flow in the rear region of the back face d.

As already mentioned, the half-airfoils 48 of the blades 38 are adapted to be at a predetermined pitch angle α with respect to the hub 36 of the axial fan 32 via the root structure 34_cAnd (6) assembling. In other words, during assembly of the axial fan 32, the half-airfoils 48 and possibly the single airfoils 42 of the blades 38 may be at a pitch angle α predetermined during design_cAnd (4) orientation.

In the embodiment of the invention depicted in fig. 14 to 17, the blade 38 has a constant chord. In contrast, in the embodiment of the invention depicted in fig. 9 to 13, the radially outer portion 40 of the blade 38 is tapered, i.e. the chord converges towards the radially outer tip.

In the embodiment of the blade 38 shown in fig. 9, the radial extension f of the radially inner portion 44 of the blade 38 is approximately equal to the radial extension e of the radially outer portion 40. That is, the radial extension f of the radially inner portion 44 of the vane 38 is about 50% of a.

The axial view of FIG. 11 allows qualitative assessment of the differences between a simple airfoil 42 of the radially outer portion 40 and a composite airfoil 46 of the radially inner portion 44 of the blade 38. As can be appreciated, the chord of the composite airfoil 46 is more oblique than the chord of the simple airfoil 42 relative to the plane π. In other words, the presence of the flap 50 allows increasing the angle of inclination of the radially inner portion 44 without introducing a deflection of the blade 38.

This phenomenon is more prominent in other embodiments described below with reference to fig. 14 to 17. In these embodiments, one or more radially intermediate portions 62 are included between radially inner portion 44 and radially outer portion 40. Each radially intermediate portion 62 has a composite airfoil 46, the composite airfoil 46 including a forward half airfoil 48 and an aft flap 50, as already described above.

Preferably, the angle of deflection of the different flaps 50 of the blade 38 increases from the inside towards the outside.

Preferably, the various portions of the blade 38 have substantially equal radial extension to each other.

Preferably, the different airfoils (single or composite) of the blade 38 have substantially equal chords c.

For purposes of this discussion, "substantially equal" means that the difference between certain measurements is less than 10% of the larger measurement.

In particular, for the embodiment of fig. 14 to 17, the radially intermediate portion 62 is interposed between the radially inner portion 44 and the radially outer portion 40. As can be appreciated by a comparison of fig. 15, 16 and 17, the angle of deflection of the flap 50 of radially intermediate portion 62 is less than the angle of deflection of the flap 50 of radially inner portion 44. This feature introduces a piecewise constant twist along the radial extension of the blade 38.

The twisting of the blades 38 has a positive effect on the efficiency of the axial fan 32, since it results in different relative velocities and different angles of inclination with respect to the fluid. However, if the blades 38 of a large diameter axial flow fan are made, it is not possible to introduce twist without adding unacceptable cost. On the other hand, the solution of the invention introduces only equivalent deflections (albeit in approximate form).

For the radially outer portion 40 of the vane 38 of fig. 14, it must be considered that it is represented in cross-section in fig. 15. In this schematic view, the cross-section takes the form of a simple airfoil 42, which is shown in more detail in FIG. 18 a. Fig. 18b schematically shows another possible solution according to the invention, in which the radially outer portion 40 of the blade 38 has a composite airfoil 46. In particular, FIG. 18b shows details of the leading edge of the flap 50, the trailing edge of the half airfoil 48, and the channel 54 defined thereby.

In the embodiment of the blade 38 shown in fig. 14, the radial extension f of the radially inner portion 44 is substantially equal to the radial extension g of the radially intermediate portion 62, and both are substantially equal to the radial extension e of the radially outer portion 40. In other words, the radial extension f of the radially inner portion 44, the radial extension g of the radially intermediate portion 62 and the radial extension e of the radially outer portion 40 are each approximately 33% of a.

In some embodiments of the invention, the blade 38 further comprises a wall 74 at the boundary between two adjacent radial portions, the wall 74 being adapted to at least partially close an opening formed between two adjacent flap portions 50 oriented at different deflection angles in the radial direction. For example, in each of the embodiments of the invention depicted in fig. 21-24, the blade 38 includes a wall 74 at the boundary between the radially outer portion 40 and the radially inner portion 44. In other embodiments, the blade 38 may include more than one wall 74. For example, in an embodiment similar to the embodiment of fig. 14, the vane 38 may include a wall 74 at the boundary between the radially outer portion 40 and the radially intermediate portion 62 and another wall 74 at the boundary between the radially intermediate portion 62 and the radially inner portion 44.

The wall 74 may have different shapes and extend in different tangential directions. For example, in some embodiments, the wall 74 tangentially engages the entire blade 38, while in other embodiments, the wall 74 tangentially engages only the flap 50. In some cases, as in the example of FIG. 22, the wall 74 may extend such that the wall 74 extends beyond the chord c in the tangential direction, forward of the leading edge and aft of the trailing edge of the blade 38. In other cases, as in the example of FIG. 21, the wall 74 may extend aft from the leading edge of the flap 50 to behind the trailing edge of the blade 38. In still other cases, as in the example of fig. 23, the wall 74 may be comprised of a combination of walls 74 as described above with respect to fig. 21 and 22. Finally, in yet other cases, as in the example of fig. 24, the wall 74 takes the form of a hybrid linear (mixilinear) triangle, completely closing in the radial direction forming an opening between two adjacent flap portions 50 oriented at different deflection angles.

The wall 74 may be located on the side of the forming plate 58, in place of the forming plate 58, or integral with the forming plate 58.

The wall 74 allows to limit the turbulence, since the air recirculation is made possible by the interruption of the flap 50 extending in the radial direction of the blade 38. In addition, the wall 74 extending forward of the leading edge also performs a similar function to a skid plate (or wingknife) sometimes used on arrow-shaped wings of aircraft.

In some embodiments of the invention, such as the embodiment of FIG. 13, the blade 38 also includes a winglet 76 (or wingtip device) at the radial tip. The winglet 76 (known per se) allows to limit turbulence due to air recirculation at the radial tip of the blade 38.

One possible method of making the blade 38 according to the invention is described below.

As mentioned above, the blades 38 for the large-diameter axial fan 32 are generally obtained from extruded (aluminum) or pultruded (fiber-reinforced composite) semi-finished products. The sections of the semi-finished product that are constant along their entire extension are shaped so as to reproduce the predetermined airfoil. For a blade 38 with a reduced chord c, the airfoil may be unitary, i.e., made of a single piece. For example, in the case of an extruded aluminum airfoil, for chords approximately within 500mm, the aluminum airfoil may be unitary, i.e., made from a single piece. For another example, in the case of pultruded fiberglass airfoils, for chords approximately within 1000mm, the fiberglass airfoil may be unitary, i.e., made from a single piece. Conversely, for blades 38 having a chord c greater than the indicated value, the airfoil is preferably formed by juxtaposing two or more components 64. For example, the first member 64₁May form a front portion of the wing, and the second part 64₂May constitute the rear portion of the tab. Generally, the integral flap and/or the individual components 64 that make up the flap are packagedIncluding an outer wall shaped to form the desired airfoil and an inner wall having a structural reinforcement function and defining a closed cell within the airfoil. This structure allows to provide the blade 38 with considerable mechanical strength, in particular with respect to the bending and torsional stresses to which it is subjected.

In both cases, whether a one-piece airfoil or an airfoil constructed from different parts 64, the blade 38 according to the invention can be manufactured in a simple and economical manner, introducing only a small number of process flows and few additional elements with respect to the prior art.

In the case of an airfoil being one-piece, an extruded or pultruded semi-finished product may be longitudinally cut at least the extended length of the blade portion 38 to be fabricated with the composite airfoil 46. In this way, the situation becomes that the fin is made up of two separate parts 64₁And 64₂The situation obtained is similar. To obtain the composite airfoil 46 according to the invention, the two parts 64 of the original airfoil may be completed by suitable accessory-shaped bars 66₁And 64₂. First appendage shaped bar 66₁(will contact the posterior component 64₁Coupled) is shaped to form a suitable leading edge of the flap 50. Second appendage shaped bar 66₂(will contact the front member 64₂Coupled) is shaped to complete the half airfoil 48 as described above. In particular, a second appendage shaped bar 66₂Is to define a smooth and regular channel 54 for passing flow from the front face v to the back face d of the composite airfoil 46.

Thus, in accordance with the above description, at least one portion is provided that is intended to employ the desired composite airfoil 46. Starting from a semi-finished product with a simple airfoil 42, on the other hand, the remaining radially outer portion 40 is obtained with an extension e. The radially outer portion 40 with the simple airfoil 42 is structurally attached to the component 64 with the radially inner portion 44 of the half airfoil 48₂. Preferably, the above-mentioned shaped plate 58 is added at the radial tip of the radially inner portion 44 for mounting the flap 50. Then, the deflection angle α can be determined during the design step_fThe flap 50 is constrained to the contoured plate 58.

The addition of the root structure 34 to the axially inner end of the blade 38 forms a blade assembly 30 for mounting on the hub 36.

Here, it should be noted that the bars 66 described above and necessary for changing the shape of the airfoil component do not have any structural function, but only have to perform a shape function for aerodynamic purposes. Thus, such an accessory-shaped rod 66 is not a critical component and can be made at low cost, for example by simply extruding a polymeric material. The ease of production of these accessory-shaped bars 66 allows the production of various types of bars, which can also be developed specifically for a single application. In this regard, the following description with reference to fig. 18 to 20 is also considered. Moreover, still due to their easy construction, the attachment-shaped bars 66 do not entail a significant increase in the production costs of the axial fan 32 as a whole.

Fig. 18 to 20 show (although schematically) details of the regions where changes are made to airfoils of known type in accordance with the present invention. Fig. 18a shows a detail of a simple airfoil 42 that may be applied in the radially outer portion 40 of the blade 38. In this particular example, the tab is made of three distinct components: rear part 64₁Middle part 64₃And a front part 64₂。

FIG. 18b shows an alternative embodiment in which the simple airfoil 42 is replaced with a composite airfoil 46 having the same geometric characteristics. In this example, by using two accessory-shaped rods 66₁And 66₂In place of the middle part 64₃To modify the airfoil. The flap 50 is then assembled at a deflection angle such that the composite airfoil 46 substantially conforms to the simple airfoil 42 of FIG. 18 a.

According to an embodiment of the invention, the airfoil is modified to form a composite airfoil 46 suitable for use in the radially inner portion 44 of the blade 38. In this particular example, the middle component 64₃Is removed and used with two accessory-shaped rods 66₁And 66₂Instead of it. As can be seen in fig. 16, 17 and 18, to the rear part 64₁First attachment-shaped rod 66₁Shaped to form the leading edge of the flap 50. Referring again to fig. 18b, 19 and 20, it is noted that the second appendage-shaped bar 66₂(to be coupled to the front member 64₂) Shaped differently to complete the half airfoil 48 of the present invention. In particular, in fig. 18b, a second appendage shaped bar 66₂Is limited to simulating the back of a similar simple airfoil 42 and defines a smooth passage 54 between the half-airfoil 48 and the flap 50. In the detail of fig. 19, a second appendage-shaped bar 66₂A smooth and converging channel 54 can be defined between the half-airfoil 48 and the flap 50. In practice it is known that the converging channel 54 allows to make optimal use of the energy obtained by the flow during its passage through the channel 54. In the detail of fig. 20, it can finally be noted that the bar 66 of the second appendix shape₂Further differences and the possibility of a greater deflection angle alpha for flaps 50 than previously described with reference to figures 18b and 19_fDefining smooth and converging channels 54. In other words, due to the low cost of the appendage-shaped bar 66, different types can be provided, for example, different deflection angles α intended for the flap 50_fOr even form a stick 66 in the shape of an accessory dedicated to a single application. It is worth mentioning that the deflection angle α of the flap 50 is_fDetermined during the design phase. During assembly of the axial fan 32, the single flap 50 is fixed to the blade 38 and then maintained in the same position throughout the operating life until a design revision is required. Thus, the deflection angle α determined for the flap 50 in a particular application can be used in the design phase_fTo select the most appropriate attachment shape of the rod 66.

According to another aspect, the present invention relates to a rotor 56 comprising a hub 36 and a plurality of blades 38 as described above. The number of blades 38 of the rotor 56 is determined during the design phase. Studies carried out by the applicant have shown that, thanks to the particular shape of the blades 38 according to the invention, it is generally possible to reduce the number of blades 38 in the rotor 56 according to the invention compared to the number of conventional blades 38 required in rotors 56 of known type. This of course allows a significant saving in the procurement costs of the axial fan 32 and also allows the axial fan 32 to be operated more regularly. As is known to those skilled in the art, as the number of blades 38 increases, the aerodynamic interaction between each blade 38 and the following blade in the rotational motion also increases. This interaction tends to deteriorate the overall operation of the axial fan 32.

According to another aspect, the present invention relates to an axial fan 32 comprising the rotor 56 described above and a motor 68 adapted to rotate the rotor 56 about an axis of rotation X. The motor 68 must be able to provide the power required to keep the rotor 56 rotating indefinitely at the design steady state, in a manner known per se.

According to another embodiment of the invention, the axial fan 32 further comprises a duct 70. Thus, in a manner known per se, the axial fan 32 is preferably a ducted axial fan 32. The duct 70 serves to limit aerodynamic effects that interfere with airflow near the end of each blade 38. The presence of the duct 70, which helps to maintain the air flow in the axial direction, increases the overall efficiency of the axial fan 32.

Preferably, the axial fan 32 further comprises a frame 72 adapted to securely hold the axial fan 32 while the rotor 56 rotates about the rotation axis X. The frame 72 must be adapted to securely hold the axial fan 32 during transient start and stop speeds and during design steady state under all operating conditions. In this type of application, as known to the person skilled in the art, the main problem from the structural point of view is the vibrations and cyclic stresses from which it derives. Therefore, the frame 72 must be made with careful consideration of its frequency to avoid resonance phenomena that can have catastrophic consequences.

As can be easily understood by a person skilled in the art, the present invention allows to overcome the drawbacks highlighted above with reference to the prior art.

In particular, the present invention provides a blade 38 for an axial fan 32 that allows for improving the overall efficiency of the axial fan 32. In particular, comparing the curves of fig. 7 and 8 with each other, it can be qualitatively appreciated that the blade 38 and the axial fan 32 according to the invention allow even more efficient use of the radially innermost section.

Further, the present inventionThe invention provides a blade 38 for an axial fan 32 that allows for a change in configuration to change the characteristic curve of the axial fan 32. In this regard, the graph of FIG. 6, which is similar to the graph of FIG. 5, may be considered. As will be appreciated by those skilled in the art, while the graph represents a curve in a qualitative manner, the technical features of the present invention allow for an arbitrary conversion efficiency curve ε on the flow-pressure surface_nSo as to make the point of maximum efficiency P epsilon_maxAnd operating point P_fSubstantially coincident. In other words, the potential of the fan 32 is fully utilized over almost the entire operating life of the fan 32 according to the present invention. This results in a sharp reduction in the energy used to operate the fan.

It is to be understood that the specific features relating to the various embodiments of the invention have been described for purposes of illustration and not limitation. Further modifications and variations of the present invention will be apparent to those skilled in the art to meet contingent and specific requirements. For example, features described in connection with one embodiment of the invention may be derived therefrom and applied to other embodiments of the invention. Such modifications and variations, however, are included within the scope of the invention as defined by the appended claims.