The present invention relates to a ducted axial fan. This expression refers herein and hereinafter to an axial fan having a diameter Dr greater than 0.5 meters, preferably greater than 1 meter.
In the industrial field, the use of axial fans is known, typically in order to ensure an adequate air flow around special radiating surfaces, in implants that require the dissipation of significant amounts of heat.
Axial fans, e.g. for industrial use, typically comprise a central hub which defines a rotation axis and on which a plurality of blades is mounted. The hub rotation rotates the blades and, as the skilled person can understand, imposes different tangential speeds for the different sections of each blade. In fact, the tangential speed of each blade section is the product of the angular speed (which is the same for all sections) and the radial distance with respect to the rotation axis (which increases moving away from the rotation axis).
For this reason, as is known to the skilled person, the axial fan blades are not able to effectively operate along the entire radial span thereof. The tangential speed of the radially innermost sections of the blade is often too low to achieve effective relative motion with respect to the air flow. It follows that the actual operation of the fan is mainly entrusted to the radially outer sections that guarantee almost all of the total air flow rate generated by the axial fan.
As the skilled person can understand, such flow distribution makes the axial fan as a whole not very efficient. While some technical solutions have been proposed to better exploit the radially inner sections of the blades, there is also a need to improve the efficiency of the radially outer sections. In a manner known per se, in fact, the outer sections are subject to the tip effects that limit their efficiency. As already mentioned, since most of the flow is precisely generated by the radially outer portions, even a small inefficiency in percentage terms in this area results in a great inefficiency in absolute terms for the entire fan.
Along the intermediate portions of an aerodynamic surface, whether it is a wing or, as in this case, a fan blade, the high-pressure air zone and the low-pressure air zone are physically separated from each other by the presence of the blade itself. At the tip of the blade, this separation ceases to exist and therefore an air flow is spontaneously generated that tends to move from the high-pressure zone to the low-pressure zone. In this way a tip vortex is generated which induces an important resistance to the advancement of the blade in the air.
A first solution proposed for this type of problem was to duct the fan, thus confining it inside a shroud with a diameter slightly greater than the outer diameter of the fan itself. This shroud is referred to below as duct.
With the addition of the duct the dimensions of the tip vortexes are significantly reduced, and consequently the amounts of air moved by these vortexes and therefore the induced resistance are reduced. However, as the skilled person can well understand, not only it is impossible to zero the distance between the tip of the blades and the inner diameter of the duct, but such distance cannot even be reduced beyond a certain limit. In fact, any contact between the duct and the blade tips must be avoided in the most absolute way and a safe distance must be provided for this purpose. Therefore, because of their size and the cost they have to maintain, the blades cannot be made with precision tolerances. In addition, the blades may be subjected to vibratory phenomena and may be deformed during operation. Even in the presence of an optimal duct, the tip vortexes cannot therefore be eliminated.
Another solution, borrowed from the aeronautics, is to provide an accessory surface, called wingtip device or winglet, at the tip of each blade. First of all, the winglet has the function of constituting a baffle that opposes the air motion, thus counteracting the formation of the tip vortex. In addition, depending on the shapes adopted, the winglet can also affect the residual tip vortex, optimizing it and thus limiting noise formation.
These solutions, although widely appreciated, are not without drawbacks. In fact, despite the arrangement of the duct and winglets, possibly also in addition to each other, the formation of the tip vortexes remains to some extent inevitable. Thus, the efficiency of the axial fans remains limited.
Therefore, the object of the present invention is to overcome the drawbacks underlined above with respect to the prior art.
In particular, a task of the present invention is to provide a ducted axial fan which has an improved efficiency.
Furthermore, it is a task of the present invention to provide a ducted axial fan that limits the formation of tip vortexes more than known type fans.
Furthermore, it is a task of the present invention to provide a ducted axial fan which, in addition to introducing further advantages, also maintains the advantages already obtained from known type fans.
Such object and tasks are achieved by means of a ducted axial fan according with claim 1 as disclosed herein.
To better understand the invention and appreciate its advantages, some of its exemplary and non-limiting embodiments are described below with reference to the accompanying drawings, wherein:
In the context of the present discussion, some terminological conventions have been adopted in order to make reading easier and smoother. These terminological conventions are clarified below with reference to the appended figures.
The term “duct” hereinafter refers to the side wall or shroud, usually cylindrical, which surrounds the ducted fan creating a channel within which the air flow is constrained.
The fan according to the invention is intended to create an air flow directed from an intake zone (below in the accompanying drawings) to an output zone (above in the accompanying drawings). It is therefore understood that in relation to the flow direction (indicated with a in the drawings) the terms “upstream”, “preceding”, and the like, with respect to the terms “downstream”, “next”, and the like, are unequivocally defined.
The terms “converging” and “diverging” should also be interpreted in relation to the flow direction a.
Since the fan according to the invention univocally defines a rotation axis X, in relation to this axis the terms “axial”, “radial”, “tangential” and “circumferential” are defined.
“Slightly” different quantities are described below. The adverb “slightly” is intended to indicate differences within 10% of the higher quantity between the two, preferably within 5% of the higher quantity between the two.
The invention relates to a ducted axial fan, indicated below as a whole with 20. The fan 20 comprises:
In the fan 20 according to the invention, the duct 26 comprises an annular seat 30 which circumferentially extends around the rotor 22; and the tips of the blades 24 are at least partially received in the annular seat 30 of the duct 26.
That is, at the annular seat 30, the outer diameter Dr of the rotor 22 is greater than the inner diameter Ds of the annular seat 30 (see for example
By way of example, the outer diameter Dr of the rotor 22 is greater than 0.5 meters, preferably greater than 1 meter.
Preferably, the rotor 22 of the fan 20 comprises a hub 23 defining the rotation axis X. A plurality of blades 24 is mounted on the hub 23.
Preferably the blades 24 are made structurally independent from the hub 23 and are subsequently mounted on the hub 23 so as to be able to vary the pitch according to the specific design needs. Preferably, the blades 24 are mounted onto the hub 23 by bolts (see e.g.
Preferably, at least one blade 24 of the fan 20 comprises a tip winglet 32, also referred to simply as winglet 32. Winglet 32 is a per se known device that is arranged at the tip of the blades 24 to reduce their noise and to reduce the resistance induced by the formation of tip vortexes. Preferably, the winglet 32 has a baffle 34 at least partially extending in the axial direction. Advantageously, the main development of the baffle 34 of the winglet 32 follows a surface defined by the axial direction and the circumferential or tangential direction.
A duct of the known type has a circular cylindrical shape at least in the axial segment comprising the rotor. Furthermore, in a manner known per se, the duct has an inner diameter slightly greater than the outer diameter of the relative rotor.
The duct 26 according to the invention, and in particular the annular seat 30 thereof, may take on different configurations, depending on the embodiments.
According to some embodiments, the duct 26 has a circular cylindrical shape in the axial segment comprising the rotor 22 and has an inner diameter Dd slightly greater than the outer diameter Dr of the rotor 22.
According to other embodiments, the duct 26 has a circular cylindrical shape and in the segment immediately upstream of the rotor 22 has an inner diameter slightly smaller than the outer diameter Dr of the rotor 22. In these embodiments the duct 26 is then interrupted near the rotor 22, where the annular seat 30 is arranged. In this case, upstream of the rotor 22, the inner diameter of the duct 26 coincides with the inner diameter Ds of the annular seat 30. Downstream of the rotor 22, in some embodiments the duct 26 assumes an inner diameter Dd slightly larger than the outer diameter of the rotor 22, while in other embodiments the duct 26 again assumes an inner diameter Ds slightly smaller than the outer diameter of the rotor 22.
According to some embodiments, the duct 26 has a circular cylindrical shape and in the segment immediately upstream of the rotor 22 and in correspondence of the rotor 22 (i.e. where the annular seat 30 is arranged) has an inner diameter Dd slightly greater than the outer diameter Dr of the rotor 22. In certain such embodiments the duct 26 continues downstream of the rotor 22 with an inner diameter slightly smaller than the outer diameter of the rotor 22. In this case, downstream of the rotor 22, the inner diameter of the duct 26 coincides with the inner diameter Ds of the annular seat 30.
According to some embodiments, the annular seat 30 comprises an aerodynamic smoothing surface 36. For example, the annular seat 30 may comprise a converging aerodynamic smoothing surface 36c, preferably arranged immediately upstream of the rotor 22. Alternatively or additionally, the annular seat 30 may comprise a divergent aerodynamic smoothing surface 36d, preferably arranged immediately downstream of the rotor 22.
According to some embodiments, the aerodynamic smoothing surface 36 (converging 36c and/or diverging 36d) determines a narrowing in the channel 28 defined by the duct 26.
According to some embodiments, the annular seat 30 is open in the axial direction. For example, the annular seat 30 may be axially open upstream (i.e., towards the intake zone) or downstream (i.e., towards the output zone).
According to some embodiments, the annular seat 30 is radially open towards the inside of the duct 26. Preferably the annular seat 30 extends in the axial direction upstream and/or downstream.
According to some embodiments, the annular seat 30 develops overall outside the duct 26, while in other embodiments the annular seat 30 develops overall inside the duct 26.
According to some embodiments, at least one blade 24 of the fan 20 comprises a tip winglet 32 having a baffle 34 extending in the axial direction. For example, the baffle 34 of the winglet 32 may extend axially upstream, downstream, or both ways. Preferably, each blade 24 comprises a winglet 32.
The winglet 32 may take different shapes.
In certain embodiments, the duct 26 of the fan 20 according to the invention comprises a converging mouth 38. In a per se known manner, the converging mouth 38 is defined at the upstream end of the duct 26 and serves the function of receiving the air flow into the intake zone and gently conveying it to the rotor 22. In the embodiments of
In the embodiment schematically shown in
In the embodiment schematically shown in
The embodiment schematically shown in
In the embodiment schematically shown in
In the embodiment schematically depicted in
In the embodiment schematically depicted in
The embodiment schematically shown in
The embodiment schematically shown in
The embodiment schematically shown in
The embodiment schematically shown in
In the embodiment schematically shown in
The embodiment schematically shown in
The embodiment schematically shown in
The embodiment schematically shown in
These embodiments schematized in
The configurations of the duct 26 and annular seat 30 described above with reference to
As the skilled person can see by observing
The embodiments of
In the embodiments of
Each of the variants described above allows to obtain some specific advantages, some of which are described below by way of example.
Embodiments comprising a traditional duct 26 to which aerodynamic smoothing surfaces 36 are added allow an existing fan 20 to be modified in order to be in accordance with the invention. Such embodiments are shown in
Embodiments including a narrowing of the channel 28 at the annular seat 30, allow for local acceleration of the air flow. In this regard, it should be noted that the difference between the inner diameter Dd of the duct 26 and the inner diameter Ds of the seat may in some cases reach up to 5% of the inner diameter Dd of the duct 26. In most cases, however, this difference is less than 2% of Dd. Since this reduction is located precisely at the radial periphery, where the flow speed is greater, the local effect of the narrowing on the flow speed is even more evident. Such embodiments are shown in
Embodiments comprising an enlargement of the channel 28 at the annular seat 30, allow for optimal arrangement of the air flow for applications requiring a diverging outlet at the discharge of the entire duct 26. Such embodiments are shown in
Preferably the fan 20 according to the invention also comprises a motor (not shown) suitable for rotating the rotor 22 at the design speed. Furthermore, the fan 20 according to the invention preferably comprises a structure (not shown) suitable for firmly supporting the duct 26, the rotor 22 and possibly the motor in all operating conditions.
According to some embodiments, schematically depicted in
A field in which variable pitch ducted fans 20 are particularly appreciated is the aeronautical field. Various types of aircraft employ variable pitch ducted fans 20, for example for aircraft propulsion and/or control.
A particular example of a variable pitch ducted fan 20 is the ducted tail rotor of a helicopter 40 (see by way of example
Even in this case, it is particularly advantageous to arrange on the duct 26 an annular seat 30 circumferentially extending around the rotor 22, wherein the tips of the blades 24 are at least partially received in the annular seat 30.
In this type of application, the embodiments schematically depicted in
The foregoing description dwells on the technical features that distinguish the invention from prior art solutions. For all the other features, which may be common to the prior art and the invention, reference may be made to the introduction describing and commenting on the prior art.
As the skilled person can easily understand, the invention allows to overcome the drawbacks previously highlighted with reference to the prior art.
In particular, the present invention provides a ducted axial fan which has an improved efficiency.
Furthermore, the present invention provides a ducted axial fan which limits the formation of tip vortexes more than known type fans.
Furthermore, the present invention provides a ducted axial fan which, in addition to introducing further advantages, also maintains the advantages already obtained by known type fans.
It is understood that the specific features are described in relation to different embodiments of the invention by way of non-limiting examples.
Obviously, one skilled in the art will be able to make further modifications and variations to the present invention, in order to meet contingent and specific needs. For example, the technical features described in relation to an embodiment of the invention may be extrapolated from it and applied to other embodiments of the invention. Such modifications and variations are also contained within the scope of the invention, as defined by the following claims.
Number | Date | Country | Kind |
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102019000007935 | Jun 2019 | IT | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2020/054312 | 5/7/2020 | WO |
Publishing Document | Publishing Date | Country | Kind |
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WO2020/245674 | 12/10/2020 | WO | A |
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109 334 952 | Feb 2019 | CN |
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Number | Date | Country | |
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20220252080 A1 | Aug 2022 | US |