Output director vane for an aircraft turbine engine, with an improved lubricant cooling function using a heat conduction matrix housed in an inner duct of the vane

A guide vane for a dual flow aircraft turbine engine, the aerodynamic part of the vane including an inner duct for lubricant cooling extending in a main direction and being partly bounded by a pressure side wall and a suction side wall of the vane. A heat conduction matrix is lodged in the duct, and presents main heat transfer wings extending parallel to the direction, and laid out in staggered rows.

TECHNICAL FIELD

This invention relates to the aircraft dual flow turbine engines field, and in particular the design of guide vanes arranged in the entirety or part of an air flow from a turbine engine fan.

This pertains preferably to outlet guide vanes, also known as OGV, designed to straighten the airflow at the fan outlet. Alternatively or simultaneously, if necessary, guide vanes could be placed at the fan inlet. The guide vanes are classically arranged in the turbine engine secondary vein.

The invention preferably pertains to an aircraft turbojet equipped with such outlet guide vanes.

PRIOR STATE OF THE ART

On some dual-flow turbojets, there have been instances where the outlet guide vanes are implemented downstream of the fan to straighten the flow coming out of it, and also eventually to provide a structural function. This last function is indeed intended to allow the duct of efforts from the centre of the turbine engine to an outer ring located in the extension of the fan housing. In this case, a motor attachment is classically arranged on or near this outer ring, to ensure the attachment between the turbine engine and a hanging mast on the aircraft.

Recently, it has also proposed to allocate an additional function to the outlet guide vanes. It is a heat exchanger function between the outside air traversing the crown of the outlet guide vanes, and the lubricant circulating inside the vanes. For example, this heat exchanger function is known from document U.S. Pat. No. 8,616,834, or document EN 2 989 110.

The lubricant designed to be cooled by output guide vanes can come from different zones of the turbine engine. Indeed, a lubricant can be circulating through the lubrication enclosures for the antifriction bearings supporting the engine shafts and/or the fan hub, or even a lubricant dedicated to the lubrication of the mechanical transmission components of the AGB (“Accessory Geared Box”). Finally, it can also be used for lubrication of a gearbox to drive the fan, where such gearbox is expected on the turbine engine in order to decrease the fan rotation speed.

The growing lubricant needs require us to adapt accordingly the heat dissipation ability associated with heat exchangers used for lubricant cooling. The fact of attributing a heat exchanger role to the outlet guide vanes, as in the solutions mentioned in the two documents cited above, allows in particular to decrease, or even to remove conventional exchangers of type ACOC (Air Cooled Oil Cooler). These ACOC exchangers are generally arranged in the secondary vein, their reduction/suppression allows to limit the disruption of the secondary flow and thus increase the overall turbine engine performance.

However, the solutions proposed in the prior art remain perfectible. In particular, there is a need to improve the heat exchanges to further increase the heat dissipation capacity. There is a need for reinforcement of the mechanical strength when facing high pressures generated by the circulation of lubricant within these vanes. This need for reinforcement of the mechanical strength is also even more important in the particular case of a guide vane with a structural function.

DISCLOSURE OF THE INVENTION

To meet these needs at least partially, the purpose of the invention is first aimed at a guide vane to be arranged in all or part of an air flow from a dual flow aircraft turbine engine fan, the guide vane including a foot, a head, and an aerodynamic flow straightening part laid out between the vane foot and head, said aerodynamic vane part having a first inside lubricant cooling duct extending in a first main cooling lubricant flow direction from the vane foot to the head, said first inner duct being partly bounded by a pressure side wall and a vane suction side wall.

According to the invention, the vane has a first matrix of heat conduction lodged in said first inner duct and including rows of main heat transfer fins following one another in the first direction parallel to which extend such main fins, these being spaced from each other in the first direction as well as a transverse direction of the vane going from a leading edge to a trailing edge of its aerodynamic part, so that at least some of the said main fins are arranged substantially staggered. In addition, each row includes junction fins connecting each two main fins directly consecutive according to transversal management, said junction fins on the same row being alternately in inside contact with the pressure wall and the suction wall in order to form, with the main fins they connect, a transverse structure having a general cradle form, also named crenellated.

Thus, the orientation and arrangement of the fins provide a satisfactory mechanical strength and high heat performance, while limiting the load losses suffered by the lubricant traversing through the first inner duct equipped in the fins.

The invention also shows at least one of the following optional features, taken alone or in combination.

The director vane includes, at the level of the foot or the head of the vane, an opening for the introduction of the first heat conduction matrix in the first interior duct. The location of the opening introduction significantly reduces the risk of leakage and of accidental introduction of lubricant in the fan air flow. On the other hand, this design allows creating vane parts in a single pass that bound the first inner duct, to obtain a better mechanical strength.

The first heat conduction matrix includes at least one zone in which said heat transfer fins are planned in a density between 1 and 5 fins/cm2.

Said first heat conduction matrix provides a variable density of fins, even if alternatively, a reasonably uniform density can be planned within this first matrix. This ability to vary the density of the fins in particular to locally adapt the heat exchange between the lubricant and the secondary flow. As an indication, the density can be reduced in zones where the heat exchange coefficient with the air is the greatest, while conversely, the fin density is preferentially increased in zones where the heat transfer coefficient is the lowest.

This ability to vary the fin density within the first inner duct, in a transverse direction to the vane, also allows to check the homogeneity/heterogeneity of lubricant flow in this same direction, depending on the needs encountered. This faculty is also preferably implemented in the second duct mentioned below.

The first heat conduction matrix may present at least a first zone and a second zone offset from the first zone in the transverse direction, the second zone with an average height between the pressure side and suction side that is lower than the average height of the first zone, and said first zone having an average fin density greater than that of the second zone. This special design allows advantageously to get a more or less homogeneous lubricant flow in the transverse direction of the first inner duct, despite its evolutionary height along this same direction. In the same spirit, it is possible to consider a variable fin pitch, so that you have an always equal hydraulic cross-section.

In addition, said first duct may define a lubricant thawing channel extending along the first main direction, said channel being devoid of fins all along it and along the first heat conduction matrix. Alternatively, it may be a channel in which the main wings of the first matrix are located, but in a lower density than that adopted in the adjacent areas. In both cases, this allows to manage the specific flight phases in which the lubricant drops to very low temperatures, giving it a high viscosity. Indeed, thanks to this so-called “thawing” channel planned within the first inner duct, the lubricant can flow easier through this duct through the dedicated channel, and allows at the same time to warm the frozen lubricant between the fins of the zones adjacent to said channel. In this respect, it is stated that thawing channel is preferentially planned at one of the ends of the first inner duct, depending on the transverse direction of the latter.

It should be noted that the vane might only include a single first duct, ensuring the flow of lubricant radially outward. In this case of figure, the crown of guide vanes would include at least one other vane of similar design, with an inner duct also equipped with a heat conduction matrix, ensuring the flow of lubricant radially inward. Nevertheless, the lubricant must not necessarily return radially towards the hub via another vane. It can for example be reintroduced radially inwards by other known elements from the turbine engine.

However, the aerodynamic vane part is preferably also a second inside lubricant cooling duct spreading in a second lubricant flow from the head to the foot of the vane, said second inner duct being partly bounded by the vane pressure side wall and suction side wall, a second heat conduction matrix being housed in said second inner duct and including rows of successive main heat transfer fins along the second direction at the same time that extend such main fins, these being spaced from each other in the second direction as well as the transverse direction to at least some of the said main fins are arranged substantially in staggered manner in the second inner duct. In addition, each row includes junction fins connecting each two main fins directly consecutive according to transversal management, said junction fins on the same row being alternately in inside contact with the pressure wall and the suction wall in order to form, with the main fins they connect, a transverse structure having a general cradle form.

One possibility, the first and second inner ducts each extend separately throughout the aerodynamic part of the vane.

According to another possibility, the fluids of the first and second inner ducts are connected to one another near the head of the vane, and the average density of fins within the first inner duct is preferably less than the density of fins within the second inner duct. Indeed, since the lubricant is colder in the return direction adopted within the second inner duct, it makes it possible to increase the heat power exchanged by increasing the average fin density in this second duct.

Preferably, the guide vane has a structural function, in the sense that it permits transmitting forces from the centre of the turbine engine to an outer ring located in the extension of the fan housing.

The invention is also intended for aircraft turbojets, preferably a turbojet including a plurality of guide vanes such as those described above, arranged downstream or upstream of a turbine engine fan.

Finally, the invention is a method for manufacturing such a guide vane, the said aerodynamic vane part being made from a single piece so as to reveal the first inner duct, and the first heat conduction matrix is inserted in the said first inner duct. The matrix can be produced in a conventional manner, or else using the additive manufacturing technique. It is noted that the additive manufacturing proves to be perfectly suited to the production of the heat conduction matrix, in particular because this technique makes it possible to easily vary the density of the main conduction heat fins.

Other advantages and features of the invention will appear in the open-ended detailed description below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 1, it represents a dual-flow and a dual-body turbojet1, with a high dilution rate. The turbojet1is classically comprised of a gas generator2on either sides of which are arranged a low pressure compressor4and one low pressure turbine12, this gas generator2comprising a high pressure compressor6, a combustion chamber8and a high pressure turbine10. Subsequently, the terms “front” and “back” are considered in an opposite direction14to the main flow direction of the gases within the turbojet, this direction14being parallel to its longitudinal axis3. However, the terms “upstream” and “downstream” are considered according to the main flow direction of the gas within the turbojet.

The low pressure compressor4and the low pressure turbine12form a low pressure body, and are connected to each other by a low-pressure shaft11centred on the axis3. Similarly, the high pressure compressor6and the high-pressure turbine10form a high pressure body, and are connected to each other by a high pressure shaft13centred on the axis3, and arranged around the low pressure shaft11. The shafts are supported by antifriction bearings19, which are lubricated by being arranged in oil enclosures. The same applies to the fan hub17, also supported by the antifriction bearings19.

The turbojet1is also comprised of, at the front of the gas generator2and the low pressure compressor4, a single fan15which is arranged here directly in the back of an engine air intake cone. The fan15is rotating about the axis3, and surrounded by a fan housing9. InFIG. 1, it is not driven directly by the low pressure shaft11, but only indirectly driven by the shaft via a gearbox20, which allows it to turn at a slower speed. Nevertheless, a direct drive solution of the fan15, by the low pressure shaft11, is part of the invention.

In addition, the turbojet1defines a primary vein16intended to be traversed by a primary flow, as well as a secondary vein18intended to be traversed by a secondary flow located radially outward from the primary flow, the fan flow thus being divided. As skilled industry persons know, the secondary vein18is bounded radially outward in part by an external ring23, preferably metal, extending to the rear fan housing9.

Although this has not been represented, the turbojet1is equipped with a set of equipment, for example of types fuel pump, hydraulic pump, alternator, starter, variable pitch stator actuator (VSV), discharge vane actuator, or even electric power generator. This includes equipment for lubrication of the gearbox20. These equipment are driven by an accessory box or AGB (not shown), which is also lubricated.

Downstream from the fan15, in the secondary vein18, a crown of guide vanes is planned which here are outlet guide vanes24(OGV). These stator vanes24connect the external ring23to a housing26surrounding the low pressure compressor4. They are spaced from each other on the circumference, and allow to straighten the secondary flow after it passes through the fan15. In addition, these vanes24may also have a structural function, as is the case in some examples which are described herein. They ensure the transfer of the forces from the gearbox and the antifriction bearings19on the engine shafts and the fan hub, towards the outer ring23. Then, these forces may transit through an engine attachment30attached on the ring23and linking the turbojet to a hanging mast (not shown) of the aircraft.

Finally, the outlet guide vanes24ensure, in the examples that are currently described, a third heat exchanger function between the secondary airflow traversing the crown of vanes, and the lubricant circulating inside the vanes24. The lubricant designed to be cooled by the outlet guide vanes24is the one used for the lubrication of antifriction bearings19, and/or the turbojet equipment, and/or accessories box, and/or the gearbox20. These vanes24are thus part of the fluid circuit(s) in which the lubricant is put into circulation to successively lubricate the associated elements, then to be cooled.

In reference toFIGS. 2 to 5now, we will describe one of outlet guide vanes24, according to a first preferred embodiment of the invention. In this respect, it is noted that the invention as it will be described with reference toFIGS. 2 to 5may apply to all vanes24in the stator crown centred on the 3 axis, or only some of these vanes.

The vane24can be strictly of radial orientation as shown inFIG. 1, or be slightly tilted axially as shown inFIG. 2. In all cases, it is preferentially straight in the side view such as shown onFIG. 2, while extending in a longest extent direction25.

The outlet guide vane24is comprised of an aerodynamic part32which corresponds to its central part, i.e. the one exposed to the secondary flow. On either side of this aerodynamic part32used to straighten the flow out of the fan, the vane24is respectively comprised of a foot34and a head36.

The foot34serves for the attachment of the vane24on the low pressure compressor housing, while the head is used to attaching the same vane on the outer ring extending the fan housing. In addition, the vane24comprises at the foot and head levels, platforms40used to reconstruct the secondary vein between the vanes24, in the circumferential direction.

The aerodynamic part32of vane, without its heat conduction matrices which will be described below, is from a single source, for example by so-called additive manufacturing using 3D printing or direct manufacturing. For example, additive manufacturing of the aerodynamic part32is carried out by one any of the following techniques:Selective Laser Melting (SLM) or Electron Beam Melting (EBM);Selective Laser Sintering (SLS) or by electron beam;Any other type of powder solidification technique under the action of an energy source of medium to high power, the principle is to melt or sinter a bed of metal powder by laser beam or electron beam.

The powder used is aluminium or titanium-based, or based on another metal material or any other material with good heat conduction characteristics.

The aerodynamic part32of the vane could, however, be made using more conventional techniques, allowing a hollowed out portion to appear in which the matrix would then be introduced, before placing a closing plate for example by welding, gluing or soldering.

Moreover, the manufacturing of a single part may also include the foot34and/or head36and/or platforms40, without getting out of the scope of the invention.

In this first preferred embodiment of the invention, the aerodynamic part32is equipped with two inner ducts50a,50bsubstantially parallel one to the other, and parallel to the longest extent direction25. More specifically, this is a first lubricant cooling inner duct50a, which extends in a first main direction52aof the lubricant flow. This direction52ais substantially parallel to the longest extent direction25, and presents a direction going from the foot34to the head36. Similarly, a second lubricant cooling inner duct50bis planned, which extends in a second main direction52bof lubricant flow within this duct. This direction52bis substantially parallel to the longest extent direction25, and presents a reverse direction going from the head36to the foot34. So, the first duct50ais planned to be traversed radially outward by the lubricant, while the second duct50bis expected to be traversed radially inward. To address the transition from one to the other, near the head36, the radial external ends of the fluids of the two ducts50a,50bare connected by an elbow54to 180°, corresponding to a low made in the aerodynamic part32.

Alternatively and in an equivalent manner for a vane of similar design, the first inner duct extends along its first main direction of flow of the lubricant which has a direction from the head to the foot, even though the vane could comprise only a single first duct. Similarly, in the case of the vane provided with the second inside lubricant cooling duct, this duct may extend along its second main direction having a direction going from the foot to the head.

The radial internal ends of the two ducts50a,50bare related to the lubricant circuit, sketched by the element56inFIG. 2. This circuit56includes in particular a pump (not shown), which can apply a desired flow direction to the lubricant within ducts50a,50b, namely the introduction of the lubricant by the inside radial end of the first duct50s, and the extraction of the lubricant at the inside radial end of the second duct50b. Couplings66ensure fluid communication between the inside radial ends of the ducts50a,50band circuit56, these fittings66traversing the foot34.

The two ducts50a,50bas well as the elbow54form together a general U form, with the first duct50aand the second duct50bseparated from one another in a transverse direction60of the vane substantially orthogonal to the longest extent direction25. In this first preferred embodiment as well as in all other modes, to optimize the heat exchanges, the first duct50ais located on the trailing edge62side of the vane24, while the second duct50bis located on the leading edge64side. However, a reverse situation can be retained, without getting out of the scope of the invention.

The aerodynamic part32of the outlet guide vane24has a pressure side wall70, a suction side wall72, a full zone74connecting the two walls70,72near the trailing edge62, a full zone76connecting the two walls70,72near the leading edge64, as well as a central full zone78. This last zone78connects the two walls70,72to the level of a substantially central portion of these, depending on the direction of the vane cord It also serves as a structural reinforcement and extends from the foot34to the elbow54, while the full zones74,76extend substantially on the entire length of the part32, in the longest extent direction25. The first duct50ais formed between the walls70,72and between the full zones74,78, while the second duct50bis formed between the walls70,72and the full zones76,78. The pressure and suction side walls70,72present substantially constant thickness, next to ducts50a,50bthat they bound. However,50a,50bducts extend transversely in the direction60having a variable height between the two walls70,72, as this can be seen inFIG. 4. Alternatively, these ducts could have a constant height, as shown schematically inFIG. 4afor the first duct50a. In the latter case, the two walls70,72then adopt a variable thickness to obtain the aerodynamic profile of the vane.

The two lubricant cooling inner ducts50a,50bhave the particular feature of integrating heat conduction matrices, provided in particular with main heat transfer fins. These matrices are also called convection matrices.

In the first preferred embodiment of the invention, the arrangement and shape of the main fins80are substantially identical in the two matrices50a′,50b′ respectively housed in the two ducts50a,50b. The main fins80are also planned to have the same densities, although this may be otherwise, as this will come out of the other embodiments which will be described later.

The two matrices50a′,50b′ being substantially identical, only the first matrix50a′ will be described, but it must be understood that this description is also applicable by analogy to the second matrix50b′ housed in the second inner duct50b.

As is visible inFIGS. 3-4, the first heat conduction matrix50a′ includes rows81of main heat transfer fins80, these rows following each other in accordance with the first direction52a.

The main fins80are locally arranged substantially orthogonally to the pressure side and suction side walls70,72. In addition, they each extend in parallel to the first direction52a, these fins being spaced from each other in this same first direction52a, as well as depending on the transverse direction60. They have an average height Hm, between the two walls,70,72, of the order of 4 to 8 mm. Their thickness E, depending on the transverse direction60, presents a preferably constant value between 0.5 and 1.5 mm, preferably while their length L in the direction52apresents a preferably constant value between 1 and 4 mm. Moreover, the spreads/steps “P” between the fins80according to each of the two directions52,60, are for example of the order of 2 to 4 mm.

In at least one zone of the duct50a′, and preferably in the entirety of the latter, the fins80are arranged staggered, with a density for example of about 3 fins/cm2. For example, more generally, the average density is included between about 1 and 5 fins/cm2.

The special staggered arrangement of the fins80, combined with their arranged length L in the main direction of flow52a, allows obtaining high heat performance by limiting the load losses suffered by the lubricant in operation.

In addition, each row79includes junction fins80′ connecting every two main fins directly80directly consecutive under the transverse direction60. The junction fins80′ are arranged substantially orthogonally to the main fins80, being located flat on the pressure side wall70or suction side wall72. Specifically, the fins on the same row79are alternately in inside contact with the pressure side wall70, and in inside contact with the suction side wall72. Each row forms, with all of its main fins80and its junction fins80′, a transverse structure with a general cradle form. As shown inFIG. 3a, the general cradle shaped rows79are offset transversely one from the other with a length corresponding to half a step “P”. The junction fins80′ are of shape and size substantially identical to those of the main fins80. In particular, they have the same length “L” and the same thickness “E”.

As this has been shown inFIG. 3c, junction fins80′ are attached to the ends of the main fins80that they connect. Moreover, the junction fins80′ located on the pressure side are connected to each other at the level of their edges, as well as the junction fins80′ located on the suction side are connected to each other, also at the level of their edges. This allows the embodiment of all of the heat conduction matrix50′ by additive manufacturing, for example in any one of the techniques previously exposed.

Once completed, each matrix50a′,50b′ is inserted in its associated duct50a,50b, from the foot34of the vane manufactured in one piece. The insertion is performed via an introduction opening49a,49bmade through said vane foot34, and presenting a section substantially identical to ducts50a,50b. These introduction ports49a,49b, shown inFIG. 2, then come out in the connections66leading to the circuit56. A solution with plugs might also be used to partially plug the introduction ports49a,49b, after insertion of the matrices in the ducts. In this case, the weaker section connections66would connect to the plugs, at the level of a lubricant flow channel made through each of these plugs.

Each heat conduction matrix50a′,50b′ extends through all or part of the radial length of its associated duct50a,50b. Preferably, more than 80% of the radial length of each duct50a,50bis occupied by its corresponding matrix50a′,50b′.

During this operation of the turbine engine, the lubricant82drawn inFIG. 5is introduced in the first inner duct50a, in the first direction52aheading radially outward. At this stage, the lubricant82presents a high temperature. A heat exchange is performed between this lubricant82conforming to the shape of the first heat conduction matrix fins (not shown inFIG. 5), and the secondary flow81conforming to the shape of the outer surface of the pressure side walls and suction side walls70,72supporting these fins. The lubricant82, after been redirected by the elbow54in the second duct50b, suffers in the latter a similar cooling, also by heat exchange with the secondary air flow81and circulating in the second main direction52bof flow. Then the cooled lubricant82is extracted from vane24, and redirected by the closed-circuit56towards the elements to lubricate.

Referring now toFIG. 6, a second preferred embodiment in which ducts50a,50bare not connected within the aerodynamic part32of vane24. They indeed stretch each separately on the length of the aerodynamic part32, to connect the fluids to outside the vane24. For example, to do this, a connection elbow56is planned arranged radially inward from the head of the vane36, for example in support on this head.

Now, with reference toFIG. 7representing a third preferred embodiment of the invention, it is expected that the density of the heat transfer fins80in the first and/or the second matrix50a′,50b′ is variable, that is non-uniform. Indeed, in this third mode, we seek a significantly homogeneous lubricant flow obtaining the transverse direction60of the first duct50a, despite its evolving height between the two pressure side and suction side walls70,72. Thus, for the first matrix50′, a first zone Z1is planned for example located upstream in the transverse direction60and thus far from the trailing edge62, as well as an adjacent second zone Z2located further downstream in the transverse direction60, and thus closer to the trailing edge62. The spacing between the pressure side and suction side walls70,72is growing from the downstream end of the duct50a. Therefore, the second Z2shows fins whose average height Hm2is less than the average height Hm1of fins80of the first zone Z1. Also, to get the substantially same uniformity of the lubricant flow in the transverse direction60of the duct50a, it is preferentially planned that the first zone Z1has an average density of fins80higher than the density expected within the second zone Z2. This higher density in the zone Z1is essentially achieved by bringing the fins80closer to each other, in the transverse direction60.

Although it was not represented, a symmetrical layout can be adopted in the second duct, the spacing between the pressure side and suction side walls70,72narrows towards the leading edge.

FIG. 8represents a fourth preferred embodiment of the invention, in which the average density of fins80within the first matrix50a′ is less than the density of fins in the second matrix50b′. This allows increasing the heat power exchanged at the level of lubricant in the return direction, at a stage where it is colder because of the heat power has already been exchanged within the first ducts50a, in the lubricant outbound direction.

Finally,FIGS. 9 and 10represent a fifth preferred embodiment, in which it is expected a thawing channel90a,90b, in each of the two inner ducts50a,50b. In the first duct50a, the channel90aruns parallel to the first direction52a, by being located closer to the trailing edge62. Symmetrically, channel90bruns parallel to the second direction52bby being located closer to the leading edge64. Here the position near the trailing edge was privileged, because this is the zone in which the heat exchange with the secondary air flow is the highest.

Each of these two channels90a,90bspans the entire length of its associated duct, coming out in the elbow54. In this fifth preferred embodiment, each thawing channel90a,90bis deprived if fins80on its entire length, that is completely empty to promote circulation of cold lubricant by limiting load losses. Each channel90a,90bis thus bounded between the surface bounding the inner duct50a,50b, and an edge of the associated matrix50a′,50b′.

The presence of these channels90a,90ballows managing the particular flight phases in which this lubricant shows low temperatures, which makes it viscous and giving it so-called “freezing” aspect. Through these channels90a,90b, viscous lubricant can more easily flow through the inner ducts50a,50b, using the channels90a,90blocated at the ends. The lubricant circulation within these channels90a,90ballows gradually warming the frozen lubricant in the other parts of the matrices50a′,50b′, between the main fins80.

For an optimal operation, the width Lc of each channel90a,90b, in the transverse direction60, is greater than the average transverse step Pm between the main fins80of its associated duct50a,50b. The ratio between these two dimensions Lc, Pm is preferably greater than 1.5, and more preferably greater than 2.

Alternatively, the channels90a,90bcould present some main heat transfer fins80, by integrating these channels in the matrices. At the level of the channels, the density of the fins80would then be lower than the one adopted in other zones of the matrices. This reduced density within the integrated channels90a,90bwould then be obtained mainly by increasing the average transverse step between the fins80, within these thawing channels90a,90b.

Of course, various changes can be made by a skilled person to the invention that has just been described, only as open-ended examples. In particular, the technical characteristics specific to each of the five embodiments described above can be combined between them, without getting out of the scope of the invention. Finally, it is noted that in the non illustrated case of the inlet guide vanes to straighten the airflow upstream of the fan, these vanes are arranged in the entire air flow of the fan around an inlet cone of non-rotating air, the vane feet being then related to this fixed cone of intake air.