Air intake and method for de-icing an air intake of a nacelle of an aircraft jet engine

A de-icing device for an air intake of an aircraft jet engine nacelle extending along an axis in which a flow of air flows from upstream to downstream, the intake comprising an inner wall and an outer wall connected by a leading edge, the inner wall comprising a plurality of blowing lines, each blowing line comprising a plurality of through-openings configured to blow elementary streams from the hot air source in order to de-ice said inner wall, the blowing lines being parallel to one another in a cylindrical projection plane, each blowing line having a depth defined along the axis X and a length defined along the axis Y in the cylindrical projection plane, two adjacent blowing lines being spaced apart by a distance, the ratio of the distances L3/D3 being between 1 and 2.

TECHNICAL FIELD

The present invention relates to the field of aircraft turbojet engines and is more particularly directed to a device for de-icing an air intake of a nacelle of an aircraft turbojet engine.

BACKGROUND

In a known manner, an aircraft comprises one or more turbojet engines to allow its propulsion by acceleration of an air flow which circulates from upstream to downstream in the turbojet engine.

With reference toFIG.1, a turbojet engine100extending along an axis X and comprising a fan101rotatably mounted about axis X in an external shell102in order to accelerate an air flow F from upstream to downstream is represented. Hereinafter, the terms upstream and downstream are defined with respect to the circulation of the air flow F. The turbojet engine100comprises at its upstream end an air intake200comprising an internal wall201pointing to axis X and an external wall202which is opposite to the internal wall201, the walls201,202are connected by a leading edge203also called an “air intake lip”. Thus, the air intake200allows separation of the incoming air flow F into an internal air flow FINT guided by the internal wall201and an external air flow FEXT guided by the external wall202. Hereinafter, the terms internal and external are defined radially with respect to axis X of the turbojet engine100.

In a known way, during the flight of an aircraft, due to the temperature and pressure conditions, ice is likely to accumulate at the leading edge203and the internal wall201of the air intake200and to form ice blocks that are likely to be ingested by the turbojet engine100. Such ingestions have to be avoided in order to improve the life of the turbojet engine100and reduce malfunctions.

To eliminate ice accumulation, with reference toFIG.1, it is known to circulate a flow of hot air FAC through an internal cavity204formed between the interior wall201and the exterior wall202of the air intake200. Such a circulation of hot air allows the internal wall201to be heated, by thermal conduction, and thus ice accumulation which melts as it accumulates to be avoided. Such a circulation of a hot air flow FAC remains complex given that the air intake200can also fulfill an acoustic function and can generally comprise a honeycomb structure on its internal wall201. To this end, it has been suggested by patent application FR2912781 and patent application WO2015/071609 to provide channels for circulating a hot air flow in the honeycomb structure.

Incidentally, a de-icing device that has through openings in the internal and external wall to eject the hot air flow is also known. Such a technical solution is not retained because it consumes a lot of energy as the air is ejected in a punctual way and only achieves an imperfect de-icing.

An air intake internal wall comprising through openings, evenly distributed over the internal wall, in order to blow a hot air flow radially outwardly of the internal wall into the engine air stream is also known. In practice, the high number of through openings significantly increases the hot air consumption and is detrimental to the acoustic treatment. This is particularly problematic for a high bypass ratio turbojet engine with a large diameter air intake. In addition, the blowing efficiency is not optimal since several through openings are aligned in parallel to the axis of the turbojet engine, which lowers the heating efficiency upon circulating an incident air flow from upstream to downstream facing two through openings aligned in parallel to axis X due to pressure balances. The hot air consumption is thus high. Further, the surface located between two alignments of through openings is insufficiently heated, which affects the quality of de-icing. One purpose of the present invention is to enable the prevention of ice accumulation while allowing efficient and economical acoustic treatment.

In addition, another purpose is to provide an air intake that has the aforementioned advantages while being simple and inexpensive to manufacture.

SUMMARY

For this purpose, the invention relates to a de-icing device for a nacelle of an air intake of an aircraft turbojet engine extending along an axis X in which an air flow circulates from upstream to downstream, the air intake annularly extending about axis X and comprising an internal wall pointing to axis X and an external wall which is opposite to the internal wall, the walls being connected by a leading edge and a front internal partition wall so as to delimit an annular cavity, the de-icing device comprising at least one hot air source in the annular cavity.

The invention is remarkable in that the internal wall comprises a plurality of blowing lines, each blowing line comprising a plurality of through openings configured to blow elementary flows from the hot air source in order to de-ice said internal wall, the blowing lines being parallel to each other in a cylindrical projection plane defined with respect to axis X of the turbojet engine and to an axis Y defining the angular position with respect to axis X, each blowing line having a depth P3 defined along axis X and a length L3 defined along axis Y in the cylindrical projection plane, two adjacent blowing lines being spaced apart by a distance D3 along axis Y, the distance ratio L3/D3 being between 1 and 2.

Thus, unlike prior art, which provided for the blowing openings to be arranged in a distributed and homogeneous manner on the surface of the internal wall, the invention advantageously suggests to organize them in lines by spacing them so as to limit any excessive coverage or overlap. Advantageously, each line of current flowing from upstream to downstream on the internal wall comes into contact with at least one blowing line, which ensures effective de-icing. In addition, the distance ratio L3/D3 limits any excessive coverage, which limits the number of through openings for blowing. This makes de-icing more economical, which is advantageous for a high bypass ratio turbojet engine with a large diameter air intake.

Preferably, with each blowing line being spaced apart by a tilt angle θ with respect to axis X in the cylindrical projection plane, the tilt angle is between 20° and 70°. Such a tilt angle allows for a compromise between efficiency and economy. The smaller the tilt angle, the greater the number of blowing lines and the more effective the de-icing.

Preferably, each blowing line comprises at least 5 through openings, preferably at least 10 through openings, more preferably at least 15. A large number of through openings is optimal for a turbojet engine. Furthermore, it allows a distance ratio L3/D3 that is relevant for a turbojet engine to be defined.

Preferably, the through openings of the same blowing line are spaced apart by a first pitch Px along axis X. The through openings, at the same longitudinal position along axis X, are spaced apart by a second pitch Py along axis Y according to the following relationship: Py=Px*α with α a constant greater than 2, preferably 5, more preferably 10. Such pitches allow to emphasize that the through openings are not homogeneously distributed but organized along lines.

Preferably, the internal wall comprises at least one overlapping zone ZP of the blowing lines, the overlapping zone ZP comprising at least one upstream blowing line and one downstream blowing line. Thus, an overlap allows two blowing lines to act on the same angular portion of the air intake.

According to one aspect, the downstream blowing line does not comprise any through openings in the overlapping zone ZP. In other words, only the upstream blowing line comprises through openings in the overlapping zone ZP. This allows for downstream de-icing due to circulation of streamlines while limiting the number of through openings.

According to another aspect, the through openings are alternating along direction Y between the upstream blowing line and the downstream blowing line. Thus, it is advantageously avoided that a same streamline passes through two through openings of two different blowing lines, the performance of the de-icing being then not affected.

Preferably, the density of through openings is constant along direction Y. Thus, whether the blowing lines overlap or not, the same amount of hot air is delivered substantially peripherally. The presence of through openings for blowing at different positions along axis X allows for overall de-icing.

Preferably, the internal wall comprising at least one acoustic attenuation structure comprising a plurality of acoustic attenuation openings, the acoustic attenuation openings are distributed on the internal wall outside the blowing lines. Thus, the internal wall provides through openings for heating on the one hand, and openings for acoustic attenuation on the other hand. By virtue of the invention, the number of through openings dedicated to blowing is advantageously reduced, which allows the number of acoustic attenuation ports and, therefore, the acoustic performance to be maximized.

Preferably, the honeycomb structure defines, on the one hand, acoustic cells each comprising at least one acoustic attenuation port and, on the other hand, circulation channels forming the blowing lines and comprising the through openings for blowing. Thus, the blowing lines are in the form of hot air conduction channels through which openings are pierced in order to allow blowing. A blowing line thus allows, even in the absence of through openings, the internal wall to be heated by thermal conduction.

Preferably, each through opening has a cross-sectional area greater than 3 mm2in order to allow efficient blowing. Further preferably, two adjacent through openings in a blowing line are spaced apart by a distance defined along axis Y of between 1 and 2.5 times the diameter of a through opening. This prevents the formation of unheated internal wall portions between two consecutive through openings.

Preferably, each acoustic attenuation port has a diameter of less than 0.5 mm to allow for optimal attenuation.

The invention also relates to an air intake having a de-icing device as previously set forth. The invention also relates to a nacelle comprising an air intake as previously set forth. The invention also relates to a turbojet engine comprising a nacelle as previously set forth.

The invention further relates to a method for de-icing, by means of a de-icing device as previously set forth, an air intake of an aircraft turbojet engine nacelle extending along an axis X in which an air flow circulates from upstream to downstream, the air intake annularly extending about axis X and comprising an internal wall pointing to axis X and an external wall which is opposite to the internal wall, the method comprising a step of blowing a plurality of elementary flows from the hot air source through the through openings of the blowing lines so as to de-ice the internal wall.

It should be noted that the figures set out the invention in detail to implement the invention, said figures of course being able to be used to better define the invention if necessary.

DETAILED DESCRIPTION

With reference toFIG.2, a turbojet engine1extending along an axis X and comprising a fan11rotatably mounted about axis X in an external shell12in order to accelerate an air flow F from upstream to downstream is represented. Hereafter, the terms upstream and downstream are defined in relation to the circulation of the air flow F. The turbojet engine1comprises, at its upstream end, an air intake2comprising an internal wall21pointing to axis X and an external wall22which is opposite to the internal wall21, the walls21,22are connected by a leading edge23known to those skilled in the art under the designation of “lip”. The air intake2further comprises a front internal wall25so as to delimit an annular cavity24known to those skilled in the art as “D-Duct”.

Thus, the air intake2allows the incoming air flow F to be separated into an internal air flow FINTguided by the internal wall21and an external air flow FEXTguided by the external wall22.

Hereafter, the terms internal and external are defined radially with respect to axis X of the turbojet engine1.

In a known way, during the flight of an aircraft, due to the temperature and pressure conditions, ice is likely to accumulate at the internal wall21and the leading edge23of the air intake2and to form ice blocks which are likely to be ingested by the turbojet engine1. Such ingestions have to be avoided in order to improve the life time of the turbojet engine and to reduce malfunctions.

With reference toFIG.2, the air intake2comprises a hot air source9mounted in the annular cavity24. The hot air source9is preferably in the form of a hot air supply from the turbojet engine1, which can be a piccolo tube or a circular air flow generated by a nozzle known as a “swirl”, in order to provide a pressurized hot air flow at a temperature of about 250° C. Such a hot air source9is known from prior art and will not be set forth in more detail.

In order to allow an optimal de-icing, as illustrated inFIGS.3to4, the internal wall21comprises a plurality of blowing lines3, each blowing line3comprising a plurality of through openings4configured to blow respectively elementary flows Fe coming from the hot air source9in order to de-ice said internal wall21.

Such elementary flows Fe are advantageous given that they make it possible, on the one hand, to blow off ice particles directly accumulated on the through openings4and, on the other hand, to heat the internal wall21upon circulating the elementary flow Fe after it is ejected from a through opening4.

In particular, an elementary flow Fe makes it possible to heat a portion of the internal wall21which is located downstream of the through opening4from which it is ejected. Indeed, the internal air flow FINTcirculating in the turbojet engine1drives each elementary flow Fe along an axial direction X downstream, called a streamline. Advantageously, the elementary flow Fe makes it possible to distribute heat to the internal wall21as it circulates downstream, thus avoiding any ice accumulation. The de-icing is thus global even if the through openings4are few.

Preferably, the internal wall21can comprise, outside the blowing lines3, acoustic treatment zones. The acoustic treatment zones preferably comprise a noise-reducing honeycomb structure50as illustrated inFIG.6B. In a known manner, the honeycomb structure50thus has an internal skin Pint and an external skin Pext, spaced apart from each other, so as to form cells, especially of the Helmholtz type. In a known manner, the internal skin Pint of the honeycomb structure50belongs to the internal wall21of the air intake2.

Preferably, the internal wall21, that is, the internal skin Pint of the honeycomb structure50, comprises a plurality of acoustic attenuation ports5allowing acoustic waves to enter the cells of the honeycomb structure50to allow their attenuation. With reference toFIG.6A, an internal wall21is represented with through openings4for blowing and through holes5for acoustic attenuation. Preferably, as illustrated inFIG.6B, the cells are blind, that is, have only a single port5, in order to provide optimal acoustic attenuation. Preferably, the blowing lines3are in the form of channels51formed in the honeycomb structure50that allow hot air to be conducted and elementary flows Fe to be blown via the through openings4. Thus, the de-icing is carried out by blowing but also by thermal conduction.

An acoustic attenuation port5thus has a different function from a through opening4intended for blowing. Such a difference in function is further reflected in structural differences. An acoustic attenuation port5has a reduced diameter, preferably less than 0.5 mm, in comparison with a through opening4(set forth later).

Preferably, the acoustic attenuation ports5are distributed on the internal wall21outside the through openings4in order to maximize the acoustic treatment performance.

To improve the de-icing performance, it is preferable to increase the dimension and number of through openings4. However, the larger the dimension and number of through openings4, the smaller the number of acoustic attenuation ports5and the lower the acoustic treatment performance. Furthermore, the hot air consumption also increases, which is detrimental to the performance of the turbojet engine1. Making through openings4is thus the result of a compromise, as will be set forth in the following.

As schematically illustrated inFIGS.2to4, the internal wall21of the air intake2is not cylindrical, that is located at the same radial distance from axis X, but curved for aerodynamic reasons. Also, for the sake of clarity and brevity, the internal wall21will be set forth in a cylindrical projection plane P, that is located at a same radial distance from axis X, in order to define the geometrical characteristics of the blowing lines3.

With reference toFIG.5, the cylindrical projection plane P is defined in an orthogonal reference frame in which axis X is the axis of the turbojet engine1and axis Y corresponds to the angular opening and ranges from −180° to +180°.

According to the invention, with reference toFIG.5, the blowing lines3are parallel to each other in the cylindrical projection plane P. Each blowing line3is spaced apart by a tilt angle θ with respect to axis X in the cylindrical projection plane P, the tilt angle θ being between 20° and 70°. Thus, as illustrated inFIG.5, due to the tilt angle θ, an elementary flow Fe from a through opening4does not circulate over another through opening4during its downstream circulation along axis X. This advantageously avoids any loss of efficiency due to overlapping caused by multiple blowing at the same radial distance from axis X. The heating efficiency by the elementary flows Fe is improved given that all portions of the internal wall21located downstream of the through openings4are heated. As will be set forth later, even if the through openings4are distinct from each other, the elementary flows Fe allow the internal wall21to be heated by convection but also by conduction in order to avoid any ice appearance.

The tilt angle θ results from a compromise between the de-icing efficiency and the efficiency of the acoustic attenuation4. A tilt angle θ, between 35° and 55°, ensures the best compromise.

Thereafter, with reference toFIG.5, each blowing line has a depth defined along axis X designated as P3 and a length defined along axis Y designated as L3.

Preferably, the depth P3 corresponds to the total depth of the internal wall21of the air intake2. The length L3 can be derived from the depth P3 and the tilt angle θ by the following trigonometric formula: cos θ=P3/L3

Preferably, with reference toFIG.5, in order to ensure a homogeneous de-icing of the internal wall21, two adjacent blowing lines3are spaced apart by the same spacing distance D3 defined along axis Y.

Preferably, each blowing line3has at least 5 through openings4, preferably at least 10 through openings4, more preferably at least 15 through openings4. A large number of through openings4allows the distance ratio L3/D3, which is not relevant for a small number of through openings4per line, for example 2 or 3, to be precisely defined.

A large number of through openings4furthermore allows optimal de-icing of a turbojet engine, in particular, with a fan diameter between 1000 mm and 3000 mm. Preferably, the depth P3 ranges from 120 mm to 350 mm.

According to the invention, the distance ratio L3/D3 is between 1 and 2, preferably between 1 and 1.5, so as to allow uniform de-icing of the air intake while limiting overlapping of the blowing lines3along direction Y in order to avoid through openings4being aligned along axis X, which would be detrimental to the de-icing performance.

Blowing lines3which are rectilinear are represented inFIG.5, but it goes without saying that they could be curved.

With reference toFIG.6A, a blowing line3is represented in a close-up manner. Preferably, each blowing line3has a plurality of through openings4. Preferably, each through opening4emits an elementary flow Fe of hot air that circulates downstream due to the internal air flow FINT. In practice, each elementary flow Fe allows an elementary portion Pe of the internal wall downstream of the through opening4and which is a function of the distance to the through opening4to be heated by convection and conduction.

Preferably, each through opening4has a cross-section area s1 greater than 3 mm2so as to optimally de-ice. Preferably, the cross-section area s1 is between 3 mm2and 6 mm2so as to ensure a compromise between optimal de-icing and limited hot air consumption.

Preferably, two through openings4are spaced apart by the same distance d2, preferably between 1 and 2.5 the diameter of a through opening. A density of through openings4along axis Y, between 25% and 50%, ensures a compromise between de-icing performance and acoustic attenuation. Preferably, the density of through openings4is substantially constant along direction Y. By substantially constant, it is meant a local variation of less than 10% with respect to the average density.

With reference toFIG.6A, the through openings4of a same blowing line3are spaced apart by a first pitch Px along axis X. The through openings4at a same longitudinal position along axis X are spaced apart by a second pitch Py along axis Y according to the following relationship: Py=Px*α with α a constant greater than 2, preferably greater than 5, more preferably greater than 10. In this example, the second pitch Py corresponds to the distance D3.

Indeed, as illustrated inFIG.5, the through openings4are irregularly distributed, which is contrary to prior art which aimed at a regular and homogeneous distribution.

Referring henceforth toFIG.7, each through opening4comprises an emission axis Ds that extends substantially along axis DNnormal to the internal wall21in which the through opening4is locally formed. Preferably, the emission axis Ds is tilted downstream with respect to the normal axis DNby a blowing angle σ. Preferably, better de-icing performance is achieved with a blowing angle σ between 0° and 30°.

In this exemplary embodiment, rectangular through openings4have been schematically represented, but it goes without saying that other shapes could be suitable, especially slots, circular openings or any other calibrated opening.

As previously explained, each through opening4has a passage cross-section area greater than or equal to 3 mm2so as to provide an effective elementary flow Fe. Such a through opening4is advantageously distinguished from an acoustic attenuation port5, the diameter of which is less than 0.5 mm.

According to one aspect of the invention, with reference toFIGS.8to10, the spacing distance D3 is less than the length L3 and this results in the blowing lines3overlapping along axis Y, that is, by projection along axis X onto axis Y. Preferably, the ratio L3/D3 is less than 2, preferably 1.5, in order to avoid the formation of excessively de-iced angular portion and the loss of acoustically treated surface. Subsequently, an overlapping zone ZP of length ZP3 equal to L3-D3 is defined. An overlapping zone ZP comprises, by definition, at least one part of an upstream blowing line3A and at least one part of a downstream blowing line3B as illustrated inFIGS.8to10.

In this first example, with reference toFIG.8, each blowing line3A,3B comprises through openings4A,4B. Preferably, the length ZP3 of the overlapping zone ZP is reduced so as not to be detrimental to the performance by aligning the through openings4along axis X. Such an embodiment allows to maximize the de-icing performance by multiplying the elementary flows Fe. Thereby, in this embodiment, the density of through openings4is greater in an overlapping zone ZP.

According to an alternative embodiment, with reference toFIG.9, only the part of upstream blowing line3A in the overlapping zone ZP has through openings4A, the part of downstream blowing line3B in the overlapping zone ZP does not comprise through openings. Thus, only the upstream blowing line3A participates in de-icing the overlapping zone ZP, which allows the consumption of hot air for de-icing to be limited. Thereby, in this embodiment, the angular density of through openings4is constant both inside and outside an overlapping zone ZP.

According to another alternative embodiment, with reference toFIG.10, each part of blowing line3A,3B belonging to the overlapping zone ZP comprises through openings4A,4B. Nevertheless, along direction Y, the through openings4A,4B are alternating so as to maintain a constant density of through openings4both inside and outside an overlapping zone ZP. The de-icing performance is thus optimized and the de-icing is distributed into the upstream blowing line3A and the downstream blowing line3B.

Preferably, an overlapping zone ZP comprises no more than two blowing lines3in order to allow for maximizing acoustic attenuation.

It has been previously set forth with reference toFIG.5an internal wall21comprising a plurality of blowing lines3that are parallel to each other in the cylindrical projection plane P and with each blowing line3being spaced apart by a tilt angle θ with respect to axis X in the cylindrical projection plane P.

In another embodiment of the invention, with reference toFIGS.11and12, the internal wall21comprises a first plurality of blowing lines3-1and a second plurality of blowing lines3-2, each comprising through openings4-1,4-2. Preferably, each first blowing line3-1is spaced apart by a first tilt angle θ-1with respect to axis X in the cylindrical projection plane P while each second blowing line3-2is spaced apart by a second tilt angle θ-2with respect to axis X in the cylindrical projection plane P.

In this exemplary embodiment, the first tilt angle θ-1and the second tilt angle θ-2have different signs so as to provide different de-icing. The use of two pluralities of blowing lines3-1,3-2allows a synergic de-icing between the elementary flows Fe coming from the different pluralities of blowing lines3-1,3-2. It goes without saying that the internal wall21could comprise more than two pluralities of blowing lines3-1,3-2.

In operation, the hot air source9feeds the blowing lines3which allow for conductive heating of the internal wall21as the hot air flows through the conduction channels51of the honeycomb structure50the blowing lines3of which have the shape. Furthermore, the hot air source9feeds the through openings4of the blowing lines3which allow for conductive heating. As these are distributed around the periphery of the internal wall21, de-icing is carried out evenly. The tilt of the blowing lines3as well as the judicious spacing of the blowing lines3between them avoids that numerous through openings4are aligned along axis X which would be detrimental to the de-icing performance. Thus, each through opening4emits an elementary flow Fe of hot air which is guided along axis X by the internal air flow FINTof the turbojet engine1in order to de-ice, by convection and conduction, a portion of the internal wall located downstream of the through opening4.

Any streamline thus intercepts at least one blowing line3, which allows optimal de-icing even if the number of blowing lines3is reduced. Unlike prior art, which taught uniform heating, only a few local blowing lines3allow for overall de-icing. The spacing of the blowing lines3is advantageous given that it allows any accumulated ice to be made liquid without allowing it to be converted back into ice as it circulates downstream.