FR3092316A1 - Aircraft propulsion unit - Google Patents

Abstract

Aircraft propulsion unit The invention relates to a propulsion assembly element (7) intended to be mounted on a propulsion assembly for an aircraft comprising a nacelle and a turbojet engine supported by the nacelle and intended to be in contact with an inlet flow of cold air, the propulsion unit (7) comprising a first wall (8) and a second wall (9) in contact with the air flow, the first and second walls (8,9) being joined at a first end of the propulsion unit element (4, 5, 6, 7) called the leading edge (38) and at a second end of the propulsion unit element (4,5,6,7) called edge leakage (39) the first and second walls (8,9) delimiting a cavity (12), and a piezoelectric device (10) for protecting against icing housed inside the cavity (12) and comprising at least one piezoelectric actuator (11). According to the invention, the piezoelectric actuator (11) is in contact with the two opposing walls (8, 9) of the propellant assembly element (7) to set them into vibration. Figure for the abstract: Fig. 2

Description

Aircraft propulsion unit

The present invention relates to a propulsion assembly element, a propulsion assembly for an aircraft comprising such an element and a method of assembling a propulsion assembly element.

An aircraft is propelled by one or more propulsion assemblies each comprising a turbomachine (turbojet, turbofan or turboprop for example), housed in a tubular nacelle.

Each propulsion unit is attached to the aircraft by a mast generally located under a wing or at fuselage level.

A nacelle generally has a structure comprising an air inlet upstream of the turbojet engine, a middle section intended to surround a fan of the turbojet engine, a downstream section housing thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is generally terminated by an exhaust nozzle, the outlet of which is located downstream of the turbojet engine.

The air inlet comprises, on the one hand, an inlet lip adapted to allow optimum capture towards the turbojet engine of the air necessary to supply the fan and the internal compressors of the turbojet engine, and on the other hand, a downstream structure on which the lip is attached and intended to properly channel the air towards the blades of the fan.

However, certain phases of flight in an icing environment can lead to the formation of ice (or accretion) on certain parts of the compressor (casing arms or rectifiers for example), on the blades, the structural arms, the primary/secondary stream separation nozzles or spinners.

The phenomenon can lead to turbojet operability problems by obstructing the primary stream or by extinguishing the combustion chamber following the detachment of blocks of ice, for example.

Depending on the architecture of the turbojet engine and the aerodynamic conditions, it may be necessary to prevent the formation of ice (anti-icing) or it may be necessary to cause the detachment of the ice formed (de-icing) on all or part of the compressor blade.

Conventional anti-icing systems use hot air circulation inside the component to be protected.

The use of electric heating system is also known.

Another known alternative is to use an electromechanical system, which has the advantage, compared to a heating system, of having lower energy consumption.

The document FR2922522 filed by the company AIRCELLE SA discloses piezoelectric actuation means for electromechanically defrosting a set of lips of an air inlet of a turbojet engine nacelle comprising several piezoelectric cylinder actuators in contact with the inner surface of the lip assembly.

However, these piezoelectric actuation means are bulky and cannot be integrated into parts having small profiles (thin thickness and small radius of curvature of the leading edge).

In fact, for a blade profile or a jet engine splitter, the zone most sensitive to the formation of ice is located around the leading edge. This area having a small radius of curvature, the implementation of piezoelectric actuators closer to this area is not easy.

The invention aims to solve all or part of these drawbacks by proposing a propulsion assembly element, intended to be mounted on a propulsion assembly for an aircraft, having a small profile and incorporating an effective piezoelectric protection device against icing.

The invention relates to a propulsion assembly element intended to be mounted on an aircraft propulsion assembly comprising a nacelle and a turbojet engine supported by the nacelle and which is intended to be in contact with an air intake flow.

The propulsion assembly element comprises a first wall and a second wall in contact with the air flow; the first and second walls being joined to a first end of the propulsion assembly element called the leading edge and at a second end of the propulsion assembly element called the trailing edge, the first and second walls delimiting a cavity. The propulsion assembly member further includes a piezoelectric icing protection device housed within the cavity and including at least one piezoelectric actuator to prevent icing of at least a portion of the assembly member propellant.

According to the invention, the piezoelectric actuator is in contact with the two opposite walls of the propulsion assembly element to set them in vibration.

Preferably, the piezoelectric de-icing device comprises means for stressing each piezoelectric actuator against the two walls of the propulsion assembly element.

The piezoelectric actuators have a planar shape and comprise a central orifice and two opposite faces, a first face of which is in contact with the first wall of the propulsion assembly element and a second face in contact with the second wall of the propulsion element. propulsion unit.

Each wall of the propulsion assembly element comprises at least one stud projecting from an internal surface of the wall and against which is positioned a face of the piezoelectric actuator.

The means for stressing each piezoelectric actuator comprise a clamping device making it possible to clamp a first face of the piezoelectric actuator against a face of a first stud positioned on the first wall of the propulsion assembly element and to clamp a second face of the piezoelectric actuator against a face of a second stud positioned on the second wall of the propulsion assembly element in opposition with respect to the first stud.

The clamping device comprises a screw comprising a threaded portion screwing into the central hole of the piezoelectric actuator and a screw head.

The first stud of the first wall of the propulsion assembly element comprises a housing in which the screw head is housed and retained.

The second stud of the second wall of the propulsion assembly element comprises a threaded orifice into which the threaded portion of the screw is screwed until the two studs are compressed against the faces of the piezoelectric actuator.

The second stud of the second wall of the propulsion assembly element comprises a central element protruding from the face of the second stud in the direction of the first stud and fitting into the central orifice of the piezoelectric actuator.

The threaded hole is formed inside the central element.

The piezoelectric actuators are positioned at the mid-torque of the propulsion assembly element and close to the leading edge of the propulsion assembly element.

The walls include a thinned part located upstream and close to the piezoelectric de-icing device.

The walls of the propulsion unit are two separate elements fixed together by the clamping device.

The piezoelectric de-icing device generates vibrations at a frequency close to or equal to that of the resonant frequency of the propulsion assembly element. The vibration frequency varies over time around the resonant frequency.

The above features can be used alone or in combination, each providing a particular benefit.

The invention thus provides a propulsion assembly element for an aircraft having a small profile (or a small thickness) which incorporates a piezoelectric de-icing device preventing the formation of ice or de-icing the propulsion assembly element effectively. Turbojet malfunction problems are thus avoided.

The piezoelectric de-icing device can be integrated in an area having a small radius of curvature or a small thickness.

The invention allows the implementation of piezoelectric actuators as close as possible to the leading edge of the propulsion assembly element, which is the area most sensitive to the formation of ice.

The vibration of the surface of the propulsion unit at high frequency makes it possible to reduce the wettability of the surface, and at high energy, to atomize the drops of water that have been deposited. If the layer of ice is already present, it is also possible to break this layer by deformation of the surface.

The means of stressing or pre-stressing the ceramic discs make it possible to optimize their mechanical performance.

This solution is also less energy consuming compared to a hot air sampling system, or an electrothermal system, because it is based on a mechanical action.

In addition, the fact of not using a heating system makes it possible to lift the limitation on the use of certain materials that cannot be used at high temperature.

Compared to other electromechanical de-icing solutions based on deformations of a profile, the proposed piezoelectric de-icing device has the advantage of inducing very small deformations, and thus limits aerodynamic disturbances.

The invention also relates to a propulsion assembly for an aircraft comprising at least one propulsion assembly element as defined previously.

The invention also relates to a method of assembling such a propulsion assembly element.

• positionnement d’au moins un actuateur piézoélectrique sur la deuxième paroi de l’élément d’ensemble propulsif,
• assemblage de la première paroi avec la deuxième paroi de façon à fermer une cavité dans l’élément d’ensemble propulsif qui intégre l’actuateur piézoélectrique, et
• mise en contrainte de chaque actuateur piézoélectrique contre les deux parois, de l’élément d’ensemble propulsif par des moyens de mise sous contrainte.

According to the invention, the method comprises the following steps:

• positioning of at least one piezoelectric actuator on the second wall of the propulsion assembly element,
• assembly of the first wall with the second wall so as to close a cavity in the propulsion assembly element which incorporates the piezoelectric actuator, and
• stressing each piezoelectric actuator against the two walls of the propulsion assembly element by stressing means.

• insertion d’une tête de vis d’une vis dans un logement prévu dans un premier plot de la première paroi,
• insertion d’un élément central, faisant saillie sur une face d’un deuxième plot prévu sur la deuxième paroi, dans un orifice central de l’actuateur piézoélectrique,
• positionnement de la première paroi contre la deuxième paroi, et
• vissage d’une portion filetée prévue sur la vis dans un orifice fileté prévu dans l’élément central du deuxième plot de façon à comprimer les deux plots, contre l’actuateur piézoélectrique.

Preferably, the assembly process comprises the following steps:

• insertion of a screw head of a screw in a housing provided in a first stud of the first wall,
• insertion of a central element, projecting on one face of a second stud provided on the second wall, into a central orifice of the piezoelectric actuator,
• positioning the first wall against the second wall, and
• screwing a threaded portion provided on the screw into a threaded orifice provided in the central element of the second stud so as to compress the two studs, against the piezoelectric actuator.

The assembly method according to the invention makes it possible to facilitate the integration of the piezoelectric actuators in the propulsion assembly element.

Other characteristics and advantages of the invention will become apparent on reading the following description, given solely by way of example, with reference to the appended figures, which illustrate:

is a diagram of a propulsion unit for an aircraft comprising a nacelle and a turbojet engine;

is a cross-sectional diagram of a turbojet engine blade presented as an example of a propulsion assembly element;

is a diagram of the walls of this propulsion assembly element before their assembly;

is a diagram of the propulsion assembly element after the positioning of the piezoelectric actuators on one of the walls of the propulsion assembly element;

is a diagram of the propulsion assembly element obtained after assembly;

is a diagram of the propulsion unit in transparency;

is a diagram of a screw assembled on a wall of the propulsion assembly element;

is a cross-sectional diagram of the propulsion assembly element according to another variant;

is a cross-sectional diagram of a splitter lip as another example of a propulsion assembly element.

FIG. 1 represents a propulsion unit 1 for an aircraft comprising a nacelle 2 and a turbojet engine 3 supported by the nacelle 2.

The propulsion assembly 1 comprises propulsion assembly elements 4, 5, 6, 7 intended to be in contact with a cold air inlet flow such as blades 7a, secondary flow straightening vanes 7b, arms secondary flow structures 7c, primary flow straightening vanes 7d, primary flow structural arms 7e, primary/secondary stream separation slats 4, a fan cone 5 or an air inlet lip 6, for example.

The propulsion assembly element 4, 5, 6, 7 is positioned in the upstream part of the propulsion assembly 1 which is defined with respect to the direction of air circulation in the propulsion assembly 1.

Figures 2 to 8 illustrate a flow straightening vane 7b of a turbojet engine 3 as an example of propulsion assembly elements 4, 5, 6, 7.

As illustrated in Figure 2, the propulsion assembly element 4, 5, 6, 7 is hollow and comprises comprising a first wall (8) and a second wall (9) in contact with the air flow, the first and second walls (8,9) being joined to a first end of the propulsion assembly element (4, 5, 6, 7) called the leading edge (38) and to a second end of the element of the propulsion assembly (4,5,6,7) called the trailing edge (39) the first and second walls (8,9) delimiting a cavity (12). In operation, frost tends to form on the leading edge of the propulsion unit.

The first wall 8 and the second wall 9 are preferably separate parts, assembled to each other.

The propulsion assembly element 4, 5, 6, 7 comprises a piezoelectric device 10 for protection against icing housed inside the cavity 12.

The thickness of the cavity 12 must be sufficient to receive the piezoelectric device 10 for protection against icing.

As appears, for example in Figure 2, the piezoelectric device 10 for protection against icing comprises at least one piezoelectric actuator 11 which is in contact with the two opposite walls 8, 9 of the propulsion assembly element 4, 5 , 6, 7 at a time to make them vibrate.

The contact of the piezoelectric device 10 for protection against icing with the two walls makes it possible to effectively transmit the vibrations to these walls and to cause them to vibrate simultaneously in the direction A which is perpendicular to the plane of the walls 8, 9, as illustrated in the figure. 6.

The piezoelectric device 10 for protection against icing may comprise several piezoelectric actuators 11, as represented in FIG. 6, which shows three of them.

The piezoelectric actuators 11 are spaced apart and can be aligned, as shown in the example embodiment represented in FIG. 4. It is also envisaged to arrange the piezoelectric actuators according to other geometric distributions, for example, staggered.

The piezoelectric actuators 11 are powered by power supply means.

The piezoelectric actuators 11 are positioned at the location of the main torque of the propulsion assembly element 4, 5, 6, 7.

The piezoelectric actuators 11 are positioned close to the leading edge 38 of the propulsion assembly element 4, 5, 6, 7.

They are preferably positioned in the upstream part of the propulsion assembly element 4, 5, 6, 7, the upstream being defined with respect to the direction of air circulation.

This improves the efficiency of the area to be anti-iced or de-iced.

The piezoelectric actuators 11 can have a disc shape as shown in the figures, knowing other planar geometric configurations are envisaged (square or other); as shown in the figures, the piezoelectric actuators 11 comprise a central orifice 14 and two opposite faces 16, 17, a first face 16 of which is in contact with the first wall 8 of the propulsion assembly element 4, 5, 6, 7 and a second face 17 in contact with the second wall 9 of the propulsion assembly element 4, 5, 6, 7.

The piezoelectric actuators 11 each comprise at least one ceramic disk or ring 15 which may be made of PZ26 ceramic for example.

Figure 2 shows two ceramic discs 15 stacked on top of each other.

The ceramic discs 15 are coupled together to optimize the vibrations.

Each wall 8, 9 of the propulsion assembly element 4, 5, 6, 7 comprises at least one stud 18, 19 projecting from an internal surface 20, 21 of the wall 8, 9, as shown in Figure 3 .

The studs 18, 19 are preformed on the internal surfaces 20, 21 of the walls 8, 9 and, in the illustrated embodiment, have a disk shape since the piezoelectric actuators 11 themselves have a disk shape. In the cases of figures where the piezoelectric actuators 11 have a geometry other than circular, the pads 18, 19 have a geometry complementary to that of the piezoelectric actuators 11.

Each of the faces 16, 17 of the piezoelectric actuator 11 is positioned against a respective pad 18, 19. The pads 18, 19 form a support or an interface between the piezoelectric actuators 11 and the walls 8, 9.

The piezoelectric device 10 for protection against icing comprises means 13 for placing each piezoelectric actuator 11 under stress against the two walls 8, 9 of the propulsion assembly element 4, 5, 6, 7.

Advantageously, the stressing means 13 of each piezoelectric actuator 11 comprise a clamping device 22, as illustrated in FIG. 2, making it possible to clamp a first face 16 of the piezoelectric actuator 11 against a face 23 of a first stud 18 positioned on the first wall 8 of the propulsion assembly element 4, 5, 6, 7 and to clamp a second face 17 of the piezoelectric actuator 11 against a face 24 of a second stud 19 positioned on the second wall 9 of the propulsion assembly element 4, 5, 6, 7 in opposition with respect to the first stud 18.

The faces 16, 17 of the piezoelectric actuator 11 and the faces 23, 24 of the pads 18, 19 are advantageously flat and substantially parallel to each other. They are substantially parallel to the general direction of the internal surfaces 20, 21 of the walls 8, 9. In other words, they are parallel to a longitudinal plane perpendicular to the direction A.

The clamping device 22 comprises a screw 25 comprising a threaded portion 26 screwing into the central hole 14 of the piezoelectric actuator 11 and a screw head 27, by way of example.

The first stud 18 of the first wall 8 of the propulsion assembly element 4, 5, 6, 7 comprises a housing 28 in which the screw head 27 is housed and retained.

The housing 28 is integrated into the first stud 18. The first stud 18 comprises a lateral slot 32, as shown in Figure 7, communicating with the housing 28 to allow the insertion of the screw 25 in a direction parallel to the internal surface 20, 21 of the walls 8, 9 and before the assembly of the latter.

The housing 28 is delimited by a portion 33 of the first wall 8 and an internal wall 34 of the first stud 18 which is substantially parallel to the portion 33 of the first wall 8.

The screw head 27 is held between the portion 33 of the first wall 8 and the inner wall 34 of the first stud 18.

The portion 33 of the first wall 8 is traversed by an orifice 35 allowing access from the outside to the screw head 27 to screw the screw 25 with a tool such as a Phillips screwdriver, for example.

The internal wall 34 of the first stud 18 is crossed by an orifice 36 allowing the passage of the threaded portion 26 of the screw 25.

The second stud 19 of the second wall 9 of the propulsion assembly element 4, 5, 6, 7 comprises a threaded hole 29 into which the threaded portion 26 of the screw 25 is screwed until the two studs 18 are compressed, 19 against the faces 16, 17 of the piezoelectric actuator 11.

After screwing in screw 25, internal wall 34 of first stud 18 is compressed between screw head 27 and piezoelectric actuator 11.

The second stud 19 of the second wall 9 of the propulsion assembly element 4, 5, 6, 7 comprises a central element 30 projecting from the face 24 of the second stud 19 in the direction of the first stud 18 in the direction A.

The central element 30 fits into the central hole 14 of the piezoelectric actuator 11, the threaded hole 29 being formed inside the central element 30.

The screw 25 makes the connection between the walls 8, 9 and allows, by the screwing system, to compress the walls 8, 9 towards each other and to tighten them against the faces 16, 17 of the piezoelectric actuator 11.

Each face 23, 24 of studs 18, 19 exerts a force directed towards piezoelectric actuator 11, parallel to direction A.

The screws 25 can be tightened with the same torque or with a different torque.

Preferably, the outer surface 37 of the first wall 8 of the propulsion assembly element 4, 5, 6, 7 is smoothed after the stressing of the piezoelectric actuators 11.

According to a variant represented in FIG. 8, the walls 8, 9 comprise a thinned part 31 located upstream and close to the piezoelectric device 10 for protection against icing.

The thinned part 31 is positioned close to the leading edge 38 of the propulsion assembly element 4, 5, 6, 7.

The area to be anti-iced is thinned in order to increase the flexibility of the structure in this area.

The walls 8, 9 of the propulsion assembly element 4, 5, 6, 7 are two distinct elements, fixed together by the clamping device 22. This makes it possible to simplify the integration of the piezoelectric device 10 for protection against icing. .

Figure 9 shows another example in which the propulsion assembly element 4, 5, 6, 7 is a primary/secondary vein separation nozzle 4.

The splitter 4 comprises the same elements as those previously described for the blade 7b.

Cavity 12 is an annular cavity at an angle of 360°.

The first wall 8 corresponds to a so-called "IGV" platform and the second wall 9 corresponds to the main part of the separation spout.

The piezoelectric device 10 for protection against icing makes it possible to vibrate the tip of the separation spout 4.

The size of the ceramic discs 15 is reduced to the maximum in order to bring them as close as possible to the leading edge 38.

The piezoelectric device 10 for protection against icing generates vibrations at a frequency close to or equal to that of the resonant frequency of the propulsion assembly element 4, 5, 6, 7, the frequency varying over time around the resonant frequency.

It is preferable to use a well-chosen resonance mode, maximizing the amplitude of the vibration and the mechanical efficiency.

The resonance mode of the system can change depending on parameters of the airstream, such as air temperature or flow velocity.

In order to always work around the resonance mode, a possible solution consists in operating not at a constant frequency, but with a frequency sweep or modulation corresponding to a sinusoidal signal with a frequency changing over time.

The parameters of the modulation are chosen in order to remain throughout the flight phases of the aircraft around the resonant frequency of the system.

According to a possible control method, the frequency is modulated according to the mode or the resonant frequency which is a function of the temperature and/or of the engine speed.

For this, the piezoelectric actuators 11 are connected to a control device capable of modulating the vibration frequency as a function of these parameters.

The invention also relates to a method for assembling a propulsion assembly element 4, 5, 6, 7 intended to be mounted on a propulsion assembly 1 for an aircraft, as described above.

According to the invention, the assembly method comprises a step of positioning the piezoelectric actuator(s) 11 on the second wall 9 of the propulsion assembly element 4, 5, 6, 7, as shown in Figure 4.

More precisely, the central element 30 protruding from the face 24 of the second stud 19 provided on the second wall 9 is inserted into the central orifice 14 of the piezoelectric actuator 11.

In parallel, the screw head 27 of the screw 25 is inserted into the housing 28 provided in the first stud 18 of the first wall 8, as illustrated in FIG. 7. Fixing by gluing is also envisaged.

The assembly method comprises a step of assembling the first wall 8 with the second wall 9 so as to close the cavity 12 in the propulsion assembly element 4, 5, 6, 7 which incorporates the piezoelectric actuator(s) 11.

The first wall 8 is positioned against the second wall 9.

The assembly method includes a step of stressing each piezoelectric actuator 11 against the two walls 8, 9 of the propulsion assembly element 4, 5, 6, 7 by stressing means 13.

The threaded portion 26 of the screw 25 is screwed into a threaded hole 29 provided in the central element 30 of the second stud 19 so as to clamp and compress the two studs 18, 19 against the piezoelectric actuator 11.

The stressing means 13 serve both to pre-stress the piezoelectric actuators 11 and to fix the walls 8, 9 together.

Figure 5 shows the propulsion assembly element 4, 5, 6, 7 obtained, which is a blade 7b in this example.

Claims (14)

Propulsion assembly element (4, 5, 6, 7) intended to be mounted on an aircraft propulsion assembly (1) comprising a nacelle (2) and a turbojet engine (3) supported by the nacelle (2) and intended to be in contact with an air inlet flow, the propulsion assembly element (4, 5, 6, 7) comprising a first wall (8) and a second wall (9) in contact with the air flow , the first and second walls (8,9) being joined to a first end of the propulsion assembly element (4, 5, 6, 7) called the leading edge (38) and to a second end of the element of the propulsion unit (4,5,6,7) called the trailing edge (39) the first and second walls (8,9) delimiting a cavity (12) and a protection device against piezoelectric icing (10 ) housed inside the cavity (12) and comprising at least one piezoelectric actuator (11), characterized in that the piezoelectric actuator (11) is in contact with the two opposite walls (8, 9) of the propulsion unit (4, 5, 6, 7) to make them vibrate. Element of the propulsion assembly (4, 5, 6, 7) according to claim 1, characterized in that the piezoelectric device (10) for protection against icing comprises means for placing under stress (13) each piezoelectric actuator (11 ) against the two walls (8, 9) of the propulsion assembly element (4, 5, 6, 7). Propulsion unit element (4, 5, 6, 7) according to Claim 1 or 2, characterized in that the piezoelectric actuators (11) have the shape of a disc and comprise a central orifice (14) and two opposite faces (16 , 17) including a first face (16) in contact with the first wall (8) of the propulsion assembly element (4, 5, 6, 7) and a second face (17) in contact with the second wall ( 9) of the propulsion assembly element (4, 5, 6, 7). Propulsion assembly element (4, 5, 6, 7) according to claim 3, characterized in that each wall (8, 9) of the propulsion assembly element (4, 5, 6, 7) comprises at least a pad (18, 19) projecting from an internal surface (20, 21) of the wall (8, 9) and against which is positioned a face (16, 17) of the piezoelectric actuator (11). Propulsion assembly element (4, 5, 6, 7) according to any one of Claims 2 to 4, characterized in that the means for placing under stress (13) of each piezoelectric actuator (11) comprise a clamping device (22) making it possible to clamp the first face (16) of the piezoelectric actuator (11) against a face (23) of a first stud (18) positioned on the first wall (8) of the propulsion assembly element (4, 5, 6, 7) and to clamp the second face (17) of the piezoelectric actuator (11) against a face (24) of a second stud (19) positioned on the second wall (9) of the propulsion assembly element (4, 5, 6, 7) in opposition with respect to the first stud (18). Propulsion assembly element (4, 5, 6, 7) according to claim 5, characterized in that the tightening device (22) comprises a screw (25) comprising a threaded portion (26) screwing into the central hole (14) of the piezoelectric actuator (11) and a screw head (27), the first stud (18) of the first wall (8) of the propulsion assembly element (4, 5, 6, 7) comprising a housing (28) in which is housed and retained the screw head (27) and the second stud (19) of the second wall (9) of the propulsion assembly element (4, 5, 6, 7) comprising a threaded orifice (29) into which the threaded portion (26) of the screw (25) is screwed until the two studs (18, 19) are compressed against the respective faces (16, 17) of the piezoelectric actuator ( 11). Propulsion assembly element (4, 5, 6, 7) according to claim 6, characterized in that the second stud (19) of the second wall (9) of the propulsion assembly element (4, 5, 6 , 7) comprises a central element (30) projecting from the face (24) of the second stud (19) in the direction of the first stud (18) and being inserted into the central orifice (14) of the piezoelectric actuator ( 11), the threaded hole (29) being formed inside the central element (30). Propulsion assembly element (4, 5, 6, 7) according to any one of Claims 1 to 7, characterized in that the piezoelectric actuators (11) are positioned at the location of the main torque of the propulsion element. propulsion assembly (4, 5, 6, 7) and close to the leading edge (38) of the propulsion assembly element (4, 5, 6, 7). Propulsion assembly element (4, 5, 6, 7) according to any one of Claims 1 to 8, characterized in that the walls (8, 9) comprise a thinned part (31) located upstream and close to the piezoelectric device (10) for protection against icing. Propulsion assembly element (4, 5, 6, 7) according to any one of Claims 1 to 9, characterized in that the walls (8, 9) of the propulsion assembly element (4, 5, 6 , 7) are two separate elements intended to be fixed together by the clamping device (22). Propulsion unit element (4, 5, 6, 7) according to any one of Claims 1 to 10, characterized in that the piezoelectric device (10) for protection against icing generates vibrations at a frequency close to or equal to to that of the resonant frequency of the propulsion assembly element (4, 5, 6, 7), the frequency of vibration varying in time around the resonant frequency. Propulsion assembly (1) for an aircraft comprising a nacelle (2) and a turbojet engine (3) supported by the nacelle (2), characterized in that it comprises at least one element of the propulsion assembly (4, 5, 6, 7 ) as defined in any one of claims 1 to 11. Method of assembling a propulsion assembly element (4, 5, 6, 7) intended to be mounted on a propulsion assembly (1) for an aircraft comprising a nacelle (2) and a turbojet engine (3) supported by the nacelle (2), said propulsion assembly element (4, 5, 6, 7) being intended to be in contact with an air intake flow and comprising a cavity (12) delimited by two walls (8, 9) opposite ones, including a first wall (8) and a second wall (9), and a piezoelectric device (10) for protection against icing housed inside the cavity (12) and comprising at least one piezoelectric actuator (11),
characterized in that it comprises the following steps:
- positioning of at least one piezoelectric actuator (11) on the second wall (9) of the propulsion assembly element (4, 5, 6, 7),
- assembly of the first wall (8) with the second wall (9) so as to close a cavity (12) in the propulsion assembly element (4, 5, 6, 7) which incorporates the piezoelectric actuator (11 ),
- Stressing of each piezoelectric actuator (11) against the two walls (8, 9) of the propulsion assembly element (4, 5, 6, 7) by stressing means (13). Assembly method according to claim 13, characterized in that it comprises the following steps:
- insertion of a screw head (27) of a screw (25) in a housing (28) provided in a first stud (18) of the first wall (8),
- insertion of a central element (30), projecting from one face (24) of a second stud (19) provided on the second wall (9), into a central orifice (14) of the piezoelectric actuator (11 ),
- positioning of the first wall (8) against the second wall (9),
- screwing of a threaded portion (26) provided on the screw (25) into a threaded hole (29) provided in the central element (30) of the second stud (19) so as to compress the two studs (18, 19 ) against the piezoelectric actuator (11).