Unducted aeronautical propulsion unit for an aircraft

Abstract

The invention relates to an aeronautical propulsion unit (100) comprising: - an outer casing (102); - a hub (104) mounted so as to pivot with respect to the outer casing (102) about a main axis (X) extending in an upstream-downstream direction of the aircraft; - a pusher propeller (106) mounted on the hub (104) so as to be pivotable with respect to the outer casing (102); and - a stationary flow straightener (112) mounted on the outer casing (102) downstream of the pusher propeller (106) along the main axis (X), the stationary flow straightener (112) extending about the main axis (X), the stationary flow straightener (112) comprising stator blades (114). For at least one stator blade (114) of the stationary flow straightener (112), the position of maximum thickness is between 0.1 and 0.5 for all blade assembly heights (H') and / or the position of maximum thickness (Xepmax) is strictly decreasing over at least 60% of the blade assembly height H', preferably over at least 75% of the blade assembly height (H').

Description

Description TITLE: UNCOUPELED AERONAUTICAL PROPELLER FOR AIRCRAFT Technical field of the invention

[0001] The present invention relates to an unducted aeronautical propeller for an aircraft, as well as to an aircraft comprising such an aeronautical propeller. Technological background

[0002] The search for minimizing polluting emissions linked to air transport involves, in particular, improving all the efficiencies of propulsion systems, and more particularly the propulsive efficiency which characterizes the efficiency with which the energy communicated to the air passing through the engine is converted into useful thrust.

[0003] The elements influencing this propulsive efficiency in the first order are those linked to the low pressure parts of the propulsion system, which contribute immediately to the generation of thrust: low pressure turbine, low pressure transmission system, fan and secondary flow guiding the flow of the latter. The known guiding principle for improving the propulsive efficiency is to reduce the compression ratio of the fan, thereby reducing the flow velocity at the engine outlet and the losses by kinetic energy linked to it.

[0004] One of the main consequences of this reduction in flow speed at the engine outlet is that it is necessary to process a higher mass flow of air in the low pressure part (secondary flow) in order to ensure a given level of thrust, fixed by the characteristics of the aircraft: this therefore leads to an increase in the engine bypass ratio. The bypass ratio, or BPR (ByPass Ratio), is defined as the ratio between the mass flow passing through the secondary flow (cold flow), and the mass flow passing through the primary flow (hot flow) and supplying the combustion chamber in particular.

[0005] This increase in secondary flow has the direct effect of requiring an increase in the fan diameter, and consequently the external dimensions of the retention casing surrounding it, as well as the nacelle constituting the aerodynamic envelope of the casing in question. To target high dilution rates, the casing becoming too large and too heavy (generating significant capture drag), the latter is removed to move to configurations with unducted propellers. Several concepts of unducted turbomachines are conceivable, but the present invention relates to an unducted turbomachine with (at least) one upstream variable-pitch propeller (this propeller being called an "Open Fan") and a downstream rectifier with fixed or variable pitch. In the case where such a turbomachine has a single propeller, it is called an unducted single fan (USF) engine.

[0006] Thus, the state of the art discloses an unducted aeronautical propeller for an aircraft, comprising: - an external casing; - a hub mounted to pivot relative to the external casing around a main axis extending in an upstream-downstream direction of the aircraft; - a propulsive propeller mounted on the hub so as to pivot relative to the external casing;and - a fixed rectifier mounted on the outer casing downstream of the propulsion propeller along the main axis, the fixed rectifier extending around the main axis, the fixed rectifier comprising stator blades each having: • a pressure face and an extrados face extending between a leading edge and a trailing edge of the stator blade, • for each section of the stator blade perpendicular to a stacking axis, the section being at a blade height along this stacking axis: ○ a curve, called a skeleton, midway between the pressure face and the extrados, ○ a distance, called a chord, between the leading edge and the trailing edge, and ○ a thickness between the pressure face and the extrados perpendicular to the skeleton, this thickness being normalized with respect to the chord having a maximum at a position on the chord, normalized with respect to the chord. ;

[0007] This type of turbomachine can be presented as a pusher (from the English "pusher") with the propeller and the rectifier downstream of the turbomachine (and mounted at the rear of the aircraft) or as a puller (from the English "puller") with the propeller and the rectifier upstream of the turbomachine (and mounted under the wing of the aircraft or mounted at the rear of the fuselage).

[0008] From an aerodynamic point of view, the main role of the rectifier is to straighten all or part of the airflow coming from the propeller, in order to generate thrust contributing to the aircraft's forward motion. This thrust is generated by deflecting the air onto the stator blades, characterized by an inlet angle different from the outlet angle. The secondary role of the rectifier is to limit the overall losses of the propeller / rectifier doublet, by allowing recovery of the rotating flow (gyration) downstream of the propeller. Indeed, without a rectifier, this rotating flow would be responsible for high aerodynamic losses, involving a significant degradation of the thrust and therefore of the efficiency of the propulsion system. In the case of an unducted propeller installed on an aircraft, the role of the rectifier is also to adapt the airflow to the various elements integrated or close to the engine, such as the pylon, in order to guarantee the operability and performance of the installed propulsion system. Thus, several families (or geometries) of rectifiers are possible, notably on one side and the other of the pylon.From an aero-acoustic point of view, the shape of the stator blades must minimize noise sources originating from the interaction of the propeller wake and the propeller blade tip vortex with the stator surface. It is known that flat plates or excessively thin profiles at the leading edge can induce separations and / or increase interaction noise. Finally, from a mechanical point of view, the blade shape and the material constituting it must enable it to withstand the static, dynamic and ingestion loads as specified by the regulations.

[0009] The aim of the invention is to provide a stator blade of an unducted rectifier meeting multi-skill criteria (aerodynamic, mechanical and acoustic) allowing an unducted engine to operate efficiently over its entire flight envelope. Furthermore, the state of the art includes the following documents: FR 3125797 A1, US 2023 / 249810 A1, US 2010 / 260609 A1, US 9340277 B2. Summary of the invention

[0010] There is therefore proposed an unducted aeronautical propeller for an aircraft, comprising: - an external casing; - a hub mounted pivotally relative to the external casing around a main axis extending in an upstream-downstream direction of the aircraft; - a propulsive propeller mounted on the hub so as to be pivotable relative to the external casing; and - a fixed rectifier mounted on the outer casing downstream of the propulsion propeller along the main axis, the fixed rectifier extending around the main axis, the fixed rectifier comprising stator blades each having: • a pressure face and an extrados face extending between a leading edge and a trailing edge of the stator blade, • for each section of the stator blade perpendicular to a stacking axis, the section being at a blade height along this stacking axis: ○ a curve, called a skeleton, midway between the pressure face and the extrados, ○ a distance, called a chord, between the leading edge and the trailing edge, and ○ a thickness between the pressure face and the extrados perpendicular to the skeleton, this thickness being normalized with respect to the chord and having a maximum at a position on the chord, normalized with respect to the chord;characterized in that, for at least one stator blade of the fixed rectifier, the maximum thickness position is between 0.1 and 0.5 for all the blade heights and / or in that the maximum thickness position is strictly decreasing over at least 60% of the blade height H', preferably at least 75% of the blade height. ;

[0011] The proposed thickness law ensures the efficient operation of the stator blade for the different flight conditions encountered, from an aerodynamic point of view (performance and operability criteria respected), acoustic (maximum noise emission criterion respected) and mechanical (lifespan and ingestion criteria respected).

[0012] The invention may further comprise one or more of the following optional features, in any technically possible combination.

[0013] Optionally, the maximum thickness position is maximum between 0% and 20% of the blade height.

[0014] Also optionally, the maximum thickness position is greater than or equal to 0.15, preferably greater than or equal to 0.25, or preferably greater than or equal to 0.3.

[0015] Also optionally, the maximum thickness position decreases from a maximum value located at a blade height of less than 0.1 to a maximum thickness position at a blade height R1 of between 20% and 40%, the maximum thickness position at the blade height R1 being between 0.2 and 0.4, preferably between 0.25 and 0.35.

[0016] Optionally also, on the upper part of the blading, i.e. above a height equal to 50%, the maximum thickness position decreases strictly with the blading height, from 50% of the blading height, up to a value between 0.15 and 0.35, preferably between 0.2 and 0.3, this value being reached at a blading height R2 between 55% and 100%.

[0017] Optionally also, the decrease in the maximum thickness position is more pronounced between blade height R1 and blade height R2 than between 0% and blade height R1.

[0018] Optionally also, the maximum thickness position is decreasing up to a blading height R3 between 65% and 100%, from which the maximum thickness position is increasing up to 100% of the blading height.

[0019] Also optionally, the maximum thickness is between 0.01 and 0.3, preferably between 0.02 and 0.3, for all blade heights.

[0020] Also optionally, the maximum thickness is maximum at zero blade height and is between 0.05 and 0.25, preferably between 0.08 and 0.18, or even more preferably between 0.1 and 0.14.

[0021] Optionally also, the maximum thickness is strictly decreasing from zero blading height to a blading height R4 between 35% and 85%.

[0022] Also optionally, the maximum thickness is minimum at the R4 blade height, where the maximum thickness is between 35% and 85% of the maximum thickness at zero blade height, preferably between 50% and 80% of the maximum thickness at zero blade height.

[0023] Also optionally, between the R4 blade height and the 100% blade height, the maximum thickness is strictly increasing.

[0024] Also optionally, the maximum thickness at 100% blade height is between 125% and 400% of the maximum thickness at R4 blade height.

[0025] An aircraft comprising an aeronautical propeller (100) according to the invention is also provided. Brief description of the figures

[0026] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: - Figure 1 is a side view of an aeronautical propeller according to the invention, - Figure 2 is a sectional view of a rectifier of the propeller of Figure 1, - Figure 3 is a section of a stator blade of the rectifier perpendicular to a stacking axis, - Figure 4 is a view similar to that of Figure 3, illustrating a skeleton of the stator blade, - Figure 5 groups together a view similar to that of Figure 4, with a thickness curve as a function of a position along a chord of the stator blade, - Figure 6 groups together three curves of evolution of the maximum thickness position as a function of a blade height, and - Figure 7 groups together three curves of evolution of the maximum thickness as a function of a height blading, Detailed description of the invention

[0027] In the following description, when a characteristic applies to at least one element, it can also apply to all of these elements. Similarly, when a characteristic applies for at least one value within an interval, it can also apply for all values ​​within that interval.

[0028] With reference to Figure 1, an aeronautical thruster 100 in which the invention is implemented will now be described.

[0029] The 100 aeronautical propeller is unducted (from the English "Unducted Single Fan", also designated by the acronym USF) and is designed to participate in the propulsion of an aircraft. For example, it is intended to be supported by a pylon attached to a wing of the aircraft.

[0030] The aeronautical propeller 100 firstly comprises an external casing 102 and a hub 104 pivotally mounted relative to the external casing 102 around a main axis X.

[0031] Subsequently, the terms “upstream” and “downstream” will be used to specify the relative position of the elements of the aeronautical propeller 100 along the main axis X in a direction of flow of an air flow PHI when the aircraft is propelled by the aeronautical propeller 100. For example, the aircraft can be propelled by the aeronautical propeller 100 in cruising mode at a flight Mach number greater than 0.7.

[0032] The hub 104 is thus, for example, located upstream of the external casing 102.

[0033] The aeronautical propeller 100 further comprises a motor 105 for driving the hub 104. The motor 105 extends, for example, into the external casing 102.

[0034] The engine 105 comprises, for example, at least one thermal engine, in particular a turbomachine, a turboshaft engine, a turbojet engine or a turbofan, and / or at least one electric motor, and / or at least one hydrogen engine.

[0035] The aeronautical propeller 100 further comprises, for example, an air inlet 107 for supplying primary flow to the engine 105.

[0036] HELIX

[0037] The aeronautical propeller 100 further comprises an unducted propulsive propeller 106 mounted on the hub 104 so as to be pivotable relative to the external casing 102 around the main axis X. The propeller 106 is therefore driven in rotation around the main axis X by the motor 105 via the hub 104.

[0038] The propeller 106 is for example located upstream of the engine 105. Such an arrangement is known as a "tractor" (from the English "puller"). Alternatively, the engine 105 could be in a "pusher" arrangement.

[0039] As it rotates, the propeller 106 is designed to drive the airflow PHI downstream to propel the aircraft in flight. The propeller 106 has blades for this purpose rotor blades 108 (for example between 3 and 25, preferably between 8 and 16) organized for example in a single annular row around the main axis X. The rotor blades 108 may for example all be identical and angularly spaced regularly around the main axis X.

[0040] At least one rotor blade 108 is for example variable pitch, around a respective pitch axis Y. The pitch of each variable pitch rotor blade 108 is defined by a pitch angle C around the rotor pitch axis Y.

[0041] The Y alignment axis can pass through the main X axis or be slightly offset from the main X axis, for example by an offset of at most 10 cm, for example by a further offset of at most 5 cm, for example by a further offset of at most 2 cm, for example by a further offset of at most 1 cm.

[0042] Furthermore, the Y setting axis may be perpendicular to the main X axis, as shown in the figures. Alternatively, the Y setting axis may be at an angle slightly different from 90° to the main X axis, due to manufacturing tolerances or intentionally. The Y setting axis may thus be, for example, perpendicular to the main X axis to within 5°, for example, within 2°, for example, within 1°, for example, within 0.1°.

[0043] In a preferred embodiment, all of the rotor blades 108 are variable pitch.

[0044] Furthermore, each variable-pitch rotor blade 108 of the propeller 106 has an external radius Re equal by definition to the distance between the main axis X and the point of the rotor blade 108 furthest from the main axis X among all the possible pitch angles C. Each variable-pitch rotor blade 108 further has an internal radius Ri equal by definition to the distance between the main axis X and the point of the rotor blade 108114 closest to the main axis X among all the possible pitch angles C.

[0045] The propeller 106 thus has a diameter D equal to twice the external radius Re. This diameter D is also called the “engine diameter”.

[0046] Furthermore, each rotor blade 108 is formed from a stack of sections (also called “sections” or “profiles”) along an axis, called the stacking axis. In other words, the sections considered are perpendicular to the stacking axis. In the case where the rotor pitch axis Y is perpendicular to the axis principal X and intersects the latter, the stacking axis corresponds to the rotor pitch axis Y.

[0047] When the rotor pitch axis Y is offset from the main axis X and / or makes an angle other than 90° with the main axis X, the rotor pitch axis Y has a radial component taken as the stacking axis. This radial component corresponds to the projection of the rotor pitch axis Y onto the perpendicular to the main axis X.

[0048] RECTIFIER

[0049] The aeronautical thruster 100 further comprises a fixed rectifier 112 (in English, “Outlet Guide Vane” or OGV) which is not shrouded and mounted on the external casing 102 downstream of the propeller 106, for example downstream of the air inlet 107, so that the latter is located between the propeller 106 and the rectifier 112.

[0050] The rectifier 112 forms a stator fixed to the external casing 102 and extending around the main axis X, but not being able to rotate around the latter. The rectifier 112 comprises stator blades 114 (for example between 3 and 25, preferably between 8 and 16) organized for example in a single annular row around the main axis X. Preferably, the number of stator blades 114 is different from the number of rotor blades 108, in order to reduce the noise of the aeronautical thruster 100. In particular, the number of rotor blades 108 is greater than the number of stator blades 114. Indeed, in the case where the number of rotor blades 108 and the number of stator blades 114 were equal, the rotor blades 108 would be followed by wakes which would interact simultaneously with the stator blades 114, which would increase the sound levels.The stator blades 114 may, for example, all be identical or different and spaced angularly in a regular manner or in a heterogeneous manner around the main axis X, so that at least two stator blades 114 have a different angular spacing around the main axis X.

[0051] The rectifier 112 is designed to straighten at least a portion of the PHI airflow passing through the propeller 106, in order to improve the performance of the aeronautical thruster 100. More specifically, the rectifier 112 aims to take up the gyration of the flow induced by the propulsive propeller 106 in order to improve the performance of the unducted configuration. Nevertheless, its presence induces a dominant noise source resulting from the interaction with the wake of the propeller 106 (and the blade tip vortex when the truncation of the stator blades 114 is not sufficient). It is therefore necessary to reduce the noise generated by the rectifier 112 and its interaction with the wake of the propeller 106 while preserving good aerodynamic performance, because the reduction of noise emissions and consumption is a major issue for non-ducted engine architectures.

[0052] For example, at least one stator blade 114 has variable pitch around a respective stator pitch axis Y'.

[0053] The stator setting axis Y' may pass through the main axis X or be slightly offset from the main axis X, for example by an offset of at most 10 cm, for example by a further offset of at most 5 cm, for example by a further offset of at most 2 cm, for example by a further offset of at most 1 cm.

[0054] Furthermore, the stator alignment axis Y' may be perpendicular to the main axis X, as illustrated in the figures. Alternatively, the stator alignment axis Y' may be at an angle slightly different from 90° to the main axis X, due to manufacturing tolerances or intentionally. The stator alignment axis Y' may thus be, for example, perpendicular to the main axis X to within 5°, for example, within 2°, for example, within 1°, for example, within 0.1°.

[0055] In a preferred embodiment, all of the stator blades 114 are variable pitch.

[0056] Furthermore, each variable-pitch stator blade 114 of the rectifier 112 has an external radius Re' equal by definition to the distance between the main axis X and the point of the stator blade 114 furthest from the main axis X among all the possible pitch angles C'. Each variable-pitch stator blade 114 also has an internal radius Ri' equal by definition to the distance between the main axis X and the point of the stator blade 114 closest to the main axis X among all the possible pitch angles C'.

[0057] Furthermore, at a given radius between Ri' and Re', two consecutive stator blades 114 have a spacing E corresponding to this radius multiplied by the arc of a circle connecting these two blades at this radius.

[0058] Furthermore, the Y, Y' alignment axes are separated by a distance S on the main X axis. This distance S is the distance between the point on the main X axis closest to the Y alignment axis and the point on the main X axis closest to the Y' alignment axis. In the case where the Y, Y' alignment axes both intersect the main X axis, this distance S is the distance between the two points of intersection.

[0059] STATOR BLADE

[0060] Subsequently, any one of the stator blades 114 will be described in more detail, all others being similar.

[0061] With reference to Figure 2, the stator blade 114 firstly comprises a leading edge BA' where the air flow PHI arrives from the propeller 106 and a trailing edge BF' from which the air flow PHI moves away.

[0062] The leading edge BA' extends from a root BA'_P close to the outer casing 102 to a head BA'_T distant from the outer casing 102. Similarly, the trailing edge BF' extends from a root BF'_P close to the outer casing 102 to a head BF'_T distant from the outer casing 102.

[0063] The stator blade 114 may be truncated, as in the example illustrated, that is to say that there is a truncated section 602 for example straight, connecting the heads BA'_T, BF'_T. Alternatively, the stator blade could be non-truncated, in which case the heads BA'_T, BF'_T are merged.

[0064] Furthermore, the stator blade 114 is formed from a stack of sections (also called “sections” or “profiles”) along an axis, called the stacking axis. In other words, the sections considered are perpendicular to the stacking axis. In the case where the stator pitch axis Y' is perpendicular to the main axis X and intersects the latter, the stacking axis corresponds to the stator pitch axis Y'. This is the case illustrated in the figures.

[0065] When the stator alignment axis Y' is offset from the main axis X and / or makes an angle other than 90° with the main axis X, the stator alignment axis Y' has a radial component taken as the stacking axis. This radial component corresponds to the projection of the stator alignment axis Y' onto the perpendicular to the main axis X.

[0066] Hereinafter, when applied in the context of the stator blade 114, the term "height" will refer to the distance between two points along the stacking axis, i.e., between the orthogonal projections of these points onto the stacking axis.

[0067] It is thus possible to define an upstream blade height H'amont to position oneself on the leading edge BA'. The upstream blade height H'amont is thus the ratio between a height h' BA from the foot BA'_P and a total height H' BA of the leading edge BA' between the foot BA'_P and the head BA'_T: H' amont = h' BA / H' BA The upstream blading height H'amont can thus be expressed in percentages and varies between 0% (position at the foot BA'_P) and 100% (position at the head BA'_T). Similarly, it is possible to define a downstream blading height H' aval to position itself on the trailing edge BF'. The downstream blade height H' avalis thus the ratio between a height h' BF from the foot BF'_P and a total height H' BF of the trailing edge BF' between the foot BF'_P and the head BF'_T: H' aval = h' BF / H' BF . The downstream blade height H' aval can thus be expressed in percentages and varies between 0% (position at the foot BF'_P) and 100% (position at the head BF'_T).

[0068] In the following, when we speak of blading height, noted H', without specifying downstream or upstream, this could mean either the upstream blading height H' amont , or the downstream blade height H' aval .

[0069] Figure 3 is a section of the stator blade 114 perpendicular to the stacking axis, at a certain height.

[0070] As can be seen, the stator blade 114 has a lower surface face 702 and an upper surface face 704, respectively concave and convex, connected to each other by the leading edge BA' and the trailing edge BF'. The leading edge BA' therefore makes it possible to separate the lower surface face 702 from the upper surface face 704 in the upstream part of the stator blade 114, while the trailing edge BF' makes it possible to separate the lower surface face 702 from the upper surface face 704 in its rear part.

[0071] When the leading edge BA' and the trailing edge BF' are present in the section considered (i.e., for example, in the example illustrated, below the truncated section 602), the leading edge BA' and the trailing edge BF' may be connected by a chord line 706 whose orientation changes according to the blade height H' (i.e., the upstream blade height H'amont or downstream H'aval considered). The leading edge BA' and the trailing edge BF' are separated, on the chord line 706, by a distance, called chord L', which may change according to the blade height H'.

[0072] With reference to Figure 4, for each section of the stator blade 114, it is possible to define a skeleton 902, such as the curve halfway between the intrados 702 and the extrados 704. The skeleton 902 can for example be obtained, as illustrated in figure 4, as the set of centers of the circles inscribed in the section, that is to say flush with both the intrados 702 and the extrados 704.

[0073] With reference to Figure 5, for each section of the stator blade 114, it is then possible to define, along the chord line 706, between the leading edge BA' and the trailing edge BF', a thickness Ep of the stator blade 114, as the distance between the intrados 702 and the extrados 704 perpendicular to the skeleton 902. More precisely, for each point along the chord line L' between the leading edge BA' and the trailing edge BF', identified by an abscissa x, this distance is taken at the point of the skeleton 902 placed on the perpendicular to the chord line 702 at the abscissa x. The thickness Ep and the abscissa x are normalized with respect to the chord L': Ep = absolute thickness / L' and x = absolute position / L'. Thus, in particular the abscissa is 0 when the point is on the leading edge BA' and 1 when the point is on the trailing edge BF'. The thickness Ep is therefore a function of the blade height H' and the abscissa x.

[0074] For a given blade height H', the thickness Ep along the chord line 706 has a maximum, noted Epmax, located at a position (i.e. a value of the abscissa x) noted Xepmax. The maximum thickness position Xepmax is therefore a function of the blade height H'.

[0075] THICKNESS LAW

[0076] The invention aims to optimize the radial evolution of the maximum thickness Epmax, this evolution being called “thickness law”. To obtain this optimization, the maximum thickness Epmax of each of at least a portion of the stator blades 114, preferably of all the stator blades 114, has one or both of the following characteristics.

[0077] According to a first characteristic, to optimize the aeronautical, acoustic and mechanical behavior of the stator blade 114, the maximum thickness position Xepmax is between 0.1 and 0.5 for all the blade heights H'. This maximum thickness position allows optimal operation of the stator blade 114 from a multi-trade point of view.

[0078] According to a second characteristic, the maximum thickness position Xepmax is monotonically decreasing over at least 60% of the blade height H', i.e. over any length range 60% included in the interval 0% - 100%, for example the range 15% - 75%, preferably at least 75% of the blade height H'. This criterion is linked to the reduction of mass at the head (necessary from a mechanical point of view) and the need for defrosting at the leading edge of the stator and which imposes maximum thicknesses close to the leading edge to integrate the defrosting solution (for example, a heating mat). Within the framework of this second characteristic, the maximum thickness Epmax can have one or more of the following sub-characteristics.

[0079] According to a first sub-characteristic, the maximum thickness position Xepmax is maximum between 0% and 20% of the blade height H'. This makes it possible not to generate a sonic passage section near the hub or casing.

[0080] According to a second sub-characteristic, the maximum thickness position Xepmax is, between 0% and 20% of the blade height H', i.e. for at least one value in the interval 0% - 20%, greater than or equal to 0.15, preferably greater than or equal to 0.25, or even preferably greater than or equal to 0.3. This is particularly important for the rectifiers on both sides of the pylon.

[0081] According to a third sub-characteristic, the maximum thickness position Xepmax decreases from a maximum value located at a blade height H' of less than 0.1 to a maximum thickness position Xepmax at a blade height R1 of between 20% and 40%, the maximum thickness position Xepmax at the blade height R1 being between 0.2 and 0.4, preferably between 0.25 and 0.35. This makes it possible to optimize the aerodynamic performance of the profiles located in the height interval between the blade root and R1 of the stator blade 114, while respecting the mechanical constraints linked mainly to the thickness of the leading edge BA': minimum manufacturable thickness and resistance to ingestion for example.

[0082] According to a fourth sub-characteristic, on the upper part of the blading, i.e. above a height equal to 50%, the maximum thickness position Xepmax decreases strictly from 50% of the blading height with the blading height H' down to a value between 0.15 and 0.35, preferably between 0.2 and 0.3, this value being reached at a blading height R2 between 55% and 100%. Indeed, when the blading height H' increases, the thickness of the profiles decreases towards the head. Profiles with low thickness can detach more easily, which generates aerodynamic losses and increases noise. A workaround is to place the maximum thickness position Xepmax close to the leading edge BA', which makes the profile more robust in case of over-incidence (as can be the case during landing and / or takeoff phases).

[0083] According to a fifth sub-characteristic, the decrease in the maximum thickness position Xpemax is more pronounced between the blade height R1 and the blade height R2 (i.e. in the upper part of the stator blade 114) than between 0% and the blade height R1 (lower part of the stator blade 114). In other words: Xepmax(R1) – Xepmax(R2) > Xepmax(0) – Xepmax(R1). This ensures that the maximum thickness position on the root sections does not vary too much, which is beneficial for the mechanical strength of the stator blade 114.

[0084] According to a sixth sub-characteristic, the maximum thickness position Xepmax decreases up to a blade height R3 of between 65% and 100%, from which the maximum thickness position Xepmax increases up to 100% of the blade height H'. This results from a greater decrease in the chord L' in the tip area of ​​the stator blade 114 than the decrease in the maximum thickness position Xepmax. The load of the rectifier 112 is in fact less significant in the upper part of the stator blade 114 than in the lower part, and the tip vortex of the stator blade 114 does not constitute a significant source of noise. It is therefore advantageous to reduce the chord L' to reduce the mass of the stator blade 114, while maintaining healthy aerodynamics on the stator blade 114.

[0085] According to a seventh sub-characteristic, the maximum thickness Epmax is between 0.01 and 0.3, preferably between 0.02 and 0.3, for all blade heights H'. This ensures good aerodynamic, acoustic and mechanical performance.

[0086] According to an eighth sub-characteristic, the maximum thickness Epmax is maximum at the root (H' = 0) and is between 0.05 and 0.25, preferably between 0.08 and 0.18, or even preferably between 0.1 and 0.14. This ensures that the thickness of the profile at the root (or at the level of the embedding) is sufficient to hold and transmit the aerodynamic and mechanical forces on the blade.

[0087] According to a ninth sub-characteristic, the maximum thickness Epmax is strictly decreasing from the root (H' = 0) up to a blading height R4 between 35% and 85%.

[0088] According to a tenth sub-characteristic, the maximum thickness Epmax is minimal at the blade height R4, where the maximum thickness Epmax is between 35% and 85% of the maximum thickness Epmax at the foot (H' = 0), preferably between 50% and 80% of the maximum thickness Epmax at the foot (H' = 0).

[0089] According to an eleventh sub-characteristic, between the blade height R4 and the blade height H' at the head (H' = 100%), the maximum thickness Epmax is strictly increasing. This behavior is mainly caused by a reduction in the chord L' on the upper part of the stator blade 114. Indeed, the stator blade 114 being less loaded on its upper part, it is possible to reduce the chord L' (mass gain) while maintaining good aerodynamic performance (no mass losses or separations).

[0090] According to a twelfth sub-characteristic, the maximum thickness Epmax at the head (H' = 100%) is between 125% and 400% of the maximum thickness Epmax at the blading height R4.

[0091] Figure 6 illustrates three curves 602, 604, 606 of maximum thickness position Xepmax as a function of the blade height H' conforming to all the characteristics and sub-characteristics stated above relating to the maximum thickness position Xepmax.

[0092] Figure 7 illustrates three curves 802, 804, 806 of maximum thickness Epmax as a function of the blade height H' conforming to all the characteristics and sub-characteristics stated above relating to the maximum thickness Epmax.

[0093] ACTIVITY FACTOR

[0094] A parameter that allows us to give a first estimate of the chord distribution along the span of a stator blade 114 is its Activity Factor (AF), which is defined as follows: !" = where Ri' corresponds either to the internal radius Ri'BA of the stator blade 114 at the leading edge BA', or to the internal radius Ri'BF of the stator blade 114 at the trailing edge BF'; Re' corresponds either to the external radius Re' BA of the stator blade 114 to the leading edge BA', or to the external radius Re'BF of the stator blade 114 to the trailing edge BF'; 0 represents a radial distance from the main axis X, divided by the external radius Re'; L'(0) represents the chord L' between the leading edge BA' and the trailing edge BF' of a section (or aerodynamic profile) of the stator blade 114 in the plane perpendicular to the radial component of the pitch axis Y' at said radial distance 0.

[0095] The activity factor of the stator blade 114 is preferably between 40 and 225, more preferably between 90 and 160.

[0096] This implies that the chord L' of the stator blades 114 is relatively large in the lower part of the stator blade 114, which, in combination with a significant thickness at the root of the stator blade, makes it possible to ensure the mechanical strength of the stator blade 114. In addition, the larger the chord L' in the lower part, the more the gyration of the flow downstream of the propeller 106 increases (aerodynamic advantage), which makes it possible to optimize the noise reduction by unloading the tip of the rotor blade 108 of the propeller 106 and of the stator blade 114 from the rectifier 112, where the flow speeds are higher.

[0097] OTHER POSSIBLE FEATURES OF THE AIRCRAFT PROPELLER

[0098] Preferably, the number of rotor blades of the propeller 106 and the number of stator blades 114 of the rectifier 112 are different. This makes it possible to minimize the noise of the aeronautical propeller 100. Indeed, in the case where there is the same number of rotor blades 108 and stator blades 114, the set of wakes of the propeller 106 interacts with the stator blades 114 simultaneously, which increases the noise levels. Preferably, there are more rotor blades 108 than stator blades 114, for example two more rotor blades 108 than stator blades 114.

[0099] More preferably, the strength, noted П and defined, at a given radius, as the ratio between the chord L' and the spacing E between two consecutive stator blades 114 (the spacing E corresponding to this radius value multiplied by the arc of a circle connecting these two blades at this radius), is less than 3 over the entire blading height H'. The strength П is furthermore preferably less than 1 at the head (blading height H' equal to 100%).

[0100] More preferably, the ratio between the spacing between the stacking axis of the propeller 106 and the stacking axis of the rectifier 112 (the distance S in the illustrated example) and the motor diameter D is between 0.01 and 0.5, preferably between 0.15 and 0.35, i.e.: 0.01 < S / D < 0.5, preferably 0.15 < S / D < 0.35.

[0101] More preferably, the trailing edge of the rotor blades 108 of the propeller 106 is located at an axial position further upstream than the leading edge BA' of the stator blades 114 of the rectifier 112 in order to avoid interference between the rotating propeller 106 and the rectifier 112.

[0102] FIXED STATOR BLADE

[0103] In the case where one of the stator blades 114 is fixed (for example for integration constraints, such as for example if there is a lack of space under the hub to integrate the pitch change system or to reduce the weight), the stacking axis is defined by the axis perpendicular to the main axis X and passing through the latter, and also passing through the leading edge BA' at the blade root BA'_P.

[0104] SPECIAL METHODS OF IMPLEMENTATION

[0105] In a particular embodiment, at least two stator blades 114 have an identical thickness law below the radial position R4. This makes it possible to have a single geometric blade definition with two different max radius heights Re2 (or clipping values), while respecting the conditions on the thickness of one or more of the preceding characteristics on the thickness at the blade tip.

[0106] In a particular embodiment, at least two stator blades have different thickness laws, each of these laws however respecting at least the first characteristic and / or the second characteristic described previously. In the case of an unducted fan (USF) engine installed on an aircraft, each stator blade 114 may indeed have a different aerodynamic load (or airflow forces on the blade). This behavior is caused by installation effects, leading to a non-axisymmetric aerodynamic environment around the main axis X. Thus, the thickness law of each stator blade 114 can be optimized relative to its maximum aerodynamic load, the latter being able to be different from one stator blade 114 to another.This makes it possible, for example, to reduce the thickness of certain stator blades 114 compared to others, leading to a gain in mass and therefore in fuel consumption (from the English “Specific Fuel Consumption” or SFC) of the entire propulsion system.

[0107] Each stator blade has a leading edge thickness EpBA defined as the thickness Ep (normalized) at positions x between 0 and 0.1. In a particular embodiment, the leading edge thickness EpBA, for all blade heights H', is between 0.005 and 0.12, in order to make the blade robust to the angle of attack. Thus, even for operating conditions resulting in a wide variation in angle of attack seen by the stator blade, the minimum value of the leading edge thickness EpBA ensures correct aerodynamic operation of the stator blade 114 over the entire blade height H': no detachment or separation of the flow, which would lead to additional losses and therefore a degradation of the overall efficiency of the engine.

[0108] In a particular embodiment, the thickness of the leading edge EpBA makes it possible to take into account the integration of a thermal system intended to de-ice the leading edge area, during all or part of the aircraft's mission.

[0109] In a particular embodiment, at least two stator blades have different leading edge thicknesses EpBA, each being however between 0.005 and 0.12. This embodiment corresponds to an optimization of the leading edge of each stator blade installed on an aircraft. Indeed, the range of incidence variation seen by each stator blade may be different given the installation effects. Determining the thickness of the leading edge EpBA of each stator blade ensures robustness to incidence for each stator blade, while avoiding excessively large thicknesses for the stator blades being subjected to smaller ranges of incidence variation. This optimization makes it possible to maximize the aerodynamic performance of the rectifier while limiting its mass, leading to a gain in current consumption.

[0110] CONCLUSION

[0111] In conclusion, it will be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0112] In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should be interpreted to include all equivalents the prediction of which is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching just disclosed to them.

Claims

Claims [1] Unducted aeronautical propeller (100) for an aircraft, comprising: - an external casing (102); - a hub (104) pivotally mounted relative to the external casing (102) around a main axis (X) extending in an upstream-downstream direction of the aircraft; - a propulsive propeller (106) mounted on the hub (104) so ​​as to be pivotable relative to the external casing (102); and - a fixed rectifier (112) mounted on the outer casing (102) downstream of the propulsion propeller (106) along the main axis (X), the fixed rectifier (112) extending around the main axis (X), the fixed rectifier (112) comprising stator blades (114) each having: • an intrados face (702) and an extrados face (704) extending between a leading edge (BA') and a trailing edge (BF') of the stator blade (114), • for each section of the stator blade (114) perpendicular to a stacking axis (Y'),the section being at a blade height (H') along this stacking axis (Y'): ○ a curve, called skeleton (902), midway between the intrados (702) and the extrados (704), ○ a distance, called chord (L'), between the leading edge (BA') and the trailing edge (BF'), and ○ a thickness (Ep) between the intrados (702) and the extrados perpendicular to the skeleton (902), this thickness (Ep) being normalized with respect to the chord (L') and having a maximum (Epmax) at a position (Xepmax) on the chord (L'), normalized with respect to the chord (L'); characterized in that for at least one stator blade (114) of the fixed rectifier (112), the maximum thickness position (Xepmax) is between 0.1 and 0.5 for all the blade heights (H') and / or in that the maximum thickness position (Xepmax) is strictly decreasing over at least 60% of the blade height H', preferably at least 75% of the blade height (H'). [2] Aeronautical thruster (100) according to claim 1,in which the maximum thickness position (Xepmax) is maximum between 0% and 20% of the blade height (H')., [3] Aeronautical thruster (100) according to claim 2, wherein the maximum thickness position (Xepmax) is greater than or equal to 0.15, preferably greater than or equal to 0.25, or even more preferably greater than or equal to 0.

3. [4] Aeronautical thruster (100) according to any one of claims 1 to 3, wherein the maximum thickness position (Xepmax) decreases from a maximum value located at a blade height (H') less than 0.1 to a maximum thickness position (Xepmax) at a blade height R1 of between 20% and 40%, the maximum thickness position (Xepmax) at the blade height R1 being between 0.2 and 0.4, preferably between 0.25 and 0.35.[5] Aeronautical propeller (100) according to any one of claims 1 to 4, in which, on the upper part of the blading, that is to say above a height equal to 50%, the position of maximum thickness (Xepmax) decreases strictly with the blading height (H'), from 50% of the blading height, up to a value between 0.15 and 0.35, preferably between 0.2 and 0.3, this value being reached at a blading height R2 between 55% and 100%. [6] An aeronautical thruster (100) according to claims 4 and 5 taken together, wherein the decrease in the maximum thickness position (Xpemax) is more pronounced between the blade height R1 and the blade height R2 than between 0% and the blade height R1.[7] Aeronautical thruster (100) according to any one of claims 1 to 6, wherein the maximum thickness position (Xepmax) is decreasing up to a blade height R3 of between 65% and 100%, from which the maximum thickness position (Xepmax) is increasing up to 100% of the blade height (H'). [8] Aeronautical thruster (100) according to any one of claims 1 to 7, wherein the maximum thickness (Epmax) is between 0.01 and 0.3, preferably between 0.02 and 0.3, for all blade heights (H'). [9] Aeronautical propeller (100) according to any one of claims 1 to 8, in which the maximum thickness (Epmax) is maximum at zero blade height (H') and is between 0.05 and 0.25, preferably between 0.08 and 0.18, or even preferably between 0.1 and 0.

14. [10] Aeronautical propeller (100) according to any one of claims 1 to 9, wherein the maximum thickness (Epmax) is strictly decreasing from the zero blade height (H') to a blade height R4 of between 35% and 85%. [11] Aeronautical propeller (100) according to claim 10, wherein the maximum thickness (Epmax) is minimal at the blade height R4, where the maximum thickness (Epmax) is between 35% and 85% of the maximum thickness (Epmax) at the zero blade height (H'), preferably between 50% and 80% of the maximum thickness (Epmax) at the zero blade height (H'). [12] Aeronautical propeller (100) according to claim 10 or 11, in which, between the blade height R4 and the blade height (H') of 100%, the maximum thickness (Epmax) is strictly increasing.[13] Aeronautical propeller (100) according to any one of claims 10 to 12, in which the maximum thickness (Epmax) at the 100% blade height is between 125% and 400% of the maximum thickness (Epmax) at the R4 blade height. [14] Aircraft comprising an aeronautical propeller (100) according to any one of claims 1 to 13.

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