Aeronautical thruster with improved aeroacoustics

Abstract

Aeronautical thruster (40) having a longitudinal axis (X) and comprising an upstream rotor row and a downstream stator row (16) having unducted blades (18). Two adjacent blades of the downstream stator row (16) have between them, about the longitudinal axis (X), an azimuthal spacing (Δθ), and at least some of these spacings differ from one another such that at least some of the blades of the downstream stator have a heterogeneous distribution about the longitudinal axis (X).

Description

Description Title: AERONAUTICAL PROPELLER WITH IMPROVED AEROCOUSTICS Technical field

[0001] The present disclosure relates to the field of longitudinal axis aeronautical propellers each comprising a hub and (at least) two annular rows of unducted blades, one upstream, the other downstream, along the longitudinal axis.

[0002] In accordance with the foregoing and the following, throughout the text, the relative qualifiers "upstream" and "downstream" are defined in relation to each other with reference to the flow, in the cruising flight phase, of the gases in the turbomachine in the longitudinal direction (i.e. the direction of the longitudinal axis).

[0003] The aeronautical propulsion system may comprise (at least) a thermal engine, in particular a turbomachine, turboshaft, turbojet, turbofan, and / or (at least) an electric motor, and / or (at least) a hydrogen engine, and / or (at least) a hybrid engine: thermal and / or electric and / or hydrogen. Prior art

[0004] Reference will be made hereinafter more particularly, and therefore without limitation, to the case of turbomachines, since the type(s) of engine included in the propulsion unit is not decisive here. By turbomachine is meant a propulsion unit in which there is an exchange of energy between a flowing fluid and a rotor.

[0005] In this context, it is recalled, by way of example, that a turbomachine with an "unducted" fan (or turboprop of the "Propfan" or "Open Fan" or "Open rotor" or "Counter-Rotating Open Rotor" type) is a type of turbomachine in which the fan extends outside the engine casing (or nacelle), unlike conventional turbomachines (of the "Turbofan" type) in which the fan is ducted.

[0006] The absence of fairing, like unfairly fairinged turbomachines, leads to an increase in the noise level emitted by aeronautical propellers, which typically include at least one upstream rotor row whose blades impact the blades of a downstream stator row.

[0007] Indeed, the noise generated by the annular rows of unducted blades propagates in the free field. A main cause of the emitted noise is linked to vortex structures generated in the airflow at the free radially external ends of the rotor row blades. These blade tip vortices can interact with the blades of the downstream stator row.

[0008] One of the challenges of these architectures is the certification of noise levels during takeoff and landing operations. The noise levels emitted by aircraft are subject to increasingly strict regulations.

[0009] The main sources of noise on unducted turbomachines are listed below: - interaction noise of the vortex generated at the tips of the blades and the rotor wake, if this is followed downstream of a stator, the upstream rotor interacting with the leading edge of the blades of the downstream stator. This source of noise contributes to the increase in: -- broadband noise, because the turbulence rate on the wake is often very high at the blade tip, -- tonal noise, linked to the periodic nature of the upstream rotor wake and the vortex during rotor blade rotations, - blade noise due to the stationary load of the blades (source of tonal noise on a rotor) and the development of the boundary layer on the blades (rotor or stator); thus, the broadband noise source is generated during the passage of the turbulent boundary layer at the trailing edge of the blades; the increase in the chord of the blades on unducted turbomachines increases the surface area over which the boundary layer develops.

[0010] It should be noted that the absence of a nacelle on unducted turbomachines implies a significant reduction in surfaces with acoustic treatments (honeycomb type resonators, absorbent materials, in particular porous materials, etc.), and therefore means allowing noise reduction.

[0011] Furthermore, when a rotor is subjected to a non-uniform upstream flow that is not parallel to the engine axis - the aforementioned longitudinal axis - (incidence flight, with crosswind or installation effects), forces and moments appear in the propeller plane called 1 P forces.

[0012] In incidence, an upstream rotor followed by a downstream stator does not only provide a tractive force in the horizontal axis of advance of the aircraft (this is not necessarily the longitudinal axis (axis of the aeronautical engine / propeller); it is the horizontal direction of advance). For example, when the aeronautical propeller is installed under a wing, and / or the propeller can be oriented with a certain incidence relative to the upstream flow, a descending rotor blade sees an increase in incidence and is therefore subjected to increased forces unlike a rising blade on which reduced forces are exerted. Consequently, over a revolution engine, the same rotor blade is subjected to variable forces which depend on its azimuthal position around the longitudinal axis.

[0013] Downstream stator blades will therefore also have a variable load depending on their azimuthal position. Axially opposite the upstream rotor blades, if at the position of a blade considered on the stator the incidence seen by the blade is more or less significant, the descending stator blades will be less loaded and will have less rotation to straighten, while the rising blades will be more loaded and will have more rotation to straighten.

[0014] It should also be noted that the upstream incidence angle a (aircraft incidence) is not completely filtered by the upstream rotor. In addition to the variation in 1 P forces, the stator blades will be subjected to different incidences, due to the aircraft incidence and the often presence of a pylon (or equivalent) / wing pair, depending on their azimuthal position.

[0015] The stator blades located on the upper part of the motor (zone 12H) will be over-impacted, therefore more loaded; The stator blades located on the lower part of the motor (zone 6H) will be under-impacted, therefore less loaded.

[0016] As conventionally, the 3H, 6H, 9H, 12H positions are considered as on a clock and oriented clockwise, seen from the front, from upstream / front on the considered propeller or aircraft.

[0017] However, various solutions of the prior art are often relatively suitable only in an isolated configuration of the aeronautical thruster and at zero incidence. Indeed, the presence of surrounding elements (mast, wing, fuselage, etc.), a non-zero incidence of the airflow perceived by the thruster and the shape of the blades of the rotor row can modify, on the one hand, the contraction and the axisymmetry around the longitudinal axis X of the flow tube of the airflow downstream of the rotor row, and / or on the other hand, the size of the vortices present in the airflow downstream of the rotor row so that the truncation of the blades of the downstream stator row defined from an isolated configuration and at zero incidence no longer prevents the interaction between the blades of the downstream stator row and the vortices formed by the blades of the rotor row located upstream.

[0018] This description aims to provide a solution to these drawbacks. Summary

[0019] At this stage, it is immediately specified that, even if the preceding prior art therefore relates to a turbomachine, the solution of the invention applies to any unducted and / or “Open Rotor” type aeronautical propeller, since part of the The aforementioned problem is not necessarily specific to the aforementioned type of aeronautical propellant.

[0020] In this context, it is therefore here, and generally, proposed an aeronautical propeller having a longitudinal axis (X) and comprising a casing and, spaced from each other along said longitudinal axis (X), an upstream rotor row of rotor blades, unducted, and a downstream stator row of stator blades, unducted and extending around the casing, two adjacent blades of said downstream stator row of stator blades having between them, around the longitudinal axis (X, or stator axis), an azimuthal spacing (A0, A0j) defined by the angle between respective axes: -- either adaptation of a pitch angle of said two adjacent blades, when these axes are projected in a plane perpendicular to the longitudinal axis (X) and if said two adjacent blades have a variable pitch angle, -- either radial to the longitudinal axis (X) and / or passing through the radially inner ends or the radially outer ends of said two adjacent blades, or through their centers of gravity, respectively, if said two adjacent blades have a fixed pitch angle, -- either, for one of said respective axes, for adapting a pitch angle of one of said two adjacent blades, when the blade has a variable pitch angle, and, the other, radial to the longitudinal axis (X) and / or passing through the radially internal end or through the radially external end or through the center of gravity of said adjacent blade, when the latter has a fixed pitch angle and around the longitudinal axis (X), an angular position at 12H is defined as positioned vertically upwards relative to the longitudinal axis (X) and an angular position at 6H as positioned vertically downwards relative to the longitudinal axis (X), the assembly being characterized in that at least some of said blades of said downstream stator row of stator blades have a heterogeneous distribution around the longitudinal axis (X),such that there are at least two said adjacent blades of said downstream stator row of stator blades which have between them a said azimuthal spacing A0 or A0j, such that A0j 360° / V; A0j > (3607V) +1° or A0j < (3607V) -1°, with V which defines the number of blades on said downstream stator row of stator blades; and / or that there are at least two azimuthal spacings between the stator blades of the downstream stator row such that A0j and A0j are distinct when ij with, i,j < V and i,j = 1, 2, ... .,

[0021] Preferably, we will even choose A0j > (3607V) +3° or A0j < (3607V) -3°, or even preferably A0j > (3607V) +5° or A0j < (360° / V) -5°, in order to optimize the effects expected; these values ​​having been noted as particularly relevant, with regard to the aforementioned effects sought, whereas different values ​​could be expected.

[0022] A0i and A0j respectively define two distinct azimuthal spacings between any two adjacent blades. I and j are distinct indices (natural integers: i,j=1, 2, ...) when ij is less than or equal to the number of stator blades (i,j < V), V defining the number of blades on the downstream stator row of stator blades. In other words: i and j are different and can take any (any) integer value among 1, 2, 3, ... and (at most) V.

[0023] In other words: at least some of the azimuthal spacings of the stator blades are different from each other.

[0024] Heterogeneous, non-homogeneous, irregular and non-uniform are synonyms here concerning this azimuthal distribution, therefore around the longitudinal axis X (heterogeneous = which varies, which is not unique everywhere). Conventionally, the pitch angle of a blade can be the angle formed by the chord of one of the profiles and a plane perpendicular to the longitudinal axis, X, for example, the plane of rotation of the blade. The blade being twisted, by convention we say that the pitch is that of the profile located at 70% of the maximum radius.

[0025] Such a configuration makes it possible to take into account aerodynamic, acoustic and / or integration constraints, if only in terms of compromises between them. In addition, this configuration is advantageous from a specifically acoustic point of view to decorrelate the noise sources emitted by the stator or modify the directivity of the sound that is radiated by the stator blades, that is, the areas where the acoustic radiation is maximum.

[0026] Furthermore, increasing the number of stator blades at azimuthal positions close to the pylon (mast or cradle) and / or the wing or fuselage can be beneficial in reducing the potential effect (pressure rise) of this assembly towards the upstream rotor; locally increasing (relatively) the number of stator blades can therefore help to "filter" or reduce the pressure rise, towards the upstream rotor, linked to the presence of a mast, pylon or cradle, or a wing (set of lifting surfaces of an aircraft) or the fuselage.

[0027] From an acoustic point of view, the heterogeneous distribution of stator blades in the azimuthal direction (i.e. circumferentially, around the axis around which the blades of said downstream stator row are arranged; longitudinal axis X in the example), makes it possible to modify the directivity of the interaction noise generated during the interaction of the wake of the upstream rotor with the downstream stator.

[0028] This makes it possible to define angular ranges around the main axis of the aeronautical propeller on which the number of stator blades will be reduced to reduce the noise emitted towards the ground ("community noise") and / or towards the passenger cabin ("cabin noise").

[0029] From an aerodynamic point of view, the heterogeneous distribution of stator blades allows for better distribution of the aerodynamic load of the stators during the incidence flight phases (for example, the angle of attack is high during takeoff and / or landing), and the heterogeneity of the stator blade load linked to the 1 P forces (forces on the propeller blade in a direction perpendicular to the engine axis, which modifies the flow downstream of the upstream rotor depending on its azimuthal position).

[0030] From an integration point of view, the heterogeneous distribution of stator blades makes it possible to bypass the servitudes under the casing or the hub, to reduce the pressure rise of the wing / lifting surface downstream of the stator blades and / or to avoid the interaction of the stator wakes with the wing, as well as to adapt to the integration of the pylon if necessary. Note that it is known that a pylon is located upstream of the rotor / stator blades (so-called "pusher" configuration), unlike a preferred "puller" configuration with the pylon, and / or a row of stator blades, downstream or at the level of the stator blades, for a USF type architecture. From an acoustic point of view, an advantage of a "puller" type configuration is to avoid the impact of the wake of the pylon, mast or cradle with the rotor blade assembly.From an aerodynamic point of view, an advantage of a "puller" type configuration is that it does not introduce distortion or heterogeneity into the airflow upstream of the rotor, which can degrade its performance and increase vibration response phenomena on the rotor blades. A puller configuration also allows the engine to be installed under the wing, which is an advantage for the aircraft manufacturer, for the aircraft's center of gravity.

[0031] Thus, the above solution also has the advantage of being particularly suitable for a USF type aeronautical propeller. In this context, although a "puller" type USF may be preferred, a "pusher" type USF can be considered.

[0032] In this document and in US 9242721, the associated problems and technical effects are different. The problem identified in US 9242721 is the formation of rotor blade root shocks when the number of upstream rotor blades increases. The shocks create aerodynamic losses and the decrease in the number of rotor blades increases the noise, because the blades are more loaded. To solve this problem for a counter-rotating rotor architecture (CROR type), US 9242721 proposes an additional stator blade wheel upstream of the rotor. The purpose of this stator wheel (technical effect) is to avoid the formation of shocks at the blade root (to improve efficiency / aerodynamics) and to be able to increase the number of rotor blades (to reduce noise).

[0033] On the contrary, in the present solution, it may be preferred that the USF type thruster comprises a single annular row of unducted rotor blades, which is the aforementioned upstream row of rotor blades, thus avoiding weight, technical integration complications and aerodynamic interactions between the counter-rotating rotors.

[0034] The term "unducted" used in reference to the upstream rotor row and the downstream stator row indicates that the blades of the upstream rotor row and the blades of the downstream stator row are not surrounded by a nacelle (in other words the stator blades have a radially external free end), unlike conventional aeronautical thrusters in which the fan is ducted inside a nacelle.

[0035] Taking into account the above, it is therefore around a hub that the upstream rotor row, unshrouded, will extend, and around a (fixed) casing, located downstream, that the stator row, also unshrouded, will extend.

[0036] The blades of the upstream rotor row and / or the downstream stator row can be variable pitch; all or only some.

[0037] All azimuthal spacings between two adjacent blades of the series of blades of said downstream row of stator blades may be different from each other.

[0038] This can be advantageous from an acoustic point of view to decorrelate noise sources emitted by the stator or to modify the directivity of the sound, i.e., the areas where acoustic radiation is maximum.

[0039] A relevant situation may also arise if all the blades of the downstream stator row have a homogeneous distribution around the longitudinal axis (X), except at the location of a single angular sector. This "homogeneous distribution" may be such that: A0 < 3607V, for any azimuthal spacing between two (circumferentially) adjacent / successive blades concerned. The aforementioned angular sector will be favorably limited between 15° and 75°, or preferably between 25° and 60°. Thus, it will be possible to limit the noise emitted by the stator blades in connection with a less complex design than in other "heterogeneous" situations, while maintaining an optimized number of rotor and / or stator blades.

[0040] Thus, it will be possible to take into account the presence of a prominence or a non-axisymmetric hub around the longitudinal axis X extending between two blades of said downstream annular row of stator blades, or axially adjacent to these two blades. In the presence of a pylon, a cradle or a mast for attaching the propeller to the aircraft, it will be possible to have an increased azimuthal spacing between the two stator blades on one side and the other of the prominence, for example of the pylon.

[0041] This will be particularly valid for a number of stator blades V of interest varying between 8 and 14.

[0042] In the above favourable context, the number of blades in the downstream stator row of stator blades will usefully be greater than or equal to 5, for this research into limiting the noise emitted by the stator blades and / or efficiency: ease of production / maintenance / dynamic effect on the flow.

[0043] The increase in spacing will, if necessary, allow the integration of the aeronautical propeller attachment system, and / or the blade pitch (change) system, and / or the passage of service conduits (oil, air, etc.) under the hub, typically in the nacelle then located downstream.

[0044] It may also be advantageous if, on at least one of the upstream rotor row of rotor blades and the downstream stator row of stator blades, there is a ratio C / E between the chord, C, and the azimuthal spacing E between two consecutive blades, around the longitudinal axis (X) such that C / E is less than 3 over the entire span.

[0045] And even more advantageously, the C / E ratio may be less than 1 at the radially external ends of two blades of the same row (upstream and / or downstream) consecutive, or adjacent, circumferentially or azimuthally.

[0046] This criterion will be usefully respected for a number of stator blades (between 8 and 14) that one can choose to favor. An advantage of a low solidity (C / E ratio) (C / E preferably less than 1 at the tip) is to reduce blade-to-blade interactions. From an aerodynamic point of view, if C / E is large (greater than 3 or 4), the channel or section of passage of the flow between the blades is reduced. This increases the speed of the flow between the blades, which can produce the generation of shock waves (between the blades) and therefore losses of efficiency at certain operating points. From an acoustic point of view, the lower the solidity (C / E), the more the correlation of noise sources between the blades is reduced.

[0047] It is recalled that, conventionally, E is the length (units in meters) of the arc of circumference between the axes (such as 180a / 180b below) of two adjacent stator blades. It can be related to A0 by the equation: E=r*A0 when A0 is measured in radians and r corresponds to the radial position around the longitudinal axis (X).

[0048] It may also be provided that the upstream rotor row of rotor blades and the downstream stator row of stator blades have different numbers of blades.

[0049] In the prior art, a disadvantage is associated with the addition of stators upstream of the rotor blades. Indeed, this risks creating new sources of noise, such as the interaction of the wakes of the upstream stator with the blades of the downstream rotor. Thus, the noise reduction that could be expected by increasing the number of blades of the upstream propeller may be (at least partially) masked by the new sources of noise.

[0050] On the contrary, in the present solution, it will be possible to favor the number of blades of the upstream rotor being actually greater than the number of blades of the downstream stator, thus limiting the sources of parasitic or additional noise.

[0051] Thus, for example, in the case where the rotor blades and the stator blades are distributed homogeneously in the azimuthal direction, using the solution of the invention with twelve said blades in the upstream rotor row of rotor blades and eight said blades in the downstream stator row of stator blades would generate four rotor wakes that could interact simultaneously with four stator blades, which could increase the noise emitted by the aeronautical propeller. But, with a heterogeneous azimuthal distribution of stator blades, this problem can be avoided, while therefore retaining the aforementioned optimized number of rotor and stator blades.

[0052] This is an example that illustrates the interest of a heterogeneous azimuthal distribution of stators, but this will not necessarily be the preferred case. The preferred number of blades could in fact be (rotor-stator): 12-10 or 14-12 or even 14-11.

[0053] At least for uniformization / limitation of wakes and limitation of noise, it is also proposed that there are at least 2 families of stator blades in the row of stator blades, preferably at least 3 families of stator blades, and in which each family of stator blades comprises one or more stator blades having the same geometric characteristics (comprising at least the chord (C), the thickness (e), the height (such as L2 or L21 hereinafter) of a stator blade) in which at least one of said geometric characteristics (at least chord, thickness, height) is different from the same geometric characteristics (chord, thickness, height) of the stator blades of another family of stator blades.

[0054] A set of geometric characteristics of a stator blade may include chord, thickness, and height.

[0055] The set of geometric characteristics of a stator blade may further include at least one of camber, sweep, and dihedral.

[0056] There are also provided at least 3 families of stator blades, preferably at least 5 families of stator blades, and wherein each family of stator blades comprises a stator blade, wherein at least one of the geometric characteristics of the set of geometric characteristics is different from the same geometric characteristics of a stator blade of another family of stator blades.

[0057] There are also provided at least 3 families of stator blades, preferably at least 5 families of stator blades, and wherein each family of stator blades comprises at least two or exactly two stator blades having the same set of geometric characteristics, wherein at least one of the geometric characteristics of the set of geometric characteristics is different from the same geometric characteristics of the stator blades of another family of stator blades.

[0058] There are also provided at least 3 families of stator blades, preferably at least 5 families of stator blades, and in which each family of stator blades comprises one or more stator blades, the stator blades of the same family which comprises several stator blades having the same set of geometric characteristics, in which at least one of the geometric characteristics of the set of geometric characteristics is different from the same geometric characteristics of the stator blades of another family of stator blades.

[0059] It may also be provided that the row of stator blades comprises at least 3 adjacent stator blades each belonging to different stator blade families. In other words, for 3 adjacent stator blades each belonging to different stator blade families, it may be provided that the row of stator blades comprises 3 stator blades separated from each other by azimuthal spacings A0j and A0j+i with i= 1, 2,... and each belonging to different stator blade families.

[0060] Also provide: - that max{A0i} - min{A9j} < 120°, preferably <75°, or even preferably <50°, for i,j = 1, 2,... when ij with i,j < V and V>5 (V: number of blades on said downstream row of stator blades), and / or - that IIA0i-A9adjacentll 120°, preferably <75°, or even preferably <50° with V>5, would make it possible to avoid an excessively large angular sector being completely devoid of stator blades, which could reduce the straightening of the flow downstream of the upstream rotor, thus generating: - an aerodynamic problem linked to a loss of thrust and / or efficiency, and / or - problems with the distribution and / or balancing of weight around the longitudinal axis X and with regard to the aforementioned integration.

[0061] One benefit of the mentioned optimization of angle values ​​is to ensure that there are no more different azimuthal spacings than stator blades (physically impossible), as defined.

[0062] A0i and AQadjacent are two angular sectors or azimuthal spacings (A0, A0j, A0j) adjacent to each other in the circumferential direction, i.e. having a common stator axis (axis around which the blades of the stator 16 are circumferentially arranged).

[0063] The stator axis (axis around which the stator blades are radially arranged) can of course be the longitudinal axis X, in general.

[0064] Furthermore, providing that the number of different azimuthal spacings (A0, A0j, A0j), on all the blades of said downstream row of stator blades, is between 2 and 6 would make it possible to better adapt the geometry of the blade to the local properties of the flow (under incidence) and / or to better distribute the weight of the blade grid (or blades, the two terms are confused) around the longitudinal axis (X) of the thruster.

[0065] Concerning the "incidence" aspect, it is noted that the aircraft incidence (angle a below) can be defined as the angle between the longitudinal axis of the fuselage (axis X1 below) and the direction of the flow upstream of the fuselage (or the direction of forward movement of the aircraft). It can have an angle (angle p below) different from zero degrees between the longitudinal axis X of the propeller and the longitudinal axis X1 of the fuselage - reference 33 below - or of the aircraft, when these axes are projected into a vertical plane passing through the 12H and / or 6H positions and containing the longitudinal axis X of the propeller (the angle p is sometimes called "tilt angle" or "cant angle" in English). This is the plane to be taken into account in figure 2 mentioned below, where the angle p is represented (here, in a non-exclusive / limiting manner, in a situation of mounting the propeller under a wing - reference 31 below - of the aircraft concerned).

[0066] The longitudinal axis of the fuselage (or of the aircraft, axis X1 hereinafter) can be defined as the roll axis of the aircraft, which can correspond to: - to an axis going from the nose (upstream; reference 33a below) to the tail (downstream) of the fuselage, or alternatively - to the axis which passes through the most upstream and most downstream position of the fuselage, in cruising flight. These X and X1 axes may not be parallel ( ? ¥= 0°). For example, this can be useful for reducing the incidence and therefore the 1P forces which are perceived by the rotor blades during the take-off phases. In order to minimize these penalizing effects for the aerodynamics and mechanical strength of the blades, (the absolute value of) the angle II / 3II can vary between 0.5° and 30°, preferably between 2° and 20°, or even preferably between 3° and 10°.

[0067] The "absolute value" aspect of the angle (ll / JII) is important because the inclination: - should typically be downwards if installing the thruster under an aircraft wing, but - could be upwards, in case of installation towards the rear of the fuselage, this to limit the effects of incidence during takeoff and / or landing.

[0068] In this regard, it may also be relevant that the invention can be applied to an aircraft (which will have a longitudinal axis (X1) and will comprise an aeronautical propeller as defined in the present text, with all or part of the characteristics mentioned, a fuselage and a wing to which or to which the propeller will be fixed), this aircraft being usefully such: -- that (the absolute value II / / II of) the angle / 3 between the longitudinal axis (X) of the aeronautical propeller and the longitudinal axis of the aircraft (X1) would vary between 0.5° and 30°, preferably between 2° and 20°, or even preferably between 3° and 10°, and / or -- that we would have: d1 d2, and, d1 or d2 less than 0.75*D, preferably less than 0.5*D or even preferably less than 0.3*D.

[0069] The interest in the angle / 3 is, as above, in increased efficiency during takeoff and / or landing and / or installation towards the rear of the fuselage; The interest linked to d1 or d2 is to cover cases of fixing the aeronautical propeller to (in particular under) a wing or, more generally still, to in particular (under) any wing, of the aircraft concerned.

[0070] It will be noted that, for a propeller according to the invention, fixed in front of the wing of an aircraft seen from the front / front: - d1 can be defined as the axial distance (along the longitudinal axis X) between the trailing edge (BF) of the stator blade at the free end (reference 25 below) and the leading edge (BA) of the airfoil (or wing), and this for the stator blade closest (azimuthal) to the leading edge of the airfoil (or wing) and contained in the angular sector between 12H and 6H passing through 9H (for example, in figure 10 mentioned below, d1 is measured relative to the surrounded blade referenced d1), and - d2 can be defined as the axial distance (along the longitudinal axis X) between the trailing edge of the stator blade at the free end and the leading edge of the wing (or wing), and this for the stator blade closest (azimuthal) to the leading edge of the wing and contained in the angular sector between 12H and 6H passing through 3H (for example, in the same figure 10, d2 is measured relative to the surrounded blade marked d2).

[0071] In other words: - d1 can then concern the most radially inner stator blade (located as mentioned above: typically around 9 o'clock, for a propeller placed under the right wing of the aircraft or around 3 o'clock, for a propeller placed under the left wing), and - d2 can then concern the most radially outer stator blade (located as mentioned above: typically around 3H for a propeller placed under the right wing, or around 9H, for a propeller placed under the left wing).

[0072] Furthermore, to respond to cases of inappropriate blade loads (see above), it may be relevant for the invention to be applicable to said aircraft which would then have the specific feature that the absolute value of said angle / ? (II0II) would vary between 0.5° and 30°, preferably between 2° and 20°, or even preferably between 3° and 10°.

[0073] Furthermore, provide that the relationship between: - the distance (S), along the longitudinal axis (X), between the two median planes, perpendicular to the longitudinal axis, respectively of the upstream rotor row of rotor blades and the downstream stator row of stator blades, and - the maximum diameter of the aeronautical propeller (D), at the radially external ends of the blades of the upstream rotor row of rotor blades or of the downstream stator row of stator blades, (in other words that the spacing (S) between the axis of adaptation of the pitch angle - or the axis where the centers of gravity of said blades are located - of the two upstream / downstream rows and the engine diameter (D), therefore S / D) is between 0.01 and 0.8, and even preferably between 0.15 and 0.35, would make it possible to limit certain critical wake interferences between the two rows of blades and therefore to reduce noise while limiting the axial length of the aeronautical propeller.

[0074] If ground noise is to be reduced, the number of stator blades that can radiate towards the ground should be reduced, so the angularly largest azimuthal spacing(s) (A0, AOj, AOj) will then be located between the blades arranged between the angular positions between 8H and 4H (in the case of a configuration pusher with pylon at 3H or 9H, there may be stator blades 16 between 10H and 2H), in particular or preferably at 2H and 4H and / or at 8H and 10H.

[0075] If we wish to promote a balance of the weight of the propeller and avoid a residual moment on the longitudinal axis X linked to the heterogeneous distribution of the stators, we will favor: - around the longitudinal axis (X) and seen from upstream, a distribution of the blades of the downstream row of stator blades located between 2H and 4H and that between 8H and 10H which will be symmetrical with respect to an axis of symmetry passing through the longitudinal axis (X) and through 12H and 6H, and - that said stator blades of the downstream row are positioned at symmetrical positions (0 and - 0) relative to the axis passing through the longitudinal axis (X) and through 12H and 6H have identical blade thicknesses and heights.

[0076] It is recalled that: - a (blade) thickness corresponds to the maximum length or distance between the intrados and the extrados of a section of this blade, in the direction perpendicular to a straight line which connects the leading edge with the trailing edge of the section, - a height (of blade) is measured between a radially internal end 23 (at the hub or nacelle) and a radially external end 25 (free end) of the blade considered.

[0077] To ensure that there is only one rotor blade wake interacting with one stator blade at a time, and therefore reduce noise sources, we will seek to ensure that the azimuthal spacing between the blade pitch angle adaptation axes of the upstream rotor row and the downstream stator row is defined by: H0 r , n - 0s, mil >1° or preferably >2°, where 0 r ,n and 0s, mcorrespond to the angular position of the adaptation axis of the pitch angle of the n-th blade of the upstream row of rotor blades and the m-th blade of the downstream annular row of stator blades, respectively at a time when the axes of change of pitch of a blade of the upstream row of rotor blades and of a blade of the downstream row of stator blades are aligned, when they are projected onto a plane perpendicular to the longitudinal axis (X), n being a natural integer varying between 1 and B, B being the number of blades of the upstream row of rotor blades and m a natural integer varying between 1 and V. More generally, this will be the axis as defined by "stator axis", for a stator blade with fixed or variable pitch.

[0078] In connection with this unique wake effect, at least some of said blades of said upstream row of rotor blades and / or of the downstream row of stator blades may usefully have variations in chord (C) and thickness (e) between them.

[0079] And, at least some of the blades of said upstream row of rotor blades could also have a heterogeneous distribution around the longitudinal axis (X).

[0080] In addition to an aeronautical propeller as mentioned above, the present description also concerns an aircraft having a longitudinal aircraft axis (X1), the aircraft comprising at least one said aeronautical propeller and a structure to which the aeronautical propeller is fixed.

[0081] In this case, the aircraft structure will typically comprise a fuselage, and the angular sector around the longitudinal axis (X) where the number of blades in the downstream annular row of stator blades is greatest may be located in the upper part and / or towards the fuselage.

[0082] This will limit noise emissions to the ground and protect populations in the vicinity of airports. The noise from the blades located upwards and / or inwards could have reduced radiation towards the ground due to their azimuthal position and the possible screening effects produced by the wing (if located under / on the wing), the fuselage and the mast, pylon or cradle for attaching the propeller to the aircraft.

[0083] If, in a different way, it is desired to minimize the noise radiated towards the passenger cabin and the acoustic interaction with the fuselage, then it will be preferred that the angular sector around the longitudinal axis (X) where the number of blades of the downstream row of stator blades is the greatest is located in the upper part and / or in an area of ​​the downstream row of stator blades furthest from the fuselage.

[0084] Furthermore, increasing the number of stator blades at azimuthal positions close to the mast, pylon or attachment cradle and the wing (if it is immediately close) may also be of interest in reducing the potential effect (pressure rise) towards the upstream rotor. It will then be favourably chosen that the angular sector around the longitudinal axis (X) where the number of blades in the downstream row of stator blades is greater is located where the distance, parallel to the longitudinal axis (X), between the trailing edge of the blades in the downstream row of stator blades and the leading edge of the wing is the smallest.

[0085] Another possible consideration is that the stators opposite the upstream rotor blades are more loaded and have more gyration to straighten. For this, it is recommended that the angular sector around the longitudinal axis (X) where the number of blades in the downstream row of stator blades is greater be located on a side of the thruster where the relevant blades in the upstream row of rotor blades are intended to be ascending, taking into account the direction of rotation defined for the upstream row of rotor blades.

[0086] This increase in the number of blades on this side will allow the stator load to be better distributed, which will also be of interest in reducing noise.

[0087] Each blade of the upstream rotor row may extend in a radial direction from the hub so as to define a radial dimension (or blade height) between said hub and a radially outer end of the blade in question, the individual dimension (possibly of each) of the blades of the upstream rotor row being greater than the radial dimension of each blade of the downstream stator row in question between said casing and a radially outer end of the blade in question. In other words, the blades of the downstream stator row may be truncated at their free end relative to the blades of the upstream annular row. This limits the impact of the vortices formed at the radially outer end of the blades of the upstream rotor row on the blades of the downstream stator row. The term "truncated blade" means that the blade has a reduced radial dimension and / or a reduced radially outer end (or end surface).Alternatively, it may be provided that at least one blade of the upstream row has a radial dimension greater than that of at least one blade of the downstream row. Alternatively again, it may be provided that at least one blade of the upstream rotor row has a radial dimension greater than the individual radial dimension (possibly of each) of the blades of the downstream row.

[0088] The radial dimension of a blade is measured between a radially inner end of the blade, this being located at the (i.e. closest to) the hub (respectively the casing) of the aeronautical propeller, and a radially outer end of the blade. The radially inner end of a blade can be, longitudinally, at the leading edge of the blade (for example, for a fixed blade) or at the pitch change axis of the blade in question. The radially inner end of a blade is also called the "blade root".

[0089] An angular position of each blade about the longitudinal axis can be denoted by the angular position about the longitudinal axis of the inner end of the respective blade. The radially outer end of the blade is the opposite end of the radially inner end. The radially outer end of the blade can be the free end of the blade. The radially inner end and the individual radially outer end (possibly of each) of the blades can be radially aligned, i.e. at the same longitudinal position, or be longitudinally offset from each other.

[0090] The downstream stator row can have between 3 and 25 blades. The number of blades in the upstream rotor row can be different from the number of blades in the annular row. downstream, and we favor B>V+1 or even preferably B>V+2. This makes it possible to further minimize the noise level emitted by the aeronautical propeller.

[0091] As already indicated with reference to the C / E ratio, the strength of the downstream annular row, defined as the ratio between the chord and the spacing between two circumferentially consecutive blades in the circumferential direction, may be less than 3 over the entire radial dimension of each blade. In particular, in a preferred embodiment, the strength is less than 1 at the radially outer end of the blades.

[0092] The ratio between the distance in the longitudinal direction between a median plane of each annular row which is normal to the longitudinal axis, and the diameter of the aeronautical propeller can vary between 0.01 and 0.8, and even preferably between 0.15 and 0.35. The median plane normal to the respective longitudinal axis of each annular row can be the plane containing a respective pitch change axis of each of the blades of the corresponding annular row.

[0093] This limits, or even avoids, interference between the annular rows of blades.

[0094] The upstream rotor row and the downstream stator row may be located at an upstream end portion of the aeronautical thruster in the longitudinal direction or at a downstream end portion of the aeronautical thruster in the longitudinal direction.

[0095] The aeronautical thruster may have a so-called "puller" configuration (upstream rotor row and downstream stator row located at an upstream end portion of the aeronautical thruster) or a so-called "pusher" configuration (upstream rotor row and downstream stator row located at a downstream end portion of the aeronautical thruster).

[0096] In the puller configuration, the upstream rotor row and the downstream stator row may surround a section of the compressor(s) or the gearbox of the aeronautical propeller. In the pusher configuration, the upstream rotor row and the downstream stator row may surround a section of the turbine(s) of the aeronautical propeller.

[0097] In one aspect, the aeronautical propeller may successively comprise, along the longitudinal axis (X), from upstream to downstream: - at least one compressor, - at least one combustion chamber, - at least one turbine driving the compressor(s), and - an air inlet to the compressor(s), the air inlet being located downstream of the upstream rotor row of rotor blades, and upstream of the downstream stator row of stator blades, in other words, longitudinally along the thruster, between the rotor blades and the stator blades.

[0098] According to another aspect, a propulsion assembly for an aircraft is described, comprising an aeronautical propeller as described above and a pylon for attaching the aeronautical propeller to the aircraft, the attachment pylon being connected to one of the blades of the downstream stator row so as to form a single aerodynamic assembly.

[0099] According to another aspect, there is described an aircraft comprising an aeronautical propulsion unit as described above or a propulsion assembly as described above. Brief description of the drawings Other features, details and advantages will become apparent from reading the detailed description below, and from analyzing the attached drawings, in which all the blades are unfaired, and: [Fig.1] is a partial schematic sectional view of a turbomachine usable here, therefore with upstream rotor and downstream stator, in a “pusher” configuration, [Fig.2] is a schematic view of a propeller in a configuration which can be "pulled", in a phase which can be take-off, with therefore an airplane incidence (angle a); [Fig.3] is a partial schematic sectional view of a turbomachine usable here, in a “puller” configuration, [Fig.4] can represent the turbomachine of figure 3 in the section plane IV-IV (stator) normal to the longitudinal axis X, with an example of a possible arrangement of the annular row of blades of the downstream stator, [Fig.5] is a schematic view, following the same sectional plane as that of figure 4, from the front (seen from upstream) illustrating another arrangement of the annular row of blades of the downstream stator; [Fig.6] is a schematic view, still following the same section plane, illustrating another arrangement of the annular row of blades of the downstream stator; [Fig.7] is a schematic view, still following the same section plane, illustrating another arrangement of the annular row of blades of the downstream stator; [Fig.8] is a schematic view, still following the same section plane, illustrating another arrangement of the annular row of blades of the downstream stator; [Fig.9] is a schematic view, still following the same section plane, illustrating a other arrangement of the annular row of blades of the downstream stator; [Fig.10] is a half-schematic front view (seen from upstream) of the solution of Figure 9, with an under-wing attachment of the propeller; [Fig.11] is a schematic half-top view of Fig. 10, with a stator blade configuration that may be that of Fig. 4 or 9; [Fig.12] is a schematic view, still following the same sectional plane as that of fig.4, illustrating another arrangement of the annular row of blades of the downstream stator; [Fig.13] is a schematic view, still following the same section plane, illustrating another arrangement of the annular row of blades of the downstream stator; [Fig.14] schematizes, still following the same section plane, a desired azimuthal spacing between the blades of the upstream rotor and those of the downstream stator; [Fig.15] is a diagram of the single-piece integration of at least one downstream stator blade in the system for attaching the propeller to the aircraft; [Fig.16] shows another solution, with mounting via a fixing cradle between the propeller and a wing of the aircraft; [Fig.17] shows a diagram of an aircraft equipped with two propellers fixed to the fuselage via masts, each propeller respecting a heterogeneous azimuthal spacing of the blades, on the downstream stator, [Fig.18] and [Fig.19] schematize a stator blade (downstream blade) and a way of considering the pitch angle of this blade, figure 19 corresponding to section XVIII-XVIII of figure 18, the latter and figure 2 showing air flows around the propeller (lines with multiple arrows); [Fig.20] shows schematically what the angle, or "azimuthal spacing" AOj or A0j is between two consecutive stator blades, and [Fig.21] can complete figure 2, and schematizes a case of aircraft incidence, side view, with a propeller in a configuration which can be "puller", in a phase which can be take-off, with therefore a non-zero angle P, in the example. Description of the embodiments

[0100] For example, an aeronautical propeller compatible with what the invention proposes could be a turbomachine, like that of figures 1 to 3.

[0101] Any propellant referred to here, such as the turbomachine 10, comprises a hub 12 located upstream (AM) of a motor casing 13. An upstream rotor row 14, annular, of unducted blades 18 is mounted on the hub 12 (around it), and a downstream stator row 16, annular, of unducted blades 18 is mounted on the motor casing 13 (around it). The two rows are spaced from each other along a longitudinal axis X of the turbomachine 10.

[0102] The hub 12 and the engine casing 13 may be combined under the term nacelle 40, the nacelle 40 being the structure around which the rotor 14 and stator 16 blades 18 are arranged and extend. The nacelle 40 is itself fixed to the aircraft that the aeronautical propeller referred to here is to drive.

[0103] As will already have been understood, the orientation qualifiers, such as “longitudinal”, “radial” or “circumferential”, are defined with reference to the longitudinal axis X of the thruster considered, as on the turbomachine 10. The longitudinal direction here corresponds to the direction of advance of the thruster or to the axis of rotation of the blades of the upstream rotor 14. In particular, the longitudinal direction may coincide with a horizontal direction, i.e. perpendicular to the gravitational field. The relative qualifiers “upstream” (AM) and “downstream” (AV) are defined with respect to each other with reference to the flow of gases in the thruster, in the longitudinal direction. The angular position of each of the blades 18 around the longitudinal axis X is identified with respect to a time dial (here seen from upstream for example) whose angular positions at 12H, 3H, 6H and 9H are positioned in a conventional manner.The angular position at 12H is therefore positioned vertically upwards relative to the longitudinal axis X and the angular position at 6H is positioned vertically downwards relative to the longitudinal axis X. The angular position at 3H is positioned horizontally to the right relative to the longitudinal axis X and the angular position at 6H is positioned horizontally to the left relative to the longitudinal axis X. An axis extending radially through the angular positions at 12H and 6H is thus perpendicular to an axis extending radially through the angular positions at 3H and 9H. Absolute position qualifiers, such as the terms "up", "down", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., and the orientation qualifiers, such as the terms “vertical” and “horizontal” refer here to the orientation of the figures and are considered in an operational state of the thruster, typically when it is installed on an aircraft placed on the ground. In this state of the turbomachine 10, the axis passing through the angular positions at 12H and 6H extends in the direction of the gravity field, i.e. vertically. It can however be deduced that a rolling movement of the aircraft in flight on which the thruster is mounted will be such as to cause a rotation of the vertical and horizontal directions as considered in the figures around the longitudinal axis X. In the same way, a rolling movement of the aircraft in flight on which the thruster is mounted will be such as to cause a rotation of the axis passing through the angular positions at 12H and 6H and of the axis passing through the. angular positions at 3H and 9H about the longitudinal axis X. A “lateral zone” of the turbomachine 10 refers to an area that is circumferentially in the vicinity of the angular position at 3H or the angular position at 9H. Similarly, an “upper zone” and a “lower zone” of the thruster refer, respectively, to an area that is circumferentially in the vicinity of the angular position at 12H and to an area that is circumferentially in the vicinity of the angular position at 6H.

[0104] Thus, the downstream stator row 16 (or stator) is fixed around the longitudinal axis X. In other words, the downstream stator row 16 is not driven in rotation around the longitudinal axis X. This does not exclude the possibility that each blade 18 of the downstream stator row 16 may have variable pitch.

[0105] If the aeronautical propulsion system considered is (or comprises) a turbomachine, this will therefore be a turbine engine comprising successively, parallel to the longitudinal axis (X), from upstream to downstream inside the nacelle 40 (including under the engine casing 13): - one (or more) compressor(s) 2, - at least one combustion chamber 4, - one (or more) turbine(s) 6 driving the compressor(s), and - at least one exhaust nozzle 8.

[0106] Among these unducted fan turbomachines, there are known “Unducted Single (or Stator) Fan” (USF) type turbomachines in each of which, as illustrated in figures 1 to 3, the upstream rotor row 14 of unducted blades 18 is mounted to rotate about the longitudinal axis X and the downstream stator row 16 of unducted blades 18 is fixed. The direction of rotation of the blades 18 of the upstream rotor row 14 (or rotor) is not decisive.

[0107] The downstream stator row 16 may be centered on an axis coinciding or not with the longitudinal axis X. In the examples presented, the downstream stator row 16 is centered on the longitudinal axis X. Such a configuration of the upstream rotor row 14 and the downstream stator row 16 makes it possible to utilize, through the downstream stator row 16, the turning energy of the air flow coming from the upstream rotor row 14. The efficiency of the turbomachine 10 is thus improved, in particular compared to a single rotating propeller (like that 14) in the case of a conventional turboprop. The upstream rotor row 14 is driven in rotation around the longitudinal axis X by the turbine(s) 6 which itself drives the compressor(s) 2. The turbomachine 10 generally comprises a speed reduction box (“gearbox” in English) in order to decouple the rotation speed of the turbines 6 relative to the rotation speed of the upstream rotor row 14. Furthermore, one of the advantages of a USF type turbomachine compared to a “Counter-Rotating Open Rotor” type turbomachine is to reduce the tonal noise emitted by the turbomachine because the downstream stator row 16 of unducted blades 18 is fixed.

[0108] As shown diagrammatically in Figures 2 and 3, the thruster may have a so-called “puller” configuration (upstream rotor row 14 and downstream stator row 16 located at an upstream end portion of the thruster) or, as shown diagrammatically in Figure 1, a so-called “pusher” configuration (upstream rotor row 14 and downstream stator row 16 located at a downstream end portion of the thruster).

[0109] In the puller configuration, the upstream rotor row 14 and the downstream stator row 16 may surround a section of the compressor(s) 2 of the turbomachine or of the speed reduction box. In the pusher configuration, the upstream rotor row 14 and the downstream stator row 16 may surround a section of the turbine(s) 6 of the turbomachine 10.

[0110] Regardless of the type of propellant (turbomachine, hybrid, etc.), a fixing system 27 will make it possible to fix the propellant to the aircraft 29 which is equipped with it, and more precisely to its wing 31, or to its fuselage 33, or any other suitable part. Typically, for this purpose, it will be possible to use: - for a fuselage: a 35 mast (as in the examples in figures 3,7), or - for attachment to a wing or a canopy: a pylon 37 (as for example in figures 3, 11 or a cradle 39 (as for example in figure 16).

[0111] The blades 18 of the upstream rotor row 14 and / or of the downstream stator row 16 may have variable pitch. It is thus possible to adapt the pitch of the blades 18 of the turbomachine 10 according to the operating point of the thruster or the flight phase. A pitch change system 38 may be provided, located partly in the nacelle 40 (hub 12 and / or casing 13) in order to adapt the incidence of the blades for each flight phase. Each blade 18 may thus be adjusted in rotation about a respective pitch change axis 19. The individual pitch change axis 19 (possibly of each) of the blades 18 is an axis: - extending radially and / or positioned longitudinally at a medial portion of the respective blade, and - around which the pitch angle of a blade can be adapted.

[0112] In this regard, this disclosure covers cases where: - the timing change axis is perpendicular to the longitudinal axis X, - the timing change axis is not perpendicular to the longitudinal axis X, i.e. say that it is inclined. For example, if the timing change axis has a longitudinal component and / or a circumferential component, with reference to the longitudinal axis X.

[0113] In order to (re)define, if necessary, more precisely the pitch angle of a blade, it is specified that each downstream stator blade 18 defines an aerodynamic profile. For this purpose, each downstream stator blade comprises a stack of sections 30 in the radial direction. One of the sections 30 is shown in Figure 18. Each section 30 extends in a respective section plane which is perpendicular to the radial direction of extension of the corresponding downstream stator blade. Each section 30 comprises an upstream leading edge and a downstream trailing edge between which extend a pressure line 330 and an extrados line 340. Each section 30 defines an aerodynamic profile. Each section 30 also comprises a chord C defined by a straight portion connecting the leading edge to the trailing edge.

[0114] The pitch angle y of each downstream stator blade 18 (see for example figures 18-19) will correspond to the angle formed between, on the one hand, a first axis A1 which is defined by the intersection between the section plane of a reference section 30 among the stack of sections 30 of the downstream stator blade and a plane perpendicular to the longitudinal axis X which may include the pitch axis AC of the downstream stator blade (when the pitch change axis is perpendicular to the axis X, which is normally the case, but not obligatory), and on the other hand, the chord C of the reference section 30 of the downstream stator blade 16. The pitch angle y is measured on the upstream side of the plane perpendicular to the longitudinal axis X which, as above, may include the pitch axis AC of the downstream stator blade 18.The setting angle is measured positively in a direction going from the first axis A1 to the chord C of the reference section 30, and more particularly in a direction coinciding with the direction going from the intrados line 330 to the extrados line 340.

[0115] The reference section 30 of each downstream stator blade 18 is here located, on the corresponding downstream stator blade 16, at a radial distance from the longitudinal axis X which corresponds to 75% of the radially external radius of the corresponding downstream stator blade.

[0116] Each blade 18 of the upstream rotor row 14 and of the downstream stator row 16 extends in a radial direction from the hub 12 so as to define a radial dimension between said hub 12 and a radially outer end of the respective blade 18. In other words, the radial dimension of a blade 18 corresponds to its height between said radially inner 23 and radially outer 25 ends. The radially inner end of each blade 18 is located at the hub 12 of the turbomachine 10. Each blade 18 can in particular be fixed to the hub 12 of the turbomachine 10 at the radially inner end. The radially external end of each blade 18 is here a free end (i.e. non-ducted). It is specified that the span of a blade 18 is consequently the radial distance between its internal 23 and external 25 ends (see figure 9), with: L1 = Re1-Ri1 for a blade in the upstream rotor row, and L2 = Re2-Ri2 for a blade in the downstream stator row.

[0117] Furthermore, each blade 18 of the upstream rotor row 14 and of the downstream stator row 16 has a radially internal radius respectively Ri1, Ri2 considered as the radial distance from the longitudinal axis X of the radially internal end of the blade 18, for example located at the (i.e. closest to) the hub 12 (rotor row) or the casing 13 (stator row). The radially internal end 23 is, in FIG. 3, close to the pitch change axis of the respective blade. The radially internal end of each blade may alternatively be close to the leading edge at the blade root. A radially external radius, such as Re1 or Re2 in FIG. 3, of each blade 18 is considered as the radial distance from the longitudinal axis X of the radially external end of said blade 18, i.e., as the maximum radius of the blade.

[0118] As can be understood by looking at FIG. 4 as an example, the radially outer end 25 of the blades 18 of the upstream rotor row 14 and of the downstream stator row 16 are inscribed, respectively, in an outer casing 20 of the upstream rotor row 14 and an outer casing 22 of the downstream stator row 16.

[0119] A projection, in the section plane IV-IV (see figure 1 or 3), of the external envelope 20 of the downstream stator row 16 can define a circle of radius Re2, or of diameter Ds, which can be centered on the longitudinal axis X (Ds = 2*Re2).

[0120] The diameter D or circle of radius Re1, in a radial section plane at the level of the external envelope 20 of the upstream rotor row 14, can represent the external diameter of the propellant considered, the turbomachine 10 in the example (see figure 1 or 3).

[0121] The radial dimension of each blade 18 of the downstream stator row 16 may be less than the individual radial dimension (possibly of each) of the blades 18 of the upstream rotor row 14 so as to limit the impact of the vortices formed at the radially outer end of the blades 18 of the upstream rotor row 14 with the blades 18 of the downstream stator row 16. The outer casing 20 of the upstream rotor row 14 will then surround the outer casing 22 of the downstream stator row 16 when they are projected in a common projection plane normal to the longitudinal axis X, such as here the section plane IV-IV.

[0122] This must be compatible with clipping (i.e. truncation of the downstream stator blades, as in the solution(s) associated with figures 3 or 15, as non-limiting examples) over 360°, it being specified that homogeneous clipping is not necessarily a requirement. In other words, there may be at least one blade 18 of the downstream stator row (16) having a radius Re2 making it possible to define the circle 22, but other blades of the downstream stator row 16 could have a radius less than Re2.

[0123] Furthermore, to also promote more balanced control of the loads on the blades and the noise generated, it is proposed: - that each blade of the downstream stator row of stator blades 16 therefore has a height, L2 or L21 in the non-limiting example of figure 9, between the radially internal end 23 and the radially external end 25, - the respective heights, such as L2 and L21, of at least two blades 18 of said downstream stator row 16 are usefully and advantageously different.

[0124] It should also be noted that the projection of the outer casing of the downstream stator row 16 in a common projection plane normal to the longitudinal axis X, such as the section plane IV-IV in the example, may also define a circle, or even an oval as above, the center of which may be offset from the longitudinal axis X, for example in the direction of the axis passing through the angular positions at 12H and 6H. The radial distance between the center of the outer casing 22 of the downstream stator row 16 in the form of a circle and the longitudinal axis X may be between 0.005 Ds and 0.2 Ds.

[0125] The circle / oval defined by the outer casing 22 of the downstream stator row 16 may have a radius (for example maximum if an oval shape is concerned) Re2 less than the radius (for example maximum if an oval shape is concerned) Re1 of the outer casing 20 of the upstream rotor row 14.

[0126] Thus, the heterogeneous distribution of the blades 18 of the downstream stator 16 (in the azimuthal direction) may be compatible with other noise reduction technologies, such as “360° clipping”. It is therefore possible, over at least one angular sector: - to arrange heterogeneously (in the circumferential direction) the blades 18 of the downstream stator 16, and - that the blades 18 of the downstream stator 16 each have, or individually, a maximum radius (Re2) or height less than a maximum radius (Re1) or height of the blades 18 of the upstream rotor 14.

[0127] In this case, there may be shorter stator blades 16 between 8H and 4H (in the case of a pusher configuration with a pylon at 3H or 9H, there may be stator blades 16 between 10H and 2H). However, it may be particularly or preferably preferred stator blades in the lower part (between 4H and 8H) and on the sides (between 2H and 4H or between 8H and 10H, towards the outside and / or towards the fuselage); all in order to minimize interaction noise during the incidence phases (landing / takeoff).

[0128] The center of the circle in which the radially external end 25 of each blade 18 of the downstream stator row of stator blades 16 is inscribed could be offset relative to the longitudinal axis X, this making it possible to adapt the configuration of these blades to their environment (position on the aircraft / types of noise to be controlled / fluid flow to be favored / mechanical constraints to be satisfied, etc.).

[0129] Having fewer said stator blades 16 than said upstream rotor blades 14 may also be useful, to combine noise reduction, aerodynamic efficiency, lower stress loading of certain downstream stator blades and limitation of weight and size. It is recommended that: B > V+1, or preferably B > V+2.

[0130] In accordance with an important aspect mentioned above, it is therefore interesting here to have a heterogeneous azimuthal spacing of the blades of the downstream stator 16, for the reasons mentioned: aerodynamic, acoustic and / or integration constraints.

[0131] Several implementation methods are possible depending on the objective (aerodynamics, acoustics, integration, etc.) or the multi-trade compromise sought.

[0132] As already indicated, two adjacent blades, such as 18a, 18b, of the downstream stator row of stator blades 16 have between them, around the longitudinal axis (X), an azimuthal spacing (A0, A0j, A0j) defined by the angle between respective axes 180a, 180b.

[0133] These respective axes, on the stator 16, are axes: - either adaptation of a pitch angle (axis 19 mentioned above) of said two adjacent blades, when these axes are projected in a plane perpendicular to the longitudinal axis X and if said two adjacent blades have a variable pitch angle, - either radial to the longitudinal axis X and / or passing through the radially internal ends 23 or the radially external ends 25 (max radius, Re2 on the Error! Source of the reference not found.), or through the centers of gravity of said two adjacent blades, respectively, if said two adjacent blades have a fixed pitch angle, - either : -- for one of said respective axes, adaptation of a pitch angle of one of said two adjacent blades (above-mentioned axis 19), when the blade, such as 18a, has a variable pitch angle, -- the other being radial to the longitudinal axis X and / or passing through the end radially internal 23 or by the radially external end 25 or by the center of gravity of said adjacent blade, such as 18b, when the latter has a fixed pitch angle.

[0134] Thus the axes 180a, 180b, 19 are interchangeable in the cases presented and can be interchanged, in particular in the figures.

[0135] As an example, Figure 20 shows schematically what the angle, or "azimuthal spacing" A9j or A9j is between two consecutive stator blades, such as the blades 18a, 18b with respective radial axes 180a, 180b. This is the smaller angle of the two, circumferentially, between said axes 180a, 180b, here around the axis X.

[0136] In the case where one of the stator blades 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 38 or to reduce the weight), the main axis of the blade can therefore be defined by the line perpendicular to the longitudinal axis X passing through the leading edge (BA) at the blade embedding / root 23 or passing through the center of gravity of the blade or at the blade tip 25 (max radius, Re2).

[0137] In this context, to present the heterogeneous distribution sought around the longitudinal axis X, at least some of said blades 18 of the downstream stator row 16 are arranged in such a way that there are at least two said adjacent blades, such as 18a, 18b, of the downstream stator row 16 which have between them an azimuthal spacing A9 or A9j, such that: A9i 3607V; A9i > (3607V) +1 ° or A9i < (3607V) -1 °, with V which defines the number of blades 18 on said downstream stator row 16; and / or that there are at least two azimuthal spacings (between the blades 18 of the downstream stator row 16) such that the values ​​of A9j and A9j are distinct when ij with i,j = 1, 2, ... and i,j < V.

[0138] Note that i and j are indices. ij, i,j < V and i,j = 1, 2, ... with V which therefore defines the number of blades on said downstream stator row of stator blades; that is to say i and j are different and can take an integer value (any) among 1, 2, 3, ... and (at most) V. It is only if all the azimuthal spacings are different (therefore heterogeneous) that i or j can take the value i=V or j=V.

[0139] A deviation of at least 1° is thus necessary to induce a significant effect linked to heterogeneous azimuthal spacing, preferably > 3° or even preferably > 5°.

[0140] In a generic manner, and as can be seen by way of non-limiting example in Figure 3, said azimuthal spacings are each defined by the circumferential distance E between two consecutive blades, 18a, 18b, which distance varies according to the position radial and azimuthal spacings of the blades 18 concerned. These azimuthal spacings can therefore be characterized by the aforementioned angle A0, A0j or A0j, when these axes are projected in a plane perpendicular to the longitudinal axis, X, of the aeronautical propeller. As a reminder, E=r*A0 (or Ej=r*A0j), with A0 measured in radians and r which is the radial distance measured in meters relative to the longitudinal axis X.

[0141] In a very generic embodiment, all the spacings between two adjacent blades of said downstream stator row 16 in the azimuthal direction may be different, as illustrated in FIG. 5. This may be advantageous from an acoustic point of view to decorrelate the noise sources emitted by the stator 16 or modify the directivity of the sound, i.e., the areas where the acoustic radiation is maximum.

[0142] Even if, on the downstream stator row 16, only one or only some of said azimuthal spacings between two adjacent blades is / are different, under the conditions specified above, from the majority of the other azimuthal spacings between two said adjacent blades, which would then be identical, it will be noted that in a preferred embodiment, one or more of the parameters or characteristics below is / are respected by the proposed solution: - a) at least two adjacent blades 18 have an azimuthal spacing (A0 or A0 such as A0 ; #= where V is the number of downstream stator blades 16. This ensures that at least one stator blade 16 is not positioned homogeneously around the longitudinal axis, X, of the aeronautical propeller, - b) max{A0i] - min{A0 ;} < 120°, preferably < 75°, or even preferably < 50°, for i,j = 1, 2,... with ij and i,j < V (if the number of stator blades 16 allows it, i.e. if for example V > 5); this ensures that the difference between the azimuthal spacing of any two adjacent blades 18 is limited. For example, in Figure 4, this criterion implies that A07- A08 < 120°; the interest is to avoid too large an angular sector being completely devoid of stator blades, which could reduce the straightening of the flow downstream of the rotor 14 and therefore produce a loss of thrust and efficiency. This can also pose problems for the distribution of the weight around the longitudinal axis X and the integration of the thruster on the aircraft; - c) ||A0j - A0 adjacent|| < 120°, preferably < 75° or even preferably < 50° (if the number of stator blades allows it, i.e. if for example V > 5); this ensures that the gap between two adjacent (consecutive) azimuthal spacings is limited. This criterion can be particularly useful to avoid excessively large spacing differences over an angular sector. The interest is to avoid an excessively large angular sector being completely devoid of stator blades 16, which could again reduce the flow straightening downstream of the rotor 14 and therefore produce a loss of thrust and efficiency. Problems of weight distribution around the longitudinal axis X and / or integration may also arise.

[0143] The above value ranges should also be sufficient to be able to modify the sound directivity (and thus reduce noise towards the ground / fuselage) by increasing the azimuthal spacing between the stator blades 16 in a desired angular region around the longitudinal axis X.

[0144] On the first point, we have already explained the impact of the forces and moments called 1 P forces, in the plane of the rotor 14 and the unsteady forces and dependent on the azimuthal position of the blade 18. For example, when the aeronautical propeller is installed under the wing, a descending blade is subjected to increased forces compared to a rising rotor blade. Note that this can however be the opposite in the case where the aeronautical propeller is installed at the rear. Indeed, the wing can create a downward flow ("downwash", negative incidence) downstream of its trailing edge. In this case, a rising blade can be subjected to increased forces compared to a descending blade. Thus, we can find ourselves in a situation of negative or positive upstream incidence. Located downstream of the upstream propeller 14, the stator blades 16 will also have a variable load depending on their azimuthal position. We can then choose the following: - the stator blades opposite the descending blades of the rotor 14 being less loaded and having less gyration to straighten, a need for fewer stator blades 16 is taken into account in this zone. For example, a need for fewer stator blades 16 in the right lateral zone (from 45° to 135° with 0° the position at 12H) in the case of a rotor 14 rotating clockwise seen from the front (upstream), and / or - the stator blades 16 axially opposite the rising blades of the rotor 14 being more loaded and having more gyration to straighten, a need for more stator blades in this zone is taken into account: For example, need for more stator blades 16 in the left lateral zone (from -45° to -135° with 0° the position at 12H) in the case of a rotor 14 rotating clockwise, seen from the front (upstream).

[0145] Preferably, the number of azimuthal spacings / angles (A0A0 ; , A0 ;) different varies between 2 and 6. Indeed, increasing the number of different spacings may increase the number of stator blades to be designed (several families / groups of blades would be possible). A design of each stator blade adapted to its azimuthal position may be necessary. For example, local chord modifications may be necessary to minimize azimuthal deviations on the stator blade load, and the grid strength, which is defined by the C / E ratio at a given radial position. Other geometric parameters of the blades could also vary: thickness, camber, arrow, dihedral, ... This would make it possible to better adapt the geometry of the blade to the local properties of the flow (under incidence) and / or to better distribute the weight of the stator blades 16 around the longitudinal axis of the aeronautical propeller to facilitate the balancing of the engine.

[0146] Below, several embodiments compatible with the above characteristics, and which may be favored, are presented.

[0147] It has been identified that the noise from the interaction between the wake of the upstream rotor 14 and the downstream stator 16 produces acoustic radiation on the stator blades of the “dipole” type. This implies that the interaction noise from the stator 16 is not axisymmetric, but depends on the azimuthal position (or even the pitch if it exists) of the stator blades 16. Thus, by using at least one of the above characteristics a), b) or c), which can therefore be combined in whole or in part, it will be possible to optimize the azimuthal position of the blades of the stator 16 in order to reduce the noise emitted towards the ground and / or towards the cabin (fuselage) and the passengers, and / or in any desired direction, in order to act on at least one of the following criteria: limit noise disturbance, promote the aerodynamics of the propeller, improve the performance and integration of the aeronautical propeller installed in the aircraft.

[0148] Assuming that the pitch deviations between the stator blades 16 measured at 0.75xRe2 (reference radius) are negligible (~ 0°, as for example in cruise flight in isolated configuration), that the pitch angles of the stator blades 16 are -90° and that most of the noise is generated at the radially outer end 25 of the blades, the blades that emit the most noise towards the ground are located at angles that vary between [2H - 4H] and [8H and 10H], Thus, one of the preferred embodiments envisages increasing the spacing between the blades (or limiting the number of blades) in these angular sectors on the sides of the stator 16 (around 3H and 9H), as illustrated for example in Figure 6.

[0149] In another configuration which conforms to at least one of the above characteristics a), b) or c) and which may be preferred, it will be possible, as illustrated by way of example in figures 7 to 10, - either place a larger number of stator blades 16: -- in the upper part (between 10 a.m. and 2 a.m.) and / or -- inwards, fuselage side 33 (between 2 and 4 o'clock if the fuselage is to the right of the propeller, front / upstream view, or between 8 and 10 o'clock if the fuselage is to the left of the propeller, front / upstream view); this will limit noise emissions towards the population. Indeed, the noise of stator blades 16 located upwards and / or inwards could have reduced radiation towards the ground due to their azimuthal position and possible screening effects produced by a said fixing system 27, the wing 31 (if located under / on the wing) or a fuselage 33, - or, if it is desired to minimize the noise radiated towards the passenger cabin (fuselage 33), place a greater number of stator blades 16 towards the outside, diametrically opposite the fuselage 33 (between 8H and 10H if the fuselage is to the right of the propeller, seen from the front / upstream, or between 2H and 4H if the fuselage is to the left of the propeller, seen from the front / upstream), so that the most numerous stator blades 16 are the furthest from the fuselage.

[0150] The final choice will depend on the noise reduction objectives for the thruster architecture, as shown in Figures 5 to 9.

[0151] In all these cases, increasing the number of stator blades 16 (i.e. therefore reducing the azimuthal spacing: A0 or A0, or A0 ;) in the upper part of the stator can be beneficial both for acoustics and for aerodynamics, with the reservation that this can present a difficulty for integration under the casing 13 if there is a mast, pylon or fixing cradle 27 or any structure or system for attaching the propeller to the aircraft.

[0152] Regarding acoustics, it is (a priori) the stator blades 16, in the upper part, which radiate the least noise towards the ground. For aerodynamics, these are among the most loaded stator blades 16, because the upstream incidence (angle a / aircraft incidence, as in the example of figure 2) is not totally filtered by the upstream rotor 14.

[0153] Thus, as illustrated by way of example in figures 10-11, increasing the number of blades in the upper part of the stator 16 would make it possible to better distribute this load. Furthermore, increasing the number of stator blades 16 at the azimuthal positions close to the attachment system 27, the wing 31 or the fuselage 33 may also be of interest in reducing the potential effect (pressure rise) of this obstacle (and / or the mast and / or the wing) towards the upstream rotor 14. In other words, thus increasing the number of stator blades 16 may help to “filter” or reduce the rise, linked to the presence of said obstacle, of the pressure towards the upstream rotor 14. It will then be preferable to increase the number of stator blades 16 in the angular sector of the stator 16 where the distance between the trailing edge BF of the stator blades 16 and the leading edge 310 of the wing (or even the attachment system 27) is smaller.In this regard, we recall the useful case where d1 < d2, as in the solution illustrated as an example in Figure 11. This is. particularly relevant when d1 or d2 is / are less than 0.75*D, preferably 0.5*D or even more preferably 0.3*D.

[0154] In yet another configuration both conforming to at least one of the above characteristics a), b) or c) and which may be preferred, it will be possible, as illustrated by way of example in Figure 12 and for mainly aerodynamic reasons, to increase the number of blades (or therefore reduce the azimuthal spacing) on ​​the side of the descending blade 18 of the upstream rotor 14. Indeed, the blades of the stator 16 axially opposite the descending blades of the upstream rotor 14 will be more loaded and will therefore have more gyration to straighten. Increasing the number of blades of the stator 16 on this side would make it possible to better distribute the load of these stator blades 16, which may also be of interest for reducing noise.

[0155] In yet another configuration both conforming to at least one of the above characteristics a), b) or c) and which may be preferred, it may be provided, as illustrated by way of example in FIG. 13, that the distributions of the blades 18 of the stator 16, right side (around 9H, seen from the front / upstream of the thruster) and left side (around 3H, seen from the front / upstream of the thruster) are symmetrical (for example, with respect to an axis of symmetry passing through 12H and 6H).

[0156] This makes it possible to balance the weight of the propeller and to avoid a residual moment on the longitudinal axis X linked to the heterogeneous distribution of the blades of the stator 16.

[0157] In this case, the stator blades 16 located at symmetrical positions (0 and - 0) relative to the vertical axis passing through 12H and 6H will favorably present identical geometric characteristics, in particular the thickness (e) - see example figure 19 -, the blade height L2, L21 (or clipping),..., the blade pitch angle not being concerned, this being able to be variable in order to adapt the incidence of the blades to the local properties of the flow, which will make it possible to better distribute or homogenize the load of the blades in the azimuthal direction, in particular during the phases of flight in incidence (angle a).

[0158] Another critical criterion that one may usefully wish to take into account for the aforementioned purposes is linked to the azimuthal gap or spacing between the blades of the upstream rotor 14 and those of the downstream stator 16. This azimuthal spacing between the axes of the blades, or change in pitch of the rotor 14 and stator 16 blades, is given by the relation: H0r , n - 0s, mil >1° or preferably >2°, where 0 r , n and 0 s , m correspond to the angular positions of the axis of the n-th rotor blade 14 and the m-th stator blade 16, respectively at a time when the blade axes or pitch change axes of a rotor blade 14 and a stator blade 16 are aligned, when projected onto a plane perpendicular to the axis longitudinal (X). It is recalled that n is a natural whole number and varies between 1 and B (number of rotor blades 14) and m varies between 1 and V (number of stator blades 16).

[0159] The interest of this criterion is to ensure that there is only one rotor blade wake 14 interacting with a stator blade 16 at a time, which makes it possible to reduce the noise sources. The implementation thus proposed makes it possible to change the periodicity of the interaction between the rotor blade wake 14 and the stator 16 at the origin of the tonal interaction noise. The acoustic impact results in a reduction in the amplitude of the BPF - blade passing frequency - (noise level) and therefore in the emergence of said BPF compared to the broadband noise. The in-flight noise (Effective Perceived Noise Level, EPNL, according to the acoustic regulations) can thus be lower, due to a reduced emergence of the lines compared to the broadband noise. The total acoustic energy remains roughly the same, but is redistributed to higher order harmonics.Thus, if the number of rotor 14 and stator 16 blades does not allow this constraint to be respected with a uniform spacing (as in the case illustrated in figure 14 with twelve rotor 14 blades and eight stator 16 blades), it is possible to vary the azimuthal position / spacing of certain rotor 14 and / or stator 16 blades in a non-uniform manner. In this case, possible variations in chord and thickness of the blades are possible in order to maintain a quasi-constant average C / E solidity at each radial position. In this figure 14, where the upstream rotor 14 and the downstream stator 16 are seen from the front, seen from the upstream of the rotor, the blades of the downstream stator are partially hidden and the lines with:. - a discontinuous line of points indicates the stacking axes or the axes 19 of variation of the pitch of the rotor blades 14, and - a discontinuous line of dots and dashes indicates the stacking axes or said axes (19) of variation in the pitch of the stator blades 16.

[0160] At least to minimize azimuthal deviations on the stator blade load and / or correlate noise sources between the blades, a law defining the fluctuation of solidity in azimuth, for each given radius, can thus be defined, making it possible to maintain and guarantee an average azimuthal solidity for each radius: ) = S in k (r)A^ / v k=1 k where n(r) denotes the average solidity at a given radius r, II fe (r) = C k (D k (r) the solidity between two blades, such as 18a, 18b adjacent (consecutive) of stator 16, at a given radius r, V the number of blades of stator 16 and Ai9 k the angular pitch between these two blades, at the same given radius r. This corresponds to the C / E solidity resulting from an average weighted by the azimuthal spacing; see figure 8 as a non-limiting example.

[0161] The mean azimuthal solidity n(r) can be expected to be less than 3 over the entire span and / or less than 1 at the radially outer ends.

[0162] The angular pitch between two downstream stator blades 16 or two adjacent axes is therefore considered, as defined for Ai9 k . The difference between Ai9 k and A0j is such that: - for Ai9 k with k=1,2,..,V; it can therefore have two different indices with the same azimuthal spacing (i.e., the same value in radians or degrees). Note that for example, in figures 8 and 9 there are several equal azimuthal spacings and all called in the same way A9i; - for A9j with i=1, 2,...and i < V: each index then corresponds to a different azimuthal spacing or having a different value in radians / degrees. This is the definition that must be used by default in the context of this disclosure.

[0163] Thus, it appeared, unexpectedly, that if n(r) respects the same criteria as C / E, then the performance of the results is increased by more than 3%, results in support.

[0164] Yet another aspect may be considered, namely integrating at least one blade 18 of the downstream stator 16 into the fixing system 27 (bifurcation) in order to reduce the effects of the installation. This stator will then have a complementary structural function.

[0165] Figure 15 represents an example of such a case. This figure shows a propulsion assembly 24 for an aircraft. The propulsion assembly 24 comprises a propellant 10 and the system, such as the pylon 37, for attaching 27 the propellant 10 to the aircraft. The attachment system 27 (pylon 26) is connected to one of the blades 18 of the downstream stator row 16 so as to form a single aerodynamic assembly. For this purpose, the attachment system 27 (pylon 37) can be connected to one of the blades 18 of the downstream stator 16 by continuity of material. In other words, the attachment system 27 (pylon 26) can be made of one material with one of the blades 18 of the downstream stator 16.

[0166] Alternatively: - the fixing system 27 (pylon 37) can be connected to one of the blades 18 of the downstream annular row 16 by means of one (or more) fixing means, or - the part of the downstream stator 16 integrated into the attachment system can have a variable setting. The attachment system 27 (pylon 37) also has an aerodynamic profile similar to an aerodynamic profile of the blades 18 of the downstream stator 16. The attachment system 27 (pylon 37) therefore has the same effect on the air flow from the upstream annular row 14 as the blades 18 of the downstream stator 16. Such an arrangement makes it possible to further reduce the noise emitted by the thruster 10.

[0167] If the stator blades are identical (i.e. belong to the same family of stator blades), the channel between the pylon 37 and the blades 18 of the downstream annular row 16 is reduced, which can generate shocks and accelerate the flow, subsequently causing an increase in aerodynamic losses and therefore a drop in efficiency.

[0168] In the case of a pylon 37 connected to one of the blades 18 of the downstream annular row 16 by means of one (or more) fixing means, the downstream annular row 16 may comprise blades 18 belonging to at least 3 families of stator blades.

[0169] The pylon being connected to one of the blades 18 of the downstream annular row 16, it can be considered as part of a family of stator blades.

[0170] It may be provided that the pylon 37 and the two blades adjacent to the pylon 37 of the downstream annular row each belong to a distinct family of stator blades. In other words, the two blades 18 of the downstream annular row located on either side of the pylon 37, and the pylon 37 belong to three different families of stator blades.

[0171] This makes it possible to better adapt the aerodynamic operation of the stator blades, and, in particular, to avoid possible separations at the leading edge because there are modifications in the flow incidence at the leading edge of the stator blades induced by the presence of the pylon.

[0172] Yet another noise reduction factor can be identified, when, as for example in Figure 3 or 15: - the rotor 14 and the stator 16 are located towards an upstream end of the propeller ("puller" configuration), - the nacelle 40 has an opening 41 defining an air inlet which may in particular be an inlet of a primary air flow towards the turbomachine 10 (precisely towards the compressor 2), and - on the nacelle 40, the opening 41 is located axially between the rotor 14 and the stator 16, and even more precisely, and preferably, between the axes of the respective blades 18 of the rotor 14 and stator 16.

[0173] This makes it possible to reduce the span (and therefore Re2-Ri2 by increasing Ri2) of the downstream stator 16, particularly in connection with "clipping". The size of a blade, and particularly its span, is a contributor to radiated noise. Thus, such a configuration will reduce the noise of the turbomachine.

[0174] On the nacelle, the air inlet 41 can be placed over 360° (crown) or along only an angular sector. The air inlet 41 can have a spout projecting from the nacelle.

[0175] With such a configuration, the turbomachine 10 (gas turbine / core engine) will operate in a conventional manner, so that the air entering the opening 41 will be accelerated and compressed by the compressor(s) 2 before serving in the combustion chamber(s) and then passing into the turbine(s).

[0176] Independently of the nacelle, that is to say just as soon as the propeller comprises a turbomachine 10 (with gas turbine) comprising: - a hub 12 provided with an upstream rotor row 14, and - a motor casing 13 provided with a downstream stator row 16 located downstream (AV) of an upstream rotor row 14, an air inlet - such as 41 - bringing air to the compressor(s) will be usefully located: -- downstream of the upstream rotor row 14 of rotor blades, and -- upstream of the downstream stator row 16 of stator blades, in other words, longitudinally along the thruster, between the rotor blades and the stator blades.

[0177] As we have understood, such a turbomachine can then successively comprise, along the longitudinal axis (X), from upstream to downstream: - at least one compressor 2, - at least one combustion chamber 6, - at least one turbine 4 driving the compressor(s), and - said air inlet 41.

[0178] This has the consequence that the radial dimension of the blades 18 of the downstream annular row 16 could be further reduced in order to escape the vortices formed at the end of the blades 18 of the upstream annular row 14, which reduces the efficiency of the turbomachine 10.

Claims

Claims

1. Aeronautical thruster (10) having a longitudinal axis (X) and comprising a casing (13) and, spaced from each other along said longitudinal axis (X), an upstream rotor row of rotor blades (14), unducted, and a downstream stator row of stator blades (16), unducted and extending around the casing (13), two adjacent blades (18a, 18b) of said downstream stator row of stator blades (16) having between them, around the longitudinal axis (X), an azimuthal spacing (A0, AOj, AOj) defined by the angle between respective axes (180a, 180b, 19): -- either adaptation of a pitch angle of said two adjacent blades, when these axes are projected in a plane perpendicular to the longitudinal axis (X) and if said two adjacent blades have a variable pitch angle, -- either radial to the longitudinal axis (X) and passing through the radially inner ends (23) or the radially outer ends (25) of said two adjacent blades or through their centers of gravity, respectively, if said two adjacent blades have a fixed pitch angle, -- either, for one of said respective axes, for adapting a pitch angle of one of said two adjacent blades, when the blade has a variable pitch angle, and, the other, radial to the longitudinal axis (X) and / or passing through the radially internal end (23) or through the radially external end (25) or through the center of gravity of said adjacent blade, when the latter has a fixed pitch angle, and around the longitudinal axis (X), an angular position at 12H is defined as positioned vertically upwards relative to the longitudinal axis (X) and an angular position at 6H as positioned vertically downwards relative to the longitudinal axis (X), the assembly being characterized in that at least some of said blades of said downstream stator row of stator blades (16) have a heterogeneous distribution around the longitudinal axis (X), such that: - that there are at least two said adjacent blades of said downstream stator row of stator blades (16) which have between them a said azimuthal spacing A0j, such that A9j 3607V; AOj > (3607V) +1 ° or AOj < (360° / V) -1 °, and / or - that there are at least two azimuthal spacings such that the values ​​of A0j and AOj are distinct when ij with i,j = 1, 2,... and i,j < V, with V which defines the number of blades on said downstream stator row of stator blades (16), in which there are at least 3 families of stator blades, preferably at least 5 families of stator blades, and in which each family of stator blades comprises one or more stator blades, the stator blades of the same family which comprises several stator blades having the same set of geometric characteristics, in which at least one geometric characteristic of the set of geometric characteristics is different from the same geometric characteristics of stator blades of another family of stator blades.

2. An aeronautical propeller (10) according to claim 1, which, of the USF type, comprises a single annular row of unducted rotor blades (14), which is said upstream rotor row of rotor blades.

3. Aeronautical thruster (10) according to any one of the preceding claims, in which A0j > (360° / V) +3° or A0j < (3607V) -3°, or even preferably A0j > (3607V) +5° or A0j < (3607V) -5°.

4. An aeronautical thruster (10) according to any preceding claim, wherein all azimuthal spacings between two adjacent blades of the series of blades of said downstream stator row of stator blades (16) are different from each other.

5. Aeronautical thruster (10) according to any one of the preceding claims, in which, on at least one of the upstream rotor row of rotor blades (14) and downstream stator row of stator blades (16), there is a ratio C / E between the chord, C, and the azimuthal spacing E between two consecutive downstream stator blades (16), around the longitudinal axis (X) such that C / E is less than 3 over the entire span.

6. Aeronautical propeller (10) according to claim 5, in which the C / E ratio is less than 1 at the radially external ends (25) of two blades of the same row, upstream rotor and / or downstream stator, said blades being consecutive, or adjacent, circumferentially or azimuthally.

7. Aeronautical thruster (10) according to any one of the preceding claims, in which, on at least one of the upstream rotor row of rotor blades (14) and downstream stator row of stator blades (16), the average azimuthal solidity n(r) is less than 3 over the entire span and / or less than 1 at the radially outer ends, where n(r) denotes the average solidity at a given radius r, n k (r) = C k (D k (r) the solidity between two adjacent stator blades at a given radius r, V the number of stator blades and A7 k the angular pitch between these two blades, at the same given radius r.

8. An aeronautical propeller (10) according to any one of the preceding claims, wherein the upstream rotor row of rotor blades (14) and the downstream stator row of stator blades (16) have different numbers of blades (18).

9. An aeronautical thruster (10) according to any preceding claim, wherein: - at least some of the blades (18) of at least one of those of the upstream rotor row of rotor blades (14) and of the downstream stator row of stator blades (16) are connected to a variable timing system (38) allowing their timing angle to be changed by rotation around their respective axes (19, 180a, 180b), each radial to the longitudinal axis (X).

10. An aeronautical propeller (10) according to any one of the preceding claims, wherein all the blades (18) of the downstream stator row of stator blades (16) have a homogeneous distribution around the longitudinal axis (X), except at the location of a single angular sector.

11. An aeronautical thruster (10) according to claim 10, wherein all the blades (18) of the downstream stator row of stator blades (16) have a homogeneous distribution around the longitudinal axis (X) such that A0 < 3607V, for any azimuthal spacing between two (circumferentially) adjacent / successive blades concerned except at the location of a single angular sector where the azimuthal spacing is different and limited between 15° and 75°, or preferably between 25° and 60°.

12. Aeronautical propeller (10) according to any one of the preceding claims, in which the number B of blades of the upstream rotor row of rotor blades (14) is greater than the number V of blades (18) of the downstream stator row of stator blades (16), and preferably B > V+1, or even preferably B > V+2.

13. Aeronautical thruster (10) according to any one of the preceding claims, in which the radially external ends of the blades (18) of the downstream stator row of stator blades (16) are inscribed in an external envelope (22) of which a projection in a plane (IV-IV) perpendicular to the longitudinal axis (X) defines a circle.

14. Aeronautical propeller (10) according to any one of the preceding claims, in which the radially external end of each blade (18) of the upstream rotor row of rotor blades (14) is inscribed in a first circle (20) and the radially external end of each blade (18) of the downstream stator row of stator blades (16) is inscribed in a second circle (22), the radius (Re2) of the second circle (22) being less than the radius (Re1) of the first circle (20).

15. Aeronautical thruster (10) according to claim 13 or 14, wherein the center of said circle in which the radially outer end of each blade (18) of the downstream stator row of stator blades (16) is inscribed is offset relative to the longitudinal axis (X).

16. An aeronautical thruster (10) according to any preceding claim, wherein: - each blade of the downstream stator row of stator blades (16) has a height (L2, L21) between the radially inner end (23) and the radially outer end (25), and - the respective heights (L2, L21) of at least two blades (18) of said downstream stator row (16) are different.

17. Aeronautical thruster (10) according to any one of the preceding claims, in which max{A0j} - min{A0j} < 120°, preferably <75°, or even preferably <50° for i,j = 1, 2,... with ij and i,j < V.

18. An aeronautical thruster (10) according to any preceding claim, wherein ||A0j - A0 adjacent || < 120°, preferably <75°, or preferably <50° for i= 1, 2, ... with i < V.

19. Aeronautical propeller (10) according to any one of claims 16 and 17, in which the number of blades (18) of the downstream stator row of stator blades (16) is greater than or equal to 5, V>5.

20. An aeronautical thruster (10) according to any one of the preceding claims, wherein the number of different azimuthal spacings (A0, A0j, A0j) on all the blades (18) of said downstream stator row of stator blades (16) is between 2 and 6.

21. An aeronautical propeller (10) according to any preceding claim, wherein the ratio between: - the distance (S), along the longitudinal axis (X), between the two median planes, perpendicular to the longitudinal axis, respectively of the upstream rotor row of rotor blades (14) and of the downstream stator row of stator blades (16), and - the maximum diameter (D) of the aeronautical propeller (10), at the radially external ends of the blades (18) of the upstream rotor row of rotor blades (14) or of the downstream stator row of stator blades (16), is between 0.01 and 0.8, or preferably between 0.15 and 0.

35.

22. An aeronautical thruster (10) according to any preceding claim, wherein the azimuthal spacing between the rotor (14) and stator (16) blade axes (180a, 180b, 19) is given by the relationship: H0 r , n - 0s, mil >1° or preferably >2° at a time when the blade axes (180a, 180b, 19) of a rotor blade (14) and a stator blade (16) are aligned, when projected onto a plane perpendicular to the longitudinal axis (X).

23. Aeronautical propeller (10) according to any one of the preceding claims, in which the numbers of blades (18) of the upstream rotor row (14) and of the downstream stator row (16) are, respectively, 12 and 10, or 14 and 12 or 14 and 11.

24. Aeronautical thruster (10) according to any one of the preceding claims, comprising successively, along the longitudinal axis (X), from upstream to downstream: - at least one compressor (2), - at least one combustion chamber (4), - at least one turbine (6) driving the compressor(s), and - an air inlet (41) to the compressor(s) (2), the air inlet (41) being located downstream of the upstream rotor row of rotor blades (14), and upstream of the downstream stator row of stator blades (16).

25. An aeronautical propeller (10) according to any preceding claim, wherein the set of geometric characteristics of a stator blade comprises chord, thickness and height.

26. An aeronautical propeller (10) according to the preceding claim, wherein the set of geometric characteristics of a stator blade further comprises at least one of camber, sweep and dihedral.

27. ​​An aeronautical propeller (10) according to any one of the preceding claims, wherein the row of stator blades comprises at least 3 adjacent stator blades each belonging to different stator blade families.

28. An aeronautical propeller (10) according to any one of the preceding claims, wherein a fixing system (27) is connected to one of the blades (18) of the downstream annular row by means of one or more fixing means.

29. Aeronautical thruster (10) according to the preceding claim, in which the fixing system (27) is a pylon (37).

30. Aeronautical propeller (10) according to the preceding claim, in which the pylon (37) and the two blades (18) adjacent to the pylon (37) of the downstream annular row each belong to a distinct family of stator blades.

31. Aircraft having a longitudinal axis (X1) and comprising an aeronautical propeller (10) according to any one of the preceding claims, a fuselage (33) and a wing (31) to which or to which the aeronautical propeller (10) is fixed, in which the absolute value of the angle (ll / JII) between the longitudinal axis (X) of the aeronautical propeller and the longitudinal axis of the aircraft (X1) varies between 0.5° and 30°, preferably between 2° and 20°, or even more preferably between 3° and 10°.

32. Aircraft having a longitudinal axis (X1) and comprising an aeronautical propeller (10) according to any one of claims 1 to 24, a fuselage (33) and a wing or sail (31) to which or to which the aeronautical propeller (10) is fixed, in which d1 d2 and d1 or d2 is less than 0.75*D, preferably 0.5*D or even more preferably 0.3*D, with: - d1 which can be defined as the axial distance (X) between the trailing edge (BF) of the stator blade towards the free end (25) and the leading edge (BA) of the airfoil (or wing), and this for the stator blade closest azimuthally to the leading edge of the airfoil, or wing, and contained in the angular sector between 12H and 6H passing through 9H, and - d2 can be defined as the axial distance (X) between the trailing edge (BF) of the stator blade at the free end and the leading edge of the airfoil, or wing, and this for the blade stator closest azimuthally to the leading edge of the wing, or wing, and contained in the angular sector between 12H and 6H passing through 3H.

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