Aeronautical thruster

Abstract

The invention relates to an aeronautical thruster (10) with a longitudinal axis (X), comprising a hub (12), an annular row of non-ducted upstream rotor blades (14) and an annular row of non-ducted downstream stator blades (16), each downstream stator blade (16) being of variable pitch, and wherein at least one of the downstream stator blades (16) is in a fixed-pitch configuration relative to another of the downstream stator blades (16) in that it has a pitch angle (γ) less than the pitch angle (γ) of the other downstream stator blade (16).

Description

Description Title: AERONAUTICAL PROPELLER technical field

[0001] This disclosure falls within the domain of longitudinal axis aeronautical propulsion systems comprising (at least) two annular rows of unfaired blades, one upstream and one downstream, along the longitudinal axis.

[0002] The aeronautical propulsion system may include (at least) a thermal engine, in particular a turbomachine, turbomotor, 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. Previous technique

[0003] We will only refer hereafter to the case of turbomachinery, since the type(s) of engine included in the aeronautical propulsion system is not decisive here.

[0004] An open-rotor turbomachine (also known as a Propfan, Open Rotor, or Counter-Rotating Open Rotor turboprop) is a type of turbomachine in which the fan (or propeller) extends outside the engine casing (or nacelle), unlike conventional turbomachines (of the Turbofan type) in which the fan is enclosed. An example of such a turbomachine is shown in Figure 1. The turbomachine 10 comprises a hub 12, defining the engine casing, on which are mounted an annular row of upstream unfaired blades 14 and an annular row of downstream unfaired blades 16, spaced apart along a longitudinal axis X of the turbomachine 10. The annular row of upstream blades 14 and the annular row of downstream blades 16 define an upstream propeller and a downstream propeller, respectively.The orientation qualifiers, such as "longitudinal", "radial" or "circumferential", are defined with reference to the longitudinal axis X of the turbomachine 10. The relative qualifiers "upstream" and "downstream" are defined with respect to each other with reference to the gas flow in the turbomachine 10 along the longitudinal axis X. Furthermore, the turbomachine 10 comprises, from upstream to downstream inside the engine casing, one (or more) compressor(s) 2, at least one combustion chamber 4, one (or more) turbine(s) 6 and at least one exhaust nozzle 8.

[0005] Among these unducted fan turbomachines, we know the "Unducted Single (or Stator) Fan" (USF) type turbomachines, in each of which, as illustrated in Figure 1, the annular row of upstream unducted blades 14 is mounted to rotate freely around the longitudinal axis X and the annular row of downstream unducted blades 16 is fixed. In other words, the upstream annular row of blades 14 is rotor-type and the downstream annular row of blades 16 is stator-type. The direction of rotation of the upstream rotor blades 14 is not critical. The downstream annular row of stator blades 16 can be centered on an axis that may or may not coincide with the longitudinal axis X. As illustrated in Figure 1, the downstream annular row of stator blades 16 is centered on the longitudinal axis X. Such a USF-type configuration allows the gyration energy of the airflow from the upstream propeller to be utilized via the downstream propeller 16. The efficiency of the turbomachine 10 is thus improved, particularly compared to a conventional turbomachine with a single rotating propeller. The upstream rotor blades 16, which are not shrouded, are driven in rotation around the longitudinal axis X by the turbine(s) 6 which in turn drive the compressor(s) 2.The turbomachine 10 generally includes a gearbox to decouple the rotational speed of the turbines 6 from the rotational speed of the upstream propeller. Furthermore, one of the advantages of a USF-type turbomachine compared to a counter-rotating open-rotor turbomachine is the reduction of tonal noise emitted by the turbomachine because the unshrouded downstream stator blades 16 are not driven in rotation around the longitudinal axis X.

[0006] The turbomachine 10 may have a so-called "pusher" configuration in which the upstream annular row of rotor blades 14 and the downstream annular row of stator blades 16 are located at a downstream end portion of the turbomachine 10 (configuration shown in Figure 1), or the turbomachine 10 may have a so-called "puller" configuration in which the upstream annular row of rotor blades 14 and the downstream annular row of stator blades 16 are located at an upstream end portion of the turbomachine 10.

[0007] In the puller configuration, the upstream annular row of rotor blades 14 and the downstream annular row of stator blades 16 can surround a section of the compressor(s) 2 of the turbomachine or the speed reduction gearbox. In the pusher configuration, the upstream annular row of blades 14 and the downstream annular row of stator blades 14 can surround a section of the turbine(s) 6 of the turbomachine 10.

[0008] The absence of a fairing leads to an increase in the noise level emitted by the turbomachine 10. Indeed, the noise generated by the unfaired annular rows of upstream rotor blades 14 and downstream stator blades 16 propagates in an open field. A primary cause of the emitted noise is related, on the one hand, to the interaction of the wake of the upstream rotor blades 14 on the downstream stator blades 16, and on the other hand, to structures vortices generated in the airflow at the radially external free ends of the upstream rotor blades 14 which impact the downstream stator blades 16.

[0009] However, excessive noise levels are detrimental to passenger comfort on the aircraft where the turbomachine is installed. Furthermore, current standards impose a maximum noise threshold, particularly in areas close to the ground, i.e., during takeoff and landing.

[0010] Furthermore, when the upstream airflow perceived by the turbomachine 10 is not parallel to the longitudinal axis X (particularly during landing and takeoff phases), the forces generated on each upstream rotor blade 14 vary according to its position around the longitudinal axis X as it rotates around the longitudinal axis X. Thus, the directivity of the far-field acoustic radiation is not axisymmetric. Therefore, the angle of incidence of the airflow perceived by the turbomachine 10 is modified heterogeneously by the upstream propeller around the longitudinal axis X.As a result, the aerodynamic load applied to each of the downstream stator blades 16 differs according to the position around the longitudinal axis X of the downstream stator blade 16, which can lead to a thrust supplied by the downstream propeller that is not satisfactory during the angle-of-attack operating phases of the turbomachine 10, particularly during the landing and takeoff phases.

[0011] Furthermore, during operation, the presence of aircraft structural elements (mast, fuselage, wing, slat, flaps, etc.) located near the downstream propeller can modify the airflow conditions (pressure, longitudinal component of the flow velocity, etc.), locally around the longitudinal axis X, at the level of the annular row of downstream stator blades 16. However, a heterogeneous airflow around the longitudinal axis X at the level of the downstream propeller also has the disadvantage of causing an aerodynamic load applied to each of the downstream stator blades 16 which differs according to the position around the longitudinal axis X of the downstream stator blade 16. Summary

[0012] A longitudinal axis aeronautical propulsion system is proposed comprising a hub, an annular row of unfaired upstream rotor blades and an annular row of unfaired downstream stator blades, the annular row of upstream rotor blades and the annular row of downstream stator blades being spaced apart along the longitudinal axis, each downstream stator blade having variable pitch, and wherein at least one of the downstream stator blades is in a closed pitch configuration relative to another of the downstream stator blades in that it has a pitch angle lower than the pitch angle of the other downstream stator blade.

[0013] Each downstream stator blade can thus be rotated around its pitch axis to change the angle of incidence of the airflow on the downstream stator blade. The rotational adjustment of each downstream stator blade around its respective pitch axis can be carried out according to an operating phase in angle of incidence of the aircraft propulsion system (for example, landing and / or takeoff phase), and / or according to the airflow conditions taken locally at the level of the downstream stator blade, these conditions being able to depend, according to the position of the downstream stator blade around the longitudinal axis, on the wake of the upstream rotor blades and / or the presence of structural elements of an aircraft on which the aircraft propulsion system is mounted (mast, fuselage, wing, slat, flaps, etc.).This allows, on the one hand, for a reduction in the noise level emitted by the aeronautical propulsion system, and on the other hand, for an improvement in the aerodynamic performance of the downstream annular row of stator blades.

[0014] The upstream annular row of rotor blades rotates freely around the longitudinal axis. The downstream annular row of unshod stator blades is prevented from rotating around the longitudinal axis. Therefore, the downstream annular row of stator blades is fixed around the longitudinal axis. In other words, the downstream stator blades do not rotate around the longitudinal axis.

[0015] The term "unfaired" used in reference to the upstream rotor blades and downstream stator blades indicates that the upstream rotor blades and downstream stator blades are not surrounded by a nacelle, unlike conventional aircraft propulsion systems in which the fan is faired inside a nacelle.

[0016] The upstream annular row of rotor blades and the downstream annular row of stator blades can respectively define an upstream propeller and a downstream propeller. The downstream annular row of stator blades can be a rectifier.

[0017] Each blade (upstream and / or downstream) can extend radially. Each blade can extend between a radially inward end, located at the (i.e., closest to) hub of the aircraft propulsion system, and a radially outward end. The radially inward end can be, longitudinally, at a leading edge of the blade or at the pitch axis of the blade in question. The radially inward end is also called the "root" of the blade. The position of each blade around the longitudinal axis can be determined by the position around the longitudinal axis of the respective radially inward end of the blade. The radially outward end of each blade is the opposite end from the radially inward end of the blade. The radially outward end can be the free end of the blade. The radially inward and radially outward ends of each of the blades can be radially aligned and / or at the same longitudinal position. It is not excluded that the radially inner end and the radially outer end of each of the blades may be longitudinally and / or circumferentially offset from each other.

[0018] The position of each blade (upstream and / or downstream) around the longitudinal axis can be expressed as an angular position around the longitudinal axis. The angular position of each blade (upstream and / or downstream) can be located relative to a clock face (here viewed from upstream, for example) whose angular positions at 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock are conventionally positioned. The angular position at 12 o'clock is therefore positioned vertically upwards relative to the longitudinal axis. The angular position at 6 o'clock is positioned vertically downwards relative to the longitudinal axis. The angular position at 3 o'clock is positioned horizontally to the right relative to the longitudinal axis. The angular position at 6 o'clock is positioned horizontally to the left relative to the longitudinal axis.An axis extending radially through the angular positions at 12 and 6 o'clock is thus perpendicular to an axis extending radially through the angular positions at 3 and 9 o'clock. Qualifiers of absolute position, such as "up," "down," "left," "right," etc., or of relative position, such as "above," "below," "superior," "inferior," etc., and qualifiers of orientation, such as "vertical" and "horizontal," can be considered in an operational state of the aeronautical propulsion system, typically when it is installed on an aircraft on the ground. In this state of the aeronautical propulsion system, the axis passing through the angular positions at 12 and 6 o'clock extends in the direction of the gravitational field, that is, vertically.

[0019] The angular position of each blade (upstream and / or downstream) can be defined by an angle measured around the longitudinal axis positively in the clockwise direction with respect to the angular position at 12 o'clock. The angle can be measured between an axis perpendicular to the longitudinal axis of the aeronautical propulsion passing through the radially inner end (or the radially outer end) of the downstream stator blade and the axis passing through the angular positions at 12H and 6H. Thus, the angular position of a blade located at the angular position at 12H can be defined by an angle equal to 0°, the angular position of a blade located at the angular position at 3H can be defined by an angle equal to 90°, the angular position of a blade located at the angular position at 6H can be defined by an angle equal to 180° (or equivalently to -180°) and the angular position of a blade located at the angular position at 9H can be defined by an angle equal to 270° (or equivalently to -90°).

[0020] Each blade has an external radial radius. The external radial radius of a blade can be considered the radial distance from the longitudinal axis of the outermost end of the blade. In other words, it is the maximum radius of the blade. The maximum external radial radius among the upstream rotor blade annular row corresponds to the external radial radius of the upstream propeller. Each upstream rotor blade can have the same external radial radius. In this case, the external radial radius of each upstream rotor blade corresponds to the external radial radius of the upstream propeller. The maximum external radial radius among the downstream stator blade annular row corresponds to the external radial radius of the downstream propeller. Each downstream stator blade can have the same external radial radius. In this case, the external radial radius of each downstream stator blade corresponds to the external radial radius of the downstream propeller.The annular row of stator blades may comprise two stator blades (possibly circumferentially consecutive) that have different external radial radii. Independently or in combination, the annular row of stator blades may comprise two stator blades (possibly circumferentially consecutive) that have different internal radial radii.

[0021] Each blade (upstream and / or downstream) can have an aerodynamic profile. To this end, each blade can comprise a stack of sections along the radial direction. For each blade, a stacking line can be defined that passes through the center of gravity of each blade section. It is possible that the stacking line of one or more blades may form a non-linear curve. In a particular case, the stacking line of one or more blades may extend radially in a straight line. Each section extends in a respective cross-section plane that is perpendicular to the radial direction of extension of the corresponding blade. Each section can include a leading edge upstream and a trailing edge downstream, between which extend an intrados line and an extrados line. Each section can define an aerodynamic profile.Each section can include a chord defined by a straight portion connecting the leading edge to the trailing edge. When referring to the aerodynamic profile of a section or a blade, this refers to the two-dimensional conformation of the section, or respectively the three-dimensional conformation of the blade, independently of the blade pitch angle or the angular position of the blade around the longitudinal axis.

[0022] The leading edge and trailing edge of all the sections in the stack of sections can respectively form, for each blade, a leading edge and a trailing edge of the blade. Similarly, the intrados and extrados lines of all the sections of the stack of sections can respectively form, for each blade, an intrados face and an extrados face of the downstream stator blade.

[0023] Each stator blade has its own pitch axis. The pitch axis of each downstream stator blade can lie in a plane perpendicular to the longitudinal axis. In other words, the pitch axis of each downstream stator blade can extend in a direction with a zero longitudinal component. The pitch axis of each downstream stator blade can extend radially. It is possible that the pitch axis includes a radial component and / or a longitudinal component and / or a circumferential component.

[0024] The pitch angle of each downstream stator blade can be defined as the angle formed between, on the one hand, a first axis defined by the intersection of the cross-sectional plane of a reference section within the stack of blade sections and a plane perpendicular to the longitudinal axis (which may include the pitch axis of the downstream stator blade), and on the other hand, the chord of the reference section of the downstream stator blade. The angle can be measured from the upstream side of the plane perpendicular to the longitudinal axis. The angle can be measured positively in a direction from the first axis to the chord of the reference section, and more specifically in a direction coinciding with the direction from the lower surface to the upper surface.

[0025] One of the downstream stator blades can be said to have a "closed pitch" relative to another downstream stator blade when it has a pitch angle that is less than the pitch angle of the other downstream stator blade, preferably by at least 0.1°, and more preferably by at least 1°. One of the downstream stator blades can be said to have an "open pitch" relative to another downstream stator blade when it has a pitch angle that is greater than the pitch angle of the other downstream stator blade, preferably by at least 0.1°, and more preferably by at least 1°.

[0026] Regardless of the setting configuration of each of the downstream stator blades, the lower surface and the upper surface can be, for each of the downstream stator blades, positioned relative to each other in the same direction in the circumferential direction.

[0027] Each downstream stator blade can be pivotally mounted about a respective pitch axis extending in a direction that includes at least one radial component. The aeronautical propulsion system may further include means for independently or collectively driving each of the downstream stator blades in rotation about its respective pitch axis. For example, the aeronautical propulsion system may include means for collectively driving each of the downstream stator blades arranged in a angular sector around the longitudinal axis rotating around the respective pitch axis. In particular, each downstream stator blade can be connected, at its radially inner end, to a pitch arm which is adapted to rotate around the pitch axis of the downstream stator blade.

[0028] The reference section of each downstream stator blade can be located at the radially inner end of the downstream stator blade. Alternatively, the reference section of each downstream stator blade can be located, on the corresponding downstream stator blade, at a radial distance from the longitudinal axis that corresponds to 75% of the radially outer radius of the corresponding downstream stator blade. Alternatively still, the reference section of each downstream stator blade can be located, on the downstream stator blade, at a radial distance from the longitudinal axis that corresponds to 75% of the radially outer radius of the downstream stator blade with the smallest radially outer radius among the annular row of downstream stator blades.

[0029] Two downstream stator blades may have different pitch angles. The difference between the pitch angles of two downstream stator blades may be less than 120°, preferably less than 60°. In particular, two circumferentially consecutive downstream stator blades may have different pitch angles. The difference between the pitch angles of two circumferentially consecutive downstream stator blades may be less than 45°, preferably less than 20°.

[0030] The pitch angle of each downstream stator blade can be determined as a function of the angular position of the downstream stator blade around the longitudinal axis according to a linear, parabolic, logarithmic, sinusoidal or exponential law.

[0031] Each downstream stator blade can have a different pitch angle than the pitch angle of one (or more) circumferentially adjacent downstream stator blade(s). This allows for local adjustment of the flow incidence perceived by each downstream stator blade, as well as reducing the correlation of noise sources and thus reducing the noise level emitted by the aircraft propulsion system. Each downstream stator blade can have a different pitch angle than the pitch angle of the other downstream stator blades.

[0032] The aircraft propulsion system can include between 2 and 25 upstream rotor blades. The propulsion system can include between 2 and 25 downstream stator blades.

[0033] The number of upstream rotor blades can differ from the number of downstream stator blades. This reduces the number of upstream rotor blades that are simultaneously positioned circumferentially around the longitudinal axis opposite one of the downstream stator blades longitudinally. Thus, this reduces the number of The wakes of upstream rotor blades interact simultaneously with the downstream stator blades. This reduces the noise emitted by the propulsion system. In particular, the number of upstream rotor blades can be greater than the number of downstream stator blades. Each downstream stator blade is a source of noise, so reducing the number of downstream stator blades further reduces the noise level emitted by the propulsion system.

[0034] The strength of the annular row of downstream stator blades, defined as the ratio of the chord to the circumferential spacing between two circumferentially consecutive downstream stator blades, can be less than or equal to 3 over the entire radial dimension of each downstream stator blade. In particular, in a preferred embodiment, the strength is less than or equal to 1 at an external radial end of each downstream stator blade.

[0035] Similarly, the strength of the annular row of upstream rotor blades, defined as the ratio of the chord to the circumferential spacing between two circumferentially consecutive upstream rotor blades, can be less than or equal to 3 over the entire radial dimension of each upstream rotor blade. In particular, in a preferred embodiment, the strength is less than or equal to 1 at an outer radial end of each upstream rotor blade.

[0036] The ratio between, on the one hand, the longitudinal distance separating a median plane of the upstream rotor blade annular row from a median plane of the downstream stator blade annular row, and on the other hand, the diameter of the aerodynamic propulsion unit, can vary between 0.01 and 0.8, preferably between 0.1 and 0.5. The median plane of each blade annular row can be normal to the longitudinal axis. The median plane of each blade annular row can be the plane containing the pitch axis of each of the blades in the corresponding annular row. Alternatively, the median plane of each blade annular row can be the plane containing the pitch axis of at least one of the blades in the corresponding annular row. The diameter of the aerodynamic propulsion unit can be defined as twice the radially external radius of the upstream propeller.The trailing edge of each blade in the upstream annular row is located longitudinally upstream of a leading edge of each blade in the downstream annular row. This limits, or even prevents, interference between annular rows of blades.

[0037] The hub can be axisymmetric around the longitudinal axis.

[0038] The downstream stator blades among the annular row of downstream stator blades which are located around the longitudinal axis in a first angular sector around the longitudinal axis can each be in the closed pitch configuration relative to the less one downstream stator blade among the annular row of downstream stator blades which is situated around the longitudinal axis in a second angular sector around the longitudinal axis, the second angular sector being distinct from the first angular sector.

[0039] The annular row of downstream stator blades can include at least two circumferentially consecutive downstream stator blades in each of the first and second angular sectors. This allows for a significant pitching effect on at least the two circumferentially consecutive blades, which will interact with a flow exhibiting similar characteristics (angle of attack, velocity, etc.).

[0040] At least two downstream stator blades, each located in the first sector, must have identical dimensional characteristics. In other words, at least two downstream stator blades, each located in the first sector, must have an identical aerodynamic profile. It is understood that for each cross-section of one of the two downstream stator blades, there is a corresponding cross-section of the other downstream stator blade that is located at the same radial distance from the longitudinal axis and has the same aerodynamic profile.

[0041] The downstream stator blades among the annular row of downstream stator blades which are situated around the longitudinal axis in a first angular sector around the longitudinal axis can each be in the closed pitch configuration relative to each of the downstream stator blades among the annular row of downstream stator blades which are situated around the longitudinal axis in the second angular sector around the longitudinal axis.

[0042] The first angular sector can extend over an angular range less than or equal to 180°, preferably less than or equal to 120°, or even more preferably less than or equal to 90°.

[0043] The first angular sector can be centered on a 12 o'clock angular position. This arrangement facilitates bypassing the airflow around an aircraft structural element on which the aeronautical propulsion system is mounted, located near the system at the 12 o'clock angular position (for example, an aircraft wing or the mast in an underwing installation). This also reduces pressure distortion between the structural element and the downstream stator blades, and prevents boundary layer separation and the formation of recirculation zones on the downstream stator blades, which would increase aerodynamic losses and noise levels.

[0044] The first angular sector can be centered on an angular position at 3H or 9H. Such an arrangement makes it easier to bypass the airflow around a structural element of an aircraft on which the aeronautical propulsion system is mounted, which is located near the aeronautical propulsion system at the angular position at 3H, respectively at 9H (for example, the fuselage of the aircraft on which the aeronautical propulsion system is mounted, the angular position at 3H or 9H depending on the side of the aircraft fuselage relative to which the aeronautical propulsion system is mounted, or the mast in an aeronautical propulsion system installation at the rear of the aircraft).This also helps to reduce pressure distortion rise between the structural element and the downstream stator blades, and to avoid boundary layer separation and the formation of recirculation zones on the downstream stator blades which would increase aerodynamic losses and noise levels.

[0045] Such a configuration also makes it possible to reduce the level of noise emitted by the aeronautical propulsion system in the direction of an angular position at 6H (i.e. for example in the direction of the ground).

[0046] The noise resulting from the interaction between the wake of the upstream rotor blades and the downstream stator blades produces a dipolar acoustic radiation emitted by the downstream stator blades. Consequently, the interaction noise radiated by the downstream stator blades is not axisymmetric around the longitudinal axis and depends on the circumferential position of the downstream stator blades around the longitudinal axis. Thus, the directivity of the noise emitted by the downstream stator blades located in the first angular sector differs from the directivity of the noise emitted by the other downstream stator blades. This allows for noise reduction in a free-field direction corresponding to the first angular sector.

[0047] The first angular sector can be centered on an angular position at 6H. Such a configuration makes it possible to reduce the noise level emitted by the aeronautical propulsion system in the direction of an angular position at 3H and an angular position at 9H (i.e. for example in the direction of the cabin of an aircraft on which the aeronautical propulsion system is mounted).

[0048] The downstream stator blades among the annular row of downstream stator blades situated around the longitudinal axis in a first angular sub-sector of the second angular sector around the longitudinal axis may each be in the open pitch configuration relative to the downstream stator blades situated around the longitudinal axis in a second angular sub-sector of the second angular sector around the longitudinal axis, the second angular sub-sector being distinct from the first angular sub-sector.

[0049] The first angular subsector can extend over an angular range less than or equal to 180°, preferably less than or equal to 120°, preferably even less than or equal to 90°.

[0050] The first angular sector can be centered on one of the angular positions at 3H and 9H, and the first sub-angular sector can be centered on the other of the angular positions at 3H and 9H. The upstream rotor blades can be driven in a direction of rotation about the longitudinal axis such that the upstream rotor blades located in the first angular sector are driven in rotation about the longitudinal axis in a direction from an angular position at 6H to an angular position at 12H, and the upstream rotor blades located in the first sub-angular sector are driven in rotation about the longitudinal axis in a direction from the angular position at 12H to the angular position at 6H.Also, the upstream rotor blades are said to be "upward" when they are located in the first angular sector in that they are driven towards the angular position at 12H and the upstream rotor blades are said to be "downward" when they are located in the first sub-angular sector in that they are driven towards the angular position at 6H.

[0051] Such a configuration of the downstream annular row ensures that the downstream stator blades located respectively in the first angular sector and the first sub-angular sector are subjected to a similar aerodynamic load despite different upstream rotor blade wakes depending on whether the upstream rotor blades are located in the first angular sector or the first sub-angular sector, this resulting from forces exerted on the upstream rotor blades which depend on their position around the longitudinal axis during their rotation around the longitudinal axis, particularly during the operating phases at angle of attack of the aeronautical propulsion system, for example during the landing and takeoff phases.

[0052] The first angular sector can be centered on an angular position at either 12 o'clock or 6 o'clock, and the first angular sub-sector can be centered on an angular position at either 12 o'clock or 6 o'clock. This configuration of the downstream annular row ensures that the downstream stator blades located in the first angular sector and the first angular sub-sector are subjected to a similar aerodynamic load when the airflow incident on the downstream annular row of stator blades has a non-zero angle of incidence with respect to the longitudinal axis, for example, in the presence of a crosswind.

[0053] The downstream stator blades among the annular row of downstream stator blades located around the longitudinal axis in a first angular sub-sector of the second angular sector around the longitudinal axis can each be in the closed pitch configuration relative to the downstream stator blades located around the longitudinal axis in a second angular sub-sector of the second angular sector around the longitudinal axis, the second angular sub-sector being distinct from the first angular sub-sector.

[0054] The first angular subsector can extend over an angular range less than or equal to 180°, preferably less than or equal to 120°, preferably even less than or equal to 90°.

[0055] The first angular sector can be centered on an angular position at 9 o'clock and the first sub-angular sector can be centered on an angular position at 3 o'clock. Such a configuration also reduces the noise level emitted by the aircraft propulsion system in the direction of an angular position at 6 o'clock (i.e., towards the ground).

[0056] The first angular sector can be centered on an angular position at either 12 o'clock or 6 o'clock, and the first sub-angular sector can be centered on an angular position at either 12 o'clock or 6 o'clock. This configuration reduces the noise level emitted by the aircraft propulsion system in the direction of an angular position at 3 o'clock and an angular position at 9 o'clock (i.e., for example, in the direction of the cabin of an aircraft on which the aircraft propulsion system is mounted).

[0057] Each of the downstream stator blades located around the longitudinal axis in the first angular sector or in the second angular sector, or where appropriate in the first angular sub-sector of the second angular sector or in the second angular sub-sector of the second angular sector, may have an identical pitch angle to within 1°.

[0058] At least two downstream stator blades located around the longitudinal axis in the first angular sector or in the second angular sector, or where appropriate in the first angular sub-sector of the second angular sector or in the second angular sub-sector of the second angular sector, may have identical dimensional characteristics.

[0059] At least two downstream stator blades located around the longitudinal axis in the first angular sector or in the second angular sector, or where appropriate in the first angular sub-sector of the second angular sector or in the second angular sub-sector of the second angular sector, may exhibit different dimensional characteristics.

[0060] For each pair of a first downstream stator blade and a second downstream stator blade, each section of the first downstream stator blade may have an aerodynamic profile identical to a corresponding section of the second downstream stator blade over an upstream end portion extending longitudinally over a relative chord length of between 5% and 50%, preferably between 10% and 30%, said corresponding sections of the first downstream stator blade and the second downstream stator blade each being arranged at the same radial distance from the longitudinal axis.

[0061] According to another aspect, a propulsion assembly is proposed comprising an aeronautical propulsion system as described above and a pylon adapted for attaching the aeronautical propulsion system to a fuselage or wing of the aircraft, the pylon extending in a direction including at least one radial direction from a radially internal end by which it is connected to the hub of the propulsion system, the pylon comprising a leading edge and a trailing edge between which extend on each side in the circumferential direction an upper surface face and an lower surface face, the upper surface face and the lower surface face of the pylon being, at least on an upstream part of the pylon, arranged circumferentially on each side of a radial plane defined by the longitudinal axis and a radial axis passing, at least in part, through the leading edge of the pylon, and in which the annular row of downstream stator blades of the aeronautical propulsion system may comprise: - a first group comprising one or more downstream blade(s), each having a downstream end located circumferentially on the same side as the extrados face of the pylon with respect to the radial plane, the first group comprising at least the downstream stator blade that is closest circumferentially to the radial plane and whose downstream end is located circumferentially on the same side as the extrados face of the pylon with respect to the radial plane, - a second group comprising one or more downstream blade(s) which each have a downstream end located circumferentially on the same side as the intrados face of the pylon with respect to the radial plane, the second group comprising at least the downstream stator blade which is closest circumferentially to the radial plane and whose downstream end is located circumferentially on the same side as the intrados face of the pylon with respect to the radial plane.

[0062] Each downstream stator blade of the first group can be in a closed pitch configuration relative to each downstream stator blade of the second group.

[0063] Such a configuration of the downstream annular row ensures that the downstream stator blades of the first group and the downstream stator blades of the second group are subjected to a relatively similar aerodynamic load despite conditions airflow at the level of the downstream annular row of stator blades which are different on either side of the radial plane due to the presence of the pylon.

[0064] Such an arrangement makes it easier to bypass the flow around the pylon, thus reducing a rise in pressure distortion between the pylon and the downstream stator blades of the first type, and avoiding boundary layer separations and the formation of recirculation zones on the downstream stator blades of the first type, which would increase aerodynamic losses and noise levels.

[0065] The "intrados face" and "extrados face" of the pylon refer to the end faces of the pylon in the circumferential direction, positioned relative to each other in the same circumferential direction as the intrados and extrados faces of each of the downstream stator blades. The pylon may have a shape that does not have an aerodynamic profile.

[0066] In other words, each downstream stator blade of the second group is in an open pitch configuration relative to each downstream stator blade of the first group.

[0067] The pylon can be positioned around the axis of rotation at an angular position of 12 o'clock or 6 o'clock around the longitudinal axis of the aircraft propeller. This configuration allows the aircraft propeller to be mounted under or on top of the aircraft wing. The pylon can also be positioned around the axis of rotation at an angular position of 3 o'clock or 9 o'clock around the longitudinal axis of the aircraft propeller. This configuration allows the aircraft propeller to be mounted on the rear section of the aircraft fuselage.

[0068] The pylon may be arranged longitudinally, in whole or in part, downstream of the annular row of downstream stator blades. The pylon may be arranged circumferentially, in whole or in part, between two circumferentially adjacent downstream stator blades of the first type.

[0069] The downstream stator blades of the first group may be circumferentially consecutive in pairs and / or the downstream stator blades of the second group are circumferentially consecutive in pairs.

[0070] According to another aspect, it is proposed an aircraft comprising an aeronautical propulsion system as described above or a propulsion assembly as described above.

[0071] According to another aspect, a method of using the aeronautical propulsion system as described above or the propulsion assembly as described above is proposed, the method including the adjustment of the pitch angle of each downstream stator blade according to an operating phase in incidence of the aeronautical propulsion system.

[0072] An operating phase at an angle of incidence can be characterized by one or more of the following characteristics: - a Mach number of the propulsion system between 0 and 0.4; - the propulsion system includes a high-lift device (beak, flap) in at least a partially deployed state; - the altitude of the propulsion system is less than or equal to 5000 m; - the slope of the trajectory of the propulsion system is between -1° and -10° (landing angle of attack phase) or between 1° and 20° (takeoff angle of attack phase); - the propulsion system is fixed to an aircraft whose angle of attack (i.e. the angle between the forward speed and the main axis of an aircraft fuselage) is between 0° and 10° (landing angle of attack phase) or between 0° and 15° (takeoff angle of attack phase).

[0073] The method may include recording one or more of the preceding characteristics and transmitting the characteristic(s) as data to a digital control system (for example, an interface between a cockpit and the propulsion system, called "Full Authority Digital Engine Control," also known as "FADEC"). The pitch angle of each downstream stator blade of the second type can be determined by using this data, particularly via the digital control system. Brief description of the drawings

[0074] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, on which:

[0075] Figure 1 is a partial schematic cross-sectional view of an unfaired fan turbomachine according to the prior art;

[0076] Figure 2 is a partial schematic view of an unshod fan turbomachine according to the present description;

[0077] Figure 3 includes figure 3a which is a schematic view of a downstream stator blade of the turbomachine of figure 2 and figure 3b which is a schematic view of the downstream stator blade of figure 3a in the section plane lll-lll;

[0078] Figure 4 is a schematic cross-sectional view of an annular row of downstream stator blades of the turbomachine of Figure 2 in a first configuration;

[0079] Figure 5 is a schematic cross-sectional view of an annular row of downstream stator blades of the turbomachine of Figure 2 in a second configuration;

[0080] Figure 6 is a schematic cross-sectional view of an annular row of downstream stator blades of the turbomachine of Figure 2 according to a third configuration;

[0081] Figure 7 includes figures 7a and 7b, which are respectively a schematic cross-sectional view of an annular row of downstream stator blades of the turbomachine of figure 2 according to a fourth configuration and a graph illustrating the fourth configuration of the annular row of downstream stator blades;

[0082] Figure 8 includes figures 8a and 8b, which are respectively a schematic cross-sectional view of an annular row of downstream stator blades of the turbomachine of figure 2 according to a fifth configuration and a graph illustrating the fifth configuration of the annular row of downstream stator blades;

[0083] Figure 9 includes figures 9a and 9b, each of which is a schematic cross-sectional view of an annular row of downstream stator blades of the turbomachine of figure 2 according to a respective variant of a sixth configuration;

[0084] Figure 10 includes figures 10a and 10b, each of which is a schematic cross-sectional view of an annular row of downstream stator blades of the turbomachine of figure 2 according to a respective variant of a seventh configuration;

[0085] Figure 11 is a circumferentially extended schematic partial view of an eighth configuration of the downstream annular row of stator blades of the turbomachine of Figure 2. Description of the implementation methods

[0086] Reference is now made to Figure 2. Figure 2 represents a propulsion system for an aircraft comprising a turbomachine 10 with longitudinal axis X and a pylon 18 adapted for attaching the turbomachine 10 to the aircraft, here at the level of an aircraft wing. Alternatively, the pylon 18 can be adapted to attach the turbomachine 10 to a fuselage, particularly the rear fuselage, of the aircraft. As before, orientation qualifiers, such as "longitudinal," "radial," or "circumferential," are defined with reference to the longitudinal axis X of the turbomachine 10. The relative qualifiers "upstream" and "downstream" are defined with respect to each other with reference to the gas flow in the turbomachine 10 along the longitudinal axis X.

[0087] The turbomachine 10 includes a hub 12. The hub 12 is axisymmetric about the longitudinal axis X. The turbomachine 10 further includes an annular row of unshod upstream rotor blades 14 and an annular row of unshod downstream stator blades 16. The annular row of upstream rotor blades 14 and the annular row of downstream stator blades 16 are spaced apart along the longitudinal axis X. The term "unshod" used with reference to the upstream rotor blades 14 and the downstream stator blades 16 indicates that the upstream rotor blades 14 and the downstream stator blades 16 are not surrounded by a nacelle, unlike the 10 classic turbomachines in which the fan is enclosed inside a nacelle.

[0088] The annular row of upstream rotor blades 14 is free to rotate about the longitudinal axis X. The annular row of unshod downstream stator blades 16 is fixed to rotate about the longitudinal axis X. The annular row of downstream stator blades 16 is therefore fixed about the longitudinal axis X. In other words, the downstream stator blades 16 are not driven to rotate about the longitudinal axis X. The annular row of upstream rotor blades 14 and the annular row of downstream stator blades 16 define an upstream propeller and a downstream propeller, respectively.

[0089] Figure 4 shows the annular row of downstream stator blades 16 in a first configuration, and Figure 3 shows one of the downstream stator blades 16 in more detail. Each downstream stator blade extends radially between a radially inner end 20, located at the (i.e., closest to) hub 12 of the turbomachine 10, and a radially outer end 21. In the example shown, the radially inner end 20 is, longitudinally, at a leading edge 22 of the blade. The radially inner end 20 is also called the "foot" of the blade. The position of each blade around the longitudinal axis X, as considered hereafter, is determined by the position around the longitudinal axis X of the radially inner end 20 of the respective blade. The radially external end 21 of each downstream stator blade 16 is the opposite end of the radially internal end 20 of the blade.The radially external end 21 is the free end of the downstream stator blade 16.

[0090] The position of each of the downstream stator blades 16 around the longitudinal axis X is expressed as an angular position around the longitudinal axis X. The angular position of each of the downstream stator blades 16 is located relative to a clock face (here considered as viewed from upstream, for example) whose angular positions at 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock are conventionally positioned. The angular position at 12 o'clock is therefore positioned vertically upwards relative to the longitudinal axis X. The angular position at 6 o'clock is positioned vertically downwards relative to the longitudinal axis X. The angular position at 3 o'clock is positioned horizontally to the right relative to the longitudinal axis X. The angular position at 9 o'clock 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. Qualifiers of absolute position, such as the terms "up", "down", "left", "right", etc., or of relative position, such as the terms "above", "below", "superior", "inferior", etc., and qualifiers of orientation, such as the terms "vertical" and "horizontal" can be. considered in an operational state of the turbomachine 10, typically when it is installed on an aircraft 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 gravitational field, i.e. vertically.

[0091] The angular position of each downstream stator blade 16 is also defined by an angle 0 measured around the longitudinal axis X positively in the clockwise direction with respect to the angular position at 12H. For example, for each downstream stator blade 16, the angle 0 can be measured between an axis perpendicular to the longitudinal axis X of the turbomachine 10 passing through the radially inner end 20 (or the radially outer end 21) of the downstream stator blade 16 and the axis passing through the angular positions at 12H and 6H.Thus, the angular position of a downstream stator blade 16 located at the angular position at 12H is defined by an angle 0 equal to 0°, the angular position of a downstream stator blade 16 located at the angular position at 3H is defined by an angle 0 equal to 90°, the angular position of a downstream stator blade 16 located at the angular position at 6H is defined by an angle 0 equal to 180° (or equivalently to -180°) and the angular position of a downstream stator blade 16 located at the angular position at 9H is defined by an angle 0 equal to 270° (or equivalently to -90°).

[0092] Each downstream stator blade 16 has an external radial radius. The external radial radius of a blade is the radial distance from the longitudinal axis X of the external radial end 21 of the blade. In other words, it is the maximum radius of the blade. In the illustrated example, each downstream stator blade 16 has an identical external radial radius, which thus corresponds to the external radial radius of the downstream propeller.

[0093] Each downstream stator blade 16 defines an airfoil. To this end, each downstream stator blade 16 comprises a stack of sections 30 along the radial direction. One of the sections 30 is shown in Figure 3b. Each section 30 extends in a respective cross-section plane that is perpendicular to the radial direction of extension of the corresponding downstream stator blade 16. Each section 30 comprises a leading edge 31 upstream and a trailing edge 32 downstream, between which extend an intrados line 33 and an extrados line 34. Each section 30 defines an airfoil. Each section 30 also includes a chord C defined by a straight portion connecting the leading edge 31 at the vanishing point 32.

[0094] The leading edge 31 and trailing edge 32 of all the sections 30 in the stack of sections 30 form, respectively, for each downstream stator blade 16, a leading edge 22 and a trailing edge 23 of the blade. Similarly, the lower surface line 33 and the upper surface line 34 of all the sections 30 in the stack of sections 30 form respectively, for each downstream stator blade 16, an intrados face 24 (visible in figure 3a) and an extrados face (not visible in figure 3a) of the downstream stator blade 16.

[0095] In the illustrated examples described below, each downstream stator blade 16 has identical dimensional characteristics. In other words, each downstream stator blade 16 has an identical airfoil profile. It is therefore understood that for each cross-section 30 of one of the downstream stator blades 16, there is a corresponding cross-section 30 of another downstream stator blade 16 that is positioned at the same radial distance from the longitudinal axis and has the same airfoil profile. According to an alternative not shown, at least two downstream stator blades 16 may have different dimensional characteristics. In other words, at least two downstream stator blades 16 may have different airfoil profiles.

[0096] Each downstream stator blade 16 has a respective pitch axis AC. As can be seen in Figure 3a, the pitch axis AC of each downstream stator blade 16 lies in a plane perpendicular to the longitudinal axis X. In particular, the pitch axis AC of each downstream stator blade 16 extends radially in the illustrated example.

[0097] As shown in Figure 3b, the pitch angle y of each downstream stator blade 16 corresponds to the angle formed between, on the one hand, a first axis A1, which is defined by the intersection between the cross-sectional plane of a reference section 30 among the stack of sections 30 of the downstream stator blade 16 and a plane perpendicular to the longitudinal axis X that includes the pitch axis AC of the downstream stator blade 16, 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 from the upstream side of the plane perpendicular to the longitudinal axis X that includes the pitch axis AC of the downstream stator blade 16. The pitch angle y is measured positively in a direction from the first axis A1 to the chord C of the reference section 30, and more particularly in a direction coinciding with the direction from the intrados line 33 towards the extrados line 34.

[0098] The reference section 30 of each downstream stator blade 16 is located here, 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 16.

[0099] In the following, a first downstream stator blade 16 is said to have a "closed pitch" relative to a second downstream stator blade 16 when it has a pitch angle y less than the pitch angle y of the second downstream stator blade 16. Conversely, a first downstream stator blade 16 is said to have an "open pitch" relative to a second downstream stator blade 16 when it has a pitch angle y greater than the pitch angle y of the second downstream stator blade 16.

[0100] Regardless of the setting configuration of each of the downstream stator blades 16, the intrados face 24 and the extrados face are, for each of the downstream stator blades 16, positioned relative to each other in the same direction in the circumferential direction.

[0101] The strength of the annular row of downstream stator blades 16, defined as the ratio between the chord C, and the spacing in the circumferential direction between two circumferentially consecutive downstream stator blades 16, can be less than or equal to 3 over the entire radial dimension of each downstream stator blade 16. In particular, in a preferred embodiment, the strength is less than or equal to 1 at the level of an external radial end 21 of each downstream stator blade 16.

[0102] The ratio between, on the one hand, the longitudinal distance L separating a median plane PAM of the upstream rotor blade annular row 14 and a median plane PAV of the downstream stator blade annular row, and on the other hand, the diameter D of the turbomachine 10 can vary between 0.01 and 0.8, preferably between 0.1 and 0.5. The median plane PAM, PAV of each blade annular row is normal to the longitudinal axis X. The median plane PAM, PAV of each blade annular row is the plane containing the pitch axis AC of each blade in the corresponding annular row. The diameter D of the turbomachine 10 corresponds here to the diameter of the upstream propeller. The trailing edge of each of the blades in the upstream annular row 14 is located longitudinally upstream of a leading edge 22 of each of the blades in the downstream annular row 16. Thus, interference between the annular rows of blades is limited, or even avoided.

[0103] The pylon 18 has a radially internal end 20 by which it is connected to the hub 12 of the turbomachine 10. The pylon 18 extends radially overall in that it extends in a direction comprising at least one radial component. It is not excluded that the pylon 18 extends in a direction also comprising a longitudinal component and / or a circumferential component. In the example in Figure 2, the pylon extends in a direction comprising a radial component and a longitudinal component. The pylon 18 comprises a leading edge 41 and a trailing edge 42 between which, on each side, extend in the circumferential direction, an upper surface 44 and an lower surface 43. The upper surface 44 and the lower surface 43 of the pylon 18 are, at least on an upstream portion of the pylon 18, arranged circumferentially on each side of a radial plane defined by the longitudinal axis X and a radial axis passing through the leading edge 41 of the radially internal end of pylon 18. In the illustrated example, pylon 18 has an aerodynamic profile.

[0104] In the example shown in Figure 2, the pylon 18 is positioned around the axis of rotation at an angular position of 12H around the longitudinal axis X of the turbomachine 10. This configuration allows the turbomachine 10 to be fixed under the wing of the aircraft. Furthermore, the pylon 18 is arranged longitudinally downstream of the downstream annular row of stator blades 16.

[0105] Each downstream stator blade 16 has variable pitch. Each downstream stator blade 16 can therefore be rotated around its pitch axis AC to change the angle of incidence of the airflow on the downstream stator blade 16. In addition, at least one of the downstream stator blades 16 is in a closed pitch configuration relative to another of the downstream stator blades 16.The rotational adjustment of each downstream stator blade 16 around its respective pitch axis AC can then be performed according to the angle of attack of the turbomachine 10, which varies depending on the operating phase (e.g., landing and / or takeoff), and / or according to the local airflow conditions at the downstream stator blade 16. These conditions may depend, depending on the position of the downstream stator blade 16 around the longitudinal axis X, on the wake of the upstream rotor blades 14 and / or the presence of structural elements of an aircraft on which the turbomachine 10 is mounted (mast, fuselage, wing, slats, flaps, tail assembly, etc.). This allows, on the one hand, for a reduction in the noise level emitted by the turbomachine 10, and on the other hand, for an improvement in the aerodynamic performance of the annular row of downstream stator blades 16.

[0106] To achieve this, each downstream stator blade 16 can be pivotally mounted about a respective swashplate axis AC, which here extends radially, to change the angle of incidence of the airflow on each downstream stator blade 16. The turbomachine 10 can further include means for independently or collectively driving each of the downstream stator blades 16 in rotation about the respective swashplate axis AC. For example, the turbomachine 10 can include means for collectively driving each of the downstream stator blades 16 arranged in an angular sector about the longitudinal axis X in rotation about the respective swashplate axis AC. These means can be arranged radially inside the hub 12. In particular, each downstream stator blade 16 can be connected, at its inner radial end, to a swashplate arm adapted to rotate about the swashplate axis AC of the downstream stator blade 16.

[0107] According to the first configuration of the annular row of downstream stator blades 16, the downstream stator blades 16 among the annular row of downstream stator blades 16 which are located around the longitudinal axis X in a first angular sector S1 around the longitudinal axis X. Each is rotated around the respective pitch axis AC so as to be in the closed pitch configuration relative to at least one downstream stator blade 16 among the annular row of downstream stator blades 16, which is located around the longitudinal axis X in a second angular sector S2 around the longitudinal axis X. The second angular sector S2 is distinct from the first angular sector S1. Here, the first angular sector S1 and the second angular sector are complementary in that they extend over angular ranges whose sum is equal to 360°.

[0108] In particular, in the first configuration, the downstream stator blades 16 among the annular row of downstream stator blades 16 which are located in the first angular sector S1 around the longitudinal axis X are each in the closed pitch configuration relative to each of the downstream stator blades 16 among the annular row of downstream stator blades 16 which are located around the longitudinal axis X in the second angular sector S2 around the longitudinal axis X.

[0109] According to the first configuration, the first angular sector S1 extends over an angular range of 180°. Advantageously, the first angular sector S1 is centered on the angular position at 12H. This arrangement facilitates bypassing the airflow around a structural element of an aircraft on which the turbomachine 10 is mounted, located near the turbomachine 10 at the angular position at 12H (for example, a wing of the aircraft on which the turbomachine 10 is mounted). This reduces the interaction with the airflow around a structural element of an aircraft on which the turbomachine 10 is mounted, located near the turbomachine 10 at the angular position at 12H.This also helps to reduce pressure distortion rise between the structural element and the downstream stator blades 16, and to avoid boundary layer separations and the formation of recirculation zones on the downstream stator blades 16 which would increase aerodynamic losses and noise levels.

[0110] Figure 5 shows a second configuration of the annular row of downstream stator blades 16. The second configuration differs from the first configuration in that the first angular sector S1 is advantageously centered on the angular position at 9H. This arrangement facilitates the bypassing of the airflow around a structural element of an aircraft on which the turbomachine 10 is mounted, located near the turbomachine 10 at the angular position at 9H (for example, the fuselage of the aircraft on which the turbomachine 10 is mounted). This also reduces pressure distortion rise between the structural element and the downstream stator blades 16, and prevents boundary layer separation. and the formation of recirculation zones on the downstream stator blades 16, which would increase aerodynamic losses and noise levels. Such a configuration also reduces the noise level emitted by the turbomachine 10 in the direction of the angular position at 6H (i.e., towards the ground), as it has been observed that a closed-pitch configuration reduces the noise level emitted by the blade.

[0111] According to an unrepresented variant, the first sector can be centered on the angular position at 3H to achieve a similar effect when the aircraft structural element (in particular the fuselage) is located close to the turbomachine 10 at the angular position at 9H (the angular position at 3H or 9H depending on the side of the aircraft fuselage relative to which the turbomachine 10 is mounted).

[0112] Figure 6 shows a third configuration of the downstream stator annular array 16. The third configuration differs from the first and second configurations in that the first angular sector S1 is advantageously centered on the angular position at 6H. Such a configuration reduces the noise level emitted by the turbomachine 10 towards the angular position at 3H and the angular position at 9H (i.e., towards the cabin of an aircraft on which the turbomachine 10 is mounted), as it has been found that a closed-pitch configuration reduces the noise level emitted by the blade.

[0113] Figure 7a shows a fourth configuration of the downstream stator blade annular row 16. Figure 7b is a graph illustrating this fourth configuration. The graph represents the pitch angle y of each of the downstream stator blades 16 as a function of the angle 0 associated with the blade's angular position. In this fourth configuration, the first angular sector S1 is centered on the angular position at 9H and extends over an angular range of less than 90°. The second angular sector S2 is centered on the angular position at 3H.

[0114] Furthermore, the downstream stator blades 16 among the annular row of downstream stator blades 16 which are located around the longitudinal axis X in a first angular sub-sector S2i of the second angular sector S2 around the longitudinal axis X are each rotated around the respective pitch axis AC so as to be in the open pitch configuration relative to the downstream stator blades 16 located around the longitudinal axis X in a second angular sub-sector S22 of the second angular sector S2 around the longitudinal axis X. The second angular sub-sector S22 is distinct from the first angular sub-sector S2i.

[0115] The downstream stator blades 16 are among the annular row of downstream stator blades 16 which are located around the longitudinal axis X in the first angular sub-sector S2i are also each rotated around the respective AC pitch axis so as to be in the open pitch configuration relative to the downstream stator blades 16 located around the longitudinal axis X in a third angular sub-sector S23 of the second angular sector S2 around the longitudinal axis X. The third angular sub-sector S23 is distinct from the first angular sub-sector S2i and the second angular sub-sector S22.

[0116] The first angular sub-sector S2i extends over an angular range of less than 90°. The second angular sub-sector S22 and the third angular sub-sector S23 each extend over an angular range greater than 90°.

[0117] The first angular sub-sector S2i is advantageously centered on the other among the angular positions at 3H. Moreover, as shown in Figure 7a, the upstream rotor blades 14 among the annular row of upstream rotor blades 14 are driven in a direction of rotation R1 around the longitudinal axis X such that the upstream rotor blades 14 which are located in the first angular sector S1 are driven in rotation around the longitudinal axis X in a direction from the angular position at 6H to the angular position at 12H and the upstream rotor blades 14 among the annular row of upstream rotor blades 14 which are located in the first angular sub-sector S2i are driven in rotation around the longitudinal axis X in a direction from the angular position at 12H to the angular position at 6H.Such a configuration of the downstream annular row ensures that the downstream stator blades 16 located respectively in the first angular sector S1 and the first angular sub-sector S2i are subjected to a similar aerodynamic load despite different upstream rotor blade wakes 14 depending on whether the upstream rotor blades 14 are located in the first angular sector S1 or the first angular sub-sector S2i, this resulting from forces exerted on the upstream rotor blades 14 which depend on their position around the longitudinal axis X during their rotation around the longitudinal axis X and during an angle-of-attack phase.

[0118] The second angular sub-sector S22 and the third angular sub-sector S23 are respectively centered on the angular positions at 12H and 6H.

[0119] The difference in pitch angle y between two downstream stator blades 16 is less than 120°, preferably less than 60°. In particular, two circumferentially consecutive downstream stator blades 16 may have different pitch angles y. The difference in pitch angle y between two circumferentially consecutive downstream stator blades 16 is less than 45°, preferably less than 20°.

[0120] Figure 8a shows a fifth configuration of the annular row of downstream stator blades 16. Figure 8b is a graphic that illustrates the fifth configuration of The downstream annular row of stator blades 16. The graph represents the pitch angle y of each of the downstream stator blades as a function of the angle 0 associated with the angular position of the blade. The fifth configuration differs from the fourth configuration in that the first angular sector S1 is advantageously centered on an angular position at 12H and the first angular sub-sector S2i is advantageously centered on an angular position at 6H. Such a configuration of the downstream annular row ensures that the downstream stator blades 16 located respectively in the first angular sector S1 and the first angular sub-sector S2i are subjected to the same aerodynamic load when the airflow incident on the downstream annular row of stator blades 16 has a non-zero incidence with respect to the longitudinal axis X, for example in the presence of a crosswind.

[0121] Figure 9a shows a first variant of a sixth configuration of the downstream stator blade annular row 16. According to the first variant of the sixth configuration, the first angular sector S1 is centered on the angular position at 9H and extends over an angular range of less than 90°. The second angular sector S2 is centered on the angular position at 3H.

[0122] Furthermore, the downstream stator blades 16 among the annular row of downstream stator blades 16 which are situated around the longitudinal axis X in a first angular sub-sector S2i of the second angular sector S2 around the longitudinal axis X are each rotated around the respective pitch axis AC so as to be in the closed pitch configuration relative to the downstream stator blades 16 situated around the longitudinal axis X in a second angular sub-sector S22 of the second angular sector S2 around the longitudinal axis X.

[0123] The downstream stator blades 16 among the annular row of downstream stator blades 16 which are located around the longitudinal axis X in the first angular sub-sector S2i are also each rotated around the respective pitch axis AC so as to be in the closed pitch configuration relative to the downstream stator blades 16 located around the longitudinal axis X in a third angular sub-sector S23 of the second angular sector S2 around the longitudinal axis X. The third angular sub-sector S23 is distinct from the first angular sub-sector S2i and the second angular sector S2.

[0124] The first angular sub-sector S2i extends over an angular range of less than 90°. The second angular sub-sector S22 and the third angular sub-sector S23 each extend over an angular range greater than 90°.

[0125] The first angular sub-sector S2i is advantageously centered on the angular position at 3H. Such a configuration also allows for a further reduction in the level of noise emitted by the turbomachine 10 in the direction of an angular position at 6H (i.e. in the direction of the ground), especially with respect to the second configuration.

[0126] The second angular sub-sector S22 and the third angular sub-sector S23 are respectively centered on the angular positions at 6H and 12H.

[0127] Figure 9b represents a second variant of the sixth configuration of the downstream stator blade annular row 16. According to the second variant of the sixth configuration differs from the first variant in that the first angular sector S1 and the first angular sub-sector S2i each extend over an angular range greater than 90° and the second angular sub-sector S22 and the third angular sub-sector S23 each extend over an angular range less than 90°.

[0128] Figure 10 shows a seventh configuration of the downstream stator blade annular array 16. The seventh configuration differs from the fourth configuration in that the first angular sector S1 is advantageously centered on an angular position at 12H and the first sub-angular sector S2i is advantageously centered on an angular position at 6H. Such a configuration makes it possible to reduce the noise level emitted by the turbomachine 10 in the direction of an angular position at 3H and an angular position at 9H (i.e., in the direction of the cabin of an aircraft on which the turbomachine 10 is mounted, regardless of the side of the aircraft fuselage relative to which the turbomachine 10 is mounted).

[0129] The second angular sub-sector S22 and the third angular sub-sector S23 are respectively centered on the angular positions at 3H and 9H.

[0130] According to a first variant of the seventh configuration shown in Figure 10a, the first angular sector S1 and the first angular subsector S2i each extend over an angular range of less than 90°, and the second angular subsector S22 and the third angular subsector S23 each extend over an angular range of more than 90°. According to a second variant of the seventh configuration shown in Figure 10b, the first angular sector S1 and the first angular subsector S2i each extend over an angular range of more than 90°, and the second angular subsector S22 and the third angular subsector S23 each extend over an angular range of less than 90°.

[0131] Figure 11 shows an eighth configuration of the downstream stator blade annular row 16. In the eighth configuration, the downstream stator blade annular row 16 of the turbomachine 10 comprises: - a first group G1 comprising two circumferentially adjacent downstream blades, each having a downstream end located circumferentially on the same side as the extrados face 44 of pylon 18 with respect to the radial plane, the first group G1 comprising at least the downstream stator blade 16 which is closest circumferentially to the radial plane and whose downstream end is located circumferentially on the same side as the extrados face 44 of pylon 18 with respect to the radial plane, - a second group G2 comprising two circumferentially adjacent downstream blades, each having a downstream end located circumferentially on the same side as the intrados face 43 of the pylon 18 with respect to the radial plane, the second group G2 comprising at least the downstream stator blade 16 which is closest circumferentially to the radial plane and whose downstream end is located circumferentially on the same side as the intrados face 43 of the pylon 18 with respect to the radial plane.

[0132] Each downstream stator blade 16 of the first group G1 is in a closed pitch configuration relative to each downstream stator blade 16 of the second group G2. In other words, each downstream stator blade 16 of the second group G2 is in an open pitch configuration relative to each downstream stator blade 16 of the first group G1.

[0133] Such a configuration of the downstream annular row ensures that the downstream stator blades 16 of the first group G1 and the downstream stator blades 16 of the second group G2 are subjected to a relatively similar aerodynamic load despite airflow conditions at the level of the downstream annular row of stator blades 16 which are different on either side of the radial plane due to the presence of the pylon 18.

[0134] Such an arrangement makes it easier to bypass the flow around pylon 18, thus reducing a rise in pressure distortion between pylon 18 and the downstream stator blades 16 of the first type, and avoiding boundary layer separations and the formation of recirculation zones on the downstream stator blades 16 of the first type which would increase aerodynamic losses and noise levels.

Claims

Demands

1. Aeronautical propulsion (10) of longitudinal axis (X) comprising a hub (12), an annular row of upstream rotor blades (14) not shrouded and an annular row of downstream stator blades (16) not shrouded, each downstream stator blade (16) being of variable pitch, and wherein at least one of the downstream stator blades (16) is in a closed pitch configuration relative to another of the downstream stator blades (16) in that it has a pitch angle (y) less than the pitch angle (y) of the other downstream stator blade (16).

2. Aeronautical propulsion (10) according to the preceding claim, wherein the difference between the pitch angle of two downstream stator blades (16) is less than 120°, preferably less than 60°.

3. Aeronautical propulsion (10) according to any one of the preceding claims, wherein the difference between the pitch angle of two circumferentially consecutive downstream stator blades (16) is less than 45°, preferably less than 20°.

4. Aeronautical propulsion (10) according to any one of the preceding claims, wherein the downstream stator blades (16) among the annular row of downstream stator blades (16) which are situated around the longitudinal axis (X) in a first angular sector (S1) around the longitudinal axis (X) are each in the closed pitch configuration relative to at least one downstream stator blade (16) among the annular row of downstream stator blades (16) which is situated around the longitudinal axis (X) in a second angular sector (S2) around the longitudinal axis (X), the second angular sector (S2) being distinct from the first angular sector (S1).

5. Aeronautical propulsion (10) according to the preceding claim, wherein the annular row of downstream stator blades (16) comprises at least two downstream stator blades (16) circumferentially consecutive in each of the first angular sector (S1) and the second angular sector (S2).

6. Aeronautical propulsion (10) according to claim 4 or 5, wherein the first angular sector (S1) extends over an angular range less than or equal to 180°, preferably less than or equal to 120°, or even more preferably less than or equal to 90°.

7. Aeronautical propulsion system (10) according to any one of claims 4 to 6, wherein the first angular sector (S1) is centered on a angular position chosen from an angular position at 12 o'clock, an angular position at 3 o'clock, an angular position at 6 o'clock and an angular position at 9 o'clock.

8. Aeronautical propulsion (10) according to any one of claims 4 to 7, wherein the downstream stator blades (16) among the annular row of downstream stator blades (16) which are situated around the longitudinal axis in a first angular sub-sector (S2i) of the second angular sector (S2) around the longitudinal axis are each in the open pitch configuration relative to the downstream stator blades (16) situated around the longitudinal axis (X) in a second angular sub-sector (S22) of the second angular sector (S2) around the longitudinal axis (X), the second angular sub-sector (S22) being distinct from the first angular sub-sector (S2i).

9. An aircraft propulsion system (10) according to the preceding claim, wherein the first angular sector (S1) is centered on one of the angular positions at 3H and 9H and the first angular sub-sector (S2i) is centered on the other of the angular positions at 3H and 9H, and wherein the upstream rotor blades (14) are driven in a direction of rotation (R1) about the longitudinal axis (X) such that the upstream rotor blades (14) located in the first angular sector (S1) are driven in rotation about the longitudinal axis (X) from an angular position at 6H to an angular position at 12H and the upstream rotor blades (14) located in the first angular sub-sector (S2i) are driven in rotation about the longitudinal axis (X) from the angular position at 12H to the angular position at 6 AM.

10. Aeronautical propulsion (10) according to claim 8, wherein the first angular sector (S1) is centered on an angular position at 12H and the first angular sub-sector (S2i) is centered on an angular position at 6H.

11. Aeronautical propulsion (10) according to any one of claims 4 to 7, wherein the downstream stator blades (16) among the annular row of downstream stator blades (16) which are situated around the longitudinal axis (X) in a first angular sub-sector (S2i) of the second angular sector (S2) around the longitudinal axis (X) are each in the closed pitch configuration relative to the downstream stator blades (16) situated around the longitudinal axis (X) in a second angular sub-sector (S22) of the second angular sector (S2) around the longitudinal axis (X), the second angular sub-sector (S22) being distinct from the first angular sub-sector (S2i).

12. Aeronautical propulsion (10) according to the preceding claim, wherein the first angular sector (S1) is centered on an angular position at 9H and the first angular sub-sector (S2i) is centered on an angular position at 3H.

13. Aeronautical propulsion (10) according to claim 11, wherein the first angular sector (S1) is centered on an angular position at 12H and the first angular sub-sector (S2i) is centered on an angular position at 6H.

14. Aeronautical propulsion (10) according to any one of claims 8 to 13, wherein the first angular sub-sector (S2i) extends over an angular range less than or equal to 180°, preferably less than or equal to 120°, preferably still less than or equal to 90°.

15. Aeronautical propulsion (10) according to any one of claims 4 to 14, wherein each of the downstream stator blades (16) situated around the longitudinal axis (X) in the first angular sector (S1) or in the second angular sector (S2), or where appropriate in the first angular sub-sector (S2i) of the second angular sector (S2) or in the second angular sub-sector (S22) of the second angular sector (S2), has a pitch angle (y) identical to within 1°.

16. Aeronautical propulsion (10) according to any one of claims 4 to 15, wherein at least two downstream stator blades (16) located around the longitudinal axis (X) in the first angular sector (S1) or in the second angular sector (S2), or where appropriate in the first angular sub-sector (S2i) of the second angular sector (S2) or in the second angular sub-sector (S22) of the second angular sector (S2), have identical dimensional characteristics.

17. Aeronautical propulsion (10) according to any one of claims 4 to 15, wherein at least two downstream stator blades (16) located around the longitudinal axis (X) in the first angular sector (S1) or in the second angular sector (S2), or where appropriate in the first angular sub-sector (S2i) of the second angular sector (S2) or in the second angular sub-sector (S22) of the second angular sector (S2), have different dimensional characteristics.

18. Propulsion assembly for an aircraft, the propulsion assembly comprising an aircraft propulsion unit (10) according to any one of the preceding claims and a pylon (18) adapted for attaching the aircraft propulsion unit to a fuselage or wing of the aircraft, the pylon extending in a direction comprising at least one radial direction from a radially internal end through which it is connected to the hub (12) of the aircraft propulsion unit (10), the pylon (18) comprising a leading edge (41) and a trailing edge (42) between which extend on each side in the direction circumferential an extrados face (44) and an intrados face (43), the extrados face (44) and the intrados face (43) of the pylon (18) being, at least on an upstream part of the pylon (18), arranged circumferentially on each side of a radial plane defined by the longitudinal axis (X) and a radial axis passing, at least in part, through the leading edge (41) of the pylon (18), and in which the annular row of downstream stator blades (16) of the aeronautical propulsion unit (10) comprises: - a first group (G1) comprising one or more downstream blade(s) (16) which each have a downstream end located circumferentially on the same side as the extrados face (44) of the pylon (18) with respect to the radial plane, the first group (G1) comprising at least the downstream stator blade (16) which is closest circumferentially to the radial plane and whose downstream end is located circumferentially on the same side as the extrados face (44) of the pylon (18) with respect to the radial plane, - a second group (G2) comprising one or more downstream blade(s) (16) which each have a downstream end located circumferentially on the same side as the intrados face (43) of the pylon (18) with respect to the radial plane, the second group (G2) comprising at least the downstream stator blade (16) which is closest circumferentially to the radial plane and whose downstream end is located circumferentially on the same side as the intrados face (43) of the pylon (18) with respect to the radial plane, and in which each downstream stator blade (16) of the first group (G1) is in a closed pitch configuration relative to each downstream stator blade (16) of the second group (G2).

19. Propulsive assembly according to the preceding claim, wherein the downstream stator blades (16) of the first group (G1) are circumferentially consecutive in pairs and / or the downstream stator blades (16) of the second group (G2) are circumferentially consecutive in pairs.

20. Method of using the aeronautical propulsion system according to any one of claims 1 to 17 or of the propulsion assembly according to claim 18 or 19, the method comprising adjusting the pitch angle (y) of each downstream stator blade (16) as a function of an incidence operating phase of the aeronautical propulsion system (10).

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