Unducted fan for aeronautical propulsion

Abstract

The invention relates to an unducted propulsive fan (100) comprising at least a first row of blades (110) that are able to rotate about a central axis (X). Each of the blades (110) of the first row comprises a profiled body extending radially from an inner radius Ri to an outer radius Re in relation to the central axis (X) and comprising a pressure side (111) and a suction side (112) connecting a leading edge (BA) to a trailing edge (BF). The trailing edge (BF) of the profiled body of each blade (110) of the first row of blades (110) has sawteeth and the profiled body of each blade (110) of the first row of blades (110) has an activity factor FA between 100 and 225.

Description

Description Title of the invention: Unducted fan for aeronautical propulsion Technical Field

[0001] The technical field of this presentation is that of propulsion and in particular that of unducted propulsive fans, such as those intended in particular to be driven by a gas turbine engine in aeronautical propulsion. Prior art

[0002] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various carbon emission restrictions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those already in operation, requiring the implementation of technological solutions to ensure their compliance with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

[0004] Consequently, the Applicant is constantly working to reduce its climate impact through the use of methods and the exploitation of virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as an essential complement to technological progress, aeronautical biofuels.

[0006] The search for minimizing polluting emissions linked to air transport involves, in particular, improving all the efficiencies of propulsion systems, and more particularly the propulsive efficiency which characterizes the efficiency with which the energy used is converted into useful thrust.

[0007] The elements that influence this propulsive efficiency in the first order are those that contribute directly to the generation of thrust, including in particular the propulsive fans. The known guiding principle for improving propulsive efficiency is to reduce the compression ratio of the fan, thereby reducing the air flow velocity at the fan outlet and the associated kinetic energy losses.

[0008] To achieve the same thrust, this reduction in flow velocity at the outlet of the propulsive fan must normally be compensated by a greater mass flow rate of air, and therefore a larger fan diameter. When this fan is driven by a gas turbine engine, this normally also implies a greater bypass ratio (BPR), which is the ratio between the mass flow rate of the secondary flow of the fan and that of the primary flow feeding the combustion chamber of the gas turbine engine.

[0009] When the fan is shrouded, the increase in the fan diameter also implies an increase in the external dimensions of the retention casing surrounding it, as well as of the nacelle constituting the aerodynamic envelope of the casing in question, and therefore its drag, as well as that of their mass. In order to avoid these disadvantages, it is possible to shorten the axial length of the nacelle and to thin it, which reduces the space available for acoustic treatments that serve to reduce noise. Furthermore, several types of unducted propulsive fans have been considered, including in particular those known by the English acronyms "USF" and "CROR". In both types, the propulsive fan comprises two rows of blades arranged radially around one or more central axes, one upstream and the other downstream, the terms "upstream" and "downstream" being understood, in the context of this disclosure, as being defined in relation to the usual direction of air circulation through the fan. However, in "USF" ("Unducted Single Fan") type propulsive fans only the upstream row rotates around the central axis, while in "CROR" ("Counter-Rotating Open Rotor") type propulsive fans the two rows rotate in opposite directions.However, in both types, blades in each of the two rows can be variable pitch.

[0010] A disadvantage of unducted propulsive fans is the level of noise emissions. Indeed, in the absence of a casing or nacelle surrounding the fan, the noise emissions from the latter are directly diffused into the environment. In addition, the interactions between successive rows of blades can aggravate these noise emissions, in particular at the harmonics of the blade passing frequency (BPF). Significant research and development efforts have therefore been directed, in particular by the Applicant, towards reducing these noise emissions. To this end, it has been proposed, in particular in the publications of international patent applications WO 2023 / 007098 A1 and WO 2019 / 158875 A1, to form teeth or undulations on the trailing edge of the blades of unducted propulsive fans, so as to reduce or distribute their marginal vortices.This solution has also been proposed for ducted fans, for example in French patent application publications FR 2 986 285 A1 and FR 3 103 231 A1. Furthermore, it has also been proposed to incorporate teeth or undulations in the leading edge for similar reasons, for example in European patent application publication EP 2 760 737 A1 and in US patents 11,560,796 and US 11,047,238. Statement of the invention

[0011] This disclosure is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributing to reducing their environmental impact, particularly in terms of noise emissions. For this purpose, a first aspect of this disclosure relates to an unducted propulsive fan, comprising at least a first row of blades capable of rotating around a central axis, each of the blades of the first row comprising a profiled body extending radially from an inner radius Ri to an outer radius R e relative to the central axis and comprising an intrados and an extrados connecting a leading edge to a trailing edge. The profiled body of each blade of the first row of blades has an activity factor FA between 100 and 225, preferably between 150 and 200, said activity factor FA being defined according to the equation: 100,000 FA = 16 where represents a radial distance from the central axis, divided by the outer radius R e , and c(f) represents a local chord between the leading and trailing edges of the profiled body at said radial distance . Furthermore, the trailing edge of the profiled body of at least one blade of the first row of blades has saw teeth.

[0012] The activity factor FA between 100 and 225, relatively high, is conducive to better propulsive efficiency, but implies that the chord is relatively large in the upper part of the blade, that is to say close to its external radius R e. Since the boundary layer thickness at the trailing edge normally increases with chord, such a relatively high FA activity factor is normally associated with an increase in the inherent, broadband fan noise and the characteristic width or scale of the blade wake vortices. The inventors have, however, found that the teeth at the trailing edge make it possible to limit noise emissions even with such a high FA activity factor, so as to combine high propulsive efficiency with moderate noise emissions.

[0013] The trailing edge may in particular have spacings between adjacent tooth apexes which decrease monotonically in the radial direction towards the outer radius R e. By "monotonic" decrease, in the context of this disclosure, it is meant that the spacing between the apexes of adjacent teeth located most radially to the outside is less than that between the apexes of adjacent teeth located most radially to the inside and that, from the spacing between the apexes of adjacent teeth located most radially to the inside to the spacing between the apexes of adjacent teeth located most radially to the outside, each spacing is equal to or less than the preceding adjacent spacing. However, it is alternatively envisaged that the spacings between apexes of adjacent teeth are increasing in the radial direction towards the outer radius R e .

[0014] Thus, it is conceivable that each spacing among said spacings between adjacent tooth apexes is different, that is to say that, from the spacing between the apexes of the adjacent teeth located most radially on the inside to the spacing between the apexes of the adjacent teeth located most radially on the outside, each spacing is less than the preceding adjacent spacing if the spacings between adjacent tooth apexes decrease towards the outer radius R e .

[0015] However, it is alternatively conceivable that at least two adjacent spacings, but preferably not more than five, or even three, among said spacings between adjacent tooth tips, preferably in an upper part of the blade, close to its outer radius, are substantially identical, in particular in order to simplify the production of the blades.

[0016] Each of the blades in the first row of blades can have an elongation equal to the outer radius R e multiplied by a coefficient between 0.8 m' 1 and 2.4 m' 1 , preferably between 1 and 2 m' 1 and 2.2 m' 1 , or preferably between 1.4 m 1 and 1.8 m' 1 . Such an elongation, normalized by the outer radius R e of the blade, and therefore the diameter D of the row of blades, allows for good distribution of the aerodynamic load.

[0017] If the spacings between adjacent tooth tips decrease monotonically from the inner radius Ri to the outer radius R e , it is possible that a ratio between a maximum spacing and a minimum spacing among said spacings between adjacent tooth apices is less than 15, preferably less than 8, and even more preferably less than 5, so as to limit the number of teeth and / or the number of different spacings and thus simplify the production of the blades. This ratio may also in particular be greater than 1.25.

[0018] A maximum spacing among the spacings between adjacent tooth tips may be between 0.05 and 0.4 times the height of the profiled body of the blade, i.e., the difference between said outer radii R e and interior R i;preferably between 0.1 and 0.35 times said height, more preferably between 0.15 and 0.3 times said height. It is thus possible to obtain a maximum spacing which may be of the order of magnitude of the wavelength of the second harmonic r2 of the blade passage frequency ("BPF") during the take-off phase of the aircraft, which may be particularly important in terms of acoustic nuisance. This wavelength of the second harmonic of the BPF may be estimated according to the equation: in which c0 represents the speed of sound (in m / s), B the number of blades and Q the rotation speed of the first row of blades (in revolutions per minute).

[0019] The trailing edge may be formed such that any ratio between adjacent spacings among said spacings between adjacent tooth tips is between 1 and 2, preferably between 1.03 and 1.5. In particular, each ratio between adjacent spacings may be approximately equal to one plus the inverse of a positive integer. By "approximately" is meant that it may be subject to a margin of error of ±30%, or preferably ±10%. This allows for decreasing adjacent spacings depending on the wavelength of the blade passing frequency ("BPF") or its harmonics.

[0020] The trailing edge may be configured such that each of the teeth of the trailing edge has a height between 0.1 and 2 times a spacing between the top of the same tooth and the top of an adjacent tooth, preferably between 0.2 and 1.6 times the spacing between the top of the same tooth and the top of the adjacent tooth, more preferably between 0.3 and 1.2 times the spacing between the top of the same tooth and the top of the adjacent tooth. The choice of this ratio makes it possible to better reduce noise emissions, while ensuring good mechanical strength.

[0021] Said trailing edge teeth may take the form of undulations, in particular sinusoidal, although other forms are also conceivable. If the teeth are sinusoidal, the trailing edge may be configured such that each spacing between adjacent tooth apexes is equal to the square of the height of one of the adjacent teeth, multiplied by a coefficient between 0.005 mm' 1 and 1 mm'1 , preferably between 0.01 mm' 1 and 0.8 mm' 1 , still preferably between 0.02 mm' 1 and 0.6 mm' 1 . Indeed, when the teeth are sinusoidal, the radius of curvature at the hollows between adjacent teeth is proportional to the ratio between the spacing and the square of the height. However, a radius of curvature that is too small at the hollows increases the mechanical constraints and makes the blade difficult to manufacture, while a radius of curvature that is too large would be less effective in reducing noise emissions.

[0022] The propulsive fan may have pitch angles, at the radial positions of the tooth tips, which decrease monotonically in the radial direction towards the outer radius R e. In addition or alternatively to this, the radial position of each tooth tip may correspond substantially to a radial position of a local maximum or local minimum of pitch angle. "Substantially" may be understood in this context to mean that the radial positions of tooth tips and the radial positions of local maxima or minima of pitch angle correspond to within 5%, preferably within 2%, of the height of the profiled body of the blade.

[0023] Said trailing edge of the at least one blade of the first row of blades may comprise at least one portion without teeth, and in particular two portions without teeth separated from each other in the radial direction. In particular, the at least portion without teeth may comprise a high portion extending to the outer radius R e. This upper part without teeth may extend over only 45% of the blade height or less, preferably over only 20% of the blade height or less. Thus, if at least a second row of blades, rotating or static, is arranged downstream of the first row, and this second row is of smaller diameter than the first row, which is usually referred to by the English term "clipping", the omission of the teeth on the upper part makes it easier to manufacture the blades and the mechanical strength without affecting the aerodynamic interactions between the upstream and rear rows, since the blades of the rear row may not be impacted by the wake and / or the head vortex of the upper part, devoid of teeth, of the blades of the front row.

[0024] However, it is also possible to have parts of the trailing edge without teeth elsewhere than on an upper part of the blades. For example, when an air inlet, in particular a gas turbine engine air inlet, is arranged downstream of the first row of blades, and in particular of a lower part of the blades of the first part of the blades, adjacent to their inner radius Ri, it is possible for this part of the blades arranged upstream of the air inlet to be without teeth, thus preventing them from being able to enter the air inlet in the event of breakage of one or more teeth. Furthermore, it is also possible for a middle part of the blades, extending for example between the lower quarter and the upper quarter of the height of the blades, to be without teeth on the trailing edge, in order to reduce the mechanical stresses in this particularly stressed area.

[0025] One or more of said teeth may be inclined radially outwards, in order to locally redirect the flow. In particular, teeth located in a high part of the blade, for example less than 45% of the height of the blade away from the outer radius R e , preferably less than 20% of the blade height distance from the outer radius R e , can be inclined radially outwards in order to move the blade tip vortices outwards and thus reduce their interactions with, for example, a second row of blades located downstream of the first row. It is also possible to gradually increase the inclination of the teeth according to their radial distance from the central axis.

[0026] As indicated previously, a second row of blades can be arranged downstream of the first row of blades, in particular according to the so-called “USF” configuration, in which this second row of blades is not not rotating around the central axis, although the so-called "CROR" configuration, in which the second row of blades is counter-rotating relative to the first row of blades, is also conceivable. In either case, at least one blade of the first and / or second row may be variable-pitch. A leading edge of at least one blade of the second row of blades may have a belly, and the trailing edge of at least one blade of the first row of blades may then have at least one tooth tip at a radial distance from the central axis approximately equal to a radial distance of said belly relative to the central axis. By "approximately equal", it can be understood, in this context, that the radial distance of the tooth tip is equal to that of the belly, ±20% (or even only ±10%) of the height of the blade of the first row.

[0027] A second aspect of the present disclosure relates to a thruster that may comprise the unducted propulsive fan, according to the first aspect, and a gas turbine engine for actuating the unducted propulsive fan. The thruster may in particular also comprise a reduction gear interposed between the gas turbine engine and the propulsive fan, in order to reduce the rotational speed of the propulsive fan relative to an output speed of the gas turbine engine. However, other actuation means are also conceivable, such as for example a hybrid thruster in which the gas turbine engine would be combined with an electric motor, which could be interposed in series between the gas turbine engine and the fan, or be arranged in parallel with the gas turbine engine in a transmission line. An electric thruster, comprising only an electric motor for actuating the propulsive fan, is also conceivable.

[0028] A third aspect of the present disclosure relates to an aircraft comprising a propellant as described above. Brief description of the drawings

[0029] The invention will be well understood and its advantages will appear better, on reading the detailed description which follows, of embodiments shown in as non-limiting examples. The description refers to the attached drawings which are schematic and are intended above all to illustrate the principles of the disclosure.

[0030] In these drawings, from one figure to another, identical or equivalent elements (or parts of elements) are identified by the same reference signs. In these attached drawings:

[0031] [Fig. 1] Figure 1 schematically illustrates an aircraft.

[0032] [Fig. 2] Figure 2 schematically illustrates a propeller, suitable for propelling the aircraft of Figure 1, equipped with a propulsive fan according to a first embodiment.

[0033] [Fig. 3A] Figure 3A shows a side view of a blade of the propulsive fan of the first embodiment.

[0034] [Fig. 3B] Figure 3B represents a sectional view of the blade of Figure 3A along plane BB.

[0035] [Fig. 3C] Figure 3C illustrates an evolution of the chord of the blade of Figure 3A as a function of the radial distance from the central axis of the propulsive fan.

[0036] [Fig. 3D] Figure 3D illustrates the evolution of the pitch angle of the blade of Figure 3A as a function of the radial distance from the central axis of the propulsive fan.

[0037] [Fig. 3E] Figure 3E illustrates an alternative shape of the trailing edge of the blade of Figure 3A.

[0038] [Fig. 4] Figure 4 represents a side view of a blade of a propulsive fan according to a second embodiment.

[0039] [Fig. 5] Figure 5 illustrates a propulsive fan according to a third embodiment.

[0040] [Fig. 6] Figure 6 illustrates a propulsive fan according to a fourth embodiment.

[0041] [Fig. 7] Figure 7 illustrates a propulsive fan according to a fifth embodiment.

[0042] [Fig. 8] Figure 8 illustrates a side view of a propulsive fan blade according to a sixth embodiment.

[0043] [Fig. 9] Figure 9 illustrates a side view of a propulsive fan blade according to a seventh embodiment.

[0044] [Fig. 10] Figure 10 illustrates a side view of a propulsive fan blade according to an eighth embodiment. Description of the embodiments

[0045] In order to make the disclosure more concrete, embodiments are described in detail below, with reference to the accompanying drawings. It is recalled, however, that the invention is not limited to these embodiments.

[0046] As illustrated in FIG. 1, an aircraft 1 may incorporate one or more propellers 10 with unducted propulsive fans 100 according to the present description. These propellers 10 may in particular be arranged, as illustrated, under the wings 2, but other alternative arrangements, for example at the rear of the fuselage of the aircraft 1, are also conceivable.

[0047] As illustrated in Figure 2, the propellant 10 may also comprise a gas turbine engine 11 and a reduction gear 12. In the direction of air flow, this gas turbine engine 11 may comprise a low-pressure compressor 13, a high-pressure compressor 14, a combustion chamber 15, a high-pressure turbine 16, a low-pressure turbine 17 and a nozzle 18, surrounded by a fairing 19 terminating in the nozzle 18. The high-pressure turbine 16 may be connected to the high-pressure compressor 14 by a first rotary shaft 21 for driving the latter, while the low-pressure turbine 7 may be connected to the low-pressure compressor 3 by a second rotary shaft 22 coaxial with the first rotary shaft 21, in a similar manner. The reduction gear 12 may connect the second rotary shaft 22 to the propellant fan 100 for actuating the latter.Although in the illustrated example the propulsive fan 100 is arranged at the front of the thruster 10, in a so-called “puller” configuration, it is also possible to arrange it at the rear of the thruster, in a “pusher” configuration.

[0048] In addition to or replacing the gas turbine engine 11, the thruster 10 could however comprise another type of motor, and in particular an electric motor, for actuating the fan, directly and / or through a transmission such as the reducer 12. The thruster 10 could therefore be a hybrid thruster, in series or parallel, or even purely electric.

[0049] The propulsive fan 100 may comprise two rows of blades: a first row of blades 110 and a second row of blades 120, downstream of the first row of blades 110. The two rows may in particular be coaxial, with the blades of the two rows 110, 120 arranged radially around the same central axis X, but it is also conceivable that they have different central axes, and in particular parallel ones. Each of the rows may contain, for example, between 8 and 16 blades, in particular between 10 and 14. However, the first row may have a greater number of blades than the second row to minimize the noise emitted by the propulsive fan 100, for example the first row may have at least 2 more blades than the second row.

[0050] Each of the blades 1, 10, 120 of the two rows may comprise a profiled body extending radially, relative to a profiled body, from an inner radius to an outer radius of the corresponding row, as illustrated in FIGS. 2 and 3A. However, the inner radii Ri and / or outer radii R e of the first row may be different from the inner radii R, 1 and / or exterior R e ' of the second row. In particular, as shown in the figures, the outer radius R e ' of the second row may be less than the outer radius R e of the first row ("clipping"), in order to avoid interference of the blade tip vortices of the first row with the blades 120 of the second row. The outer radius R e of the first row can be, for example, between 0.5 and 3 m, in particular between 1.5 and 2.5 m. The ratio Rj / R e between the inner radii Ri and the outer radii R eof the first row of blades 1 10 can be for example between 0.1 and 0.5, in particular between 0.25 and 0.35, even more particularly between 0.26 and 0.32.

[0051] The profiled body of each blade 1 10, 120 can be formed by aerodynamic profiles stacked along a corresponding radial stacking axis Z, Z', so as to form, as illustrated in FIG. 3B, a lower surface 1 1 1 and a extrados 112, each extending from a leading edge BA to a trailing edge BF. For example, for an aerodynamic section or profile of the blade 110, the leading edge BA can be defined as the upstream end along the direction of flow of the fluid. The leading edge BA can be characterized by a local minimum on the radius of curvature defining the profile in its upstream portion. The trailing edge BF can be defined as the downstream end along the direction of flow of the fluid. The trailing edge BF can also be characterized by a local minimum on the radius of curvature defining the profile in its rear portion when the trailing edge BF is rounded, although, to simplify the manufacturing process, the trailing edge BF can alternatively be truncated, as illustrated in FIG. 3E. These aerodynamic sections or profiles can in particular be cambered.Each of the stacked profiles has a chord c which is defined as the distance between the leading edge BA and the trailing edge BF on a straight line connecting them and having a pitch angle y relative to a plane perpendicular to the central axis X. The chord c and the pitch angle y can be variable depending on the radial distance r from the central axis X of the propulsive fan.

[0052] Conventionally, the pitch angle y of an aerodynamic profile corresponds to the angle formed between, on the one hand, a first axis 150 which is defined by the intersection between the plane of the aerodynamic profile at the radial distance r and a plane perpendicular to the central axis X, and on the other hand, a straight line connecting the leading edge BA and the trailing edge BF of the aerodynamic profile at the radial distance r. The pitch angle y is measured on the upstream side of the plane perpendicular to the central axis X. The pitch angle y is measured positively in a direction going from the first axis 150 to the straight line connecting the leading edge BA and the trailing edge BF, and more particularly in a direction coinciding with the direction going from the intrados line 111 to the extrados line 112.

[0053] As illustrated in Figure 3A, the inner radii Ri and outer radii R eof a blade 110 of the first row can be measured on the trailing edge BF and correspond, respectively, to the minimum and maximum radial positions relative to the central axis X. When the blade 110 is of variable pitch, the radial distances can be measured with the blade 110 placed at any pitch angle allowing the usual direction of air circulation through the fan. For example, when the pitch angle y is equal to 60° for a blade section 110 located approximately 75% of R e , which may be representative of the blade pitch angle 110 in cruise. Similarly, the inner radii R and outer radii R e' of a blade 120 of the first row can be measured on the leading edge BA' and correspond, respectively, to the minimum and maximum radial positions relative to the central axis X. When the blade 120 is of variable pitch, the radial distances can be measured with the blade 120 placed at any pitch angle allowing the usual direction of air circulation through the fan. For example when the pitch angle y' is equal to 80° for a section of the blade 120 located approximately 75% of R e '.

[0054] Each of the two rows of blades may have a strength less than, for example, 2.5 over the entire height H, H' of the blades 110, 120, or even less than 0.5 at the outer radius R e , R e ' of the row. By "blade height" is meant, in the context of this presentation, the difference between the external radius R e , and the inner radius R i;Ri' of its profiled body, and by "solidity", the ratio between the chord c of each blade 110, 120 of a row and the distance between two adjacent blades in the same row at the same radial distance r from the central axis X. Each of the blades of the first row of blades can have an elongation equal to the outer radius R e multiplied by a coefficient between 0.8 m' 1 and 2.4 m' 1 , preferably between 1 and 2 m' 1 and 2.2 m' 1 , or preferably between 1.4 m 1 and 1.8 m' 1 . In the context of this presentation, "elongation" means the ratio between the height H and the mean chord C of the blade. As for the mean chord C, it can be calculated from the distribution c(r) of the local chord c as a function of the radial distance, according to the equation:

[0055] The axial distance between the stacking axes Z, Z' of the two rows of blades may be, for example, between 0.05 and 1.2, in particular between 0.36 and 0.6 times the outer radius R e of the first row of blades 110, and above all sufficient to prevent interference of the trailing edges BF of the blades 110 of the first row with the leading edges of the blades 120 of the second row. Each of the blades 110, 120 can be rotatable about a radial axis or axis of change of setting, which may in particular be the corresponding stacking axis Z, Z', in order to adjust its setting and therefore its incidence relative to the direction of air flow according to the flight phase. This setting change axis may preferably be perpendicular to the central axis X, alternatively inclined relative to the central axis X.

[0056] As illustrated in Figure 2, at least the first row of blades 110 may be able to rotate around the central axis X, and in particular be mechanically connected, for its rotational drive around the central axis X, to the gas turbine engine 11, possibly via a reducer 12. Furthermore, in order to take advantage of the increase in the dynamic pressure of the air downstream of this first row of blades 110, an air inlet 20 of the gas turbine engine 11 may in particular be arranged between the two rows of blades 110, 120. This air inlet 20 may for example be annular, with a nozzle 23 separating the air inlet 20 from the fairing 19.

[0057] On the other hand, the second row of blades 120 may be, as also illustrated in FIG. 2, non-rotatable about the central axis X, according to a non-ducted configuration of the “USF” type. However, it is alternatively conceivable that it is also rotatable about the central axis X, and in particular also be mechanically connected to the gas turbine engine 11 to be driven in rotation about the central axis X, although in the opposite direction of rotation to that of the first row of blades 110, according to a “CROR” type configuration. In this case, it is also conceivable that the rotational speed of the second row of blades 120 is less than or equal to the rotational speed of the first row of blades, in particular during a takeoff and / or landing phase of the aircraft 1.This makes it possible to reduce the speed of the flow which interacts with the second row of blades 120 and therefore to reduce the interaction noise and to limit (or avoid) the formation of shocks.

[0058] The trailing edge BF of the profiled body of each blade 110 of the first row may have a number N of teeth with tooth heights hj where j=1, 2, ... N in increasing order in the radial direction from the inner radius Ri to the outer radius R e , and a number M of spacings À k between adjacent tooth apices, where k=1,2,...M and M < N-1 in ascending order in the radial direction from the inner radius Ri to the outer radius R e. In the context of this presentation, "tooth apex" means a local maximum of the chord c in the radial direction and "tooth height" means the difference between the chord at the tooth apex and the chord at a trough, i.e. a local minimum of the chord, located between the apex of this tooth and that of the adjacent tooth. It should be noted that a tooth apex can be characterized by a zero derivative of c(r) and a negative second derivative of c(r), while a trough can be characterized by a zero derivative of c(r) and a positive second derivative of c(r).

[0059] Following the camber of the stacked profiles of the blade 1 10, the variations of the chord c may be accompanied by variations of the pitch angle y, as illustrated in Figure 3C and 3D, in order to optimize the aerodynamic operation of the blade 1 10. In particular, the pitch angle y may have a local maximum or a local minimum at the radial position of each tooth tip, more or less up to, for example, 5%, preferably 2%, of the height H of the profiled body of the blade 1 10.

[0060] The ratio between a maximum spacing To m ax and a minimum spacing A m in among said spacings To k for k=1, 2,...M between adjacent tooth apices can be less than 15, preferably less than 8, and even more preferably less than 5. This ratio between the maximum spacing À m ax and the minimum spacing A m in can also be greater than 1.25. The maximum spacing À max can also be between 0.05 and 0.4 times the height H of the profiled body of the blade 110, preferably between 0.1 and 0.35 times said height, more preferably between 0.15 and 0.3 times said height.

[0061] Each of the teeth can have a height hj between 0.1 and 2 times a spacing À k between the top of the same tooth and the top of an adjacent tooth, preferably between 0.2 and 1.6 times the spacing A k between the top of the same tooth and the top of the adjacent tooth, preferably still between 0.3 and 1.2 times the spacing A k between the top of the same tooth and the top of the adjacent tooth.

[0062] As illustrated in Figures 2 and 3A, the teeth may take the form of undulations, and in particular of substantially sinusoidal undulations, even if other alternative shapes such as triangular teeth are also conceivable. The trailing edge can be configured such that each spacing Àk between adjacent tooth apexes can be equal to the square of the height of one of the adjacent teeth, multiplied by a coefficient between 0.005 mm' 1 and 1 mm' 1 , preferably between 0.01 mm' 1 and 0.8 mm' 1 , still preferably between 0.02 mm' 1 and 0.6 mm' 1 , especially if the teeth are sinusoidal. Thus, a compromise can be obtained, for the radius of curvature of the teeth, between aerodynamic efficiency and mechanical strength.

[0063] As also illustrated in Figures 2 and 3A, the succession of teeth can extend over the entire height H of the profiled body of the blade 110, from the inner radius Ri to the outer radius R e. In particular, the trailing edge BF may have a last hollow or tooth crest at a radial distance, relative to the outer radius R e , of less than 30%, or even 20%, of the height H, in particular to redirect the flow of the blade tip vortices radially outwards and thus avoid undesirable interactions with the blades 120 of the second row downstream. In addition, the trailing edge BF may have a first hollow or tooth crest at a radial distance, relative to the inner radius Ri, of less than 30%, or even 20%, of the height H, in particular to avoid or limit boundary layer separation near the root of the blade 110 which could also have an undesirable interaction with the blades 120 of the second row downstream or degrade the aerodynamic performance of the air inlet 20.

[0064] Furthermore, when the leading edge BA' of the blades 120 of the second row has an antinode V at a radial distance r v of the central axis X, between the inner radius Ri' and the outer radius R e ' of this second, the trailing edge BF of the blades 110 of the first row may have at least one tooth tip at a radial distance from the central axis X equal to the radial distance r v , more or less at most 20%, or even 10%, of the height H, in order to reduce the undesirable interactions between the wake of the blades 110 of the first row and the belly zone V of the blades 120 of the second row. Indeed, at the belly zone V of the blades 120, the axial distance between the trailing edge BF of the blades 110 and the leading edge BA' of the blades 120 can be reduced, and the leading edge BA' of the blades 120 has a reduced or zero sweep angle, which can increase the interaction noise. From an aerodynamic point of view, the tips of the teeth make it possible to reduce the speed deficit locally in the wake of the blades 1 10, hence the interest in placing a tip of a tooth of the trailing edge BF of the blades 1 10 at the radial position of the belly V of the leading edge BA' of the blades 120 to reduce the interaction noise. By "belly" of the leading edge of a blade, is meant, in the context of the present disclosure, the most advanced point of the leading edge in the upstream axial direction.

[0065] The spacings To k can vary, and in particular decrease monotonically in the radial direction towards the outer radius R e , such that À1> À2À3>... AM-I AM- Thus, any ratio between adjacent spacings À k and To k+imay be between 1 and 2, preferably between 1.03 and 1.5. Furthermore, as illustrated in Figure 3D, the alignment angles y at the radial positions of the vertices may also decrease monotonically in the radial direction towards the outer radius R e , such that y(r1) > y(r2) y(r3)... y(r N-1 ) > y(r N ), in order to adapt them to a relative flow angle which decreases towards the outer radius R e due to the rotation of the blades. However, it is alternatively possible that the spacings À k are increasing in the radial direction towards the outer radius R e .. As illustrated in Figures 2 and 3A, all spacings can be different, so that as the spacings λk decrease towards the outer radius R e , Ài> À2> À3... À M -I>ÀM- In particular, each ratio between adjacent spacings À k and To k+ican be approximately equal to one plus the reciprocal of a positive integer.

[0066] Alternatively, it is nevertheless conceivable that some of the spacings are identical, while maintaining a decrease or an increase, monotonous on all of the spacings. Thus, according to a second embodiment illustrated in FIG. 4, at least two, for example two to five, in particular two, three or four spacings can be substantially identical. The identical spacings can in particular be located in an upper part BFh of the trailing edge BF of the blade 110, adjacent to the outer radius R e , and extending for example over the upper 45% or 20% of the height H of the profiled body of the blade 1 10. The other characteristics of the propulsive fan may however be identical or equivalent to those of the first embodiment and consequently receive the same references in Figure 4 as in the previous figures.

[0067] Furthermore, although in the two previous embodiments the teeth extend over the entire height H of the profiled body of the blade 110, it is also conceivable that at least a portion of the trailing edge is devoid of teeth. Thus, according to a third embodiment illustrated in FIG. 5, a high portion BFh of the trailing edge BF of the blade 110, adjacent to the outer radius R e , may be devoid of teeth. In this embodiment, this upper part BFh devoid of teeth may for example extend from a radial distance r substantially identical to the outer radius R e' of a row of blades 120 of smaller diameter arranged downstream. The other characteristics of the propulsive fan may however remain identical to those of the previous embodiments, and consequently receive the same references in Figure 5 as in the previous figures.

[0068] Although in the third embodiment the part without teeth is an upper part of the trailing edge, it is also conceivable to have, alternatively or in addition to this, one or more different parts of the trailing edge BF of the blades 110 without teeth. Thus, according to a fourth embodiment illustrated in FIG. 6, a lower part BFb of the trailing edge BF may also be without teeth. This lower part BFb of the trailing edge BF may in particular extend from the inner radius Ri and up to a radial distance r which may be, for example, equal to or greater than the radial position Rb of the nozzle 23 of an air inlet 20 arranged downstream of the blades 110, and this in particular in order to prevent the teeth from being able to enter the air inlet 20 in the event of tooth fracture, which could degrade the operation of the thruster.The other characteristics of the propulsive fan may however remain identical to those of the previous embodiments, and consequently receive the same references in Figure 6 as in the previous figures.

[0069] Alternatively, however, at least one toothless portion may be a central portion BFc of the trailing edge BF of the blade 110, extending neither to the inner radius Ri nor to the outer radius R e , as in the fifth and sixth embodiments respectively illustrated in the figures 7 and 8. This central part BFc without teeth can in particular extend between two tooth tops, as in the fifth embodiment illustrated in figure 7, or alternatively between two hollows, as in the sixth embodiment illustrated in figure 8.

[0070] The teeth can be inclined radially outwards. With such an inclination, even if the spacing between adjacent tooth tips decreases monotonically, the radial distance Ar a between at least one tooth crest and the adjacent outwardly inclined trough may be less than the radial distance Ar b between said adjacent hollow and the next peak outwards. It is conceivable that only the teeth located on a high part BFh of the trailing edge are inclined outwards, as in the seventh embodiment illustrated in Figure 9, with possibly a transition zone in which this inclination increases gradually. However, it is also conceivable, as in the eighth embodiment illustrated in Figure 10, that all the teeth are inclined outwards.

[0071] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments discussed may be combined in additional embodiments. Therefore, the description and drawings are to be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. Unducted propulsive fan (100) comprising at least a first row of blades (110) capable of rotating about a central axis (X), each of the blades (110) of the first row comprising a profiled body extending radially from an inner radius R to an outer radius R e relative to the central axis (X) and comprising a lower surface (111) and an upper surface (112) connecting a leading edge (BA) to a trailing edge (BF), in which the profiled body of each blade (110) of the first row of blades (110) has an activity factor FA between 100 and 225, preferably between 150 and 200, said activity factor FA being defined according to the equation: 100,000 FA 16 where f represents a radial distance from the central axis (X), divided by the outer radius R e, and c( represents a local chord between the leading (BA) and trailing (BF) edges of the profiled body at said radial distance, and characterized in that it also comprises a second row of blades (120) arranged downstream of the first row of blades (110), in that the trailing edge (BF) of the profiled body of at least one blade (110) of the first row of blades (110) has saw teeth, and a leading edge (BA') of at least one blade (120) of the second row of blades (120) has a belly (V) and the trailing edge (BF) of at least one blade (110) of the first row of blades (110) has at least one tooth tip at a radial distance (q) from the central axis (X) approximately equal to a radial distance (r v ) of said belly (V) relative to the central axis (X).

2. An unducted propulsive fan (100) according to claim 1, wherein the trailing edge (BF) has spacings (À k) between adjacent tooth apexes which decrease monotonically in the radial direction towards the outer radius R e .

3. An unducted propulsive fan (100) according to claim 2, wherein each spacing (A k ) among said spacings (At k ) between adjacent tooth apexes is different.

4. An unducted propulsive fan (100) according to claim 2, wherein at least two adjacent ones of said spacings (A k ) between adjacent tooth tops are substantially identical.

5. An unducted propulsive fan (100) according to any one of claims 2 to 4, wherein a ratio of a maximum spacing to a minimum spacing among said spacings (A k) between adjacent tooth apexes is less than 15, preferably less than 8, and more preferably less than 5 and greater than 1.

25.

6. An unducted propulsive fan (100) according to any one of claims 2 to 5, wherein a maximum spacing among said spacings (A k ) between adjacent tooth apexes is between 0.05 and 0.4 times a difference between said outer radii R e and interior R, preferably between 0.1 and 0.35 times the difference between said exterior radii R e and interior R, still preferably between 0.15 and 0.3 times the difference between said exterior radii R e and interior R.

7. An unducted propulsive fan (100) according to any one of claims 2 to 6, wherein a minimum spacing among said spacings (A k) between adjacent tooth apexes is between 0.01 and 0.2 times a difference between said outer radii R e and interior R, preferably between 0.02 and 0.15 times the difference between said exterior radii R e and interior R, still preferably between 0.04 and 0.12 times the difference between said exterior radii R e and interior R.

8. An unducted propulsive fan (100) according to any one of claims 2 to 7, wherein any ratio between adjacent ones of said spacings (A k ) between adjacent tooth apexes is between 1 and 2, preferably between 1.03 and 1.5

9. Unducted propulsive fan (100) according to any one of claims 2 to 8, having pitch angles (Yj), at the radial positions (q) of the tooth apexes, which decrease monotonically in the radial direction towards the outer radius R e .

10. An unducted propulsive fan (100) according to any preceding claim, wherein each of the blades (110) of the first row of blades (110) has an aspect ratio equal to the outer radius R e multiplied by a coefficient between 0.8 m 1 and 2.4 m 1 , preferably between 1.2 m -1 and 2.2 m' 1 , or preferably between 1.4 m -1 and 1.8 m' 1 .

11. An unducted propulsive fan (100) according to any preceding claim, wherein each of the trailing edge teeth (BF) has a height (hj) between 0.1 and 2 times a spacing (À k ) between the top of the same tooth and the top of an adjacent tooth, preferably between 0.2 and 1.6 times a spacing (À k ) between the top of the same tooth and the top of the adjacent tooth, still preferably between 0.3 and 1.2 times a spacing (À k) between the top of the same tooth and the top of the adjacent tooth.

12. An unducted propulsive fan (100) according to any preceding claim, wherein the radial position (q) of each tooth tip substantially corresponds to a radial position of a local maximum or a local minimum of pitch angle.

13. An unducted propulsive fan (100) according to one of the preceding claims, wherein each spacing (A k ) between adjacent tooth tops is equal to the square of a tooth height (hj) of one of the adjacent teeth, multiplied by a coefficient between 0.005 mm 1 and 1 mm 4 , preferably between 0.01 mm 4 and 0.8 mm 4 , still preferably between 0.02 mm 4 and 0.6 mm 1 .

14. Unducted propulsive fan (100) according to any one of the preceding claims, wherein said trailing edge (BF) of the at least one blade (110) of the first row of blades (110) comprises at least one toothless portion, in particular two toothless portions separated from each other in the radial direction.

15. An unducted propulsive fan (100) according to claim 14, wherein the at least one toothless portion comprises a high portion (BFh) extending to the outer radius R e .

16. An unducted propulsive fan (100) according to any preceding claim, wherein one or more of said teeth are radially outwardly inclined.

17. An unducted propulsive fan (100) according to any preceding claim, wherein the second row of blades (120) is not rotatable about the central axis (X).

18. A thruster (10) comprising the unducted propulsive fan (100) according to any preceding claim and a gas turbine engine (11) for driving the unducted propulsive fan (100).

19. An aircraft (1) comprising the propellant of claim 18.

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