Unfaired fan for aircraft propulsion

Abstract

Unfaired fan for aeronautical propulsion. Unfaired 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 comprises a streamlined body extending radially from an inner radius Ri to an outer radius Re with respect to the central axis (X) and comprising an intrados (111) and an extrados (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 teeth with spacings (λk) between adjacent tooth apexes that decrease monotonically in a radial direction towards the outer radius Re and the profiled body of each blade (110) of the first row of blades (110) has an activity factor FA between 100 and 225. Figure for the abstract: Fig. 2.

Description

Title of the invention: Unfaired fan for aeronautical propulsion technical field

[0001] The technical field of this presentation is that of propulsion and in particular that of unfaired propulsive fans, such as those intended 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 restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0003] Technological research efforts have already made it possible to significantly improve 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 by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the lightening of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

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

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

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

[0009] When the fan is enclosed, increasing the fan diameter also increases the external dimensions of the surrounding retaining casing, as well as the nacelle forming the aerodynamic envelope of said casing, and therefore its drag, as well as their mass. To avoid these drawbacks, it is possible to shorten the axial length of the nacelle and thin it, which reduces the space available for acoustic treatments used for noise reduction. Furthermore, several types of unenclosed propulsion fans have been considered, including 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" are understood, in the context of this discussion, as defined with respect to the usual direction of airflow through the fan. However, in "USF" ("Unducted Single Fan") propulsive fans, only the upstream row rotates around the central axis, while in "CROR" ("Counter-Rotating Open Rotor") propulsive fans, both rows rotate in opposite directions. Nevertheless, in both types, blades in each of the two rows may have variable pitch.

[0010] One drawback of unfaired propulsion fans is the level of noise emissions. Indeed, in the absence of a casing or nacelle surrounding the fan, its noise emissions are directly diffused into the environment. Furthermore, the interactions between successive rows of blades can exacerbate these noise emissions, particularly at the harmonics of the blade passing frequency (BPF). Significant research and development efforts have therefore been directed, notably by the Applicant, towards reducing these noise emissions. To this end, it has been proposed, in particular in the pu Publications of international patent applications WO 2023 / 007098 A1 and WO 2019 / 158875 A1 describe the formation of teeth or undulations on the trailing edge of the blades of unfaired propulsion fans, in order to reduce or distribute their wingtip vortices. This solution has also been proposed for faired fans, for example in French patent applications FR 2 986 285 A1 and FR 3 103 231 A1. Furthermore, it has also been proposed to incorporate teeth or undulations on the leading edge for similar reasons, for example in European patent application EP 2 760 737 A1 and in US patents 11,560,796 and 11,047,238. Description of the invention

[0011] The present description is the result of technological research aimed at significantly improving aircraft performance and, in this respect, contributing to the reduction of their environmental impact, particularly in terms of noise emissions. To this end, a first aspect of the present description concerns an unfaired propulsive fan, comprising at least one first row of blades capable of rotating about a central axis. Each blade in the first row comprises a streamlined body extending radially from an inner radius R to an outer radius Re with respect to the central axis and comprising an intrados and an extrados connecting a leading edge to a trailing edge. The streamlined body of each blade in the first row has an activity factor FA between 100 and 225, preferably between 150 and 2001. Said activity factor FA is defined according to the equation: FA- 100,000 df) • 3 ^where f represents a radial distance with respect to the axis central, divided by the outer radius Re, and c(f) represents a local chord between the leading and trailing edges of the airfoil body at said radial distance F. In addition, the trailing edge of the airfoil body of at least one blade of the first row of blades has teeth with spacings between adjacent tooth apexes that decrease monotonically in a radial direction towards the outer radius Re.

[0012] The activity factor FA between 100 and 225, which is relatively high, is conducive to better propulsive efficiency, but implies that the chord is relatively large in the upper part of the blade, i.e., near its outer radius Re. Since the boundary layer thickness at the trailing edge normally increases with the chord, such a relatively high activity factor FA is normally associated with an increase in the fan's own broadband noise and the characteristic width or scale of the blade wake vortices. However, the inventors have found that the trailing-edge teeth, with their decreasing spacing towards the outer radius Re, make it possible to limit noise emissions even with such a high activity factor FA, thus combining high propulsive efficiency with this. with moderate noise emissions.

[0013] By "monotonous", in the context of the present exposition, it is understood that the spacing between the tops of the adjacent teeth located most radially outside is less than that between the tops of the adjacent teeth located most radially inside and that, from the spacing between the tops of the adjacent teeth located most radially inside to the spacing between the tops of the adjacent teeth located most radially outside, each spacing is equal to or less than the preceding adjacent spacing.

[0014] Thus, it is conceivable that each spacing among said spacings between adjacent tooth vertices is different, that is to say that, from the spacing between the vertices of the adjacent teeth located most radially inside to the spacing between the vertices of the adjacent teeth located most radially outside, each spacing is less than the previous adjacent spacing.

[0015] However, it is alternatively conceivable that at least two adjacent spacings, but preferably no more than five, or even three, among said spacings between adjacent tooth tips, preferably in an upper part of the blade, near its outer radius, are substantially identical, in particular to simplify the production of the blades.

[0016] Each of the blades in the first row of blades can have an aspect ratio equal to the outer radius Re multiplied by a coefficient between 0.8 m1 and 2.4 m1, preferably between 1.2 m1 and 2.2 m1, or even more preferably between 1.4 m1 and 1.8 m1. Such an aspect ratio, normalized by the outer radius Re of the blade, and therefore the diameter D of the row of blades, makes it possible to obtain a good distribution of the aerodynamic load.

[0017] Although the spacings between adjacent tooth tips decrease monotonically from the inner radius R to the outer radius Re, it is conceivable that a ratio between a maximum spacing and a minimum spacing among said spacings between adjacent tooth tips 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.

[0018] A maximum spacing among said spacings between adjacent tooth tips can be between 0.05 and 0.4 times the height of the airfoil body of the blade, that is, the difference between said outer radius Re and inner radius R; preferably between 0.1 and 0.35 times said height, and even more preferably between 0.15 and 0.3 times said height. A maximum spacing can thus be obtained that can be on the order of the wavelength of the second harmonic r2 of the blade passage frequency (“BPF”) during the aircraft takeoff phase, which can be particularly important in terms of noise. This wavelength of the second harmonic of the BPF can be estimated according to the equation: " _ 30¾ in which c0 represents the speed of sound (in m / s), B the number of blades and 7 2 " bü Q is the rotation speed of the first row of blades (in revolutions per minute).

[0019] The trailing edge can 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 can be approximately equal to one plus the inverse of a positive integer. By "approximately" it is meant that it can be subject to a margin of error of ±30%, or preferably ±10%. This allows for adjacent spacings to decrease with respect to the wavelength of the blade passage frequency ("BPF") or its harmonics.

[0020] The trailing edge can be configured such that each tooth of the trailing edge has a height between 0.1 and 2 times the spacing between the crest of the same tooth and the crest of an adjacent tooth, preferably between 0.2 and 1.6 times the spacing between the crest of the same tooth and the crest of the adjacent tooth, and even more preferably between 0.3 and 1.2 times the spacing between the crest of the same tooth and the crest of the adjacent tooth. Choosing this ratio allows for better noise reduction while ensuring good mechanical strength.

[0021] The trailing edge teeth can take the form of undulations, particularly sinusoidal ones, although other shapes are also conceivable. If the teeth are sinusoidal, the trailing edge can be configured such that each spacing between the crests of adjacent teeth is equal to the square of the height of one of the adjacent teeth, multiplied by a coefficient between 0.005 mm¹ and 1 mm², preferably between 0.01 mm¹ and 0.8 mm², and even more preferably between 0.02 mm¹ and 0.6 mm². Indeed, when the teeth are sinusoidal, the radius of curvature at the concave gaps 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 concave gaps increases mechanical stresses and makes manufacturing the blade difficult, while a radius of curvature that is too large would be less effective for reducing noise emissions.

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

[0023] Said trailing edge of at least one blade of the first row of blades may This includes a toothless portion. In particular, this toothless portion can be an upper section extending to the outer radius Re. This toothless upper section can extend over only 45% of the blade height or less, preferably 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 has a smaller diameter than the first row—a phenomenon commonly referred to as "clipping"—the omission of teeth on the upper portion facilitates blade manufacturing and mechanical strength without affecting the aerodynamic interactions between the upstream and aft rows, since the blades of the aft row may not be impacted by the wake and / or the leading edge vortex of the toothless upper portion of the blades in the forward row.

[0024] However, it is also conceivable to have sections of the trailing edge without teeth in areas other than the upper part of the blades. For example, when an air inlet, particularly a gas turbine engine air inlet, is located downstream of the first row of blades, and specifically of a lower portion of the blades of the first row of blades, adjacent to their inner radius R, it is conceivable that this portion of the blades upstream of the air inlet be without teeth, thus preventing the failure of one or more teeth to enter the air inlet. Furthermore, it is also conceivable that a middle section of the blades, extending, for example, between the lower and upper quarters of the blade height, be without teeth on the trailing edge, in order to reduce 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 an upper part of the blade, for example at less than 45% of the blade height from the outer radius Re, preferably at less than 20% of the blade height from the outer radius Re, may be inclined radially outwards in order to direct 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 previously stated, a second row of blades can be arranged downstream of the first row of blades, particularly in the so-called "USF" configuration, in which this second row of blades does not rotate about the central axis, although the so-called "CROR" configuration, in which the second row of blades rotates counter-clockwise with respect to the first row of blades, is also possible. In either case, at least one blade of the first and / or the The second row may have variable pitch. A leading edge of at least one blade in the second row may have a belly, and the trailing edge of at least one blade in the first row may then have at least one tooth crest at a radial distance from the centerline approximately equal to a radial distance of said belly from the centerline. By "approximately equal," we can understand, in this context, that the radial distance of the tooth crest is equal to that of the belly, ±20% (or even only ±10%) of the height of the blade in the first row.

[0027] A second aspect of the present description concerns a propulsion system that may include the uncased propulsion fan, as described in the first aspect, and a gas turbine engine for driving the uncased propulsion fan. The propulsion system may also include a reduction gear interposed between the gas turbine engine and the propulsion fan, in order to reduce the rotational speed of the propulsion fan relative to the output speed of the gas turbine engine. However, other actuation methods are also conceivable, such as a hybrid propulsion system in which the gas turbine engine is combined with an electric motor, which could be interposed in series between the gas turbine engine and the fan, or arranged in parallel with the gas turbine engine in a transmission line.An electric propulsion system, comprising only an electric motor to power the propulsion blower, is also a possibility.

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

[0029] The invention will be better understood and its advantages will become clearer upon reading the following detailed description of embodiments shown by way of non-limiting examples. The description refers to the accompanying drawings, which are schematic and intended primarily to illustrate the principles presented.

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

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

[0032] [Fig.2] Fig.2 schematically illustrates a propulsion system suitable for the propulsion of the aircraft of [Fig.1], equipped with a propulsive blower according to a first embodiment.

[0033] [Fig.3A] Fig.3A represents a side view of a blade of the propulsion blower of the first embodiment.

[0034] [Fig. 3B] [Fig. 3B] represents a cross-sectional view of the blade of [Fig. 3A] along the plan BB.

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

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

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

[0038] [Fig.4] Fig.4 shows a side view of a propeller fan blade according to a second embodiment.

[0039] [Fig. 5] Fig. 5 illustrates a propulsive blower following a third mode of realization.

[0040] [Fig.6] Figure [Fig.6] illustrates a propulsive blower following a fourth mode of realization.

[0041] [Fig.7] Fig.7 illustrates a propulsive blower following a fifth mode of realization.

[0042] [Fig. 8] The [Fig. 8] illustrates a side view of a propulsion blower blade according to a sixth embodiment.

[0043] [Fig. 9] The [Fig. 9] illustrates a side view of a propulsion blower blade according to a seventh embodiment.

[0044] [Fig. 10] The [Fig. 10] illustrates a side view of a propulsion blower blade according to an eighth embodiment. Description of the implementation methods

[0045] To make the explanation more concrete, embodiments are described in detail below, with reference to the accompanying drawings. It should be noted, however, that the invention is not limited to these embodiments.

[0046] As illustrated in [Fig. 1], an aircraft 1 may incorporate one or more unfaired, propeller-driven thrusters 100 according to the present description. These thrusters 10 may, in particular, be arranged, as illustrated, at the rear of the fuselage of the aircraft 1, but other alternative arrangements, for example under the wings 2, are also conceivable.

[0047] As illustrated in [Fig. 2], the propulsion unit 10 may also include a gas turbine engine 11 and a reduction gear 12. In the direction of the airflow, this gas turbine engine 11 may include 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 shroud 19 leading into the nozzle 18. The high-pressure turbine 16 may be connected to the high-pressure compressor The pressure 14 is driven by a first rotating shaft 21, while the low-pressure turbine 7 can be connected to the low-pressure compressor 3 by a second rotating shaft 22 coaxial with the first rotating shaft 21, in a similar manner. The reduction gear 12 can connect the second rotating shaft 22 to the propulsion fan 100 to drive the latter. Although in the illustrated example the propulsion fan 100 is positioned at the front of the thruster 10, in a so-called "puller" configuration, it is also possible to position it at the rear of the thruster, in a "pusher" configuration.

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

[0049] The propulsion 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 both rows 110 and 120 arranged radially around the same central axis X, but it is also possible for them to 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 propulsion fan 100; for example, the first row may have at least 2 more blades than the second row.

[0050] Each of the blades 110, 120 of the two rows may include 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 Figures 2 and 3A. However, the inner radius R and / or outer radius Re of the first row may be different from the inner radius R and / or outer radius Re' of the second row. In particular, as illustrated in the figures, the outer radius Re' of the second row may be smaller than the outer radius Re of the first row ("clipping"), in order to avoid interference from the blade tip vortices of the first row with the blades 120 of the second row. The outer radius Re of the first row may be, for example, between 0.5 and 3 m, in particular between 1.5 and 2.5 m.The ratio R; / Re between the inner radius R; and outer radius Re of the first row of blades 110 can be for example between 0.1 and 0.5, in particular between 0.25 and 0.35, and even more particularly between 0.26 and 0.32.

[0051] The streamlined body of each blade 110, 120 can be formed by aerodynamic profiles stacked along a corresponding radial stacking axis Z, Z', in such a way to form, as illustrated in [Fig. 3B], an intrados 111 and an extrados 112, each extending from a leading edge BA to a trailing edge BF. For example, for a cross-section or airfoil of the blade 110, the leading edge BA can be defined as the upstream end along the fluid flow direction. The leading edge BA can be characterized by a local minimum on the radius of curvature defining the airfoil in its upstream part. The trailing edge BF can be defined as the downstream end along the fluid flow direction. The trailing edge BF can also be characterized by a local minimum on the radius of curvature defining the airfoil in its rear part 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 cross-sections or airfoils 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 with respect to a plane perpendicular to the central axis X. The chord c and the pitch angle y can vary depending on the radial distance r to the central axis X of the propulsive fan.

[0052] Conventionally, the angle of incidence y of an airfoil 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 airfoil 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 airfoil at the radial distance r. The angle of incidence y is measured on the upstream side of the plane perpendicular to the central axis X. The angle of incidence 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 lower surface line 111 to the upper surface line 112.

[0053] As illustrated in [Fig. 3A], the inner radius R and outer radius Re of a first-row blade 110 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 has a variable pitch, the radial distances can be measured with the blade 110 placed at any pitch angle allowing the usual direction of airflow through the fan. For example, when the pitch angle y is equal to 60° for a cross-section of the blade 110 located approximately 75% of Re, which can be representative of the pitch angle of the blades 110 in cruise. Similarly, the inner radius R and outer radius Re' of a first-row blade 120 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 120 blade has variable pitch, radial distances can be measured with the 120 blade. placed at any pitch angle allowing the usual direction of airflow through the blower. For example, when the pitch angle y' is equal to 80° for a blade section 120 located approximately 75% of Re'.

[0054] Each of the two rows of blades can have a strength less than, for example, 2.5 over the entire height H, H' of the blades 110, 110', or even less than 0.5 at the outer radius Re, Re' of the row. For the purposes of this discussion, "blade height" means the difference between the outer radius Re and the inner radius R of its streamlined body. "Strength" means the ratio between the chord c of each blade in 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 blade in the first row can have an aspect ratio equal to the outer radius Re multiplied by a coefficient between 0.8 m and 2.4 m, preferably between 1.2 m and 2.2 m, or preferably between 1.4 m and 1.8 m. "Aspect ratio" for the purposes of this discussion 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 can be, for example, between 0.05 and 1.2, in particular between 0.36 and 0.6 times the outer radius Re of the first row of blades 110, and above all sufficient to prevent interference between the trailing edges BF of the blades 110 of the first row and the leading edges of the blades 120 of the second row. Each of the blades 110, 120 can be rotated about a radial axis or pitch-change axis, which can in particular be the corresponding stacking axis Z, Z', in order to adjust its pitch and therefore its angle of attack relative to the airflow direction according to the flight phase. This pitch-change axis can preferably be perpendicular to the central axis X, or alternatively inclined relative to the central axis X.

[0056] As illustrated in [Fig. 2], at least the first row of blades 110 can be adapted to rotate about the central axis X, and in particular be mechanically connected, for its rotational drive about the central axis X, to the gas turbine engine 11, possibly via a reduction gear 12. Furthermore, in order to take advantage of the increase in the dynamic air pressure downstream of this first row of blades 110, an air inlet 20 of the gas turbine engine 11 can, in particular, be arranged between the two rows of blades 110, 120. This air inlet 20 can, 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 can be, as also illustrated in [Fig. 2], non-rotating around the central axis X, following a non- The turbine is shrouded in a "USF" type design. Alternatively, it is also possible for it to rotate around the central axis X, and in particular to be mechanically connected to the gas turbine engine 11 to be driven in rotation around the central axis X, albeit in the opposite direction to that of the first row of blades 110, following a "CROR" type configuration. In this case, it is also possible for the rotational speed of the second row of blades 120 to be less than or equal to the rotational speed of the first row of blades, particularly during takeoff and / or landing of the aircraft 1. This reduces the velocity of the flow interacting with the second row of blades 120 and thus reduces interaction noise and limits (or avoids) the formation of shocks.

[0058] The trailing edge BF of the profiled body of each blade 110 of the first row can have a number N of teeth with tooth heights hj where j=l,2,.. .N in increasing order in the radial direction of the inner radius R; to the outer radius Re, and a number M of spacings Xk between adjacent tooth crests, where k=l,2,.. .M and M < Nl in increasing order in the radial direction of the inner radius R; to the outer radius Re. In the context of this exposition, "tooth crest" means a local maximum of the chord c in the radial direction and "tooth height" means the difference between the chord at the tooth crest and the chord at a hollow, i.e. a local minimum of the chord, located between the crest of this tooth and that of the adjacent tooth.It should be noted that a tooth peak can be characterized by a zero derivative of c(r) and a negative second derivative of c(r), while a pit can be characterized by a zero derivative of c(r) and a positive second derivative of c(r).

[0059] Due to the camber of the stacked profiles of the blade 110, variations in the chord c can be accompanied by variations in the pitch angle y, as illustrated in [Fig.3C] and 3D, in order to optimize the aerodynamic operation of the blade 110. In particular, the pitch angle y can have a local maximum or a local minimum at the radial position q of each tooth apex, plus or minus up to, for example, 5%, preferably 2%, of the height H of the profiled body of the blade 110.

[0060] The ratio between a maximum spacing Xmax and a minimum spacing Xmin among said spacings Xk for k=l,2,.. .M between adjacent tooth tips can be less than 15, preferably less than 8, and even more preferably less than 5. The maximum spacing Xmax 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, even 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 Xk between the vertex of the same tooth and the vertex of an adjacent tooth, preferably between 0.2 and 1.6 times the spacing Xk between the vertex of the same tooth and the vertex of the tooth adjacent, preferably between 0.3 and 1.2 times the Xk spacing between the apex of the same tooth and the apex of the adjacent tooth.

[0062] As illustrated in Figures 2 and 3A, the teeth can take the form of undulations, and in particular of substantially sinusoidal undulations, although other alternative forms such as triangular teeth are also conceivable. In particular, when the teeth take the form of sinusoidal undulations, each spacing Xk between the apexes of adjacent teeth can be equal to the square of the height of one of the adjacent teeth, multiplied by a coefficient between 0.005 mm₁ and 1 mm₀, preferably between 0.01 mm₁ and 0.8 mm₀, and even more preferably between 0.02 mm₁ and 0.6 mm₀. 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 R to the outer radius Re. In particular, the trailing edge BF can have a final hollow or tooth crest at a radial distance, relative to the outer radius Re, 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 R, 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 a belly V at a radial distance rv from the central axis X, between the inner radius R / and the outer radius Re' of this second, the trailing edge BF of the blades 110 of the first row can have at least one tooth apex at a radial distance q from the central axis X equal to the radial distance rv, plus or minus 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 area of ​​the belly V of the blades 120 of the second row. Indeed, at the level of the belly area V of the 120 blades, the axial distance between the trailing edge BF of the 110 blades and the leading edge BA' of the 120 blades can be reduced, and the leading edge BA' of the 120 blades has a reduced or zero sweep angle, which can increase interaction noise.From an aerodynamic point of view, the tooth tips help to reduce the local velocity deficit in the wake of the 110 blades, hence the advantage of placing a tip of a tooth of the trailing edge BF of the 110 blades at the radial position of the belly V of the edge. The leading edge of the 120 blades is designed to reduce interaction noise. In the context of this presentation, the "stomach" of the leading edge of a blade refers to the most advanced point of the leading edge in the upstream axial direction.

[0065] The spacings Xk can decrease monotonically in a radial direction towards the outer radius Re, such that Xi > X2 > X3 > ... XM_i > XM. Thus, any ratio between adjacent spacings Xk and Xk+i can be between 1 and 2, preferably between 1.03 and 1.5. Furthermore, as illustrated in [Fig. 3D], the pitch angles y at the radial positions q of the vertices can also decrease monotonically in a radial direction towards the outer radius Re, such that y(q) > y(r2) > y(r3) ... y(rN.i) > y(rN), in order to adapt them to a relative flow angle that decreases towards the outer radius Re due to the rotation of the blades. As illustrated in Figures 2 and 3A, all the spacings can be different, such that Xi > X2 > X3 ... XM4 > XM. In particular, each ratio between adjacent spacings Xk and Xk+i can be approximately equal to one plus the inverse of a positive integer.

[0066] Alternatively, it is nevertheless conceivable that some of the spacings may be identical, while maintaining a monotonic decrease over all 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 may be substantially identical. The identical spacings may, in particular, be located in an upper portion BFh of the trailing edge BF of the blade 110, adjacent to the outer radius Re, and extending, for example, over the upper 45% or 20% of the height H of the airfoil body of the blade 110. The other characteristics of the propulsion fan may, however, be identical or equivalent to those of the first embodiment and consequently receive the same reference numerals in [Fig. 4] as in the preceding figures.

[0067] Furthermore, although in the two preceding embodiments the teeth extend over the entire height H of the streamlined body of the blade 110, it is also possible for at least a portion of the trailing edge to be toothless. Thus, according to a third embodiment illustrated in [Fig. 5], an upper portion BFh of the trailing edge BF of the blade 110, adjacent to the outer radius Re, may be toothless. In this embodiment, this toothless upper portion BFh may, for example, extend from a radial distance r substantially identical to the outer radius Re' of a row of smaller diameter blades 120 arranged downstream. The other characteristics of the propulsion fan may, however, remain identical to those of the preceding embodiments, and consequently receive the same reference numerals in [Fig. 5] as in the preceding figures.

[0068] Although in the third embodiment the toothless part is an upper part of the trailing edge, it is also possible to have, alternatively or In addition to this, one or more different portions of the trailing edge BF of the blades 110 may be toothless. Thus, according to a fourth embodiment illustrated in [Fig. 6], a lower portion BFb of the trailing edge BF may also be toothless. This lower portion BFb of the trailing edge BF may extend from the inner radius R 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 located downstream of the blades 110. This is done, in particular, to prevent the teeth from breaking and entering the air inlet 20, which could impair the operation of the propulsion system. The other characteristics of the propulsion fan may, however, remain identical to those of the previous embodiments and, consequently, are given the same reference numerals in [Fig. 6] as in the preceding figures.

[0069] Alternatively, however, at least one toothless portion may be a central portion BFc of the trailing edge BF of the blade 110, not extending to the inner radius R; nor to the outer radius Re, as in the fifth and sixth embodiments respectively illustrated in Figures 7 and 8. This toothless central portion BFc may in particular extend between two tooth crests, as in the fifth embodiment illustrated in [Fig. 7], or alternatively between two hollows, as in the sixth embodiment illustrated in [Fig. 8].

[0070] The teeth can be inclined radially outwards. With such an inclination, even if the spacing between adjacent tooth crests decreases monotonically, the radial distance Ara between at least one tooth crest and the adjacent outward groove can be less than the radial distance Arb between said adjacent groove and the next outward-facing crest. It is conceivable that only the teeth located on a high portion BFh of the trailing edge are inclined outwards, as in the seventh embodiment illustrated in [Fig. 9], possibly with a transition zone in which this inclination gradually increases. However, it is also conceivable, as in the eighth embodiment illustrated in [Fig. 10], that all the teeth are inclined outwards.

[0071] Although the present invention has been described with reference to specific embodiments, it is evident that various modifications and changes can 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 mentioned can be combined in additional embodiments. Therefore, the description and drawings should 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 with an inner radius R;at an outer radius Re 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), wherein 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 f1 df) j j-°where f represents a radial distance by FA = 16 relative to the central axis (X), divided by the outer radius Re, and c(ç) represents a local chord between the leading (BA) and trailing (BF) edges of the profiled body at said radial distance, and wherein the trailing edge (BF) of the profiled body of at least one blade (110) of the first row of blades (110) has teeth with spacings (Xk) between adjacent tooth apexes which decrease monotonically in the radial direction towards the outer radius Re.;

2. An unducted propulsive fan (100) according to claim 1, wherein each spacing (Xk) of said spacings (Xk) between adjacent tooth tips is different.

3. An unducted propulsive fan (100) according to claim 1, wherein at least two adjacent ones of said spacings (Xk) between adjacent tooth tips are substantially identical.

4. Unducted propulsive fan (100) according to any one of the preceding claims, in which each of the blades (110) of the first row of blades (110) has an elongation equal to the outer radius Re multiplied by a coefficient between 0.8 m 1 and 2.4 m *, preferably between 1.2 m 1 and 2.2 m1, or even more preferably between 1.4 m1 and 1.8 m1.

5. An unducted propulsive fan (100) according to any preceding claim, wherein a ratio of a maximum spacing to a minimum spacing among said spacings (Xk) between adjacent tooth apices is less than 15, preferably less than 8, and preferably less than 5.

6. An unducted propulsive fan (100) according to any preceding claim, wherein a maximum spacing among said spacings (Xk) between adjacent tooth apexes is between 0.05 and 0.4 times a difference between said outer radii Re and inner radii R;, preferably between 0.1 and 0.35 times the difference between said outer radii Re and inner radii R;, more preferably between 0.15 and 0.3 times the difference between said outer radii Re and inner radii n

7. Kp Unducted propulsive fan (100) according to any one of the preceding claims, wherein a minimum spacing among said spacings (Xk) between adjacent tooth tips is between 0.01 and 0.2 times a difference between said outer radii Re and inner radii R;, preferably between 0.02 and 0.15 times the difference between said outer radii Re and inner radii R;, more preferably between 0.04 and 0.12 times the difference between said outer radii Re and inner radii R;.

8. An unducted propulsive fan (100) according to any preceding claim, wherein any ratio between adjacent spacings among said spacings (Xk) between adjacent tooth tips is between 1 and 2, preferably between 1.03 and 1.5

9. 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 (Xk) between the top of the same tooth and the top of an adjacent tooth, preferably between 0.2 and 1.6 times the spacing (Xk) 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 (Xk) between the top of the same tooth and the top of the adjacent tooth.

10. Unducted propulsive fan (100) according to any one of the preceding claims, having pitch angles (Yj), at the radial positions (q) of the apexes of the teeth, which decrease monotonically in the radial direction towards the outer radius Re.

11. 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.

12. An unducted propulsive fan (100) according to one of the claims- preceding indications, in which each spacing (Xk) between tops of adjacent teeth is equal to the square of a tooth height (hj) of one of the adjacent teeth, multiplied by a coefficient between 0.005 mm1 and 1 mm ', preferably between 0.01 mm1 and 0.8 mm ', more preferably between 0.02 mm 1 and 0.6 mm '.

13. An unducted propulsive fan (100) according to any preceding claim, wherein said trailing edge (BF) of the at least one blade (110) of the first row of blades (110) comprises a portion devoid of teeth.

14. An unducted propulsive fan (100) according to claim 13, wherein said toothless portion is a high portion (BFh) extending to the outer radius Re.

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

16. An unducted propulsive fan (100) according to any preceding claim, comprising a second row of blades (120) disposed downstream of the first row of blades (110).

17. Unducted propulsive fan (100) according to claim 17, wherein 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 (rv) of said belly (V) relative to the central axis (X).

18. An unducted propulsive fan (100) according to any one of claims 16 or 17, wherein the second row of blades (120) is not rotatable about the central axis (X).

19. 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).

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

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