Fan for aircraft propulsion

Abstract

Aircraft propulsion fan. Propulsive fan (100) comprising two rows of blades (110, 120) and a second row of blades (120) arranged downstream of the first row of blades (110). The leading edge (LA) of a blade (120) of the second row and the trailing edge (BF) of a blade (110) of the first row are at least partially saw-toothed. The radial position of each tooth crest in the leading edge (LA) of the blade (120) of the second row is substantially identical to that of a groove in the trailing edge (BF) of the blade (110) of the first row, and / or the radial position of each groove in the leading edge (LA) of the blade (120) of the second row is substantially identical to that of a corresponding tooth crest in the trailing edge (BF) of the blade (110) of the first row. Figure for the summary: Fig. 3.

Description

Title of the invention: Blower for aeronautical propulsion technical field

[0001] The technical field of the present exposition is that of propulsion and in particular that of propulsive blowers, such as those intended to be driven by a gas turbine engine in aeronautical propulsion. Previous technique

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working 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 account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and 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 weight reduction 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 which contribute directly to thrust generation, notably the propulsive fans. The known guiding principle for improving propulsive efficiency is to reduce the fan's compression ratio, thereby decreasing the airflow velocity at the fan's 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 cold flow from the fan (secondary flow) and that supplying the combustion chamber of the gas turbine engine (primary flow).

[0009] When the fan is ducted, 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 make it thinner. Furthermore, several types of unducted propulsive 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" being 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") type propulsion fans, only the upstream row rotates around the central axis, while in "CROR" ("Counter-Rotating Open Rotor") type propulsion fans, both rows rotate in opposite directions. However, in both types, the blades of each of the two rows can have variable pitch.

[0010] Interactions between successive rows of blades and vanes can generate noise emissions, particularly at the harmonics of the blade passing frequency (BPF). However, in shrouded fans, the shortening and thinning of the nacelle to try to compensate for the increase in drag and mass associated with a larger diameter has the disadvantage of reducing the space available for acoustic treatments used for noise reduction, whereas in unshrouded fans, the absence of a casing or nacelle surrounding the fan allows the direct diffusion of these noise emissions to the environment.

[0011] Significant research and development efforts have therefore been directed, in particular by the Applicant, to reduce these noise emissions. To this end, it has been proposed, notably in the 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 unfaired propulsion fans, so as to reduce or distribute their wingtip vortices. This solution has also been proposed for faired fans, for example in the 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 the European patent application EP 2 760 737 A1 and in US patents 11,560,796 and 11,047,238. Description of the invention

[0012] 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 this description concerns a propulsion fan comprising a first row of blades and a second row of blades located downstream of the first row of blades. The first row of blades is capable of rotating about a central axis relative to the second row of blades. For the purposes of this description, the term "blade" refers to both rotating blades and righting blades. Thus, the second row of blades can be counter-rotating with respect to the first row of blades, or stator-shaped.Each blade in the first and second rows of blades can therefore have an intrados and an extrados extending, in a radial direction relative to the central axis, from a blade root to a blade tip and, in a blade width direction, from a leading edge to a trailing edge.

[0013] The leading edge of at least one blade in the second row of blades and the trailing edge of at least one blade in the first row of blades may be at least partially serrated, each with a plurality of serration crests interspersed between grooves. In the context of this description, "serration" is understood broadly, encompassing simple undulations of varying degrees. A "serration crest" is defined as a convexity forming a local maximum of the position of a leading edge in the upstream axial direction or of a trailing edge in the downstream axial direction, and a "groove" of the leading edge is defined as a concavity forming a local minimum of the position of the leading edge in the upstream axial direction or of the trailing edge in the downstream axial direction. In particular, the leading edge of at least one blade in the second row of blades may have at least three serration crests.

[0014] A distance from the central axis, in a radial direction perpendicular to the axis The central distance of each tooth crest in the leading edge of at least one blade in the second row can be substantially identical to a distance from the central axis, in a radial direction perpendicular to the central axis, of a corresponding groove in the trailing edge of at least one blade in the first row. Alternatively, or in addition to this, a distance from the central axis, in a radial direction perpendicular to the central axis, of each groove in the leading edge of at least one blade in the second row is substantially identical to a distance from the central axis, in a radial direction perpendicular to the central axis, of a corresponding tooth crest in the trailing edge of at least one blade in the first row. For the purposes of this discussion, "substantially identical" distances may be understood to differ by no more than 10%, or even 5%, or 3%, of the greatest span of the blades in the first or second row.

[0015] Thanks to this complementary alignment of the sawtooth contours of the trailing edges of the blades in the first row with the sawtooth contours of the leading edges of the blades in the second row, it is possible to bring the two rows of blades closer together in the direction of the central axis to obtain better aerodynamic efficiency, while avoiding contact between the blades of the two rows. These alignments of the sawtooth contours at the trailing edge of the blades in the first row and the sawtooth contours at the leading edge of the blades in the second row maximize acoustic gains and thus reduce interaction noise.Indeed, the speed deficit, and therefore the aerodynamic excitation of the wake of the first row blades, increases at the tooth troughs at the trailing edge of the first row blades, which can be compensated by a reduced acoustic response at the tooth tips at the leading edge of the second row blades.

[0016] In said at least one blade of the second row of blades, a camber and / or an angle, with respect to a direction parallel to the central axis, of a straight line connecting the leading edge to the trailing edge or of a skeleton line equidistant from the lower and upper surfaces to the leading edge, may be greater in a blade profile at the level of a dip in the leading edge than in blade profiles at the levels of two adjacent tooth tips. For the purposes of this description, "skeleton line" means a segment equidistant from the lower and upper surfaces along its entire length, and connecting the leading edge to the trailing edge in a plane perpendicular to the radial direction.For the purposes of this discussion, "camber" means a ratio between a maximum distance, perpendicular to the straight line connecting the leading edge to the trailing edge in a plane perpendicular to the radial direction, from this straight line to the corresponding skeleton line, and the length of said straight line connecting the leading edge to the trailing edge in a plane perpendicular to the . radial direction. These more pronounced angles and / or camber at the level of the hollow make it possible to reduce the incidence of the flow and therefore eliminate or at least reduce the separation of the flow and / or the generation of vortices and / or the generation of shocks, and therefore the aerodynamic losses.

[0017] The number of tooth tips on the leading edge of at least one blade in the second row of blades may be less than or equal to the number of tooth tips on the trailing edge of at least one blade in the first row of blades.

[0018] The leading edge of at least one blade in the second plurality of blades may include at least one inclined tooth crest for which a first radial distance from the inclined tooth crest to a first hollow adjacent to the inclined tooth crest, closer to the central axis than the inclined tooth crest, may be less than a second radial distance from the first hollow adjacent to the inclined tooth crest to an adjacent tooth crest even closer to the central axis than the first hollow adjacent to the inclined tooth crest, and a third radial distance from the inclined tooth crest to a second hollow adjacent to the inclined tooth crest, further from the central axis than the inclined tooth crest. Thus, at least this inclined tooth may be inclined towards the central axis of the first and second rows of blades.

[0019] Thanks to this inclination towards the central axis, the leading edge's sweep angle can be locally increased between the crest of the inclined tooth and the second adjacent hollow of the crest of the inclined tooth, further from the central axis. This helps to decorrelate the acoustic sources, i.e., prevent them from being activated simultaneously. This decorrelation can generate destructive interference between the acoustic sources and thus contribute to noise reduction.

[0020] A straight line connecting the crest of an inclined tooth to a point equidistant from the first and second hollows adjacent to the crest of the inclined tooth may have, with respect to a line parallel to the central axis passing through said point equidistant from the first and second adjacent hollows of the crest of the inclined tooth, an angle of inclination towards the central axis of less than 60° and in particular less than 45° and / or greater than 10°. The inclination of the tooth can thus be optimized to reduce noise generation and / or aerodynamic losses.In this case, a straight line connecting said adjacent tooth apex to a point equidistant from two adjacent hollows to said adjacent tooth apex on a straight line connecting the two adjacent hollows to said adjacent tooth apex may have, with respect to a line parallel to the central axis passing through said point equidistant from the two hollows adjacent to the adjacent tooth apex, an angle of inclination towards the central axis lower than said angle of inclination of the straight line connecting the inclined tooth apex to the point equidistant from the first and . The second set of grooves is adjacent to the apex of the inclined tooth. Since the adjacent tooth apex is closer to the central axis than the inclined tooth apex, a decreasing inclination law can be obtained for successive teeth towards the central axis. In particular, this decrease can be monotonic. By "monotonous" decrease, in the context of this discussion, we mean that each successive tooth, in a radial direction towards the central axis, can have an inclination towards the central axis equal to or less than the inclination towards the central axis of the preceding tooth. With more inclined teeth, and therefore more pronounced leading-edge sweep angles, near the blade tip, it is possible to better suppress the negative effects of interactions with the blade tip vortices of the first row of blades, in the region where they will be most significant.On the other hand, less inclined teeth near the blade root can help avoid other negative interactions between the tooth and the boundary layer near the blade root.

[0021] The leading edge of at least one blade in the second row of blades may have no tooth crests at a radial distance, relative to the blade tip, of less than 15% of the span, in the radial direction from the blade root to the blade tip. Indeed, since the chord at the blade tip can be small, it can be difficult to place a tooth there from the point of view of mechanical strength, manufacturing, or maintainability of the blades. When the leading edge is thus devoid of tooth crests at the blade tip, any sweep angle, relative to the radial direction, of the leading edge of at least one blade in the second row of blades, at a radial distance from the blade tip less than 15% of the span, may be greater than 50°.In this case, any sweep angle relative to the radial direction, from the leading edge of at least one blade in the second row of blades, at a radial distance from the blade tip less than 5% of the span, can be greater than 55°. As mentioned previously, a pronounced sweep angle contributes to the decorrelation of acoustic sources, which can be particularly significant at the blade tip.

[0022] At least one blade of the first and / or second rows of blades may have variable pitch around a corresponding radial axis perpendicular to the central axis, in order to optimize its efficiency at different speeds.

[0023] The leading edge of at least one blade in the second row of blades may, in particular, have spacings between adjacent tooth tips that decrease monotonically in a radial direction towards the blade tip. Thus, the larger spacings near the blade root allow for better dissipation of acoustic energy from the interaction of the boundary layer and / or the blade root vortices of the first row of blades with the blade roots of the second row of blades. Furthermore, the sweep angle may be smaller near the root of the blade, which would allow in-phase radiation and / or destructive interference from acoustic sources over a large portion of the blade's span adjacent to the blade root. Larger spacings in this region of the blade better counteract this local effect.

[0024] Any ratio between adjacent spacings among said spacings between adjacent tooth apexes can be between 1 and 1.6, in particular between 1.05 and 1.4, so as to allow a gradual evolution between spacings.

[0025] The second row of blades may, in particular, be stator-shaped, as in conventional shrouded propulsive fans or in unshrouded propulsive fans with a so-called "USF" configuration. However, it is alternatively possible for the second row of blades to be counter-rotating with respect to the first row of blades, as in the unshrouded fan configuration known as "CROR". Furthermore, the propulsive fan may be unshrouded around the first and second rows of blades or, alternatively, comprise a nacelle surrounding the first and / or second rows of blades.

[0026] A second aspect of the present description concerns a propulsion system that may include the propulsion fan described in the first aspect and a gas turbine engine for driving the 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 for driving the propulsion fan, is also conceivable.

[0027] A third aspect of the present exposition relates to an aircraft comprising a propulsion system as described above. Brief description of the drawings

[0028] 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.

[0029] 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:

[0030] [Fig.1] Fig.1 schematically illustrates an aircraft.

[0031] [Fig.2] Fig.2 schematically illustrates a propulsion system suitable for the propulsion of the aircraft of [Fig.1], equipped with an unfaired propulsive fan according to a first embodiment.

[0032] [Fig.3] Fig.3 schematically illustrates the propulsive blower according to the first embodiment.

[0033] [Fig.4A] The [Fig.4A] represents a cross-sectional view of a blade of the propulsion blower of the [Fig.3] in a plane perpendicular to a radial stacking axis.

[0034] [Fig.4B] The [Fig.4B] illustrates an alternative shape of the trailing edge of the blade of the [Fig.4A].

[0035] [Fig.5] Fig.5 represents a detailed side view of a blade of the second row of blades of the propulsion blower according to the first embodiment.

[0036] [Fig.6A] The [Fig.6A] illustrates a superposition of two profiles, respectively at the level of a leading edge tooth apex and an adjacent hollow, of a blade of the second row of blades of the propulsion fan according to a first variant of the first embodiment.

[0037] [Fig.6B] The [Fig.6B] illustrates a superposition of two profiles, respectively at the level of a leading edge tooth apex and an adjacent hollow, of a blade of the second row of blades of the propulsion fan according to a second variant of the first embodiment.

[0038] [Fig.6C] The [Fig.6C] illustrates a superposition of two profiles, respectively at the level of a leading edge tooth apex and an adjacent hollow, of a blade of the second row of blades of the propulsion fan according to a third variant of the first embodiment.

[0039] [Fig.7] Fig.7 illustrates a side view of a blade of the second row of blades of the propulsion blower according to a second embodiment.

[0040] [Fig.8] Figure [Fig.8] schematically illustrates an aircraft with a propulsion system equipped with a ducted propulsive fan according to a third embodiment

[0041] [Fig.9] Fig.9 schematically illustrates the propulsion unit equipped with the streamlined propulsion blower according to the third embodiment. Description of the implementation methods

[0042] 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.

[0043] As illustrated in [Fig. 1], an aircraft 1 may incorporate one or more propeller 10s with a propulsive fan 100 as described herein. These propellers 10 may, in particular, be arranged, as illustrated, under the wings 2, but other arrangements are also possible. Alternative positions, for example at the rear of the fuselage of aircraft 1, are also conceivable.

[0044] 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 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 14 by a first rotating shaft 21 for driving the latter, while the low-pressure turbine 17 may be connected to the low-pressure compressor 13 by a second rotating shaft 22 coaxial with the first rotating shaft 21, in a similar manner. The reduction gear 12 may connect the second rotating shaft 22 to the propulsion fan 100 for actuation of the latter.Although in the illustrated example the propulsive blower 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.

[0045] 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.

[0046] 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. Each row may contain, for example, between 8 and 16 blades, in particular between 10 and 14 blades. However, the first row of blades 110 and the second row of blades 120 may not have the same number of blades. In particular, the first row may have at least two more blades than the second row.

[0047] The first and / or second row of blades 110, 120 may have an outside diameter De of between 1 and 6 meters, in particular between 3 and 5 meters. The first and / or second row of blades 110, 120 may have a strength factor of less than 2.5 along the span (from the blade roots to the blade tips), and in particular a strength factor of less than 0.5 at the blade tips. "Strength factor," in the context of this description, is understood to be the ratio between the chord c, i.e., the distance between the leading edge BA and the trailing edge BF in a plane perpendicular to a radial axis Z perpendicular to the central axis X, and the distance between the corresponding radial axes Z of two adjacent blades 110, 120 in the same row, at the same radial distance from the central axis as the plane in which the chord c is measured.

[0048] In a first embodiment illustrated in Figures 1 to 3, the propulsion fan 100 may be without fairing around the first and second rows of blades 110, 120. In this case, the propulsion fan 100 may be of the "USF" type, in which only the first row of blades 110 is driven in rotation by the gas turbine engine 11 through the reducer 12, or of the "CROR" type, in which the first and second rows of blades 110, 120 are driven in rotation in opposite directions by the gas turbine engine 11 through the reducer 12.

[0049] In all cases, each of the blades 110, 120 may have a profiled body extending radially, with respect to the central axis X, over a span H from a blade root 113, 123 with an inner diameter D of the corresponding row to a blade tip 114, 124 with an outer diameter De of the corresponding row, as illustrated in [Fig. 3]. However, the inner diameter D and / or outer diameter De of the first row may be different from the inner diameter D and / or outer diameter De of the second row. For each row, the span H of the blades 110, 120, corresponding to half the difference between the corresponding outer diameter De and inner diameter D, may therefore be different. In particular, the outside diameter De of the second row of blades 120 may be less than the outside diameter De of the first row of blades 110 in order to limit or avoid interaction with the blade tip vortices of the first row of blades 110.It is also possible that, in one or both of the first and second rows of blades 110, 120, the span H of the blades 110, 120 is heterogeneous, meaning that at least two blades 110, 120 in the same row have different spans H. In particular, the blades 120 in the second row may have variable clipping relative to the outside diameter De of the first row of blades 110, in order to avoid interaction with the vortices released from the tips of the blades 110 in the first row during flight phases at angle of attack, and thus reduce noise during these phases, such as takeoff and / or landing. Indeed, this interaction can be a dominant noise source that can reduce or partially mask the benefits provided by the saw teeth on the leading edges of the 120 blades in the second row.

[0050] The streamlined body of each blade 110, 120 can be formed by stacked airfoils (or "sections") from the blade root 113, 123 to the blade tip 114, 124 along a corresponding radial stacking axis Z, Z', perpendicular to the central axis X, so as to form, as illustrated in [Fig. 4A], an intrados 111, 121 and an extrados 112, 122, each extending from a leading edge BA to a trailing edge BF. Each of these airfoils is therefore defined in a corresponding plane per pendulum to the radial axis Z, Z'. For example, for a cross-section or aerodynamic profile of the blade 110, 120, 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 profile 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 profile 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. 4B].

[0051] 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 along a straight line connecting them and having a pitch angle θ with respect to a plane perpendicular to the central axis X. Conventionally, the pitch angle θ 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 pitch angle θ is measured from the upstream side of the plane perpendicular to the central axis X.The angle of incidence can be measured positively in a direction 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 from the intrados line 111,121 to the extrados line 112,122. .

[0052] These sections or aerodynamic profiles may, in particular, be cambered. More specifically, in each section or aerodynamic profile, a skeleton line S, which is a segment connecting the leading edge BA to the trailing edge BF and equidistant from the lower surface 111,121 and the upper surface 112,122 along its entire length, may be cambered so as to exhibit, with respect to a direction parallel to the central axis X, an angle of inclination [3i] at the leading edge BA and an angle of inclination

[32] at the trailing edge BF. The camber of the section or aerodynamic profile may be defined as the ratio f / c between a maximum distance f, perpendicular to the chord line c, from the skeleton line S to the chord line c, and the chord c.

[0053] Each cross-section or aerodynamic profile can also have a maximum thickness e, which can be defined as the maximum distance, perpendicular to the skeleton line S, between the lower surface 111, 121 and the upper surface 112, 122. The chord c, the pitch angle y, the leading edge and trailing edge angles [3i] and

[32] , the camber f / c, and the thickness e can all be variable over the span H of each blade 110, 120. In particular, the thickness e can have a maximum near the blade root 113,123, in particular at less than 20% of the span H of the blade root 113,123, even more particularly at less than 10% of the span H of the blade root 113,123. This helps to strengthen the mechanical strength of the blade 110, 120.

[0054] Each of the blades 110, 120 can have an aspect ratio equal to the outside diameter De of the corresponding row, multiplied by a coefficient between 0.3 m1 and 1.2 m1, in particular between 0.4 m1 and 0.8 m1. "Aspect ratio," in the context of this description, is understood to be 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 r to the central axis X, according to the equation: cT^Dih->,i2c(r)^r

[0055] Furthermore, each of the blades 120 of the second row may have a relatively low activity factor, for example between 40 and 225, in particular between 90 and 160. In the context of this discussion, "activity factor" is understood to mean the value FA resulting from the following equation, where corresponds to twice the ratio between the radial distance r from the central axis X and the outside diameter De: FA =

[0056] A relatively low activity factor FA therefore implies a relatively large chord near the blade root 123, which can facilitate the straightening of the flow downstream of the first row of blades 110, with a consequent aerodynamic advantage, while optimizing noise reduction through more pronounced saw teeth.

[0057] The axial distance between the stacking axes Z, Z' of the two rows can be, for example, between 0.005 and 0.5, in particular between 0.18 and 0.3 times the outside diameter De of the first row of blades 110, and above all sufficient to prevent interference between the trailing edges BF of the blades 110 and the leading edges of the blades 120. Each of the blades 110 and / or the blades 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.

[0058] In order to take advantage of the increase in dynamic air pressure downstream of the first row of blades 110, an air inlet 20 of the gas turbine engine 11 can, in particular, be arranged between the blades 110 and the vanes 120. This air inlet 20 can, for example, be annular, with a nozzle 23 separating the air inlet 20 from the fairing 19, as illustrated in [Fig.3].

[0059] The leading edge BA of at least one blade 120 of the second row of blades 120 may be at least partially saw-toothed and have a number N of teeth with tooth heights hj where j=l,2,.. .N in increasing order in the radial direction from the blade root 123 to the blade tip 124, and a number M of spacings Xk between adjacent tooth apexes, where k=l,2,.. .M also in increasing order in the radial direction from the blade root 123 to the blade tip 124, and M < Nl .The number N of teeth may be equal to or greater than 3, for example between 3 and 10, more particularly between 4 and 6, in order to obtain a significant noise reduction while limiting any aerodynamic losses related to the teeth.

[0060] The Xk spacings can vary, and in particular decrease monotonically in a radial direction towards the blade tip 124, such that Xi > X2 > X3 > ... XM4 > XM. Thus, any ratio between adjacent Xk and Xk+i spacings can be between 1 and 1.6, in particular between 1.05 and 1.4. As illustrated in Figures 2 and 3A, all the spacings can be different, such that Xi > X2 > X3... In particular, Each ratio between adjacent spacings Xk and Xk+i can be approximately equal to one plus the inverse of a positive integer. Alternatively, it is nevertheless conceivable that some of the spacings are identical, while maintaining a monotonic decrease, or increase, over the set of spacings.

[0061] In relation to the leading edges BA of the blades 120 of the second row of blades 120, the trailing edges BF of the blades 110 of the first row of blades can also be at least partially saw-toothed, with alternating tooth peaks and troughs.In particular, in order to allow a rapprochement of the respective radial axes Z, Z' of stacking of the blades 110 of the first row of blades 110 and of the blades 120 of the second row of blades 120, and thus a better aerodynamic efficiency, while avoiding contact between the blades 110, 120 of the two rows, the troughs of the trailing edges BF of the blades 110 of the first row can be substantially aligned, in axial direction parallel to the central axis X, with the crests of the leading edges BA of the blades 120 of the second row and, conversely, the crests of the trailing edges BF of the blades 110 of the first row can be substantially aligned, in axial direction parallel to the central axis X, with the troughs of the leading edges BA of the blades of the second row.These alignments of the tooth troughs at the trailing edge (BF) of the 110 blades and the tooth crests at the leading edge (BA) of the 120 blades, or vice versa, maximize acoustic gains and thus reduce interaction noise. Indeed, the velocity deficit, and therefore the aerodynamic excitation of the wake of the 110 blades, increases at the tooth troughs at the trailing edge (BF) of the first row of 110 blades. This can be compensated for by a reduced acoustic response at the tooth crests at the leading edge of the blades. 120 from the second row.

[0062] Thus, the distance from the central axis X, in a radial direction perpendicular to the central axis X, of each hollow in the trailing edge BF of each blade 110 of the first row can be substantially identical to the distance from the axis X, in a radial direction perpendicular to the central axis X, of a corresponding tooth crest in the leading edge BA of each of the blades 120 of the second row, and the distance from the central axis X, in a radial direction perpendicular to the central axis X, of each tooth crest in the trailing edge BF of each blade 110 of the first row can be substantially identical to the distance from the axis X, in a radial direction perpendicular to the central axis X, of a corresponding hollow in the leading edge BA of each of the blades 120 of the second row.By "substantially identical" distances, in the context of this presentation, we mean that they do not differ by more than 10%, or even 5%, or even 3% of the greatest span H of the blades 110, 120 of the first or second rows.

[0063] At least one of the teeth of the leading edge BA of at least one of the blades 120 of the second row of blades 120 can be inclined towards the central axis X. Thus, as illustrated in detail in [Fig.5], for at least one inclined tooth apex, a first distance da, in the radial direction, from the inclined tooth apex to a first adjacent hollow of the inclined tooth apex, closer to the central axis X than the inclined tooth apex, is less than a second distance db, in the radial direction, from the first adjacent hollow of the inclined tooth apex to an adjacent tooth apex, even closer to the central axis X than the first adjacent hollow of the inclined tooth apex, and a third distance dc, in the radial direction, from the inclined tooth apex to a second adjacent hollow of the inclined tooth apex, further from the central axis X than the inclined tooth apex.

[0064] Thus, a straight line connecting the crest of the inclined tooth to a point equidistant from the first and second adjacent hollows of the crest of the inclined tooth on a straight line connecting the first and second adjacent hollows of the crest of the inclined tooth may have, with respect to a line parallel to the central axis X passing through said point equidistant from the first and second adjacent hollows of the crest of the inclined tooth, an angle of inclination 0; towards the central axis X less than 60° and in particular less than 45° and / or greater than 10°.

[0065] Furthermore, several, or even all, of the teeth on the leading edge BA of each blade 120 of the second row can be inclined towards the central axis X. The angle of inclination 0 of each successive tooth can decrease towards the central axis X, such that, as also illustrated in [Fig. 5], a straight line connecting said tooth apex adjacent to a point equidistant from two adjacent hollows of said tooth apex adjacent to a straight line connecting the two adjacent hollows The said adjacent tooth apex presents, with respect to a line parallel to the central axis X passing through the said point equidistant from the two adjacent hollows of the adjacent tooth apex, an angle of inclination 0^ towards the central axis X less than the angle of inclination 0;. We can thus obtain a monotonically decreasing inclination law for successive teeth in the direction of the central axis X, or a monotonically increasing inclination law in the opposite direction, such that 0i> 02> ...> 0N, and 0i > 0N, where i=l,2,.. .N in increasing order in the radial direction from the blade root 123 to the blade tip 124.

[0066] Due to the camber of the stacked airfoils of the blade 120, variations in the chord c may be accompanied by variations in the pitch angle y, the leading edge inclination angle [3i], and / or the camber f / c, as illustrated respectively in Figures 6A to 6C, in order to optimize the aerodynamic performance of the blade 120. Thus, as illustrated in [Fig. 6A], the pitch angle y may be more pronounced for an airfoil psd at a tooth crest than for an airfoil pc at an adjacent groove. Conversely, the complementary angle 90°-y, which is the angle of a straight line connecting the leading edge BA to the trailing edge BF with respect to a direction parallel to the central axis X, may be greater for the airfoil pc at the adjacent groove than for the airfoil psd at the tooth crest.Alternatively or in addition, the leading edge (BA) bank angle [3i] can be greater for the pc airfoil at the adjacent trough than for the psd airfoil at the tooth crest, as illustrated in [Fig. 6B], and / or the camber f / c can be greater for the pc airfoil at the adjacent trough than for the psd airfoil at the tooth crest, as illustrated in [Fig. 6C]. These three options, separately or in combination, can reduce the angle of attack and the flow velocity and / or acceleration at the trough, thereby eliminating or at least reducing flow separation and / or vortex generation and / or shock generation, and thus aerodynamic losses.

[0067] Although in the embodiment illustrated in Figures 1 to 6C the leading edge BA of the blade 120 is saw-toothed over substantially the entire span H of the blade 120, it is alternatively conceivable that this leading edge BA may be devoid of tooth crests over a portion of the span of the blade 120. In particular, according to a second embodiment illustrated by way of example in [Fig. 7], the leading edge BA of the blade 120 may have no tooth crests at a radial distance, relative to the blade tip 124, of less than 15% of the span H. Thus, any sweep angle a, relative to the radial direction, of the leading edge BA of the blade 120, at a radial distance from the blade tip H less than 15% of the span, may be greater than 50°.The sweep of the blade 120 can still increase towards the blade tip, such that any sweep angle has with respect to the radial direction, from the leading edge BA of the blade 120, at a radial distance from the blade tip less than . 5% of the wingspan, i.e. greater than 55°.

[0068] Furthermore, although in the preceding embodiments the propulsion fan is not shrouded, it is also alternatively conceivable, as in a third embodiment illustrated by way of example in Figures 8 and 9, that the propulsion fan 100 is a shrouded fan, also comprising a nacelle 130 surrounding the first and second rows of blades 110, 120. This nacelle 130 can also include a retention housing 140 around the blades 110, with an abradable to limit damage in case of contact between the radially external end of the blades 110 and the housing, and / or acoustic treatments for noise reduction. In this case, the second row of blades 120 can be stator-shaped around the central axis X, so as to be able to serve not only the flow downstream of the first row of blades 110, but also to support the nacelle 130.In such a stator, the number of stator blades 120 can, for example, be twice the number of rotor blades 110 by adding 4 to this product. It would nevertheless also be conceivable, in a shrouded propulsion fan 100, for the second row of blades 120 to be counter-rotating with respect to the first row of blades 110.

[0069] 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

Demands

1. A propulsion fan (100) comprising a first row of blades (110) and a second row of blades (120) disposed downstream of the first row of blades (110), the first row of blades (110) being capable of rotating about a central axis (X) relative to the second row of blades (120), each blade (110, 120) of the first and second rows of blades (110, 120) having an intrados (111, 121) and an extrados (112, 122) extending, in a radial direction relative to the central axis (X), from a blade root (113, 123) to a blade tip (114, 124) and, in a blade width direction, from a leading edge (LA) to a trailing edge (BF), the leading edge (LA) of at least one blade (120) of the second row of blades (120) and the trailing edge (BF) of at least one blade (110) of the first row of blades (110) being at least partially saw-toothed, each with a plurality of tooth apexes interspersed between grooves,a distance from the central axis (X), in a radial direction perpendicular to the central axis (X), from each tooth crest in the leading edge (BA) of at least one of the blades (120) of the second row being substantially identical to a distance from the central axis (X), in a radial direction perpendicular to the central axis (X), from a corresponding groove in the trailing edge (BF) of at least one blade (110) of the first row, and / or, a distance from the central axis (X), in a radial direction perpendicular to the central axis (X), of each groove in the leading edge (BA) of at least one of the blades (120) of the second row being substantially identical to a distance from the central axis (X), in a radial direction perpendicular to the central axis (X), of a corresponding tooth crest in the trailing edge (BF) of at least one blade (110) of the first row.

2. A propulsion fan (100) according to claim 1, wherein, in said at least one blade (120) of the second row of blades (120), a camber and / or an angle, with respect to a direction parallel to the central axis (X), of a straight line connecting the leading edge (BA) to the trailing edge (BF) or of a skeleton line equidistant from the lower surface (121) and the upper surface (122) to the leading edge (BA), are greater in a blade profile at the level of a dip in the leading edge (BA) than in blade profiles at the levels of two tooth tips adjacent.

3. Propulsive blower (100) according to any one of the preceding claims, wherein the leading edge (BA) of at least one blade (120) of the second row of blades (120) has at least three tooth tops.

4. Propulsive blower (100) according to any one of the preceding claims, wherein a number of tooth crests on the leading edge (BA) of at least one blade (120) of the second row of blades (120) is less than or equal to a number of tooth crests on the trailing edge (BF) of at least one blade (110) of the first row of blades (110).

5. Propulsive blower (100) according to any one of the preceding claims, wherein the leading edge (BA) of at least one blade (120) of the second plurality of blades (120) comprises at least one inclined tooth crest for which a first distance, in the radial direction, from the inclined tooth crest to a first hollow adjacent to the inclined tooth crest, closer to the central axis (X) than the inclined tooth crest, is less than a second distance, in the radial direction, from the first adjacent hollow of the inclined tooth crest to an adjacent tooth crest even closer to the central axis (X) than the first hollow adjacent to the inclined tooth crest, and a third distance, in the radial direction, from the inclined tooth crest to a second hollow adjacent to the inclined tooth crest, further from the central axis (X) than the inclined tooth crest.

6. Propulsive blower (100) according to claim 5, wherein a straight line connecting the crest of inclined tooth to a point equidistant from the first and second hollows adjacent to the crest of inclined tooth on a straight line connecting the first and second hollows adjacent to the crest of inclined tooth has, with respect to a line parallel to the central axis (X) passing through said point equidistant from the first and second hollows adjacent to the crest of inclined tooth, an angle of inclination towards the central axis (X) less than 60° and in particular less than 45° and / or greater than 10°.

7. Propulsive blower (100) according to claim 6, wherein a straight line connecting said adjacent tooth crest to a point equidistant from two adjacent hollows on said adjacent tooth crest, on a straight line connecting the two adjacent hollows of said adjacent tooth crest, has, with respect to a line parallel to the central axis (X) passing through said point equidistant from the two hollows adjacent to the crest of the adjacent tooth, an angle of inclination towards the central axis (X) less than said angle of inclination of the straight line connecting the crest of the inclined tooth to the point equidistant from the first and second hollows adjacent to the crest of the inclined tooth.

8. Propulsive blower (100) according to any one of the preceding claims, wherein the leading edge (BA) of at least one blade (120) of the second row of blades (120) does not have any tooth apex at a radial distance, relative to the blade tip (124), of less than 15% of a span, in the radial direction, from the blade root (123) to the blade tip (124).

9. Propulsive blower (100) according to claim 8, wherein any sweep angle, with respect to the radial direction, of the leading edge (BA) of at least one blade (120) of the second row of blades (120), at a radial distance from the blade head (124) less than 15% of the span, is greater than 50°.

10. Propulsive blower (100) according to claim 9, wherein any sweep angle with respect to the radial direction, of the leading edge (BA) of at least one blade (120) of the second row of blades (120), at a radial distance from the blade head (124) less than 5% of the span, is greater than 55°.

11. Propulsive blower according to any one of the preceding claims, wherein at least one blade (110, 120) of the first and / or second rows of blades (110, 120) has variable pitch around a corresponding radial axis (Z,Z') perpendicular to the central axis (X).

12. Propulsive blower (100) according to any one of the preceding claims, wherein the leading edge (BA) of at least one blade (120) of the second row of blades (120) has spacings (Xk) between adjacent tooth tips that decrease monotonically in a radial direction towards the blade head (124).

13. Propulsive blower (100) according to any one of the preceding claims, wherein any ratio between adjacent spacings among said spacings (Xk) between adjacent tooth apexes is between 1 and 1.6, in particular between 1.05 and 1.

4.

14. Propulsive blower (100) according to any one of the preceding claims, wherein the second row of blades (120) is stator.

15. Propulsive blower (100) according to any one of the claims 1 to 12, in which the second row of blades (120) is counter-rotating with respect to the first row of blades (110).

16. Propulsive blower (100) according to any one of the preceding claims, without fairing around the first and second rows of blades (110, 120).

17. Propulsive blower (100) according to any one of claims 1 to 14, further comprising a nacelle (130) surrounding at least the first and / or second rows of blades (110, 120).

18. Propeller (10) comprising the propulsion blower (100) according to any one of the preceding claims and a gas turbine engine (11) for actuation of the propulsion blower (100).

19. Aircraft (1) comprising the propulsion unit (10) of claim 18.

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