Fan for aeronautical propulsion

Abstract

The invention relates to a propulsive fan (100) comprising two rows of blades (110, 120). The leading edge (BA) of at least one blade (120) of the second row is at least partially saw-toothed. For at least one inclined-tooth point, a first distance (da), in the radial direction, from the inclined-tooth point to a first adjacent gullet that is closer to the central axis (X) than the inclined-tooth point, is shorter than a second distance (db), in the radial direction, from the first adjacent gullet of the inclined-tooth point to an adjacent tooth point that is even closer to the central axis (X) than the first adjacent gullet of the inclined-tooth point, and shorter than a third distance (dc), in the radial direction, from the inclined-tooth point to a second adjacent gullet that is farther from the central axis (X) than the inclined-tooth point.

Description

Description Title of the invention: Fan for aeronautical propulsion Technical Field

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

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

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

[0004] Consequently, the Applicant is constantly working to reduce its climate impact by using methods and operating virtuous development and manufacturing processes and minimizing 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, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and, as an essential complement to technological progress, aeronautical biofuels.

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

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

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

[0009] When the fan is shrouded, the increase in the fan diameter also implies an increase in the external dimensions of the retention casing surrounding it, as well as of the nacelle constituting the aerodynamic envelope of the casing in question, and therefore its drag, as well as that of their mass. In order to avoid these disadvantages, it is possible to shorten the axial length of the nacelle and to thin it. Furthermore, several types of unshrouded propulsive fans have been considered, including in particular those known by the English acronyms " USF" and "CROR". In both types, the propulsive fan comprises two rows of blades arranged radially around one or more central axes, one upstream and the other downstream, the terms "upstream" and "downstream" being understood, in the context of the present disclosure, as being defined with respect to the usual direction of air circulation through the fan. However, in "USF" ("Unducted Single Fan") type propulsive fans only the upstream row is rotatable around the central axis, while in "CROR" ("Counter-Rotating Open Rotor") type propulsive fans the two rows are rotatable in opposite directions. However, in both types, blades of each of the two rows may be 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 ducted fans, shortening and thinning the nacelle to try to compensate for the increased drag and mass associated with a larger diameter has the disadvantage of reducing the space available for acoustic treatments used to reduce noise, while in unducted fans, the absence of a casing or nacelle surrounding the fan allows these noise emissions to be directly diffused into the environment.

[0011] Significant research and development efforts have therefore been directed, in particular by the Applicant, towards reducing these noise emissions. To this end, it has been proposed, in particular in the publications of international patent applications WO 2023 / 007098 A1 and WO 2019 / 158875 A1, to form teeth or undulations on the trailing edge of the blades of unducted propulsive fans, so as to reduce or distribute their marginal vortices. This solution has also been proposed for ducted fans, for example in the publications of 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 into the leading edge for similar reasons, for example in European patent application publication EP 2 760 737 A1 and in US patents 11,560,796 and US 11,047,238. Statement of the invention

[0012] This disclosure is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributing to reducing their environmental impact, particularly in terms of noise emissions. For this purpose, a first aspect of this disclosure relates to a propulsive fan comprising a first row of blades and a second row of blades arranged downstream of the first row of blades, the first row of blades being capable of rotating around a central axis relative to the second row of blades. In the context of this disclosure, the term "blade" refers to both rotating blades and straightening vanes. Thus, the second row of blades may be counter-rotating relative to the first row of blades or stator-type.Each blade of the first and second rows of blades may therefore have a lower surface and an upper surface 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 of the second row of blades may be at least partially saw-toothed, with a plurality of tooth apexes, and in particular at least three tooth apexes, interspersed between troughs, including at least one inclined tooth apex. In the context of the present disclosure, "saw-toothed" is understood to mean broadly, and may cover simple undulations of varying degrees of severity. "Tooth apex" of the leading edge means a convexity forming a local maximum of its position in the upstream axial direction, and "trough" of the leading edge means a concavity forming a local minimum of its position in the upstream axial direction.A first distance, in a radial direction, from the inclined tooth tip to a first adjacent trough of the inclined tooth tip, closer to the central axis than the inclined tooth tip, may be less than a second distance, in a radial direction, from the first adjacent trough of the inclined tooth tip to an adjacent tooth tip, even closer to the central axis than the first adjacent trough of the inclined tooth tip, and a third distance, in a radial direction, from the inclined tooth tip to a second adjacent trough of the inclined tooth tip, further from the central axis than the tip. inclined tooth. Thus, at least this inclined tooth can be inclined towards the central axis of the first and second rows of blades.

[0014] Due to this inclination towards the central axis, the sweep angle of the leading edge can be locally increased between the inclined tooth tip and the second adjacent trough of the inclined tooth tip, further from the central axis, which helps to de-correlate the acoustic sources, i.e. to prevent them from being activated at the same time. This de-correlation can generate destructive interference between the acoustic sources and thus contribute to noise reduction.

[0015] In said at least one blade of the second row of blades, a camber and / or an angle, relative 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 intrados and the extrados to the leading edge, may be greater in a blade profile at said first adjacent trough than in blade profiles at the inclined tooth and adjacent tooth tips. For the purposes of this disclosure, the term "skeleton line" means a segment, equidistant from the intrados and the extrados over its entire length, and connecting the leading edge to the trailing edge in a plane perpendicular to the radial direction.In the context of this disclosure, the term "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 angles and / or camber, which are more pronounced at the level of the trough, reduce the incidence of the flow there and therefore eliminate or at least reduce the separation of the flow and / or the generation of vortices and / or the generation of aerodynamic flow shocks, and therefore the aerodynamic losses.

[0016] A straight line connecting the inclined tooth apex to a point equidistant from the first and second adjacent troughs of the inclined tooth apex on a straight line connecting the first and second adjacent troughs of the inclined tooth apex may have, with respect to a line parallel to the central axis passing through said point equidistant from the first and second adjacent troughs of the apex of 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 top to a point equidistant from two adjacent troughs of said adjacent tooth top on a straight line connecting the two adjacent troughs of said adjacent tooth top may have, with respect to a line parallel to the central axis passing through said point equidistant from the two adjacent troughs of the adjacent tooth top, an angle of inclination towards the central axis less than said angle of inclination of the straight line connecting the inclined tooth top to the point equidistant from the first and second adjacent troughs of said inclined tooth top.Since said adjacent tooth apex is closer to the central axis than said inclined tooth apex, a decreasing inclination law can thus be obtained for successive teeth in the direction of the central axis. In particular, this decrease can be monotonic. By decrease. "monotonic" in the context of this disclosure means that each successive tooth, radially toward the centerline, may have a centerline inclination equal to or less than the centerline inclination of the preceding tooth. With more inclined teeth, and thus steeper 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 may help to avoid further negative interactions between the tooth and the boundary layer near the blade root.

[0017] The leading edge of at least one blade of the second row of blades may not have any tooth tips at a radial distance, relative to the blade head, of less than 15% of a span, in the radial direction, from the blade root to the blade head. Indeed, since the chord at the blade head may be small, it may prove complex 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 tips at the blade tip, any angle of sweep, relative to the radial direction, of the leading edge of at least one blade of 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, of the leading edge of at least one blade of the second row of blades, at a radial distance from the blade tip less than 5% of the span, may be greater than 55°. As previously indicated, a pronounced sweep angle contributes to the de-correlation of acoustic sources, which may be particularly important at the blade tip.

[0018] At least one blade of the first and / or second rows of blades may be variable pitch around a corresponding radial axis perpendicular to the central axis, in order to optimize the efficiency at different speeds.

[0019] The leading edge of at least one blade of the second row of blades may in particular have spacings between adjacent tooth tips that decrease monotonically in the radial direction towards the blade tip. Thus, the larger spacings near the blade root make it possible to better dissipate the acoustic energy originating 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 larger spacings near the blade root may make it possible to avoid in-phase radiation on this region of the blade, even if the sweep angle is lower there near the blade root.

[0020] Any ratio between adjacent spacings among said spacings between adjacent tooth apexes is between 1 and 1.6, in particular between 1.05 and 1.4, so as to allow a gradual evolution between spacings.

[0021] The second row of blades may in particular be stationary in rotation about the central axis as in conventional ducted propulsive fans or in unducted propulsive fans of so-called “USF” configuration. However, it is alternatively conceivable that the second row of blades is counter-rotating about the central axis relative to the first row of blades, as in the unducted fan configuration known as “CROR”. Furthermore, the propulsive fan may be without a shroud around the first and second rows of blades or, alternatively, comprise a nacelle surrounding the first and / or second rows of blades.

[0022] A second aspect of the present disclosure relates to a thruster that may comprise the propulsive fan according to the first aspect and a gas turbine engine for actuating the propulsive fan. The thruster may in particular also comprise a reduction gear interposed between the gas turbine engine and the propulsive fan, in order to reduce the rotational speed of the propulsive fan relative to an output speed of the gas turbine engine. However, other actuation means are also conceivable, such as for example a hybrid thruster in which the gas turbine engine would be combined with an electric motor, which could be interposed in series between the gas turbine engine and the fan, or be arranged in parallel with the gas turbine engine in a transmission line. An electric thruster, comprising only an electric motor for actuating the propulsive fan, is also conceivable.

[0023] A third aspect of the present disclosure relates to an aircraft comprising a propeller as described above. Brief description of the drawings

[0024] The invention will be better understood and its advantages will become more apparent upon reading the following detailed description of embodiments shown as non-limiting examples. The description refers to the appended drawings which are schematic and are intended primarily to illustrate the principles of the disclosure.

[0025] In these drawings, from one figure to another, identical or equivalent elements (or parts of elements) are identified by the same reference signs. In these attached drawings:

[0026] [Fig. 1] Figure 1 schematically illustrates an aircraft.

[0027] [Fig. 2] Figure 2 schematically illustrates in section a propeller, suitable for propelling the aircraft of Figure 1, equipped with an unducted propulsive fan according to a first embodiment.

[0028] [Fig. 3] Figure 3 schematically illustrates the propulsive fan according to the first embodiment.

[0029] [Fig. 4A] Figure 4A shows a sectional view of a blade of the propulsive fan of Figure 3 in a plane perpendicular to a radial stacking axis.

[0030] [Fig. 4B] Figure 4B illustrates an alternative shape of the trailing edge of the blade of Figure 4A.

[0031] [Fig. 5] Figure 5 represents a detailed side view of a blade of the second row of blades of the propulsive fan according to the first embodiment.

[0032] [Fig. 6A] Figure 6A illustrates a superposition of two profiles, respectively at the levels of a leading edge tooth tip and an adjacent hollow, of a blade of the second row of blades of the propulsive fan according to a first variant of the first embodiment.

[0033] [Fig. 6B] Figure 6B illustrates a superposition of two profiles, respectively at the levels of a leading edge tooth tip and an adjacent hollow, of a blade of the second row of blades of the propulsive fan according to a second variant of the first embodiment.

[0034] [Fig. 6C] Figure 6C illustrates a superposition of two profiles, respectively at the levels of a leading edge tooth tip and an adjacent hollow, of a blade of the second row of blades of the propulsive fan according to a third variant of the first embodiment.

[0035] [Fig. 7] Figure 7 represents a side view of a blade of the second row of blades of the propulsive fan according to a second embodiment.

[0036] [Fig. 8] Figure 8 schematically illustrates an aircraft with a propeller equipped with a ducted propulsive fan according to a third embodiment

[0037] [Fig. 9] Figure 9 schematically illustrates the thruster equipped with the ducted propulsive fan according to the third embodiment. Description of the embodiments

[0038] In order to make the disclosure more concrete, embodiments are described in detail below, with reference to the accompanying drawings. It is recalled, however, that the invention is not limited to these embodiments.

[0039] As illustrated in FIG. 1, an aircraft 1 may incorporate one or more propellers 10 with a propulsive fan 100 according to the present description. These propellers 10 may in particular be arranged, as illustrated, under the wings 2, but other alternative arrangements, for example at the rear of the fuselage of the aircraft 1, are also conceivable.

[0040] As illustrated in Figure 2, the propellant 10 may also comprise a gas turbine engine 11 and a reduction gear 12. In the direction of air flow, this gas turbine engine 11 may comprise a low-pressure compressor 13, a high-pressure compressor 14, a combustion chamber 15, a high-pressure turbine 16, a low-pressure turbine 17 and a nozzle 18, surrounded by a fairing 19 terminating in the nozzle 18. The high-pressure turbine 16 may be connected to the high-pressure compressor 14 by a first rotary shaft 21 for driving the latter, while the low-pressure turbine 17 may be connected to the low-pressure compressor 13 by a second rotary shaft 22 coaxial with the first rotary shaft 21, in a similar manner. The reduction gear 12 may connect the second rotary shaft 22 to the propellant fan 100 for actuating the latter.Although in the illustrated example the propulsive fan 100 is arranged at the front of the thruster 10, in a so-called “puller” configuration, it is also possible to arrange it at the rear of the thruster, in a “pusher” configuration.

[0041] In addition to or replacing the gas turbine engine 11, the thruster 10 could however comprise another type of motor, and in particular an electric motor, for actuating the fan, directly and / or through a transmission such as the reducer 12. The thruster 10 could therefore be a hybrid thruster, in series or parallel, or even purely electric.

[0042] The propulsive fan 100 may comprise two rows of blades: a first row of blades 110 and a second row of blades 120, downstream of the first row of blades 110. The two rows may in particular be coaxial, with the blades of the two rows 110, 120 arranged radially around the same central axis X. Each of the rows 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 2 more blades than the second row.

[0043] The first and / or second row of blades 110, 120 may have an external diameter D ebetween 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 tip. In the context of the present disclosure, the term "strength factor" is understood to mean 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.

[0044] In a first embodiment illustrated in Figures 1 to 3, the propulsive fan 100 may be devoid of fairing around the first and second rows of blades 110, 120. In this case, the propulsive fan 100 may be of the “USF” type, in which only the first row of blades 110 is rotated by the gas turbine engine 11 through the reduction gear 12, or of the “CROR” type, in which the first and second rows of blades 110, 120 are rotated in opposite directions by the gas turbine engine 11 through the reduction gear 12.

[0045] In all cases, each of the blades 110,120 may comprise a profiled body extending radially, relative to the central axis X, over a span H from a blade root 113,123 with an internal diameter Dj of the row corresponding to a blade head 114,124 with an external diameter D eof the corresponding row, as shown in Figure 3. However, the inner diameters Di and / or outer diameters D e of the first row may be different from the diameters interior Di and / or exterior D e of the second row. For each row, the span H of the blades 110,120, corresponding to half the difference between the external diameters D e and internal diameter D, corresponding, can therefore be different. In particular, the external diameter D e of the second row of blades 120 may be less than the outer diameter D eof the first row of blades 110 in order to limit or avoid the interaction of the blades 120 of the second row with the blade tip vortices of the first row of blades 110. It is also possible that, in one and / or the other of the first and second rows of blades 110, 120, the span H of the blades 110, 120 is heterogeneous, that is to say that at least two blades 110, 120 of the same row of blades have different spans H. In particular, the blades 120 of the second row may have a truncation (in English: "clipping") variable with respect to the external diameter D eof the first row of blades 110, in order to avoid interaction with the vortices detached by the end of the blades 110 of the first row during the phases of flight at incidence and thus reduce the noise during the phases of flight at incidence, such as takeoff and / or landing. Indeed, this interaction can be a dominant source of noise which can reduce or partially mask the benefits provided by the saw teeth on the leading edges BA of the blades 120 of the second row.

[0046] The profiled body of each blade 110, 120 may be formed by aerodynamic profiles (or "sections") stacked from the blade root 113, 123 to the blade head 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, a lower surface 111, 121 and an upper surface 112, 122 each extending from a leading edge BA to a trailing edge BF. Each of these aerodynamic profiles is therefore defined in a corresponding plane perpendicular to the radial axis Z, Z'. For example, for a section or aerodynamic profile of the blade 110, 120, the leading edge BA may be defined as the upstream end following the direction of flow of the fluid. The leading edge BA can be characterized by a local minimum on the radius of curvature defining the profile in its upstream part. The trailing edge BF can be defined as the downstream end following the direction of fluid flow.The BF trailing edge 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 may alternatively be truncated, as illustrated in Figure 4B.

[0047] Each of the stacked profiles has a chord c which is defined as the distance between the leading edge BA and the trailing edge BF on a straight line connecting them and having a pitch angle Y relative to a plane perpendicular to the central axis X. Conventionally, the pitch angle y of an aerodynamic profile corresponds to the angle formed between, on the one hand, a first axis 150 which is defined by the intersection between the plane of the aerodynamic profile at the radial distance r and a plane perpendicular to the central axis X, and on the other hand, a straight line connecting the leading edge BA and the trailing edge BF of the aerodynamic profile at the radial distance r. The pitch angle y is measured on the upstream side of the plane perpendicular to the central axis X.The setting angle y can be measured positively in a direction going from the first axis 150 to the straight line connecting the leading edge BA and the trailing edge BF, and more particularly in a direction coinciding with the direction going from the intrados line 11 1 , 121 towards the extrados line 112, 122.

[0048] These sections or aerodynamic profiles may in particular be cambered. More particularly, 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 intrados 11 1 , 121 and the extrados 1 12, 122 over its entire length, may be cambered, so as to present, with respect to a direction parallel to the central axis X, an angle of inclination Pi at the leading edge BA and an angle of inclination p 2at the trailing edge BF. The camber of the section or aerodynamic profile can 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.

[0049] Each 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 intrados 1 11 , 121 and the extrados 1 12,122. The chord c, the pitch angle y, the angles of inclination on the leading edge and p 2 at the trailing edge BF, 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 may 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 makes it possible to reinforce the mechanical strength of the blade 110, 120.

[0050] Each of the blades 110, 120 may have an elongation equal to the outer diameter D e of the corresponding row, multiplied by a coefficient between 0.3 m 1 and 1.2 m' 1 , especially between 0.4 m' 1 and 0.8 m' 1 . We understand by "elongation", in the context of this presentation, 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 from the central axis X, according to the equation:

[0051] 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 the present disclosure, the term “activity factor” means the value FA resulting from the following equation, in which Ç corresponds to twice the ratio between the radial distance r relative to the central axis X and the external diameter D e : 100000 r 1 ^) , FA = d , 16 jDi D e 5 From~

[0052] 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 thanks to more pronounced saw teeth.

[0053] The axial distance between the stacking axes Z, Z' of the two rows may be, for example, between 0.005 and 0.5, in particular between 0.18 and 0.3 times the outer diameter D e of the first row of blades 110, and above all sufficient to prevent interference of the trailing edges BF of the blades 110 with the leading edges of the blades 120. Each of the blades 110 and / or 120 can be rotatable around a radial axis or pitch change axis, which can in particular be the corresponding stacking axis Z, Z', in order to adjust its setting and therefore its incidence relative to the airflow direction according to the flight phase. This setting change axis may preferably be perpendicular to the central axis X, alternatively inclined relative to the central axis X.

[0054] In order to take advantage of the increase in the dynamic pressure of the air downstream of the first row of blades 110, an air inlet 20 of the gas turbine engine 11 may in particular be arranged between the blades 110 and the vanes 120. This air inlet 20 may for example be annular, with a nozzle 23 separating the air inlet 20 from the fairing 19, as illustrated in FIG. 3.

[0055] 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=1, 2,... N in ascending order in the radial direction from the blade root 123 to the blade tip 124, and a number M of spacings A kbetween adjacent tooth tips, where k=1, 2,...M also in increasing order in the radial direction from the blade root 123 to the blade head 124, and M < N-1. 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 possible aerodynamic losses linked to the teeth.

[0056] The spacings To k may vary, and in particular decrease monotonically in the radial direction towards the blade head 124, such that Δ-, > Δ 2 > To 3 >... ÀM-1 AM- Thus, any ratio between adjacent spacings À k and To k+i can be between 1 and 1.6, in particular between 1.05 and 1.4. As illustrated in Figures 2 and 3A, all spacings can be different, so that In particular, each ratio between adjacent spacings A k and To k+ican 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 growth, over all the spacings.

[0057] With respect 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 may also be at least partially saw-toothed, with tooth tops and alternating hollows. 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 hollows of the trailing edges BF of the blades 110 of the first row can be substantially aligned, in the axial direction parallel to the central axis X, with the tops of the leading edges BA of the blades 120 of the second row and, conversely, the tops of the trailing edges BF of the blades 110 of the first row can be substantially aligned, in the axial direction parallel to the central axis X, with the hollows 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 blades 110 and of the tooth tips at the leading edge BA of the blades 120, or vice versa, make it possible to maximize the acoustic gains and therefore the reduction of interaction noise. Indeed, the speed deficit and therefore the aerodynamic excitation of the wake of the blades 110 increases at the level of the tooth troughs at the trailing edge BF of the blades 110 of the first row, which can be compensated by a reduced acoustic response at the level of the tooth tips at the leading edge of the blades 120 of the second row.

[0058] 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 may be substantially identical to the distance from the axis X, in a radial direction perpendicular to the central axis X, of a corresponding tooth tip 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 tip in the trailing edge BF of each blade 110 of the first row may 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, it is meant that they do not differ by more than 10%, or even 5%, or even 3% of the largest span H of the blades 110, 120 of the first or second rows.

[0059] 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 tip a first distance d a , in the radial direction, from the inclined tooth tip to a first adjacent trough of the inclined tooth tip, closer to the central axis X than the inclined tooth tip, is less than a second distance db, in the radial direction, from the first adjacent trough of the inclined tooth tip to an adjacent tooth tip, even closer to the central axis X than the first adjacent trough of the inclined tooth tip, and a third distance d c, in a radial direction, from the inclined tooth tip to a second adjacent trough of the inclined tooth tip, further from the central axis X than the inclined tooth tip.

[0060] Thus, a straight line connecting the inclined tooth apex to a point equidistant from the first and second adjacent troughs of the inclined tooth apex on a straight line connecting the first and second adjacent troughs of the inclined tooth apex may have, relative to a line parallel to the central axis X crossing said point equidistant from the first and second adjacent troughs of the inclined tooth apex, an inclination angle 0, towards the central axis X less than 60° and in particular less than 45° and / or greater than 10°.

[0061] Furthermore, several of the teeth, or even all of the teeth of the leading edge BA of each blade 120 of the second row, may thus be inclined towards the central axis X. The angle of inclination 0 of each successive tooth may decrease towards the central axis X, in such a way that, as also illustrated in FIG. 5, a straight line connecting said adjacent tooth apex to a point equidistant from two adjacent troughs of said adjacent tooth apex on a straight line connecting the two adjacent troughs of said adjacent tooth apex has, with respect to a line parallel to the central axis X crossing said point equidistant from the two adjacent troughs of the adjacent tooth apex, an angle of inclination 0M towards the central axis X less than the angle of inclination 0j. It is thus possible to obtain a monotonically decreasing inclination law for the successive teeth in the direction of the central axis X, or monotonically increasing in the opposite direction, in such a way that 01 < 0 2^ ...^ 0N, and 01 < 0 N , where i=1,2,...N in ascending order in radial direction from blade root 123 to blade tip 124.

[0062] Following the camber of the stacked profiles of the blade 120, the variations of the chord c can be accompanied by variations of the pitch angle y, of leading edge BA, and / or the camber f / c, as respectively illustrated in Figures 6A to 60, in order to optimize the aerodynamic operation of the blade 120. Thus, as illustrated in Figure 6A, the pitch angle y can be more pronounced for a profile p sd at the level of a tooth summit than for a profile p c at the level of an adjacent hollow. 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 profile p c at the level of the adjacent hollow as for the profile pS d at the level of the tooth tip. Alternatively or in addition, the inclination angle p 1 at the leading edge BA can be higher for the p profile c at the level of the adjacent hollow as for the profile p sd at the tooth tip, as shown in Figure 6B, and / or the camber f / c may be greater for profile Pc at the adjacent trough than for profile p sd at the tooth tip, as shown in Figure 6C. All three options, separately or in combination, can reduce the incidence and velocity and / or acceleration of the flow at the trough and thus eliminate or at least reduce flow separation and / or vortex generation and / or shock generation, and thus aerodynamic losses.

[0063] 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 is devoid of tooth tips over a portion of the span of the blade 120. In particular, according to a second embodiment illustrated by way of example in Figure 7, the leading edge BA of the blade 120 may have no tooth tips at a radial distance, relative to the blade head 124, of less than 15% of the span H. Thus, any sweep angle θ, relative to the radial direction, of the leading edge BA of the blade 120, at a radial distance from the blade head H less than 15% of the span, may be greater than 50°. The blade deflection 120 may further increase towards the blade tip, such that any deflection angle a relative to the radial direction, from the edge BA attack angle of blade 120, at a radial distance from the blade head less than 5% of the span, or greater than 55°.

[0064] Furthermore, although in the preceding embodiments the propulsive fan is not ducted, it is also alternatively conceivable, as in a third embodiment illustrated by way of example in FIGS. 8 and 9, that the propulsive fan 100 is a ducted fan, also comprising a nacelle 130 surrounding the first and second rows of blades 110, 120. This nacelle 130 may also comprise a retention casing 140 around the blades 110, with an abradable material to limit damage in the event of contact between the radially external end of the blades 110 and the casing, and / or acoustic treatments for noise reduction. In this case, the second row of blades 120 may be stator-like 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 rectifier blades 120 may for example be twice the number of rotor blades 110 by adding 4 to this product. It would nevertheless also be possible, in a ducted propulsive fan 100, for the second row of blades 120 to be counter-rotating relative to the first row of blades 110.

[0065] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments recited may be combined in additional embodiments. Therefore, the description and drawings are to be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. A propulsive fan (100) comprising a first row of blades (110) and a second row of blades (120) arranged downstream of the first row of blades (110), the first row of blades (110) being rotatable 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 a lower surface (111, 121) and an upper surface (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 (BA) to a trailing edge (BF), the leading edge (BA) of at least one blade (120) of the second row of blades (120) being at least partially saw-toothed, with a plurality of tooth apexes interposed between hollows, including at least one inclined tooth apex for which a first distance (d a), in the radial direction, from the inclined tooth tip to a first adjacent trough of the inclined tooth tip, closer to the central axis (X) than the inclined tooth tip, is less than a second distance (db), in the radial direction, from the first adjacent trough of the inclined tooth tip to an adjacent tooth tip, even closer to the central axis (X) than the first adjacent trough of the inclined tooth tip, and a third distance (d c), in the radial direction, from the inclined tooth tip to a second adjacent trough of the inclined tooth tip, further from the central axis (X) than the inclined tooth tip, characterized in that a straight line connecting the inclined tooth tip to a point equidistant from the first and second adjacent troughs of the inclined tooth tip on a straight line connecting the first and second adjacent troughs of the inclined tooth tip has, with respect to a line parallel to the central axis (X) passing through said point equidistant from the first and second adjacent troughs of the inclined tooth tip, an inclination angle towards the central axis (X) of less than 60° and in particular less than 45° and / or greater than 10°, and a straight line connecting said adjacent tooth tip to a point equidistant from two adjacent troughs of said adjacent tooth apex on a straight line connecting the two adjacent troughs of said adjacent tooth apex has, with respect to a line parallel to the central axis (X) passing through said point equidistant from the two adjacent troughs of the adjacent tooth apex, an angle of inclination towards the central axis (X) less than said angle of inclination of the straight line connecting the inclined tooth apex to the point equidistant from the first and second adjacent troughs of the inclined tooth apex.

2. A propulsive 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, relative 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 intrados (121) and the extrados (122) to the leading edge (BA), are greater in a blade profile at said first adjacent trough than in blade profiles at the inclined tooth and adjacent tooth tips.

3. A propulsive fan (100) according to any preceding claim, wherein the leading edge (BA) of each blade (120) of the second row of blades (120) has at least three tooth tips.

4. A propulsive fan (100) according to any one of the preceding claims, wherein the leading edge (BA) of said at least one blade (120) of the second row of blades (120) has no tooth apex at a radial distance, relative to the blade head (124), of less than 15% of a span, in the radial direction, from the blade root (123) to the blade head (124).

5. A propulsive fan (100) according to claim 4, wherein any sweep angle, relative 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°.

6. A propulsive fan (100) according to claim 5, wherein any sweep angle relative 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°.

7. A propellant fan 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) is variable pitch around a corresponding radial axis (Z, Z') perpendicular to the central axis (X).

8. A propellant fan (100) according to any preceding claim, wherein the leading edge (BA) of at least one blade (120) of the second row of blades (120) has spacings (À k) between adjacent tooth apexes which decrease monotonically in the radial direction towards the blade head (124).

9. A propellant fan (100) according to any preceding claim, wherein any ratio between adjacent ones of said spacings (A k ) between adjacent tooth apices is between 1 and 1.6, particularly between 1.05 and 1.

4.

10. A propulsive fan (100) according to any preceding claim, wherein the second row of blades (120) is stationary in rotation about the central axis (X).

11. A propellant fan (100) according to any one of claims 1 to 10, wherein the second row of blades (120) is counter-rotating about the central axis (X) relative to the first row of blades (110).

12. A propulsive fan (100) according to any preceding claim, without a fairing around the first and second rows of blades (110, 120).

13. A propulsive fan (100) according to any preceding claim, further comprising a nacelle (130) surrounding at least the first and / or second rows of blades (110, 120).

14. Propellant (10) comprising the propulsive fan (100) according to any one of the preceding claims and a gas turbine engine (11) for driving the propulsive fan (100).

15. An aircraft (1) comprising the propellant (10) of claim 14.

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