Fan blade for aeronautical propulsion

Abstract

The invention relates to a blade (110) of a propulsive fan (100) that has a saw-toothed trailing edge (BF), wherein a first and a second skeleton line connect the leading edge (BA) to a tooth peak and to an adjacent trough in the trailing edge (BF), respectively, and the absolute value of a variation (ΔβS) of an angle (βS) of inclination of the first skeleton line is smaller than a variation (ΔβC) of an angle (βC) of inclination of the other skeleton line on corresponding end segments, which are adjacent to the trailing edge (BF). Each of said end segments of the first and second skeleton lines extend over 30%, or 20%, of a total length of the relevant skeleton line between the leading edge (BA) and the trailing edge (BF).

Description

Description Title of the invention: Fan blade for aircraft propulsion Technical Field

[0001] The technical field of this presentation 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 different countries. 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 less energy-intensive and more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences, with the aim of improving the energy efficiency of aircraft.

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

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly 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 primary factors influencing propulsive efficiency are those that directly contribute 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 outlet and the associated kinetic energy losses.

[0008] To achieve the same thrust, this decrease in flow velocity at the outlet of the propulsion fan must normally be compensated for 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 also normally implies a higher bypass ratio (BPR), which is the ratio between the mass flow rate of the cold flow from the fan (secondary flow) and that feeding the combustion chamber of the gas turbine engine (primary flow).

[0009] When the fan is enclosed, increasing its diameter also increases the external dimensions of the surrounding retaining casing, as well as the nacelle that forms the aerodynamic envelope of the 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 unenclosed propulsive fans have been considered, including those known by the English acronyms " USF and CROR. In both types, the propulsion fan comprises two rows of blades arranged radially around one or more central axes, one upstream and one downstream. The terms "upstream" and "downstream" are understood, in the context of this discussion, as defined with respect to the usual direction of airflow through the fan. However, in USF (Unducted Single Fan) propulsion fans, only the upstream row rotates around the central axis, while in CROR (Counter-Rotating Open Rotor) propulsion fans, both rows rotate in opposite directions. Nevertheless, in both types, blades in each of the two rows may 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 increased drag and mass associated with a larger diameter has the disadvantage of reducing the space available for acoustic treatments used for noise reduction, while in unshrouded fans, the absence of a casing or nacelle surrounding the fan allows the direct diffusion of these noise emissions into the environment.

[0011] Significant research and development efforts have therefore been directed, notably by the Applicant, towards reducing these noise emissions. To this end, it has been proposed, particularly in international patent applications WO 2023 / 007098 A1 and WO 2019 / 158875 A1, to create teeth or undulations on the trailing edge of the blades of unshod propulsion fans, in order to reduce or distribute their wingtip vortices. This solution has also been proposed for shod fans, for example in French patent applications FR 2 986 285 A1 and FR 3 103 231 A1.

[0012] However, these sawtooth trailing edges can also generate so-called "horseshoe" vortices on the sides of each tooth, due to the cross-flow of air from the lower surface to the upper surface of each blade. This cross-flow and the horseshoe vortices... The resulting horsepower can generate aerodynamic losses, while also restricting the effectiveness of the teeth to reduce noise emissions. Furthermore, from a mechanical standpoint, stress concentrations can be induced at the gaps between adjacent teeth. Description of the invention

[0013] This presentation is the result of technological research aimed at significantly improving aircraft performance to reduce energy consumption while simultaneously limiting noise emissions, thereby contributing to a reduction in environmental impact. The first aspect of this presentation concerns a propeller fan blade. Such a blade comprises an intrados and an extrados extending, in a blade span direction, from a blade root to a blade tip, and, in a blade width direction, from a leading edge to a trailing edge.In the blade according to this first aspect, the trailing edge is at least partially saw-toothed. A first skeleton line connects the leading edge, in a first transverse plane, to a tooth crest in the trailing edge, and a second skeleton line connects the leading edge, in a second transverse plane, to a groove adjacent to said tooth crest in the trailing edge. In the context of this disclosure, the term "skeleton line" generally refers to a line equidistant from the lower and upper surfaces and connecting the leading edge to the trailing edge in a transverse plane, that is, perpendicular to the span direction of the blade.

[0014] In the blade according to this first aspect, the absolute value of a variation in the angle of inclination on a terminal segment of the first skeleton line is less than the absolute value of a variation in the angle of inclination on a terminal segment of the second skeleton line. Each of these terminal segments of the first and second skeleton lines extends over 30%, or even 20%, of the total length of the respective skeleton line between the leading edge and the trailing edge. In the context of this application, "angle of inclination" generally means an angle of inclination of the skeleton line with respect to a direction parallel to a central axis of rotation of the blade, by "terminal segment" a partial segment of the skeleton line extending from the trailing edge and therefore adjacent to it.

[0015] Thanks to the minimal variation in the inclination angle of the skeleton line on the terminal segment at the tooth crest, it is possible to restrict crossflow and the formation of horseshoe vortices on the tooth flank between the tooth crest and the adjacent hollow, resulting in aerodynamic and aeroacoustic benefits. This configuration also reduces mechanical stress at the hollow, thus ensuring greater mechanical strength even with a lighter construction.

[0016] To reduce the variation in the inclination angle of the first skeleton line on the terminal segment, the first skeleton line may have an inflection point inside the terminal segment of the first skeleton line. "Inside the terminal segment" means, in the context of the present invention, at any point on the terminal segment except its endpoints, thus excluding the trailing edge itself.

[0017] In order to restrict the aerodynamic load on the tooth, an absolute value of the inclination angle of the first skeleton line at the trailing edge may be greater, for example by between 0.5° and 8°, in particular by between 1° and 6°, than an absolute value, at the trailing edge, of the inclination angle of the second skeleton line, and / or an absolute value of a pitch angle of a chord line in the first transverse plane may be greater than an absolute value of a pitch angle in the second transverse plane.

[0018] To ensure the reduction of noise emissions, the trailing edge may have at least three tooth peaks with respective adjacent hollows.

[0019] In this case, an absolute value of the trailing edge inclination angle of each skeleton line connecting the leading edge to one of the at least three tooth vertices may be greater, for example, by between 0.5° and 8°, and in particular by between 1° and 6°, than an absolute value of the trailing edge inclination angle of at least one other skeleton line in a parallel transverse plane passing through a respective adjacent groove. Alternatively, or in In addition to this, an absolute value of the difference between the trailing edge inclination angle of the skeleton line connecting the leading edge to one of the at least three tooth tips and the trailing edge inclination angle of at least one other skeleton line in a parallel transverse plane passing through a respective adjacent groove is maximized for a tooth tip located, relative to the blade root, in the blade span direction, at least one-quarter of the span between the blade root and the blade tip, specifically between 0.35 and 0.9 times said span. This allows for greater trailing edge inclination angle variations at positions along the span where the tooth amplitudes are greater or the chord is greater, and therefore at locations where mechanical stresses may be higher.

[0020] The trailing edge teeth can take the form of undulations, particularly sinusoidal ones, although other shapes are also possible. Furthermore, in order to limit stress concentrations in the trailing edge recesses, each spacing, in the blade's span direction, between two adjacent tooth crests can be equal to the square of a tooth height, perpendicular to the blade's span direction, between one of the two adjacent tooth crests and a trailing edge recess located between the two adjacent tooth crests, multiplied by a coefficient between 0.005 mm -1 and 1 mm -1 , in particular between 0.01 mm -1 and 0.8 mm -1 , even more specifically between 0.02 mm -1 and 0.6 mm -1This is especially true if the teeth are sinusoidal. Indeed, when the teeth are sinusoidal, the radius of curvature at the gaps between adjacent teeth is proportional to the ratio of the spacing to the square of the height. However, a radius of curvature that is too small at the gaps increases mechanical stress and makes blade manufacturing difficult, while a radius of curvature that is too large would be less effective at reducing noise emissions.

[0021] A radial position of each tooth apex at the trailing edge can correspond substantially to a radial position of a local maximum of the chord line angle and / or a local minimum of the skeleton line angle at the trailing edge. In this context, "substantially" can be understood to mean that the radial positions of tooth apexes and the radial positions local maxima or minima of pitch angle correspond to within 5%, or even within 2%, of the height of the profiled body of the blade.

[0022] In order to ensure its mechanical resistance, the blade may have a maximum thickness, between the extrados and the intrados, of less than 20%, in particular less than 10%, of the span relative to the blade root, in the span direction.

[0023] The blade can be one with variable pitch around an axis substantially aligned with the wingspan direction, in order to adapt it to different flight regimes and engine regimes.

[0024] A second aspect of this presentation concerns a propulsive fan comprising a first rotor with at least one row of blades as described in the first aspect. The first rotor may have between 10 and 22 blades, particularly between 12 and 14 blades. An outside diameter De of the first rotor may be between 1 and 6 m, particularly between 3 and 5 m. The strength of the first rotor may be less than 2.5 over the entire span of the blades, and particularly less than 0.5 at the blade tips. "Strength" can be understood as the ratio between the chord of each blade or vane in a row and the distance between two adjacent rotor blades at the same radial distance from a central axis of the rotor. Each blade of the first rotor may have an aspect ratio equal to the outside diameter De of the first rotor multiplied by a coefficient between 0.3 m -1 and 1.2 m -1 , preferably between 0.4 m -1 and 0.8 m -1Such an elongation, normalized by the outside diameter De of the first rotor, allows for good distribution of the aerodynamic load. This can be understood as... "Aspect ratio," in the context of this discussion, refers to the ratio between the wingspan 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, according to in which Di represents the inner diameter of the first rotor.

[0025] Furthermore, the first rotor exhibits an activity factor between 100 and 300, particularly between 150 and 225. By "activity factor" we can understand, in The context of this presentation, the following result: 100,000 FA = 16 where the normalized radial distance represents twice the radial distance r from the central axis, divided by the outside diameter De, and c(f) represents the local chord between the leading and trailing edges of the airfoil at said normalized radial distance. Indeed, relatively high activity factors imply a relatively large chord towards the blade tip. However, this can imply a greater boundary layer thickness, and consequently increase the self-noise (broadband) and the width of the propeller wakes, hence the interest in using noise reduction technologies such as teeth or undulations at the trailing edge. The first rotor can have a hub ratio between 0.15 and 0.45, in particular between 0.25 and 0.35, or even more specifically between 0.26 and 0.3. For the purposes of this discussion, "hub ratio" can be understood as the ratio of the outside diameter De to the inside diameter Di.

[0026] To direct the airflow downstream of the engine and thus increase its propulsive efficiency, the propulsion fan may include a stator with at least one row of outlet guide vanes (OGVs), positioned downstream of at least one row of blades of the first rotor, for example, in a single-fan (USF) configuration. Alternatively, however, the propulsion fan may include a second rotor with at least one additional row of blades positioned downstream of at least one row of blades of the first rotor, and rotating in the opposite direction to the first rotor. The propulsion fan may be, in particular, an unshod fan, but it is also possible for it to include a shroud surrounding at least one row of blades.

[0027] A third aspect of this presentation concerns a propulsion system comprising the propulsion fan described in the first presentation and an engine, which may in particular be 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 a speed output 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 a possibility.

[0028] A fourth aspect of this presentation concerns an aircraft comprising one or more propulsion systems according to the third aspect. Brief description of the drawings

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

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

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

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

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

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

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

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

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

[0038] [Fig. 4] Figure 4 illustrates the evolution of the angle of inclination of the first and second skeleton lines over their length, corresponding respectively to the position of a tooth apex and an adjacent hollow on the trailing edge of the blade in Figure 3A.

[0039] [Fig. 5] Figure 5 schematically illustrates an aircraft following an alternative embodiment in which the propulsion fan is enclosed.

[0040] [Fig. 6] Figure 6 schematically illustrates a propulsion system of the aircraft in Figure 5. Description of the implementation methods

[0041] To make the explanation more concrete, embodiments are described in detail below, with reference to the attached drawings. It should be noted, however, that the invention is not limited to these embodiments.

[0042] As illustrated in Figure 1, an aircraft 1 can incorporate one or more propeller 10s with a propulsive fan 100 as described herein. These propellers 10 can, 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.

[0043] As illustrated in Figure 2, the propulsion unit 10 may also include a gas turbine engine 11 and a reduction gear 12. In the direction of the airflow, this gas turbine engine 11 may include a low-pressure compressor 13, a high-pressure compressor 14, a combustion chamber 15, a high-pressure turbine 16, a low-pressure turbine 17, and a nozzle 18, surrounded by a shroud 19 leading into the nozzle 18. The high-pressure turbine 16 may be connected to the high-pressure compressor 14 by a first rotating shaft 21 for driving the latter, while the low-pressure turbine Pressure 17 can 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 gearbox 12 can connect the second rotary shaft 22 to the propulsion blower 100 for its actuation. Although in the illustrated example the propulsion 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.

[0044] In addition to or as a replacement for the gas turbine engine 11, the thruster 10 could, however, include another type of engine, and in particular an electric motor, for the operation of the blower, 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.

[0045] The propulsion fan 100 may comprise a rotor with a row of blades 110 and a stator with a row of guide vanes 120, located downstream of the blade row 110. Alternatively, however, the propulsion fan 100 may comprise, instead of the stator, a second rotor, counter-rotating with respect to the first rotor, such that the row 120 is a second row of blades, located downstream of the blade row 110 of the first rotor. The two rows may, in particular, be coaxial, with the blades of both rows 110 and 120 arranged radially around the same central axis X, but it is also conceivable that they may have different central axes, and in particular, parallel axes. Each row may contain, for example, between 10 and 22 blades, in particular between 12 and 14.

[0046] Each of the blades 110 may have a profiled body extending radially, with respect to the central axis X, from an inner diameter to an outer diameter of the corresponding row, as illustrated in Figures 2 and 3A. The outer diameter De of the first rotor may be between 1 and 6 m, in particular between 3 and 5 m. The inner diameters Di and / or outer diameter De of the first row may also be different from the inner diameters Di' and / or outer diameter D e ' of the second row.

[0047] The streamlined body of each blade 110 can be formed by aerodynamic profiles stacked along a radial stacking axis Z, so as to form, as illustrated in Figure 3B, an intrados 111 and an extrados 112, each extending from a leading edge BA to a trailing edge BF and, over a span H corresponding to half the difference between the outer diameter De and the inner diameter Di, from a blade root 113 to a blade tip 114. Similarly, the streamlined body of each blade 120 can also be formed by aerodynamic profiles stacked along a radial stacking axis Z' over a span H' corresponding to half the difference between the outer diameter De' and the inner diameter Di'.

[0048] For example, in a cross-section or airfoil profile of blade 110, the leading edge (BA) can be defined as the upstream end along the fluid flow direction. The leading edge (BA) can be characterized by a local minimum on the radius of curvature defining the profile in its upstream portion. 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 portion when the trailing edge (BF) is rounded, although, to simplify the manufacturing process, the trailing edge (BF) can alternatively be truncated, as illustrated in Figure 3E. These cross-sections or airfoils can, in particular, be cambered.Each stacked airfoil has a chord c, defined as the distance between the leading edge BA and the trailing edge BF along a straight line connecting them, and an angle of incidence θ with respect to a plane perpendicular to the central axis X. It also has a skeleton line LS, equidistant from the lower surface 111 and the upper surface 112, connecting the leading edge BA to the trailing edge BF. The chord c and the angle of incidence θ can vary depending on the radial distance r from the central axis X of the propulsion fan, while the angle of inclination θ with respect to a direction parallel to the central axis X can also vary along the entire length of each skeleton line LS.

[0049] Conventionally, the pitch angle y of an airfoil corresponds to the angle formed between, on the one hand, a first axis 150 which is defined by the intersection between the plane of the airfoil at the radial distance r and a plane perpendicular to the central axis X, and on the other hand, a straight line connecting the leading edge BA and trailing edge BF of the airfoil at radial distance r. The angle of incidence y is measured from the upstream side of the plane perpendicular to the central axis X. The angle of incidence y is 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 lower surface line 111 to the upper surface line 112.

[0050] As illustrated in Figure 3A, the inner diameter Di and outer diameter De of the blade row 110 can be measured on the trailing edges BF of the blades 110 and correspond, respectively, to the minimum and maximum radial positions relative to the central axis X. When the blade 110 has a variable pitch, these radial positions can be measured with the blade 110 placed at any pitch angle that allows the usual direction of airflow through the fan. For example, the pitch angle y for a cross-section of the blade 110 located at a radial distance r of approximately 3xD e / 8, which can be considered a reference y-angle for blade 110, can be between 60° and 80° in cruise. The pitch angle p can be measured with blade 110 set at this reference y-angle.

[0051] At least one of the two rows may have a strength less than, for example, 2.5 over the entire span H, H' of the respective blades 110 or vanes 120, or even less than 0.5 to the outside diameter De, De' of the row. Each of the blades 110 may have an aspect ratio equal to the outside diameter De of the first rotor multiplied by a coefficient between 0.3 and 1. 1 and 1, 2 rrr 1 , preferably between 0.4 nr 1 and 0.8 rrr 1 .

[0052] The S / D ratio eThe axial distance S between the stacking axes Z, Z' of the two rows and the outside diameter De of the blade row 110 can be, for example, between 0.005 and 0.5, in particular between 0.18 and 0.3, 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 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 with respect to the central axis X.

[0053] As illustrated in Figure 2, the row of blades 110 can be adapted to rotate around the central axis X, and in particular to be mechanically connected, for its rotational drive around the central axis X, to the gas turbine engine 11, possibly via a reduction gear 12. Furthermore, in order to take advantage of the increase in the dynamic air pressure downstream of this first row of blades 110, an air inlet 20 of the gas turbine engine 11 can, in particular, be arranged between the 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.

[0054] As illustrated in Figs. 2, 3A and 3C, the trailing edge BF of each blade 110 in the first row can have a number N of teeth with tooth heights hj where j=1,2,...N in increasing order in the radial direction from the inner diameter Di to the outer diameter De, and a number M of spacings Àk between adjacent tooth crests, where k=1,2,...M and M < N-1 in increasing order in the radial direction from the inner diameter Di to the outer diameter De. In the context of this discussion, a "tooth crest" can be understood as a local maximum of the chord c in the radial direction and a "trough" as a local minimum of the chord, located between the crest of that tooth and that of the adjacent tooth. It should be noted that a tooth peak can therefore be characterized by a zero derivative of c(r) and a negative second derivative of c(r), while a hollow can be characterized by a zero derivative of c(r) and a positive second derivative of c(r).

[0055] Each of the teeth can have a height hj between 0.1 and 2 times a spacing Àk between the vertex of the same tooth and the vertex of an adjacent tooth, preferably between 0.2 and 1.6 times the spacing Àk between the vertex of the same tooth and the vertex of the adjacent tooth, again preferably between 0.3 and 1.2 times the spacing Àk between the vertex of the same tooth and the vertex of the adjacent tooth.

[0056] As illustrated in Figures 2, 3A and 3C, the teeth can take the form of undulations, and in particular of substantially sinusoidal undulations, even if Other alternative shapes, such as triangular teeth, are also conceivable. The trailing edge BF can be configured such that each spacing Àk between the vertices of adjacent teeth can be equal to the square of the height of one of the adjacent teeth, multiplied by a coefficient between 0.005 mm' 1 and 1 mm' 1 , preferably between 0.01 mm' 1 and 0.8 mm'1 preferably between 0.02 mm' 1 and 0.6 mm' 1 This is especially true if the teeth are sinusoidal. Therefore, a compromise can be achieved, for the radius of curvature of the teeth, between aerodynamic efficiency and mechanical strength.

[0057] As also illustrated in figures 2, 3A and 3C, the succession of teeth can extend over the entire span H of the blade 110, from the inner diameter Di to the outer diameter De. Alternatively, however, it is conceivable that at least a part of the trailing edge is toothless.

[0058] Due to the camber of the stacked profiles of the blade 110, variations in the chord c can be accompanied by variations in the pitch angle y, as illustrated in the 3D figure, in order to optimize the aerodynamic operation of the blade 110. In particular, the pitch angle y can have a local maximum or a local minimum at the radial position q of each tooth apex, plus or minus up to, for example, 5%, preferably 2%, of the span H of the blade 110.

[0059] The teeth at the trailing edge BF of the blade 110, combined with the pressure difference between the lower surface 111 and the upper surface 112, can generate crossflow and the formation of horseshoe vortices on their flanks. To restrict these phenomena and improve aeroacoustic performance, as well as to relieve mechanical stresses at the concave surfaces, the airfoils at at least one tooth crest, or even three tooth crests, can be decambered relative to the airfoils at the adjacent concave surfaces. In particular, as can be seen in Fig.4, illustrating with a first curve A the evolution of the inclination angle 0 of a first skeleton line over its length, and with a second curve B the evolution of the inclination angle 0 of a second skeleton line over its length, the absolute value of the variation Afk of the inclination angle 0 on a terminal segment of at least a first skeleton line LS connecting the leading edge BA to a tooth apex of the trailing edge BF may be less than the absolute value of the. The variation Af of the inclination angle [3] on a terminal segment of at least one second skeleton line LS connecting the leading edge BA to an adjacent hollow in the trailing edge BF. These terminal segments can each extend over 30%, or even 20%, of the total length of the respective skeleton line LS. To achieve this, the first skeleton line LS may, in particular, have an inflection point on its terminal segment. Such an inflection point corresponds to a zero value of the second derivative of the skeleton line LS, and therefore to a local maximum or minimum of its first derivative, which corresponds to its inclination. Thus, in Fig. 4, this inflection point is represented as the local minimum of the inclination angle [3] on the curve A.Furthermore, an absolute value of the inclination angle [3 of the first skeleton line LS at the trailing edge BF can thus be greater, for example by between 0.5° and 8°, in particular by between 1° and 6°, than an absolute value, at the trailing edge BF, of the inclination angle P of the second skeleton line LS.

[0060] Furthermore, when the blade 110 has several saw teeth on its trailing edge BF, the angles of inclination [3 at the trailing edge BF of the said first skeleton lines LS connecting the leading edge BA to the tooth tops at the trailing edge BF can be decreasing in the radial direction from the inner diameter Di to the outer diameter De.

[0061] As illustrated in Figs. 1 and 2, the propulsion fan 100 can be, in particular, an unshod fan. Alternatively, however, as illustrated in Figs. 5 and 6, the propulsion fan 100 could be a shod fan, also comprising a nacelle 130 surrounding at least the blades 110. This nacelle 130 can also include a retaining housing 140 around the blades 110, with an abradable material to limit damage in case of contact between the radially outer end of the blades 110 and the housing, and / or acoustic treatments for noise reduction.

[0062] 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. Propeller fan blade (110) (100), having an intrados (111) and an extrados (112) extending, in a blade span direction, from a blade root to a blade tip and, in a blade width direction, from a leading edge (BA) to a trailing edge (BF) at least partially saw-toothed, wherein a first skeleton line, equidistant from the intrados (111) and the extrados (112), connects the leading edge (BA), in a first transverse plane perpendicular to the blade span direction, to a tooth apex in the trailing edge (BF), and a second skeleton line, equidistant from the intrados (111) and the extrados (112), connects the leading edge (BA), in a second transverse plane perpendicular to the blade span direction, to a hollow, adjacent said tooth apex, in the trailing edge (BF), and an absolute value of a variation (A0A) of an angle of inclination (P),with respect to a direction parallel to a central axis (X) of rotation of the blade (110), on a terminal segment, adjacent to the trailing edge (BF), of the first skeleton line is less than an absolute value of a variation (A0B) of an angle of inclination (P), with respect to the direction parallel to a central axis (X) of rotation of the blade (110) on a terminal segment, adjacent to the trailing edge (BF), of the second skeleton line, each of said terminal segments of the first and second skeleton lines extending over 30%, or even 20%, of a total length of the respective skeleton line between the leading edge (BA) and the trailing edge (BF).

2. Pale (110) according to claim 1, wherein the first skeleton line has an inflection point inside the terminal segment of the first skeleton line.

3. Blade (110) according to any one of claims 1 or 2, wherein an absolute value of the inclination angle (P) of the first skeleton line to the trailing edge (BF) is greater, for example, by between 0.5° and 8°, in particular by between 1° and 6°, than an absolute value, at trailing edge (BF), of the angle of inclination (P) of the second skeleton line.

4. Blade (110) according to any one of claims 1 to 3, wherein an absolute value of a pitch angle of a chord line in the first transverse plane is greater than an absolute value of a pitch angle in the second transverse plane.

5. Blade (110) according to any one of claims 1 to 4, wherein the trailing edge (BF) has at least three tooth peaks with respective adjacent hollows.

6. Blade (110) according to claim 5, wherein an absolute value of an angle of inclination (P), at the trailing edge (BF), of each skeleton line connecting the leading edge (BA) to one of the at least three tooth vertices is greater, for example by between 0.5° and 8°, in particular by between 1° and 6°, than an absolute value of an angle of inclination (P) at the trailing edge (BF) of at least one other skeleton line in a parallel transverse plane passing through a respective adjacent hollow.

7. Blade (110) according to claim 5 or 6, wherein an absolute value of a difference between the angle of inclination (P), at the trailing edge (BF), of the skeleton line connecting the leading edge to one of the at least three tooth tips and the angle of inclination (P) at the trailing edge (BF) of the at least one other skeleton line in a parallel transverse plane passing through a respective adjacent hollow is maximum for a tooth tip located, with respect to the blade root, in the span direction (H) of the blade (110), at least one quarter of the span (H) between the blade root and the blade tip, in particular at between 0.35 and 0.9 times said span (H).

8. Blade (110) according to any one of claims 5 to 7, wherein each spacing (Àk), in the span direction of the blade (110), between two adjacent tooth crests is equal to the square of a tooth height (hj), perpendicular to the span direction of the blade (100), between one of the two adjacent tooth crests and a trailing edge depression (BF) located between the two adjacent tooth crests, multiplied by a coefficient between 0.005 mm 1 and 1 mm 1 , in particular between 0.01 mm 1 and 0.8 mm 1 , even more specifically between 0.02 mm 1 and 0.6 mm 4 .

9. Blade (110) according to any one of claims 1 to 8, wherein a radial position (q) of each tooth apex at the trailing edge (BF) corresponds substantially to a radial position of a local maximum of chord line pitch angle and / or a local minimum of skeleton line inclination angle (P) at the trailing edge (BF).

10. Blade (110) according to any one of claims 1 to 9, having a maximum thickness, between the extrados and the intrados, of less than 20%, in particular less than 10%, of the span (H) of the blade root, in the span direction.

11. Blade (110) according to any one of claims 1 to 10, with variable pitch about an axis substantially aligned with the span direction.

12. Propulsive blower (100) comprising a first rotor with at least one row of blades (110) according to any one of claims 1 to 11.

13. Propulsive blower (100) according to claim 12, wherein the first rotor comprises between 10 and 22 blades (110), in particular between 12 and 14 blades (110).

14. Propulsive blower (100) according to any one of claims 12 or 13, wherein an outside diameter of the D e the first rotor is between 1 and 6 m, in particular between 3 and 5 m.

15. Propulsive blower (100) according to any one of claims 12 to 14, wherein the strength of the first rotor is less than 2.5 over the entire span (H) of the blades (110), and in particular less than 0.5 at the tip of the blades (110).

16. A propulsion blower (100) according to any one of claims 12 to 15, wherein each blade (110) of the first rotor has an elongation equal to an outside diameter (D e ) of the first rotor multiplied by a coefficient between 0.3 m-1 and 1.2 m -1 , preferably between 0.4 m -1 and 0.8 m -1 .

17. Propulsive blower (100) according to any one of claims 12 to 16, wherein the first rotor has an activity factor between 100 and 300, in particular between 150 and 225.

18. Propulsive blower (100) according to any one of claims 12 to 17, wherein the first rotor has a hub ratio between 0.15 and 0.45, in particular between 0.25 and 0.35, or even more in particular between 0.26 and 0.

3.

19. Propulsive blower (100) according to any one of claims 12 to 18, comprising a stator with at least one row of guide vanes (120), disposed downstream of at least one row of blades (110) of the first rotor.

20. Propulsive blower (100) according to any one of claims 12 to 18, comprising a second rotor with at least one other row of blades (120) arranged downstream of at least one row of blades (110) of the first rotor, counter-rotating with respect to the first rotor.

21. Propeller (10) comprising the propulsive blower (100) according to any one of claims 12 to 20 and a motor (11) for actuation of the propulsive blower (100).

22. Propulsion system (10) according to claim 21, wherein the engine (11) is a gas turbine engine

23. Aircraft (1) comprising the propulsion unit (10) according to any one of claims 21 or 22.

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