Optimised fan section of an aeronautical propulsion system

Abstract

The invention relates to a fan section in which an axial chord parameter, corresponding to a ratio of the product of an average axial chord and an axial chord at the blade root to the product of a vane height (47) and the axial chord at the blade tip, is less than or equal to a velocity parameter corresponding to a difference between the product of a peripheral velocity at the blade tip expressed in m / s and the value 3.243x103 s / m, and the value 8.3411x101, wherein the fan section is configured for the fan rotor to have a maximum allowable speed of 280 rad / s or more.

Description

[0001] DESCRIPTION

[0002] OPTIMIZED FAN SECTION OF AN AERONAUTICAL PROPULSION SYSTEM

[0003] FIELD OF INVENTION

[0004] This application relates generally to the field of propulsion systems, and more specifically to aeronautical propulsion systems with a high, or even very high, dilution rate.

[0005] STATE OF THE ART

[0006] An aeronautical propulsion system generally comprises, from upstream to downstream in the direction of gas flow, a blower section, a compressor section which may include a low pressure compressor and a high pressure compressor, a combustion chamber and a turbine section which may include a high pressure turbine and a low pressure turbine.

[0007] When the propulsion system is in operation, the high-pressure compressor is driven in rotation by the high-pressure turbine via a high-pressure shaft. The blower and, if equipped, the low-pressure compressor are driven in rotation by the low-pressure turbine via a low-pressure shaft.

[0008] 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.

[0009] 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.

[0010] Consequently, the Applicant is constantly working to reduce its negative 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.

[0011] 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.

[0012] One of the objectives of technological research is therefore to improve the environmental performance of aircraft. This is why, in all phases of design and development, relevant factors are taken into account 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, all with the aim of improving the energy efficiency of aircraft.

[0013] Thus, in order to improve the propulsion efficiency of the propulsion system and reduce its specific fuel consumption as well as the noise emitted by the fan section, propulsion systems with a high bypass ratio (also known as the bypass ratio, abbreviated as BPR) have been proposed. The bypass ratio is the ratio of the secondary airflow rate to the primary airflow rate. To achieve high bypass ratios, the fan section can be decoupled from the low-pressure turbine, thereby allowing their respective rotational speeds to be optimized independently. Generally, this decoupling is achieved using a reduction mechanism located between the upstream end of the low-pressure shaft and a rotor of the fan section.The fan section rotor is then driven by the low-pressure shaft via the reduction mechanism at a rotational speed lower than that of the low-pressure shaft. Improving the system's propulsive efficiency can also be achieved by optimizing the fan section size. Indeed, due to its large diameter (designed in particular to achieve high bypass ratios and low fan pressure ratios), the fan section represents a significant portion of the propulsion system in terms of mass and therefore specific fuel consumption. Simultaneously, the fan section generates a very large share of the propulsion system's thrust.

[0014] SUMMARY OF THE INVENTION

[0015] One objective of this application is to optimize the fan section of the propulsion system, particularly to increase fan efficiency. To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this respect, contributes to reducing the environmental impact of aircraft.

[0016] This objective is achieved within the framework of this application through a fan section of an aeronautical propulsion system, the fan section comprising:

[0017] - an indoor platform,

[0018] - a fan rotor comprising a blade including a blade and a blade root fixed to the fan rotor, the blade extending radially outwards over a blade height relative to an axis of the propulsion system from an internal radial limit located at the interface of the inner platform to a blade tip, the blade comprising a leading edge and a trailing edge, the blade comprising a composite material structure including a fibrous reinforcement obtained by three-dimensional weaving of weft and warp strands and a matrix in which the fibrous reinforcement is embedded, the blade having a lower portion including the blade root, and an upper portion including the blade tip, a stiffness of the lower portion being greater than a stiffness of the upper portion, the blade having: - an axial chord at the blade root extending to the internal radial limit (37) along an axis of the fan from the leading edge to the trailing edge,

[0019] - an axial chord at the apex of the blade extending along the axis from the leading edge to the trailing edge, and

[0020] - a mean axial chord equal to the average between the axial chord at the blade root and the axial chord at the blade tip, in which the blade has an axial chord parameter corresponding to a ratio of a product of the mean axial chord by the axial chord at the blade root to a product of the blade height by the axial chord at the blade tip, and a velocity parameter corresponding to a difference of a product of a peripheral velocity at the blade tip expressed in m / s by the value 3.243x10' 3 s / m and the value 8.3411x10 1, the peripheral speed being measured at maximum permissible speed, the blower section being configured so that the blower rotor has a maximum permissible speed greater than or equal to 280 rad / s, the blade being configured so that the axial chord parameter is less than or equal to the speed parameter.

[0021] Such a system is advantageously and optionally complemented by the following characteristics: the speed parameter is a first speed parameter, the blade having a second speed parameter corresponding to a difference of a product of a peripheral speed at the blade tip expressed in m / s by the value 2.756x10' 3 s / m and the value 7.06x10' 1, the blade being configured so that the axial chord parameter is greater than or equal to the second speed parameter; an intermediate portion extending from the lower portion to the upper portion, the lower portion extending from the internal radial limit towards the blade tip to the intermediate portion over a height greater than or equal to 15% and less than or equal to 25% of the blade height, the intermediate portion extending over a height greater than or equal to 5% and less than or equal to 30% of the blade height;the weft strands comprise first weft strands and second weft strands, the lower portion comprising first weft strands and no second weft strands, the upper portion comprising second weft strands and no first weft strands, a stiffness of the first weft strands being greater than a stiffness of the second weft strands, a density of first strands increasing progressively in the intermediate portion from the lower portion to the upper portion, a density of second strands increasing progressively in the intermediate portion from the upper portion to the lower portion; a density of strands in the lower portion is greater than a density of strands in the upper portion, a density of strands increasing progressively in the intermediate portion from the upper portion to the lower portion;a warp strand and weft strand crossing density in the lower portion is greater than a warp strand and weft strand crossing density in the upper portion, a warp strand and weft strand crossing density increasing progressively in the middle portion from the upper portion to the lower portion; the warp strands define a plurality of warp planes, each warp plane being separated from an immediately adjacent warp plane by a line of weft strands, a percentage of the warp and / or weft strands of the third portion modified between two immediately adjacent warp planes being less than or equal to 30% and preferably greater than or equal to 5% and less than or equal to 15%;a diameter of the blower rotor is, when the blower is shrouded, greater than or equal to 177.8 cm and less than or equal to 304.8 cm, in particular greater than or equal to 213.36 cm and less than or equal to 266.7 cm and preferably greater than or equal to 215.9 cm and less than or equal to 266.7 cm, and, when the blower is unshrouded, greater than or equal to 203.2 cm and less than or equal to 469.9 cm, in particular greater than or equal to 254 cm and less than or equal to 469.9 cm, and preferably greater than or equal to 304.8 cm and less than or equal to 396.2 cm; the blade being a first blade of a plurality of blades included in the blower rotor, a number of the plurality of blades being greater than or equal to 16 and less than or equal to 24;the blower blade has a direct chord at the blade tip extending from the leading edge to the trailing edge along the blade tip, the axial chord at the blade tip being a projection along the X-axis of the direct chord at the blade tip, the blower rotor having a strength greater than or equal to 0.9 and less than or equal to 1.3, preferably greater than or equal to 1.0 and less than or equal to 1.3, where the strength is equal to a ratio between the direct chord at the blade tip and an inter-blade pitch at the blade tip; and the fan blade has a direct chord at the blade apex extending from the leading edge to the trailing edge along the blade apex, the axial chord at the blade apex being a projection along the X-axis of the direct chord at the blade apex, the fan rotor having a strength strictly less than 1.0, where the strength is equal to a ratio between the direct chord at the blade apex and an inter-blade pitch at the blade apex.;

[0022] The presentation also covers an aeronautical propulsion system comprising:

[0023] - a movable drive shaft rotating around an axis;

[0024] - a blower shaft;

[0025] - a blower section such as has been described so far, with the blower rotor being driven in rotation by the blower shaft; and

[0026] - a reduction mechanism coupling the drive shaft and the blower shaft in order to drive the blower shaft at a rotational speed lower than the rotational speed of the drive shaft.

[0027] Such a system is advantageously and optionally complemented by the following features:

[0028] - the system is configured to provide a thrust between 80,068 N and

[0029] 331,374 N, preferably between 88,964 N and 155,688 N;

[0030] - a dilution ratio of the propulsion system is greater than or equal to 10; when the fan section is enclosed, the dilution ratio is preferably greater than or equal to 10 and less than or equal to 35, or even greater than or equal to 10 and less than or equal to 18; and when the fan section is unenclosed, the dilution ratio is greater than or equal to 40 and less than or equal to 80; and

[0031] - the blower rotor has a hub-to-head ratio greater than or equal to 0.22 and less than or equal to 0.32.

[0032] The presentation also covers a method for sizing a fan section of an aeronautical propulsion system, the fan section comprising:

[0033] - an indoor platform,

[0034] - a fan rotor comprising a blade including a blade and a blade root fixed to the fan rotor, the blade extending radially outwards over a blade height relative to an axis of the propulsion system from an internal radial limit located at the interface of the inner platform to a blade tip, the blade comprising a leading edge and a trailing edge, the blade comprising a composite material structure including a fibrous reinforcement obtained by three-dimensional weaving of weft and warp strands and a matrix in which the fibrous reinforcement is embedded, the blade having a lower portion including the blade root, and an upper portion including the blade tip, a height of the lower portion being greater than or equal to 15% and less than or equal to 25% of the blade height, a stiffness of the lower portion being greater than a stiffness of the upper portion, the blade having:

[0035] - an axial chord at the base of the blade extending to the internal radial limit along an axis of the fan from the leading edge to the trailing edge,

[0036] - an axial chord at the apex of the blade extending to the apex of the blade along the axis of the leading edge at the trailing edge, and

[0037] - a mean axial chord equal to the average between the axial chord at the blade root and the axial chord at the blade tip, in which the blade has an axial chord parameter corresponding to the ratio of a product of the mean axial chord by the axial chord at the blade root to a product of the blade height by the axial chord at the blade tip and a velocity parameter corresponding to the difference of a product of a peripheral velocity at the blade tip expressed in m / s by the value 3.243x10 3 s / m and the value 8.3411x10 1, the peripheral speed being measured at maximum permissible speed, the blower section being configured so that the blower rotor has a maximum permissible speed greater than or equal to 280 rad / s, the process including a step of sizing the blower section so that the axial chord parameter is less than or equal to the speed parameter.

[0038] The presentation finally focuses on a manufacturing process for a fan section of an aeronautical propulsion system, including the dimensioning of the fan section as presented so far and the manufacturing of the section.

[0039] PRESENTATION OF THE DRAWINGS

[0040] Other features and advantages will become clearer from the following description, which is purely illustrative and not exhaustive, and should be read in conjunction with the attached figures, including:

[0041] - Figure 1 schematically represents an aircraft including propulsion systems,

[0042] - Figure 2 schematically represents, in partial view and in cross-section, an example of a propulsion system in which the fan section is enclosed,

[0043] - Figure 3 schematically represents, in partial view and in cross-section, an example of a propulsion system in which the fan section is unfaired,

[0044] - Figure 4 schematically represents a first example of a planetary reduction mechanism,

[0045] - Figure 5 schematically represents a first example of an epicycloidal reduction mechanism,

[0046] - Figure 6 schematically represents, in partial view and cross-section, an example of a fan section in which the fan section is enclosed; - Figure 7 schematically represents, in partial view and cross-section, an example of a fan section in which the fan section is unenclosed.

[0047] - Figure 8 schematically illustrates a partial weft plane of the fibrous reinforcement in Figure 7,

[0048] - Figure 9 schematically represents a cross-section of two blades in a blower section, and

[0049] - Figure 10 schematically represents, in partial view and cavalier perspective, an example of a blower section.

[0050] DETAILED DESCRIPTION OF A METHOD OF IMPLEMENTATION

[0051] In the example illustrated in Figure 1, the aircraft is an airplane 100 comprising a fuselage 101 and two wings 102. In this example, the aircraft includes two propulsion systems 1, each propulsion system 1 being attached to a respective wing 102 of the airplane 100 by means of a pylon. In another embodiment, the aircraft could include one or more propulsion systems attached to the fuselage 101.

[0052] Figure 2 schematically represents, in partial view and in cross-section, a first example of a propulsion system 1.

[0053] In this example, propulsion system 1 is a twin-shaft, shrouded-fan gas turbine engine.

[0054] In Figure 2, the propulsion system 1 has a principal direction extending along a longitudinal axis X. The propulsion system 1 comprises a fan section 2 and a primary body 3, often called the "gas generator". The X direction also defines the principal direction of gas flow through the propulsion system 1.

[0055] The blower section 2 includes a blower 22 and a blower housing 12. The blower 22 includes a blower rotor 9. The blower housing 12 surrounds the blower rotor 9. The blower rotor 9 is mounted to rotate relative to the blower housing 12.

[0056] In the example illustrated in Figure 2, the fan section 2 is enclosed. The propulsion system 1 comprises a fan casing 12 surrounding the fan section 2, or alternatively, a nacelle 28 surrounding the fan section 2. Referring to Figure 6, which shows an example where the fan section 2 is enclosed, the fan section 2 includes an inner platform 34 and an inner face 35 of the fan casing 12 or the nacelle 28, defining between them a gas flow channel 36. The flow channel 36 thus extends from the inner platform 34 to the inner face 35. The term "platform" here refers to any element of the propulsion system from which a fan blade can be mounted, or at least any element of the propulsion system from which a fan blade can extend substantially radially.The platform can be, in particular, a hub or a housing that surrounds the X-axis of the propulsion system. The inner face 35 of the fan housing or nacelle is also referred to as the "outer platform 35" in the following text. The inner face 35 surrounds the inner platform 34, such that the inner platform 34 lies radially between the X-axis of the propulsion system and the inner face 35. The inner platform 34 and the inner face 35 each define a flow-stream side surface.

[0057] These surfaces can be at varying distances from the X-axis of the propulsion system, as illustrated in Figure 6. The inner surface defined by the inner platform 34 can move away from the X-axis of the propulsion system when traversing this inner surface in the direction of gas flow. The outer surface defined by the outer platform 35 can move closer to the X-axis of the propulsion system when traversing this outer surface in the direction of gas flow.

[0058] The outer surface defined by the outer platform 35 and the inner surface defined by the inner platform 34 can alternatively be cylindrical surfaces, each at a constant radial distance to the X axis of the propulsion system.

[0059] The blower rotor 9 includes at least one blade 14 extending into the channel 36.

[0060] The fan blade 14 has a leading edge 14a and a trailing edge 14b (see, for example, Figure 6). The leading edge 14a is configured to extend in relation to the flow of gases entering the fan rotor 9. It corresponds to the forward part of an airfoil that faces the airflow and divides the airflow into an intrados (lower surface) flow and an extrados (upper surface) flow. The trailing edge 14b, on the other hand, corresponds to the rear part of the airfoil, where the intrados and extrados flows meet.Note here that, when the blade 14 includes a leading edge shield and / or trailing edge shield, the leading edge 14a (respectively the trailing edge 14b) of the blade 14 corresponds to the front part of the shield profile which reconstitutes the leading edge (respectively the rear part of the shield profile which reconstitutes the trailing edge 14b) and whose function is to divide the flow into an intrados flow and an extrados flow (respectively to join the flows).

[0061] The blade 14 comprises a blade root 25 fixed to the fan rotor and a blade extending from the blade root 25 to a blade height 47 radially outward from the X-axis of the propulsion system 1. The blade includes an internal radial boundary 37 located at the interface of the blade and the inner platform 34. The blade extends to a blade height 47 from the internal radial boundary 37 to a blade tip 21. The blade height 47 is measured along a radial axis R orthogonal to the X-axis of the propulsion system and passing through the X-axis of the propulsion system. Preferably, and with reference to Figure 6, the blade height 47 is measured between an intersection 43 between the inner platform 34 and the leading edge 14a and an upstream point 45 of the blade tip 21 located on the leading edge 14a.When the fan section is faired, blade 14 extends into channel 36, blade apex 21 is located on outer platform 35 and upstream point 45 is located at the intersection between outer platform 35 and leading edge 14a.

[0062] The fan blade 14 also has a direct chord at the blade apex 39 extending from the leading edge 14a to the trailing edge 14b along the blade apex 21 and a direct chord at the blade foot 38 extending from the leading edge 14a to the trailing edge 14b along the internal radial limit 37. The direct chord or normal chord is used to designate the distance of the segment between the leading edge and the trailing edge without the segment being projected.

[0063] The direct rope at the summit of dawn 39 extends from the upstream point 45 of the summit of dawn 21 located on the leading edge 14a to a downstream point 46 of the summit of dawn 21 located on the trailing edge 14b.

[0064] When the blower section is faired, the direct chord at the top of the blade 39 extends along the outer platform 35 and corresponds to the length of the straight segment which connects on the one hand the upstream intersection point 45 between the outer platform 35 and the leading edge 14a and on the other hand the downstream intersection point 46 between the outer platform 35.

[0065] Similarly, the direct chord at the base of the blade 38 extends from point 43 of the internal radial boundary 37 located on the leading edge 14a to point 44 of the internal radial boundary 37 located on the trailing edge 14b. The direct chord at the base of the blade 38 extends from the leading edge 14a to the trailing edge 14b along the inner platform 34. The direct chord at the base of the blade 38 corresponds to the length of the straight segment that connects, on the one hand, the point of intersection 43 between the inner platform 34 and the leading edge 14a and, on the other hand, the downstream point of intersection 44 between the inner platform 34.

[0066] It should be noted that the straight segments mentioned above are not necessarily contained in a radial plane defined by the X axis of the propulsion system and a radial direction X. Similarly, the points of the chord are not necessarily all at the same distance from the X axis of the propulsion system.

[0067] The fan blade 14 also has an axial chord at the blade apex extending along the X-axis from the leading edge 14a to the trailing edge 14b and an axial chord at the blade root extending along the X-axis from the leading edge 14a to the trailing edge 14b. The term axial chord at the blade apex (respectively at the blade root) refers to the length of the projection along the X-axis of the direct chord at the blade apex (respectively at the blade root).

[0068] We can define an average axial chord equal to the average between the axial chord at the base of the blade and the axial chord at the top of the blade.

[0069] D is the diameter of the fan rotor, measured in a plane normal to the X-axis of the propulsion system from the X-axis to the upstream intersection point 45 between the blade tip 21 and the leading edge 14a of the blade. The diameter D is expressed in meters. When the fan is shrouded, the diameter D of the fan rotor 9 can be between 70 inches (177.8 cm) and 120 inches (304.8 cm) inclusive, in particular between 84 inches (213.36 cm) and 120 inches (304.8 cm) inclusive, and preferably between 85 inches (215.9 cm) and 105 inches (266.7 cm) inclusive. For example, the diameter D of the fan rotor 9 is approximately 90 inches (228.6 cm). These different values ​​of diameter D allow the propulsion system 1 to be integrated in a conventional manner, in particular under a wing of aircraft 100.Blade 14 has an axial chord parameter pc corresponding to a ratio of a product of the average axial chord by the axial chord at the base of the blade to a product of the blade height 47 by the axial chord at the top of the blade.

[0070] It respects the relation Pc= (C xm x C x o) / (hx C x ioo) in which C xm denotes the mean axial chord, C x o denotes the axial chord at the base of the blade, h denotes the blade height 47 and C x ioo denotes the axial chord at the apex of the dawn.

[0071] Blade 14 has a first velocity parameter pv1 corresponding to the difference between the product of a peripheral velocity at the blade tip, expressed in m / s, and the value 3.243x10 3 s / m and the value 8.3411x10 1The peripheral speed is measured at the maximum permissible speed. This speed corresponds to the maximum speed of the blower during normal operation. This term is also known by its English name, 'Maximum Permissible Rotational Speed'.

[0072] The first speed parameter follows the relationship Pvl = 3.243 x 10 -3 x U e - 8.3411 x 10 -1 which can also be written as Pvl = 0.003243 x U e - 0.83411 and in which Ue denotes the peripheral speed.

[0073] The peripheral velocity is the velocity of a point on the blade tip 21, for example point 45 on the blade tip 21 located on the leading edge 14a, in the circumferential direction, i.e. along the circumferential axis 0. The circumferential axis 0 is an axis passing through the point on the blade tip 21, the circumferential axis 0 being orthogonal to the X axis of the propulsion system and to the radial axis R when the radial axis R passes through the point on the blade tip 21. The peripheral velocity at the blade tip can be greater than or equal to 260 m / s and less than or equal to 400 m / s, for example greater than or equal to 270 m / s and less than or equal to 380 m / s.

[0074] In order to optimize the performance of propulsion system 1, the chord parameter is less than or equal to the velocity parameter.

[0075] The axial chord parameter is sufficiently small here to significantly increase the axial chord at the blade tip compared to other blade parameters. The blade tip corresponds to the part of the blade where the axial and tangential velocities are highest. It is therefore the part of the blade that contributes most to the engine's efficiency. By increasing the axial chord at the blade tip, the blade's efficiency is increased.

[0076] Choosing a relatively low value for the axial chord parameter tends to reduce the margin of error with the natural mode of vibration in bending of the blade. Bending here refers to a deformation of the blade during which the blade tip approaches the internal radial limit, the blade curving around a direction parallel to the drive axis, i.e., the X-axis of the propulsion system. The margin depends, in particular, on the difference between the blade's rotational speed at maximum permissible speed and the frequency of its natural mode of vibration in bending.

[0077] We can also define a second speed parameter, pv2.

[0078] Blade 14 presents the second velocity parameter pv2 which corresponds to a difference between the product of a peripheral velocity at the blade tip expressed in m / s and the value 2.756x10' 3 s / m and the value 7.06x10' 1 .

[0079] The second speed parameter follows the relationship Pv2 = 2.756 x 10-3 x U e - 7.06 x 10 -1 which can also be written as Pv2 = 0.002756 x U e - 0.706 and in which Ue denotes the peripheral speed.

[0080] Advantageously, the axial chord parameter is greater than or equal to the second velocity parameter.

[0081] In order to increase the margin, the blade includes a composite material having a lower portion stiffness 55 greater than an upper portion stiffness 57.

[0082] In relation to figures 6 and 7, the blade 14 comprises a composite material structure including a fibrous reinforcement obtained by three-dimensional weaving of weft strands 53 and warp strands 54 and a matrix in which the fibrous reinforcement is embedded.

[0083] Three-dimensional weaving refers to the way in which warp threads follow sinuous paths to interlock weft threads belonging to different weft layers, with the exception of unlinking. It should be noted that a three-dimensional weave, particularly an interlock weave, can include 2D surface weaves. Various three-dimensional weaves can be used, such as interlock, multi-satin, or multi-silk weaves, for example, as described in WO 2006 / 136755.

[0084] In relation to figure 6, the direction of a warp strand 54 goes from the foot of the blade 37 to the top of the blade 21 and the direction of a weft yarn goes from the leading edge 14a to the trailing edge 14b.

[0085] In fiber reinforcement, warp planes and weft planes can be defined. A warp plane is a plane generally orthogonal to the principal directions of extension of a plurality of columns of warp strands from the blade root 35 to the blade tip 21, each warp strand crossing the warp plane. A weft plane is a plane generally orthogonal to the principal directions of extension of a plurality of lines of weft strands from the leading or trailing edge, each weft strand crossing the weft plane. A warp plane is formed by a plurality of columns of warp strands, each column of warp strands being separated from the immediately adjacent column of warp strands by a weft plane. A weft plane is formed by a plurality of lines of weft strands, each line of weft strands being separated from the immediately adjacent line of weft strands by a warp plane.Within the composite material structure, we can define a strand density corresponding to the number of strands per unit volume of the structure.

[0086] The fiber reinforcement can be formed from a single-piece fibrous preform obtained by three-dimensional weaving. It comprises fibers that may be made of carbon, glass, basalt, or aramid, among other materials. A carbon fiber may have a Young's modulus greater than or equal to 230 GPa and less than or equal to 450 GPa, and preferably greater than or equal to 250 GPa and less than or equal to 300 GPa, and even more preferably greater than or equal to 275 GPa and less than or equal to 280 GPa. A glass fiber may have a Young's modulus greater than or equal to 160 GPa and less than or equal to 170 GPa, for example, 165 GPa. A basalt fiber may have a Young's modulus greater than or equal to 200 GPa and less than or equal to 250 GPa, for example, 227 GPa. An aramid fiber can, in particular, have a Young's modulus greater than or equal to 280 GPa and less than or equal to 320 GPa, for example 302 GPa.

[0087] The matrix itself is typically a polymer matrix, for example epoxy, bismaleimide or polyimide. The blade 14 is then formed by molding using a vacuum resin injection process of the RTM type (for "Resin Transfer Moulding" i.e. resin transfer moulding) or VARTM type (for "Vacuum Resin Transfer Moulding" i.e. vacuum resin transfer moulding).

[0088] The fibrous reinforcement is formed by three-dimensional weaving of warp and weft strands. The weft strands 53 and warp strands 54 are interlaced in the same plane. Different weaving patterns are possible to create the interlacing.

[0089] Within the composite material structure, we can define a density of crossings between warp and weft strands corresponding to the number of crossings of warp and weft strands per unit volume of the structure.

[0090] The blade 14 has a lower portion 55 which includes the blade foot 25. The lower portion 55 extends radially outwards from the blade foot 25 to the internal radial limit 37 and beyond the internal radial limit 37 to a first intermediate level 56 located between the internal radial limit 37 and the blade tip 21. For example, the lower portion 55 extends from the internal radial limit 37 to the blade tip 21 over a height h1 greater than or equal to 15% and less than or equal to 25% of the blade height. In this case, the first intermediate level 56 is separated from the internal radial limit 37 by a length greater than or equal to 15% and less than or equal to 25% of the blade height, and the first intermediate level 56 is separated from the blade tip 21 by a length greater than or equal to 75% and less than or equal to 85% of the blade height.

[0091] The blade 14 has an upper portion 57. The upper portion 57 extends radially towards the X axis of the propulsion system from the blade tip 21 to a second intermediate level 59 located between the first intermediate level 56 and the blade tip 21.

[0092] The blade 14 may have an intermediate portion 58 located between the lower portion 55 and the upper portion 57. The intermediate portion extends from the lower portion 55 to the upper portion 57, that is to say, the intermediate portion extends from the first intermediate level 56 to the second intermediate level 59. For example, the intermediate portion 58 extends over a height h3 greater than or equal to 5% and less than or equal to 30% of the blade height.

[0093] When the intermediate portion 58 extends over a height h3 greater than or equal to 5% and less than or equal to 30% of the blade height and when the lower portion 55 extends from the internal radial limit 37 towards the blade tip 21 over a height h1 greater than or equal to 15% and less than or equal to 25% of the blade height, then the upper portion 57 extends from the blade tip 21 over a height h2 greater than or equal to 45% and less than or equal to 80% of the blade height, and the second intermediate level 59 is separated from the blade tip 21 by a length greater than or equal to 45% and less than or equal to 80% of the blade height.

[0094] The stiffness of the lower portion 55 is greater than the stiffness of the upper portion 57.

[0095] By stiffness, we understand here the Young's modulus (E). In one embodiment, the stiffness of the lower portion 55 is between 1.2 and 1.5 times the stiffness of the upper portion 57.

[0096] The difference in stiffness between the lower portion 55 and the upper portion 57 can be obtained in different ways.

[0097] In a first option, the weft strands 53 comprise first weft strands and second weft strands, the lower portion 55 comprising first weft strands and no second weft strands, and the upper portion 57 comprising second weft strands and no first weft strands, the stiffness of the first weft strands being greater than the stiffness of the second weft strands. The first and second weft strands extend continuously from the leading edge to the trailing edge.

[0098] According to this first option, the density of the first strands gradually decreases in the intermediate portion 58 from the lower portion 55 towards the upper portion 57, and the density of the second strands gradually decreases in the intermediate portion 58 from the upper portion 57 towards the lower portion 55. These progressive decreases can, for example, be achieved by successively removing the first strands from the weaving of the preform, at the level of the different warp and / or weft planes constituting the parts of the intermediate portion 58 and by cutting them at the level of the surface of the fibrous reinforcement before injection, and by simultaneously introducing the second strands between these warp and / or weft planes, as described in document FR3087701.

[0099] With reference to Figures 7 and 8, warp planes C2 and C3 are located in the intermediate portion 58, warp plane C1 is located in the lower portion 55, and warp plane C4 is located in the upper portion 57. Figure 8 illustrates a cross-sectional view of the fibrous preform along a weft plane including the stacking axis of the blade 14, the weft plane being substantially parallel to the radial axis R. Note that in Figure 8, only the weft strands are shown, the warp strands having been omitted to simplify the figure. As can be seen in Figure 8, the first two rows of weft strands L1 and L2, which are part of the inner portion 11 of the fibrous reinforcement 5, consist only of first strands 60. These first two rows of weft strands L1 and L2 are located in the lower portion 55.

[0100] The third weft strand line L3 is part of the intermediate portion 58, near the first intermediate level 56. This third weft strand line L3 includes a single second strand 61. The following weft strand lines L4-L10 each include a second strand 61 in addition to the weft strand line immediately preceding it, up to the eleventh weft strand line L11 and the following ones which include only second strands 61 and therefore form part of the upper portion 57.

[0101] Thus, the lower portion 55, the upper portion 57, and the intermediate portion 58 are formed as a single piece during the three-dimensional weaving of the blade 14. In order to ensure the transition of mechanical properties between the lower portion 55 and the upper portion 57 at the intermediate portion 58, the percentage relative to the total number of weft strands in a row of second strands 61 introduced between two immediately adjacent weft strand rows, i.e., separated by only one column of warp strands from the intermediate portion 58, is at most 30%. Preferably, this percentage is between 5% and 15%.

[0102] The first strands of the warp have a relatively high Young's modulus, for example, greater than 250 GPa, preferably greater than 270 GPa, and their function is to meet the blade design criteria related to the blade's frequency status, particularly regarding the margin between, on the one hand, the blade's rotational frequency and, more generally, the driving harmonics, and on the other hand, the natural frequency of the blade's bending modes. For example, the first strands may include carbon fibers, typically HS* T300 carbon fibers (E = 284 GPa, A = 1.5%), HS TR30S (E = 356 GPa, A = 1.9%), or HS T700 (E = 395 GPa, A = 2.1%), or even high-modulus aramid fibers such as Dupont Kevlar 49 (E = 302, A = 2.4%). E here denotes Young's modulus E and A is the elongation at break.

[0103] The second strands may, for example, include glass fibers, typically E-GLASS type glass fibers (E = 165 GPa, A = 4.4%) or S-2 GLASS type glass fibers (E = 267 GPa, A = 5.2%), or basalt fibers (E = 227 GPa, A = 3%), or even polyester fibers (E = 268 GPa, A = 3.5%).

[0104] In a second option, a strand density of 55 in the lower portion is greater than a strand density of 57 in the upper portion.

[0105] In a third option, a crossing density between warp and weft strands in the lower portion 55 is greater than a crossing density between warp and weft strands in the upper portion 57.

[0106] The three options can be combined two at a time or all three simultaneously.

[0107] In general, to ensure the transition of mechanical properties between the lower portion 55 and the upper portion 57, at most 30% of the warp and / or weft strands are preferably modified between two immediately adjacent warp planes (i.e., separated by only one weft line) or between two immediately adjacent weft planes (i.e., separated by only one warp column). Preferably, between 5% and 15% of the strands are modified between two immediately adjacent planes. For example, in the first option, between two successive warp planes, at most 30% of the first strands 60 removed from the fiber preform and an equal number of second strands 61 introduced into the fiber preform from the surface to replace the first strands 60 removed. For example, in the second option, at most 30% of the strands can be added between two successive warp planes.For example, in the third option, a maximum of 30% overlap can be added between two successive chain planes.

[0108] The fan rotor 9 may comprise a plurality of fan blades 14. Each of the fan blades 14 may be fixed relative to the fan hub 13 or have a variable pitch. In the latter case, each of the fan blades 14 is pivotally mounted relative to the fan hub 13 along a pitch axis and is connected to a pitch-changing mechanism (not shown) mounted in the propulsion system 1. The pitch-changing mechanism allows the pitch angle of the fan blades 14 to be adjusted according to the flight phases.

[0109] The blower rotor 9 preferably comprises at least fourteen blower blades 14 and at most twenty-four blower blades 14, even more preferably at least sixteen blower blades 14 and at most twenty-four blower blades 14, or at most twenty-two blower blades 14. Figure 10 illustrates the case where the blower rotor 9 comprises twenty-two blades.

[0110] The fan section 2 may also include a fan stator 16 fixedly mounted on the fan housing 12. The fan stator 16 includes fixed blades 17, generally called outlet guide vanes (OGVs). This set of fixed blades straightens and regulates the airflow downstream of the fan rotor 9 to contribute to engine thrust. This set of fixed blades also acts as a noise reducer.

[0111] Alternatively, the outlet blades 17 could have variable pitch. If so, and similarly to the fan blades 14 of the fan rotor 9, the base of the outlet blades 17 is pivotally mounted about a pitch axis and is connected to a pitch-changing mechanism (not shown), the pitch being adjusted according to the flight phases by the pitch-changing mechanism.

[0112] The number of outlet blades 17 depends on the acoustic criteria defined for the propulsion system 1 and is at least equal to the number of blower blades 14.

[0113] The primary body 3 comprises a compressor section 29, a combustion chamber 6 and a turbine section 30.

[0114] Compressor section 29 includes a low pressure compressor 4 and a high pressure compressor 5.

[0115] The low-pressure compressor 4 includes a rotor 41 suitable for being driven in rotation relative to the housing 31 of the propulsion system 1 and a stator 42 fixedly mounted on the housing 31.

[0116] The rotor 41 of the low-pressure compressor 4 includes movable wheels 4a and the stator 42 of the low-pressure compressor 4 includes fixed wheels 4b. The movable wheels 4a are arranged alternately with the fixed wheels 4b, thus forming a succession of low-pressure compressor stages.

[0117] Similarly, the high-pressure compressor 5 includes a rotor 51 suitable for being driven in rotation relative to the housing 31 of the propulsion system 1 and a stator 52 fixedly mounted on the housing 31.

[0118] The rotor 51 of the high-pressure compressor 5 comprises rotating wheels 5a, and the stator 52 of the high-pressure compressor 5 comprises stationary wheels 5b. The rotating wheels 5a are arranged alternately with the stationary wheels 5b, thus forming a succession of high-pressure compressor stages. The turbine section 30 comprises a high-pressure turbine 7 and a low-pressure turbine 8.

[0119] The high-pressure turbine 7 comprises a rotor 71 suitable for being driven in rotation relative to the casing 31 of the propulsion system 1 and a stator 72 fixedly mounted on the casing 31.

[0120] The rotor 71 of the high-pressure turbine 7 comprises rotating wheels 7a and the stator 72 of the high-pressure turbine 7 comprises fixed wheels 7b. The rotating wheels 7a are arranged alternately with the fixed wheels 7b, thus forming a succession of high-pressure turbine stages.

[0121] Similarly, the low-pressure turbine 8 comprises a rotor 81 suitable for being driven in rotation relative to the casing 31 of the propulsion system 1 and a stator 82 fixedly mounted on the casing 31.

[0122] The rotor 81 of the low-pressure turbine 8 comprises moving wheels 8a and the stator 82 of the low-pressure turbine 8 comprises fixed wheels 8b. The moving wheels 8a are arranged alternately with the fixed wheels 8b, thus forming a succession of low-pressure turbine stages.

[0123] The propulsion system 1 includes a low-pressure shaft 11 connecting the rotor 41 of the low-pressure turbine 4 to the rotor 81 of the low-pressure compressor 8, the low-pressure shaft 11 being mounted rotatably relative to the housing 31 around the longitudinal axis X.

[0124] When the propulsion system 1 is in operation, the rotor 81 of the low-pressure turbine 8 drives the rotor 41 of the low-pressure compressor 4 through the low-pressure shaft 11.

[0125] The propulsion system 1 further comprises a blower shaft 20 and a reduction mechanism 19. The blower rotor 9 is fixedly mounted on the blower shaft 20. The reduction mechanism 19 has an inlet and an outlet. The inlet of the reduction mechanism 19 is connected to the low-pressure shaft 11, and the outlet of the reduction mechanism 19 is connected to the blower shaft 20. Thus, when the propulsion system 1 is in operation, the rotor 81 of the low-pressure turbine 8 drives not only the rotor 41 of the low-pressure compressor 4, but also the blower rotor 9, via the low-pressure shaft 11, the reduction mechanism 19, and the blower shaft 20. Thanks to the reduction mechanism 19, the blower rotor 9 is driven to rotate at a speed lower than the rotational speed of the rotor 41 of the low-pressure turbine 4.

[0126] The reduction mechanism 19 thus allows independent control of the rotation speed of the blower 22 and the rotation speed of the low pressure turbine 8 and the low pressure compressor 4.

[0127] The low-pressure turbine 8, the low-pressure shaft 11, the low-pressure compressor 4, the blower shaft 20, the reduction mechanism 19 and the blower 22 together form the "low-pressure body" of the propulsion system 1.

[0128] The propulsion system 1 further includes a high-pressure shaft 10 connecting the rotor 51 of the high-pressure turbine 5 to the rotor 71 of the high-pressure compressor 7, the high-pressure shaft 10 being mounted rotatably relative to the housing 31 around the longitudinal axis X. The high-pressure shaft 10 is coaxial with the low-pressure shaft 11 and extends around the low-pressure shaft 11.

[0129] When the propulsion system 1 is in operation, the rotor 81 of the low-pressure turbine 8 drives the rotor 51 of the low-pressure compressor 5 through the low-pressure shaft 11.

[0130] The high-pressure turbine 7, the high-pressure shaft 10 and the high-pressure compressor 4 together form the "high-pressure body" of the propulsion system 1.

[0131] The low-pressure shaft 11 and the high-pressure shaft 10 can be co-rotating, i.e., driven in the same direction of rotation around the longitudinal axis X. Alternatively, the low-pressure shaft 11 and the high-pressure shaft 10 can be contra-rotating, i.e., driven in opposite directions of rotation around the longitudinal axis X.

[0132] The dual-body propulsion system 1 may include, in particular, a single-stage high-pressure turbine 7, i.e. comprising exactly one stage, or a two-stage high-pressure turbine 7, i.e. comprising exactly two stages (as illustrated in the example in Figure 2).

[0133] The high-pressure compressor 5 comprises at least eight stages (as illustrated in the example in Figure 2) and at most eleven stages.

[0134] The low-pressure turbine 8 comprises at least three stages (as illustrated in the example in Figure 2) and at most seven stages.

[0135] The low-pressure compressor 4 comprises at least two stages and at most four stages. When the propulsion system is in operation, an airflow F entering the propulsion system 1 passes through the blower 22 and is then divided between a primary airflow F1 and a secondary airflow F2, which flow from upstream to downstream in the propulsion system 1 in the direction of gas flow through the propulsion system.

[0136] The secondary airflow F2, also called the "bypass airflow", flows in the secondary vein, around the primary body 3. The secondary airflow F2 cools the periphery of the primary body 3 and is used to generate most of the thrust provided by the propulsion system 1.

[0137] The primary airflow F1 flows in a primary channel within the primary body 3, passing successively through the compressor section 29 (low-pressure compressor 4 and high-pressure compressor 5), the combustion chamber 6 where it is mixed with fuel to serve as an oxidizer, and the turbine section 30 (high-pressure turbine 7 and low-pressure turbine 8). The passage of the primary airflow F1 through the turbine section 30, receiving energy from the combustion chamber 6, causes the impellers 7a, 8a of the turbine section 30 to rotate, which in turn drives the impellers 4a, 5a of the compressor section 29 as well as the blower rotor 9.

[0138] To improve the propulsive efficiency of propulsion system 1 and reduce its specific fuel consumption and the noise emitted by the fan section 2, propulsion system 1 may have a high bypass ratio. A "high" bypass ratio is defined as a ratio greater than or equal to 10, for example, between 10 and 80 inclusive, preferably between 10 and 35 inclusive, preferably between 10 and 18 inclusive. The bypass ratio is defined as the ratio of the mass flow rate of the secondary airflow F2 to the mass flow rate of the primary airflow F1, these mass flow rates being measured when propulsion system 1 is stationary, uninstalled, in takeoff mode in a standard atmosphere (as defined by the International Civil Aviation Organization (ICAO) Manual, Doc 7488 / 3, 3rd edition) and at sea level.By "not installed", it is meant that the measurements are carried out when the propulsion system 1 is on a test bench (and not installed on an aircraft), the measurements then being simpler to carry out.

[0139] In a propulsion system including a reduction mechanism 19 such as that illustrated in Figure 2, the decoupling between the rotational speed of the blower 22 and the rotational speed of the low-pressure turbine 8 makes it possible to reduce the rotational speed and the pressure ratio of the blower rotor 9 while increasing the power extracted by the low-pressure turbine 8. Indeed, the overall efficiency of the propulsion system 1 is conditioned to the first order by the propulsion efficiency, which is favorably influenced by minimizing the variation in kinetic energy of the air as it passes through the propulsion system 1.In a propulsion system with a high dilution ratio, the majority of the flow generating the propulsive force consists of the secondary airflow F2 of the propulsion system 1, the kinetic energy of the secondary airflow F2 being mainly affected by the compression which the secondary airflow F2 undergoes when passing through the blower section 2. The propulsive efficiency and the pressure ratio of the blower section 2 are therefore linked: the lower the pressure ratio of the blower section 2, the better the propulsive efficiency. In order to improve the propulsive efficiency of the propulsion system 1, the blower pressure ratio, which corresponds to the ratio between the average pressure at the outlet of the blower stator 16 (or, in the absence of a stator 16, of the blower rotor 9) and the average pressure at the inlet of the blower rotor 9, is less than or equal to 1.70, preferably less than or equal to 1.50, for example between 0.90 and 1.45.The average pressures are measured here over the height of at least one of the blower blades 14, that is to say from the surface which radially delimits inside the airflow duct at the inlet of the blower rotor 9 to the top 21 of blower blade 14.

[0140] The peripheral speed at the top 21 of the blower blades 14 can also be between 260 meters per second (ms 1 ) and 400 meters per second (ms 1 ) included. The blower pressure ratio can then be between 1.20 and 1.45.

[0141] In a direct-drive propulsion system, the fan rotor 9 can alternatively be directly coupled to the low-pressure shaft 11, i.e., without a reduction mechanism. The low-pressure shaft 11 is then combined with the fan shaft 20 so that the fan rotor 9 is driven by the low-pressure shaft 11 at the same rotational speed as the rotor 81 of the low-pressure turbine 8.

[0142] The propulsion system 1 is configured to provide a thrust of between 18,000 Ibf (80,068 N) and 70,000 Ibf (331,374 N), preferably between 20,000 Ibf (88,964 N) and 51,000 Ibf (226,859 N), or even between 20,000 Ibf (88,964 N) and 35,000 Ibf (155,688 N). Thrust is measured when propulsion system 1 is stationary, uninstalled, in takeoff mode in a standard atmosphere (as defined by the International Civil Aviation Organization (ICAO) Manual, Doc 7488 / 3, 3rd edition) and at sea level. "Uninstalled" here means that the measurements are taken when propulsion system 1 is on a test bench (and not installed on an aircraft 100), as the measurements are then simpler to perform.

[0143] Figure 3 schematically represents, in partial view and in cross-section, a second example of a propulsion system 1.

[0144] In Figure 3, components identical or similar to those of the propulsion system in Figure 2 are designated by identical references.

[0145] In the example illustrated in Figure 3, the propulsion system 1 is a twin-spool gas turbine engine with an unducted fan. This is a gas turbine engine of the "Unducted Single Fan" type in Anglo-Saxon terminology.

[0146] Unlike the first example in Figure 2, the blower rotor 9, which can also be referred to as the "propeller," is not enclosed by a blower housing. In this case, the blower section does not include an external platform.

[0147] Since the fan section 2 is unfaired, the fan blades 14 have variable pitch. Each fan blade 14 is pivotally mounted relative to the fan hub 13 along a pitch axis and is connected to a pitch-change mechanism 15 mounted in the propulsion system 1. The pitch-change mechanism allows the pitch angle of the fan blades 14 to be adjusted according to the flight phases. Similarly, the outlet blades 17 have variable pitch; the base of the outlet blades 17 is pivotally mounted along a pitch axis and connected to a pitch-change mechanism 15, with the pitch being adjusted according to the flight phases by the pitch-change mechanism.

[0148] Alternatively, the blower rotor 9 can be placed at the rear of the primary body 3 so as to be of the pusher type or at the front of the primary body 3 so as to be of the tractor type.

[0149] The absence of a fairing around the fan rotor 9 allows for a significant increase in the bypass ratio without the propulsion system 1 being negatively impacted by the mass of the housings 12 (or nacelles) designed to surround the fan section 2. The bypass ratio of the propulsion system 1, including an unfaired fan section 2, is thus greater than or equal to 40, for example, between 40 and 80 inclusive. Furthermore, the peripheral speed at the tip 21 of the fan blades 14 of the fan rotor(s) 9 can be between 210 meters per second (m / s) 1 ) and 260 meters per second (ms 1 ) included. The blower pressure ratio can then preferably be between 0.90 and 1.20 inclusive.

[0150] When the rotor 9 is unshod, the diameter D of the blower rotor 9 can be between 80 inches (203.2 cm) and 185 inches (469.9 cm) inclusive. Preferably, the diameter D is greater than or equal to 100 inches (254 cm), for example, between 120 inches (304.8 cm) and 156 inches (396.2 cm). The diameter of the blower rotor 9 is measured here in a plane normal to the longitudinal axis X, which is the axis of rotation of the blower rotor 9, at the intersection between a vertex 21 and a leading edge 22 of the blower blades 14.

[0151] It should be noted that, since Figure 2 and Figure 3 are partial views, diameter D is only partially visible.

[0152] The reduction mechanism 19 may include an epicycloidal or planetary reduction mechanism, single-stage or two-stage.

[0153] For example, Figure 4 illustrates a planetary (or "star") type reduction mechanism 19. The reduction mechanism 19 comprises a sun pinion 19a (input of the reduction mechanism 19), centered on an axis of rotation of the reduction mechanism 19 generally coincident with the longitudinal axis X and configured to be driven in rotation by the low-pressure shaft 11, a ring gear 19b (output of the reduction mechanism 19) coaxial with the sun pinion 19a and configured to drive in rotation the blower shaft 20 around its axis X of rotation, and a series of satellites 19c distributed circumferentially around the axis X of rotation of the rotor 9 of the blower section 2, between the sun pinion 19a and the ring gear 19b, each satellite gear 19c being internally meshed with the sun pinion 19a and externally with the ring gear 19b.The series of satellites 19c is mounted on a satellite carrier 19d which is fixed relative to a stator part 19e of the propulsion system 1, for example relative to a housing of the compressor section 4, 5.

[0154] In another example, Figure 5 illustrates an epicyclic (or "planetary") reduction mechanism 19, in which case the ring gear 19b is fixedly mounted on the stator part 19e of the propulsion system 1 and the fan shaft 20 is driven in rotation by the planet carrier 19d. 7

[0155] Regardless of the configuration of the reduction mechanism 19, the diameter of the ring gear 19b and the planet carrier 19d are greater than the diameter of the solar pinion 19a, so that the rotational speed of the rotor 9 of the blower section 2 is less than the rotational speed of the low pressure shaft 11.

[0156] The reduction ratio of the reduction mechanism 19 is greater than or equal to 2.5 and less than or equal to 11. The reduction ratio can be greater than or equal to 2.7 and less than or equal to 3.5, typically around 3.0.

[0157] In order to further optimize the performance of the propulsion system 1, a strength of the blower rotor 9 can be greater than or equal to 0.9 and less than or equal to 1.3. The strength is equal to the ratio between the direct chord at the blade tip 39 and an inter-blade pitch 23.The blade pitch 23 corresponds to the angular distance between the upstream intersection points P1 and P2 of two adjacent blades 14, that is, the distance along the circumferential axis 0 from point P1 to point P2; the blade pitch 23 is therefore equal to the external radius Re of the fan rotor 9 (half-diameter) multiplied by the angle between a first straight line D1, contained in a plane normal to the X-axis, which originates from the upstream intersection point P1 (see figures 9 and 10) of a first blade 14 and intersects the X-axis, and a second straight line D2, contained in the plane normal to the X-axis, which originates from the upstream intersection point P2 of a second blade 14 immediately adjacent to the first blade 14 and intersects the X-axis. Since strength is a ratio of distances, it is measured when the propulsion system 1 is cold.

[0158] The fan rotor 9 may also have a hub-to-head ratio between 0.22 and 0.32. In the case of a fan rotor with fixed pitch, the hub-to-head ratio may be between 0.24 and 0.32. In the case of a fan rotor with variable pitch, the hub-to-head ratio is preferably between 0.24 and 0.32 to allow the integration of the pitch change mechanism 15. The hub-to-head ratio corresponds to the ratio between the internal radius Ri and the external radius Re of the fan rotor 9. The internal radius Ri corresponds to the distance between the axis of rotation X and the point of intersection between the leading edge 14a and the inner platform 34 at the inlet of the fan rotor 9 (and corresponds to the point of connection of the leading edge 14a with the aerodynamic surface of a platform of the fan rotor 9).The external radius Re corresponds to the distance between the axis of rotation X and the point of intersection between the leading edge 14a and the blade tip 21 (and corresponds to half the fan diameter D). The lower the hub-to-head ratio, the more efficient the fan rotor 9. However, decreasing the hub-to-head ratio of the fan rotor 9 results in an increase in the mechanical load on the hub 13 of the fan rotor 9.

[0159] In a first option, the strength can be greater than or equal to 1.0 and less than or equal to 1.3. This first option is particularly suitable for a rotor 9 comprising twenty-two blades 14. In a propulsion system 1 with a reduction mechanism 19, the rotational speed of the fan rotor 9 is reduced, for example, to between 260 m / s and 400 m / s. Its pressure ratio can also be reduced, for example, to between 1.05 and 1.5, or even between 1.1 and 1.45, so that the velocity difference between the outlet and inlet of the fan rotor 9 is reduced while optimizing the efficiency of the fan section 2. The flow at the blade tip 14 through the fan rotor 9 is then supersonic. In particular, a supersonic shock is generated at the fan blades 14.However, this supersonic shock cannot be eliminated, especially during cruise: it must therefore be controlled to prevent it from deteriorating the efficiency of the fan section 2. By dimensioning and manufacturing the fan rotor 9 with twenty-two blades so that its strength is greater than or equal to 1.0 and less than or equal to 1.3, the inter-blade pitch 23 and the direct chord at the blade tip 39 are such that the supersonic shock is stable in maximum permissible regime and moves only in the divergent part of the inter-blade channel. The inter-blade channel corresponds to the passage between two adjacent blades 14 which extends between an inlet plane, which is normal to the airflow F into the inlet of the blower rotor 9 and passes through the leading edge 14a of the first blade 14, and an outlet plane which is parallel to the inlet plane and passes through the trailing edge 14b of the second blade 14.This channel, from upstream to downstream through the fan rotor 9, has a convergent section extending from the inlet plane to an intermediate plane corresponding to the channel's minimum cross-section, and a divergent section extending from the intermediate plane to the outlet plane. The Applicant observed that when the supersonic shock reached the convergent section of the inter-blade channel 24, it became unstable and reduced the efficiency of the fan section 2. Conversely, when the supersonic shock remains in the divergent section, for example, near the intermediate plane, the supersonic shock is stable at maximum permissible operating conditions.The longer the inter-blade channel, i.e. the greater the distance between the inlet and outlet planes, the easier it is to design a convergent-divergent channel and therefore to maintain the supersonic shock in the divergent part of the channel; However, increasing the length of the inter-blade channel results in an increase in the direct chord at the blade tip 39, and therefore an increase in the mass of the fan rotor 9 (and consequently the specific fuel consumption of the propulsion system 1) and a reduction in the efficiency of the fan section 2. It should be noted in particular that the length of the inter-blade channel and the direct chord are linked to the inter-blade pitch by the strength of the fan rotor 9. For a fan rotor 9 with twenty-two blades, a strength between 1.0 and 1.3 is then a good compromise between the length of the inter-blade channel 24 in order to control the supersonic shock in the fan rotor 9 and the efficiency of the fan section 2.

[0160] In a second option, the strength can be strictly less than 1.0. This second option is particularly suitable for a fan rotor 9 comprising between seventeen and twenty blades 14. Indeed, the direct chord at the blade tip 39 is then reduced relative to the available space (high inter-blade pitch 23), which makes it possible to reduce the mass of the blade 14 and modify its frequency position, since modifying the direct chord at the blade tip 39 has a significant impact on the first deformation mode of the blade 14 (at the same operating range). In fact, when the deformation mode of the blades 14 occurs in a stabilized regime of the fan rotor 9 (in particular, the maximum permissible regime), one solution may be to increase the thickness of the blade root in order to improve the margins and shift this deformation mode.This increase in the thickness of the blades 14 at the blade root, however, implies an increase in the overall size of the root, which influences the circumferential dimensions of the recesses that receive the root and therefore the design for managing the mechanical resistance of the disc. Increasing the thickness of the blades 14 is thus likely to increase the hub-to-head ratio of the fan rotor 9. However, increasing the hub-to-head ratio is detrimental to the aerodynamic efficiency of the fan rotor 9. Conversely, dimensioning the fan rotor 9 so that its strength is less than 1.0 makes it possible to reduce the direct chord at the blade tip 39 and to shift the first mode of deformation of the blades 14 into an unstabilized operating range or outside the operating range of the fan rotor, without thickening the blades 14. Therefore, it is not necessary to increase the hub-to-head ratio.

[0161] The distances (length, radius, diameter, etc.) are measured at ambient temperature (approximately 20°C) when the propulsion system 1 is cold, i.e. when the propulsion system 1 has been stopped for a sufficient period for the parts of the propulsion system to be at ambient temperature, it being understood that these dimensions vary little with respect to the conditions in which the propulsion system 1 is in takeoff mode.

[0162] Example of a completed project

[0163] We now present two examples of the realization of a propulsion system, each comprising a blower section.

[0164] Common to both examples, propulsion system 1 is a twin-shaft gas turbine engine with a shrouded fan. The fan rotor comprises 18 composite material blades that are fixed relative to the fan hub.

[0165] The blower rotor 9 has a hub-to-head ratio of 0.27

[0166] The blower section includes a blower stator fixed to the blower housing. The blower stator comprises 40 fixed blades that are fixed relative to the blower housing.

[0167] The low-pressure shaft and the high-pressure shaft are co-rotating.

[0168] The propulsion system includes a two-stage high-pressure turbine.

[0169] The high-pressure compressor has 10 stages.

[0170] The low-pressure turbine comprises 6 stages.

[0171] The low-pressure compressor has 3 stages.

[0172] The propulsion system has a dilution ratio of 10

[0173] The propulsion system provides a thrust of 120,000 N

[0174] The diameter of the blower rotor is 1.98 m.

[0175] Between the two examples, it is the increase in rotational speed that allows the aerodynamic load of the fan rotor to be reduced, thus improving its efficiency and therefore reducing specific consumption.

[0176]

[0177] According to this table, the inequality Pv1 > Pc1 is respected in the case of the second example but not in the case of the first example.

Claims

DEMANDS 1. Fan section (2) of an aeronautical propulsion system (1), the fan section (2) comprising: - an indoor platform (34), - a fan rotor (9) comprising a blade (14) comprising a blade and a blade root (25) fixed to the fan rotor (9), the blade extending over a blade height (47) radially outwards relative to an axis (X) of the propulsion system (1) from an internal radial limit (37) located at the interface of the inner platform (34) to a blade tip (21), the blade (14) comprising a leading edge (14a) and a trailing edge (14b), the blade (14) comprising a composite material structure comprising a fibrous reinforcement obtained by three-dimensional weaving of weft strands (53) and warp strands (54) and a matrix in which the fibrous reinforcement is embedded, the blade (14) having a lower portion (55) comprising the blade root (25), and an upper portion (57) comprising the blade tip (21), a stiffness of the lower portion (55) being greater than a stiffness of the upper portion (57), the blade (14) exhibiting: - an axial chord at the base of the blade extending to the internal radial limit (37) along an axis (X) of the fan from the leading edge (14a) to the trailing edge (14b), - an axial chord at the apex of the blade extending to the apex of the blade along the axis (X) from the leading edge (14a) to the trailing edge (14b), and - a mean axial chord equal to the average between the axial chord at the blade root and the axial chord at the blade tip, in which the blade (14) has an axial chord parameter corresponding to a ratio of a product of the mean axial chord by the axial chord at the blade root to a product of the blade height (47) by the axial chord at the blade tip, and a velocity parameter corresponding to a difference of a product of a peripheral velocity at the blade tip expressed in m / s by the value 3.243x10' 3 s / m and the value 8.3411x10 1 the peripheral speed being measured at maximum permissible operating speed, the blower section being configured so that the blower rotor has a maximum allowable speed greater than or equal to 280 rad / s, the blade (14) being configured so that the axial chord parameter is less than or equal to the speed parameter.

2. Blower section (2) according to claim 1, wherein the velocity parameter is a first velocity parameter, the blade (14) having a second velocity parameter corresponding to a difference of a product of a peripheral velocity at the blade tip expressed in m / s by the value 2.756x10' 3 s / m and the value 7.06x10 1 , the blade (14) being configured so that the axial chord parameter is greater than or equal to the second velocity parameter.

3. Fan section (2) according to any one of claims 1 and 2 comprising an intermediate portion (58) extending from the lower portion (55) to the upper portion (57), the lower portion (55) extending from the internal radial limit (37) towards the blade tip (57) to the intermediate portion (58) over a height greater than or equal to 15% and less than or equal to 25% of the blade height, the intermediate portion (58) extending over a height greater than or equal to 5% and less than or equal to 30% of the blade height.

4. Blower section (2) according to claim 3, wherein the weft strands (53) comprise first weft strands and second weft strands, the lower portion (55) comprising first weft strands and no second weft strands, the upper portion (57) comprising second weft strands and no first weft strands, a stiffness of the first weft strands being greater than a stiffness of the second weft strands, a density of the first strands increasing progressively in the intermediate portion (58) from the lower portion (55) to the upper portion (57), a density of the second strands increasing progressively in the intermediate portion (58) from the upper portion (57) to the lower portion (55).

5. Blower section (2) according to any one of claims 3 and 4, wherein a strand density of in the lower portion (55) is greater than a strand density of in the upper portion (57), a strand density increasing progressively in the intermediate portion (58) from the upper portion (57) to the lower portion (55).

6. Blower section (2) according to any one of claims 3 to 5, wherein a warp strand and weft strand crossing density in the lower portion (55) is greater than a warp strand and weft strand crossing density in the upper portion (57), a warp strand and weft strand crossing density increasing progressively in the intermediate portion (58) from the upper portion (57) to the lower portion (55).

7. Blower section (2) according to any one of claims 1 to 6, wherein the warp strands define a plurality of warp planes (C1-C4), each warp plane (C1-C4) being separated from an immediately adjacent warp plane (C1-C4) by a line of weft strands (L1-L12), a percentage of the warp and / or weft strands of the third modified portion between two immediately adjacent warp planes (C1-C4) being less than or equal to 30% and preferably greater than or equal to 5% and less than or equal to 15%.

8. Blower section (2) according to any one of claims 1 to 7, wherein a diameter (D) of the blower rotor (9) is, when the blower is shrouded, greater than or equal to 177.8 cm and less than or equal to 304.8 cm, in particular greater than or equal to 213.36 cm and less than or equal to 266.7 cm and preferably greater than or equal to 215.9 cm and less than or equal to 266.7 cm, and, when the blower is unshrouded, greater than or equal to 203.2 cm and less than or equal to 469.9 cm, in particular greater than or equal to 254 cm and less than or equal to 469.9 cm, and preferably greater than or equal to 304.8 cm and less than or equal to 396.2 cm.

9. Blower section (2) according to any one of claims 1 to 8, the blade being a first blade of a plurality of blades included in the rotor of blower, a number of the plurality of blades being greater than or equal to 16 and less than or equal to 24.

10. Fan section (2) according to claim 9, wherein the fan blade (14) has a direct chord at the blade tip (39) extending from the leading edge (14a) to the trailing edge (14b) along the blade tip (21), the axial chord at the blade tip being a projection along the X-axis of the direct chord at the blade tip, the fan rotor (9) having a strength greater than or equal to 0.9 and less than or equal to 1.3, preferably greater than or equal to 1.0 and less than or equal to 1.3, where the strength is equal to a ratio between the direct chord at the blade tip and an inter-blade pitch at the blade tip.

11. Fan section (2) according to claim 9, wherein the fan blade (14) has a direct chord at blade tip (39) extending from the leading edge (14a) to the trailing edge (14b) along the blade tip (21), the axial chord at blade tip being a projection along the X-axis of the direct chord at blade tip, the fan rotor (9) having a strength strictly less than 1.0, where the strength is equal to a ratio between the direct chord at blade tip (39) and an inter-blade pitch (23) at blade tip.

12. Aeronautical propulsion system (1) comprising: - a drive shaft (11) that rotates about an axis (X); - a blower shaft (20); - a blower section (2) according to any one of claims 1 to 11, the blower rotor (9) being driven in rotation by the blower shaft (20); and - a reduction mechanism (19) coupling the drive shaft (11) and the blower shaft (20) in order to drive the blower shaft (20) at a rotational speed lower than the rotational speed of the drive shaft (11).

13. Propulsion system (1) according to claim 12, configured to provide a thrust of between 80,068 N and 331,374 N, preferably between 88,964 N and 155,688 N.

14. Propulsion system (1) according to any one of claims 12 and 13, wherein a dilution ratio of the propulsion system (1) is greater than or equal to 10, when the fan section is shrouded the dilution ratio is preferably greater than or equal to 10 and less than or equal to 35 or greater than or equal to 10 and less than or equal to 18, and when the fan section is unshrouded the dilution ratio is greater than or equal to 40 and less than or equal to 80.

15. Propulsion system (1) according to any one of claims 12 to 14, wherein the blower rotor (9) has a hub-to-head ratio greater than or equal to 0.22 and less than or equal to 0.

32.

16. Method for dimensioning a fan section (2) of an aeronautical propulsion system, the fan section (2) comprising: - an indoor platform (34), - a fan rotor (9) comprising a blade (14) comprising a blade and a blade root (25) fixed to the fan rotor (9), the blade extending radially outwards over a blade height (47) relative to an axis (X) of the propulsion system (1) from an internal radial limit (37) located at the interface of the inner platform (34) to a blade tip (21), the blade (14) comprising a leading edge (14a) and a trailing edge (14b), the blade (14) comprising a composite material structure comprising a fibrous reinforcement obtained by three-dimensional weaving of weft strands (53) and warp strands (54) and a matrix in which the fibrous reinforcement is embedded, the blade (14) having a lower portion (55) comprising the blade root (25), and an upper portion (57) comprising the blade tip (21), a height of the lower portion being greater than or equal to 15% and less than or equal to 25% of the blade height,a stiffness of the lower portion (55) being greater than a stiffness of the upper portion (57), the blade (14) exhibiting:, - an axial chord at the base of the blade extending to the internal radial limit (37) along an axis (X) of the fan from the leading edge (14a) to the trailing edge (14b), - an axial chord at the apex of the blade extending to the apex of the blade along the axis (X) of the leading edge (14a) to the trailing edge (14b), and - a mean axial chord equal to the average between the axial chord at the blade root and the axial chord at the blade tip, in which the blade (14) has an axial chord parameter corresponding to the ratio of a product of the mean axial chord by the axial chord at the blade root to a product of the blade height (47) by the axial chord at the blade tip and a velocity parameter corresponding to the difference of a product of a peripheral velocity at the blade tip expressed in m / s by the value 3.243x10' 3s / m and the value 8.3411x10 1 , the peripheral speed being measured at maximum permissible speed, the blower section being configured so that the blower rotor has a maximum permissible speed greater than or equal to 280 rad / s, the process comprising a blower section dimensioning step (2) so that the axial chord parameter is less than or equal to the speed parameter.

17. Method of manufacturing a fan section (2) of an aeronautical propulsion system (1) comprising dimensioning the fan section according to claim 16 and manufacturing the fan section.

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