Optimised fan section of an aeronautical propulsion system

Abstract

The invention relates to an aeronautical propulsion system comprising a ducted fan section, wherein a ratio of a product of a blade mean axial chord and a blade root axial chord to a product of the square of a blade height (47) and a blade tip axial chord is less than or equal to a difference between a product of a maximum rotational speed and the value 2.501×10-3 s / rad and the value 1.7148×10-1, a stiffness of a lower portion (55) of the blade being greater than a stiffness of an upper portion (57), and a ratio of the blade root axial chord to a product of the square of the mean axial chord, the blade height (47) and the blade tip axial chord is less than or equal to a difference between a product of the rotational speed and the value 2.515×10- 1 s / rad and the value 52.701, a stiffness of the upstream portion being greater than a stiffness of the downstream portion.

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 comprising a shrouded fan and exhibiting a high, or even very high, bypass ratio.

[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 reduce its mass. 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 an aeronautical propulsion system comprising:

[0017] - a movable drive shaft rotating around an axis;

[0018] - a blower shaft;

[0019] - 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; and

[0020] - a shrouded fan section, the fan section comprising:

[0021] -- an indoor platform,

[0022] -- a fan rotor driven in rotation by the fan shaft; the fan rotor comprising a blade, the blade comprising a blade and a blade root fixed to the fan rotor, the blade extending radially outwards over a blade height of one 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 comprising 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 comprising the blade root, an upper portion comprising the blade tip, an upstream portion comprising the leading edge and a downstream portion comprising the trailing edge, the blade having:

[0023] - an axial chord at the base of the blade extending along an axis of the fan from the leading edge to the trailing edge,

[0024] - an axial chord at the apex of the blade extending along the axis from the leading edge to the trailing edge, and

[0025] - an average axial chord equal to the average between the axial chord at the base of the blade and the axial chord at the tip of the blade, in which the blade exhibits:

[0026] - a first axial chord parameter corresponding to a ratio of a product of the average axial chord by the axial chord at the blade root to a product of the square of the blade height by the axial chord at the blade tip,

[0027] - a first speed parameter corresponding to a difference in the product of a maximum permissible speed of the blower rotor expressed in rad / s by the value 2.501x10' 3 s / rad and the value 1.7148x10' 1 ,

[0028] - a second axial chord parameter corresponding to a ratio of the axial chord at the blade root to a product of the square of the average axial chord by the blade height and by the axial chord at the blade tip, and

[0029] - a second speed parameter corresponding to a difference of a product of the maximum permissible speed of the blower rotor expressed in rad / s by the value 2.515x10' 1s / rad and of the value 52.701, the fan section being configured so that the fan rotor has a maximum allowable speed greater than or equal to 280 rad / s, the blade being configured such that the first axial chord parameter is less than or equal to the first speed parameter, a lower portion stiffness is greater than an upper portion stiffness, and the second axial chord parameter is less than or equal to the second speed parameter, an upstream portion stiffness is greater than a downstream portion stiffness, the propulsion system comprising a nacelle surrounding the fan section, the nacelle comprising an upper upstream axial end with respect to a direction of gas flow in the propulsion system, the upper upstream axial end being located vertically above the axis, the nacelle comprising a lower upstream axial end located vertically below the axis,an average distance between a first distance along the axis separating the upper upstream axial end and an intersection between the inner face of the casing above the axis and the leading edge of the blade when the blade is above the axis, and a second distance along the axis separating the lower upstream axial end and an intersection between the inner face of the casing below the axis and the leading edge of the blade when the blade is below the axis, a ratio of the average distance to a diameter of the blower rotor being greater than or equal to 0.2 and less than or equal to 0.4.

[0030] Such a system is advantageously and optionally complemented by the following features:

[0031] - the blade has a third speed parameter corresponding to a difference in the product of a maximum permissible speed of the blower rotor expressed in rad / s by the value 1.722x10' 3s / rad and the value 1.2948x10' 1 , a fourth speed parameter corresponding to a difference of a product of the maximum permissible speed of the blower rotor expressed in rad / s by the value 1.885x10' 1 s / rad and the value 35.801, the blade being configured so that the first axial chord parameter is greater than or equal to the third velocity parameter, and the second axial chord parameter is greater than the fourth velocity parameter;

[0032] - the fan section comprises 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 comprising 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 the first strands increasing progressively in the intermediate portion from the lower portion to the upper portion, a density of the second strands increasing progressively in the intermediate portion from the upper portion to the lower portion;

[0033] - the fan blade has at each blade height a direct chord extending from the leading edge to the trailing edge, the fan section comprising a central portion extending from the upstream portion to the downstream portion, the upstream portion extending from the leading edge to the trailing edge to the central portion over a length greater than or equal to 25% and less than or equal to 40% of the direct chord length, the central portion extending over a length greater than or equal to 5% and less than or equal to 10% of the direct chord length, the warp strands comprising first warp strands and second warp strands, the upstream portion comprising more first warp strands than second warp strands and the downstream portion comprising second warp strands and no first warp strands, a stiffness of the first warp strands being greater than a stiffness of the second warp strands,a density of the first strands gradually decreasing in the central portion of the upstream portion towards the downstream portion, a density of the second strands gradually increasing in the central portion of the upstream portion towards the downstream portion;

[0034] - a blower rotor diameter is 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;

[0035] - the blade being the 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 17 and less than or equal to 22;

[0036] - the blower rotor includes a blower hub, each blade being mounted pivotally relative to the blower hub so as to present a variable pitch;

[0037] - the system is configured to provide a thrust between 80,068 N and 331,374 N, preferably between 88,964 N and 155,688 N; - a bypass ratio of the propulsion system greater than or equal to 10, 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

[0038] - the blower rotor has a hub-to-head ratio greater than or equal to 0.22 and less than or equal to 0.32.

[0039] The presentation also covers a method for sizing an aeronautical propulsion system, the propulsion system comprising

[0040] - a movable drive shaft rotating around an axis;

[0041] - a blower shaft;

[0042] - 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; and

[0043] - a shrouded fan section, the fan section comprising:

[0044] - an indoor platform,

[0045] - a fan rotor driven in rotation by the fan shaft; the fan rotor comprising a blade, the blade comprising 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 comprising 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 comprising the blade root, an upper portion comprising the blade tip, an upstream portion comprising the leading edge and a downstream portion comprising the trailing edge, the blade having:

[0046] - an axial chord at the base of the blade extending along an axis of the fan from the leading edge to the trailing edge, - an axial chord at the tip of the blade extending along the axis from the leading edge to the trailing edge, and

[0047] - an average axial chord equal to the average between the axial chord at the base of the blade and the axial chord at the tip of the blade, in which the blade exhibits:

[0048] - a first axial chord parameter corresponding to a ratio of a product of the average axial chord by the axial chord at the blade root to a product of the square of the blade height by the axial chord at the blade tip,

[0049] - a first speed parameter corresponding to a difference in the product of a maximum permissible speed of the blower rotor expressed in rad / s by the value 2.501x10' 3 s / rad and the value 1.7148x10' 1 ,

[0050] - a second axial chord parameter corresponding to a ratio of the axial chord at the blade root to a product of the square of the average axial chord by the blade height and by the axial chord at the blade tip, and

[0051] - a second speed parameter corresponding to a difference of a product of the maximum permissible speed of the blower rotor expressed in rad / s by the value 2.515x10' 1s / rad and of the value 52.701, the propulsion system comprising a nacelle surrounding the fan section, the nacelle comprising an upper upstream axial end with respect to a direction of gas flow in the propulsion system, the upper upstream axial end being located vertically above the axis, the nacelle comprising a lower upstream axial end located vertically below the axis, an average distance between a first distance along the axis separating the upper upstream axial end and an intersection between the inner face of the casing above the axis and the leading edge of the blade when the blade is above the axis and a second distance along the axis separating the lower upstream axial end and an intersection between the inner face of the casing below the axis and the leading edge of the blade when the blade is below the axis,a ratio of the average distance to a diameter of the blower rotor being greater than or equal to 0.2 and less than or equal to 0.4, the blower section being configured so that the blower rotor has a maximum allowable speed greater than or equal to 280 rad / s, the method comprising a blower section dimensioning step such that the first axial chord parameter is less than or equal to the first velocity parameter, a stiffness of the lower portion is greater than a stiffness of the upper portion, and the second axial chord parameter is less than or equal to the second velocity parameter, a stiffness of the upstream portion is greater than a stiffness of the downstream portion.

[0052] 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.

[0053] PRESENTATION OF THE DRAWINGS

[0054] 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:

[0055] - Figure 1 schematically represents an aircraft including propulsion systems,

[0056] - Figure 2 schematically represents, in partial view and in cross-section, an example of a propulsion system,

[0057] - Figure 3 schematically represents a first example of a planetary reduction mechanism,

[0058] - Figure 4 schematically represents a first example of an epicycloidal reduction mechanism,

[0059] - Figure 5 schematically represents, in partial view and in cross-section, an example of a blower section,

[0060] - Figure 6 schematically represents, in partial view and in cross-section, an example of a blower section,

[0061] - Figure 7 schematically illustrates a partial weft plane of the fibrous reinforcement in Figure 6,

[0062] - Figure 8 schematically represents, in partial view and in cross-section, an example of a blower section; - Figure 9 schematically illustrates a partial warp plane of the fibrous reinforcement of Figure 8.

[0063] - Figure 10 schematically represents a cross-section of two blades in a blower section,

[0064] - Figure 11 schematically represents, in partial view and cavalier perspective, an example of a blower section, and

[0065] - Figure 12 schematically represents, in partial view and in section, an example of a blower section.

[0066] DETAILED DESCRIPTION OF A METHOD OF IMPLEMENTATION

[0067] 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.

[0068] Figure 2 schematically represents, in partial view and in cross-section, a first example of a propulsion system 1.

[0069] In this example, propulsion system 1 is a twin-shaft, shrouded-fan gas turbine engine.

[0070] 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.

[0071] 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.

[0072] 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 5, 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 1 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 1. 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.

[0073] These surfaces can be at varying distances from the X-axis of the propulsion system 1, as illustrated in Figure 5. The inner surface defined by the inner platform 34 can move away from the X-axis of the propulsion system 1 when traversing this inner surface in the direction of gas flow. The outer surface defined by the outer platform 35 can move towards the X-axis of the propulsion system 1 when traversing this outer surface in the direction of gas flow.

[0074] 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 1.

[0075] The blower rotor 9 includes at least one blade 14 extending into the channel 36.

[0076] The fan blade 14 has a leading edge 14a and a trailing edge 14b (see, for example, Figure 5). 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).

[0077] The blade 14 comprises a blade root 25 fixed to the fan rotor and a blade extending in the groove 36 over a blade height 47 radially outwards relative to 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 over the blade height 47 from the internal radial boundary 37 to a blade tip 21 located on the outer platform 35. The blade height 47 is measured along a radial axis R orthogonal to the X-axis of the propulsion system 1 and passing through the X-axis of the propulsion system 1. Preferably, and with reference to Figure 5, 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.

[0078] The blower blade 14 also has a straight chord at the blade apex 39 extending from the leading edge 14a to the trailing edge 14b along the blade apex 21 and a straight curve at the blade foot 38 extending from the leading edge 14a to the trailing edge 14b along the blade foot 37. The term straight chord or normal chord refers to the distance of the segment between the leading edge and the trailing edge without the segment being projected.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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).

[0084] 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.

[0085] D is the diameter of the fan rotor, measured in a plane normal to the X-axis of the propulsion system 1 from the X-axis to the intersection point 45 between the blade tip 21 and the leading edge 14a of the blade. The diameter D is expressed in meters. The diameter D of the fan rotor 9 can be between 70 inches (177.8 cm) and 120 inches (304.8 cm) inclusive, specifically between 84 inches (213.36 cm) and 105 inches (266.7 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 conventionally, particularly under a wing of aircraft 100. First axial chord parameter - first and third velocity parameters of: curve 1F - marked in bending

[0086] Blade 1 has a first axial chord parameter corresponding to the ratio of the product of the mean axial chord and the axial chord at the blade root to the product of the square of the blade height 47 and the axial chord at the blade tip. The first axial chord parameter is calculated by expressing its constituent terms in meters; the value of the first axial chord parameter is considered dimensionless. The first axial chord parameter can be denoted Pc1.

[0087] It respects the relationship Pci = ^ mXCx0 in which C xm denotes the axial chord h xC xl average, C x0 denotes the axial chord, h denotes the blade height 47 and C xl00 designates the axial chord at the apex of the blade.

[0088] The blade 14 has a first speed parameter corresponding to a difference in the product of a maximum permissible speed of the blower rotor 9 expressed in rad / s by the value 2.501x10'3 s / rad and the value 1.7148x10' 1 The maximum permissible 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'. The first speed parameter can be denoted Pv1. It follows the relationship Pvl = 2.501 x 10 -3 x X n - 1.7148 x 10 -1 which can also be written as Pvl = 0.002501 x X n - 0.17148 and in which X n refers to the maximum permissible regime.

[0089] In order to optimize the performance of propulsion system 1, the first axial chord parameter is less than or equal to the first velocity parameter.

[0090] We can also define a third pv3 speed parameter.

[0091] Blade 14 presents the third speed parameter Pv3 which corresponds to a difference of a product of a maximum permissible speed of the blower rotor 9 expressed in rad / s by the value l, 722x10 3 s / rad and the value 1.2948x10' 1 .

[0092] It respects the relationship Pv3 = 1.722 x 10 -3 x X n - 1.2948 x 10 -1 which can also be written as Pv3 = 0.001722 x X n - 0.12948 and in which Xn denotes the maximum permissible regime.

[0093] Advantageously, the first axial chord parameter is greater than or equal to the third velocity parameter. In order to optimize the bending margin, the blade comprises a composite material having a lower portion stiffness 55 greater than an upper portion stiffness 57.

[0094] Choosing a relatively low value for the first axial chord parameter, particularly one lower than the first speed parameter, tends to increase blade efficiency. This efficiency depends, in particular, on a significant value for the axial chord at the blade tip relative to the other blade parameters. The blade tip corresponds to the part of the blade where the axial and tangential speeds are highest. It is therefore the part of the blade that contributes most to the engine's efficiency. By decreasing the first axial chord parameter, the axial chord at the blade tip and the blade efficiency are increased.

[0095] Second axial chord parameter - second and fourth velocity parameters of: 1T curve - torsional mark

[0096] Blade 14 exhibits a second axial chord parameter, corresponding to the ratio of the axial chord at the blade root to the product of the square of the average axial chord, the blade height 47, and the axial chord at the blade tip. The second axial chord parameter is calculated by expressing its constituent terms in meters; the value of the second axial chord parameter is considered dimensionless. The second axial chord parameter can be denoted Pc2.

[0097] It respects the relation Pc2 = — C xm xhx -C xl00 .

[0098] The blade 14 has a second speed parameter corresponding to a difference in the product of the maximum permissible speed of the blower rotor 9, expressed in rad / s, and the value 2.515x10' 1 s / rad and the value 52.701. The second speed parameter can be noted as Pv2.

[0099] It respects the relationship Pv2 = 2.515 x 10 -1 x X n- 52.701 which can also be written as Pv2 = 0.2515 x X n - 52,701.

[0100] In order to optimize the performance of propulsion system 1, the second axial chord parameter is less than or equal to the second velocity parameter.

[0101] A fourth speed parameter, Pv4, can also be defined. Blade 14 exhibits the third speed parameter, Pv4, which corresponds to the difference between the product of the maximum permissible speed of the blower rotor 9, expressed in rad / s, and the value 1.885 x 10⁻¹⁰⁴. 1 s / rad and the value 35.801.

[0102] It respects the relationship Pv4 = 1.885 x 10 -1 x X n - 35.801 which can also be written as Pv4 = 0.1885 x X n - 35,801 and in which Xn denotes the maximum permissible regime.

[0103] Advantageously, the second axial chord parameter is greater than or equal to the fourth velocity parameter.

[0104] To optimize the torsional margin, the blade includes a composite material with a stiffness of upstream portion 75 greater than a stiffness of downstream portion 77. These weaving arrangements allow the stiffness at the leading edge to be increased.

[0105] Choosing a relatively low value for the second axial chord parameter, and particularly one lower than the second speed parameter, tends to increase blade efficiency. This efficiency depends, in particular, on a significant value for the axial chord at the blade tip relative to the other blade parameters. The blade tip corresponds to the part of the blade where the axial and tangential speeds 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.

[0106] Short gondola

[0107] The propulsion system 1 includes a nacelle 28. Thanks to the values ​​retained of the first chord parameter and the second chord parameter, it is possible to choose particular geometric conditions in relation to the diameter D of the blower rotor 9 and the distance separating the blower rotor and the inlet of the nacelle.

[0108] It should be noted that the nacelle has an upstream axial end, relative to the direction of gas flow in the propulsion system, located more or less far from the fan 22 depending on the angle around the X-axis. Referring to Figure 12, the nacelle 28 comprises an upper part 280 situated vertically above the X-axis and a lower part 281 situated vertically below the X-axis. The upper part 280 includes an upper upstream axial end 330, and the lower part 281 includes a lower upstream axial end 331. The upper upstream axial end 330 is located upstream of the lower upstream axial end 331, such that the upper part 280 extends forward beyond the lower part 281. The axial distance between the upper upstream axial end 330 and the fan 22 is greater than the axial distance between the axial end lower upstream 331 and the blower 22.The nacelle 28 exhibits continuity around the X-axis, such that the axial distance between the upstream axial end for a certain angle around the X-axis and the blower 22 varies according to the angle between a maximum at noon, i.e., above the X-axis at the upper upstream axial end 330, and a minimum at 6 o'clock, i.e., below the X-axis at the lower upstream axial end 331. The nacelle is globally symmetrical with respect to a vertical plane passing through the X-axis. Figure 8 shows a cross-section in this vertical plane.

[0109] To characterize the distance between the blower inlet and the upstream end of the nacelle, we choose the average distance Lm between: the distance 480 separating the upper upstream axial end along the X-axis

[0110] 330 and the intersection point 450 between the inner face 350 of the housing above the X-axis and the leading edge of the blade 140 when it is above the X-axis, and the distance 481 separating along the X-axis the lower upstream axial end

[0111] 331 and the intersection point 451 between the inner face 351 of the casing below the X axis and the leading edge of the blade 141 when it is below the X axis.

[0112] The ratio of the average distance Lm to the diameter D of the blower rotor 9 is greater than or equal to 0.2 and less than or equal to 0.4.

[0113] The value of the first axial chord parameter and the value of the second chord parameter are chosen to optimize a compromise between sufficient margins with the natural modes of vibration in bending and torsion of the blade, good motor efficiency, low motor mass and a level of blade manufacturing complexity.

[0114] Choosing a relatively low value for the first (respectively second) axial chord parameter, and in particular below the first (respectively second) velocity parameter, tends to decrease the margin with the natural mode of vibration in bending (respectively torsion) of the blade, called the bending (respectively torsion) margin.

[0115] Bending, as defined here, is 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 natural frequency of its vibration during bending.

[0116] Torsion here refers to a deformation of the blade during which the blade tip rotates around a radial axis relative to the blade root, the blade curving around a direction radial to the drive axis, i.e., the X-axis of the propulsion system. The margin with the blade's natural torsional mode depends, in particular, on the difference between the blade's rotational frequency at maximum permissible speed and the frequency of its natural torsional vibration mode.

[0117] In order to increase the margins in bending and torsion, on the one hand the stiffness of the lower portion 55 is greater than the stiffness of an upper portion 57 and on the other hand the stiffness of the upstream portion 75 is greater than the stiffness of a downstream portion 77. This condition increases the level of manufacturing complexity of the blade.

[0118] Being in such a regime allows sufficient blade stability to be able to work in a short nacelle so that a ratio of the average distance Lm to the diameter D of the blower rotor 9 greater than or equal to 0.2 and less than or equal to 0.4 can be imposed. Such a short nacelle corresponds to a low nacelle mass, which increases the efficiency of the engine.

[0119] Fiber reinforcement

[0120] In relation to figures 5 and 6, 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.

[0121] 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.

[0122] In relation to Figure 5, 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 1a to the trailing edge 14b.

[0123] 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 lines of weft strands, each line of weft strand being separated from the immediately adjacent line of weft strands by a warp plane. A weft 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.Within the composite material structure, we can define a strand density corresponding to the number of strands per unit volume of the structure.

[0124] 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.

[0125] The matrix, meanwhile, 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).

[0126] The fibrous reinforcement is formed by three-dimensional weaving of warp and weft strands.

[0127] The weft strands 53 and the warp strands 54 are interlaced in the same plane. Different weaving patterns are possible for creating the interlacing.

[0128] 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.

[0129] Radial stiffnesses - first axial chord parameter

[0130] The blade includes a lower portion 55 which includes the blade foot 25. In relation to Figures 5 and 6, 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] The stiffness of the lower portion 55 is greater than the stiffness of the upper portion 57. Stiffness here refers to 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.

[0135] The difference in stiffness between the lower portion 55 and the upper portion 57 can be obtained in different ways.

[0136] 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.

[0137] 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.With reference to Figures 6 and 7, 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 7 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 7, only the weft strands have been shown, the warp strands having been omitted to simplify the reading of the figure.

[0138] As can be seen in Figure 7, the first two lines of weft strands L1 and L2, which are part of the internal portion 11 of the fibrous reinforcement 5, only include first strands 60. These first two lines of weft strands L1, L2 are located in the lower portion 55.

[0139] 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.

[0140] 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%.

[0141] The first weft strands 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 weft 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.

[0142] The second weft strands can, 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 polyester fibers (E = 268 GPa, A = 3.5%). In a second option, a weft strand density in the lower portion 55 is greater than a weft strand density in the upper portion 57.

[0143] 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.

[0144] The three options can be combined two at a time or all three simultaneously.

[0145] 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.

[0146] Axial stiffness - second axial chord parameter

[0147] The blade 14 has an upstream portion 75 which includes the leading edge 14a. The upstream portion 75 extends axially downstream from the leading edge 14a of the blade 25 to a third intermediate level 76 located between the leading edge 1a and the trailing edge 14b.

[0148] The upstream portion 75 extends over the entire height h of the blade 14, from the foot 25 to the apex 21. The upstream portion 75 extends substantially axially over a portion of the direct chord length of the composite material structure. This direct chord length varies between the foot 25 and the apex 21 of the blade 14. For example, at the foot of the blade 25, the upstream portion 75 can extend axially over a length between 25% and 40% of the chord length L, for example, over a length equal to approximately one-third of the direct chord length at the foot 25 of the blade. At mid-height h / 2 of the blade, the upstream portion 75 can extend axially over a length between 10% and 30% of the direct chord length, for example over a length equal to about a quarter of the direct chord length at mid-height of the blade 14. At the top 21, the upstream portion 75 can be narrower or even have a length of zero.

[0149] The blade 14 has a downstream portion 77 which includes the trailing edge 14b. With reference to Figure 8, the downstream portion 77 extends radially upstream from the trailing edge 14b to a fourth intermediate level 79 located between the third intermediate level 76 and the trailing edge 14b.

[0150] Dawn 14 may have a central portion 78 located between the upstream portion 75 and the downstream portion 77. With reference to Figure 8, the central portion extends from the upstream portion 75 to the downstream portion 77, that is to say the intermediate portion extends from the third intermediate level 76 to the fourth intermediate level 79.

[0151] The central portion 78 extends axially over a length between 5% and 10% of the direct chord length. The axial length of the central portion 78 can be constant over the entire blade height to ensure a smooth transition between the upstream portion 75 and the downstream portion 77. Alternatively, the length of the central portion 78 can be roughly proportional to the length of the upstream portion 75. In this embodiment, the length of the central portion 78 is maximum at the root 25 of the blade 14, then from 40% to 50% of the height h, the length of the central portion 78 can gradually decrease until it becomes practically zero at the tip 21.

[0152] The stiffness of the upstream portion 75 is greater than the stiffness of the downstream portion 77. Here, stiffness refers to 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.

[0153] The difference in stiffness between the upstream portion 75 and the downstream portion 77 can be obtained in different ways.

[0154] In a first option, the chain strands 54 comprise first and second chain strands, the upstream portion 75 comprising more first chain strands than second chain strands, and the downstream portion 77 comprising second chain strands and no first chain strands, with the stiffness of the first chain strands being greater than the stiffness of the second chain strands. The first and second chain strands extend continuously from the leading edge to the trailing edge.

[0155] According to this first option, the density of the first strands gradually decreases in the central portion 78 from the upstream portion 75 towards the downstream portion 77, and the density of the second strands gradually decreases in the central portion 78 from the downstream portion 77 towards the upstream portion 75. These gradual 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 central portion 78 and 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.

[0156] A schematic example of the CO warp plane of the fibrous reinforcement of blade 1 in Figure 8 is shown in Figure 9. The CO warp plane is a cross-sectional view of the fibrous preform along a plane normal to the stacking axis Z, at the foot 25 of blade 14 (see section plane EE in Figure 8). Note that Figure 9 illustrates a CO warp plane in which only the warp strands (i.e., in the stacking direction of the sections) are shown, the weft strands having been omitted to simplify the figure. This Figure 9 thus schematically illustrates a first example of warp strand hybridization.

[0157] As can be seen in Figure 9, within the upstream portion 75, which here extends over approximately one-third of the length of the rope L at the foot 25 of the blade 14, between 70% and 90% of the warp strands are first strands 83, the remainder being made up of second strands 84. Within the central portion 78, the density of first strands 84 gradually decreases from the upstream portion 75 towards the downstream portion 77, until it becomes zero (the density of second strands 83 increasing progressively in a complementary manner).

[0158] The first warp strands 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 warp 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.

[0159] The second warp 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 polyester fibers (E = 268 GPa, A = 3.5%). In a second option, a warp strand density in the upstream portion 75 is greater than a warp strand density in the downstream portion 77.

[0160] In a third option, a crossing density between warp strands and weft strands in the upstream portion 75 is greater than a crossing density between warp strands and weft strands in the downstream portion 77.

[0161] The three options can be combined two at a time or all three simultaneously.

[0162] In general, to ensure the transition of mechanical properties between the upstream portion 75 and the downstream portion 77, 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 weft planes, at most 30% of the first strands 83 removed from the fiber preform and an equal number of second strands 84 introduced into the fiber preform from the surface to replace the first strands 83 removed. For example, in the second option, at most 30% of the warp strands can be added between two successive weft planes.For example, in the third option, a maximum of 30% overlap can be added between two successive grid planes.

[0163] Number of dawns

[0164] 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.

[0165] The blower rotor 9 preferably comprises at least ten blower blades 14 and at most twenty-four blower blades 14, even more preferably at least seventeen blower blades 14 and at most twenty-two blower blades 14. Figure 11 illustrates the case where the blower rotor 9 comprises twenty-two blades.

[0166] 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.

[0167] 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.

[0168] 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 fan blades 14. Engine architecture

[0169] In relation to Figure 2, the primary body 3 comprises a compressor section 29, a combustion chamber 6 and a turbine section 30.

[0170] Compressor section 29 includes a low pressure compressor 4 and a high pressure compressor 5.

[0171] 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.

[0172] 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.

[0173] 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.

[0174] The rotor 51 of the high-pressure compressor 5 includes movable wheels 5a and the stator 52 of the high-pressure compressor 5 includes fixed wheels 5b. The movable wheels 5a are arranged alternately with the fixed wheels 5b, thus forming a succession of high-pressure compressor stages.

[0175] Turbine section 30 includes a high-pressure turbine 7 and a low-pressure turbine 8.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] Thanks to the reduction mechanism 19, the blower rotor 9 is driven into rotation at a speed lower than the rotational speed of the rotor 41 of the low pressure turbine 4.

[0184] 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.

[0185] 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.

[0186] The propulsion system 1 further comprises 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 rotatably mounted relative to the housing 31 about 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. 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 via the low-pressure shaft 11.

[0187] 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.

[0188] 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.

[0189] 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).

[0190] The high-pressure compressor 5 comprises at least eight stages (as illustrated in the example in Figure 2) and at most eleven stages.

[0191] The low-pressure turbine 8 comprises at least three stages (as illustrated in the example in Figure 2) and at most seven stages.

[0192] The low-pressure compressor 4 comprises at least two stages and at most four stages.

[0193] When propulsion system 1 is in operation, an airflow F entering propulsion system 1 passes through the blower 22 and is then divided between a primary airflow F1 and a secondary airflow F2, which flow upstream to downstream in propulsion system 1 in the direction of gas flow through propulsion system 1.

[0194] The secondary airflow F2, also called the "bypass airflow", flows in the secondary vein, around the primary body 3. The secondary airflow F2 helps to cool the periphery of the primary body 3 and is used to generate most of the thrust provided by the propulsion system 1.

[0195] 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.

[0196] 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.

[0197] In a propulsion system 1 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 1 with a high dilution ratio, the bulk 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 1, 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.

[0198] 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.

[0199] In a direct-drive propulsion system 1, 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.

[0200] 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).

[0201] 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.

[0202] Reduction mechanism

[0203] The reduction mechanism 19 may include an epicycloidal or planetary reduction mechanism, single-stage or two-stage.

[0204] For example, Figure 3 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 the blower shaft 20 in rotation 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.

[0205] In another example, Figure 4 illustrates an epicycloidal (or "planetary" in English) type reduction mechanism 19, in which case the ring 19b is fixedly mounted on the stator part 19e of the propulsion system 1 and the blower shaft 20 is driven in rotation by the planet carrier 19d.

[0206] Regardless of the configuration of the reduction mechanism 19, the diameter of the ring gear 19b and the satellite 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.

[0207] Regardless of the configuration of the reduction mechanism 19, the diameter of the ring gear 19b and the satellite 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.

[0208] 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.

[0209] Solidity

[0210] To further optimize the performance of the propulsion system 1, the strength of the fan 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 inter-blade pitch 23 is illustrated in Figure 10.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, lying in a plane normal to the X-axis, which originates from the upstream intersection point P1 (see Figures 10 and 11) of a first blade 1 and intersects the X-axis, and a second straight line D2, lying 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.

[0211] 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 in order 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.

[0212] 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, particularly during cruise: it must therefore be controlled to prevent it from degrading the efficiency of the fan section 2. By sizing and manufacturing the fan rotor 9 with twenty-two blades such 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 at maximum permissible speed and propagates only in the diverging part of the inter-blade channel. The inter-blade channel corresponds to the passage between two adjacent blades 1, extending from an inlet plane, which is normal to the airflow F at the inlet of the fan rotor 9 and passes through the leading edge 14a of the first blade 14, to 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.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. The distances (length, radius, diameter, etc.)) are measured at room temperature (approximately 20°C) when the propulsion system 1 is cold, i.e. when the propulsion system 1 has been at rest for a sufficient period for the parts of the propulsion system 1 to be at room temperature, it being understood that these dimensions vary little with respect to the conditions in which the propulsion system 1 is in takeoff mode.

[0213] We now present two examples of the realization of a propulsion system, each comprising a blower section.

[0214] 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.

[0215] The blower rotor 9 has a hub-to-head ratio of 0.27

[0216] 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.

[0217] The low-pressure shaft and the high-pressure shaft are co-rotating.

[0218] The propulsion system includes a two-stage high-pressure turbine.

[0219] The high-pressure compressor has 10 stages.

[0220] The low-pressure turbine comprises 6 stages.

[0221] The low-pressure compressor has 3 stages.

[0222] The propulsion system has a dilution ratio of 10

[0223] The propulsion system provides a thrust of 120,000 N

[0224] The diameter of the blower rotor is 1.98 m.

[0225] In the first example, the motor does not meet the requirements for blades made of an improved composite material to achieve acceptable vibration behavior. Therefore, the fan blade of this motor is made of a standard composite material.

[0226] In the second example, the engine is improved because it meets the requirements for blades made of an enhanced composite material to achieve acceptable vibration behavior. If a standard composite material is used, the blade's frequency response will not be acceptable.

[0227] Between the two examples, it is the reduction of the chord at the base that allows a reduction in the length of the rotor fan and it is the increase of the chord at the top that allows an improvement in the efficiency of the fan.

[0228]

[0229] 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 and the inequality Pv2 > Pc2 is respected in the case of the second example but not in the case of the first example.

Claims

DEMANDS 1. Aeronautical propulsion system (1) comprising: - a drive shaft (11) that rotates about an axis (X); - a blower shaft (20); - 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); and - a shrouded fan section (2), the fan section (2) comprising: -- an interior platform (34), -- a blower rotor (9) driven in rotation by the blower shaft (20);the fan rotor (9) comprising a blade (14), the 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), an upper portion (57) comprising the blade tip (21), an upstream portion (75) comprising the leading edge (14b) and a downstream portion (77) comprising the trailing edge (14a), the blade (14) having:; - an axial chord at the base of the blade extending along an axis (X) from the blower of the leading edge (14a) to the trailing edge (14b), - an axial chord at the apex of the blade extending 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 base of the blade and the axial chord at the top of the blade, in which the blade (14) presents: - a first axial chord parameter 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 square of the blade height (47) by the axial chord at the tip of the blade, - a first speed parameter corresponding to a difference of a product of a maximum permissible speed of the blower rotor (9) expressed in rad / s by the value 2.501x10' 3 s / rad and the value 1.7148x10' 1 , - a second axial chord parameter corresponding to a ratio of the axial chord at the blade root to a product of the square of the average axial chord by the blade height (47) and by the axial chord at the blade tip, and - a second speed parameter corresponding to a difference of a product of the maximum permissible speed of the blower rotor (9) expressed in rad / s by the value 2.515x10' 1s / rad and of the value 52.701, the fan section being configured so that the fan rotor has a maximum allowable speed greater than or equal to 280 rad / s, the blade (14) being configured such that the first axial chord parameter is less than or equal to the first speed parameter, a stiffness of the lower portion (55) is greater than a stiffness of the upper portion (57), and the second axial chord parameter is less than or equal to the second speed parameter, a stiffness of the upstream portion (75) is greater than a stiffness of the downstream portion (77), the propulsion system (1) comprising a nacelle (28) surrounding the fan section (2), the nacelle (28) comprising an upper upstream axial end (330) with respect to a direction of gas flow in the propulsion system, the upper upstream axial end (330) being located vertically above the axis (X),the nacelle (28) comprising a lower upstream axial end (331) located vertically below the axis (X), an average distance between a first distance (480) along the axis (X) separating the upper upstream axial end (330) and an intersection (450) between the inner face (350) of the housing above the axis (X) and the leading edge of the blade when the blade is above the axis (X) and a second distance (481) along the axis (X) separating the lower upstream axial end (331) and an intersection (451) between the inner face (351) of the housing below the axis (X) and the leading edge of the blade when the blade is in, below the axis (X), a ratio of the average distance to a diameter (D) of the blower rotor (9) being greater than or equal to 0.2 and less than or equal to 0.

4.

2. Blower section (2) according to claim 1, wherein the blade (14) has: - a third speed parameter corresponding to a difference of a product of a maximum permissible speed of the blower rotor (9) expressed in rad / s by the value 1.722x10' 3 s / rad and the value 1.2948x10' 1 , - a fourth speed parameter corresponding to a difference of a product of the maximum permissible speed of the blower rotor (9) expressed in rad / s by the value 1.885x10' 1 s / rad and of the value 35.801, the blade (14) being configured so that the first axial chord parameter is greater than or equal to the third velocity parameter, and the second axial chord parameter is greater than the fourth velocity parameter.

3. Fan section (2) according to any one of claims 1 and 2, wherein the fan section comprises 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) to 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, the weft strands (53) comprising 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,where the stiffness of the first weft strands is greater than the stiffness of the second weft strands, the density of the first strands increases progressively in the intermediate portion (58) from the lower portion (55) to the upper portion (57), and the density of the second strands increases progressively in the intermediate portion (58) from the upper portion (57) to the lower portion (55).

4. Fan section (2) according to any one of claims 1 to 3, wherein the fan blade (14) has at each blade height a direct chord extending from the leading edge (14a) to the trailing edge (14b), the fan section comprising a central portion (78) extending from the upstream portion (75) to the downstream portion (77), the upstream portion (75) extending from the leading edge (14a) to the trailing edge (14b) to the central portion (78) over a length greater than or equal to 25% and less than or equal to 40% of the direct chord length, the central portion (78) extending over a length greater than or equal to 5% and less than or equal to 10% of the direct chord length, the warp strands comprising first warp strands and second warp strands,the upstream portion (75) comprising more first warp strands than second warp strands and the downstream portion (77) comprising second warp strands and no first warp strands, a stiffness of the first warp strands being greater than a stiffness of the second warp strands, a density of first strands decreasing progressively in the central portion (78) of the upstream portion (75) towards the downstream portion (77), a density of second strands increasing progressively in the central portion (58) of the upstream portion (75) towards the downstream portion (77).

5. Blower section (2) according to any one of claims 1 to 4, wherein a diameter (D) of the blower rotor (9) is 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.

6. Blower section (2) according to any one of claims 1 to 5, the blade (14) being a first blade of a plurality of blades included in the blower rotor (9), a number of the plurality of blades being greater than or equal to 17 and less than or equal to 22.

7. Blower section (2) according to any one of claims 1 to 6, wherein the blower rotor (2) comprises a blower hub (13), each blade (14) being pivotally mounted relative to the blower hub (13) so as to have variable pitch.

8. Propulsion system (1) according to any one of claims 1 to 7, configured to provide a thrust of between 80,068 N and 331,374 N, preferably between 88,964 N and 155,688 N.

9. Propulsion system (1) according to any one of claims 1 to 8, wherein a dilution ratio of the propulsion system (1) is greater than or equal to 10, 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.

10. Propulsion system (1) according to any one of claims 1 to 9, 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.

11. Method for dimensioning an aeronautical propulsion system (1), the propulsion system comprising - a drive shaft (11) that rotates about an axis (X); - a blower shaft (20); - 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); and a shrouded blower section (2), the blower section (2) comprising: - an indoor platform (34), - a fan rotor (9) driven in rotation by the fan shaft (20); the fan rotor (9) comprising a blade (14), the 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) including the leaf spring foot (25), an upper portion (57) including the leaf spring apex (21), an upstream portion (75) including the leading edge (14b) and a downstream portion (77) including the trailing edge (14a), the leaf spring (14) having: - an axial chord at the base of the blade extending along an axis (X) from the blower of the leading edge (14a) to the trailing edge (14b), - an axial chord at the apex of the blade extending 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 base of the blade and the axial chord at the top of the blade, in which the blade (14) presents: - a first axial chord parameter 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 square of the blade height (47) by the axial chord at the tip of the blade, - a first speed parameter corresponding to a difference of a product of a maximum permissible speed of the blower rotor (9) expressed in rad / s by the value 2.501x10' 3 s / rad and the value 1.7148x10' 1 , - a second axial chord parameter corresponding to a ratio of the axial chord at the blade root to a product of the square of the average axial chord by the blade height (47) and by the axial chord at the blade tip, and - a second speed parameter corresponding to a difference of a product of the maximum permissible speed of the blower rotor (9) expressed in rad / s by the value 2.515x10' 1s / rad and of the value 52.701, the propulsion system (1) comprising a nacelle (28) surrounding the fan section (2), the nacelle (28) comprising an upper upstream axial end (330) with respect to a direction of gas flow in the propulsion system, the upper upstream axial end (330) being located vertically above the axis (X), the nacelle (28) comprising a lower upstream axial end (331) located vertically below the axis (X), an average distance between a first distance (480) along the axis (X) separating the upper upstream axial end (330) and an intersection (450) between the inner face (350) of the casing above the axis (X) and the leading edge of the blade when the blade is above the axis (X) and a second distance (481) along the axis (X) separating the upstream axial end lower (331) and an intersection (451) between the inner face (351) of the housing below the axis (X) and the leading edge of the blade when the blade is below the axis (X), a ratio of the average distance to a diameter (D) of the fan rotor (9) being greater than or equal to 0.2 and less than or equal to 0.4, the fan section being configured so that the fan rotor has a maximum allowable speed greater than or equal to 280 rad / s, the method comprising a step of sizing the fan section (2) such that the first axial chord parameter is less than or equal to the first speed parameter, a stiffness of the lower portion (55) is greater than a stiffness of the upper portion (57), and the second axial chord parameter is less than or equal to the second speed parameter, a stiffness of the upstream portion (75) is greater than a stiffness of the downstream portion (77).

12. Method of manufacturing a fan section (2) of an aeronautical propulsion system (1) comprising dimensioning the fan section according to claim 11 and manufacturing the fan section.

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