Central fan cone with optimized dimensions for propulsion system

Abstract

The invention relates to a propulsion system (10), in particular a high bypass ratio propulsion system, comprising a fan (12) having a hub and a plurality of variable pitch vanes (14), and a central cone (18) having an outer wall (19) and a free end (20), wherein the central cone (18) has - a first maximum radius Rmax1 defined as a distance between the X axis and a first point Xmax1 of the outer wall (19) of the central cone (18), a projection of the point Xmax1 on the X axis being positioned at a point Pmax1, - a second maximum radius Rmax2, - a first minimum radius Rmin1, - the point Pmax1 being positioned at a distance L from the free end of the central cone (18) and the central cone being configured such that the ratio Rmax1 / L is greater than or equal to 0.5 and less than or equal to 0.6. Figure for abstract: Fig. 2

Description

Title of the invention: central cone of a fan with optimized dimensions for a propulsion system Field of invention

[0001] The present invention relates to a propulsion system comprising a fan cone having optimized dimensions, said propulsion system being able to comprise in particular a variable-pitch fan with a high dilution ratio.

[0002] The invention also relates to an aircraft comprising such a propulsion system. Technological background

[0003] In the field of air transport, the current trend is to minimize the emissions of polluting and / or greenhouse gases from aircraft and limit their fuel consumption. To this end, the efficiency of propulsion systems is constantly being improved, in particular by increasing their propulsive efficiency, which characterizes the efficiency with which the energy communicated to the air passing through the engine is converted into useful thrust.

[0004] A propulsion system, also called a turbomachine, conventionally comprises a fan comprising blades which extend radially outwards from a hub, the fan being traversed by an incoming air flow. The blades each comprise a blade root by which the blades are fixed to a rotor making it possible to drive the fan in rotation during operation of the propulsion system.

[0005] Furthermore, a central cone surrounding the hub emerges from the central portion of the fan to a free end of pointed or rounded shape. The central cone extends along a longitudinal axis X of the propulsion system which corresponds to the axis of revolution of the fan. The plurality of blades of the fan generally extends in a plane P centered on the axis X and normal to the axis X. Furthermore, the central cone has a symmetry of revolution around the axis X and has a section which gradually decreases from the fan towards the free end.

[0006] During operation of the turbomachine, the fan drives an incoming air flow which is then separated into a primary air flow which passes through a primary body of the propulsion system and into a secondary air flow which bypasses the primary body, the primary and secondary air flows enabling the aircraft to be propelled.

[0007] The primary air flow successively passes through different elements of the primary body of the propulsion system, namely a compressor section which may comprise a low pressure compressor and a high pressure compressor, a combustion chamber and a turbine section which may comprise in particular a turbine high pressure and a low pressure turbine. The high pressure compressor is rotated by the high pressure turbine via a high pressure shaft. The blower and the low pressure compressor are rotated by the low pressure turbine via a low pressure shaft.

[0008] One way of improving the propulsive efficiency of propulsion systems is to reduce the compression ratio of the fan and thus the flow velocity at the outlet of the propulsion system. To do this, it is in particular possible to increase the dilution ratio of the propulsion system, i.e. the mass of secondary flow relative to the mass of primary flow, in particular by increasing the diameter of the fan to obtain a system with a high dilution ratio.

[0009] One of the disadvantages of these high bypass ratio propulsion systems is that the Mach number of the flow at the blade root is more dependent on the flight Mach number compared to a conventional propulsion system, particularly a low bypass ratio system. This high Mach number can cause problems, particularly when changing the pitch of the fan blades. Furthermore, the central cone is subject to more distortion due to the aircraft's angle of attack, which can pose risks of flow separation. Statement of the invention

[0010] An objective of the invention is to prevent the Mach number from being too high at the blade root and also to limit the distortions that the central cone may undergo. More generally, the invention aims to limit the impact of the air flow on the central cone and at the blade root, regardless of the speed of the aircraft and its angle of attack.

[0011] To this end, according to a first aspect of the invention, a propulsion system is proposed, in particular a propulsion system with a high dilution ratio, comprising a fan (12) rotatable about an axis X, said fan comprising a hub and a plurality of variable-pitch blades (14) extending radially from the hub, and a central cone (18) having an outer wall (19) and a free end (20), wherein the central cone (18) has - a first maximum radius Rmaxl defined as a distance between the X axis and a first point Xmaxl of the outer wall (19) of the central cone (18), Xmaxl being one of two points of the wall of the central cone furthest from the X axis, a projection of the point Xmaxl on the X axis being positioned at a point Pmaxl, - a second maximum radius Rmax2 defined as a distance between the X axis and the second point Xmax2 of the outer wall (19) of the central cone (18), Xmax2 being the other of the two points of the outer wall of the central cone furthest from the axis X and being located downstream of point Xmaxl, a projection of point Xmax2 on the X axis being positioned at a point Pmax2, - a first minimum radius Rminl defined as a distance between the X axis and a third point Xminl of the outer wall (19) of the central cone (18), Xminl being the point located between Xmaxl and Xmax2, closest to the X axis, a projection of the point Xminl on the X axis being positioned at a point Pminl, - the central cone being configured so that the ratio Rmaxl / L is greater than or equal to 0.5 and less than or equal to 0.6.

[0012] The propulsion system according to this first aspect of the invention has a central cone of a more elongated shape than the central cones of the propulsion systems of the prior art. This makes it possible to move the blades, and in particular the blade roots, away from the zone where the flow accelerates the most. In this way, the Mach number of the flow at the central cone is high upstream of the blade roots, then decreases until reaching a low Mach number at the blade roots. Thus, turbulence at the blade root is limited and does not hinder the rotational movement of the blades during pitch changes.

[0013] Furthermore, the central cone having such a configuration undergoes less distortion in the different phases of flight than the central cone of a propulsion system of the prior art.

[0014] According to preferred but non-limiting embodiments of the propulsion system according to the first aspect of the invention, taken individually or in combination: - a projection of the free end on the axis X is positioned at a point X0 and in which the slope of the outer wall at point X0 and away from the latter forms an angle a3 with the axis X, the angle a3 having a value greater than or equal to 70°; - the points Pmaxl and Pminl are spaced by a distance L1 and the points Pminl and Pmax2 are spaced by a distance L2, the central cone being configured so that the ratio (Rmaxl - Rminl) / Ll is less than 0.2 and the ratio (Rmax2 - Rminl) / L2 is less than 0.3; - the central cone has a second minimum radius Rmin2 less than Rmax2, Rmin2 corresponding to a distance between the X axis and a point Xmin2 of the outer wall (19) of the central cone (18), Xmin2 being a point located downstream of the point Xmax2, the projection of the point Xmin2 on the X axis being positioned at a point Pmin2 spaced from the point Pmax2 by a distance L3, and in which the central cone is configured so that the ratio (Rmax2-Rmin2) / L3 is between 0.4 and 0.6; - when the blade is in cruising setting, an intersection point XI between the leading edge of a blade and the outer wall (19) is projected onto the X axis in a PI point, an intersection point X2 between the trailing edge of a blade and the outer wall (19) is projected onto the X axis at a point P2, the points PI and P2 being spaced apart by a distance L4, the central cone (18) being configured so that -0.25 x L4 < Pminl-Pl < 0.25 x L4; - point Xmax2 is located downstream of point X2; - the propulsion system has a dilution ratio greater than or equal to 10; - the fan has at least eight blades, for example between 12 and 24 dawns; and - the propulsion system can be double-flow or triple-flow, said propulsion system being unducted and the fan blades being variable-pitch; the propulsive efficiency of the system is thus increased.

[0015] There is also provided, according to a second aspect of the invention, an aircraft comprising a propulsion system such as that described according to the first aspect of the invention. Brief description of the Figures

[0016] Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:

[0017] [Fig-1] [Fig.l] schematically represents a complete and sectional view of a propulsion system; and

[0018] [Fig.2] [Fig.2] schematically represents a partial and sectional view of a blower and its central cone according to an embodiment of the invention. Detailed description of an exemplary embodiment

[0019] The propulsion system 10 shown in [Fig.l] comprises a fan 12 having a plurality of variable-pitch blades 14 extending radially from a hub (not shown), said blades each having a radial axis Y for pivoting relative to the hub. The fan 12 also comprises a central cone 18 which extends from a first face of the fan 12 along the longitudinal axis X of the propulsion system. A setting mechanism 25 is integrated in the central cone 18 and allows the blades to be set to change and the blades to be held in the setting determined according to the flight phase.

[0020] The propulsion system also comprises a nacelle 24 which extends from a second face of the fan 12 opposite the face comprising the central cone 18 and which delimits a primary body 22 through which a part of the air flow F1 will pass to generate thrust. The nacelle comprises an upstream end 27 forming a nozzle at the entrance to the primary body 22.

[0021] In particular, during operation of the turbomachine 10, the fan 12 drives an incoming air flow F1 which is then separated into a primary air flow FA which passes through the primary body 22 via an internal circulation channel 26 and into a secondary air flow FB which bypasses the primary body 22, the primary air flows FA and secondary air flows FB enabling the aircraft to be propelled.

[0022] In the following, the terms “upstream” and “downstream” are understood to refer to a direction of flow of an air flow through the internal channel 26.

[0023] In the example shown, the turbomachine 10 is of the “puller” type, that is to say that the fan 12 is arranged upstream of the internal circulation channel 26. Furthermore, in this example, the fan is not ducted.

[0024] The primary air flow FA successively passes through different elements of the primary body 22, in particular a low-pressure compressor 30 then a high-pressure compressor 32 which supplies compressed air to a combustion chamber 34. A high-pressure turbine 36 is arranged downstream of the combustion chamber 34 and receives the exhaust gases leaving the latter. The gases are then transmitted to a low-pressure turbine 38 and are then expelled by a gas exhaust nozzle 40, thus generating thrust to propel the aircraft.

[0025] The high-pressure turbine 36 is coupled to the high-pressure compressor 32 via a high-pressure transmission shaft 42 which allows the high-pressure compressor 32 to be driven by the high-pressure turbine 36. Similarly, the low-pressure turbine 38 is coupled to the low-pressure compressor 30 via a low-pressure transmission shaft 44 which allows the low-pressure compressor 32 to be driven by the low-pressure turbine 38.

[0026] The fan 12 comprises a hub (not shown) which is driven in rotation around the axis X by the low pressure turbine 38, and this, via the low pressure shaft 44. In one embodiment, the propulsion system further comprises a reduction gear (not shown) interposed between the low pressure shaft 44 and the fan 12 in order to drive the fan 12 at a speed lower than that of the low pressure shaft 44. The use of a reduction gear makes it possible to independently optimize the rotation of the fan 12 and the low pressure turbine 38.

[0027] The propulsion system 10 also comprises a set of fixed blades 46 serving to guide the secondary air flow FB and the setting of which can possibly be modified according to the flight phases thanks to a pitch change mechanism.

[0028] The propulsion system 10 is a system with a high bypass ratio (corresponding to the ratio between the flow rate of the secondary air flow and the flow rate of the primary air flow), i.e. a dilution ratio in particular greater than or equal to 10 and less than or equal to 80, and having a low fan compression ratio, notably ranging from 1.05 to 1.45.

[0029] Depending on the flight phases, the maximum Mach number that the flow can reach at the level of the central cone 18 may, for example, be greater than 0.6.

[0030] The central cone 18 of the propulsion system 10 has an outer wall 19 and a free end 20. A projection of the free end 20 on the X axis is positioned at a point X0. The point X0 is, preferably, the (fictitious) point of intersection between the free end 20 and the X axis.

[0031] The central cone 18 has a first maximum radius Rmaxl defined as a distance between the X axis and a first point Xmaxl of the outer wall 19 of the central cone 18, Xmaxl being one of two points of the wall of the central cone furthest from the X axis. A projection of the point Xmaxl on the X axis is positioned at a point Pmaxl.

[0032] The central cone 18 also has a second maximum radius Rmax2 defined as a distance between the X axis and the second point Xmax2 of the outer wall 19 of the central cone 18, Xmax2 being the other of the two points of the outer wall of the central cone 18 furthest from the X axis. The point Xmax2 is located downstream of the point Xmaxl. A projection of the point Xmax2 onto the X axis is positioned at a point Pmax2.

[0033] Furthermore, the central cone 18 has a first minimum radius Rminl defined as a distance between the X axis and a third point Xminl of the outer wall 19 of the central cone 18, Xminl being the point located between Xmaxl and Xmax2, closest to the X axis. The point Xminl makes it possible to form a concave portion downstream of the protuberance formed by the point Xmaxl. A projection of the point Xminl on the X axis is positioned at a point Pminl.

[0034] Furthermore, the point Pmaxl is positioned at a distance L from the free end of the central cone 18 and the central cone is configured so that the ratio Rmaxl / L is greater than or equal to 0.5 and less than or equal to 0.6.

[0035] The central cone 18 thus has a more elongated shape than the propulsion systems of the prior art, which reduces the impact of the flow at the foot of the blades. Indeed, the elongated shape allows the air flow to be at its maximum acceleration sufficiently upstream of the foot of the blades so that the Mach number at the foot of the blades is low. The Mach number at the foot of the blade is thus sufficiently low so as not to hinder the rotational movement of the blades during changes in pitch.

[0036] Furthermore, in a conventional propulsion system not comprising a fairing around the fan 12, a separation of the flow is possible at the end of the central cone 18. The central cone according to an embodiment of the invention then has an end of a more rounded shape than when the fan is faired. The slope of the outer wall at point X0 and away from the latter then forms an angle a3 with the axis X, the angle a3 having a value greater than or equal to at 70°, preferably greater than or equal to 80°, and possibly equal to 90°.

[0037] The shape of the central cone 18 is thus more rounded, in particular near the free end 20 compared to a central cone of a propulsion system of the prior art. This more rounded shape allows the central cone to be less sensitive to the distortion and the incidence of the aircraft, and this, for the different phases of flight of the aircraft. Furthermore, the greater slope near the free end 20 also makes it possible to limit the separation of the flow at the level of the central cone 18.

[0038] Furthermore, the points Pmaxl and Pminl are spaced apart by a distance L1 and the points Pminl and Pmax2 are spaced apart by a distance L2, and the central cone 18 is configured so that the ratio (Rmaxl - Rminl) / Ll is less than 0.2 and the ratio (Rmax2 - Rminl) / L2 is less than 0.3.

[0039] The propulsion system according to this first aspect of the invention has a central cone having, from upstream to downstream, a first protuberance followed downstream by a concave portion then a second protuberance. A protuberance is defined as a curved portion which moves away from the X axis relative to the curvature positioned upstream and downstream of this protuberance.

[0040] This central cone shape allows the air flow to slow down in the concave part and thus allows the blades, and in particular the blade roots, to be moved away from the area where the flow accelerates the most. In this way, the Mach number of the flow at the central cone is high upstream of the blade roots, then decreases until reaching a low Mach number at the blade roots. Thus, turbulence at the blade root is limited and does not hinder the rotational movement of the blades during pitch changes.

[0041] Advantageously, the leading edge 50 of the blades 14 is positioned in this concave zone and the Mach number is thus low at the level of the root of the blades.

[0042] In particular, when the blade is in the cruising position (or setting), a point of intersection XI between the leading edge of a blade and the outer wall 19 is projected onto the axis X at a point PI, and a point of intersection X2 between the trailing edge of a blade and the outer wall 19 is projected onto the axis X at a point P2. The points PI and P2 are spaced apart by a distance L4 and the central cone 18 is configured so that -0.25 x L4 < Pminl-PI < 0.25 x L4.

[0043] Preferably, the point Xmax2 is located downstream of the point X2. The trailing edge of the blades can thus also be positioned in the concave part.

[0044] Preferably, the point Xmaxl is positioned at the top of the second protuberance. Also preferably, the point Xmax2 is positioned at the top of the second protuberance.

[0045] The point Xminl is preferably positioned at the point of the concave part which is closest to the X axis.

[0046] Furthermore, the central cone has a second minimum radius Rmin2 less than Rmax2, Rmin2 corresponding to a distance between the X axis and a point Xmin2 of the outer wall 19 of the central cone 18, Xmin2 being a point located downstream of the point Xmax2. A projection of the point Xmin2 on the X axis is positioned at a point Pmin2 spaced from the point Pmax2 by a distance L3. The central cone is configured so that the ratio (Rmax2-Rmin2) / L3 is between 0.4 and 0.6.

[0047] According to a possible embodiment, the central cone 18 may have an upstream portion 56, and in particular a portion positioned upstream of the point Xmaxl, having a super-ellipse shape. The curvature of the upstream portion 56 may preferably be defined by the following equation: \L / \ Rnuul '

[0048] wherein N is greater than or equal to 1.6 and less than or equal to 3.8, and M is greater than or equal to 1.6 and less than or equal to 3.8.

[0049] The upstream part 56 is preferably located upstream of the point Xmaxl, and preferably has the point Xmaxl as its downstream limit.

[0050] Furthermore, the upstream part 56 may have the point X0 as its upstream limit.

[0051] In an alternative embodiment, the upstream portion 56 may have as its upstream limit a point Xe located between the point X0 and the point Xmaxl. According to this alternative embodiment, an end portion 58 is located between the point X0 and the point Xe and may have a shape that is not defined by a super-ellipse equation. The end portion 58 may in particular be more pointed than if it were part of a super-ellipse shape.

[0052] Furthermore, the point Xmax2 is positioned at a distance L from the point X0 and the central cone is configured so that 0.5 < Rmaxl / L < 0.7, and preferably so that 0.5 < Rmaxl / L < 0.65.

[0053] Furthermore, the fan may comprise a number of blades 14 conventionally ranging from 12 to 24, for example between 16 and 22 blades.

[0054] According to a possible embodiment, the propulsion system can be double flow (as illustrated in [Fig.l]) or triple flow.

Claims

Claims

1. A propulsion system (10), in particular a high bypass ratio propulsion system, comprising a fan (12) rotatable about an axis X, said fan comprising a hub and a plurality of variable-pitch blades (14) extending radially from the hub, and a central cone (18) having an outer wall (19) and a free end (20), wherein the central cone (18) has - a first maximum radius Rmaxl defined as a distance between the axis X and a first point Xmaxl of the outer wall (19) of the central cone (18), Xmaxl being one of two points of the wall of the central cone furthest from the axis X, a projection of the point Xmaxl on the axis X being positioned at a point Pmaxl, - a second maximum radius Rmax2 defined as a distance between the axis X and a second point Xmax2 of the outer wall (19) of the central cone (18),Xmax2 being the other of the two points of the outer wall of the central cone furthest from the X axis and being located downstream of the point Xmaxl, a projection of the point Xmax2 on the X axis being positioned at a point Pmax2, - a first minimum radius Rminl defined as a distance between the X axis and a third point Xminl of the outer wall (19) of the central cone (18), Xminl being the point located between Xmaxl and Xmax2, closest to the X axis, a projection of the point Xminl on the X axis being positioned at a point Pminl, - the point Pmaxl being positioned at a distance L from the free end of the central cone (18) and the central cone being configured so that the ratio Rmaxl / L is greater than or equal to 0.5 and less than or equal to 0.6.,

2. A propulsion system according to claim 1, wherein a projection of the free end (20) onto the X axis is positioned at a point X0 and wherein the slope of the outer wall at and away from the point X0 forms an angle a3 with the X axis, the angle a3 having a value greater than or equal to 70°.

3. A propulsion system according to claim 1 or 2, wherein the points Pmaxl and Pminl are spaced apart by a distance L1 and the points Pminl and Pmax2 are spaced apart by a distance L2, the central cone (18) being configured so that the ratio (Rmaxl -Rminl ) / Ll is less than 0.2 and the ratio (Rmax2 - Rminl ) / L2 is less than 0.

3.

4. A propulsion system according to any one of the preceding claims, wherein the central cone has a second minimum radius Rmin2 less than Rmax2, Rmin2 corresponding to a distance between the X axis and a point Xmin2 of the outer wall (19) of the central cone (18), Xmin2 being a point located downstream of the point Xmax2, the projection of the point Xmin2 on the X axis being positioned at a point Pmin2 spaced from the point Pmax2 by a distance L3, and wherein the central cone is configured so that the ratio (Rmax2-Rmin2) / L3 is between 0.4 and 0.

6.

5. A propulsion system according to any preceding claim, wherein, when the blade is in cruising setting, a point of intersection XI between the leading edge of a blade and the outer wall (19) projects onto the X axis at a point PI, a point of intersection X2 between the trailing edge of a blade and the outer wall (19) projects onto the X axis at a point P2, the points PI and P2 being spaced apart by a distance L4, the central cone (18) being configured so that -0.25 x L4 < Pminl-Pl < 0.25 x L4.

6. A propulsion system according to claim 5, wherein the point Xmax2 is located downstream of the point X2.

7. Propulsion system according to any one of claims 1 to 6, characterized in that it has a dilution ratio greater than or equal to 10.

8. A propulsion system according to any one of claims 1 to 7, wherein the fan comprises at least eight blades (14), for example 12 to 24 blades.

9. Propulsion system according to any one of claims 1 to 8, characterized in that it is a double-flow (10) or triple-flow propulsion system, said propulsion system being unducted and the fan blades being variable-pitch.

10. Aircraft comprising a propulsion system (10) according to any one of the preceding claims.

Images