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) rotatable about an axis X, said fan comprising a plurality of variable-pitch blades (14) extending radially from a hub, said blades (14) each having a radial axis Y for pivoting relative to the hub, and a central cone (18) having an outer wall (19) and a free end (20), a projection of the free end (20) on the axis X being positioned at a point X0, in which the central cone (18) has - a first radius R1 corresponding to a distance between the axis X and a point of intersection X1 between the outer wall (19) of the central cone (18) and the pivot axis Y of a blade (14), - a second radius R2 corresponding to a distance between the axis X and a point X2 of the outer wall (19) of the central cone (18) located between point X1 and point X0 so that the ratio R2 / R1 is equal to 0.8,the central cone (18) being configured so that a first distance L1 between the point X0 and a projection of the point X1 on the X axis is such that 1.5 x R1 ≤ L1 ≤ 2.5 x R1. Figure for the 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 dual-flow streamlined propulsion system is proposed, and in particular a high-dilution-ratio propulsion system, comprising a fan rotatable about an axis X, said fan comprising a hub and a plurality of variable-pitch blades extending radially from the hub, said blades each having a radial axis Y of pivoting relative to the hub, and a central cone having an outer wall and a free end, a projection of the free end onto the X axis being positioned at a point X0, in which the central cone has - a first radius RI corresponding to a distance between the axis X and a point of intersection XI between the outer wall of the central cone and the pivot axis Y of a blade, - a second ray R2 corresponding to a distance between the X axis and a point X2 of the outer wall of the central cone located between point XI and point XO such that the ratio R2 / R1 is equal to 0.8, the central cone being configured such that a first distance L1 between point XO and a projection of point XI on the X axis is such that l.5xRl <Ll< 2,5 x RI, et de sorte que 0,5 x R2 < L1 < 1,5 x R2.

[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. Indeed, the zone where the Mach number is maximum, in particular at point X2, is far from the blade roots and the Mach number is sufficiently low at the blade roots. 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 roots 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 a preferred embodiment, the fan is ducted.

[0015] According to preferred but non-limiting embodiments of the propulsion system according to the first aspect of the invention, taken individually or in combination: - the central cone is configured so that a second distance L2 between the point X0 and a projection of the point X2 on the X axis is such that the ratio L2 / L1 has a value ranging from 0.2 to 0.6; - the central cone has a third radius R3 corresponding to a distance between the X axis and a point X3 on the outer wall of the central cone, the point X3 being located between the point X0 and the point X2 so that the ratio R3 / R1 is equal to 0.3, the outer wall of the central cone having a curvature such that the tangent to the curvature, at the point X3, forms an angle with the X axis greater than or equal to 30° and less than or equal to 70°; the shape of the central cone is thus more rounded, in particular near the free end, and less sensitive to distortion and the incidence of the aircraft; - the propulsion system comprises a fourth radius R4 corresponding to a distance between the axis X and a point X4 located on the outer wall of the central cone, the point X4 being located between the point X2 and the point XI, the fourth radius R4 being greater than the first radius RI; the central cone thus comprises a first curved zone comprising the point X4 which makes it possible to further reduce the Mach number at the foot of the blade; - point X4 is the point of the outer wall located between XO and Y furthest from the X axis and in which a fourth distance L4 between point XO and a projection of point X4 on the X axis is such that 0.5 < R4 / L4 < 0.65; point X4 is then at the top of the first curved zone; - the propulsion system comprises a fifth radius R5 corresponding to a distance between the axis X and a point X5 located on the outer wall of the central cone, the point X5 being located downstream of the point XI, the fifth radius R5 being greater than the first radius RI; the central cone thus comprises a second curved zone comprising the point X5; - the free end is rounded and has a curvature such that the tangent to the curvature, at point XO, is perpendicular to the X axis; sensitivity to distortion and incidence is thus reduced; - the propulsion system has a dilution ratio greater than or equal to 10; and - the fan has at least eight blades, for example between 10 and 24 blades.

[0016] 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

[0017] 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:

[0018] [Fig-1] [Fig.l] schematically represents a complete and sectional view of a propulsion system;

[0019] [Fig.2] [Fig.2] schematically represents a partial and sectional view of a blower and its central cone according to a first embodiment of the invention; and

[0020] [Fig.3] [Fig.3] schematically represents a partial and sectional view of a fan and its central cone according to a second embodiment of the invention. Detailed description of an example of implementation

[0021] 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 of 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.

[0022] The propulsion system also includes 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 part of the air flow Fl will pass to generate thrust.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 reducer (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 reducer makes it possible to independently optimize the rotation of the fan 12 and the low pressure turbine 38.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The central cone 18 has a first radius RI corresponding to a distance between the axis X and a point of intersection XI between the outer wall 19 of the central cone 18 and the pivot axis Y of a blade. The central cone 18 also has a second radius R2 corresponding to a distance between the axis X and a point X2 of the outer wall of the central cone 18. In order to limit the impact of the air flow on the central cone and at the blade root, the point X2 is located between the point XI and the point X0 so that the ratio R2 / R1 is equal to 0.8.

[0034] Furthermore, the central cone 18 is dimensioned so that a first distance L1 between the point X0 and a projection of the point XI on the axis X is such that 1.5 x RI < L1 < 2.5 x RL In particular, the projection of point XI on the X axis is located at point PI and the distance L1 corresponds to the distance between point X0 and point PL

[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] The maximum Mach number that the flow can reach at the level of the central cone 18 can for example be greater than 0.6.

[0037] Furthermore, the point X2 is positioned so that the projection of the point X2 onto the X axis can be located at a distance L2 from the point X0 so that the ratio L2 / L1 has a value ranging from 0.2 to 0.6. The point X2 is thus sufficiently far from the foot of the blades 14.

[0038] Furthermore, the central cone 18 may have a third R3 corresponding to a distance between the axis X and a point X3 of the outer wall of the central cone, the point X3 being located between the point X0 and the point X2 so that the ratio R3 / R1 is equal to 0.3. The outer wall of the central cone then has a curvature such that the tangent to the curvature, at the point X3, forms an angle a3 with the axis X greater than or equal to 30° and less than or equal to 70°.

[0039] The shape of the central cone 18 is thus more rounded, in particular near the free end 20 relative 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, 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 central cone 18.

[0040] According to a second embodiment, the central cone 18 further has a fourth radius R4 which corresponds to a distance between the axis X and a point X4 located on the outer wall of the central cone 18 and which is greater than the first radius RI (see [Fig.3]). The point X4 is located between the point X2 and the point XL. This fourth radius R4 greater than the first radius RI also contributes to reducing the Mach number at the blade root.

[0041] Preferably, the point X4 is the point of the outer wall located between X0 and Y furthest from the X axis. A fourth distance L4 between the point X0 and a projection of the point X4 on the X axis is then such that 0.5 < R4 / L4 < 0.65.

[0042] The central cone thus comprises a first curved zone comprising the point X4 which makes it possible to further reduce the Mach number at the foot of the blade. Preferably, the point X4 is at the top of the first curved zone.

[0043] The central cone may also comprise a fifth radius R5 which corresponds to a distance between the axis X and a point X5 located on the outer wall 19 of the central cone 18, the point X5 being located downstream of the point XL. The fifth radius is then greater than the first radius RL.

[0044] The central cone thus has a second curved zone comprising the point X5 and which is preferably positioned downstream of the trailing edge of the blades 12.

[0045] The central cone may comprise no domed area, the first domed area or the second domed area, or the first domed area and the second domed area.

[0046] Furthermore, the fan may comprise a number of blades 14 typically ranging from 10 to 24.

[0047] According to a possible embodiment, the propulsion system may be a dual-flow turbomachine (as illustrated in [Fig.l]).

Claims

Claims

1. A propulsion system (10), in particular a high bypass ratio, dual-flow ducted propulsion system (10), 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, said blades (14) each having a radial axis Y of pivoting relative to the hub, and a central cone (18) having an outer wall (19) and a free end (20), a projection of the free end (20) on the axis X being positioned at a point X0, in which the central cone (18) has - a first radius RI corresponding to a distance between the axis X and a point of intersection XI between the outer wall (19) of the central cone (18) and the pivot axis Y of a blade (14),- a second radius R2 corresponding to a distance between the X axis and a point X2 of the outer wall (19) of the central cone (18) located between the point XI and the point X0 so that the ratio R2 / R1 is equal to 0.8, the central cone (18) being configured so that a first distance L1 between the point X0 and a projection of the point XI on the X axis is such that 1.5 x RI < L1 < 2.5 x RI, and so that 0.5 x R2 < L1 < 1.5 x R2.,

2. A propulsion system according to claim 1, wherein the central cone (18) is configured such that a second distance L2 between point X0 and a projection of point X2 on the X axis is such that the ratio L2 / L1 has a value ranging from 0.2 to 0.

6.

3. A propulsion system according to claim 1 or 2, wherein the central cone (18) has a third radius R3 corresponding to a distance between the axis X and a point X3 of the outer wall (19) of the central cone (18), the point X3 being located between the point X0 and the point X2 so that the ratio R3 / R1 is equal to 0.3, the outer wall (19) of the central cone (18) having a curvature such that the tangent to the curvature, at the point X3, forms an angle a3 with the axis X greater than or equal to 30° and less than or equal to 70°.

4. Propulsion system according to any one of claims 1 to 3, comprising a fourth radius R4 corresponding to a distance between the axis X and a point X4 located on the outer wall (19) of the central cone (18), the point X4 being located between the point X2 and the point XI, the fourth radius R4 being greater than the first radius RI.

5. A propulsion system according to any one of claims 1 to 4, wherein point X4 is the point on the outer wall located between X0 and Y furthest from the X axis and wherein a fourth distance L4 between point X0 and a projection of point X4 onto the X axis is such that 0.5 < R4 / L4 < 0.

65.

6. Propulsion system according to any one of claims 1 to 5, comprising a fifth radius R5 corresponding to a distance between the axis X and a point X5 located on the outer wall (19) of the central cone (18), the point X5 being located downstream of the point XI, the fifth radius R5 being greater than the first radius RI.

7. Propulsion system according to any one of claims 1 to 6, characterized in that the free end (20) is rounded and has a curvature such that the tangent to the curvature, at point X0, is perpendicular to the X axis.

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

9. A propulsion system according to any one of claims 1 to 8, wherein the fan comprises from 10 to 24 blades.

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

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