Central fan cone with optimized dimensions for a propulsion system

Abstract

The invention relates to a propulsion system (10) comprising a fan (12) rotationally movable about an axis X, the fan having 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 Rmax1 defined as a distance between the axis X and a first point Xmax1 of the outer wall (19) of the central cone (18), Xmax1 being one of two points of the wall of the central cone that are farthest away from the axis X, a projection of the point Xmax1 onto the axis X being positioned at a point Pmax1, - 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 that are farthest away from the axis X and being downstream of the point Xmax1, a projection of the point Xmax2 onto the axis X being positioned at a point Pmax2, - a first minimum radius Rmin1 defined as a distance between the axis X and a third point Xmin1 of the outer wall (19) of the central cone (18), Xmin1 being that point located between Xmax1 and Xmax2 that is closest to the axis X, a projection of the point Xmin1 onto the axis X being positioned at a point Pmin1, - the points Pmax1 and Pmin1 being spaced apart by a distance L1 and the points Pmin1 and Pmax2 being spaced apart by a distance L2, the central cone (18) being configured such that the ratio (Rmax1 – Rmin1) / L1 is less than 0.2 and the ratio (Rmax2 – Rmin1) / L2 is less than 0.3. Figure for the abstract: Fig. 2

Description

[0001] CENTRAL FAN CONE WITH OPTIMIZED DIMENSIONS FOR PROPULSION SYSTEM

[0002] FIELD OF THE INVENTION

[0003] 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 bypass ratio.

[0004] The invention also relates to an aircraft comprising such a propulsion system.

[0005] TECHNOLOGICAL BACKGROUND

[0006] 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.

[0007] A propulsion system, also called a turbomachine, typically comprises a fan with blades extending 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 attached to a rotor enabling the fan to rotate during operation of the propulsion system.

[0008] Furthermore, a central cone surrounding the hub emerges from the central part 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 X axis and normal to the X axis. Furthermore, the central cone has a symmetry of revolution around the X axis and has a section which gradually decreases from the fan towards the free end.

[0009] 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 a secondary air flow which bypasses the primary body, the primary and secondary air flows enabling the propulsion of the aircraft.

[0010] 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 high-pressure turbine and a low-pressure turbine. The high-pressure compressor is rotated by the high-pressure turbine via a high-pressure shaft. The fan and the low-pressure compressor are rotated by the low-pressure turbine via a low-pressure shaft.

[0011] One way to improve 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 achieve this, it is possible to increase the bypass 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 bypass ratio.

[0012] One of the disadvantages of these high bypass ratio propulsion systems is that the Mach number of the flow at the blade roots is more dependent on the flight Mach number than in a conventional propulsion system, particularly in a low bypass ratio system. This high Mach number can cause problems, particularly when changing the fan blade pitch. In addition, the central cone is subject to more distortion due to the aircraft's angle of attack, which can pose a risk of flow separation.

[0013] STATEMENT OF THE INVENTION

[0014] One objective of the invention is to prevent the Mach number from being so 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 airflow on the central cone and at the blade root, regardless of the aircraft speed and its angle of attack.

[0015] To this end, according to a first aspect of the invention, a propulsion system is proposed, in particular a high bypass 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, and a central cone having an outer wall and a free end, in which the central cone has a first maximum radius Rmaxl defined as a distance between the axis X and a first point Xmaxl of the outer wall of the central cone, 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 of the central cone,Xmax2 being the other of the two points on 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 onto 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 on the outer wall of the central cone, Xminl being the point located between Xmaxl and Xmax2, closest to the X axis, a projection of the point Xminl onto the X axis being positioned at a point Pminl , the points Pmaxl and Pminl being spaced apart by a distance L1 and the points Pminl and Pmax2 being spaced apart by a distance L2, the central cone being configured so that the ratio (Rmaxl - Rminl ) / L1 is less than 0.2 and the ratio (Rmax2 - Rminl ) / L2 is less than 0.3.,

[0016] The propulsion system according to this first aspect of the invention has a central cone having, from upstream to downstream, a protuberance followed downstream by a concave portion which allows the air flow to slow down in the concave portion. This 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.

[0017] 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.

[0018] 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 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 of the central cone, 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;a point of intersection X1 between the leading edge of a blade and the outer wall projects onto the X axis at a point P1, a point of intersection X2 between the trailing edge of a blade and the outer wall projects onto the X axis at a point P2, the blade being in the cruising position, the points P1 and P2 being spaced apart by a distance L4, the central cone being configured so that -0.25 x L4 < Xminl -P1 < 0.25 x L4; the point Xmax2 is located downstream of the point X2; the point Xmaxl is positioned at a distance L from the free end of the central cone (18) and in which 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; the propulsion system may have a bypass ratio greater than or equal to 10; the fan has at least eight blades, for example between 14 and 24 blades;and the propulsion system is 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.;

[0019] 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.

[0020] BRIEF DESCRIPTION OF THE FIGURES

[0021] Other characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

[0022] Figure 1 schematically represents a complete and sectional view of a propulsion system; and Figure 2 schematically represents a partial and sectional view of a fan and its central cone according to an embodiment of the invention.

[0023] DETAILED DESCRIPTION OF AN EXAMPLE OF IMPLEMENTATION

[0024] The propulsion system 10 shown in Figure 1 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.

[0025] 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 part of the air flow F1 will pass to generate thrust.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The fan 12 comprises a hub (not shown) which is driven in rotation around the axis X by the low pressure turbine 38, 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.

[0032] The propulsion system 10 also includes a set of fixed blades 46 used to guide the secondary air flow FB and the setting of which can possibly be modified according to the flight phases using a pitch change mechanism.

[0033] 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), that is to say a bypass ratio in particular greater than or equal to 10 and less than or equal to 80, and having a low fan compression ratio, in particular ranging from 1.05 to 1.45.

[0034] Depending on the flight phases, 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.

[0035] 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.

[0036] 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.

[0037] The central cone 18 also has a second maximum radius Rmax2 defined as a distance between the X axis 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 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. 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 onto the X axis is positioned at a point Pminl.

[0038] 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 ) / L1 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 protuberance followed downstream by a concave portion which allows the air flow to slow down in the concave portion. This 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.

[0040] 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 and the central cone is configured so that the ratio (Rmax2- Rmin2) / L3 is between 0.4 and 0.6. Thus, the central cone has a concave part downstream of the point Xmaxl allowing a slowing of the air flow and therefore a reduction of the Mach number in this zone.

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

[0042] In particular, when the blade is in the cruising position, a point of intersection X1 between the leading edge of a blade and the outer wall 19 projects onto the X axis at a point P1, and 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 P1 and P2 are spaced apart by a distance L4 and the central cone 18 is configured such that -0.25 x L4 < Xminl -P1 < 0.25 x L4. Preferably, the point Xmax2 is located downstream of the point X2 and the trailing edge of the blades is thus also positioned in the concave portion.

[0043] Preferably, the shape of the central cone 18 is 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, 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.

[0044] The point Xmaxl 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.

[0045] 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 root of the blades. Indeed, the elongated shape allows the air flow to be at its maximum acceleration sufficiently upstream of the root of the blades so that the Mach number at the root of the blades is low. The Mach number at the root of the blade is thus sufficiently low so as not to hinder the rotational movement of the blades during changes in pitch.

[0046] Furthermore, the fan may comprise a number of blades 14 typically ranging from 8 to 24, for example between 12 and 24 blades.

[0047] According to a possible embodiment, the propulsion system may comprise a dual-flow (as illustrated in FIG. 1) or triple-flow turbomachine, said propulsion system being unducted and the fan blades being variable-pitch.

Claims

CLAIMS 1. 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 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 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 points Pmaxl and Pminl being spaced apart by a distance L1 and the points Pminl and Pmax2 being spaced apart by a distance L2, the central cone (18) being configured so that the ratio (Rmaxl - Rminl ) / L1 is less than 0.2 and the ratio (Rmax2 - Rminl ) / L2 is less than 0.

3.

2. Propulsion system according to claim 1, in which the central cone has a second minimum radius Rmin2 less than Rmax2, Rmin2 corresponding to a distance between the axis X 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 axis X being positioned at a point Pmin2 spaced from the point Pmax2 of 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.

3. Propulsion system according to claim 1 or 2, in which a point of intersection X1 between the leading edge of a blade and the outer wall (19) projects onto the X axis at a point P1, 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 blade being in cruising position, the points P1 and P2 being spaced apart by a distance L4, the central cone (18) being configured so that -0.25 x L4 < Xmin1 -P1 < 0.25 x L4.

4. Propulsion system according to claim 3, in which the point Xmax2 is located downstream of the point X2.

5. Propulsion system according to any one of the preceding claims, in which the point Xmaxl is positioned at a distance L from the free end of the central cone (18) and in which 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.

6. Propulsion system according to any one of claims 1 to 5, characterized in that it has a dilution ratio greater than or equal to 10.

7. Propulsion system according to any one of claims 1 to 6, in which the fan comprises at least eight blades (14), for example ranging from 12 to 24 blades.

8. Propulsion system according to any one of claims 1 to 7, 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.

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

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