Unducted turbine engine comprising stator blades having different chords

Abstract

An aircraft including at least one unducted turbine engine for the propulsion of the aircraft. The turbine engine comprising: a rotor and a stator comprising a plurality of stator blades extending radially with respect to the longitudinal axis, each stator blade being defined, in a plane transverse to the longitudinal axis, by an angular position; and at least one aerodynamic obstruction positioned close to the turbine engine. The stator of the turbine engine comprises stator blades having a first chord, referred to as conventional blades, and at least one stator blade having a second chord larger than the first chord, referred to as the elongate blade, said at least one elongate blade being positioned in an interference angular range defined opposite the aerodynamic obstacle, so as to increase the straightening of the airflow from the rotor in the interference angular range.

Claims

1. An aircraft comprising: at least one unducted turbine engine for propulsion of the aircraft, the turbine engine extending along a longitudinal axis and being configured to accelerate an air flow circulating from upstream to downstream, the turbine engine comprising a rotor and a stator mounted downstream of the rotor, the stator comprising a plurality of stator vanes for straightening the air flow coming from the rotor extending radially with respect to the longitudinal axis and distributed angularly about the longitudinal axis, each of the stator vanes comprising a leading edge and a trailing edge defining between them a chord in a plane of revolution defined with respect to the longitudinal axis, each of the stator vanes being defined, in a plane transverse to the longitudinal axis, by an angular position, and at least one aerodynamic obstacle, positioned close to the turbine engine, the aerodynamic obstacle causing a change in the circulation of the air flow downstream of the stator vanes, wherein the plurality of stator vanes includes conventional vanes each defining a first cord and at least one elongated vane defining a second cord, and wherein the second chord is larger than the first chord, said at least one elongated vane being positioned in an interference angular range defined in relation with the aerodynamic obstacle, so as to increase the straightening of the air flow from the rotor in the interference angular range.

2. The aircraft as claimed in claim 1, further comprising a connecting pylon for connecting the turbine engine to the aircraft, said pylon forming the aerodynamic obstacle.

3. The aircraft according to claim 1, wherein the stator comprises at least two of the elongated vanes positioned within the interference angular range.

4. The aircraft according to claim 1, wherein the angular positions of each the stator vanes are defined in a clockwise direction of rotation over an angular range of 0 to 360, the angular position 0 being defined as a top position relative to a vertical axis, the aerodynamic obstacle extending substantially around an angular position (), the assembly of the stator vanes positioned at the angular position of between 45 and +45 around the angular position () are the elongated vanes.

5. The aircraft according to claim 1, wherein the plurality of stator vanes comprises at least one shortened vane that defines a third chord, the third chord being smaller than the first chord so as to limit a risk of underloading at least one of the stator vanes, said at least one shortened vane is positioned in an angular range diametrically opposed to the interference angular range.

6. The aircraft as claimed in claim 5, wherein the at least one shortened vane is diametrically opposed to the at least one elongated vane.

7. The aircraft according to claim 5, wherein the first chord defines a first length, and the third chord defines a third length, and wherein the third length is equal to 70% to 95% of the first length.

8. The aircraft according to claim 1, wherein the first chord defines a first length and the second chord defines a second length, and wherein the second length is equal to between 105% and 130% of the first length.

9. The aircraft according to claim 1, wherein a chord difference between two stator vanes that are adjacent to one another is less than or equal to 25%.

10. The aircraft according to claim 1, wherein each of the stator vanes defines a maximum thickness in the plane of revolution, a relative thickness of the stator vane corresponding to a ratio of the maximum thickness to the chord, a difference in relative thickness between two of the stator vanes that are adjacent one another having different chords, is less than or equal to 25%.

Description

DESCRIPTION OF DRAWINGS

(1) The invention will be better understood on reading the following description, given by way of example, with reference to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

(2) FIG. 1 is a schematic representation of an aircraft comprising an unducted turbine engine according to one embodiment of the invention and an aerodynamic obstacle.

(3) FIG. 2 is a schematic representation of the unducted turbine engine of FIG. 1 comprising a rotor and a stator.

(4) FIG. 3 is a schematic representation of the stator vanes of FIG. 2, in cross-section in a plane of revolution about a longitudinal axis X.

(5) FIG. 4 is a schematic representation in a plane transverse to the longitudinal axis X, of the vanes of the stator of FIG. 3 in the example of an aerodynamic obstacle positioned at an angular position of 0.

(6) FIG. 5 is a schematic representation of the chord of each vane of the stator in FIG. 3 in the plane of revolution.

(7) FIG. 6 is a graph showing the evolution of the chord of each vane of the rotor in FIG. 3 as a function of their angular position in the transverse plane.

(8) FIG. 7 is a schematic representation of a second example of the distribution of elongated and shortened vanes as a function of their angular position in the case of an aerodynamic obstacle positioned around 270.

(9) It should be noted that the figures set out the invention in detail in order to implement the invention, said figures of course being able to be used to better define the invention if necessary.

DETAILED DESCRIPTION

(10) The invention is described in this document with reference to a turbine engine mounted in an aircraft, but it goes without saying that it can be applied to any type of aircraft.

(11) The aircraft A according to the invention is shown in FIGS. 1 and 2. To this end, with reference to FIG. 1, the aircraft A (in this example an aeroplane) comprises a turbine engine 1 extending longitudinally along an axis X and allowing the aeroplane to be moved by an air flow F entering the turbine engine 1 and circulating from upstream to downstream. Hereafter, the terms upstream and downstream are defined in relation to the longitudinal axis X running from upstream to downstream.

(12) Still referring to the example in FIG. 1, the aircraft A also comprises an aerodynamic obstacle OA close to the turbine engine 1, mounted downstream of the latter. The aerodynamic obstacle OA is positioned at least partly in relation with the turbine engine 1. The expression in relation with means that the aerodynamic obstacle OA and the turbine engine 1 are aligned with respect to the axis X. The term aerodynamic obstacle describes any device or system mounted in the vicinity of the turbine engine 1 and likely to disturb the air flow F coming from the turbine engine 1 and circulating from upstream to downstream. By way of a non-limiting example, such an aerodynamic obstacle OA may be a portion of the fuselage, a wing of the aircraft A or any structural device mounted on the aircraft A. In this document, as shown in FIGS. 1 and 2, the aerodynamic obstacle OA is, for example, a connecting pylon connecting the turbine engine 1 to the aircraft A. This document presents the example of an aerodynamic obstacle OA mounted downstream of the turbine engine 1, however it goes without saying that the aerodynamic obstacle OA could be mounted upstream of the turbine engine 1.

(13) In a known way, with reference to FIG. 2, the turbine engine 1 comprises a primary vein delimited by a casing, designated inter-vein casing 2, and supplied by an upstream fan, designated rotor 3, mounted so as to rotate about the axis X. The rotor 3 allows to accelerate the air flow F from upstream to downstream. In practice, the acceleration of the air flow F allows to generate a thrust force that allows the aircraft A to move.

(14) According to the invention, the turbine engine 1 is unducted, i.e. it has no outer casing. Such a configuration of the turbine engine 1 is known to those person skilled in the art under the generic name of open rotor and will not be described in larger detail in this document.

(15) Still referring to FIG. 2, the turbine engine 1 comprises a stator 4, mounted downstream of the rotor 3 and allowing the air flow F accelerated by the rotor 3 to be straightened. The stator 4 comprises a plurality of stator vanes 5, also referred to as flow straightener, extending radially with respect to the longitudinal axis X between a root 5P connected to the inter-vein casing 2 and a free head 5T. In the example shown, the flow air inlet in the primary vein is located between the rotor 3 and the stator 4.

(16) In this embodiment, the turbine engine 1 comprises only a rotor 3 and a stator 4, to give it a simple, lightweight structure. In addition, the rotor 3/stator 4 pair is mounted upstream of the turbine engine 1 to form a puller type turbine engine. It goes without saying that the rotor 3/stator 4 pair could be mounted downstream of the turbine engine 1 so as to form a pusher type turbine engine.

(17) In a known manner, with reference to FIG. 3, each stator vane 5 comprises a leading edge 5A, corresponding to the end located upstream and first coming into contact with the air flow F, and a trailing edge 5B, located downstream. Each stator vane 5 has a profile that is determined, in cross-section, in a plane of revolution PR about the longitudinal axis X of the turbine engine 1. The plane of revolution PR is determined for a predetermined radial distance. In practice, each stator vane 5 comprises a plurality of characteristic profiles, determined in a plurality of planes of revolution about the longitudinal axis X of the turbine engine, along the length of the turbine engine 1.

(18) In the plane of revolution PR, with reference to FIG. 3, each stator vane 5 has an elongated profile P from the leading edge 5A to the trailing edge 5B. In a known way, the profile P is defined according to a plurality of geometric characteristics such as a length and a thickness. In this example, the profile P of a stator vane 5 is characterised by the distance between the leading edge 5A and the trailing edge 5B, designated chord C, and the maximum thickness Ep. In this example, the maximum thickness Ep is defined orthogonally to the mean line direction of the vane LMA. As illustrated in FIG. 3, this mean line LMA (also known to the person skilled in the art as the skeleton line or camber line) connects the leading edge 5A to the trailing edge 5B and is equidistant from the pressure side and from the suction side. Similarly, still with reference to FIG. 3, a stator vane 5 is characterised by the inclination of its chord C with respect to the longitudinal axis X of the turbine engine 1. Subsequently, for a profile P, a pitch angle is defined between the longitudinal axis X and the chord C. Finally, a stator 4 is characterised by its pitch PAS corresponding to the distance between the trailing edges 5B of two adjacent stator vanes 5 as illustrated in FIG. 3.

(19) With reference to FIG. 4, the stator vanes 5 are angularly distributed around the longitudinal axis X in a plane PT transverse to the longitudinal axis X, shown in FIG. 2. Each stator vane 5 is defined, in the transverse plane PT, by an angular position , within an angular range extending between 0 and 360. In this example, the angular position 0 is defined as the top position relative to a vertical axis Z extending from bottom to top, as shown in FIG. 4. Similarly, the angular positions are defined as increasing between 0 and 360 in a clockwise direction of rotation about the longitudinal axis X from the position 0.

(20) With reference to FIGS. 4 and 5, the stator 4 comprises, in the transverse plane PT, a plurality of stator vanes 5 having a first chord C1. Such stator vanes 5 are referred to as conventional vanes 51. The first chord C1 is preferably between 200 and 600 mm.

(21) The stator 4 of the turbine engine 1 according to the invention further comprises a plurality of stator vanes 5 having a second chord C2, the second chord C2 being larger than the first chord C1 in the transverse plane PT, as shown in FIG. 5. Such stator vanes 5 are referred to as elongated vanes 52. Preferably, the second elongated chord C2 has a length of between 105% and 130% of the length of the first chord C1. Even more preferably, the length of the elongated second chord C2 is between 105% and 115% of the length of the first chord C1. In this example, the stator 4 comprises a plurality of elongated vanes 52, although it goes without saying that the stator 4 could just as easily comprise a single elongated vane 52.

(22) According to the invention, as shown in FIG. 4, each elongated vane 52 is angularly positioned at least partly within an interference angular range PAI, defined in relation with the aerodynamic obstacle OA. In other words, the aerodynamic obstacle OA and the elongated vanes 52 are aligned, at least partially, with respect to the longitudinal axis X. The elongated vanes 52 increase the straightening of the air flow from the rotor 3 in the interference angular range PAI in relation with the aerodynamic obstacle OA, so as to limit disturbances to the air flow F downstream of the turbine engine 1 in the axis of the aerodynamic obstacle OA. The geometry of each stator vane 5 is thus adapted according to its load. A longer chord C allows to avoid the overloading of a stator vane 5 which would be particularly stressed.

(23) In other words, preferably no elongated vane 52 is positioned entirely within an angular range outside the interference angular range PAI. When a vane is not facing the aerodynamic obstacle OA, it is not subjected to larger disturbances and the air flow does not have to be straightened to a larger extent.

(24) In this example shown in FIG. 4, the aerodynamic obstacle OA, i.e. the connecting pylon, extends vertically and is attached to an upper portion of the turbine engine 1 along a vertical axis Z, i.e. at an angular position of 0.

(25) In this example, as shown in FIG. 4, the stator 4 comprises three elongated vanes 52 in the interference angular range PAI, which are either entirely or partially in relation with the aerodynamic obstacle OA.

(26) This document presents the example of a stator 4 comprising three elongated vanes 52, however it goes without saying that the stator 4 could just as easily comprise a different number of elongated vanes 52. In other words, it goes without saying that the interference range PAI could just as easily comprise a single elongated vane 52, two elongated vanes 52 or a number larger than three elongated vanes 52. It also goes without saying that the interference range PAI could comprise both conventional vanes 51 and elongated vanes 52.

(27) By way of example, the stator 4 comprising ten stator vanes 5, angularly distributed around the longitudinal axis X, the elongated vanes 52 corresponding to the stator vanes 5 in relation with the aerodynamic obstacle OA, cover an angular range of between 315 and 45 in the clockwise direction of rotation as illustrated in FIG. 4.

(28) Preferably, the stator 4 of the turbine engine 1 also comprises a plurality of stator vanes 5 having a third chord C3, the third chord C3 being smaller than the first chord C1 in the transverse plane PT, as shown in FIG. 5. Such stator vanes 5 are referred to as shortened vanes 53. Preferably, the shortened third chord C3 has a length of between 70% and 95% of the length of the first chord C1. Even more preferably, the length of the shortened third chord C3 is between 85% and 95% of the length of the first chord C1.

(29) In this example, with reference to FIG. 4, each shortened vane 53 is angularly positioned, in the transverse plane PT, so as to belong to an angular range diametrically opposed to the interference angular range PAI. In particular, in this example, each shortened vane 53 is diametrically opposed to an elongated vane 52. In one embodiment, the stator 4 comprises a shortened vane 53 for each elongated vane 52. The shortened vanes 53 allow to balance the assembly of the stator 4 while limiting the risk of underloading a stator vane 5 which would be particularly less stressed. This document presents the example of a shortened vane 53 positioned diametrically opposite each elongated vane 52, however it goes without saying that the stator 4 could also comprise one (or more) shortened vane 53 which would not be diametrically opposite with an elongated vane 52. In particular, in the case of a stator 4 comprising an odd number of vanes, no diametrically opposed positioning would be achieved.

(30) Preferably, the interference angular range PA1 has no shortened vane 53, so as to avoid the presence in the interference angular range PAI of a stator vane 5 which would be overloaded by an air flow disturbed by the presence of the aerodynamic obstacle OA. In other words, each stator vane 5 positioned in the interference angular range PAI has a chord at least equal to the chord of a conventional vane 51 and the assembly of the shortened vanes 53 is positioned outside the interference angular range PAI.

(31) Even more preferably, each vane positioned outside the interference angular range PAI has a chord less than or equal to the chord of a conventional vane 51. In other words, the assembly of the stator vanes 5 positioned outside the interference angular range PAI are conventional vanes 51 or shortened vanes 53. In other words, no elongated vane 52 is positioned outside the interference angular range PAI.

(32) In this example, as shown in FIG. 4, the stator 4 comprises, in the angular range diametrically opposite with the interference angular range PAI, three shortened vanes 53, each positioned diametrically opposite one of the three elongated vanes 52.

(33) This document presents the example of a stator 4 comprising three shortened vanes 53, since it comprises three elongated vanes 52. However, it goes without saying that the stator 4 could just as easily comprise a different number of shortened vanes 53, for example a single shortened vane 53, two shortened vanes 53 or a number larger than three shortened vanes 53.

(34) In one embodiment, the number of elongated vanes 52 represents less than 50% of the total number of stator vanes 5, in the same transverse plane. Preferably, the number of elongated vanes 52 represents less than 40% of the total number of stator vanes 5, in the same transverse plane, preferably less than 30%, even more preferably less than 20% of the total number of stator vanes 5 in the same transverse plane. In this way, only the stator vanes 5 present at least partially in relation with the aerodynamic obstacle OA are elongated vanes 52, which means that the chord of a stator vane 5 is not lengthened unnecessarily,

(35) By way of example, as illustrated in FIG. 4, the stator 4 comprises ten stator vanes 5 angularly distributed around the longitudinal axis X, the elongated vanes 52 corresponding to the stator vanes 5 positioned in an angular range between 315 and 45 in the clockwise direction of rotation, the shortened vanes 53 cover an angular range between 135 and 225 in the clockwise direction of rotation. 5 FIG. 6 is a graph showing the change in the chord C1, C2, C3 of each stator vane 5 as a function of its angular position , in an example of embodiment. In summary, in this example, over the angular range from 0 to 360: each stator vane 5 whose angular position is between 0 and 45 is an elongated vane 52, each stator vane 5 whose angular position is between 45 and 135 is a conventional vane 51, each stator vane 5 whose angular position is between 135 and 225 is a shortened vane 53, each stator vane 5 whose angular position is between 225 and 315 is a conventional vane 51, and each stator vane 5 whose angular position is between 315 and 360 (i.e.) 0 is an elongated vane 52.

(36) This document presents the example in which each angular range comprises similar conventional vanes 51, elongated vanes 52 or shortened vanes 53, however it goes without saying that each angular range, as defined above, could just as easily comprise a combination of conventional vanes 51 and elongated vanes 52 or a combination of conventional vanes 51 and shortened vanes 53.

(37) Preferably, the chord difference C1, C2, C3 between two adjacent stator vanes 5 is less than 50%, and even more preferably less than 25%. This characteristic means that the performance of the turbine engine 1, and in particular the local performance of the flow in the vicinity of each stator vane 5, is not affected.

(38) This document presents the example of an aerodynamic obstacle OA extending vertically and being attached to an upper portion of the turbine engine 1, i.e. extending around the angular position 0. However, it goes without saying that the aerodynamic obstacle OA could just as easily extend differently in relation to the turbine engine 1, i.e. extend around an angular position different from 0, for example to an angular position of the order of 270 (shown in FIG. 7).

(39) By way of example, as shown in FIG. 7, in the case of a turbine engine 1 installed under a right wing of the aircraft A for example (the term right being understood along a transverse axis Y, in a front view upstream of the aircraft A), the aerodynamic obstacle OA may correspond for example to the fuselage of the aircraft, present to the left of the turbine engine 1. In this case, the interference angular range PAI is, for example, between 225 and 315 in the clockwise direction of rotation.

(40) So in this example, over the angular range from 0 to 360: each stator vane 5 whose angular position is between 0 and 45 is a conventional vane 51, each stator vane 5 whose angular position is between 45 and 135 is a shortened vane 53, each stator vane 5 whose angular position is between 135 and 225 is a conventional vane 51, each stator vane 5 whose angular position is between 225 and 315 is an elongated vane 52, and each stator vane 5 whose angular position is between 315 and 360 (i.e.) 0 is a conventional vane 51.

(41) This document presents F example of angular ranges comprising vanes of the same type (conventional 51, elongated 52 or shortened 53), however it goes without saying that the angular range between 45 and 135 could comprise both one or more conventional vanes 51 and one or more shortened vanes 53 and the angular range between 225 and 315 could comprise both one or more conventional vanes 51 and one or more elongated vanes 52.

(42) Similarly, this document presents the example of angular ranges each comprising stator vanes 5 having the same chord C1, C2, C3, although it goes without saying that the stator 4 could just as easily comprise a plurality of stator vanes 5 each having an elongated or shortened chord C of its own. In such a configuration, the stator 4 would comprise as many values of chords C as there are stator vanes 5. Such a stator 4 would offer optimum performance because each stator vane 5 would have a chord C adapted to its own environment.

(43) Preferably, the pitch PAS (shown in FIG. 3) between two stator vanes 5 is independent of the chord C, so if the pitch PAS is the same but the chord C is different between two adjacent stator vanes 5, then the relative pitch (i.e. the ratio of the pitch PAS to the chord C varies with the chord C) is different between two stator vanes 5. Alternatively, the pitch PAS between two stator vanes 5 with different chords C could be different.

(44) Preferably, the maximum thickness Ep (shown in FIG. 3) of the stator vanes 5 is different depending on whether it is a conventional vane 51, an elongated vane 52 or a shortened vane 53 so as to present a constant relative thickness (i.e. a ratio between the maximum thickness Ep and the chord C of the stator vane 5). This characteristic guarantees the mechanical characteristics of each stator vane 5 (flexibility, natural frequency, etc.). Alternatively, the conventional vanes 51, the elongated vanes 52 and the shortened vanes 53 have the same maximum thickness Ep so as to limit the variation in cross-section between two adjacent stator vanes 5, thereby limiting the local flow disturbances.

(45) Optionally, the variation in chord C between two stator vanes 5 can be coupled to a variation in the pitch angle (shown in FIG. 3) of the stator vanes 5 as described above. Advantageously, such a modification allows to limit the aerodynamic distortion of an airflow applied from downstream to upstream of the turbine engine 1 on the wheel of the stator 4, for example when the aircraft is in flight.

(46) The variable chords on the stator of an unducted turbine engine allow to take advantage of the effects of an aerodynamic obstacle in the vicinity of the turbine engine and its outgoing air flow. Lengthening the chord of the vanes in relation with this aerodynamic obstacle significantly allows to improve the performance of each stator vane, so that the vanes facing the aerodynamic obstacle are more heavily loaded, thereby improving the straightening of the air flow from the rotor and therefore the thrust of the aircraft. A distribution of the conventional vanes, elongated vanes and shortened vanes by angular ranges allows to limit the industrial constraints of stator production and assembly by limiting the number of vanes with different chords, while allowing the loading of each vane to be adapted to its direct environment.

(47) This document describes an aircraft in which a turbine engine comprises stator vanes whose chord is lengthened to adapt the vanes to a larger load due to the presence of an aerodynamic obstacle, but it goes without saying that the chord of the vanes could just as easily be adapted as a function of the load seen by the vanes during the take-off or landing phase or as a function of the load seen by the vanes positioned opposite the rising blades of the rotor during their rotation.