EP3676480B1 - Turbomachine fan flow-straightener vane, turbomachine assembly comprising such a vane, and turbomachine equipped with said vane or with said assembly - Google Patents

Description

1. Field of the invention

The present invention relates to the field of turbomachines. It relates to a turbine engine blade and in particular a fan stator blade. The invention also relates to an assembly comprising a nacelle and a fan casing secured to the nacelle and which is equipped with at least one stator vane and a turbomachine equipped with such a vane or such an assembly with a rectifier.

2. State of the art

The natural evolution of multi-flow turbojets having a fan, in particular upstream, is to increase the propulsive efficiency via a reduction in the specific thrust, obtained by decreasing the compression ratio of the fan, which results in an increase in the rate dilution or BPR (for the English designation "Bypass Ratio"), which is the ratio between the mass flow of air through one or several veins surrounding the gas generator by the mass flow of air through the generator of gas, calculated at maximum thrust when the engine is stationary in an international standard atmosphere at sea level.

The increase in the bypass ratio influences the diameter of the turbomachine which is constrained by a minimum ground clearance to be respected due to the integration of the turbomachine most often under the wing of an aircraft. The increase in the bypass ratio takes place primarily on the diameter of the fan. The fan is enveloped by a fan casing which surrounds the fan blades and which is connected to the gas generator by stator vanes known as rectifiers or outlet guide vanes for the English designation of "Outlet Guide". Vanes” (signed OGV). These stator vanes are arranged radially from the casing of the gas generator, downstream of the fan vanes and make it possible to straighten the flow generated by the latter. These blades must be arranged at a predetermined minimum axial distance from the fan blades so as to limit the acoustic interactions responsible for significant noise. The predetermined axial distance between the blades determines the length of the fan casing. Added to this is the fact that the weight of the fan casing and in particular its length impact the drag of the turbomachine.

It is known from the document US-B1-6554564 a turbomachine stator vane arranged downstream of the vanes of a fan. This stator vane has a leading edge with an angle of deflection oriented upstream (along the longitudinal axis of the turbomachine) or a trailing edge with an angle of deflection oriented downstream (along the axis longitudinal of the turbomachine) so that the chord of these stator vanes varies from the root end to the head end. This influences the axial length of the blade and the mass thereof. These stator vanes can also comprise a portion of their body with the leading edge and trailing edge having an angle of deflection oriented in the same direction, either upstream or downstream. However, with respect to these latter examples of stator vanes, the sag angle, formed between two segments of the leading edge or two segments of the trailing edge, forms an obtuse angle or an acute angle. That is, the sag angles of the leading and trailing edges form an abrupt change in direction. there is therefore no curvature between two segments of the leading edge or of the trailing edge. An example of a stator vane illustrated in FIG. 8c of this document has a lower vane portion with an angle of inclination A which is completely opposite to that of the upper vane portion. These sudden changes of direction have the disadvantage of increasing the phenomena of vortices which are also the source of noise.

3. Purpose of the invention

The object of the present invention is in particular to limit the drag of the turbomachine nacelle and to limit the mass of the assembly of propulsion while acting on the acoustic phenomena occurring in the vicinity of a stator vane.

4. Disclosure of Invention

This objective is achieved in accordance with the invention by means of a turbomachine stator blade having a longitudinal axis, the blade comprising a plurality of blade sections stacked radially with respect to the longitudinal axis along of a stacking line between a root end and a tip end, each blade section comprising a lower surface and an upper surface extending axially between an upstream leading edge and a downstream trailing edge and being tangentially opposed, between the leading and trailing edges of each blade section, a chord of profile of substantially constant length being formed between the tip end and the root end, and the stacking line having a curvature in a plane passing substantially through the longitudinal axis and through the stacking line, located in the vicinity of the leading end and oriented from downstream to upstream.

Thus, this solution makes it possible to achieve the aforementioned objective. In particular, the shape of the stator vane with this curvature makes it possible to shorten the length of the nacelle surrounding the fan casing intended to carry this stator vane, which advantageously reduces the drag. It also makes it possible to reduce the noise generated towards the end of the blade tip when the latter is mounted in the nacelle. In particular, the acoustic intensity increases with the proximity between the fan blades and the stator blades. The areas located around 75% of the height of the blade are particularly concerned by these interactions due to the speeds observed and the aerodynamic load involved. The profile of the stator blade thus makes it possible to maintain a minimum axial distance required towards the top of the stator vanes.

According to one characteristic, the curvature of the stacking line is continuous and progressive. Such a configuration reduces the formation of vortices which also generate noise. Indeed, a change abrupt would significantly influence the vortices that may form in the upper part of the dawn and which is a source of noise.

According to one characteristic of the invention, the curvature is located between 50% and 95% of the height of the blade between the root end and the tip end. This configuration makes it possible to act where the acoustic and speed interactions are the highest and where the aerodynamic load comes into play.

According to one characteristic of the invention, the shape of the blade, between 50% and 95% of the height of the blade, is determined by the following relationship: 0.1 < (L2/L1) _{50%H<H <95%H} < 0.5, L2 corresponding to the minimum distance between the leading edge of the blade and a line passing through the root end and the leading end of the blade, L1 corresponding to the length between this same line and the trailing edge of the stator vane and H being the height of the vane. This configuration makes it possible, on the one hand, to limit the maximum angle at the root end of the blade and, on the other hand, to limit the structural stresses. In other words, the curvature of the stator vane is defined between 50% and 95% of its height.

According to another characteristic, the blade has a first root portion whose stacking line extends along a straight line and a second head portion whose stacking line includes the curvature. This configuration thus only modifies the upper part of the stator vane.

According to yet another characteristic, the stacking line extending along a straight line is inclined with respect to the longitudinal axis.

According to yet another characteristic, the leading edge has a concave portion and the trailing edge has a convex portion at the curvature. Thus, the directions of the leading edge and trailing edge of the blade are substantially parallel to the direction of the stack line.

The invention also relates to an assembly comprising a dual-flow turbomachine nacelle extending along a longitudinal axis and a fan casing secured to the nacelle, the fan casing surrounding a fan and delimiting downstream of the fan an annular vein in which circulates an air flow, the fan casing comprising an annular row of stator vanes having any of the aforementioned characteristics arranged downstream of the fan vanes transversely in the annular stream. Such a characteristic makes it possible to reduce the length of the nacelle and to reduce the acoustic criterion in the upper part of the nacelle. In particular, for the same given fan diameter, an acoustic gain of approximately 2 EPNdB (“Effective Perceived Noise” or “level of noise actually perceived, in decibels”) is observed.

According to one characteristic of the invention, the nacelle has a length substantially along the longitudinal axis of between 3000 and 3800 mm.

According to another characteristic, the nacelle has a length substantially along the longitudinal axis and the fan has a diameter, substantially along the radial axis, the ratio of the length of the nacelle to the diameter of the fan being between 1 and 3 In particular, the diameter of the fan is measured at the level of a leading edge, at the level of its fan blade tip.

According to one characteristic, the relative axial distance between a fan blade and a stator blade is determined by the following condition: (d/C) with d being the distance between a trailing edge of the fan and the leading edge of the stator blade, and C being the length of the axial chord of the fan blade, the curvature of the stacking line making it possible to verify the following relationship: (d/C) _{50%H<H<95% H} > (d/C) _100%H , with H the height of the stator vane between the tip end and the root end. (d/C) _50%H<H<95%H is the distance between the trailing edge of the fan and the leading edge of the stator vane divided by the length of the axial chord of the stator vane between 50% and 95% of the stator vane height, and (d/C) _100%H is the distance between the trailing edge of the fan and the leading edge of the split stator vane by the length of the axial chord of the fan blade at the tip of the fan blade rectifier. In particular (d/C) 100%H corresponds to the blade height at the contact between the stator blade and the fan casing.

The invention also relates to an assembly comprising a dual-flow turbomachine nacelle extending along a longitudinal axis and a fan casing secured to the nacelle, the fan casing surrounding a fan and delimiting downstream of the fan an annular vein in which circulates a flow of air, the nacelle comprising an annular row of stator vanes having any of the aforementioned characteristics arranged downstream of the fan vanes transversely in the annular stream and of which an end downstream of the tip end is located downstream of a downstream end of the fan casing. Such a characteristic makes it possible to reduce the length of the nacelle and to reduce the acoustic criterion in the upper part of the nacelle. In particular, for the same given fan diameter, an acoustic gain of approximately 2 EPNdB (“Effective Perceived Noise” or “level of noise actually perceived, in decibels”) is observed.

The invention also relates to a turbomachine comprising at least one stator vane having at least any one of the aforementioned characteristics.

5. Brief description of figures

• La figure 1 représente schématiquement une turbomachine avec une soufflante en amont d'un générateur de gaz et à laquelle s'applique l'invention ;
• La figure 2 illustre de manière schématique en vue de face une aube de turbomachine selon l'invention ;
• La figure 3 représente de manière schématique une section d'aube transversale selon l'invention ;
• Les figures 4 et 5 sont des vues schématiques en coupes axiales et partielles d'une nacelle logeant une soufflante de turbomachine selon l'invention ;
• La figure 6 est une représentation schématique d'un graphique sur lequel est illustrée la variation des angles par rapport à l'axe longitudinal de la turbomachine mesurés au niveau du bord de fuite de l'aube de turbomachine ;
• La figure 7 illustre schématiquement, en coupe axiale et partielle, un autre mode de réalisation de l'invention dans lequel une nacelle enveloppe une soufflante et au moins une aube de redresseur, l'aube de redresseur comprenant une extrémité aval à l'extrémité de tête qui se trouve immédiatement en aval d'une extrémité aval du carter de soufflante ; et
• La figure 8 est une autre représentation schématique d'un graphique reprenant les angles mesurés au niveau du bord de fuite d'aubes de turbomachine et notamment de l'art antérieur par rapport à l'aube de redresseur selon l'invention.

The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly on reading the detailed explanatory description which follows, of embodiments of the invention given as purely illustrative and non-limiting examples, with reference to the appended schematic drawings in which:

• The figure 1 schematically represents a turbomachine with a fan upstream of a gas generator and to which the invention applies;
• The picture 2 schematically illustrates in front view a turbine engine blade according to the invention;
• The picture 3 schematically represents a transverse blade section according to the invention;
• The figures 4 and 5 are schematic views in axial and partial sections of a nacelle housing a turbomachine fan according to the invention;
• The figure 6 is a schematic representation of a graph on which is illustrated the variation of the angles with respect to the longitudinal axis of the turbomachine measured at the level of the trailing edge of the turbomachine blade;
• The figure 7 schematically illustrates, in axial and partial section, another embodiment of the invention in which a nacelle envelops a fan and at least one stator vane, the stator vane comprising a downstream end at the head end which located immediately downstream of a downstream end of the fan casing; and
• The figure 8 is another schematic representation of a graph showing the angles measured at the level of the trailing edge of turbine engine blades and in particular of the prior art with respect to the stator blade according to the invention.

6. Description of embodiments of the invention

The figure 1 illustrates a turbomachine 100 for an aircraft to which the invention applies. This turbomachine 100 is here a turbofan engine which extends along a longitudinal axis X. The turbofan engine generally comprises an external nacelle 101 surrounding a gas generator 102 upstream of which a fan 103 is mounted. , and in general, the terms “upstream” and “downstream” are defined with respect to the circulation of gases in the turbomachine 100. The terms “upper” and “lower” are defined with respect to a radial axis Z perpendicular to the axis X and with regard to the distance from the longitudinal axis X. A transverse axis Y is also perpendicular to the longitudinal axis X and to the radial axis Z. These axes, X, Y, Z form a orthonormal.

The gas generator 102 comprises in this example, from upstream to downstream, a low pressure compressor 104, a high pressure compressor 105, a combustion chamber 106, a high pressure turbine 107 and a low pressure turbine 108. The gas generator 102 is housed in an internal casing 109.

The fan 103 is streamlined here and is also housed in the nacelle 101. In particular, the turbomachine comprises a fan casing 56 which surrounds the fan. On this fan casing 56 is fixed a retention casing 50 which surrounds the plurality of mobile fan blades 51 which extend radially from the fan shaft mounted along the longitudinal axis X. The fan casing 56 and the retention casing 50 are integral with the nacelle 101 which envelops them. The nacelle 101 has a generally cylindrical shape. The fan casing 56 is located downstream of the retention casing 50 ensuring the retention of the fan blades 51.

The fan 103 compresses the air entering the turbomachine 100 which is divided into a hot flow circulating in an annular primary vein V1 which passes through the gas generator 102 and a cold flow circulating in an annular secondary vein V2 around the gas generator 102 In particular, the primary stream V1 and the secondary stream V2 are separated by an annular inter-stream casing 110 arranged between the nacelle 101 and the internal casing 109. In operation, the hot flow circulating in the primary stream V1 is conventionally compressed by compressor stages before entering the combustion chamber. The combustion energy is recovered by turbine stages which drive the compressor stages and the fan. The latter is driven in rotation by a power shaft of the turbomachine via, in the present example, a power transmission mechanism 57 to reduce the speed of rotation of the fan. Such a power transmission mechanism is provided in particular because of the large diameter presented by the fan. The large diameter of the fan makes it possible to increase the dilution rate. The power transmission mechanism 57 includes a reducer, arranged here axially, between a fan shaft integral with the fan and the power shaft of the gas generator 102. The flow of cold air F circulating in the secondary stream V2 is oriented along the longitudinal axis X and participates for its part in providing the thrust for the turbomachine 100.

With reference to figure 1 and 4 , each fan blade 51 has a leading edge 52, upstream and a trailing edge 53, downstream that are axially opposed (along the longitudinal axis X). The fan blades 51 each have a foot 54 located in a hub 30 through which the fan shaft passes and a head 55 facing the retention casing 50. The fan blades 51 have a diameter DF comprised, for example, between 1700 and 2800 mm. The diameter DF is measured at the level of the leading edge 52 and at the level of the tip 55 of the fan blade 51, along the radial axis Z. Preferably, but not limited to, the diameter DF is between 1900 and 2700 mm. As for the nacelle 101, this has an outer diameter DN of between 2000 and 4000 mm for example. Preferably, but not limitatively, the outside diameter DN is between 2400 and 3400 mm.

In the secondary stream V2 is arranged at least one radial stator 1 or stationary vane known by the term fan straightener vane or fan flow guide vane. The stator vane is also known by the acronym OGV for “Outlet Guide Vane” in English and therefore makes it possible to straighten the cold flow generated by the fan 103. In the present invention, the term “fixed vane” or “stator vane”, a vane which is not driven in rotation around the axis X of the turbomachine 100. In other words, this stator vane is distinct from and contrary to a moving or rotor vane of the turbomachine 100. In the present example, a plurality of stator vanes 1 are arranged transversely in the fan nacelle 101 substantially in a plane transverse to the longitudinal axis X. The nacelle 101 then surrounds the stator vanes. To straighten the flow of the fan 103, between ten and fifty stator vanes 1 are distributed circumferentially to form a stator stage. These dawns of rectifier 1 are arranged downstream of the fan 103. In the present example, these are secured to the fan casing 56. These are also regularly distributed around the axis X of the turbomachine.

With reference to figures 2 and 3 , each stator vane 1 comprises a plurality of transverse vane sections 2 stacked in a radial direction (parallel to the radial axis Z) along a stacking line L between a root end 3 and an end of head 4. The stacking line L passes through the center of gravity of each blade section 2 transverse. Each blade section comprises an intrados surface 7 and an extrados surface 8 extending substantially in an axial direction, between a leading edge 5, upstream and a trailing edge 6, downstream. The intrados and extrados surfaces 7, 8 are opposite each other in a tangential direction (parallel to the Y axis). Between the trailing edge 6 and the leading edge 5 extends a chord of profile CA. The blade section 2 comprises a curved transverse profile. The profile chord CA has a substantially constant axial length between the foot end 3 and the head end 4. In other words, the length of the profile chord at the foot end is substantially equal to the length of the profile chord at the head end.

The stacking line L of the blade sections 2 forming the blade has a curvature in the vicinity of the tip end 4 thereof. The stator vane 1 has here substantially a boomerang shape. As illustrated in the picture 2 , the curvature is oriented from downstream to upstream (radially outwards). In particular, the leading edge 5 and the trailing edge 6 follow the curvature movement of the stacking line L. That is to say that the direction of the leading edge 5 and trailing edge 6 are substantially parallel to the direction of the curvature of the stacking line L in the upper part of the blade 1. As we can note on the picture 2 , the curvature is continuous and progressive. That is, there is no sudden change in direction. The curvature of the stacking line L is oriented in a perpendicular plane passing through the longitudinal axis X. The stacking line L is therefore defined in this plane. The curvature is also located towards the tip end 4. This is located between 50% and 95% of the height H of the blade 1 taken between the root end 3 and the tip end 4 of the blade as described later in the description.

Each stator vane 1 is fixed to the internal casing 110 and to the fan casing 56 secured to the nacelle 101. The stator vanes 1 play a structural role, they allow the load to be taken up. With reference to the figure 4 , the root end 3 is connected, in this example, to the inner casing 110 while the head end 4 is connected to the fan casing 56. In the curved part of the blade 1, the leading edge 5 is concave while the trailing edge 6 is convex. We thus observe an axial deviation (or deformation) of the stacking line L. In particular, the blade 1 has a first portion whose stacking line L is substantially straight. This so-called straight stacking line is located in the lower part of the blade 1. The latter has an inclination towards the downstream, in a plane containing the longitudinal axis X, with respect to the axis X. The inclination forms an angle α of between 105° and 145° between the stacking line L and the axis X (the stacking line being oriented downstream).

Likewise, according to figure 4 , a first portion of the trailing edge 6 extends along a straight line forming an angle β1 with the longitudinal axis. This angle β1 is between 90° and 120°, the trailing edge 6 being oriented downstream. This angle β1 varies from the longitudinal axis from upstream to downstream. The blade 1 also has a second portion where the stacking line L has the curvature or a bend. The trailing edge 6 also has a curvature or bend on the second portion of the blade 1. In particular, the curvature of the trailing edge 6, in the upper part of the blade 1, is determined by an angle β1 formed between a straight line tangent T to the trailing edge 6 and the longitudinal axis X. In the present example, the angle β1 varies in the upper part of the blade 1. The upper part of the trailing edge presenting the curvature is located between 50% and 95% of the height H of the blade 1 starting from the root end of the blade. The angle β1 of curvature of the trailing edge 6 is between 75° and 90°, the trailing edge being oriented upstream and the value of 90° not being included. In other words, the angle β1 between the longitudinal axis and the trailing edge 6 is substantially constant between 0 and 50% of the height of the blade. The angle β1 then varies between 50% and 95% of the height of the blade 1. We therefore understand that there is no right angle and therefore no sudden change in direction of the trailing edge. Such a configuration makes it possible, on the one hand, to reduce the bulk and, on the other hand, to keep a predetermined minimum axial distance d close to the initial predetermined minimum axial distance of a conventional stator vane. The minimum axial distance is measured between the trailing edge 53 of the fan blade 51 and the leading edge 5 of the stator blade. Furthermore, the curved shape avoids accentuating the vortex phenomena in the vicinity of the dawn which are responsible for the noise.

The angles β1 presented by the trailing edge 6 with respect to the longitudinal axis are represented on a graph of the figure 6 and some figure 8 in comparison with trailing edge angles of state-of-the-art stator vanes. In this figure, the angles of the trailing edge of the blades of the state of the art present an angle whose value is between 90° and 120° and is constant along the height of the blade (OGV10 and OGV12) , or whose value varies between 90° and 120° between 50% and 95% of the blade height (OGV11), or whose value is between 0 and 90° and is constant along the height of the blade dawn (OGV13). The OGV14 stator vane shown on the figure 8 and which corresponds to the dawn of the prior art US-B1-6554564 which has an angle of sag in the middle part of the height of the blade. The angle value is constant over the first 50% of the blade height from the root tip and also constant but completely opposite over the last 50% of the blade height from the middle part towards the leading end of the blade. We find that there is a break in the two straight lines due to the sudden change in direction. Conversely, the stator vane of the present invention has an angle whose value is constant and between 90° and 120°, between 0 and 50% of the height of the vane, and whose value varies between 75° and 90° between 50% and 95% of the blade height. The line representing the variation of the angle of the blade 1 is continuous. In other terms, there is no break in continuity in the line representing the change in angle.

• le premier domaine de l'aube 1 est : Hauteur=[5% ; P] où la valeur de β1 est supérieure ou égale à 90°, et
• le deuxième domaine de l'aube 1 est : Hauteur=[P ; 95%] où la valeur de β1 est inférieure strictement à 90°.

In particular, it is necessary to distinguish at least two ranges of variation of the angle at the level of the trailing edge of the stator vane according to the invention. According to a mathematical representation with P a point belonging to the curve representing the height H of the stator vane 1 and in particular between 50% and 95% of the height H:

• the first domain of dawn 1 is: Height=[5%; P] where the value of β1 is greater than or equal to 90°, and
• the second domain of blade 1 is: Height=[P; 95%] where the value of β1 is strictly less than 90°.

We can thus see on the figure 4 , that the tip end 4 of the stator vane 1 is connected to the fan casing 56 in an attachment zone more upstream of the attachment zone of a prior art stator vane AR shown in dotted lines . In other words, the tip end 4 of the blade, of the present invention, is offset upstream due to the curvature. This offset and/or the curvature makes it possible to shorten the length, substantially along the longitudinal axis X, of the nacelle 101. The nacelle here has a length LN of between 3000 and 3800 mm taken between an upstream end 20 forming a lip of air inlet and a downstream end 21 forming a nozzle edge. Preferably, but not limitatively, the length LN is between 3100 and 3500 mm. The gain in reduction of the length of the nacelle is comprised, for example, between 5 and 15% compared to a standard turbomachine nacelle without the invention as the latter is shown in dotted lines on the figure 4 .

More precisely, the arrangement of the blade 1 according to the invention allows the length of the nacelle 101 to be reduced without aggravating the acoustic nuisances for the same given fan diameter. The gain in length makes it possible to reduce the aerodynamic drag of the turbomachine and/or the integration of larger surfaces of acoustic panels for equivalent drag as described later in the invention. the acoustic gain is about 2 EPNdB (“Effective Perceived Noise” in English or “level of noise actually perceived, in decibels”).

For the same given fan diameter, and with iso acoustic margin, the ratio of the length of the nacelle to the diameter of the fan (LN/DF) can be between -5% and -15% compared to a turbomachine without the invention, which implies a reduction in the length of the nacelle of between -5% and -15% compared to a turbomachine without the invention. In particular, the LN/DF ratio is for example between 1 and 3. Preferably, but not limitingly, the ratio is between 2.1 and 2.8.

The relative minimum axial distance between the fan blades and the stator vanes is determined by the relationship d/C. d is the predetermined minimum axial distance between the trailing edge 53 of the fan and the leading edge 5 of the stator vane 1. And C is the length of the axial chord of the fan. The axial chord C of the fan is measured between the leading edge 52 and the trailing edge 53 of the fan blade.

The solution can also result in the following condition to be respected: $${\left(\frac{}{\mathrm{<figure-callout\; id="50"\; label="VS"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">VS</figure-callout>}}\right)}_{50\%\mathrm{H}<H<95\%\mathrm{H}}>{\left(\frac{}{\mathrm{VS}}\right)}_{100\%\mathrm{H}}.$$

H corresponds to the outer radius of the stator vane 1 taken between the root end and the tip end of the vane 1. In other words, between 50% and 95% of the height H of the vane, the relative minimum axial distance between the fan 103 and the stator vane 1 is greater than the relative minimum axial distance measured at the leading end of the blade, that is to say for 100% of the height H of the stator vane 1.

Avec $${\left(\frac{\mathrm{d}}{\mathrm{C}}\right)}_{100\%\mathrm{H}}<\mathrm{\Omega }.$$

According to yet another characteristic of the invention, the latter makes it possible to implement the following two conditions: $${\left(\frac{\mathrm{}}{\mathrm{VS}}\right)}_{80\%\mathrm{H}}>\mathrm{<figure-callout\; id="100"\; label="\alpha \; VS"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\alpha </figure-callout>}{\left(\frac{\mathrm{}}{\mathrm{VS}}\right)}_{}{\left(\frac{\mathrm{}}{}\right)}_{100\%\mathrm{H}}.$$

With $${\left(\frac{\mathrm{}}{\mathrm{<figure-callout\; id="100"\; label="VS"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">VS</figure-callout>}}\right)}_{100\%\mathrm{H}}<\mathrm{\Omega }.$$

The parameter α corresponds to an efficiency factor. The parameter α considered to be greater than 1.1 is defined as a condition making it possible to guarantee the effectiveness of the invention. The parameter Ω is a parameter characterizing the condition Ω<3 to constrain the length of the nacelle and maintain the desired performance advantage. In particular, we consider d the distance between the fan blade and the stator blade as a function of height H (d(H)), the percentage height of blade 1 with 0% H (at the root end of blade 1) and 100% H (at the leading end of blade 1). For each distance d considered between 50% and 95% of the height of the blade, this is greater than the distance d located at the leading end of blade 1 (100% H): d(r[ 50%-95%]) > d(100%). This makes it possible to bring the stator blade closer to the fan blade at the level of the root and tip end of the blade 1 without impacting the distance of the blade 1 on the height portion of the blade included between 50% and 95% where the aeroacoustic phenomena are the most intense. In other words, the propagation distance of the fan wake as well as its dissipation are maximized and optimized.

Given that the length of the nacelle after the blades (between the tip end of the blade 1 and the downstream end 21 of the nacelle) is not shortened, it is possible to envisage an acoustic treatment of the nacelle. Such acoustic treatment may include the provision of acoustic panels to further reduce noise. These acoustic panels are advantageously, but not limitatively, arranged on an internal face of the nacelle 101 downstream of the stator vanes 1.

L2 correspond à la distance minimale entre le bord d'attaque 5 de l'aube de redresseur 1 et la ligne A passant par l'extrémité de pied et l'extrémité de tête de l'aube pris au bord d'attaque 5. L1 correspond à la longueur entre cette même ligne A et le bord de fuite 6 de l'aube de redresseur. Les bornes inférieures (0,1) et supérieures (0,5) sont déterminées de façon à limiter l'angle maximal de l'inclinaison de la ligne d'empilement L à l'extrémité de pied 3 de l'aube de redresseur 1 tout en limitant la courbure de la ligne d'empilement. Nous obtenons une forme curviligne permettant de limiter les contraintes structurelles (souplesse de l'aube de redresseur). Cela représente un avantage particulier pour une aube de redresseur peu structurale (qui ne contribue pas à la suspension du moteur).According to an embodiment illustrated in the figure 5 , the shape of the blade 1 is characterized by the following relationship: $$0.1<{\left(\frac{\mathrm{L}2}{\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}1}\right)}_{50\%\mathrm{H}<\mathrm{H}<95\%\mathrm{H}}<0.5.$$

L2 corresponds to the minimum distance between the leading edge 5 of the stator blade 1 and the line A passing through the root end and the leading end of the blade taken at the leading edge 5. L1 corresponds to the length between this same line A and the trailing edge 6 of the stator vane. The lower (0.1) and upper (0.5) limits are determined so as to limit the maximum angle of inclination of the stacking line L at the root end 3 of the stator vane 1 while limiting the curvature of the line stacking. We obtain a curvilinear shape making it possible to limit the structural constraints (flexibility of the stator vane). This is a particular advantage for a low structural stator vane (which does not contribute to engine suspension).

According to yet another embodiment illustrated in the figure 7 , the blade 1 has the same characteristics as that represented on the figures 4 and 5 . The elements described above are designated in the remainder of the description by the same numerical references. The nacelle envelops the blade 1 and the fan. As we can see, the downstream end of the tip end of the blade 1 is located downstream of the downstream end of the fan casing to reduce the mass of the turbomachine. The nacelle is made of lighter materials than the fan casing. We are thus seeking to limit the extension of the fan casing to replace it with the nacelle. The equipment of the nacelle such as a thrust reverser can be integrated further upstream, and in particular closer to the fan, which makes it possible to reduce the axial extension of the nacelle and of the turbomachine. The downstream end of the head end 4 is located opposite the nacelle 101.

Claims (10)

1. A flow-straightener vane (1) of a bypass turbomachine (100) with a longitudinal axis (X), the vane (1) comprising a plurality of vane sections (2) stacked radially with respect to the axis (X) along a stacking line (L) between a root end (3) and a tip end (4), each vane section (2) comprising an pressure-face surface (7) and an suction-face surface (8) extending axially between an upstream leading edge (5) and a downstream trailing edge (6) and being tangentially opposed,
   characterized in that between the leading (5) and trailing (6) edges of each vane section (2) there is formed a profile chord (CA) the length of which is substantially constant between the tip end (4) and the root end (3), and in that the stacking line (L) has a curvature, in a plane passing substantially through the axis (X) and through the stacking line (L), located in the vicinity of the tip end (4) and oriented from downstream to upstream.
2. The vane (1) according to claim 1, characterized in that the curvature of the stacking line (L) is continuous and progressive.
3. The vane (1) according to one of claims 1 and 2, characterized in that the curvature is located between 50% and 95% of the height of the vane (1) between the root end (2) and the tip end (4).
4. The vane (1) according to one of the preceding claims, characterized in that the shape of the vane between 50% and 95% of the height of the vane is determined by the following relationship : 0.1 < (L2/L1) _50%H<H<95%H < 0.5, with L2 corresponding to the minimum distance between the leading edge of the vane and a line (A) passing through the root end and the tip end of the vane, L1 corresponding to the length between this same line (A) and the trailing edge (6) of the vane, and H being the height of the vane.
5. The vane (1) according to one of the preceding claims, characterized in that it has a first root portion whose stacking line (L) extends along a straight line and a second tip portion whose stacking line (L) comprises the curvature.
6. The vane (1) according to any one of the preceding claims, characterized in that the leading edge (5) has a concave portion and the trailing edge (6) has a convex portion at the curvature.
7. An assembly comprising a nacelle (101) of a bypass turbomachine extending along a longitudinal axis (X) and a fan casing (56) secured to the nacelle, the fan casing (56) surrounding a fan (103) and defining downstream of the fan (103) an annular vein (55) in which an air flows circulates, characterised in that the fan casing (56) comprises an annular row of flow-straightener vanes (1) according to any one of claims 1 to 6 arranged downstream of the fan vanes (51) transversely in the annular vein (55).
8. The assembly according to the preceding claim, characterized in that the nacelle (101) has a length (LN) substantially along the longitudinal axis (X) and the fan (103) has a diameter (DF) substantially along the radial axis, the ratio (LN/DF) of the length of the nacelle to the diameter of the fan being between 1 and 3.
9. The assembly according to one of claims 7 and 8, characterized in that the relative axial distance between a fan vane (51) and a flow-straightener vane (1) is determined by the following condition:
   (d/C), where d is the predetermined minimum axial distance between a trailing edge (53) of the fan and the leading edge (5) of the flow-straightener vane (1), and C is the length of the axial chord of the fan vane (103), and in that the curvature of the stacking line (L) is determined by the following relationship: (d/C) _{50% H<H<95% H} > (d/C)_{100% H}, where H is the height of the flow-straightener vane between the tip end (4) and the root end (3).
10. A bypass turbomachine (100), characterized in that it comprises at least one flow-straightener vane according to any one of claims 1 to 6 or an assembly according to any one of claims 7 to 9.

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