TECHNICAL FIELD AND PRIOR ART

The invention relates to a blade structure (or a blade) of a compressor of a turbomachine, of the type suitable for use in an aircraft engine.

Such a compressor comprises a succession of stages arranged in series. Each stage comprises a mobile impeller (rotor), or moving blade, and a stator vane (rectifier).

Each moving blade itself comprises a circular disc on which are fixed the vanes (or blades) and rotates in front of a portion of the stator. It allows to aspirate and accelerate the air flow by bypassing the in relation to the motor axis. The rectifier rectifies the following the flow in the axis and the slow by transforming part of its velocity pressure.

There is shown schematically in Figure 1, a sectional view showing a part of such a compressor. In this figure, one identifies the moving blades 10 and the vanes 20 of the rectifiers. The latter are integral with ferrules 22, 26. The reference 27 denotes a flange for fastening the assembly to a compressor housing.

Each blade 10 is positioned on an inner platform 13 which is extended by a foot 18, itself engaged in a housing of a rotor 25. It is noted that these parts can also be made of a single block, called this set a blisk Monobloc (DAM).

Rotation of the rotor is effected about an axis AA '.

To design the blades 10, 20 of such a compressor HP (high pressure), studies are made in order to improve the aerodynamic performance of the blades, while ensuring a certain mechanical strength.

It is particularly interested in the stack of cups. The tangential stacking law corresponds to the position of the center of gravity of each section the blade in a plane perpendicular to the main radial direction of the blade, relative to a radial reference axis of the blade.

Stacking cups of the blading is an important parameter in this type of study. This variable plays a role, as the aerodynamic point of view of the mechanical point of view. The search for an optimum stacking law is therefore a consistent work in all HP compressor blades design.

It is the problem of optimizing the aerodynamic performance of each vane, in particular defined by the surge margin and yield. It is also desired, in such optimization, ensure or maintain the mechanical strength of each blade.

DISCLOSURE OF INVENTION

The invention first proposes a blade of a compressor, defined in every point of its surface by a boom angle and a dihedral angle, comprising:

- a foot,

- a head, the distance between the foot and the head, measured along an axis, said radial axis perpendicular to an axis of rotation of the compressor being called radial height (h),

- an area between the foot and the head, a first portion has an edge dihedral angle of attack strictly positive, and a second part has an edge dihedral angle strictly negative attack.

The maximum angle range is included, along said radial axis, between r = 0.25 h or 0.3 h or 0.5 h and r = 0.65 h or 0.7H.

A blade shape according to the invention, in particular the choice of a maximum angle range as above, improves the operability of the compressor, without imposing a mechanical stress and / or consumption too important. the aerodynamic performance can optimize (surge margin, yield) without degrading the mechanical strength of the blade.

The angle of the leading edge of the dihedral can be strictly negative head, and strictly positive or strictly negative Length.

If the area near the root of the blade is strictly anhedral angle, the angle Length is for example at most equal to -10 ° or -15 °.

In one embodiment, the first part, strictly dihedral angle, form a gap, or extends, at most, between the foot of the blade and a position r = 0.85H along the axis radial, dihedral angle for example being negative head.

The first part, which has an angle of strictly positive dihedron, may form a gap:

- extending along the radial axis, at most between r = 0, lh and r = 0.85 h, the dihedral angle being, for example negative Length,

- and / or having a length, measured along said radial axis, at least equal to 0.4H or between 0.1 h and 0.60 h.

Preferably, the difference between the dihedral angle measured at the foot of the blade and the dihedral angle measured at the head of the blade is less than 10 °.

The blade as above can:

- be mobile, his foot being intended to be attached to a circular disc of a rotor of said compressor, or the blade part of a blisk,

- or be fixed, forming part of a fixed stator or a variable stator.

The invention also relates to a motor of the type used in aeronautics, comprising a compressor with fixed blades and moving blades, one or more blades being of the type described above.

BREVE DESCRIPTION DES FIGURES

Figure 1 is a diagram of a section of a compressor provided with its blades, fixed and mobile.

Figure 2A is a diagram of a blade, with, in superposition, the positioning of an orthonormal triaxial frame (X, Y, Z).

The 2B and 2C are a blade cutting patterns, with, superimposed, indicating different angles useful for understanding the invention.

Figure 3 illustrates various examples of evolution of a dihedral angle of a blade of the invention.

Figure 4 shows the evolution of a sweep angle as a function of the blade height.

Figures 5A-5C show views of a blade made in accordance with the invention.

Figure 6 illustrates a comparison between the evolution of a dihedral angle of a blade according to the invention and the evolution of a dihedral angle that does not implement the teachings of the present invention;

7 shows a curve of isorégime in the Pi-D field.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

For each vane, there is defined a reference XYZ as shown schematically in Figure 2A: the X axis is the machine axis, oriented from upstream to downstream, and it is parallel to the axis of rotation AA '(see figure 1).

The Z axis is perpendicular to X and sets the altitude z, since the root of the blade (z = 0) to the top of the blade (z = h).

The Y axis is tangential, perpendicular to X and Z.

From there, we define another landmark, or local cylindrical coordinate system (X, R, u), associated with the blade concerned, wherein:

X is always the machine axis, oriented from upstream to downstream,

R is the radial axis, defined as Z, it is perpendicular to X and sets the altitude relative to the root of the blade; it is called as stacking axis,

u is the azimuthal axis oriented from the intrados of the blade to the suction side of the adjacent blade to an engine type SHAR (clockwise oriented backwards), or oriented in the reverse direction for an engine Type shav (oriented clockwise

forward) ; it is perpendicular to X and R.Dans the particular case of the blade shown in Figure 2A, the Cartesian reference frame (X, Y, Z) and the local cylindrical coordinate system (X, R, u) are merged.

Stacking the cut (it is recalled that it is the position of the center of gravity of each section of the blade in a plane parallel to (X, u) and perpendicular to the radial direction R of the main blade , relative to a radial reference axis of the blade) can be defined in different ways:

- the position x G , y G of cuts center of gravity along the axes x and y,

- or by the angles of deflection and dihedral as described for example in the Leroy H. Smith et al. "Sweep and dihedral effects in axial flow turbomachinery," September 63, ASME.

Here we chose the latter definition. arrow and dihedral angles are therefore those defined in the document Leroy H. Smith et al. Cited above. The angles a, r, u defined in this article are the angles X, R, u defined above.

These angles measure the differences between the flow directions and the blades, respectively projecting in a radial and axial plane and an axial plane and tangential to the rotating direction of the machine.

If the flow is purely axial, which is approximately the case in the inlet of the machine, the boom angle expresses the inclination of the blade in the axial direction, and the dihedral angle, the inclination of the blade in the tangential direction. A negative sign of the sweep angle expresses an inclination toward the upstream, and a positive sign, downstream; and a negative dihedral angle expresses an inclination toward the pressure side, and a positive sign, to the upper surface. The inclinations are defined from radial outward direction.

At each of the points on the surface of the blade is associated with a boom angle and a dihedral angle.

Figures 2B and 2C reproduces Figure 4 of this article. They represent sectional views, respectively:

- in the plane R, u (both perpendicular to the axis AA '), a moving blade (Figure 2B),

- in the plane R, X (which contains the axis AA '), a blade (Figure 2C).

Was added, in these figures, the reference numeral 11 which denotes a possible learning curve angles boom and dihedral. In Figure 2C, there are references 13 and 15 respectively denote the part of the blade closest to the foot and the head of the blade. In this figure also shows the leading edge 17 and trailing edge 19 of the blade shown. The reference 30 designates a power line from which an axisymmetric flow area (around the motor axis) is generated.

In addition, it is seen in Figure 2B, the angle η made in the [R; u] plane, in each of its points, the curve 11 with the axis A. It can be considered that it is of the angle at each point of the curve 11, the tangent to this curve 11 with the axis A.

The angle μ (Figure 2C) means, in each point of the curve 11, the angle thereof (or its tangent) in the [X; R] plane with the axis can be considered r.On here that the angles of deflection and the dihedral are those at the leading edge of the blade in question. In this case, curve 11 follows the leading edge of the blade, and is therefore confused with the leading edge 17. Finally, the term V x , V R , V u , the projection on the X axis , R, u, of the velocity vector of the axisymmetric flow on the row of blades in question.

We also define:

tan β = V U / V X

and:

tan F V = R / V x

By following the above notation and in accordance with the teaching of the article by LHSmith, λ the sweep angle is defined by:

and the angle of the dihedron v is defined as:

Exemplary embodiments of a blade according to the invention will be described in conjunction with Figure 3.

In this figure are represented various curves showing examples of changes in the dihedral angle in the leading edge, as defined above, depending on the position along the axis R such that it as defined above.

It will be seen from these figures, that the evolution of the dihedral angle defines a shape, called "bulbée", which includes a portion for which the dihedral angle is strictly positive values ​​and a portion (which may itself comprise two sub-parts) for which the dihedral angle is strictly negative values.

In Figure 3, there are, according to the axis (R-axis):

- a first portion, wherein the dihedral angle is strictly negative; for each of the curves I-IV shown, this corresponds, on the axis of ordinates R, 2 areas, one near the root of the blade, the other close to the tip of the blade,

- and a second portion, wherein the dihedral angle is positive; for each of the curves shown, this corresponds, on the R axis of ordinates, with one zone (or one slot), located remotely from the root of the blade and the tip of the blade.

Specifically, in case examples are illustrated in Figure

3 :

- curve I has an area (or range) of strictly positive dihedral angle which extends along axis A, between approximately 0.35H and 0,72h,

- curve II has an area (or range) of strictly positive dihedral angle which extends along axis A, between approximately 0.15H and 0,47h,

- the curve III has an area (or range) of strictly positive dihedral angle which extends along axis A, between approximately 0.17H and 0,70h,

- the curve IV has an area (or range) of strictly positive dihedral angle which extends along axis A, between approximately 0,43h and 0,72h.

In the, or several, areas other than the strictly dihedral area, the dihedral angle is strictly negative, and it is zero in only two points.

As is understood from the above explanations, the bulbée shape extends here between a first position, called the down position, located close to or on the side of the root of the blade (dimension r = 0 along the axis R ), and a second position, said upper position, located near, or side, of the head of the blade (which has the h dimension along the axis R).

The lower position is disposed between the foot of the blade (position r = 0 along the R-axis) and a position remote from the foot, located about r = 0.25H.

The high position is disposed between the head of the blade (which corresponds to a position remote from the foot by a distance h) and a position remote from the foot about 0.75H. The head of the blade, the dihedral angle is strictly negative.

Preferably, the dihedral angle has a positive value within a range:

- which extends along R, over a length between 0.1 h and 0.6 h,

- but, moreover, is arranged or strictly included within an area (identified by P in Figure 3) of the blade for which r is between 0.1 h and 0.85 h. In other words, the area (or range) to strictly dihedral angle according to R, a lower point located at least r = 0, lh (it may be beyond, for example r = 0.2H or r = 0.3H) and an upper point located at most r = 0.85H (the upper point may be short of 0.85H, for example r = 0,5h or r = 0 7h).

The two conditions above are met for four I-IV curves described above.

It comprises a blade profile according to the invention can be anhedral in the bottom and top, with, for example, a minimum angle, Length (r = 0) and / or head (r = h) less than -10 ° or even -15 °.

In yet another example, the dihedral angle has a positive value between 0.2H and 0.8H, thus over an interval of length 0.6H, which is between 0.1 pm and 0.85 pm or which is strictly included within the range 0.1 hr - 0.85 hr. For the same slot length (0.6h), it may be between 0, lh and 0.7H (which is well understood, too, between 0.1 pm and 0.85 pm).

According to another example, the area or the strictly positive dihedral angle interval extends over a length of 0.4H with a point less than 0.2H and an upper point located at 0.6h, satisfying the two conditions which have been set. For r <0.2H or r> 0.6h, the dihedral angle is strictly negative angle.

Regarding the maximum angle, it can be between approximately,

2.5 ° and 7 ° or 8 °, or even 10 ° or 15 ° or 20 °. Part, or zone, which has a maximum angle, is preferably included in the range (indicated by M in Figure 3) in which r varies approximately r = r = 0.25H to 0.65H or r = 0.7H. In other words, this maximum is preferably between r = r = 0.25H and 0.65H or 0.7H.

Thus, curve I, the maximum is at about, 0.5 h while for curve II, it is, approximately, 0.3H.

And it is seen that the angular difference between Length dihedral angle and head dihedral angle is less than about 10 °. It is less than 2 ° for the curve I, from about 5 ° to 8 ° to the curves II, III and IV.

Finally, the difference between the maximum dihedral angle (positive) and minimum dihedral angle (negative), in the case of four examples I -IV given, substantially between 20 ° and 23 °. In general this difference is less than 20 °.

We now present a variant in which the dihedral angle:

- is positive or slightly positive (e.g. it has a value between 0 ° and 5 °) near or on the side of the root of the blade (dimension r = 0 along the axis

R),

- then it grows to a maximum positive,

- and then decreases to reach a value of zero, and finally, take negative values ​​to the head of the dawn.

There is shown in Figure 3, a curve V gives, according to this embodiment, an example of evolution of the dihedral angle (as already defined above), wherein a distinction is made according to axis A:

- a first portion (comprising one single zone, or only one interval, from the root of the blade), wherein the dihedral angle is positive; this country is identified by P 'in Figure 3,

- and a second portion (comprising one single zone, or one single interval, close to the tip of the blade), wherein the dihedral angle is strictly negative.

A blade profile according to the invention can therefore be dihedral angle Length and negative leads with, for example, a minimum angle, top (r = h) less than -10 ° or even - 15 °.

For this curve V, the strictly dihedral zone extends along the axis R, between 0 and approximately 0,72h; outside this area, the dihedral angle is strictly negative, and it is zero in only 1 point. In the low position, already defined above, the dihedral angle is positive. In the high position, also already defined above, the dihedral angle is strictly negative.

Preferably, according to this embodiment, the dihedral angle has a positive value over an area that extends along R, over a length of at least 0.4 hours but which is disposed (and which may vary ) between at least r = 0 and a maximum of r = 0.85 h (in P 'in Figure 3).

Regarding the maximum angle, it can be between approximately,

3 ° and 20 °.

The area which has a maximum angle is preferably disposed between about r = 0.7 and r = 0.25H h or a more preferably, between 0.5 h and 0.5 h or between 0.7H and 0 , 65h. This arrangement improves the surge margin of optimized floor without degrading performance. Maximum positioned between 0.25H and 0.7H allows to achieve dihedral angles less than 10 ° or even at -15 ° without generating excessive slope of the dihedral curve on the upper part of the blade.

This helps avoid weakening the blade vis-à-vis the mechanical requirements inherent in the design of blades, for example vis-à-vis the modes 2S1

(Stripe) and 1T (Torsion). Maximum positioned between 0.5h and 0.5h or between 0.65 and 0.7H is in most cases the best compromise between the benefits outlined above and the search for improved performance.

Da ns all cases regarding the boom angle, one can follow a law of the type known in the prior art. Another example of a possible law is shown in Figure 4, where it is seen that the sweep angle has a value close to 20 ° at the foot of the blade, initially slightly decreases in a first zone along the z axis, and then follows a substantially linear law, until reaching to about r = 0.7H, an extremum is between -20 ° -25 °. The boom angle then decreases again, gradually as it approaches the tip of the blade.

Figures 5A-5C show views of a blade made in accordance with the invention:

- Figure 5A shows a view of the underside 12 of the blade,

- Figure 5B shows a view of the vane from its leading edge 14,

- Figure 5C represents a view of the blade from its trailing edge 16.

In these figures, the blade is shown mounted on its foot 18; the latter may have a form suitable type of fastener implementation (e.g. hammer-shaped type or foot tree or dovetail). But the invention also applies to a blade or a blisk (DAM) wherein there is no attachment; it also applies to the case of a rectifier, in which case there is no attachment.

6 illustrates the difference between a law of variation of the dihedral angle, which does not implement the teachings of the present invention (curve I) and a law according to the invention (curve II).

With respect to the law of evolution according to the curve I, the law according to the invention shown in this figure, increases the surge margin of a stage of a high pressure compressor by a factor at least equal to 1, 5. The yield (eg polytropic or isentropic efficiency) is not appreciably affected: one can even consider it a bit better (approximately several tenths of a percent; less than 0.8%) by the foot shape of the curve II.

The surge margin of a floor can be defined approximately as follows, from the flow rate D, and Pi, which is the compression ratio, or the total pressure in blade outlet divided by the total inlet pressure blade.

In the plane P, D (Figure 7) defining a curve isorégime, which gives, for a given flow rate, the compression ratio. An example of the evolution of this curve is given in Figure 7.

The surge margin is defined, in turn, as the ratio of:

- the P / D ratio of the nearest point of the pump (7 identified by "P / A PUMPING")

- and Pi / D to the point where the curve intersects the isorégime operating line report (point identified in Figure 7 by "Pi / D LINE OF OPERATION"). The operating line defines all operating points of the engine stabilized in the Pi-rate field in nominal operation.

The above description was made for a blade or a blade, rotating about the axis of the motor, during operation thereof, but it also applies to the form of a vane forming part a fixed stator or a variable stator.

CLAIMS

1. blade (10, 20) of a compressor, which is defined at each point of its surface by a boom angle and a dihedral angle, comprising:

- a foot,

- a head, the distance between the foot and the head, measured along an axis (R), said radial axis perpendicular to an axis of rotation of the compressor being called radial height (h),

- an area between the foot and the head, a first portion has an edge dihedral angle of attack strictly positive, and a second part has an edge dihedral angle strictly negative attack,

- the maximum dihedral angle region being understood, along said radial axis, between r = 0.25 and r = h 0.7 h.

2. A blade according to claim 1, the angle of the leading edge of the dihedron being strictly negative head, and strictly positive or strictly negative Length.

3. A blade according to claim 1 or 2, the angle of the leading edge of the dihedron being strictly negative Length, and less than - 10 °.

4. A blade according to one of claims 1 to 3, the first part, on board dihedral angle strictly positive, forming a gap, or extending at most, between on the one hand, foot the blade (r = 0) or a position located at r = 0, lh, and, secondly, a position r = 0.85H along the radial axis.

5. A blade according to one of claims 1 to 4, the first part, which presents an edge dihedral angle strictly positive, forming a gap having a length, measured along said radial axis, at least equal to 0, 4h and / or between 0.1 h and 0.60 h.

6. A blade according to one of claims 1 to 5, the difference between the angle of leading edge dihedral measured root of the blade and the angle of leading edge dihedral measured at the head of the vane being less than 10 °.

7. A blade according to one of the preceding claims, characterized:

- in that it is mobile, its foot being intended to be fixed to a circular disc of a rotor of said compressor, or the blade part of a blisk,

- or in that it is fixed, forming part of a fixed stator or variable stator.

8. engine of the type used in aeronautics, comprising a compressor provided with vanes (10) and blades (20), at least a portion of the vanes according to one of claims 1 to 7.