Leading edge profile of vanes

Abstract

A vane configured to be placed with a plurality of identical vanes so as to form a vane wheel for an aeroengine, the vane wheel defining an axis, the vane having an airfoil presenting a leading edge and a trailing edge, the leading-edge curve describing the shape of the leading edge of the airfoil in a view perpendicular to the airfoil presenting at least one leading-edge undulation, said at least one leading-edge undulation extending over less than 30% of a length of the airfoil from the first end of the airfoil.

Claims

1. A vane configured to be placed with a plurality of identical vanes so as to form a vane wheel for an aeroengine, the vane comprising a root and a tip at its ends, the vane wheel defining an axis, the vane comprising an airfoil presenting a leading edge and a trailing edge, a leading-edge curve describing the shape of the leading edge of the airfoil in a view perpendicular to the airfoil presenting at least one leading-edge undulation, said at least one leading-edge undulation extending over less than 30% of a length of the airfoil from an airfoil root and at least one leading-edge undulation extending from an airfoil tip over less than 30% of the length of the airfoil, the leading-edge curve being monotonic over the range going from 30% to 70% of the length of the airfoil, and an angle of attack being an angle between a tangent to a camber line at the leading edge of the airfoil and the axis of the vane wheel in a view in a longitudinal direction of the airfoil, an angle-of-attack curve describing a variation of the angle of attack along the airfoil presents at least one angle-of-attack undulation extending over less than one third of the length of the airfoil from the airfoil root, and the angle-of-attack curve presenting at least one angle-of-attack undulation extending from the airfoil tip over less than one-third of the length of the airfoil; wherein, for an undulation being a curve portion situated between two minimums and including a single maximum, at least one maximum included in an undulation of the leading-edge curve is arranged substantially at the same position in the longitudinal direction of the airfoil as a minimum defining an angle-of-attack undulation.

2. The vane according to claim 1, wherein the angle-of-attack leading edge curve presents two or three angle-of-attack leading edge undulations extending from the airfoil root over less than one-third of the length of the airfoil, and/or two or three angle-of-attack leading edge undulations extending from the airfoil tip over less than one-third of the length of the airfoil.

3. The vane according to claim 1, wherein the angle-of-attack curve presents two or three angle-of-attack undulations extending from the airfoil root over less than one-third of the length of the airfoil, and/or two or three angle-of-attack undulations extending from the airfoil tip over less than one-third of the length of the airfoil.

4. A vane wheel comprising a plurality of vanes according to claim 1.

5. A vane configured to be placed with a plurality of identical vanes so as to form a vane wheel for an aeroengine, the vane comprising a root and a tip at its ends, the vane wheel defining an axis, the vane comprising an airfoil presenting a leading edge and a trailing edge, a leading-edge curve describing the shape of the leading edge of the airfoil in a view perpendicular to the airfoil presenting at least one leading-edge undulation, said at least one leading-edge undulation extending over less than 30% of a length of the airfoil from an airfoil root and at least one leading-edge undulation extending from an airfoil tip over less than 30% of the length of the airfoil, the leading-edge curve being monotonic over the range going from 30% to 70% of the length of the airfoil, and an angle of attack being an angle between a tangent to a camber line at the leading edge of the airfoil and the axis of the vane wheel in a view in a longitudinal direction of the airfoil, an angle-of-attack curve describing a variation of the angle of attack along the airfoil presents at least one angle-of-attack undulation extending over less than one third of the length of the airfoil from the airfoil root, and the angle-of-attack curve presenting at least one angle-of-attack undulation extending from the airfoil tip over less than one-third of the length of the airfoil; wherein, for an undulation being a curve portion situated between two minimums and including a single maximum, at least one maximum of an undulation of the leading-edge curve lies closer, in the longitudinal direction of the airfoil, to a minimum of an undulation of the angle-of-attack curve than to a maximum of the undulation of the an angle-of-attack curve.

6. The vane according to claim 5, wherein the angle-of-attack leading edge curve presents two or three angle-of-attack leading edge undulations extending from the airfoil root over less than one-third of the length of the airfoil, and/or two or three angle-of-attack leading edge undulations extending from the airfoil tip over less than one-third of the length of the airfoil.

7. The vane according to claim 5, wherein the angle-of-attack curve presents two or three angle-of-attack undulations extending from the airfoil root over less than one-third of the length of the airfoil, and/or two or three angle-of-attack undulations extending from the airfoil tip over less than one-third of the length of the airfoil.

8. The vane according to claim 7, wherein at least one maximum included in an undulation of the leading-edge curve is arranged substantially at the same position in the longitudinal direction of the airfoil as a minimum defining an angle-of-attack undulation.

9. A vane wheel comprising a plurality of vanes according to claim 5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages can be better understood on reading the following detailed description of various embodiments of the invention given as non-limiting examples. The description refers to the accompanying sheets of figures, in which:

(2) FIG. 1 is a diagram of an aeroengine vane wheel;

(3) FIG. 2 is a diagram showing recirculation lines on a vane of the FIG. 1 vane wheel;

(4) FIG. 3 is a section view of the FIG. 2 vane;

(5) FIG. 4 shows the profile of the leading edge of a vane in an embodiment of the invention; and

(6) FIG. 5 shows the variation in leading edge and angle-of-attack curves in a second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(7) FIG. 1 shows a vane wheel 1 constituting a stage of an axial compressor of an aeroengine (not shown) comprising a plurality of rotor stages and a plurality of stator stages arranged in alternation along a shaft defining the axis A of the compressor. The vane wheel 1 (or nozzle) is a stator stage of the compressor, having a plurality of vanes. The stator may be invariable, the vanes being invariable relative to the casing of the compressor, or it may be a variable pitch stator, with vanes that can pivot about their longitudinal directions (corresponding to radial directions of the stator). Arrow F shows the flow direction of air relative to the vane wheel 1.

(8) In the description below, the terms “upstream” and “downstream” should be understood relative to the flow direction of air. The direction z designates a direction in which an airfoil 10 extends radially relative to the vane wheel 1, between its airfoil root 12 and its airfoil tip 14. Thus, terms involving the “height” of the airfoil or “along” the airfoil should be understood as being along this direction z. The direction y designates a direction perpendicular to the direction z, in which an airfoil 10 extends between its leading edge 10a and its trailing edge 10b. In other words, the direction y is parallel to the chord 30 of the airfoil 10. The direction x is the direction perpendicular to the directions y and z, and generally represents the thickness of the airfoil 10.

(9) FIG. 2 is a fragmentary view of a vane of the vane wheel 1 (the tip of the vane is not shown). Each vane comprises an airfoil 10 with a leading edge 10a, a trailing edge 10b, an airfoil root 12, an airfoil tip, and a suction side surface 16. The increase in static pressure on going through the vane wheel 1 can lead to an adverse pressure gradient opposing the flow direction, as represented by arrow R in FIG. 2. At the airfoil root 12, these adverse pressure gradients can give rise to separations 18 comprising radial separations 18r and/or tangential separations 18t of the flow over the suction side 16 of the airfoil 10, that can disturb the flow through the compressor and thereby degrade its performance.

(10) FIG. 3 is a section view of the airfoil 10, in a plane parallel to the plane x-y. In this view, the (mean) camber line 20 is the curve connecting the leading edge 10a to the trailing edge 10b of the airfoil 10 and defining the camber of the airfoil 10. The camber line is defined by the set of the centers of circles inscribed in the profile of the vane over its extent between its leading edge and its trailing edge, each inscribed circle being tangential to the pressure side curve and to the suction curve. The angle of attack β is the angle formed between the tangent T to the camber line 20 at the leading edge 10a of the airfoil 10 and the axis A of the wheel, when the vane is mounted on the vane wheel. In FIG. 3, the angle β is thus positive. The angle-of-attack curve defines how this angle of attack β varies along the direction z, along the airfoil 10.

(11) FIG. 4 is a side view, which is a view perpendicular to the y-z plane of an airfoil 10 similar to the airfoil 10 described above. This view is thus a view perpendicular to the airfoil 10. In this view, the leading-edge curve defines how the profile of the leading edge 10a varies along the direction z. In other words, the leading-edge curve corresponds, in the view of FIG. 4, to the variations of the upstream end (on the left in FIG. 4) of the airfoil. The airfoil 10 shown in FIG. 4 represents a vane of the invention in which the leading-edge curve includes a leading-edge undulation. The term “undulation” designates a curve portion situated between two minimums m1 and m2 on either side of a single maximum M. Furthermore, H designates the total height of the airfoil between the airfoil root 12 and the airfoil tip 14, and h designates any arbitrary height up the airfoil, such that 0≤h≤H. As can be seen, the undulations are arranged on the airfoil side relative to the reference leading-edge curve r1; in other words in the minimums m1 and m2 the airfoil presents two portions that are recessed relative to the airfoil shape defined by the reference leading-edge curve r1, and it has no portions projecting beyond this shape.

(12) In addition, FIG. 4 also shows the profile of the trailing edge 10b. In this example, the trailing edge curve is monotonic and almost straight over the full height H of the airfoil 10 (in other words, the distance between the trailing edge and the axis of the airfoil is constant over the entire height H of the airfoil 10). Consequently, the profile of the leading edge 10a, seen in a view perpendicular to the y-z plane, may also be defined by variations in the chord 30.

(13) A second embodiment of the invention with a second leading edge profile is described below with reference to FIG. 5. FIG. 5 shows variations in the leading-edge curve (continuous line in FIG. 5) and in the angle-of-attack curve (dashed line in FIG. 5) along the airfoil 10. The position along the height H of the airfoil 10 is identified by a dimensionless number h/H. The curve r2 represents the reference leading-edge curve that subtends the angle-of-attack curve 10a, and the curve r3 represents the reference angle-of-attack curve, that subtends the angle-of-attack curve.

(14) In this example, the leading-edge curve has two undulations in the leading edge 10a extending from the airfoil root 12, over a height range of the airfoil 10 corresponding to 0≤h/H≤0.3 (i.e. over about one-third of the height of the airfoil 10). The leading-edge curve also has two leading-edge undulations 10a extending from the airfoil tip 14 over a height range of the airfoil 10 corresponding to 0.7≤h/H≤1 (i.e. over about one-third of the height of the airfoil 10). Between a minimum and a maximum of the leading-edge curve, the amplitude of the variations in the leading edge 10a lies in the range 1% to 10%, preferably in the range 1% to 5%, more preferably in the range 3% to 5% of the mean length of the chord of the airfoil. In addition, over a range of height of the airfoil 10 corresponding to 0.3≤h/H≤0.7, preferably 0.2≤h/H≤0.8, the leading-edge curve 10a is monotonic.

(15) Furthermore, the leading-edge curve has three leading-edge undulations β extending from the airfoil root 12 over a range of heights of the airfoil 10 corresponding to 0≤h/H≤0.3 (i.e. over about one-third of the height of the airfoil 10). The leading-edge curve also has three angle-of-attack undulations β extending from the airfoil tip 14 over a range of heights of the airfoil 10 corresponding to 0.7≤h/H≤1 (i.e. over about one-third of the height of the airfoil 10), preferably 0.8≤h/H≤1. Between a minimum and a maximum of the angle-of-attack curve, the amplitude of variations in the angle of attack β lies in the range 0.5° to 10°, preferably in the range 0.5° to 5°, more preferably in the range 1° to 3°. In addition, over a range of heights of the airfoil 10 corresponding to 0.3≤h/H≤0.7, preferably 0.2≤h/H≤0.8, the angle-of-attack curve β is monotonic.

(16) The leading-edge undulations 10a and the angle-of-attack undulations β are mutually offset. In other words, for a given height h1 of the airfoil 10, corresponding to a maximum M10a of the leading-edge undulation, the angle-of-attack curve at the same height h1 presents a minimum mβ. Conversely, for a given height h2, a maximum Mβ of an angle-of-attack undulation corresponds to a minimum m10a of a leading-edge undulation.

(17) The combination of the leading-edge undulations and these angle-of-attack undulations, the way they are arranged at the airfoil root 12 and at the airfoil tip 14, and the way they are offset in phase makes it possible to obtain a profile for the leading edge 10a of the airfoil 10 that presents the advantage of limiting the phenomenon of separation at the airfoil root 12 and at the airfoil tip 14, thereby serving to improve the surge margin. When this configuration for the airfoil angle of attack is applied to all of the vanes of a vane wheel, and to all of the vane wheels (nozzles) of an axial compressor, the surge margin may be improved by 2%, for example, without any need to reduce the flow rate, the compression ratio, or the efficiency of the compressor.

(18) Although the present invention is described with reference to specific embodiments, it is clear that modifications and changes may be undertaken thereon without going beyond the general ambit of the invention as defined by the claims. In particular, individual characteristics of the various embodiments illustrated and/or mentioned may be combined in additional embodiments. Consequently, the description and the drawings should be considered in a sense that is illustrative rather than restrictive.