EP1961920B1 - Casing with casing treatment, compressor and turbomachine including such a casing - Google Patents

Description

The invention relates to a casing supporting series of vanes fixed between which series of vanes are arranged in rotation about a longitudinal axis, the radially outer end of said vanes being close to the internal face of the casing; a crankcase used in an aviation turbojet.

Also, the present invention relates to the production of a compressor, in particular of the axial type, in particular a compressor operating at low pressure but also a compressor operating at high pressure, comprising a casing as mentioned above.

The present invention also relates to a turbomachine, in particular a turbojet, comprising such a housing or such a compressor.

Compressors of this type, used in particular in turbojet engines, consist of a rotor comprising either a succession of separate disks stacked one after the other, or a single drum intended to receive the series of blades of the different stages. .

Conventionally, this rotor comprises grooves made by machining in order to form between two neighboring stages a space in which are interposed the vanes of the stator stages secured to a fixed part having a housing.

This casing forms a section of the radially outermost zone of the vein along which the air circulates in the turbomachine.

In the usual way, the moving blades are secured individually to the drum at the housing, distributed regularly and in number equal to that of the blades, whose shape is determined to cooperate by complementarity of shape with the foot of the blade, this which ensures the radial immobilization, for example by a fastening of the dovetail type. As regards the immobilization in translation, in particular axial, the foot of the blade relative to its housing, it is provided most often separately for each blade by a ball system, pin, clip, flange, spacer etc.

During the operation of a turbojet, in particular for the current civil engines, given the temperatures of the pressures reached by the hot air, it is necessary to provide a regulation function in case of pumping.

It is recalled that pumping is a phenomenon that is sought to avoid within the engine since it results in sudden oscillations of air pressure and air flow, which subject the blades to considerable mechanical stresses which could lead to their weakening or even their rupture. This phenomenon can be initiated by oscillations of pressure at the top of the blade, with a strong interaction between the boundary layer at the top of the blade with the boundary layer of the crankcase.

Also, the rotating detachment is a phenomenon that is created when winnowing conditions (operating point) and rotational speeds are met. In particular, this phenomenon is triggered when the profile is put into so-called positive incidence, it is then created a non-stationary phenomenon leading to a local detachment of a blade, detachment that will spread from one blade to another, during of the rotation.

• formation d'une pollution de l'ensemble d'aubes par un décollement généralisé qui va conduire au pompage ;
• risque d'excitation aéroélastique des aubes sollicitées.

This phenomenon can be particularly damaging:

• formation of a pollution of the set of blades by a general detachment which will lead to pumping;
• risk of aeroelastic excitation of the blades requested.

Currently this pumping regulation function is provided by various types of solutions among which discharge valves that allow to suck this boundary layer, or casing treatments that cover the entire annular surface of the outer ring facing the (or wheel (s) of blades to be treated.

This last solution has given rise to many different implementations. In particular, in the document EP0688400 an annular cavity communicating with the flow path is proposed by slots delimited by an annular grid of inclined ribs. In the case of the document US6514039 it is a similar technique in which is further carried out on the bar forming the intermediate piece for forming the grid, a treatment of the material, such as a laser shock matting to make it more resistant to breakage by tired.

The document US 4,540,335 discloses another example of a housing having a crankcase treatment area facing a series of other mobiles and includes the features of the preamble of claim 1.

The present invention aims to provide a housing to overcome the disadvantages of crankcase treatments of the prior art while avoiding excessive energy loss.

The present invention therefore aims to reduce locally the pumping phenomenon, increasing the current pumping margin, without reducing the efficiency of the engine.

For this purpose, according to the present invention, the casing comprises at least one ring located opposite one of the series of blades, at least one casing treatment area facing the vanes comprising at least one groove (groove or furrow) closed on itself and extending over a limited augu- lar sector of the inner wall of the housing.

The housing has different zones: so-called "smooth" zones (that is to say without specific crankcase treatment), as well as areas that will support crankcase treatment. The number of these areas supporting the crankcase treatment and the angular coverage covered by these zones depends on the machine considered, and can be reduced to an area covering 360 degrees in some cases. Moreover, each of these zones may advantageously be located on an angular sector corresponding to 1.5 to 2.5 no blades.

In this way, it is understood that by the presence of one or more crankcase treatment areas which are each located at an angular sector restricted to 1.5 to 2.5 no moving blades, local evacuation of the crankcase is allowed. the air of the boundary layer in the space between the blade and the housing, opposite the treatment zone, in order to avoid the phenomenon of pumping.

This solution makes it possible to constitute a geometrical structure which will contribute to break the organization of the detachment and thus to make it disappear.

Overall, thanks to the arrangement according to the present invention, it is possible to locally suction the boundary layer capable of generating the pumping phenomenon, without degrading the efficiency of the engine through the recirculation of air above which allows improve the stability of the system by minimizing the impact on engine operation.

According to an advantageous arrangement, said treatment zone extends axially over a distance representing 2/3 to 9/10 of the length of the blades in the axial direction.

The ratio between the open surface and the solid surface is of the order of 2

It can be provided that this crankcase treatment zone is formed directly on the inner wall of the crankcase.

Alternatively, said crankcase treatment zone is formed on a plate attached to the crankcase. In this case, it can be provided that said plate is made, in whole or in part of the surface, of an abradable material.

According to a second embodiment, the housing further comprises a cavity formed behind and radially outside the treatment zone. This cavity has the same axial extent (depending on the length of the housing) and / or transverse (depending on the width of the blade) that the treatment area, or a smaller extent in one and / or the other of directions, or a greater extent in one and / or the other direction.

In this case, it can be provided that the housing has on the same annular portion, a plurality of treatment zones and said cavity of each treatment zone is in communication with said cavity of another treatment zone. This makes it possible to promote the circulation of air between the treatment zones.

• la profondeur de ladite cavité est comprise entre 1 et 3 fois la profondeur de la zone de traitement ;
• l'étendue en direction axiale de ladite cavité est 10 à 20% fois plus importante que l'étendue en direction axiale de la zone de traitement.

In addition, one of the following provisions may be implemented:

• the depth of said cavity is between 1 and 3 times the depth of the treatment zone;
• the axial extent of said cavity is 10 to 20% larger than the axial extent of the treatment zone.

• la figure 1 est une vue schématique partielle en projection de la face interne tournée en direction des extrémités d'aubes mobiles, d'un carter selon une première variante d'un premier mode de réalisation de l'invention ;
• la figure 2 est une vue schématique partielle en coupe depuis le coté du carter de la figure 1, selon la direction II-II, et d'une portion d'extrémité d'une aube ;
• les figures 3 et 4 sont des vues similaires à celles des figures 1 et 2 pour une deuxième variante du premier mode de réalisation de l'invention ;
• la figure 5 est une vue schématique partielle en projection de la face interne tournée en direction des extrémités d'aubes mobiles, d'un carter selon une première variante d'un deuxième mode de réalisation de l'invention ;
• la figure 6 est une vue schématique partielle en coupe depuis le côté du carter de la figure 5, selon la direction VI-VI ;
• les figures 7 et 8 sont des vues similaires à celles des figures 5 et 6 pour une deuxième variante du deuxième mode de réalisation de l'invention.

Other advantages and characteristics of the invention will become apparent on reading the following description given by way of example and with reference to the appended drawings in which:

• the figure 1 is a partial schematic view in projection of the internal face turned towards the ends of moving blades, a casing according to a first variant of a first embodiment of the invention;
• the figure 2 is a partial schematic sectional view from the side of the casing of the figure 1 in the direction II-II, and an end portion of a blade;
• the Figures 3 and 4 are views similar to those of Figures 1 and 2 for a second variant of the first embodiment of the invention;
• the figure 5 is a partial schematic view in projection of the internal face turned towards the ends of moving blades, a housing according to a first variant of a second embodiment of the invention;
• the figure 6 is a partial schematic sectional view from the crankcase side of the figure 5 according to the direction VI-VI;
• the Figures 7 and 8 are views similar to those of Figures 5 and 6 for a second variant of the second embodiment of the invention.

If we go back to figure 1 there is seen a portion of a housing 10 limited by an angular sector whose direction corresponds to the height of the sheet, and extending in an axial direction which corresponds to the width of the sheet. More specifically, on the figure 1 this portion of the casing 10 is viewed in the direction of its radially inner face turned in the direction of a rotor wheel not shown on FIG. figure 1 .

However, on the figure 1 the position of three vanes 20 is schematized by three oblique lines, the difference P taken between two of these lines corresponding to what will be referred to in the following a step of blade.

As it appears on the figure 1 , the inner surface of the housing portion shown has an oval-shaped closed contour groove 12, for example machined directly into the housing.

According to an essential characteristic of the present invention, it is understood that the groove 12 forms a local housing treatment zone which does not extend over the annular peripheral assembly of the housing 10.

Specifically, it is expected that this groove 12 is a crankcase treatment area which extends over an angular sector limited to 1.5 to 2.5 P blade pitch.

This angularly limited shape of the crankcase treatment corresponds to a topology quite different from that usually encountered for this type of crankcase treatment.

If we go back to the figure 2 , it can be seen more precisely that compared to a longitudinal section of the blade 20, the gap 30 located between the blade 20 and the casing treatment zone comprising the groove 12, has at two locations a corresponding radial enlargement in the hollow of the groove 12. This configuration makes it possible to achieve the local disturbances of the rotational detachment phenomenon mentioned in the preamble.

It is understood that the housing 10 may have, over its entire periphery, several grooves 12 similar (for example two, three or more) distributed regularly.

As an indication, the groove 12 may have a width of between 5% and 25% of the pitch, to delimit an axially extending oval shape (large dimension of the oval shape) over a distance of between 60% and 90% of the length of the inter-blade channel and transversely (small dimension of the oval shape) over a distance of between 10% and 90% of the width of the inter-blade channel.

It is understood that the obtaining of such an oval-shaped closed contour groove 12 can be obtained easily by simple machining of the radially inner surface of the housing 10.

Alternatively (not shown), this contoured closed contour groove 12 may be formed on a plate attached to the housing 10, this plate may be made of abradable material.

In general, the shape of the groove (or groove), the depth and the surface covered is the result of an optimization depending on how the dawn does the work. The objective of this crankcase treatment, located on a few centimeters to a few tens of centimeters, is to modify the energy distribution of the boundary layer, to restore energy to the boundary layer of the weakened zone of the dawn subject to detachment, and also to play the role of a disrupter that prevents detachment from settling and spreading to adjacent blades.

Note that the groove or grooves can start before the leading edge and end after the trailing edge, and it may be necessary to use treatments with concentric grooves, or to have a set of mirror grooves by performing two adjacent treatments having a plane of symmetry between them.

We will now refer to the figure 3 on which we find, with identical reference signs, the elements already described on the Figures 1 and 2 . In this case, according to a second variant of the first embodiment illustrated on the Figures 1 and 2 , the groove 12 'always has a closed contour which is no longer oval but which corresponds to a set of rectilinear sections interconnected to form an irregular geometrical figure, here with eight sides.

It is quite conceivable that instead of this irregular octagon, other geometrical shapes with more or less eight sides, or a form of closed contour generally curved and different from an oval shape or any other ovoid shape. In these figures the grooves are here defined on an interaubage step portion but this portion of pitch can be extended at an angle of 360 °.

We will now refer to Figures 5 to 8 which represent several variants of the housing according to the second embodiment.

On the first variant of the second embodiment shown on the Figures 5 and 6 , there is the housing 10 which, in addition to a closed contour groove 12 of oval shape similar to that shown on the figure 1 , has an annular rear cavity 14 extending, opposite the crankcase treatment area, over the entire periphery of the housing. The grooves 12 open into this cavity 14, which thus allows communication between different treatment areas that may be present on different angular sectors.

In the case of Figures 7 and 8 there is shown a second variant of the second embodiment, in which an annular rear cavity 14 has been provided opposite a treatment zone similar to that of the second variant of the first embodiment shown in the drawings. Figures 3 and 4 , namely a closed contour contour groove 12 'of irregular octagonal shape, which opens into the cavity 14.

For each of the variants of the second embodiment, this cavity 14 preferably has a depth corresponding to one time to three times the depth of the treatment zone (of the closed contour groove 12 or 12 '), and a width in the axial direction which is preferably greater than that of the treatment zone, in particular greater than 10 to 20% (in this case the width of the treatment zone corresponds to the axial distance covered by the closed contour groove 12 or 12 ').

The cavity 14 can be obtained by machining.

In addition, it should be noted that while Figures 6 and 8 , this rear cavity 14 seems to lead to the rear surface of the housing 10, It should be understood that this is a partial representation of the wall of the casing 10 which will comprise an annular complementary piece (not shown) closing the cavity 14 , in order to allow regulated air circulation at the location of the annular cavity 14. The central parts of the treatment zones are attached to this complementary piece.

In a preferred arrangement, the treatment zone extends axially over a distance representing at least 2/3 of the length of the blades 20 in the axial direction.

According to another preferred arrangement, the depth of the cavity 14 is between 1 and 4 times the depth of the treatment zone.

Claims (15)

1. A casing (10) for supporting series of stationary vanes between which there may be located series of moving blades (20) that are movable in rotation about a longitudinal axis, such that the radially outer ends of said moving blades (20) are close to the inside face of the casing (10), the casing being characterized in that it includes, at least in an annulus designed to be situated facing one of the series of moving blades (20), at least one casing treatment zone (12, 12') formed of at least one groove (12, 12') closed over itself and extending over a limited angular sector of the inside wall of the casing.
2. A casing according to claim 1, characterized in that said zone is localized over an angular sector corresponding to 1.5 to 2.5 times the pitch of the moving blades.
3. A casing according to claim 1 or claim 2, characterized in that said treatment zone extends axially over a distance representing at least 2/3 of the length of the moving blades (20) in the axial direction.
4. A casing according to any preceding claim, characterized in that said treatment zone comprises a groove of which the closed outline is generally curved.
5. A casing according to claim 4, characterized in that said treatment zone comprises an oval groove.
6. A casing according to any one of claims 1 to 3, characterized in that said treatment zone comprises a groove defined by a set of rectilinear segments interconnected to form an irregular geometrical figure.
7. A casing according to claim 6, characterized in that said geometrical figure has eight sides.
8. A casing according to any preceding claim, characterized in that said casing treatment zone is formed in a plate fitted to the casing (10).
9. A casing according to the preceding claim, characterized in that said plate is made of an abradable material.
10. A casing according to any preceding claim, characterized in that it further includes a cavity (14) formed behind and radially outside the treatment zone.
11. A casing according to claim 10, characterized in that it includes a plurality of treatment zones and in that said cavity (14) of each treatment zone is in communication with said cavity (14) of another treatment zone.
12. A casing according to claim 10 or claim 11, characterized in that the depth of said cavity (14) lies in the range 1 to 4 times the depth of the treatment zone.
13. A casing according to claim 10, 11, or 12, characterized in that the extent in the axial direction of said cavity (14) lies in the range 10% to 20% greater than the extent in the axial direction of the treatment zone.
14. An axial compressor comprising, as its stator, a casing (10) according to any preceding claim.
15. A turbomachine, in particular a turbojet, including a compressor according to claim 14.

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