EP2710268B1 - Gas turbine diffuser blowing method and corresponding diffuser - Google Patents

Description

TECHNICAL AREA

The invention relates to a method of blowing air into a compression stage diffuser of a gas turbine, particularly in centrifugal or mixed type compressors. By mixed compressor, it is to hear a structured compressor output wheel so that the air flow is at an angle between 0 and 90 ° relative to a radial direction. The invention also relates to a compressor diffuser adapted to implement such a method.

The field of the invention is that of the operation of the compressors and the improvement of their performance, in particular the pumping margin. The performance is particularly sensitive to the flow of air from the compressor impeller. The function of the diffuser is to straighten this flow in order to optimize the transformation of the dynamic pressure of the air into static pressure.

In general, a diffuser consists of blades inclined in a space formed between two flanges. The deflection carried out by the blades can cause air detachments on the intrados or extrados of the blades. Such detachments can lead to the stalling of air streams and, if the phenomenon is amplified, pumping.

It is therefore necessary to maintain a sufficient pumping margin to avoid the very harmful consequences of pumping, which can go as far as the destruction of compressor elements.

STATE OF THE ART

Until now, to try to stabilize the flow of air and avoid pumping, some of the air could be taken from the vein upstream the bladders of the diffuser by diverting a portion of the air at the exit of the impeller and re-injecting it at the level of the flanges of the diffuser, for example according to the process described in the patent US 6699008 . But this system is not optimal, because if the reintroduction of air in the diffuser can improve the stability of the compressor, diverting air at the output of the wheel may cause new stability problems. In addition, performing a reintroduction without generating additional losses is difficult, because the air output wheel is at a lower static pressure level than that of the reinjection site.

It is also known to make cavities in the upper surface of the blades for use as a cooling fluid as described in document US 6,210,104 . The patent document FR 2937385 , in the name of the applicant, describes an improvement of this solution by gradually increasing the cross section of the cavities between the suction port and the outlet orifice. The aspiration of the fluid is then homogenized on the blades. However, it may be necessary to reject this air taken outside, which is detrimental to the overall balance of the cycle.

Other solutions provide recirculation of air from orifices formed near the leading edges of the blades and then redirected in the vein upstream of the leading edges axisymmetrically. The patent EP 2169237 implement such an arrangement to reduce the detachments with an air suction on the blades, such as patents US 6,210,104 and FR 2,937,385 already mentioned. The reintroduction that is made upstream of the vanes of the diffuser affects only the incidence at the leading edge of the diffuser. The documents US-A1-2008 / 038112 , US Patent 2399072 and US-A1-2008 / 118341 show similar solutions.

STATEMENT OF THE INVENTION

The invention aims to combat more effectively the separation of the boundary air layer by actively stabilizing this layer. To do this, the invention provides for re-energizing the boundary layer with air at higher pressure by a coupling blow / suction.

More specifically, the subject of the present invention is a method of blowing air into a compression stage diffuser of a gas turbine compressor as defined by claim 1. Such a diffuser comprises two flanges enclosing a plurality
circumferential blades. The flow of air along the blades is from a leading edge to a trailing edge of the diffuser. In this method, a coupling of an air injection into the airstream upstream of the diffuser is performed with a sample of air coming from the downstream vein by an air intake made on the side of the edges of the airstream. attack, upstream with respect to the trailing edges located downstream. A blowing of the injected air occurs in the upstream vein downstream by this air intake. The injection is oriented so that the injected air blows into the vein along the blades and / or flanges. A sample of this air is then made by suction in the vein on the side of the trailing edges, so that the pressure of the air taken is substantially greater than the air pressure flowing at the sampling. Thus, the transition from a laminar boundary layer of the airflow to a turbulent layer is initiated and / or enhanced by increasing its energy level.

The injection can be oriented from 0 ° to about ± 90 ° with respect to a normal injection face. Advantageously, the air is injected as tangentially as possible to the injection face in the direction of the air flow. Thus, the transition from a laminar boundary layer of the airflow to a turbulent layer is initiated and / or enhanced by increasing its energy level.

Such blowing thus makes it possible to "stabilize" a boundary layer by rendering it turbulent when it is laminar, and thus to delay delamination because a turbulent boundary layer is intrinsically more stable than a laminar boundary layer. When the boundary layer is turbulent, this energy supply delays the onset of detachments. In addition, even if the detachment of the air flow is already initiated, the energy supply can also allow the bonding of the boundary layer.

The phenomenon of re-energization according to the invention can be reinforced by the effect "coanda" which appears when an air jet is close to a convex wall. This effect results in an attraction of the fluid towards the wall. This coanda effect can be maximized depending on the speed and the angle of ejection of the air at the sampling level.

According to advantageous embodiments, the method according to the invention makes provision for withdrawing the air either downstream from the diffuser, in a subsequent grid of the stage or in a subsequent stage, or in the diffuser concerned, in particular near the trailing edge of the blades.

• le prélèvement d'air peut être réalisé sur les intrados et/ou extrados des aubes, et le soufflage sur les aubes intrados et/ou extrados ;
• le prélèvement peut être réalisé sur les flasques de moyeu et/ou de carter du diffuseur et le soufflage sur les flasques ;
• le prélèvement peut être réalisé sur les aubes et le soufflage sur les flasques ou inversement (par un prélèvement sur les flasques et un soufflage sur les aubes) ;
• la vitesse d'éjection de l'air, lors de son injection, est choisie entre Mach 0,7 et 1, et l'angle d'éjection est choisi entre 60° et 90° par rapport à une normale à la face d'injection des aubes et/ou des flasques d'aspiration, afin de maximiser l'effet coanda.

In the case where the air is taken from the diffuser, according to more particular modes:

• the air sampling can be carried out on the intrados and / or extrados of the blades, and the blowing on the intrados and / or extrados vanes;
• the sampling can be performed on the hub flanges and / or the diffuser housing and the blowing on the flanges;
• the sampling can be performed on the blades and the blowing on the flanges or vice versa (by a sample on the flanges and a blowing on the blades);
• the speed of ejection of the air, during its injection, is chosen between Mach 0.7 and 1, and the ejection angle is chosen between 60 ° and 90 ° with respect to a normal to the face of injection of blades and / or suction flanges, in order to maximize the coanda effect.

The invention also relates to a diffuser capable of implementing this method as defined by claim 7. Such a centrifugal or mixed compressor type diffuser comprises two flanges enclosing a plurality of circumferential vanes. At least one transverse upstream passage is made in the lower and / or upper surfaces of the blades and / or in a flange at at least one point of injection of air into the vein, located in the leading edge zone of the upstream side of the diffuser, according to the compression direction of the gas turbine. This passage is able to form a coupling injection / sampling in the vein by recirculation in the diffuser and / or along the flange off diffuser. The intake of air at at least one point in the trailing edge zone of the downstream side of the diffuser is achieved by suction in at least one groove formed along a flank of the blades and / or on the internal face of the flange.

• l'injection est réalisée par au moins un passage amont transversal, réalisé dans les intrados et/ou extrados des aubes et qui débouche dans le sillon des aubes et/ou dans la face interne du flasque ;
• les passages aval et amont transversaux sont formés par des cavités et/ou des fentes;
• les passages présentent un axe central incliné par rapport à une normale à la face sur laquelle il débouche, avec un angle sensiblement compris entre 0 et ± 90°, de préférence un angle proche de 90° pour les passages amont et proches de 0° pour les passages aval ;
• les passages peuvent être positionnés sensiblement sur toute la longueur de chaque sillon, du côté des extrados et/ou intrados, avec un passage amont et un passage aval par sillon ;
• le sillon présente une largeur constante ou évolue linéairement en fonction de l'abscisse curviligne de chaque aube ;
• le sillon est débouchant en bord de fuite et le bord de fuite présente alors des rebords courbes pour favoriser l'aspiration ;
• le sillon s'étend sensiblement entre 1 et 100% de la longueur de chaque aube ;
• les sillons sont au moins au nombre de deux, et sont disposés successivement ou parallèlement le long de chaque aube.

According to some preferred embodiments:

• the injection is performed by at least one transverse upstream passage, made in the intrados and / or extrados of the blades and which opens into the groove of the blades and / or in the inner face of the flange;
• the transverse downstream and upstream passages are formed by cavities and / or slots;
• the passages have a central axis inclined relative to a normal to the face on which it opens, with an angle substantially between 0 and ± 90 °, preferably an angle close to 90 ° for the upstream passages and close to 0 ° for downstream passages;
• the passages may be positioned substantially along the length of each groove, on the extrados and / or intrados side, with an upstream passage and a downstream passage through a groove;
• the groove has a constant width or changes linearly depending on the curvilinear abscissa of each blade;
• the groove is emerging at the trailing edge and the trailing edge then has curved edges to promote suction;
• the groove extends substantially between 1 and 100% of the length of each blade;
• the furrows are at least two in number, and are arranged successively or parallel along each dawn.

PRESENTATION OF FIGURES

• la figure 1, une vue schématique en coupe partielle d'une turbine à gaz comportant un diffuseur d'air ;
• les figures 2a à 2c, des vues en perspective d'un diffuseur à aubes avec un et deux flasques, ainsi que celle d'une aube isolée (figure 2c) ;
• les figures 3a et 3b, des vues schématiques en coupe longitudinale et supérieure d'un premier exemple de diffuseur selon l'invention à prélèvement et soufflage d'air sur aube ;
• les figures 4a et 4b, des vues schématiques en coupe longitudinale et supérieure d'un deuxième exemple de diffuseur à prélèvement et soufflage d'air sur aube selon l'invention ;
• la figure 5, des vues supérieures de variantes d'aubes des premier et deuxième exemples selon des schémas 5a à 5i, et
• les figures 6a et 6b, une vue frontale schématique et une vue de flasque agrandie d'un exemple de diffuseur à prélèvement et soufflage sur un flasque.

Other data, features and advantages of the present invention will appear on reading the following nonlimited description, with reference to the appended figures which represent, respectively:

• the figure 1 , a schematic partial sectional view of a gas turbine comprising an air diffuser;
• the Figures 2a to 2c , perspective views of a paddle diffuser with one and two flanges, as well as that of an isolated dawn ( Figure 2c );
• the Figures 3a and 3b , schematic views in longitudinal section and upper of a first example of a diffuser according to the invention for sampling and blowing air on blade;
• the Figures 4a and 4b , diagrammatic views in longitudinal section and upper of a second example of a diffuser for sampling and blowing air on blade according to the invention;
• the figure 5 upper views of blade variants of the first and second examples according to diagrams 5a to 5i, and
• the Figures 6a and 6b , a schematic front view and an enlarged flange view of an example of a diffuser for sampling and blowing on a flange.

DETAILED DESCRIPTION

The terms "downstream" and "upstream" describe positioning with respect to the flow of airflows. In all the figures, identical reference signs refer to the passages of the description in which the elements corresponding to these reference signs are defined.

Referring to the schematic partial sectional view of a helicopter gas turbine 1 according to the figure 1 , an air flow F is first drawn into a fresh air intake sleeve 2, then compressed between the blades 3 of a centrifugal compressor wheel 4 and a cover 9. The turbine is of axial symmetry around the X'X axis.

The compressor 5 is centrifuged here and the compressed flow F then exits radially from the impeller 4. When the compressor is mixed, the flow exits inclined at an angle between 0 ° and 90 ° relative to a radial direction, perpendicular to the axis X'X.

The flow F then passes through a diffuser 6, formed at the outlet of the compressor 4, to be straightened and conveyed to the combustion chamber inlet channels 7.

To perform this rectification, the diffuser 6 consists of a plurality of curved blades 60, formed between two flanges at the periphery of the wheel 4 - here radially - and therefore of revolution about the axis X'X.

The figure 2a illustrates more precisely a perspective view of the diffuser 6 with blades 60 secured to two flanges 61. On the figure 2b , where a flange has been removed for clarity, each blade 60 has, in known manner, a so-called extrados face 6e and a so-called intrados face 6i. As illustrated more precisely on dawn 60 of the Figure 2c these upper and lower faces 6i 6i extend longitudinally and substantially parallel to a mean surface Fm of the blade. In the illustrated example, these faces are connected by a tapered leading edge 6a and a rounded trailing edge 6f, in the direction of flow of the air flows. Transversally to the upper and lower surfaces, each blade 60 has plane flanks 6p integral with the flanges 61.

The blades have a change in thickness between their flanks 6p, sufficient to form grooves as described below. This thickness can reach several millimeters over 20 to 100% of the mean curvilinear abscissa Sm of the blade 60 along the average surface Fm.

With the help of Figures 3a and 3b , a first embodiment of a diffuser for sampling and blowing air on dawn will now be described.

On the longitudinal sectional view of the figure 3a and the upper view 3b, a longitudinal groove 62 now appears. This groove opens on the trailing edge 6f, without opening on the leading edge 6a. This groove is made by machining the metal alloy material of the sidewall 6p of each vane 60, forming longitudinal walls 65, substantially parallel to the intrados face 6i and extrados 6e, and bottom 66 parallel to the sidewalls 6p.

In addition, the blade 60 is provided with a series of orifices 63 opening into the air duct V between the blades 60 via cylindrical blowing cavities 64. As illustrated by FIG. figure 3b , air flows F1 and blown via the orifices 63 open on the intrados 6i. According to other exemplary embodiments, the flows F1 may also or alternatively lead to the upper surface 6e. In the example, the orifices 63 are aligned parallel to the leading edges 6a and leakage 6f.

These air blowing cavities 64 are inclined at an angle of between 0 and 90 ° downstream, for example 30 °, relative to the mean curvilinear abscissa Sm of the blade. Flows F1 open through the orifices 63 and blow in the vein V downstream. Part of these flows as well as other flows originating from adjacent blades are sucked, in the form of a flow Fi, from the vein V to the groove 62 in the region of the trailing edge 6f (at the trailing edge 6f in the example shown).

Flows Fi are then injected by suction into the groove 62 of the blade 60 on the upstream side where the pressure is lower. Recirculation of the air flows via the groove between the trailing edge 6f and attacking zones 6a performs a suction / blowing coupling. The re-energizing of the incoming air flows then makes it possible to stabilize these flows and to prevent their detachment or possibly to pick them up again if the detachment is initiated. Suction at the trailing edge, or in areas close to the trailing edge, also makes it possible to attenuate - or even eliminate - the potentially unstuck areas.

Alternatively, the cavities may open on the extrados side 6e, and / or these cavities may be replaced by one or more slots formed on a sidewall 6p. Furrows can also be machined on the two opposite sidewalls 6p, retaining a central bottom portion 66 of the grooves.

With reference to Figures 4a and 4b a second example of a dawn air sampling and blowing diffuser is illustrated by identical views that the Figures 3a and 3b . The Figures 4a and 4b repeat the reference signs of the Figures 3a and 3b , which signs refer to the same elements already defined in the preceding passages, with reference to the Figures 3a and 3b .

The difference with the first example of the diffuser is the air flow suction means Fi in the groove 62 at the trailing edge 6f. According to this second example, the flows Fi are reinjected via cavities 74 made in the intrados 6i on the trailing edge 6f side and opening into the groove 62. The suction cavities are, in the illustrated example, substantially transverse. Alternatively, they may be inclined at an angle close to ± 90 ° to the normal at curvilinear abscissa Sm of blade 60 as a function of configurations. They can also be replaced by slots such as blowing cavities 64.

Other variants for these first and second examples are illustrated in diagrams 5a to 5k of FIG. figure 5 . These diagrams show a dawn 62 in superior view

Diagrams 5a to 5c relate to vanes 60 of grooves 62a to 62c respectively of constant width "e" and opening on the trailing edge 6f (groove 62a, diagram 5a), or of width "e" linearly variable as a function of the mean curvilinear abscissa Sm of the blade 60 (grooves 62b and 62c, diagrams 5b and 5c). The groove may be opening (grooves 62a and 62c, diagrams 5a and 5c) or non-opening (groove 62b, diagram 5b) on the trailing edge 6f. When the groove is opening, the trailing edge 6f then has flanges 67 shaped to optimize the suction of air.

Furthermore, the suction cavities 74 and injection 64 can lead to the same faces: intrados 6i (diagrams 5d and 5e) or extrados 6e (diagrams 5f and 5g). They can also lead to different faces: extrados 6e for the suction cavities 74 and intrados 6i for the reinjection cavities 64 (diagram 5h), or intrados 6i for the suction cavities 74 and extrados 6th for the reinjection cavities 64 (Figure 5i). Diagrams 5d to 5i show a groove 62b of linearly increasing width and non-opening.

In addition, the cavities or slots can be positioned and uncorked at any point along the length of the groove, with angles that can tend to ± 90 ° from the normal to the curvilinear abscissa of the blade.

The grooves may, in general, extend over the entire length of the blade 60 or a minimum length, close to 0% of the total length.

In addition, several grooves may be machined on the same sidewall 6p, for example two grooves, as shown in the diagrams 5j and 5k. In the diagram 5j, the grooves 6j and 6j 'succeed one another along the blade 60. In the diagram 5k, the grooves 6k and 6k' are substantially parallel along the blade 60.

Moreover, the figure 6a illustrates a front view of a third example of diffuser 60 according to the invention. In this example, the air intake - always performed in the trailing edge region 6f of the diffuser 6 (arrow F2) is achieved by suction through an opening 70 made radially in the flange 61. The air flows F3 are redirected upstream in a housing housing 71 substantially parallel to the diffuser 6, the housing 71 and the diffuser 6 having the flange 61 as a common wall. Blowing is done by reinjection flows F4 along the inner face 61i of the flange 61 through holes 72 formed in the region of the leading edge 6a of the diffuser 6.

The holes 72 are inclined relative to the flange 61 as it appears more precisely with reference to the enlarged schematic view of the figure 6b . The diffusion of the air flow F4 is thus reinjected onto the face 61i of the flange 61 situated on the inside of the diffuser 6. The re-energization of the air drop zones with a small amount of movement is then favored at the leading edge. of the broadcaster.

The invention is not limited to the examples described and shown. Thus, the cavities and slots are not necessarily cylindrical or partially cylindrical but can vary in section: prismatic, oblong, etc. Moreover, when the sampling and the reinjection of air is carried out through the flange, the transit housing can be formed in the housing or in the hub of the diffuser.

Claims (11)

1. Method of blowing air in a compression stage diffuser (6) of a compressor (5) of a gas turbine (1), this diffuser (6) having two end plates (61) enclosing a plurality of circumferential blades (60) and the air flow (F) along the blades (60) being effected from a leading edge (6a) to a trailing edge (6f) of the diffuser (6), a coupling of an injection of air (F1) into the air passage (V) upstream of the diffuser (6) with a withdrawal of air (Fi, F4) originating from the air passage (V) downstream is carried out via an air intake (64) at the leading edges (6a), upstream relative to the trailing edges (6b) situated downstream, by blowing of the injected air (F1) in the air passage (V) from upstream to downstream, the injection being oriented so that the injected air blows into the air passage (V) along the blades (60) and/or the end plates (61), and by withdrawal of this air (Fi, F4) by suction into the air passage (V) at the trailing edges (6f) and characterised in that the method comprises the injection into each blade (60) then recirculation to the air intake (64) in the leading edge (6a) of the blade (60) in order to produce a suction/blowing coupling, so that the pressure of the air withdrawn (Fi, F4) is higher than the pressure of air (F) flowing in the region of the withdrawal.
2. Method of blowing according to claim 1, wherein the air is withdrawn either downstream of the diffuser (6), in a subsequent grille of the stage or in a subsequent stage of the compressor (5), or in the diffuser concerned (6), in particular near to the trailing edge of the blades (60).
3. Method of blowing according to claim 1, wherein the withdrawal of air is performed on the lower (6i) and/or upper (6e) surfaces of the blades (60), and the blowing on the blades (60).
4. Method of blowing according to claim 1, wherein the withdrawal is performed on the hub and/or casing end plates (61) of the diffuser, and the blowing on the end plates (61).
5. Method of blowing according to claim 1, wherein the withdrawal is performed on the blades (60) and the blowing on the end plates (61).
6. Method of blowing according to claim 1, wherein the withdrawal is performed on the end plates and the blowing on the blades.
7. Diffuser of a compressor of the centrifugal or mixed type characterised in that the compressor diffuser is capable of implementing the method of blowing according to any one of the preceding claims, wherein two end plates (61) enclose a plurality of circumferential blades (60), one upstream transverse passage (64) is produced in the lower (6i) and/or upper (6e) surfaces of the blades (60) and/or in an end plate (61) in at least one point for injection of air (64, 70) into the air passage (V), situated in the leading edge zone (6a) of the upstream side of the diffuser (6) in the compression direction of the gas turbine (1), capable of forming an injection/withdrawal coupling in the air passage (V) by a recirculation in the diffuser (6) and/or along the end plate (61) outside the diffuser, the withdrawal of air at at least one point (Fi, 74, 72) in the trailing edge zone (6f) of the downstream side of the diffuser (6) being carried out by suction in at least one groove (62; 62a to 62c; 6j, 6j'; 6k, 6k') formed along a flank (6p) of the blades (60) and/or on the internal face (61i) of the end plate (61).
8. Diffuser of a compressor according to the preceding claim, wherein the injection is carried out by at least one transverse upstream passage (64, 70) in the lower (6i) and/or upper (6e) surfaces of the blades (60) and which opens into the groove (62; 62a to 62c; 6j. 6j'; 6k, 6k') of the blades (60) and/or into the internal face (61i) of the end plate (61).
9. Diffuser of a compressor according to either claim 7 or claim 8, wherein the transverse downstream and upstream passages are formed by cavities (64, 74) and/or slots.
10. Diffuser of a compressor according to the preceding claim, wherein the passages (64, 74) have a central axis inclined with respect to the normal to the face onto which it opens, with an angle between 0 and ± 90°, preferably an angle close to 90° in the direction of flow for the upstream passages (64) and close to 0° for the downstream passages (74).
11. Diffuser of a compressor according to any one of claims 7 to 10, wherein the passages (64, 74) can be positioned over the entire length of each groove (62; 62a to 62c; 6j, 6j'; 6k, 6k'), at the upper (6e) and/or lower (6i) surfaces, with one upstream passage (74) and one downstream passage (64) per groove.

Images