Abstract:
A gas turbine stator including at least a first injector providing a passage for a main cooling air stream into a pressurized chamber. An evacuation mechanism discharges air coming from an internal labyrinth gland of a first cavity towards a lower-pressure second cavity. A second injector evacuates the air contained in the second cavity towards a main duct. The stator further includes a third injector designed to generate an overpressure close to the internal labyrinth gland in the pressurized chamber.

Description:
TECHNICAL FIELD 
   The technical field of this invention is that of gas turbines, such as axial-flow turbine engines, comprising a stator notably intended to supply air to other elements of the gas turbine. This stator in particular, is a mechanical unit, which allows relatively cool air to be supplied to the blades of the high-pressure turbine, this air intended notably to cool a part of the rotor being drawn from the bottom of the combustion chamber. 
   STATE OF THE PRIOR ART 
   In well-known embodiments of gas turbine stators of the prior art, we usually find an element such as a main injector which makes it possible to accelerate the air drawn from a cavity in the stator, a retainer for guiding the air down to the blades of the high-pressure turbine, as well as different air circuits making it possible to calibrate all the airflows throughout the system. These airflows are then injected into different cavities consequently making it possible to limit the rise in temperature of the mechanical components. According to these different types of embodiments, widespread use is made of leakproof systems such as labyrinth glands to limit as much as possible the leakage of cool air. 
     FIG. 1  represents a longitudinal half section of a stator according to the prior art. The purpose of this stator is to draw cool air from the stator cavity  20 , then deliver this air through sloping hole type injectors  21  which speed it up and adjust the direction of flow thereof. This cool air then arrives in a pressurised chamber  22  before entering into orifices  23  of the retainer so as to be directed towards the blades  24  of the rotor  34 . This main cooling air stream is symbolised by the arrow A in  FIG. 1 . The arrow B symbolises the flow of discharge air coming from the internal labyrinth gland  35 , intended to be re-injected into the main duct. Still referring to  FIG. 1 , we see that in order to allow this flow of discharge air we commonly use pipes  25  welded to different parts of the stator. 
   However, even though the labyrinth glands are commonly used to render the pressurised chamber leakproof, as notably disclosed in the document FR 2744761, these labyrinth glands cannot stop all the air leaks through this chamber. In particular, the internal labyrinth gland cannot stop some of the hot air present outside the pressurised chamber from penetrating into the latter. This consequently generates an increase in temperature of the pressurised chamber, and thus a reduction in the efficiency of the cooling system of the rotor. 
   OBJECT OF THE INVENTION 
   The aim of the invention is therefore to present a gas turbine stator resolving all the aforementioned inconveniences, thus implementing a device limiting as much as possible the leakage of hot air towards the inside of the pressurised chamber. 
   To accomplish this, the object of the invention is a gas turbine stator comprising: 
   a first injection means providing a passage for a main cooling air stream into a pressurised chamber; 
   a means for evacuating discharge air coming from an internal labyrinth gland of a first cavity towards a lower-pressure second cavity; 
   a second injection means for evacuating the air contained in said second cavity towards a main duct. 
   According to the invention, the stator is made in such a way that it further comprises a third injection means for generating an overpressure of air close to the internal labyrinth gland in said pressurised chamber. 
   The main advantage of this invention is the maximum limitation of hot air discharges, at the internal labyrinth gland heading towards the pressurised chamber. The limiting of these discharges slows down the increase in temperature in the inside of the pressurised chamber, thus making it possible to draw less cool air via the first injection means. 
   Preferably, the stator according to the invention is made so that the first injection means comprise at least one blade for producing a flow of air tangent to the rotor. 
   This configuration presents the advantage of bringing the air into excellent conditions, thus greatly reducing the rise in temperature due to the passage of air in the ducts. These rises in temperature are also limited due to the nature of the first injection means in the shape of blades with an appropriate aerodynamic profile, these means thus having identical behaviour to that of a conventional axial manifold. 
   The evacuation means used in this invention preferably comprise at least one piercing emerging on one hand into the first cavity and on the other hand into the second cavity. 
   According to this particular embodiment implementing piercings to allow for the evacuation of discharge air, an advantage of the invention resides in the reduction in manufacturing costs by using an existing part instead of adding pipes as per the prior art. This stator according to the invention also participates in the lightening of the injectors, as well as the lengthening of the service life of the stator due to the absence of welding of the pipes as is of common practice. 
   Preferably, the piercings implemented to accomplish the means of evacuating discharge air are carried out in the solid part of the blades constituting the first injection means. 
   According to a particular embodiment of the invention, the support of a part of the internal labyrinth gland comprises the first injection means. This support has a honeycomb structure alternatively made of cavities and blocks of material. The cavities are thus intended to lead to the evacuation means whereas the blocks of material comprise the third injection means. 
   Advantageously, the stator according to the invention can then have a crossover system for three flows of air assembled in a single part capable of being made in a single casting. We note that this particular configuration of the invention makes it simple to assemble the different elements of the stator. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This description will be based on the annexed drawings among which: 
       FIG. 1 , previously described, illustrates the prior art; 
       FIG. 2  represents a longitudinal half section of one part of a turbine engine in which is fitted the stator according to the invention; 
       FIG. 3  represents a perspective partial view of the stator according to the invention emphasising the co-operation between the first injection means and the means for evacuating discharge air; 
       FIG. 4  represents a longitudinal half section of one part of a turbine engine in which is fitted the stator according to the invention, when this turbine engine uses a harpoon type retainer. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In reference to  FIG. 2 , we see one part of a turbine engine notably comprising a stator according to the invention. This stator firstly comprises a pressurised chamber  16  delimited by different elements. Among these elements there is an external labyrinth gland  4   a  and  4   b  as well as an internal labyrinth gland  13   a  and  13   b . These two internal and external labyrinth glands  13   a ,  13   b ,  4   a  and  4   b  are respectively held by a support  14  fixed to the wall of a stator cavity  5  and another support  36  fixed to this support  14 . The internal labyrinth gland  13   a  and  13   b  partly delimits a boundary between the pressurised chamber  16  and a first cavity  9  adjacent to it, whereas the external labyrinth gland  4   a  and  4   b  partly delimits a boundary between the pressurised chamber  16  and a second cavity  10  also adjacent to it. The first and second cavities  9  and  10  are themselves separated by the support  14 . It is to be noted that the stator has, downstream from the second cavity  10  in the direction of the flow of a main duct of the gas turbine represented by the arrow C in  FIG. 2 , a third cavity  37  separated from the second cavity  10  by the support  36 . 
   The internal  13   a ,  13   b , and external  4   a  and  4   b  labyrinth glands are generally broken down into at least one friction part  13   a  and  4   a  fixed to the stator via supports  14  and  36  and at least one lip  13   b  and  4   b  fixed to a retainer  2 . This retainer  2  also delimits the pressurised chamber  16  and is fixed to a rotor  38  of the gas turbine. This retainer  2  comprises injection holes  6  emerging into a cavity  7  located between said retainer  2  and the rotor  38  of the gas turbine, the latter having blades  8 . 
   The stator firstly comprises first injection means  1  achieved in the support  14  and making it possible to draw cool air from the stator cavity  5 , so as to send it towards the blades  8  of the rotor  38 . As in the devices of the prior art, this air passes through the first injection means  1  to enter the pressurised chamber  16 , where a main cooling air stream transits before cooling the blades  8  of the rotor  38  passing through the injection holes  6  designed for this purpose in the retainer  2 . 
   Once through the injection holes  6  the cold air fills the cavity  7  located between the retainer  2  and the rotor  38 . This retainer  2  is to ensure the sending of this air down to the blades  8  of the rotor  38 . 
   Still with reference to  FIG. 2 , the stator comprises means for evacuating discharge air coming from the internal labyrinth gland  13   a  and  13   b  so as to evacuate the air out of the first cavity  9  adjacent to the pressurised chamber  16 , towards the second cavity  10  of lower pressure. These means of evacuating air can be fixed to the support  14 . 
   Additionally, the stator comprises second injection means for evacuating air held in the second cavity  10  in order to re-inject it into the third cavity  37  so that it may rejoin the main duct of the gas turbine. These second injection means are located in the part of the support  36  that separates the second and third cavities  10  and  37 . 
   According to the invention, the stator also comprises third injection means to generate an overpressure of air in the pressurised chamber  16 , the local overpressure being located close to the internal labyrinth gland  13   a  and  13   b . The purpose of these means is to hinder as much as possible the hot air of the first cavity  9  from escaping towards the pressurised cavity  16 , so that the latter remains at an acceptable temperature. The purpose of these third injection means is to generate a local overpressure in the pressurised chamber  16  close to the internal labyrinth gland  13   a  and  13   b  in order to balance the pressures between this pressurised chamber  16  and said first cavity  9  itself being adjacent. The cool air drawn by these third injection means comes from the same stator cavity  5  as the air drawn by the first injection means  1  to generate the main cooling air stream. 
   The stator is equipped with first injection means  1  whose shape and manufacture greatly differ from prior embodiments. Indeed, in reference to  FIG. 3 , these injection means comprise at least one blade  12  making it possible to render the flow of air coming from the stator cavity  5  tangent to the rotor  38 . These first injection means  1  are thus comparable to a conventional axial manifold, thus bringing the air under better conditions than if it had to pass through sloping piercings, as was commonly used in the past. The direct consequence of using such a device is the elimination of a bursting effect due to the jet on the retainer  2 , a major source of temperature rise of the supply air to the blades. This bursting effect is the consequence of using sloping piercings to introduce the air into the pressurised chamber. Indeed, the slope of these piercings is insufficient to prevent the main air stream from being directly projected against the retainer  2 . The collision between this flow of cool air and the retainer  2  results in the cool air in the pressurised chamber  16  unnecessarily heating up thus rendering the ventilation less efficient. It is to be specified that the invention could, however, use conventional first injection means, such as the sloping injection holes as previously disclosed. 
   According to a particular embodiment of the invention, the means for evacuating discharge air preferably comprise at least one piercing  11  in the support  14 , these piercings  11  emerging on one hand into the first cavity  9  and on the other hand into the second cavity  10 . This further makes it possible to reduce the manufacturing costs by using an existing part to achieve these evacuation means, contrary to the solutions involving adding pipes and then welding them to different elements of the stator. Additionally, the incorporating of such a technical solution makes it possible to increase the service life of the stator due to the absence of the welding of the pipes. In the aforementioned embodiment of the first injection means  1 , we can notably carry out these piercings  11  in a part of the blades  12 . As can be seen in  FIG. 3 , the blades  12  are solid and can consequently contain these means for evacuating discharge air. The making of simple piercings in the material of these blades  12  thus makes it possible to compact the unit constituted by the first injection means  1  as well as the means for evacuating discharge. 
   With reference to  FIG. 2 , we see that all of these previously described three flows, namely the one coming from the first injection means  1 , the one coming from the third injection means as well as the one coming from the means for evacuating discharge air, can exist within the same part. 
   To achieve this, it is then possible to adapt the support  14  so that it can receive these three flows. This support  14  is partly honeycombed, notably thanks to the presence of cavities  20  capable of directing the flow of air towards the evacuation means. The piercings  11  for the passage of air start in the cavities  20  and cross the blades  12  as previously described. Additionally, to achieve the honeycombed structure, these cavities  20  are set between blocks of material  15  in which the third injection means are made. 
   Furthermore, as the support  14  comprises the first injection means  1 , we obtain a triple-flow stator, these flows crossing in the support  14  without any of them disturbing the smooth flowing of the others. This part of the stator can easily be made in a single casting. Additionally, the use of casting technology makes it possible to adjust the shapes of rotor  38 , giving it a more compact appearance. This reduction in the overall size of the parts of the rotor  38  also leads to substantial reductions in manufacturing costs due to the restricted dimensions of these parts constituting the rotor  38 . 
   The third injection means can be in the form of at least one piercing  3  through the blocks of material  15 . These piercings are preferably sloping to obtain a flow of air with a large component tangent to the rotor  38 , namely according to a perpendicular direction to the sectional plane in  FIG. 2 . It is also possible that these third injection means take the form of at least one blade to render the flow of air tangent to this rotor  38 . These blades would then be of the same type as those of the first injection means represented in  FIG. 3 . 
   To evacuate the air in the second cavity  10  towards the main duct, there are the second injection means. As this is the case in reality, we can carry out at least one sloping piercing  17  in the stator so as to obtain a flow of air with a large component tangent to the rotor. These piercings  17  can be made in the support  36  between the second cavity  10  and the third cavity  37 . Note that we can also resort to a blade system with the previously described thermal and mechanical effects. Additionally, the air coming from these second injection means can also be used to cool a zone of the rotor subject to high flow temperatures from the main duct. 
   Likewise, the second injection means can also improve the efficiency of the rotating leakproof systems of the retainer  2 . In reference to  FIG. 4 , the piercings  17  emerge into a cavity  18  of the external labyrinth gland. This case arises when a harpoon type retainer  2  is used, namely when the external labyrinth gland is made so that each lip  26 ,  27  and  28  works in conjunction with a distinct honeycomb type friction part  29 ,  30  and  31 . Due to this particular layout we thus obtain at least two cavities  18  and  19  partially separated from the second cavity  10  by an element other than one of the honeycomb type friction parts  29 ,  30  and  31 . 
   We can then inject air into one of these cavities  18  or  19  via the second injection means. This air swirls when arriving in the cavities  18  and  19  and is driven in rotation before being naturally sucked from the pressurised chamber  16  towards the main duct, due to the pressure difference between these elements. The injecting of hot air into one of these cavities  18  or  19  will thus allow a reduction in the cold air to be drawn from the first injection means  1  and consequently results in an improvement in the performance of the system. Also note that injecting air into the small cavity  18  created by the succession of two labyrinths increases the pressure of this small cavity and thus provokes an additional drop in the pressure difference between this cavity  18  and the pressurised chamber  16 . 
   The main added benefit here lies in the use of a harpoon type external labyrinth gland. Indeed, this layout makes it possible to make the second injection means in a solid element, other than a honeycomb type friction element, which would disturb the air jet. The solution proves to be very advantageous in that it avoids the disturbances due to passing through honeycomb structures  29 ,  30  and  31 , and in that it has fewer manufacturing constraints than the current solutions of the prior art. 
   The second injection means thus take the form of sloping piercings  17  to obtain a flow of air with a large component tangent to the rotor  38 , or the form of blades such as those that can be used to make the first injection means  1 . The overpressure generated in the small cavity  18  considerably reduces the discharge rates of the cooling circuit, with the consequence that more cold air coming from the first injection means manages to pass through the passage holes  6 . 
   Another particularity of the invention lies in the specific layout of the support  14  and of the first injection means  1 . Traditionally, the part of the support  14  holding the friction part  13   a  of the internal labyrinth gland  13   a  and  13   b  is placed under the air outlet of the first injection means  1 . In this configuration, this part of the support  14  is then subject to minor displacements engendered by these first injection means  1 , thus creating major discharges through the internal labyrinth gland  13   a  and  13   b . To compensate for this inconvenience, the stator can then have, as can be seen in  FIG. 2 , a gap between the outlet of the first injection means  1  and the part of the support  14  holding the friction part  13   a . This gap makes it possible to interpose between these two elements the third injection means, which also engender minor displacements of the support  14  holding the friction part  13   a . It is thus possible to control the clearance in the internal labyrinth gland  13   a  and  13   b , by decoupling the aforementioned two movements of the stator. Indeed, by adjusting the mass of the blocks  15 , the air flow rates in the piercings  3  and the number of these piercings, it is thus possible to adjust the relative position of the rotor and the stator in order to limit as much as possible any eventual discharges through this internal labyrinth gland  13   a  and  13   b.    
   The same is true of the external labyrinth gland  4   a  and  4   b . Indeed it is possible to control the minor displacements of the support  36  holding the friction part  4   a , by combining the effects of the inertia mass of this support  36  and the effects of the cooling generated by the sloping piercings  17  of the second injection means. 
   The third injection means also make it possible to obtain a top-up flow rate for the cooling air circuit of the blades, as well as stabilisation of the pressure in the pressurised chamber  16 . 
   Finally, note that the support  36  of the friction part  4   a  is bolted from the inside, contrary to common practice, this technique making it possible to save space in the external part for the supporting of the manifold. 
   Naturally, various modifications can be made by a person skilled in the art to the device that has been described, solely as a non-restrictive example.