Abstract:
An arrangement for adjusting the diameter of a gas turbine stator includes a casing having a main portion and rings bordering a vein of a gas flow and located in front of respective levels of mobile blades of a rotor, and communication passages of a gas flow under pressure. The rings are surrounded by the casing and fixed thereto by circular groups of spacers. The rings include a wall extending from the casing to one of the rings and separating two chambers. The wall includes an outside edge curved into a spacer hook and engaged between the main portion of the casing and a respective appendage curved into a casing hook associated with the spacer hook. The communication passages of the gas flow under pressure exist between the chambers. At least one of the communication passages is realized by cavities through a junction of hooks.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is concerned with an arrangement for adjusting the diameter of a gas turbine stator. 
     2. Description of the Background 
     Today some gas turbines include adjusting devices to adjust the inside diameter of a stator in order to reduce the existing play between the stator and the mobile ends of rotor blades to the lowest possible value. A frequent device used to provide this diameter adjustment includes taking a portion of fresher gases originating in compressors, conveying the portion through the stator and blowing the portion onto stator driving rings extending in front of rotor blades. This makes it possible to carry out what is referred to as stator ventilation, the diameter of the stator being modified according to the temperature and flow of ventilation gases. Generally, the bleeding of gas is dual: one source known as a hot source with a fixed flow dilates the casing when necessary, while another source known as a cold source with a variable and controlled flow contracts the casing. 
     The path that the hot source ventilation gases use is a volume internal to the stator between the rings to be ventilated and the casing that surrounds them. Spacers linking the rings to the casing include transverse walls breaking the volume of the path into chambers, and through which it is necessary to create communication to make it possible for the ventilation gases to flow. Numerous examples of such communication means have been suggested in the prior art, but a good ventilation is not easy to ensure because it must be well distributed between successive rings and on the surface of each of these rings, otherwise the differences of ventilation intensity and of thermal dilation around the rings circumference will produce undulations of rings, and thus leave areas of gas escapes at the ends of the rotor blades. Moreover, openings arranged through the spacers weaken the rings, with dangerous consequences for portions of the machine subjected to strong mechanical stress, because stresses are concentrated around these openings. 
     SUMMARY OF THE INVENTION 
     The purpose of this invention is thus to suggest a gas turbine stator arrangement, the inside of which is compartmentalized, but provided with openings allowing ventilation gas to be blown onto the rings of the stator subjected to an adjustment. The openings are designed to produce a highly regular ventilation around the rings without exaggeratedly weakening structural elements through which they are drilled. 
     The present invention in its most general form relates to an arrangement for adjusting the diameter of a gas turbine stator. The stator includes a casing, rings bordering a vein of flowing gases and located in front of respective levels of mobile blades of a rotor, the rings being surrounded by the casing and fixed to the casing by circular spacers. Each ring includes a transversal wall extending from the casing to one of the rings and separating two chambers. The wall includes an outside edge curved into a spacer hook and engaged between a main portion of the casing and a respective appendage curved into a casing hook associated with the spacer hook. Communication paths of gas under pressure exist between chambers. At least one of the communication passages is carried out by cavities provided through a junction of hooks made up of one spacer hook and the casing hook with which it is associated. 
     Because spacer hooks and casing hooks are appendages or ends of these structures, they are subjected to moderate stress and the creation of openings through them produce acceptable levels of stress. Preferably, the communication means between chambers suggested herein include longitudinal notches cut through each spacer hook, a circular space located under the respective casing hook and outside the spacer hook, and radial notches made into the spacer hook between the longitudinal notches and the opening in the aforesaid chambers. 
     Two main designs of this arrangement are suggested: either radial notches are sufficiently deep to extend beyond the hook of the casing, or they include collecting portions followed by drillings; this last fitting lends itself readily to a calibration of the flow of ventilation (according to the intake section of the radial notches or drillings) and to the calming of gas in the chamber downstream from the flow (after passing through the tightened portion of drillings). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a cross sectional view of a fragment of a stator illustrating a spacer equipped with the invention and its parings; 
     FIG. 2 is a cross sectional view of the stator illustrating the presence of a second air ventilation system, optional, with the same embodiment of ventilation spacer; 
     FIG. 3 is a three dimensional plan view of a portion of the stator illustrating spacer hooks; and 
     FIGS. 4-9 are cross sectional views of different portions of the stator illustrating ways of creating drillings supplementing or facilitating ventilation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a fragment of a stator  1  of a gas turbine including some surrounding elements of FIG.  2 . Stator  1  includes a casing  2  outside, surrounding rings  3  coming opposite levels of mobile blades  5  of a rotor  6  within a vein  7  of gas flow, and rings  3  alternate with other rings  8  supporting fixed blades  9  along vein  7 . Gas turbines include several successive rings  3  and  8 , but only one of each kind is illustrated on the fragment of FIGS. 1 and 2, the invention being applied here only to a ring  3 . 
     Spacers  10  link rings  3  to casing  2 . Junctions  11 ,  12 ,  13  and  14  are generally made up of an assembly of a pair of hooks and link spacer  10  to stator  1  at the front and at the back. To reduce the play between rings  3  and mobile blades  5  during the operation of the gas turbine, fresher gases originating in a compressor upstream of a gas turbine are tapped to be blown outside of rings  3  and onto the face opposite mobile blades  5 . Spacer  10  includes a transverse wall  15  at the front between junctions  11  and  13 , a transverse wall  16  at the back between junctions  12  and  14 , and an intermediate transversal wall  17  connecting both the preceding ones and laid out obliquely and appreciably between junctions  13  and  12 . Accordingly, ventilation gases passing through casing  2 , but around rings  3  and  8 , pass initially through a first chamber  18  at the front of wall  15 , then through an intermediate chamber  19  between wall  15  and intermediate wall  17 , and finally through a downstream chamber  20  between the intermediate wall  17  and rings  3 . Downstream chamber  20  is delimited by rear wall  16  and is divided by a lid provided with drillings, or more generally one box  21  made up of several of these lids, already described in the prior art as contributing to the equalization of ventilation (for example in U.S. Pat. No. 5,273,396). The rear wall  16  is a wall external to the ventilation chambers  18 ,  19  and  20 , because the flow of ventilation stops there and another atmosphere starts from there. 
     Communications allowing gases from a compressor to flow through chambers  18 ,  19  then  20  include openings arranged mainly through junctions  11  and  12  to casing  2 . The next description below shall be read with reference to FIG.  3 . 
     Junction  11  is made up of an edge of the front of wall  15 , curved downstream (or rear) to form a spacer hook  26 , and one appendage associated with casing  2 , the end of which is curved upstream (or towards the front) to give one casing hook  27 . In a similar way, rear and intermediate walls  16  and  17  end onto a common facing backwards, forming another spacer hook  28 , whereas an appendage associated with casing  2  is also bent forwards to form another casing hook  29 . Spacer hooks  26  and  28  are inserted between casing  2  outside and respective of casing hooks  27  and  29  inside. 
     Spacer hook  26  located at the front is not a continuous or intact structure, but rather has longitudinal and parallel notches  30  regularly distributed over its circumference, cutting it straight through its outside face and thus extending from the upstream chamber  18  to the annular space  31  ranging between the end of spacer hook  26  and the bottom of casing hook  27 . Spacer hook  26  is also notched with parallel radial notches  32 , and regularly distributed over the circumference of spacer hook  26  at a middle distance of longitudinal notches  30 , and radial notches  32  have a sufficient depth to extend beyond the end of casing hook  27 . The spaces  31  and  34  arranged between the ends of spacer hooks  26  and  28  and the bottom of the casing hooks  27  and  29  will be improved if their meridian section is increased by providing rabbets  50  (as shown in FIG. 3) on external faces of the spacer hooks  26  and  28 , on the side of the casing hooks  27  and  29  and by extending longitudinal notches  30  and  33 . Rabbets  50  have several advantages including: the reduction of contact surface between the spacer and casing, hence reducing casing overheating due to conduction; better control of flow section of the air circulating in circumference because manufacturing dispersions are lower for rabbets  50  than for the bottom of the groove of the casing hooks; better control of peripheral speed of air flow and convective exchange coefficients; and greater convective heat-transferring surface on casing  1  and thus better control over the flow of heat and its homogeneity. 
     Heat exchanges are produced in spaces  31  and  34 . They are regulated by the surface casing  1  wet by gas of; the speed of air flow in circumferential direction; the number of longitudinal notches  30  and  33 , and therefore the length of circumferential paths. 
     A communication between chamber  18  and  19  is thus established, the ventilation gases flowing through longitudinal notches  30 , then through the space  31  where they disperse and finally through radial notches  32 . 
     Notches  30  and  32  that weaken structures and concentrate stress are established only on the hooks of junction  11 , i.e. on portions of edges not likely to produce high stress concentration. The movement of dispersion of the flow through space  31  contributes to regulate the flow of gas on the circumference of the machine, and thus the ventilation effect. The changes of direction to which the flow is subjected result in loss of load beneficial to the effectiveness of ventilation. Finally, gases are discharged in centripetal direction, towards rings  3 . 
     It should be obvious at this point that notches are cut only through the spacer hook  26 , but similar suitable results would most probably be obtained if radial notches had been made into the casing hook  27 . 
     A similar provision makes it possible to establish communication between chambers  19  and  20 . Longitudinal notches  33  similar to notches  30  of hook  26  are initially cut into the spacer hook  28  located at the back, and a space  34  similar to the space between the end of the spacer hook  28  and the bottom of the casing hook  29  is provided; ventilation gases discharge in this space  34  towards radial notches  35  made in between longitudinal notches  33 . However, the ventilation gases do not communicate directly with the downstream chamber  20 , but instead with drillings  36  in a variable number for each radial notch  35 . Drillings  36  extend towards chamber  20  by going through the material of spacer  10  at the junction of walls  16  and  17 . This arrangement offers the same characteristics and advantages as those of the assembly at junction  11 , and drillings  36  are directed obliquely with a strong centripetal component directing ventilation gases as required towards rings  3 . Notches  33  can still open into rabbets  50 , which prolong them towards space  34 . Gases ventilate onto rings  3  with an even greater regularity through box  21  before discharging the gases through escapes of the structure and outlet channels  51  provided through the skin of rings  3 , and into vein  7 . The stop created by the end of casing hook  29  located behind and against the rear wall  16  ensures there will be spaces established in spaces  31  and  34 , and the ring  8  located immediately upstream reinforces this push by pressing against the front wall  15  at the outside front of junction  13 . A joint  37  placed in a groove of the hook  29  and compressed by the rear wall  16  ensures the downstream sealing of junction  12 ; the section of joint  37  is made up of three lobes placed in a row and for this reason joint  37  is called an omega joint. The sealing between adjacent joint  37  and the hook  29  is doubled by the plane push  52  of the casing hook  29  against rear wall  16 , forming one line of uninterrupted sealing. Radial notches  35 , drillings  36 ,  42  and  43  are designed such that they do not interrupt this line of sealing while making space  34  to communicate with the chamber of joint  37 . 
     Arrangements of FIGS. 8 and 9 allow for the same result. As shown in FIG. 8, radial notches  53  (instead of  35 ) extend in spot-facing on a portion  54  of the rear wall  16  to provide access to drillings  36 , while reducing the width of the plane push  52 , but without removing it. As shown in FIG. 9, notches  55  (instead of  35  or  53 ) extend only in the inside face of spacer hook  28 , in front of casing hook  29 , thus lengthening a gases path in the cavities of radial notches  34 . Other fittings are also possible. The hollow portion  54  of rear wall  16  facilitates air intake into the drillings. 
     Box  21  can be a simple impact sheet with multiple drillings and can be fixed either to the ring or to the spacer. Box  21  is hung to edges  38  and  39  of rings  3 . The favorable direction of ventilation gases would allow bringing box  21  closer to gases intake in chamber  20 , by having it supported by edges  40  and  41  of spacer  10  located on walls  15  and  16 , as shown in FIG.  4 . 
     Drillings  36  have a constant section, but may be replaced by divergent drillings with the section increasing towards the downstream chamber  20 , such as a staged drilling  42  with sudden variation of diameter, as shown in FIG. 5, or nozzle drilling  43  with progressive variation of diameter, as shown in FIG.  6 . Drillings  42  and  43  would be located like drilling  36 , but the size of intake and outlet diameters would make it possible to act at the same time on the calibration of ventilation gas intake (thanks to the smaller intake diameter) and upon the quietness effect produced in chamber  20  intake (thanks to the larger outlet diameter), which would improve the supply of box  21 . 
     This invention may also be combined with more traditional communication means between chambers, such as drillings  44  of FIG. 7 provided between chamber  18  and chamber  20  through the material of spacer  10  laid out at the junction of transverse walls  15  and  17 ; the invention would then make it possible to mitigate the weakening mechanical effect produced by drillings  44 , while reducing their required number. 
     From FIG. 2, it can seen that stator I may be equipped with external ribs  45  in front or between which distribution chambers  46  of another gas ventilation network forming a cold source are laid out, these distribution chambers  46  being connected to supply pipes  47  used for the circulation of gases. Distribution chambers  46  have blowing holes in front of ribs  45  for the gas to reach them. Often, a second ventilation gas flow will be tapped from a portion of a compressor located further upstream from the first flow portion, so that the gas of this second flow will be fresher. The adjustment of the rings 3 diameter will then consist of a combined adjustment of both ventilation flows providing an excellent precision.