Abstract:
A gas turbine, with a fixed inner housing, arranged concentric to the rotor, with a through flow of working medium, is disclosed. The housing comprises at least two serial rings with an annular gap left between two directly adjacent rings, whereby an annular sealing means is arranged in at least one peripheral groove for sealing the annual gap. According to the invention, a sealing means is provided which permits a greater movement of both components forming the gap, whereby the annual gap is formed by partly overlapping rings, running against the flow direction of the working fluid in the radial sense and the front most of the two rings, in the sense of the flow direction, comprises a locating annular surface for the sealing means embodied as an annular spring element on which the spring element rests under tension such as to seal the annular gap.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2004/009964, filed Sep. 7, 2004 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 03020720.3 filed Sep. 11, 2003. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a gas turbine with a rotationally fixed inner casing which is arranged concentrically with respect to the rotor, according to the claims, and to an annular sealing means for a gas turbine, according to the claims. 
     BACKGROUND OF THE INVENTION 
     Such a gas turbine is known from EP 1 118 806 A1. A freely projecting flexural extension is provided for sealing off a gap delimited by two partially overlapping wall segments. Under thermal action, the flexural extension flexes in such a way that it closes the gap. 
     EP 896 128 discloses a sealing element for a gas turbine. The gas turbine has a guide blade ring consisting of adjacent turbine guide blades which form an annular hot-gas duct. Platforms are arranged on the turbine blades for the inner and outer delimitation of the hot-gas duct. Directly adjacent platforms form, with their end faces lying against one another, a gap which is sealed off by means of a sealing element. For this purpose, a groove is introduced in each case in each end face, said grooves lying opposite one another and the sealing element being inserted into them. The sealing element, of C-shaped cross section, projects in each case with one of the two bent ends into a groove in such a way that the two arms of the sealing element which extend transversely with respect to the groove bottom bear in each case against a flank of the groove and thus seal off the gap between the two adjacent platforms. The working fluid flowing in the hot-gas duct is thus prevented from leaving the duct through the gap. 
     Furthermore, a sealing element is known from DE 100 44 848, which seals off a gap formed between two static turbine parts. The sealing element is likewise inserted in two grooves lying opposite one another, but, in contrast to EP 896 128, has a different geometry. The action and function of this sealing element are identical to those of the abovementioned sealing element. 
     When the gas turbine is in operation, thermal expansions arise on the components acted upon by hot gas, such as the guide blades and their platforms, and may lead to a displacement of the components with respect to one another. 
     In the case of a shear displacement directed parallel to the gap, the known sealing elements allow only relatively small displacement travel. 
     SUMMARY OF THE INVENTION 
     The object of the invention is, therefore, to specify a sealing means for a gas turbine, which is effective even in the case of greater displacement travel. The object is, furthermore to specify a gas turbine appropriate for this purpose. 
     The object is achieved, with respect to the gas turbine, by means of the features of the claims and, with respect to the sealing means, by means of the features of the claims. 
     The solution for achieving the object proposes, with respect to the gas turbine, that the sealing means be designed as a spring element with a first end, with a second end and with a spring region lying between them, and that the first end be secured in one of the two rings in a circumferential groove open toward the annular gap, and that the collar arranged on the other of the two rings have, for the second end of the spring element, an annular bearing surface, against which the spring element bears, prestressed, so as to seal off the annular gap, while, in order to generate the prestress, the spring region is supported on an annular supporting surface which is provided on the collar of the one ring and which faces the annular bearing surface. 
     When the gas turbine is in operation, the two rings move in relation to one another on account of thermal expansions. These movements are parallel to the annular bearing surface, perpendicular thereto or a mixture of the two movements. In this case, the spring prestress causes the automatic follow-up of the spring element on the annular bearing surface, without the spring element losing contact with the annular bearing surface and the spring element thus losing the sealing action. Only the contact line is displaced in the axial direction along the annular bearing surface. 
     In order to generate the spring prestress, the spring element utilizes as an abutment an annular supporting surface which is arranged on the inside, facing the hot-gas duct, of the outer collar. In this case, the spring element bears at least partially between its two ends against the abutment. The sealing action can be maintained, since, as a result of the support of the spring element, the free or second end can follow especially high radial displacements, that is to say, even when the gap dimension increases appreciably, the sealing action remains maintained. 
     Since the spring element has an elongate configuration in cross section, a greater shear displacement, that is to say in the radial direction with respect to the rotor, of the two components in relation to one another is possible. 
     Advantageous embodiments are specified in the subclaims. 
     Expediently, the inner casing is designed to diverge conically toward the rotor in the flow direction. 
     A simple overlapping of the collars arranged on the adjacent rings and extending in the direction of divergence is afforded when the front wing, as seen in the flow direction, has the radially inner collar and the rear ring has the outer collar, so that, as seen radially, the annular gap runs counter to the flow direction of the working fluid. This arrangement impedes the deeper inflow of the hot gas into the gap to be sealed off, since the hot gas loses kinetic energy during penetration as a result of the reversal in flow direction brought about by a bend at right angles. The spring element is thus acted upon by the hot gas solely by a lower radially outward-directed force than the spring prestress. 
     For this purpose, the fixed end of the spring element is introduced as fixed bearing in a circumferential groove provided on the end face of the rear ring and can be connected, gas-tight, to the rear ring by welding or soldering. During movements, therefore, the spring element always co-moves in synchronism with the rear ring. 
     In a further embodiment, the annular bearing surface is provided on that side of the radially inner collar which faces away from the working fluid and therefore on the front ring. The spring element, of S-shaped cross section, can then bear sealingly as a free bearing with its free end against the annular bearing surface. 
     Especially advantageous is the embodiment in which, outside the inner casing, a cooling medium can flow, the pressure of said cooling medium being higher than the pressure of the working fluid inside the inner casing, and in which the spring action of the sealing means runs in the direction of the pressure drop. As a result, the spring action of the spring element is assisted by the appreciable pressure drop between the cooling medium and working fluid. The additional pressure force thus generated is dependent on the area of the spring element on which the cooling medium can act and becomes higher with a rising pressure difference. The additional pressure force leads to an improved sealing action. Even in the event that the spring prestress diminishes, a reliable bearing of the free end of the spring element against the annular bearing surface is thus ensured during operation. 
     The solution for achieving the object proposes, with respect to the sealing means for a gas turbine, which seals off a gap delimited by two directly adjacent components which in each case have a collar in the region of the gap and therefore partially overlap one another, that the sealing means be designed as a spring element with a first end, with a second end and with a spring region lying between them, and that the first end be secured in one of the two components in a groove open toward the gap, and that the collar arranged on the other of the two components have, for the second end of the spring element, a bearing surface against which the spring element bears, prestressed, so as to seal off the gap, while, in order to generate the prestress, the spring region is supported on a supporting surface which is provided on the collar of the one component and which faces the bearing surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages described with regard to the gas turbine in this case also apply accordingly to the sealing means. 
       The invention is explained by means of drawings in which: 
         FIG. 1  shows an annular gap with a sealing means, 
         FIG. 2  shows a part longitudinal section through a gas turbine, and 
         FIG. 3  shows the annular gap according to  FIG. 1  with offset rings, 
         FIG. 4  shows the annular gap according to  FIG. 3  after calking of the circumferential groove. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a gas turbine  1  in a part longitudinal section. It has, inside it, a rotor  3  which is rotationally mounted about an axis of rotation  2  and which is also designated as a turbine rotor or rotor shaft. An intake casing  4 , a compressor  5 , a toroidal annular combustion chamber  6  with a plurality of coaxially arranged burners  7 , a turbine  8  and an exhaust gas casing  9  succeed one another along the rotor  3 . 
     In the compressor  5 , an annular compressor duct  10  is provided, which narrows in cross section in the direction of the annular combustion chamber  6 . At the outlet, on the combustion chamber side, of the compressor  5 , a diffuser  11  is arranged, which is flow-connected to the annular combustion chamber  6 . The annular combustion chamber  6  forms a combustion space  12  for a mixture consisting of a fuel and of compressed air. A hot-gas duct  13  is flow-connected to the combustion space  12 , the hot-gas duct  13  being followed by the exhaust gas casing  9 . 
     Blade rings are in each case arranged alternately in the compressor duct  10  and in the hot-gas duct  13 . A guide blade ring  15  formed from guide blades  14  is followed in each case by a moving blade ring  17  formed from moving blades  16 . The fixed guide blades  14  are in this case connected to a guide blade carrier  18 , whereas the moving blades  16  are connected to the rotor  3  by means of a disk  19 . 
     The guide blades  14  are fastened to the guide blade carrier  18  and at their end facing the guide blade carrier  18  have platforms  21  which outwardly delimit the hot-gas duct  13 . Arranged adjacently to the platforms  21  of the guide blades  14  in the flow direction are guide rings  22  which lie opposite the tips of the moving blades  16  and which delimit the hot-gas duct  13 . The platforms  21  of the individual guide blades  14  of a guide blade ring  15  in this case form a ring  25  which is adjacent to the guide ring  22  consisting of segments and between which an annular gap  23  is enclosed. The guide ring  22  and the platform ring in this case form an inner casing  37  for the working fluid  20  flowing through the rings. 
     While the gas turbine  1  is in operation, air  21  is sucked in by the compressor  5  through the intake casing  4  and is compressed in the compressor duct  10 . Air L provided at the burner-side end of the compressor  5  is led through the diffuser  11  to the burners  7  and is mixed there with a fuel. The mixture is then burnt in the combustion space  10  so as to form a working fluid  20 . The working fluid  20  flows from there into the hot-gas duct  13 . At the guide blades  14  arranged in the turbine  8  and at the moving blades  16 , the working fluid  20  expands so as to transmit pulses, so that the rotor  3  is driven and, with it, a working machine (not illustrated) coupled to it. 
       FIG. 1  shows a detail of the gas turbine  1  with a gap, for example an annular gap  23 . The annular gap  23  is in this case formed between a first component, the platform  21  of the guide blade  14 , and a second component, the guide ring  22 .  FIG. 1  illustrates only the components essential to the invention, that is to say the illustration of guide blades  14  and moving blades  16  and of the fastening of the guide ring  22  and of the platform  21  is dispensed with. 
     As seen in the flow direction of the working fluid  20 , the platforms  21  form the front ring  25  and the guide ring  22  forms the rear ring  26 . The front ring  25  has integrally formed on it, radially on the inside, a first collar  27  which extends in the direction of the following rear ring  26  along the conical run of the hot-gas duct  13 . The rear ring  26  has integrally formed on it, radially on the outside, a further collar  28  which overlaps the first collar  27 , as seen radially from the inside outward, so that the annular gap  23  is formed in cross section as an overlap gap. An overlap gap, in which the radially outer collar  28  is arranged on the front ring  25  and the inner collar  27  is arranged on the rear ring  26 , would, of course, also be possible. 
     Along the annular gap  23 , as seen from the inside outward, the latter first has a gap portion which runs in the radial direction and which is deflected in a bend  38  by the outer collar  28 , so that said gap portion has adjoining it in the axial direction a gap portion  29  which extends counter to the flow direction of the working fluid  20 . A second bend then occurs, which deflects the annular gap  23  into the radial direction again. 
     An annular bearing surface  32  is arranged on that side of the first collar  27  which faces away from the working fluid  20 . The annular supporting surface  33  is located, opposite the annular bearing surface  32 , on the outer collar  28 . 
     A groove, preferably a circumferential groove  31 , is provided in that end face  30  of the rear ring  26  which faces the front ring  25 . 
     The first end  34  of the spring element  24  is crimped and inserted into the circumferential groove  31 . In this case, the circumferential groove  31  may be somewhat smaller in its width than double the material thickness of the spring element  24 , in order to achieve an effectively bearing and reliable connection to the rear ring  26 . The spring element  24  may likewise be soldered or welded in the circumferential groove  31  to the rear ring  26 . 
     The first end  34  of the spring element  24  has adjoining it, in cross section, a spring region which runs in a slightly convex arc and which is supported on the annular supporting surface  33 . A prestress in the spring element  34  is thereby generated which is directed in the direction of the annular bearing surface  32 . 
     The convex arc, that is to say the spring region of the spring element  24 , has adjoining it a free second end  35  formed by a concave arc  39 . In order to achieve a good displaceability of the second end  35  on the annular bearing surface  32 , the concave arc  39  of the spring element  24  bears, air-tight, against the annular bearing surface  32  along a contact line  40  directed in the circumferential direction. 
     A rear space  36  separated from the hot-gas duct  13  by the rings  25 ,  26  is separated, air-tight, from the hot-gas duct  13  by means of the spring element  24  which bears against the two rings  25 ,  26  and is likewise designed as a ring consisting of segments. 
     In order to cool the rings  25 ,  26  or ring segments acted upon by the hot working fluid  20 , in the rear space  36  a cooling fluid flows, the pressure of which is higher than that of the working fluid  20 . The prestress of the spring element  24  is assisted by the force generated by the pressure drop, so that the spring element  24  is pressed even more firmly against the annular bearing surface  32 . A low cooling fluid outflow as a result of positional deviations, not to be ruled out, between individual segments of a ring or as a result of a surface roughness of the annular bearing surface  32  serves for cooling the spring element  24 . 
     The spring element  24  may in this case be produced from a heat-resistant alloy, for example from an alloy bearing the tradename of Nimonic  90 . 
       FIG. 3  shows the two rings  25 ,  26  in a position displaced in relation to one another after thermal expansion has taken place. In respect of  FIG. 1 , the length of the gap portion  29  is shortened, as seen in the flow direction of the working fluid  20 , but the distance between the two collars  27 ,  28  or the distance of the annular bearing surface  32  from the annular supporting surface  33  has increased, as compared with  FIG. 1 . As regards the rotor  3 , the two rings  25 ,  26  forming the annular gap  23  are displaced in relation to one another both in the radial direction and in the axial direction. 
     Alternatively to  FIG. 3 ,  FIG. 4  shows a spring element  24  clamped in the manner of a joint as a result of the calking of the circumferential groove  31 , so that there is a slight movability of the spring element  24  in the manner of a hinge. 
     By virtue of the spring prestress, the free end  35  of the spring element  24  remains in contact with the annular bearing surface  32  in spite of the high displacement travel and thus seals off the rear space  36  with respect to the hot-gas path  13 . Slight leakage streams of cooling fluid through the annular gap  23  into the hot-gas duct are in this case possible, and, as compared with the prior art, an improvement in the sealing action and a reduction in leakage are furthermore achieved. 
     Owing to the annular arrangement of the platforms  21  and guide rings  22  and due to the radial mounting required for these components, the platforms  21  described in the description and claims, the guide blade rings  15 , the rings  22 ,  25 ,  26  and also the spring elements  24  are in each case to be understood as meaning only segments of the respective ring. 
     Furthermore, the sealing means proposed may be used both between adjacent platforms of an individual blade ring and in other regions of the gas turbine, for example in the combustion chamber, when an overlap gap is formed between the components to be sealed off.