Seal structure for a gas turbine

Abstract: The invention relates to a structure of a seal ring separating surface for a gas turbine, which sets a shape of an end portion in the separation surface to a perpendicular cutting surface and reduces a leaking amount of a sealing air. A seal ring holding ring (1) within a stationary blade fixes brush seals (3, 4) to an upstream side by bolts (5, 6) respectively, so as to form a seal with respect to a rotor disc (69). Further, it fixes and supports a seal ring (2) to a downstream side by a bolt (7) so as to constitute a seal with respect to a seal portion (8) in a disc (69) side. The brush seals (3, 4) and the seal ring (2) are structured such as to have a circular ring shape and a separation construction, and each of the separation pieces has a gap, so that a sealing air leaks to a downward side from an upward side through the gap, however, since the separation piece end portion is formed in a perpendicular cutting surface and a shape of the gap is formed in a bypass passage, a resistance of an air flow passage is increased and a leaking air amount is reduced.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The invention relates to a seal structure for a gas turbine, and more particularly to a seal separating surface connecting structure which reduces a leaked air amount from a seal separating surface and improves a sealing performance, and a structure which employs a brush seal so as to prevent a support plate of the brush seal from doubly contacting with a rotation side and makes a sealing interval small so as to improve a sealing performance. An example of such a seal structure is disclosed in EP 0 816 726 A. Fig. 9 is a cross sectional view which shows a general seal structure for a conventional gas turbine. In the drawing, reference numeral 61 denotes a stator blade, reference numeral 62 denotes an outer shroud thereof, and the outer shroud 62 is supported to a blade ring 70. Reference numeral 63 denotes an inner shroud, reference numeral 64 denotes a flange portion thereof and reference numeral 65 denotes a seal ring holding ring. The seal ring holding ring 65 is held to the flange portion 64 of the inner shroud 63, and supports a seal ring 66 in an inner side (a rotor side) thereof reference numerals 67 and 68 denote a seal portion, and seal fins 67a and 67b are provided in a side of a rotor disc 69, thereby constituting a seal portion in opposition to the seal portion of the seal ring 66. Reference numeral 81 denotes a rotor blade, and reference numeral 82 denotes a platform thereof, which is mounted to the rotor disc in adjacent to the stator blade 81 and rotates together with the rotor. Reference numeral 71 denotes a tube for a sealing air, which is provided within the stator blade 61, extends through the inner shroud 63 from the outer shroud 62 and is structured such as to introduce the sealing air within a cavity 75. Reference numerals 72, 73 and 74 denote a space formed with respect to the adjacent rotor blade. In the stator blade having the structure mentioned above, an air 40 introduced from an inner portion of the sealing air tube 71 within the stator blade 61 to an inner portion of the cavity 75 passes through a hole 65a in the seal ring holding ring 65 and flows to enter into the space 72 as shown by reference symbol 40a, and a part thereof flows out from the space 72 to the space 73 as a leaking air from the seal portion 68 as shown by reference symbol 40b, passes between the platforms of the rotor blade adjacent to the inner shroud 13 therefrom as shown by reference symbol 40c and flows out to a main current gas passage. Further, the air also flows out to the space 74 from the space 72 through the portion between the seal ring 66 and the seal portions 67a and 67b as shown by reference symbol 40d, and flows out from there through the portion between the inner shroud 63 and the platform 82 of the adjacent rotary blade 81 as shown by reference symbol 40f. A pressure within the cavity 75 and the spaces 72, 73 and 74 is increased in comparison with the outer main current gas passage due to the air current mentioned above, thereby preventing a combustion gas having a high temperature from entering to the inner portion. Accordingly, in order to increase a sealing performance, it is necessary to increase a sealing performance of a labyrinth seal constituted by the seal ring 66, the seal portion 67 in the rotor side and the seal portion 68 and reduce a leaking air. amount shown by reference symbols 40b, 40c, 40e and 40f, and when it is possible to reduce the flowing-out air amount, it is possible to reduce the sealing air amount, so that it is possible to improve a performance of a whole of the gas turbine. Fig. 10(a) is a schematic view as seen from a line Z-Z in Fig. 9, which illustrates an upper half. Further, Fig. 10(b) is a schematic view along a line W-W in Fig. 10(a). The seal ring 66 is formed in a circular ring shape and is separated into a plurality of portions, and in the drawing, the upper half portion is separated into three portions comprising (A), (B) and (C) (totally separated into four portions). Fins 66a, 66b and 66c are respectively mounted to the separated pieces (A), (B) and (C), which are opposed to the seal portions 67a and 67b in the side of the rotor disc 69. In the separated structure of the seal ring 66 mentioned above, a gap 51 is disposed between the separated pieces (A) and (B), a gap 52 is disposed between the separated pieces (B) and (C), and the air flows out from an upstream space 72 (refer to Fig. 9) to a downstream space 74 (refer to Fig. 9) as the leaking air shown by gaps 51 to 60 as shown in Fig. 10B, so that a seal performance of the seal ring 66 is lowered. As mentioned above, the seal structure for the conventional gas turbine is structured such that the seal ring 66 is separated into a plurality of portions, as mentioned above, and has a gap on a connecting end surface between the separated pieces of each of the seal rings. It is necessary to structure the gap such that a certain degree of gap is kept in connection with a thermal expansion of the seal ring. The gap is formed in a straight shape from the upstream of the main current gas to the downstream side, and the sealing air leaks from the upstream side to the downstream side, so that a performance of the labyrinth seal constituted by the seal portion of the seal ring 66 and the seal portion 67 of the rotor disc 69 is lowered, and the sealing air amount is increased, thereby giving an effect to the performance of the whole of the gas turbine. Further, in recent years, in order to improve the seal performance of the stator side and the rotor side in the gas turbine for a flying machine or an industry, the brush seal is going to be used. Fig. 11 is a representative cross sectional view of the industrial gas turbine, in which reference numeral 101 denotes a rotor blade, reference numeral 102 denotes a platform and reference numeral 103 denotes a seal pin within the platform 102, which is constituted by portions 103a, 103b and 103c. Reference numerals 102a and 102b denote a seal portion at both end portions in front and rear of an axial direction of the platform 102. Reference numeral 104 denotes a shank portion and seal plates 106 and 107 are provided in front and at the rear of the shank portion. Reference numeral 105 denotes a disc for a rotor, to which parts of each of the rotor blades 101 to 104 mentioned above are mounted. Reference numeral 91 denotes a stator blade, reference numeral 92 denotes an inner shroud and reference numeral 93 denotes an outer shroud. Reference numerals 92a and 92b denote both end portions in front and at the back of an axial direction of the inner shroud 92. Reference numeral 94 denotes a cavity formed within the inner shroud 92, into which the sealing air is flowed through the inner portion of the stator blade 91. Reference numeral 95 denotes a seal box, which holds a labyrinth seal 100 at one portion and a brush seal 101 at the other portion. Reference numerals 96 and 97 denote a honeycomb seal provided at both end portions 92a and 92b of the inner shroud 92. Reference numerals 98 and 99 denote a space formed with respect to each of the adjacent front and rear rotor blades, which corresponds to a flow passage for the sealing air. In the gas turbine having the structure mentioned above, the sealing air is introduced into the cavity 94 from the sealing air passage (not shown) passing through the inner shroud 92 after passing from the side of the outer shroud 93 in the stator blade 91 through the inner portion of the blade, is flowed out within the space 99 from a hole provided in a seal box 95 (not shown), passes through the honeycomb seal 96 provided at the end portion 92a of the inner shroud 92, and is flowed out to the combustion gas passage. Further, a part of the sealing air flowing out from the hole in the seal box 95 is also flowed out to the forward space 98 through the brush seal 101 and the labyrinth seal 100 with respect to the disc 105, and is flowed out to the combustion gas passage through the honeycomb seal 97 provided at the front end portion 92b of the inner shroud 92. As mentioned above, the sealing air is introduced within the cavity 94 through the inner portion of the stator blade 91, and the sealing air is introduced to the space 99 sealed by the honeycomb seal 96 from the cavity 94 with respect to the combustion gas passage and further to the forward space 98 sealed by the honeycomb seal 96 through the brush seal 101 and the labyrinth seal 100 with respect to the combustion gas passage, so that a pressure in the cavity 94 and the spaces 98 and 99 is increased higher than the pressure in the outer combustion gas passage, thereby preventing the combustion gas having a high temperature from entering to these portions. Fig. 7 is an enlarged cross sectional view of the brush seal 101 corresponding to the seal portion of the gas turbine mentioned above. In the drawing, the brush seal 101 is mounted to the upstream side of the labyrinth seal 100 in the seal box 95 so as to constitute the seal portion with respect to the disc 105 of the rotor. The brush seal 101 comprises a front portion support plate 31 and a rear portion support plate 32, a brush 33 comprising a multiplicity of narrow wires is fixed to a center portion thereof by a welding portion 35, and a front end thereof constitutes a seal portion in closely contact manner with the disc 105. A gap 34 is provided between the front portion support plate 31 and the brush 33, and the structure is made such as to move against a pressure in the upstream side. Widths Wf and Wa of support plate front ends 31a and 32a of the front portion and rear portion support plates 31 and 32 are set to about 2 mm, and the brush 33 is held at the front end portions. Fig. 8 is a plan view of the brush seal 101, which is mounted after being separated into six portions in a circular ring shape, and an end surface thereof is brought into contact with the seal brushes adjacent to each other with an incline of 45 degrees in a rotational direction R with respect to a circular ring-like center line. The brush 33 is constituted by bundling a multiplicity of wires each having a diameter of 0.1 mm, and structured such that a width is set to about 2 mm and 1500 to 2000 wires are provided at each 25 mm length of the brush seal. The brush seal 101 structured in the above manner is separated into six portion in a circumferential manner, and the front end of the brush 33 is closely contact with the disc 105 in the rotor side, thereby constituting the seal portion. As mentioned above, the brush seal is used for the seal portion between the stationary portion and the rotary portion of the gas turbine, however, as shown in Fig. 7, the widths Wf and Wa of the front ends 31a and 32a of the support plate of the brush seal 101 are large at about 2 mm since they support the front end portion of the brush 33, so that the front end of the brush 33 deforms due to a thermal deformation of the disc 5 in the rotor side. In the case that the front ends 31a and 32a are brought into contact with the disc 105, the front ends 31a and 32a give a serious damage onto the surface of the disc 105 in the rotor due to a significant rigidity thereof. Accordingly, the damage of the rotor gives a serious trouble to an operation of the gas turbine, so that a maintenance and a replacement are performed on a large scale, and it is necessary to avoid the damage of the rotor as much as possible. SUMMARY OF THE INVENTION Then, the invention is made for the purpose of providing a seal structure for a gas turbine which designs a shape of a separation end portion of a seal ring, reduces an amount of air leaking from a separation portion and improves a seal structure in the seal portion so as to improve a sealing performance. Further, the invention is made for the additional purpose of improving a shape of a front end portion of a brush seal of a gas turbine, thereby avoiding a double contact even when a rotor disc and a front end of the brush seal are brought into contact with each other so as not to give a serious damage to the rotor. In order to achieve the object mentioned above, the invention provides the following means. (1) A seal structure for a gas turbine comprising a seal ring holding ring supported to an inner shroud in a stationary blade, and a circular ring-like seal portion supported to the seal ring holding ring and surrounding a periphery of a rotor in a state of keeping a predetermined gap obtained by taking a thermal expansion into consideration between end portions of a plurality of separation pieces or contacting the end portions, thereby constituting a seal portion with the rotor, wherein the circular ring-like seal portion is constituted by a brush seal at an upstream side of a main current gas and a labyrinth seal at a downstream side, an end surface of each of separation pieces of the brush seal and the labyrinth seal is formed in such a manner as to form opposing contact surfaces formed by cutting along a polygonal line. Preferred embodiments of the invention are as follows: (2) A seal structure, wherein the seal ring holding ring is separated into two portions at the upstream side and the downstream side, and one of them supports the brush seal and the other of them supports the labyrinth seal, respectively. (3) A seal structure wherein the brush seal comprises front and rear support plates mounted to a seal support portion inside a stationary blade of a gas turbine, a brush supported between front and rear support plates and a front end of the brush sealing with respect to a rotary portion in a rotor side, wherein the front end portions of the front and rear support plates for supporting the front end portion of the brush have an axial thickness of 0.2 to 0.8 mm and are formed in a fin shape. (4) A seal structure having a brush seal for a gas turbine as recited in (3), wherein the front end portion of the support plate forms a fin shape by a smooth curved surface. (5) A seal structure having a brush seal for a gas turbine as recited in (3), wherein the front end portion of the support plate forms a fin shape by a straight tapered shape. In the seal structure in accordance with the invention, since the upstream side of the circular ring-like seal portion is constituted by the brush seal, a sealing performance is improved in comparison with the conventional labyrinth seal. Further, since the end surface of each of the separation pieces in the circular ring-like seal portion has the shape contact with each other at the cutting surface formed in the polygonal line, an air which is going to flow out to the downstream side from the upstream side through the gap is hard to be leaked in comparison with the conventional straight flow passage because the flow passage becomes a bypass passage and a flow resistance is increased, even when a gap is generated due to a thermal deformation in a contact of the cutting surface. Accordingly, a leaking air amount is reduced, a sealing performance is improved, and an air amount is reduced, so that a performance of the whole of the gas turbine is improved. In the aspect (2) in accordance with the invention, the seal ring holding ring is separated into two portions and one of them supports the brush seal and the other of them supports the labyrinth seal, respectively. Accordingly, in addition to the effect of the aspect (1) mentioned above, there is an advantage that an assembling and working performance thereof can be improved since an assembly of each of the brush seal and the labyrinth seal can be separately performed. In the brush seal in accordance with the aspect (3) of the invention, the front end portions of the front and rear support plates for supporting the front end portion of the brush have a thickness of 0.2 to 0.8 mm which is thinner than 2 mm in the conventional case, and is formed in a fin shape. In accordance with the structure mentioned above, the stationary side and the rotor side are thermally deformed, so that even when the front end of the support plate is brought into contact with the rotor side, the front end of the support plate deforms due to the thin fin shape and the elasticity. Accordingly, the support plate side is deformed without being in a double contact of the rigid body in the conventional art, or the support plate itself is broken, thereby avoiding a damage to the rotor side. Further, since the double contact can be avoided and an elastic force can be added, a seal interval can be made smaller than the conventional one, so that a sealing performance can be improved. In the aspect (4) in accordance with the invention, since the front end portion of the support plate forms the fin shape by the smooth curved surface, and in the aspect (5), the front end portion of the support plate forms the fin shape by the straight tapered shape, respectively, the front end portion gradually changes so as to form a narrow front end, so that a strength of the front end portion can be secured. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional view which shows a structure of a seal separation surface of a gas turbine in accordance with a first embodiment of the invention; Figs. 2(a), 2(b) and 2(c) are schematic views which show a detail of a seal portion in Fig. 1, in which Fig. 2(a) is a schematic view along a line X-X, Fig. 2(b) is a schematic view showing a shape of an end portion in each of separation pieces, and Fig. 2(c) is a schematic view along a line Y-Y in Fig. 2(a); Fig. 3 is a perspective view which shows a shape of a perpendicular cutting surface of a brush seal in Fig. 2; Fig. 4 is a cross sectional view which shows a structure of a seal separation surface of a gas turbine in accordance with a second embodiment of the invention; Fig. 5 is a cross sectional view of a brush seal of a gas turbine in accordance with a third embodiment of the invention; Figs. 6(a) and 6(b) are cross sectional views of a front end portion of a brush seal of a gas turbine in accordance with a fourth embodiment of the invention, in which Figs. 6(a) and 6(b) show a circular arc shape and a straight taper shape, respectively; Fig. 7 is a cross sectional view of a brush seal of a conventional gas turbine; Fig. 8 is a plan view of a separation piece of a conventional brush seal; Fig. 9 is a cross sectional view which shows a seal structure of the conventional gas turbine; Figs. 10(a) and 10(b) are schematic views which show a detail of a seal portion shown in Fig. 9, in which Fig. 10(a) is a schematic view along a line Z-Z and Fig. 10(b) is a schematic view along a line W-W in Fig. 10(a); and Fig. 11 is a general cross sectional view of a rotor blade and a stationary blade of the conventional gas turbine. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment in accordance with the invention will be particularly described below with reference to the accompanying drawings. Fig. 1 is a cross sectional view which shows a connecting structure of a seal separation surface of a gas turbine in accordance with a first embodiment of the invention, in which only a seal portion is shown in an enlarged manner. The description will be next given with reference to the conventional structure shown in Fig. 9. In Fig. 1, reference numeral 1 denotes a seal ring holding ring, and reference numeral 2 denotes a seal ring supported by the seal ring holding ring 1. Reference numerals 3 and 4 denote a brush seal, and the brush seal 3 is fixed to the seal ring holding ring 1 by a bolt 5 and is provided in place of the conventional seal portion 68 shown in Fig. 9. The brush seal 4 is provided for constituting a seal portion in place of the upstream seal portion 67 in the conventional rotor disc 69. Reference numerals 5 and 6 denote a bolt for fixing the brush seals 3 and 4 to the seal ring holding ring 1. Reference numeral 7 denotes a bolt for fixing the seal ring 2 to the seal ring holding ring 1, and reference numeral 8 denotes a seal portion in the side of the rotor disc 69 which is the same as the conventional one. The seal ring 2 is made smaller than the conventional seal ring 68 and structured such as to form a labyrinth seal with respect to the seal portion 8 in the downstream side of the rotor disc 69 and form a seal portion by the brush seals 3 and 4 at the upstream side. The other structures are the same as the conventional embodiment shown in Fig. 9, and an operation of the seal is the same, so that a description will be omitted. Fig. 2 is a schematic view along a line X-X in Fig. 1, which shows an upper half portion of the brush seal 3, and the brush seal 3 is separated into three portions comprising (A), (B) and (C) (totally into four portions) as shown in Fig. 2(a). Both end portions of each of the separation pieces respectively form perpendicular cutting surface 9a and a perpendicular cutting surface 9b opposing to the perpendicular cutting surface 9a as shown in Figs. 2(b) and 3, respectively. In this case, the perpendicular cutting surfaces 9a and 9b are not always limited to a right angle, and an angle thereof may be an acute angle or an obtuse angle, however, a right angle is preferable in view of an assembling performance and an accuracy of a gap. The separation piece forming the both end portions connects the perpendicular cutting surfaces 9a and 9b in an opposing manner as shown in Fig. 2(c), and is arranged with keeping a gap 10 in consideration with a thermal expansion. Such a gap 10 is a perpendicularly bypassing gap, and a flow resistance of the leaking air becomes higher than the straight flow passage, so that the leaking air is reduced in comparison with the conventional one. Further, an illustration is omitted, however, a width of a seal fin in the seal ring 2 becomes wide, however, the separation piece can be connected by making the width of the seal fin portion to form the perpendicular cutting surface in the same manner as that mentioned above. In this case, a shape of the brush seals 3 and 4 and the perpendicular cutting surface 9a are shown in Fig. 3, however, the brush seal is structured such as to have brushes 3a and 4a at a center thereof. In accordance with the first embodiment described above, the brush seals 3 and 4 and the seal ring 2 are respectively provided in the upstream side and the downstream side of the seal ring holding ring 1, and the separation piece is arranged in such a manner as to oppose to each other with keeping a gap 10 by setting the seal ring 2 and the separation end portions of the brush seals 3 and 4 to the perpendicular cutting surfaces 9a and 9b, whereby the leaking amount of the sealing air is reduced and the sealing performance is improved. Further, an air amount is reduced and a performance of the whole of the gas turbine is improved. Fig. 4 is a cross sectional view which shows a structure of a seal separation surface of a gas turbine in accordance with a second embodiment of the invention. In the drawing, a different point from the first embodiment shown in Fig. 1 is a structure in which the seal ring holding ring 1 is separated into portions 1a and 1b, the brush seals 3 and 4 are mounted to the portion 1a and only the seal ring 2 is mounted to the portion 1b. In accordance with the second embodiment mentioned above, it is possible to independently process and assemble the brush seals 3 and 4 to the seal ring holding ring 1a and process and assemble the seal ring 2 to the seal ring holding ring 1b, respectively, so that there is an advantage that an assembling can be easily performed. A shape, an operation and an effect of the perpendicular cutting surface of each of the separation pieces in each of the seal ring 2 and the brush seals 3 and 4 are the same as those of the first embodiment. In this case, in accordance with the first and second embodiments of the invention, the description is given of the embodiment in which the brush seals 3 and 4 are used in the upstream side of the seal ring holding ring 1 and the seal ring 2 is used in the downstream side thereof, however, of course, when the structure is made such that the perpendicular cutting surfaces 9a and 9b as shown in Fig. 2 are formed at both ends of each of the separation pieces of the seal ring 66 in accordance with the conventional embodiment shown in Fig. 9 so as to form the gap 10, the same effect can be obtained. However, in accordance with the present embodiment using the brush seals 3 and 4, the sealing performance is further improved by the brush seal in comparison with the conventional seal portion 68and the structure in which the perpendicular cutting surfaces 9a and 9b are provided only in the seal ring 66. Fig. 5 is a cross sectional view of a brush seal of a gas turbine in accordance with a third embodiment of the invention. In the drawing, since a characteristic portion of the invention exists in a portion of front ends 22 and 23 of support plates and the other structure is the same as the conventional embodiment shown in Fig. 7, a detailed description will be omitted and the description will be given by citing the portions as they are. In Fig. 5, reference numerals 22 and 23 denote front ends of front and rear support plates, and they constitute front end portions of the front and rear support plates 31 and 32, respectively. The shape thereof is structured such that plate base portions 31b and 32b having the same width Wf and Wa as the conventional ones and the front ends 22 and 23 of the support plate at the front end portion thereof are formed. A width t of the front ends 22 and 23 is within a range of 0.2 to 0.8 mm, and the most preferable range is 0.5 to 0.8 mm, and the front ends are formed in a thin fin shape. The conventional width Wf and Wa shown in Fig. 7 are about 2 mm thickness, however, the conventional front ends 31a and 32a are in doubly contact due to the rigidity thereof by contacting with the rotor side, so that the rotor side is damaged, and in some cases, a great influence is given to the operation such as a replacement of an important part of the gas turbine and the like. With respect to the preferable range mentioned above, when it is 0.5 mm or less, a working accuracy for securing a sufficient strength so as to support a pressure difference is required, and when it is 0.8 mm or more, there is a possibility that a double contact with the rotor is affected in the case of being in contact. In accordance with the present embodiment, by making the front ends 22 and 23 thin fin type, even in the case of being brought into contact with the rotor side, the front ends 22 and 23 deform and slide together with the front end of the brush 33 due to an elasticity thereof, and the front ends 22 and 23 themselves break with avoiding the breakage or without damaging the disc side, so that no fatal damage is not given to the rotor side. Further, since even when it is brought into contact in the manner mentioned above, it does not damage the rotor side and can avoid the double contact, it is possible to further reduce a gap δp between the front ends 22 and 23 and the surface of the disc 105 (refer to Fig. 11) in comparison with the conventional one, and it is possible to improve the sealing performance in comparison with the conventional brush seal, so that it is possible to widely reduce the sealing air, thereby contributing to an improvement of the performance of the whole of the gas turbine. In this case, in the embodiment mentioned above, the description is given of the embodiment in which the front ends 22 and 23 of the support plate are worked in the support plate base portions 31b and 32b in a step like so as to be formed in a thin fin shape, respectively, however, the invention is not limited to the embodiment, for example, the front end portion can be formed in a fin shape by forming them from the base portions 31b and 32b in a smooth curved surface such as a circular arc or a straight taper shape, that is, it is sufficient to form a shape which has a certain level of movability in the case of being brought into contact, avoids a double contact, and gives no damage to the rotor side. Fig. 6 shows the shape mentioned above, is a cross sectional view of a fourth embodiment, and corresponds to a structure of further improving the shape of the front end portion in the brush seal shown in Fig. 5. Fig. 6(a) shows a structure in which the front ends 22 and 23 of the support plate are changed to a circular arc shape 200, and it is substantially set such that a width t = 0.2~0.5 mm, R = 2.5 mm and Wa, Wf = 2.5 mm. Further, Fig. 6(b) shows a structure in which the front ends are set to a straight taper 201, and in the same manner it is substantially set such that a width t = 0.2 ~0.5 mm and Wa, Wf = 2.5 mm. With the circular arc shape 200 in Fig. 6(a), it is possible to secure a strength of the front end by gradually changing t, and also in the straight taper 201 in Fig. 6(b), in the same manner, it is possible to secure a strength of the front end by linearly changing it. As mentioned above, in the brush seal in accordance with the third and fourth embodiments of the invention, since the front ends 22 and 23 of the support plate are made thinner than the conventional widths Wf and Wa so as to form a thin fin shape, it is possible to prevent the rotor side from being damaged without being in doubly contact even when being brought into contact with the rotor side due to the thermal deformation and the like, so that it is possible to safely operate the gas turbine without giving a fatal damage to the rotor. Further, since the gap δp with respect to the rotor side can be made smaller than the conventional one, a sealing performance can be improved.

Claims: A seal structure for a gas turbine comprising a seal ring holding ring (1) supported to an inner shroud in a stationary blade, and a circular ring-like seal portion supported to the seal ring holding ring (1) and surrounding a periphery of a rotor in a state of keeping a predetermined gap obtained by taking a thermal expansion into consideration between end portions of a plurality of separation pieces or contacting the end portions, thereby constituting a seal portion with the rotor, said circular ring-like seal portion is constituted by a brush seal (3, 4) at an upstream side of a main current gas and a labyrinth seal (8) at a downstream side, characterized in that an end surface of each of separation pieces (A,B,C) of the brush seal (3,4) and the labyrinth seal (8) is formed in such a manner as to form opposing contact surfaces (9a,9b) formed by cutting along a polygonal line. A seal structure for a gas turbine as claimed in claim 1, characterized in that said opposing contact surfaces (9a,9b) have right, obtuse or acute angled portions. A seal structure for a gas turbine as claimed in claim 1 or 2, characterized in that said seal ring holding ring (1a, 1b) is separated into two portions at the upstream side and the downstream side, and one of them supports said brush seal (3, 4) and the other of them supports said labyrinth seal (8), respectively. A seal structure for a gas turbine as claimed in claim 1, 2 or 3 characterized in that said brush seal comprises front and rear support plates (31,32) mounted to the seal support portion, a brush (33) supported between said front and rear support plates (31, 32) and a front end of the brush (33) sealing with respect to the rotor, wherein front end portions (22, 23) of the front and rear support plates (31, 32) for supporting the front end portion of said brush (33) have an axial thickness (t) of 0.2 to 0.8 mm and are formed in a fin shape. A seal structure for a gas turbine as claimed in claim 4, characterized in that said front end portion of the support plate forms a fin shape by a smooth curved surface (200). A seal structure for a gas turbine as claimed in claim 4, characterized in that said front end portion of the support plate forms a fin shape by a straight tapered shape (201).

Inventors: AI TOSHISHIGE, YURI MASANORI, AI, TOSHISHIGE, YURI, MASANORI, Ai, Toshishige, Takasago Mach. Works, Mitsubishi, Yuri, Masanori, Takasago Mach. Works, Mitsubishi
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1999
Main classification: F01D11
IPC codes: F01D11, F16J15