Combustor and gas turbine provided with same

Abstract

This combustor is provided with: an inner cylinder; a burner disposed on the inner circumferential side of the inner cylinder; a tailpipe through which a combustion gas can flow; and a backflow prevention member that extends in the circumferential direction with respect to the combustor axis, is disposed on the inner circumferential side of the tailpipe, and is secured to the tailpipe. A tailpipe upstream-side part that includes an end of the tailpipe on the upstream side is disposed opposite an inner cylinder downstream-side part that includes an inner cylinder downstream end, which is an end of the inner cylinder on the downstream side, with a spacing therebetween in the radial direction. The tailpipe upstream-side part has a plurality of air holes at positions farther on the upstream side than the inner cylinder downstream end. The backflow prevention member has a reduced diameter part where the inner diameter gradually decreases toward the downstream side. The location of a reduced-diameter downstream end on the most downstream side within a reduced-diameter inner circumferential surface, which is the inner circumferential surface of the reduced diameter part, is farther on the downstream side than the inner cylinder downstream end.

Description

Combustor and gas turbine equipped with same

[0001] This application claims priority to Japanese Patent Application No. 2024-073510, filed on April 30, 2024, the contents of which are incorporated herein by reference.

[0002] The gas turbine includes a compressor capable of producing compressed air, a combustor capable of burning fuel in the compressed air from the compressor to produce combustion gases, and a turbine capable of being driven by the combustion gases.

[0003] The following Patent Document 1 discloses the above-described combustor for a gas turbine. This combustor includes an inner cylinder having a cylindrical shape about an axis, a burner disposed on the inner periphery of the inner cylinder and capable of ejecting fuel and air downstream in the axial direction, and a transition piece also having a cylindrical shape about the axis, through which fuel from the burner is burned in the air and through which combustion gas generated by the combustion of the fuel can flow. The inner diameter of the transition piece upstream portion, which includes the upstream end of the transition piece, is larger than the outer diameter of the inner cylinder downstream portion, which includes the downstream end of the inner cylinder, which is the downstream end of the inner cylinder. The transition piece upstream portion is disposed radially opposite the outer peripheral surface of the inner cylinder downstream portion. In other words, the cylindrical inner cylinder downstream portion is inserted into the cylindrical transition piece upstream portion.

[0004] In the combustor disclosed in Patent Document 1, sealing members called spring clips and buggy clips are arranged between the inner periphery of the upstream part of the transition piece and the outer periphery of the downstream part of the inner cylinder to allow for differential thermal expansion between the transition piece and the inner cylinder and to allow for vibration of the transition piece relative to the inner cylinder. Furthermore, this combustor employs a backflow prevention structure to prevent damage to the sealing members due to the backflow of combustion gas inside the transition piece.

[0005] Patent Document 1 discloses a number of backflow prevention structures.

[0006] Specifically, for example, the first backflow prevention structure includes a plurality of air holes penetrating the upstream portion of the transition piece from the outer circumferential side to the inner circumferential side, a guide portion that guides air that has flowed from the plurality of air holes between the upstream portion of the transition piece and the downstream portion of the inner cylinder downstream side downstream along the inner circumferential surface of the upstream portion of the transition piece, and a throttle portion that is disposed between the upstream portion of the transition piece and the downstream portion of the inner cylinder downstream side and downstream of the plurality of air holes and the guide portion. The plurality of air holes are aligned at intervals in the circumferential direction with respect to the combustor axis. The throttle portion extends radially inward with respect to the combustor axis from the inner circumferential surface of the upstream portion of the transition piece.

[0007] Air that has passed through the elastic member and air from the multiple air holes flows into the gap between the upstream portion of the transition piece and the downstream portion of the inner cylinder. This air flows into the transition piece through the gap between the throttling portion and the outer peripheral surface of the downstream portion of the inner cylinder. In this first backflow prevention structure, the downstream gap between the upstream portion of the transition piece and the downstream portion of the inner cylinder is narrowed by the throttling portion, thereby suppressing the inflow of combustion gas between the upstream portion of the transition piece and the downstream portion of the inner cylinder, while cooling the throttling portion with air from the multiple air holes. In addition, the air that flows into the transition piece through the gap between the throttling portion and the outer peripheral surface of the downstream portion of the inner cylinder also functions as an air curtain against backflowing combustion gas.

[0008] Furthermore, for example, the second backflow prevention structure includes a plurality of air holes penetrating the upstream portion of the transition piece from the outer circumferential side to the inner circumferential side, and a throttle portion disposed at an outlet position of each of the plurality of air holes. The plurality of air holes are aligned at intervals in the circumferential direction about the combustor axis. A flow path is formed in the throttle portion through which air from the plurality of air holes flows. This flow path is provided for each of the plurality of air holes. Each flow path is inclined with respect to the radial direction about the combustor axis.

[0009] The air that passes through the elastic member flows into the transition piece through a gap between the throttle portion and the outer circumferential surface of the downstream portion of the inner cylinder. Furthermore, air from the multiple air holes flows into the transition piece through the flow paths of each of the multiple air holes. This air is ejected from the throttle portion toward the radially inward direction relative to the combustor axis and toward the downstream side into the transition piece. This second backflow prevention structure also uses the throttle portion to narrow the downstream gap between the upstream portion of the transition piece and the downstream portion of the inner cylinder, thereby suppressing the inflow of combustion gas between the upstream portion of the transition piece and the downstream portion of the inner cylinder, while cooling the throttle portion with air from the multiple air holes. Furthermore, the air ejected from the throttle portion into the transition piece also functions as an air curtain against backflowing combustion gas.

[0010] International Publication No. 2012 / 132898

[0011] The backflow prevention structure described in Patent Document 1 can prevent combustion gas from flowing between the upstream portion of the transition piece and the downstream portion of the inner cylinder. However, it is desirable to further prevent combustion gas from flowing between the upstream portion of the transition piece and the downstream portion of the inner cylinder. Therefore, to further prevent the inflow of combustion gas, methods have been considered, such as increasing the inner diameter of the multiple air holes or increasing the number of air holes, thereby increasing the flow rate of air flowing out of the air holes. However, this method reduces the amount of air flowing into the inner cylinder and used to combust the fuel, increasing the fuel-air ratio in the combustion region, which can lead to an increase in NOx emissions and combustion instability known as combustion oscillation.

[0012] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a combustor that can efficiently suppress the inflow of combustion gas into the gap between the transition piece and the inner cylinder, and a gas turbine including the combustor.

[0013] To achieve the above object, a combustor according to one aspect of the present disclosure includes: an inner cylinder having a cylindrical shape about a combustor axis; a burner arranged on an inner peripheral side of the inner cylinder and capable of ejecting fuel and air toward the downstream side out of upstream and downstream sides in an axial direction along which the combustor axis extends; a transition piece having a cylindrical shape about the combustor axis, in which fuel from the burner is combusted with air and through which combustion gas generated by the combustion of the fuel can flow; and a backflow prevention member extending in a circumferential direction about the combustor axis, arranged on the inner peripheral side of the transition piece and fixed to the transition piece. An inner diameter of an upstream portion of the transition piece including the upstream end of the transition piece is larger than an outer diameter of a downstream portion of the inner cylinder including a downstream end of the inner cylinder that is the downstream end of the inner cylinder. The upstream portion of the transition piece is arranged to face an outer circumferential surface of the downstream portion of the inner cylinder at a distance in the radial direction relative to the combustor axis. The transition piece upstream section has a plurality of air holes arranged at intervals in the circumferential direction at a position upstream of the downstream end of the inner cylinder and penetrating from the outer circumferential side to the inner circumferential side of the transition piece upstream section. The plurality of air holes have inlets opening at the outer circumferential surface of the transition piece upstream section and outlets opening at the inner circumferential surface of the transition piece upstream section. The backflow prevention member has a reduced diameter section whose inner diameter gradually decreases toward the downstream side, and a joining section connected to the upstream end of the reduced diameter section and joined to the transition piece upstream section at a position downstream of the outlets for each of the plurality of air holes. The position of the most downstream reduced diameter downstream end of the reduced diameter inner circumferential surface, which is the inner circumferential surface of the reduced diameter section, is downstream of the downstream end of the inner cylinder.

[0014] The gas flow path through which gas (combustion gas, or air and fuel) flows expands rapidly from the downstream end of the inner cylinder, forming a gas vortex downstream of the downstream end of the inner cylinder. This causes the combustion gas in the transition piece to flow backward, potentially into the cylindrical gap between the upstream portion of the transition piece and the downstream portion of the inner cylinder. If a seal were placed in this cylindrical gap, the combustion gas could be damaged if it flowed into the cylindrical gap.

[0015] In this aspect, the reduced diameter portion of the backflow prevention member narrows the gap between the upstream portion of the transition piece and the downstream portion of the inner cylinder through which combustion gas flows inside the transition piece, thereby suppressing the flow of combustion gas into the tubular gap. Also, in this aspect, air from the multiple air holes flows along the reduced diameter inner circumferential surface of the reduced diameter portion, cooling the reduced diameter portion by this air, thereby suppressing thermal damage to the reduced diameter portion.

[0016] In this aspect, the individual air streams from the multiple air holes aligned in the circumferential direction flow downstream, then flow along the reduced-diameter inner circumferential surface, and are gradually dispersed in the circumferential direction as they reach the reduced-diameter downstream end. Therefore, in this aspect, the air that flows along the reduced-diameter inner circumferential surface is ejected into the transition piece almost uniformly in the circumferential direction. Therefore, the air ejected into the transition piece functions as an appropriate air curtain against the backflowing combustion gas.

[0017] In this aspect, the flow direction of the air that flows along the reduced-diameter inner circumferential surface and then is ejected into the transition piece has a downstream component and a radially inward component. Therefore, in this aspect, the air with the downstream component can prevent the combustion gas flowing toward the upstream side from flowing further upstream. Furthermore, in this aspect, the air with the radially inward component can guide the combustion gas that has come toward the cylindrical gap radially inward.

[0018] Therefore, in this aspect, it is possible to extremely efficiently prevent combustion gases inside the transition piece from flowing into the cylindrical gap between the upstream side of the transition piece and the downstream side of the inner cylinder.

[0019] To achieve the above object, one aspect of the gas turbine according to the present disclosure includes the combustor according to the above aspect, a compressor capable of compressing air to generate compressed air, a turbine capable of being driven by combustion gas from the combustor, and an intermediate casing into which the compressed air from the compressor can flow. The compressor has a compressor rotor rotatable about a rotor axis and a compressor casing that covers the compressor rotor. The turbine has a turbine rotor rotatable about the rotor axis and a turbine casing that covers the turbine rotor. The compressor rotor and the turbine rotor are connected to each other to form a gas turbine rotor. The intermediate casing is located between the compressor casing and the turbine casing. The compressor casing, the intermediate casing, and the turbine casing are connected to each other to form a gas turbine casing. The combustor is attached to the intermediate casing so that compressed air in the intermediate casing can flow into the combustor.

[0020] According to one aspect of the present disclosure, it is possible to efficiently prevent combustion gas from flowing into the gap between the transition piece and the inner cylinder.

[0021] Fig. 3 is a schematic cross-sectional view of a gas turbine in an embodiment according to the present disclosure; Fig. 4 is a cross-sectional view of the vicinity of a combustor of a gas turbine in an embodiment according to the present disclosure; Fig. 5 is a cross-sectional view of a main part of a combustor in an embodiment according to the present disclosure; Fig. 6 is an enlarged cross-sectional view of a main part in Fig. 3; Fig. 7 is a cross-sectional view along line VV in Fig. 3;

[0022] Hereinafter, an embodiment of a combustor and a gas turbine including the combustor according to the present disclosure will be described in detail with reference to the drawings.

[0023] [Embodiment of Gas Turbine] A gas turbine according to this embodiment will be described with reference to FIG.

[0024] The gas turbine in this embodiment includes a compressor 10 capable of compressing air A to generate compressed air Acom, a plurality of combustors 30 capable of burning fuel F in the compressed air Acom to generate combustion gas CG, a turbine 20 capable of being driven by the high-temperature, high-pressure combustion gas CG, and an intermediate casing 6.

[0025] The compressor 10 includes a compressor rotor 11 that can rotate about a rotor axis Ar, a compressor casing 18 that covers the compressor rotor 11, and a plurality of stator vane rows 15. The turbine 20 includes a turbine rotor 21 that can rotate about the rotor axis Ar, a turbine casing 28 that covers the turbine rotor 21, and a plurality of stator vane rows 25. In the following description, the direction in which the rotor axis Ar extends is referred to as the rotor axial direction Dr, one side of the rotor axial direction Dr is referred to as the rotor axial upstream side Dru, and the other side is referred to as the rotor axial downstream side Drd. The radial direction relative to the rotor axis Ar is simply referred to as the radial direction Drr, and the side of the radial direction Drr that is closer to the rotor axis Ar is referred to as the radial inner side Drri, and the side that is farther away from the rotor axis Ar is referred to as the radial outer side Drro.

[0026] The compressor 10 is disposed on the upstream side Dru of the rotor axis with respect to the turbine 20 .

[0027] The compressor rotor 11 and the turbine rotor 21 are located on the same rotor axis Ar and are connected to each other to form the gas turbine rotor 1. For example, a rotor of a generator GEN is connected to this gas turbine rotor 1. The intermediate casing 6 described above is disposed between the compressor casing 18 and the turbine casing 28 in the rotor axis direction Dr. The compressor casing 18, the intermediate casing 6, and the turbine casing 28 are connected to each other to form the gas turbine casing 8. Compressed air from the compressor 10 can flow into the intermediate casing 6.

[0028] The compressor rotor 11 has a rotor shaft 12 that extends in the rotor axial direction Dr around the rotor axis Ar, and a plurality of rotor blade rows 13 attached to the rotor shaft 12. The plurality of rotor blade rows 13 are aligned in the rotor axial direction Dr. Each rotor blade row 13 is composed of a plurality of rotor blades aligned in the circumferential direction about the rotor axis Ar. One of a plurality of stator blade rows 15 is arranged on the rotor axial downstream side Drd of each of the plurality of rotor blade rows 13. Each stator blade row 15 is provided inside a compressor casing 18. Each stator blade row 15 is composed of a plurality of stator blades aligned in the circumferential direction about the rotor axis Ar.

[0029] The turbine rotor 21 has a rotor shaft 22 that extends in the rotor axial direction Dr around the rotor axis Ar, and a plurality of rotor blade rows 23 attached to the rotor shaft 22. The plurality of rotor blade rows 23 are aligned in the rotor axial direction Dr. Each rotor blade row 23 is made up of a plurality of rotor blades aligned in the circumferential direction about the rotor axis Ar. One of a plurality of stator blade rows 25 is arranged on the rotor axial upstream side Dru of each of the plurality of rotor blade rows 23. Each stator blade row 25 is provided inside a turbine casing 28. Each stator blade row 25 is made up of a plurality of stator blades aligned in the circumferential direction about the rotor axis Ar.

[0030] The plurality of combustors 30 are attached to the intermediate casing 6 and aligned in the circumferential direction about the rotor axis Ar so that the compressed air Acom in the intermediate casing 6 can flow into the combustors 30 .

[0031] The compressor 10 compresses air A to generate compressed air Acom. This compressed air Acom flows into the combustor 30 via the intermediate casing 6. Fuel F is supplied to the combustor 30. In the combustor 30, the fuel F is combusted in the compressed air Acom, generating high-temperature, high-pressure combustion gas CG. This combustion gas CG is sent from the combustor 30 to the turbine casing 28. As the combustion gas CG flows through the turbine casing 28 toward the rotor axis downstream side Drd, it rotates the turbine rotor 21. The rotation of this turbine rotor 21 rotates the rotor of the generator GEN connected to the gas turbine rotor 1. As a result, the generator GEN generates electricity.

[0032] An embodiment of the combustor 30 will now be described in detail.

[0033] [Embodiment of Combustor] A combustor according to this embodiment will be described with reference to FIGS. 2 to 5. FIG.

[0034] As shown in FIG. 2 , a combustor 30 according to the present embodiment includes an inner cylinder 32 that is cylindrically shaped around the combustor axis Ac, a plurality of burners 31 that are arranged on the inner circumferential side of the inner cylinder 32, and a transition piece 42 that is cylindrically shaped around the combustor axis Ac and through which combustion gas CG generated by combustion of fuel can flow. Hereinafter, the direction in which the combustor axis Ac extends is referred to as an axial direction Dc, one of both sides of the axial direction Dc is referred to as an upstream side Dcu, and the other is referred to as a downstream side Dcd. Furthermore, a radial direction relative to the combustor axis Ac is simply referred to as a radial direction Dcr, and a side of the radial direction Dcr that approaches the combustor axis Ac is referred to as a radially inner side Dcri, and a side of the radial direction Dcr that moves away from the combustor axis Ac is referred to as a radially outer side Dcro. Furthermore, a circumferential direction centered on the combustor axis Ac is simply referred to as a circumferential direction Dcc.

[0035] The combustor axis Ac is located on an imaginary plane that includes the rotor axis Ar. An upstream side Dcu in the axial direction Dc (in which the combustor axis Ac extends) corresponds to a rotor axial upstream side Dru in the rotor axial direction Dr, and a downstream side Dcd in the axial direction Dc (in which the combustor axis Ac extends) corresponds to a rotor axial downstream side Drd in the rotor axial direction Dr. However, the combustor axis Ac is inclined with respect to the rotor axis Ar so as to gradually approach the rotor axis Ar as it moves toward the downstream side Dcd.

[0036] Both the inner cylinder 32 and the transition piece 42 are disposed within the intermediate casing 6. Therefore, compressed air Acom from the compressor 10 flows around the outer periphery of the inner cylinder 32 and the transition piece 42. The compressed air Acom flows into the inner cylinder 32 from its upstream side Dcu. Each burner 31 disposed within the inner cylinder 32 can eject fuel F supplied from the outside along with the compressed air Acom flowing into the inner cylinder 32 toward the upstream side Dcu. The downstream side Dcd ends of each burner 31 are located upstream of the inner cylinder downstream end 32de, which is the end of the downstream side Dcd of the inner cylinder 32. Within the transition piece 42, the fuel F from the multiple burners 31 is combusted in the compressed air Acom, generating high-temperature, high-pressure combustion gas CG. This combustion gas CG flows through the transition piece 42 toward the downstream side Dcd and into the turbine casing 28. Therefore, the transition piece 42 defines a combustion gas flow path through which the combustion gas CG flows. Note that, even in the region Dcd downstream of each burner 31 within the inner cylinder 32, the fuel F from the burner 31 may be combusted in the compressed air Acom.

[0037] The inner diameter of the transition piece upstream portion 43, which includes the transition piece upstream end 42ue, which is the end of the upstream side Dcu of the transition piece 42, is larger than the outer diameter of the inner cylinder downstream portion 33, which includes the inner cylinder downstream end 32de, which is the end of the downstream side Dcd of the inner cylinder 32. The transition piece upstream portion 43 is disposed opposite to, and spaced apart from, the outer peripheral surface 33o of the inner cylinder downstream portion 33. In other words, the cylindrical inner cylinder downstream portion 33 is inserted into the cylindrical transition piece upstream portion 43.

[0038] The cross-sectional area of ​​the transition piece 42 perpendicular to the combustor axis Ac gradually decreases from a throttling start position 46, which is located on the upstream side Dcu in the transition piece 42 and is located on the downstream side Dcd of the transition piece upstream section 43, toward the downstream side Dcd. Here, a casing opposing portion 47 is defined as a portion Drro in the transition piece 42 that faces the inner circumferential surface of the intermediate casing 6 and is located radially outward from the combustor axis Ac with respect to the rotor axis Ar. Also, a rotor opposing portion 49 is defined as a portion Drri inward from the combustor axis Ac with respect to the rotor axis Ar and faces the gas turbine rotor 1. As described above, since the combustor axis Ac is inclined with respect to the rotor axis Ar, the casing opposing portion 47 and the rotor opposing portion 49 are inclined with respect to the rotor axis Ar so as to gradually approach the rotor axis Ar toward the downstream side Dcd. However, at a portion Dcd downstream of the aforementioned throttling start position 46, the inclination of the casing opposing portion 47 with respect to the rotor axis Ar is steeper than the inclination of the rotor opposing portion 49 with respect to the rotor axis Ar. For this reason, on the cross section of the transition piece 42 taken along the aforementioned imaginary plane including the rotor axis Ar, the throttling portion 48, which is the portion Dcd downstream of the throttling start position 46 in the casing opposing portion 47, is inclined with respect to the portion Dcu upstream of the throttling start position 46 in the casing opposing portion 47.

[0039] 3, the combustor 30 according to the present embodiment further includes a first elastic ring 50, a second elastic ring 55, an air guide member 60, and a backflow prevention member 65. The first elastic ring 50 is sometimes called a buggy clip, and the second elastic ring 55 is sometimes called a spring clip.

[0040] 3 and 4 , the first elastic ring 50 and the second elastic ring 55 each have a cylindrical shape around the combustor axis Ac. Furthermore, the first elastic ring 50 and the second elastic ring 55 are both disposed in the cylindrical gap 40 between the inner circumferential surface 43 i of the cylindrical transition piece upstream portion 43 and the outer circumferential surface 33 o of the cylindrical inner cylinder downstream portion 33.

[0041] The second elastic ring 55 has a cylindrical fixed portion 56 fixed to the outer peripheral surface 33o of the downstream portion 33 of the inner cylinder, and a spring portion 57 integrally formed with the fixed portion 56 and extending from the fixed portion 56 in a direction having a component in the axial direction Dc. The spring portion 57 has a contact portion 59 that contacts the inner peripheral surface 43i of the upstream portion 43 of the transition piece. Because the fixed portion 56 contacts the outer peripheral surface 33o of the downstream portion 33 of the inner cylinder, the inner diameter of the fixed portion 56 is substantially the same as the outer diameter of the downstream portion 33 of the inner cylinder. On the other hand, because the contact portion 59 of the spring portion 57 contacts the inner peripheral surface 43i of the upstream portion 43 of the transition piece, the outer diameter of the contact portion 59 is larger than the outer diameter of the fixed portion 56. The spring portion 57 extends from the fixed portion 56 in a direction having a directional component toward the upstream side Dcu. The contact portion 59 of the spring portion 57 is located on the upstream side Dcu of the fixed portion 56 and on the radially outer side Dcro.

[0042] A plurality of slits 58 (see FIG. 3 ) that penetrate in the radial direction Dcr and extend in the axial direction Dc are formed at equal intervals in the circumferential direction Dcc in the spring portion 57 of the second elastic ring 55. The slits 58 are formed from the upstream end to the downstream end of the spring portion 57. The slits 58 are formed to accommodate relative displacement of the inner circumferential surface 43i of the transition piece upstream portion 43 with respect to the outer circumferential surface 33o of the inner cylinder downstream portion 33 due to differences in thermal expansion between the inner cylinder 32 and the transition piece 42, vibration of the transition piece 42, etc.

[0043] The first elastic ring 50 has a cylindrical fixed portion 51 fixed to the outer peripheral surface 33o of the inner cylinder downstream portion 33, and a spring portion 52 integrally formed with the fixed portion 51 and extending from the fixed portion 51 in a direction having a component of the axial direction Dc. The spring portion 52 of the first elastic ring 50 has a first contact portion 54a that contacts the contact portion 59 of the second elastic ring 55 and a second contact portion 54b that contacts the outer peripheral surface 33o of the inner cylinder downstream portion 33. Since the fixed portion 51 and the second contact portion 54b both contact the outer peripheral surface 33o of the inner cylinder downstream portion 33, their inner diameters are substantially the same as the outer diameter of the inner cylinder downstream portion 33. On the other hand, since the first contact portion 54a contacts the contact portion 59 of the second elastic ring 55, its outer diameter is larger than the outer diameters of the fixed portion 51 and the second contact portion 54b. The fixed portion 51 of the first elastic ring 50 is located upstream Dcu of the fixed portion 56 of the second elastic ring 55 and downstream Dcd of the contact portion 59 of the second elastic ring 55. The spring portion 52 of the first elastic ring 50 extends in a direction having a directional component toward the upstream Dcu from the fixed portion 51 of the first elastic ring 50. The first contact portion 54a of the spring portion 52 is located upstream Dcu of the fixed portion 51 and on the radially outer side Dcro. The second contact portion 54b of the spring portion 52 is located upstream Dcu of the first contact portion 54a and on the radially inner side Dcri.

[0044] A plurality of slits 53 (see FIG. 3 ) that penetrate in the radial direction Dcr and extend in the axial direction Dc are also formed at equal intervals in the circumferential direction Dcc in the spring portion 52 of the first elastic ring 50. These slits 53 are also formed from the upstream end to the downstream end of the spring portion 52. These slits 53 are also formed to accommodate relative displacement of the inner circumferential surface 43i of the transition piece upstream portion 43 with respect to the outer circumferential surface 33o of the inner cylinder downstream portion 33 due to differences in thermal expansion between the inner cylinder 32 and the transition piece 42, vibration of the transition piece 42, etc.

[0045] The first elastic ring 50 and the second elastic ring 55 described above each perform the following two functions. First function: To allow relative displacement of the inner circumferential surface 43i of the transition piece upstream portion 43 relative to the outer circumferential surface 33o of the inner circumferential portion 33 of the transition piece due to the thermal expansion difference between the inner circumferential portion 32 and the transition piece 42, vibration of the transition piece 42, etc. Second function: To prevent compressed air Acom present on the outer circumferential sides of the inner circumferential portion 32 and the transition piece 42 from flowing into the tubular gap 40 through the gap between the transition piece upstream end 42ue and the inner circumferential portion 33, and from flowing into the transition piece 42 through the gap between the transition piece upstream portion 43 and the inner circumferential portion 32de. In other words, to seal the compressed air Acom. Note that the first elastic ring 50 primarily performs the first function, and the second elastic ring 55 primarily performs the second function.

[0046] The transition piece upstream portion 43 has multiple air holes 44. Each of the multiple air holes 44 penetrates the transition piece upstream portion 43 from its outer circumferential side to its inner circumferential side. The multiple air holes 44 are arranged at intervals in the circumferential direction Dcc within a sealed region 41 in the tubular gap 40 at a position Dcu upstream of the downstream end 32de of the inner cylinder. The sealed region 41 is a region in the tubular gap 40 where the compressed air Acom that flows into the tubular gap 40 from the gap between the upstream end 42ue of the transition piece and the downstream portion 33 of the inner cylinder is prevented from flowing downstream Dcd by the second elastic ring 55. Each of the multiple air holes 44 has an inlet 44i that opens on the outer circumferential surface 43o of the transition piece upstream portion 43 and an outlet 44o that opens on the inner circumferential surface 43i of the transition piece upstream portion 43.

[0047] The air guide member 60 can guide the air Acom that has flowed into the sealed region 41 in the cylindrical gap 40 from the multiple air holes 44 along the inner circumferential surface 43i of the transition piece upstream portion 43 to the downstream side Dcd. The air guide member 60 has a guide plate 61, a blocking plate 62, and multiple gap-maintaining protrusions 63. The guide plate 61 extends in the circumferential direction Dcc so as to face, at a distance in the radial direction Dcr, an area on the inner circumferential surface 43i of the transition piece upstream portion 43 where the outlets 44o for each of the multiple air holes 44 are formed. The blocking plate 62 blocks the gap between the inner circumferential surface 43i of the transition piece upstream portion 43 and the guide plate 61 at a position Dcu upstream of the outlets 44o for each of the multiple air holes 44. The plurality of gap maintaining projections 63 protrude radially outward Dcro from the guide plate 61 at positions Dcd downstream of the outlets 44o of each of the plurality of air holes 44, and are arranged at intervals in the circumferential direction Dcc. The plurality of gap maintaining projections 63 contact the inner circumferential surface 43i of the transition piece upstream portion 43 to maintain the gap in the radial direction Dcr between the guide plate 61 and the inner circumferential surface 43i of the transition piece upstream portion 43.

[0048] The backflow prevention member 65 is disposed on the inner circumferential side of the transition piece 42 and fixed to the transition piece 42. The backflow prevention member 65 has a reduced diameter portion 66 and a joint portion 67. The reduced diameter portion 66 extends in a direction having an axial direction Dc component and in the circumferential direction Dcc, and is formed so that its inner diameter gradually decreases toward the downstream side Dcd. The joint portion 67 extends in the circumferential direction Dcc and from the end of the reduced diameter portion 66 on the upstream side Dcu toward the upstream side Dcu.

[0049] The transition piece upstream portion 43 has a recess 45 that is recessed radially outwardly Dcro from the inner circumferential surface 43i of the transition piece upstream portion 43 and extends in the circumferential direction Dcc at a position Dcd downstream of the outlets 44o of each of the plurality of air holes 44. The depth of this recess 45 corresponds to the radial thickness Dcr of the joint portion 67. The joint portion 67 enters this recess 45 and is joined to the transition piece upstream portion 43.

[0050] The guide plate 61 described above extends to a position Dcd downstream of the outlets 44 o of each of the plurality of air holes 44 and Dcu upstream of the reduced diameter portion 66 of the backflow prevention member 65 .

[0051] A reduced diameter inner circumferential surface 66i, which is the inner circumferential surface of the reduced diameter portion 66, is inclined at an angle α of 30° to 60° relative to the outer circumferential surface 33o of the inner cylinder downstream portion 33. Specifically, in this embodiment, the reduced diameter inner circumferential surface 66i is inclined at an angle α of 45° relative to the outer circumferential surface 33o of the inner cylinder downstream portion 33.

[0052] The position of the reduced diameter downstream end 66de on the most downstream side Dcd of the reduced diameter inner circumferential surface 66i is downstream Dcd of the inner cylinder downstream end 32de.

[0053] The position of the reduced diameter downstream end 66de is located radially inward (Dcri) from the inner circumferential surface 43i of the transition piece upstream portion 43 at a distance of half the gap g between the outer circumferential surface 33o of the inner cylinder downstream portion 33 and the inner circumferential surface 43i of the transition piece upstream portion 43 at the position Dc in the axial direction of the downstream end 32de of the inner cylinder. Also, the position of this reduced diameter downstream end 66de is located radially outward (Dcro) from the downstream end 32de of the inner cylinder.

[0054] As illustrated in Fig. 5 , the backflow prevention member 65 extending in the circumferential direction Dcc described above is located only on the radially outer side Drro of the combustor axis Ac with respect to the rotor axis Ar. Similarly to the backflow prevention member 65, the multiple air holes 44 aligned in the circumferential direction Dcc and the air guide member 60 extending in the circumferential direction Dcc are also located only on the radially outer side Drro of the combustor axis Ac with respect to the rotor axis Ar.

[0055] As described above, compressed air Acom discharged from the compressor 10 flows into the inner cylinder 32 from the upstream side Dcu. Each burner 31 arranged in the inner cylinder 32 ejects fuel F supplied from the outside along with the compressed air Acom that has flowed into the inner cylinder 32 toward the upstream side Dcu. In the transition piece 42, the fuel F from the multiple burners 31 is combusted in the compressed air Acom, generating high-temperature, high-pressure combustion gas CG. This combustion gas CG flows through the transition piece 42 to the downstream side Dcd and into the turbine casing 28.

[0056] The gas flow path through which the gas G (combustion gas CG, or air Acom and fuel F) flows widens rapidly from the position of the downstream end 32de of the inner cylinder, causing a vortex of the gas G to form downstream Dcd of the downstream end 32de of the inner cylinder. As a result, the combustion gas CG in the transition piece 42 may flow backward and flow into the cylindrical gap 40 between the transition piece upstream section 43 and the inner cylinder downstream section 33. If the combustion gas CG flows into this cylindrical gap 40, the first elastic ring 50 and the second elastic ring 55, which serve as sealing members, may be damaged.

[0057] In this embodiment, the reduced diameter portion 66 of the backflow prevention member 65 narrows the gap between the transition piece upstream portion 43 and the inner cylinder downstream portion 33 through which the combustion gas CG in the transition piece 42 flows, thereby suppressing the inflow of the combustion gas CG into the cylindrical gap 40. Also, in this embodiment, the air Acom from the multiple air holes 44 flows along the reduced diameter inner circumferential surface 66i of the reduced diameter portion 66, and this air Acom cools the reduced diameter portion 66, thereby suppressing thermal damage to the reduced diameter portion 66.

[0058] In this embodiment, the individual air Acom from the multiple air holes 44 arranged in the circumferential direction Dcc flows downstream Dcd, then flows along the reduced-diameter inner circumferential surface 66i, and is gradually dispersed in the circumferential direction Dcc as it reaches the reduced-diameter downstream end 66de. In particular, in this embodiment, the guide plate 61 of the air guide member 60 extending in the circumferential direction Dcc effectively disperses the individual air Acom from the multiple air holes 44 arranged in the circumferential direction Dcc in the circumferential direction Dcc. Therefore, in this embodiment, the air Acom flowing along the reduced-diameter inner circumferential surface 66i is ejected into the transition piece 42 approximately uniformly in the circumferential direction Dcc. Therefore, the air Acom ejected into the transition piece 42 functions as an appropriate air curtain against the backflowing combustion gas CG. In addition, air Acom that flows into the transition piece 42 from the gap between the transition piece upstream end 42ue and the inner cylinder downstream side portion 33 and passes through the slits 53 of the first elastic ring 50 and the slits 58 of the second elastic ring 55 arranged in the tubular gap 40 is also ejected into the transition piece 42 together with air Acom from the multiple air holes 44.

[0059] In this embodiment, as the air Acom from the multiple air holes 44 arranged in the circumferential direction Dcc flows downstream Dcd, the joint 67 of the backflow prevention member 65 does not obstruct the flow of the air Acom, and the air flows along the inner circumferential surface 43i of the transition piece upstream portion 43. Furthermore, in this embodiment, the air guide member 60 can efficiently guide the air Acom from the multiple air holes 44 to the reduced-diameter inner circumferential surface 66i. Therefore, in this embodiment, the air Acom from the multiple air holes 44 can be efficiently guided to the reduced-diameter inner circumferential surface 66i. As a result, in this embodiment, the flow rate of the air Acom flowing along the reduced-diameter inner circumferential surface 66i can be increased.

[0060] In this embodiment, the flow direction of the air Acom that flows along the reduced-diameter inner circumferential surface 66i and is then ejected into the transition piece 42 has a downstream directional component Dcd and a radially inner directional component Dcri. Therefore, in this embodiment, the air Acom having a downstream directional component Dcd can prevent the combustion gas CG that flows back toward the upstream Dcu from flowing further upstream. Furthermore, in this embodiment, the air Acom having a radially inner Dcri component can guide the combustion gas CG that has flowed toward the cylindrical gap 40 to the radially inner Dcri.

[0061] Therefore, in this embodiment, the combustion gas CG inside the transition piece 42 can be extremely efficiently prevented from flowing into the cylindrical gap 40 between the transition piece upstream portion 43 and the inner cylinder downstream portion 33.

[0062] As described above, in the present embodiment, the throttle portion 48 in the casing opposing portion 47 of the transition piece 42 is inclined relative to the upstream Dcu portion of the casing opposing portion 47 relative to the throttle start position 46. Therefore, a portion of the gas G ejected from the inner cylinder 32 to the downstream side Dcd passes through the throttle portion 48 and returns to the upstream Dcu. This increases the likelihood of backflow of the combustion gas CG in the transition piece 42 in a region that is radially outwardly relative to the rotor axis line Ar relative to the combustor axis line Ac. Therefore, in the present embodiment, the backflow prevention member 65, the plurality of air holes 44, and the air guide member 60 are disposed in a region that is radially outwardly relative to the rotor axis line Ar relative to the combustor axis line Ac, where the backflow of the combustion gas CG is likely to occur.

[0063] "Modifications" The combustor 30 in the above embodiment has the first elastic ring 50 and the second elastic ring 55 as sealing members that seal the cylindrical gap 40 between the transition piece upstream portion 43 and the inner cylinder downstream portion 33. However, instead of the first elastic ring 50 and the second elastic ring 55, other types of sealing members may be disposed in the cylindrical gap 40 as long as they can fulfill the two roles described above for the first elastic ring 50 and the second elastic ring 55.

[0064] The present disclosure is not limited to the above-described embodiments and modifications, and various additions, modifications, substitutions, partial deletions, etc. are possible within the scope of the conceptual idea and spirit of the present invention as derived from the content defined in the claims and their equivalents.

[0065] "Additional Notes" The combustor 30 in the above embodiment and modified examples can be understood as follows, for example. (1) A combustor 30 in a first aspect includes: an inner cylinder 32 having a cylindrical shape about a combustor axis Ac, a burner 31 arranged on an inner peripheral side of the inner cylinder 32 and capable of ejecting fuel F and air Acom toward the downstream side Dcd out of an upstream side Dcu and a downstream side Dcd in an axial direction Dc in which the combustor axis Ac extends, a transition piece 42 having a cylindrical shape about the combustor axis Ac, in which the fuel F from the burner 31 is combusted in the air Acom and in which combustion gas CG generated by the combustion of the fuel F can flow, and a backflow prevention member 65 extending in a circumferential direction Dcc relative to the combustor axis Ac, arranged on the inner peripheral side of the transition piece 42, and fixed to the transition piece 42. The inner diameter of a transition piece upstream portion 43 including an end of the upstream side Dcu of the transition piece 42 is larger than the outer diameter of an inner cylinder downstream portion 33 including an inner cylinder downstream end 32de, which is an end of the downstream side Dcd of the inner cylinder 32. The transition piece upstream portion 43 is disposed opposite to an outer peripheral surface 33o of the inner cylinder downstream portion 33 at an interval in the radial direction Dcr relative to the combustor axis Ac. The transition piece upstream portion 43 has a plurality of air holes 44 that are aligned at intervals in the circumferential direction Dcc at a position upstream of the inner cylinder downstream end 32de and penetrate from the outer peripheral side to the inner peripheral side of the transition piece upstream portion 43. The plurality of air holes 44 have inlets 44i that open at the outer peripheral surface 43o of the transition piece upstream portion 43 and outlets 44o that open at the inner peripheral surface 43i of the transition piece upstream portion 43. The backflow prevention member 65 has a reduced diameter section 66 whose inner diameter gradually decreases toward the downstream side Dcd, and a joint section 67 that is connected to the end of the upstream side Dcu of the reduced diameter section 66 and is joined to the transition piece upstream side section 43 at a position downstream Dcd further than the outlets 44o of each of the plurality of air holes 44. The position of a reduced diameter downstream end 66de of the most downstream side Dcd on a reduced diameter inner circumferential surface 66i that is the inner circumferential surface of the reduced diameter section 66 is further downstream Dcd than the inner cylinder downstream end 32de.

[0066] The gas flow path through which the gas G (combustion gas CG, or air Acom and fuel F) flows widens rapidly from the position of the downstream end 32de of the inner cylinder, causing a vortex of the gas G to form downstream Dcd of the downstream end 32de of the inner cylinder. As a result, the combustion gas CG in the transition piece 42 may flow backward and flow into the cylindrical gap 40 between the transition piece upstream section 43 and the inner cylinder downstream section 33. If a seal member is disposed in this cylindrical gap 40, the flow of the combustion gas CG into this cylindrical gap 40 may damage the seal member.

[0067] In this aspect, the reduced diameter portion 66 of the backflow prevention member 65 narrows the gap between the transition piece upstream portion 43 and the inner cylinder downstream portion 33 through which the combustion gas CG in the transition piece 42 flows, thereby suppressing the inflow of the combustion gas CG into the cylindrical gap 40. Also, in this aspect, the air Acom from the multiple air holes 44 flows along the reduced diameter inner circumferential surface 66i of the reduced diameter portion 66, and this air Acom cools the reduced diameter portion 66, thereby suppressing thermal damage to the reduced diameter portion 66.

[0068] In this embodiment, the individual air Acom from the multiple air holes 44 aligned in the circumferential direction Dcc flows downstream Dcd, then flows along the reduced-diameter inner circumferential surface 66i, and is gradually dispersed in the circumferential direction Dcc as it reaches the reduced-diameter downstream end 66de. Thus, in this embodiment, the air Acom that flows along the reduced-diameter inner circumferential surface 66i is ejected into the transition piece 42 approximately evenly in the circumferential direction Dcc. Therefore, the air Acom ejected into the transition piece 42 functions as an appropriate air curtain against the combustion gas CG flowing back.

[0069] In this aspect, the flow direction of the air Acom that flows along the reduced-diameter inner circumferential surface 66i and is then ejected into the transition piece 42 has a downstream directional component Dcd and a radially inner directional component Dcri. Therefore, in this aspect, the air Acom having a downstream directional component Dcd can prevent the combustion gas CG flowing toward the upstream Dcu from flowing further upstream Dcu. Furthermore, in this aspect, the air Acom having a radially inner Dcri component can guide the combustion gas CG that has come toward the cylindrical gap 40 to the radially inner Dcri.

[0070] Therefore, in this embodiment, the combustion gas CG inside the transition piece 42 can be extremely efficiently prevented from flowing into the cylindrical gap 40 between the transition piece upstream portion 43 and the inner cylinder downstream portion 33.

[0071] (2) The combustor 30 according to the second aspect is the combustor 30 according to the first aspect, wherein the reduced-diameter inner circumferential surface 66i is inclined at an angle of 30° to 60° with respect to the outer circumferential surface 33o of the inner cylinder downstream portion 33.

[0072] (3) In the combustor 30 according to the first or second aspect, the position of the reduced-diameter downstream end 66de is on a radially inner side Dcri with respect to the combustor axis Ac, the position being from the inner circumferential surface 43i of the transition piece upstream portion 43 to a position that is half of the gap g between the outer circumferential surface 33o of the inner cylinder downstream portion 33 and the inner circumferential surface 43i of the transition piece upstream portion 43 at a position of the inner cylinder downstream end 32de in the axial direction Dc.

[0073] In this embodiment, the reduced diameter portion 66 of the backflow prevention member 65 narrows the gap through which combustion gas CG flows between the upstream portion 43 of the transition piece and the downstream portion 33 of the inner cylinder, thereby suppressing the flow of combustion gas CG into the cylindrical gap 40.

[0074] (4) The combustor 30 according to a fourth aspect is the combustor 30 according to any one of the first to third aspects, wherein the position of the reduced diameter downstream end 66de is on the radially outer side Dcro of the inner cylinder downstream end 32de with respect to the combustor axis Ac.

[0075] When the combustor 30 is started, a thermal expansion difference occurs in the axial direction Dc between the inner cylinder 32 and the transition piece 42. In this embodiment, the position of the reduced diameter downstream end 66de is radially outward Dcro of the inner cylinder downstream end 32de. Therefore, even if a thermal expansion difference occurs between the inner cylinder 32 and the transition piece 42 in the axial direction Dc, the backflow prevention member 65 fixed to the transition piece 42 can be prevented from coming into contact with the inner cylinder 32 and being damaged.

[0076] (5) The combustor 30 in a fifth aspect is the combustor 30 in any one of the first to fourth aspects, and includes an air guide member 60 that can guide the air Acom that has flowed from the plurality of air holes 44 between the transition piece upstream portion 43 and the inner cylinder downstream portion 33 to the downstream side Dcd along the inner circumferential surface 43i of the transition piece upstream portion 43.

[0077] In this embodiment, the air Acom from the multiple air holes 44 can be efficiently guided to the reduced-diameter inner circumferential surface 66i. As a result, the flow rate of the air Acom flowing along the reduced-diameter inner circumferential surface 66i increases. Therefore, in this embodiment, the inflow of the combustion gas CG into the cylindrical gap 40 and thermal damage to the reduced-diameter portion 66 can be effectively suppressed.

[0078] (6) A sixth aspect of the combustor 30 is the combustor 30 of the fifth aspect, wherein the air guide member 60 includes a guide plate 61 that is disposed to face, at an interval in the radial direction Dcr, a region in the inner circumferential surface 43i of the transition piece upstream portion 43 where the outlets 44o for each of the plurality of air holes 44 are formed, and extends in the circumferential direction Dcc, and a closing plate 62 that closes a gap between the inner circumferential surface 43i of the transition piece upstream portion 43 and the guide plate 61 at a position Dcu upstream of the outlets 44o for each of the plurality of air holes 44. The guide plate 61 extends to a position downstream Dcd of the outlets 44o for each of the plurality of air holes 44 and upstream Dcu of the reduced diameter portion 66 of the backflow prevention member 65.

[0079] In this aspect, the guide plate 61 extending in the circumferential direction Dcc can effectively disperse the individual air Acom from the plurality of air holes 44 aligned in the circumferential direction Dcc in the circumferential direction Dcc. Furthermore, in this aspect, the air Acom from the plurality of air holes 44 can be efficiently guided to the reduced-diameter inner circumferential surface 66i.

[0080] (7) A seventh aspect of the combustor 30 is the combustor 30 of the sixth aspect, wherein the air guide member 60 has gap-retaining protrusions 63 that protrude from the guide plate 61 to the radially outward Dcro with respect to the combustor axis Ac at a position Dcd downstream of the outlets 44o of each of the plurality of air holes 44, are aligned at intervals in the circumferential direction Dcc, and are in contact with the inner circumferential surface 43i of the transition piece upstream portion 43.

[0081] (8) The combustor 30 according to an eighth aspect is the combustor 30 according to any one of the first to seventh aspects, wherein the joint portion 67 of the backflow prevention member 65 has a thickness in the radial direction Dcr. The transition piece upstream portion 43 has a recess 45 that is recessed from the inner circumferential surface 43i of the transition piece upstream portion 43 toward the radially outward side Dcro with respect to the combustor axis Ac and extends in the circumferential direction Dcc at a position downstream Dcd of the outlets 44o of each of the plurality of air holes 44. A depth of the recess 45 corresponds to the thickness of the joint portion 67. The joint portion 67 is inserted in the recess 45 of the transition piece upstream portion 43 and is joined to the transition piece upstream portion 43.

[0082] In this aspect, as the air Acom flows from the plurality of air holes 44 arranged in the circumferential direction Dcc to the downstream side Dcd, the joint portion 67 of the backflow prevention member 65 does not obstruct the flow of the air Acom, and the air flows along the inner circumferential surface 43i of the transition piece upstream portion 43. Therefore, in this aspect, the air Acom from the plurality of air holes 44 can be efficiently guided to the reduced-diameter inner circumferential surface 66i, and the flow rate of the air Acom flowing along the reduced-diameter inner circumferential surface 66i can be increased.

[0083] The gas turbines in the above embodiments and modified examples can be understood, for example, as follows. (9) A gas turbine in a ninth aspect includes the combustor 30 in any one of the first to eighth aspects, a compressor 10 capable of compressing air Acom to generate compressed air Acom, a turbine 20 capable of being driven by combustion gas CG from the combustor 30, and an intermediate casing 6 into which the compressed air Acom from the compressor 10 flows. The compressor 10 includes a compressor rotor 11 rotatable about a rotor axis Ar and a compressor casing 18 covering the compressor rotor 11. The turbine 20 includes a turbine rotor 21 rotatable about the rotor axis Ar and a turbine casing 28 covering the turbine rotor 21. The compressor rotor 11 and the turbine rotor 21 are connected to each other to form a gas turbine rotor 1. The intermediate casing 6 is located between the compressor casing 18 and the turbine casing 28. The compressor casing 18, the intermediate casing 6, and the turbine casing 28 are connected to one another to form a gas turbine casing 8. The combustor 30 is attached to the intermediate casing 6 so that compressed air Acom in the intermediate casing 6 can flow into the combustor 30.

[0084] (10) A gas turbine according to a tenth aspect is the gas turbine according to the ninth aspect, wherein the plurality of air holes 44 of the transition piece upstream portion 43 and the backflow prevention member 65 are both located radially outward (Drro) with respect to the rotor axis line Ar relative to the combustor axis line Ac.

[0085] In the region Drro, which is radially outward from the rotor axis Ar relative to the combustor axis Ac, the combustion gas CG in the transition piece 42 can be extremely efficiently prevented from flowing into the cylindrical gap 40 between the transition piece upstream section 43 and the inner cylinder downstream section 33.

[0086] According to one aspect of the present disclosure, it is possible to efficiently prevent combustion gas from flowing into the gap between the transition piece and the inner cylinder.

[0087] 1: Gas turbine rotor 6: Intermediate casing 8: Gas turbine casing 10: Compressor 11: Compressor rotor 12: Rotor shaft 13: Row of moving blades 15: Row of stator blades 18: Compressor casing 20: Turbine 21: Turbine rotor 22: Rotor shaft 23: Row of moving blades 25: Row of stator blades 28: Turbine casing 30: Combustor 31: Burner 32: Inner cylinder 32de: Downstream end of inner cylinder 33: Downstream side portion of inner cylinder 33o: Outer peripheral surface 40: Cylindrical gap 41: Sealing area 42: Transition piece 42ue: Upstream end of transition piece 43: Upstream side portion of transition piece 43i: Inner peripheral surface 43o: Outer peripheral surface 44: Air hole 44i: Inlet 44o: Outlet 45: Recess 46: Throttle start position 47: Casing opposing portion 48: Throttle portion 49: Rotor opposing portion 50: First elastic ring 51: Fixing portion 52: Spring portion 53: Slit 54a: First contact portion 54b: Second contact portion 55: Second elastic ring 56: Fixing portion 57: Spring portion 58: Slit 59: Contact portion 60: Air guide member 61: Guide plate 62: Closing plate 63: Spacing-maintaining convex portion 65: Backflow prevention member 66: Reduced diameter portion 66i: Reduced diameter inner circumferential surface 66de: Reduced diameter downstream end 67: Joint A: Air Acom: Compressed air (or simply air) F: Fuel G: Combustion gas, or air and fuel CG: Combustion gas g: Gap α: Angle Ac: Combustor axis Dc: Axial direction Dcu: Upstream side Dcd: Downstream side Dcc: Circumferential direction Dcr: Radial direction Dcri: Radial inner side Dcro: Radial outer side Ar: Rotor axis Dr: Rotor axis direction Dru: Upstream side of rotor axis Drd: Downstream side of rotor axis Drr: Radial direction Drri: Radial inner side Drro: Radial outer side

Claims

1. A combustion apparatus comprising: an inner cylinder having a cylindrical shape around a combustor axis; a burner arranged on the inner periphery of the inner cylinder and capable of ejecting fuel and air toward the downstream side of the upstream side and downstream side in the axial direction along which the combustor axis extends; a transition piece having a cylindrical shape around the combustor axis, in which fuel from the burner is combusted with air and through which combustion gas generated by the combustion of the fuel can flow; and a backflow prevention member extending in a circumferential direction about the combustor axis, arranged on the inner periphery of the transition piece and fixed to the transition piece, wherein the inner diameter of an upstream side portion of the transition piece including the upstream end of the transition piece is larger than the outer diameter of a downstream side portion of the inner cylinder including the downstream end of the inner cylinder that is the downstream end of the inner cylinder, and the upstream side portion of the transition piece is arranged opposite to and spaced apart in the radial direction about the combustor axis, the upstream portion of the transition piece has a plurality of air holes that are aligned at intervals in the circumferential direction at a position upstream of the downstream end of the inner cylinder and that penetrate from the outer circumferential side to the inner circumferential side of the upstream portion of the transition piece, the plurality of air holes having inlets that open at an outer circumferential surface of the upstream portion of the transition piece and outlets that open at an inner circumferential surface of the upstream portion of the transition piece, the backflow prevention member having a reduced diameter section whose inner diameter gradually decreases toward the downstream side, and a joining section that is connected to the upstream end of the reduced diameter section and is joined to the upstream portion of the transition piece at a position downstream of the outlets of each of the plurality of air holes, and a position of the reduced diameter downstream end that is the most downstream of the reduced diameter inner circumferential surface that is the inner circumferential surface of the reduced diameter section is downstream of the downstream end of the inner cylinder.

2. A combustor according to claim 1, wherein the reduced diameter inner peripheral surface is inclined at an angle of 30° to 60° with respect to the outer peripheral surface of the downstream side of the inner cylinder.

3. A combustor according to claim 1, wherein the position of the reduced diameter downstream end is radially inward with respect to the combustor axis from the inner circumferential surface of the upstream portion of the transition piece to a position that is half the distance from the inner circumferential surface of the downstream portion of the inner cylinder at a position in the axial direction of the downstream end of the inner cylinder to the outer circumferential surface of the downstream portion of the inner cylinder and the inner circumferential surface of the upstream portion of the transition piece.

4. A combustor according to claim 1, wherein the downstream end of the reduced diameter is located radially outward of the downstream end of the inner cylinder with respect to the combustor axis.

5. A combustor as claimed in claim 1, comprising an air guide member capable of guiding air that has flowed into the space between the upstream portion of the transition piece and the downstream portion of the inner cylinder from the plurality of air holes to the downstream side along the inner circumferential surface of the upstream portion of the transition piece.

6. A combustor as claimed in claim 5, wherein the air guide member comprises: a guide plate extending in the circumferential direction so as to face, at a radial interval, a region in the inner peripheral surface of the upstream portion of the transition piece where the outlets for each of the plurality of air holes are formed; and a closing plate that closes a gap between the inner peripheral surface of the upstream portion of the transition piece and the guide plate at a position upstream of the outlets for each of the plurality of air holes, wherein the guide plate extends to a position downstream of the outlets for each of the plurality of air holes and upstream of the reduced diameter portion of the backflow prevention member.

7. A combustor as claimed in claim 6, wherein the air guide member has gap-maintaining protrusions that protrude radially outward from the guide plate with respect to the combustor axis at a position upstream of the outlets of each of the plurality of air holes, are arranged at intervals in the circumferential direction, and are in contact with the inner circumferential surface of the upstream part of the transition piece.

8. A combustor according to claim 1, wherein the joint portion of the backflow prevention member has a radial thickness relative to the combustor axis, and the upstream portion of the transition piece has a recess that is recessed radially outward relative to the combustor axis from the inner peripheral surface of the upstream portion of the transition piece at a position downstream of the outlets of each of the plurality of air holes and extends in the circumferential direction, the recess having a depth corresponding to the thickness of the joint portion, and the joint portion enters the recess in the upstream portion of the transition piece and is joined to the upstream portion of the transition piece.

9. A gas turbine comprising: a combustor according to any one of claims 1 to 8; a compressor capable of compressing air to generate compressed air; a turbine capable of being driven by combustion gas from the combustor; and an intermediate casing into which the compressed air from the compressor can flow, wherein the compressor has a compressor rotor rotatable about a rotor axis and a compressor casing covering the compressor rotor, and the turbine has a turbine rotor rotatable about the rotor axis and a turbine casing covering the turbine rotor, the compressor rotor and the turbine rotor are connected to each other to form a gas turbine rotor, the intermediate casing is located between the compressor casing and the turbine casing, and the compressor casing, the intermediate casing and the turbine casing are connected to each other to form a gas turbine casing, and the combustor is attached to the intermediate casing so that the compressed air in the intermediate casing can flow into the combustor.

10. A gas turbine according to claim 9, wherein the plurality of air holes and the backflow prevention member provided in the upstream portion of the transition piece are both located radially outward of the combustor axis with respect to the rotor axis.

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