JP2012180843A - Design method of combustor tail pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the combined efficiency by optimizing a sectional shape of a combustor tail pipe.SOLUTION: The design method of the combustor tail pipe includes a process of setting the angle of the center line of a combustor with respect to the axis R of a rotor of a gas turbine, a process of setting the contraction ratio from a tail pipe inlet through which combustion gas flows in to a tail pipe outlet 222 for exhausting combustion gas, a process in which a line parallel to the center line from an inner end A of the radial direction of the tail pipe inlet extends in a downstream manner while maintaining the sectional area of the tail pipe inlet 221, a line parallel to the axis extends in an upstream manner from an inner end C of the radial direction of the tail pipe outlet, and these lines are connected to each other via an arc to form a radial inner profile line, a process of forming a radial outer profile line by smoothly connecting a radial outer end F on the cylindrical downstream side with the sectional area of the tail pipe inlet being maintained to a radial outer end D of the tail pipe outlet, and a process of monotonically reducing the sectional area from the cylindrical downstream side to the tail pipe outlet following the radial inner profile line and the radial outer profile line.

Description

  The present invention relates to a method for designing a combustor tail that optimizes the shape of the combustor tail in a turbine combustor.

  The gas turbine includes a compressor, a combustor, and a turbine. The compressor compresses the air taken in from the air intake to produce high-temperature and high-pressure compressed air. The combustor generates high-temperature and high-pressure combustion gas by supplying fuel to the compressed air and burning it. The turbine is configured by alternately arranging a plurality of turbine stationary blades and turbine blades in the exhaust passage in the casing, and the turbine blades are driven by the combustion gas supplied to the exhaust passage. For example, a rotor connected to a generator is rotationally driven. The combustion gas that has driven the turbine is converted into static pressure by a diffuser downstream of the turbine and then released to the atmosphere.

  In such a gas turbine, the combustion gas of the combustor is supplied to the turbine from the first stage turbine stationary blade. The combustion gas passage is formed in an annular shape in order to arrange the first stage turbine stationary blade along the circumference centered on the axis of the rotor. On the other hand, a plurality of combustors are arranged along a circumference centering on the axis of the rotor in a mode of supplying combustion gas to the turbine. Ideally, the combustor is arranged such that its center line is parallel to the axis of the rotor, and the combustion gas is jetted straight toward the turbine. However, due to the structure of the interior of the gas turbine cabin, the combustor center line is inclined with respect to the rotor axis (at least 30 degrees), and combustion gas is ejected obliquely from the radially outer side to the radially inner side. Are arranged as follows. In this combustor, compressed air is taken in, fuel is supplied to the compressed air from a fuel nozzle and burned to generate high-temperature and high-pressure combustion gas.

  The combustor has a transition piece. The tail pipe guides the combustion gas ejected from the fuel nozzle from the tail pipe inlet immediately after the fuel nozzle to the tail pipe outlet connected to the first stage stationary blade of the turbine. The transition piece has a circular cross-sectional shape at the transition piece inlet, and the transition of the first stage turbine stationary blade combustion gas passage in the combustor in order that the transition piece outlet supplies combustion gas to the first stage turbine stationary blade. It is formed in the arc-shaped cross-sectional shape divided | segmented by the number of. That is, the cross section of the transition piece is deformed from the transition piece inlet to the transition piece outlet. Furthermore, the tail tube needs to be throttled from the tail tube inlet to the tail tube outlet in order to stabilize the flow of combustion gas (see, for example, Patent Document 1).

JP 2006-242559 A

  In recent years, a combined cycle in which a steam generator and a steam turbine are combined downstream of the gas turbine is known in order to improve the output and efficiency as the temperature of the gas turbine increases. In order to improve combined efficiency (thermal efficiency) in such a combined cycle, it is preferable to reduce the amount of heat exchanged for cooling at the outlet of the tail cylinder of the combustor connected to the turbine. That is, the amount of heat for cooling the combustor is recovered by the heat-exchanged steam, but the combined efficiency improves if the amount of heat to be cooled can be reduced from the beginning. Therefore, it is desired to reduce the overall wall flow velocity of the transition piece in the combustor, to prevent local fluctuations in the flow velocity, to reduce the heat transfer rate, and to reduce the amount of exchange heat.

  The present invention has been made in view of the above, and an object of the present invention is to provide a method for designing a combustor tail cylinder capable of optimizing the shape of the combustor tail cylinder and improving the combined efficiency.

  In order to achieve the above object, in the method for designing a combustor transition of the present invention, the step of setting the angle of the center line of the combustor with respect to the axial center of the rotor of the gas turbine; A step of setting a squeezing ratio from an inflowing tail tube inlet to a tail tube outlet for sending combustion gas, and then maintaining the cross-sectional area of the tail tube inlet from the radially inner end of the tail tube inlet A straight line parallel to the center line extends to the downstream side, a straight line parallel to the axial center extends from the radially inner end of the tail tube outlet to the upstream side, and these straight lines are connected by a circular arc to form a radially inner outline. Next, a radially outer contour line is smoothly connected from the radially outer end on the downstream side of the tubular shape in which the cross-sectional area of the tail tube inlet is maintained to the radially outer end of the tail tube outlet. And then, from the downstream side of the tube to the tail tube outlet, the radial direction Characterized in that it comprises a step of monotonically decreasing cross-sectional area in accordance with the side outer lines and the radially outer outline.

  This combustor tail tube design method can form a combustor tail tube in which the shape including the restriction and the deformation of the cross-sectional shape from the tail tube inlet to the tail tube outlet are optimized.

  ADVANTAGE OF THE INVENTION According to this invention, combined efficiency can be improved, optimizing the deformation | transformation of the cross-sectional shape from the transition piece inlet_port | entrance of a combustor transition piece to a transition piece exit, and a throttle | throttle.

FIG. 1 is a schematic configuration diagram of a gas turbine according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a combustor in the gas turbine. FIG. 3 is a schematic view of the inner shape of the transition piece in the combustor. FIG. 4 is a diagram showing the aperture ratio of the transition piece. FIG. 5 is a graph showing the amount of heat exchanged by the combustor tail with respect to the blade height ratio Hin / Hout. FIG. 6 is a conceptual diagram showing a method for designing a combustor transition piece. FIG. 7 is a conceptual diagram illustrating a method for designing a combustor transition piece. FIG. 8 is a conceptual diagram showing a method for designing a combustor transition. FIG. 9 is a diagram showing the flow velocity in the vicinity of the inner wall surface of the combustor transition.

  1 is a schematic configuration diagram of a gas turbine according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a combustor in the gas turbine, FIG. 3 is a schematic diagram of an inner shape of a tail cylinder in the combustor, FIG. These are figures which show the aperture ratio of a transition piece.

  As shown in FIG. 1, the gas turbine includes a compressor 1, a combustor 2, and a turbine 3. A rotor 4 is disposed through the center of the compressor 1, the combustor 2, and the turbine 3. The compressor 1, the combustor 2, and the turbine 3 are arranged in parallel along the axis R of the rotor 4 in order from the upstream side to the downstream side of the flow of air or combustion gas. In the following description, the axial direction refers to a direction parallel to the axis R, the circumferential direction refers to a direction around the axis R, and the radial direction refers to a direction orthogonal to the axis R. . Further, the radially inner side is the side approaching the axis R, and the radially outer side is the side away from the axis R.

  The compressor 1 compresses air into compressed air. The compressor 1 is provided with a compressor stationary blade 13 and a compressor moving blade 14 in an air passage inside a compressor casing 12 having an air intake port 11 for taking in air. A plurality of compressor vanes 13 are attached to the compressor casing 12 side and arranged in parallel in the circumferential direction. A plurality of compressor blades 14 are attached to the rotor 4 side and arranged in parallel in the circumferential direction. A plurality of the compressor vanes 13 and the compressor rotor blades 14 are alternately provided in the axial direction.

  The combustor 2 generates high-temperature and high-pressure combustion gas by supplying fuel to the compressed air compressed by the compressor 1. The combustor 2 covers an inner cylinder 21 that mixes and burns compressed air and fuel, a tail cylinder 22 that guides combustion gas from the inner cylinder 21 to the turbine 3, an outer periphery of the inner cylinder 21, and a compression from the compressor 1. And an outer cylinder 23 that guides air to the inner cylinder 21. A plurality of (for example, 16) combustors 2 are arranged in the circumferential direction with respect to the combustor casing 24. Further, the combustor 2 is inclined in the radial direction from the radially outer side by tilting the center line S of the combustor 2 with respect to the axial center R of the rotor 4 (at least 30 degrees) due to the structural restriction of the interior of the gas turbine. It arrange | positions so that combustion gas may be ejected diagonally inside.

  Further, as shown in FIG. 2, the combustor 2 is provided with fuel nozzles 251 and 252 for mainly supplying fuel. The fuel nozzle 251 is a pilot nozzle provided at the center of the inner cylinder 21. In addition, the fuel nozzle 252 is a main nozzle provided adjacent to a plurality (for example, eight) in the circumferential direction around the pilot nozzle 251 in the inner cylinder 21. A burner cylinder 252 b that covers the main nozzle 252 is provided around the main nozzle 252.

  In the combustor 2, as shown in FIG. 2, an air flow of high-temperature and high-pressure compressed air flows into the outer cylinder 23, and this compressed air flows into the inner cylinder 21. In the inner cylinder 21, the compressed air is mixed with the fuel injected from the main nozzle 252, and flows into the tail cylinder 22 as a swirling flow of premixed air in the burner cylinder 252b. The compressed air is mixed with the fuel injected from the pilot nozzle 251, ignited by an ignition device (not shown), burned, and then burned into the tail cylinder 22 as combustion gas. At this time, flame holding for stabilizing the combustion of the premixed gas from the burner cylinder 252b of each main nozzle 252 is performed by the diffusion flame by the fuel injected from the pilot nozzle 251.

  The turbine 3 generates rotational power by the combustion gas burned in the combustor 2. The turbine 3 is provided with a turbine stationary blade 32 and a turbine rotor blade 33 in an exhaust passage inside a turbine casing 31 into which combustion gas is fed. A plurality of turbine vanes 32 are attached to the turbine casing 31 side and arranged in parallel in the circumferential direction. Further, a plurality of turbine rotor blades 33 are fixed to the outer periphery of a disk-shaped disk centered on the axis R of the rotor 4 and are arranged in parallel in the circumferential direction. A plurality of these turbine stationary blades 32 and turbine rotor blades 33 are provided alternately in the axial direction. Further, an exhaust chamber 34 having a diffuser portion 34 a continuous with the turbine 3 is provided on the downstream side of the turbine casing 31.

  The end of the rotor 4 on the side of the compressor 1 is supported by a bearing 41 and the end of the side of the exhaust chamber 34 is supported by a bearing 42 so as to be rotatable about an axis R. A drive shaft of a generator (not shown) is connected to the end of the rotor 4 on the exhaust chamber 34 side.

  In such a gas turbine, the air taken in from the air intake port 11 of the compressor 1 passes through the plurality of compressor stationary blades 13 and the compressor rotor blades 14 and is compressed, so that the compressed air has a high temperature and a high pressure. It becomes. By supplying fuel from the combustor 2 to the compressed air, high-temperature and high-pressure combustion gas is generated. Then, the combustion gas passes through the turbine stationary blade 32 and the turbine rotor blade 33 of the turbine 3, so that the rotor 4 is rotationally driven, and the generator connected to the rotor 4 is given rotational power to generate power. Do. The combustion gas after rotationally driving the rotor 4 is converted into a static pressure by the diffuser portion 34a in the exhaust chamber 34 and then released to the atmosphere.

  In the gas turbine described above, as shown in FIGS. 2 and 3, the tail cylinder 22 of the combustor 2 is formed in a cylindrical shape, and the tail cylinder inlet 221, which is one opening, is connected to the inner cylinder 21, and the other A transition piece outlet 222 that is an opening is connected to a first stage turbine stationary blade 321 that is an inlet of an exhaust passage in the turbine 3. The inner cylinder 21 to which the transition piece inlet 221 is connected is formed in a cylindrical shape. For this reason, the transition piece inlet 221 is formed in a circular cross-sectional shape (see FIG. 3). The first-stage turbine stationary blade 321 to which the transition piece outlet 222 is connected includes a blade portion 322 and an inner shroud 351 and an outer shroud 352 that support the blade portion 322 so as to sandwich the blade portion 322 in the radial direction. . The inner shroud 351 forms a radially inner wall of the first stage turbine stationary blade 321, and the outer shroud 352 forms a radially outer wall of the first stage turbine stationary blade 321. A combustion gas passage is formed in an annular shape in accordance with the circumferential arrangement of the first stage turbine stationary blade 321. Further, as described above, a plurality of the combustors 2 are arranged side by side in the circumferential direction. For this reason, the transition piece outlet 222 has an arc-shaped cross-sectional shape obtained by dividing an annular shape corresponding to the first stage turbine stationary blade 321 by the number of the combustors 2, in other words, a substantially quadrilateral shape obtained by cutting an arc portion from a sector shape. It is formed in a cross-sectional shape (see FIG. 3). That is, the cross-sectional shape of the transition piece 22 extends from the transition piece inlet 221 to the transition piece outlet 222 and is deformed. The first stage turbine stationary blade 321 to which the tail tube outlet 222 is connected has an annular circumference determined by the aerodynamic shape of the turbine 3. For this reason, the cross-sectional shape of the transition piece outlet 222 has an arc-shaped dimension obtained by dividing an annular shape corresponding to the first stage turbine stationary blade 321 by the number of combustors 2.

  Here, in the first stage turbine stationary blade 321, the downstream radial dimension between the inner shroud 351 and the outer shroud 352 is determined by the aerodynamic shape of the turbine 3. In the present embodiment, the radial dimension (downstream blade height) Hout of the downstream opening of the first stage turbine stationary blade 321 is aerodynamically determined, and the upstream end portions of the inner shroud 351 and the outer shroud 352 are arranged. The radial dimension (upstream blade height) Hin is adjusted to be the same as the radial dimension (a) of the tail tube outlet 222. Specifically, the inner shroud 351 is disposed parallel to the axis R of the rotor 4 (including manufacturing errors), and the upstream end thereof and the radially inner end of the tail tube outlet 222 are the axis of the rotor 4. It is arranged to touch the direction. The outer shroud 352 is disposed such that the upstream end thereof and the radially outer end of the transition piece outlet 222 are in contact with the axial direction of the rotor 4, and the radial dimension of the upstream opening (upstream blade height) Hin Is larger than the radial dimension (downstream blade height) Hout of the downstream opening, and is disposed obliquely with respect to the axis R of the rotor 4 so that the upstream opening gradually widens from the downstream opening.

  Further, the tail cylinder 22 of the combustor 2 is formed with a throttle so that the cross-sectional area decreases from the tail cylinder inlet 221 to the tail cylinder outlet 222 in order to stabilize the flow of combustion gas. More preferably, the drawing ratio Dout / Din of the cross-sectional area Dout of the transition piece outlet 222 to the cross-sectional area Din of the transition piece inlet 221 is 0.9. That is, when the cross-sectional area (diameter (b)) of the transition piece inlet 221 is determined, the cross-sectional area (radial dimension (a)) of the transition piece outlet 222 is determined by the drawing ratio. As shown by a solid line in FIG. 4, the range of the diameter (b) of the transition piece inlet 221 is set, and the radial dimension (a) at the cross-sectional area Dout of the transition piece outlet 222 having a drawing ratio of 0.9. On the other hand, the ratio of the radial dimension Hin of the upstream end of the inner shroud 351 and the outer shroud 352 and the radial dimension Hout of the downstream opening of the first stage turbine vane 321 is the blade height ratio Hin / Hout, This minimum value is X = 1.18. As shown by a broken line in FIG. 4, when the diameter (b) of the tail tube inlet 221 is the maximum dimension at the minimum value X = 1.18 of Hin / Hout of the first stage turbine stationary blade 321, the aperture ratio is Is 0.79. Therefore, within a range of the diameter (b) of the transition piece inlet 221, a preferable throttle ratio based on the minimum value X = 1.18 of Hin / Hout of the first stage turbine stationary blade 321 is 0.79 ≦ Dout / A range of Din ≦ 0.9 is obtained.

  In such a combustor connection structure and gas turbine, with respect to the combustor 2, the radial dimension (a) of the transition piece outlet 222 has a restriction ratio with respect to the diameter (b) of the transition piece inlet 221, 0.79 ≦ Dout / Din ≦ Optimized as a range of 0.9. For this reason, since the wall surface flow velocity of combustion gas is reduced, the amount of exchange heat at the tail tube outlet 222 portion can be reduced, and the combined efficiency can be improved.

  Further, in such a combustor connection structure and gas turbine, with respect to the first stage turbine stationary blade 321 of the turbine 3, the inner shroud 351 is arranged in parallel with the axis R of the rotor 4, and its upstream end and tail tube outlet 222 are arranged. The rotor is disposed so that the radially inner end thereof is in contact with the axial direction of the rotor 4, and the upstream end portion of the outer shroud 352 and the radially outer end of the tail tube outlet 222 are in contact with the axial direction of the rotor 4. It is arranged obliquely with respect to the four axial centers R. For this reason, in the configuration in which the center line S of the combustor 2 is disposed obliquely with respect to the axis R as shown in FIG. 2, the flow rate of the combustion gas from the tail cylinder 22 to the first stage turbine stationary blade 321 increases or decreases. Therefore, the amount of exchange heat can be reduced, and the combined efficiency can be improved.

  These will be described with reference to FIG. FIG. 5 is a graph showing the ratio of the exchange heat quantity of the combustor tail cylinder to the blade height ratio Hin / Hout. As shown in FIG. 5, the Hin / Hout ratio increases as the outer shroud 352 is not arranged obliquely with respect to the axis R of the rotor 4, that is, when Hin / Hout = 1 is used as a reference. It can be seen that the amount of exchange heat is reduced.

  6 to 8 are conceptual diagrams showing a design method of the transition piece, and FIG. 9 is a view showing a flow velocity in the vicinity of the inner wall surface of the transition piece. 6 to 9 show the inner shape of the transition piece 22.

  In the design method of the transition piece 22, first, as shown in FIG. 6, the angle of the center line S of the combustor 2 is set with respect to the axis R of the rotor 4 in the gas turbine. Here, the angle of the center line S with respect to the axis R is set to 30 degrees. An axis R shown in FIG. 6 indicates a reference line parallel to the axis R. Further, the diameter of the transition piece inlet 221 of the combustor 2 is set in advance from the predetermined range described above. As a result, the radially inner end A and the radially outer end B of the tail tube inlet 221 are determined.

  Next, with respect to the cross-sectional area Din of the transition piece inlet 221, the cross-sectional area Dout of the transition piece outlet 222 is set within the above-described range of 0.79 ≦ Dout / Din ≦ 0.9. Here, Dout / Din = 0.9 is set as a more preferable aperture ratio. As described above, since the size of the arc shape obtained by dividing the annular shape corresponding to the first stage turbine stationary blade 321 by the number of the combustors 2 is determined, the tail tube outlet 222 has a radial dimension when the cross-sectional area Dout is determined. Is also determined. Further, the radially inner end C of the transition piece outlet 222 is in a position parallel to the axial center R with respect to the radially inner side wall (inner shroud 351) of the first stage turbine stationary blade 321. Therefore, the outer end D in the radial direction of the transition piece outlet 222 is determined. Further, in order to maximize the residence time of the combustion gas in the tail cylinder 22, that is, the internal volume of the tail cylinder 22, the cylindrical shape from the tail cylinder inlet 221 is secured to the maximum, and the length of the throttle portion is made as short as possible. . Therefore, as shown in FIG. 6, the first virtual straight line 223 parallel to the center line S extends from the radial inner end A of the transition piece inlet 221 to the downstream side, and the shaft extends from the radial inner end C of the transition piece outlet 222. A second virtual straight line 224 parallel to the center R is extended upstream. As described above, the radial dimension (Hout) of the downstream opening of the first stage turbine vane 321 is determined aerodynamically, and the upstream ends of the inner shroud 351 and the outer shroud 352 are radial. The radial outer wall (outer shroud 352) of the first stage turbine vane 321 is arranged in the radial direction of the tail cylinder outlet 222 so that the dimension (Hin) is the same as the radial dimension (a) of the tail cylinder outlet 222. It is arranged obliquely with respect to the axis R of the rotor 4 toward the outer end D.

  Next, as shown in FIG. 7, the first virtual line 223 and the second virtual line 224 are connected. Specifically, the first virtual straight line 223 and the second virtual straight line 224 are in contact with each other so that the cylindrical shape from the tail tube inlet 221 is secured to the maximum and the radially inner edge of the tail tube 22 does not swell inward. An arc R1 having a radius as large as possible is provided. As a result, the radially inner end A of the transition piece inlet 221 and the radially inner end C of the transition piece outlet 222 are connected by the first imaginary straight line 223, the second imaginary straight line 224, and the arc R1, and the radially inner side of the transition piece 22 The outline is determined. Further, a radially inner end E and a radially outer end F on the downstream side of the cylindrical shape of the tail tube 22 are determined.

  Next, as shown in FIG. 8, the cylindrical radially outer end F and the radially outer end D of the tail tube outlet 222 are connected. Specifically, a straight line from the radially outer end B to the radially outer end F of the tail tube inlet 221 and an oblique radial outer wall (outer shroud) of the first stage turbine stationary blade 321 leading to the radially outer end D. 352) are smoothly connected by two arcs, or two arcs and a straight line. That is, at the radially outer end F, an arc R2 having a straight line extending from the radially outer end B to the radially outer end F as a tangent line is provided from the radially outer end F to the point G. Then, a straight line 225 connected to the arc R2 is extended from the point G to the downstream side. Further, a straight line 226 of the oblique radial outer wall (outer shroud 352) of the first stage turbine stationary blade 321 is extended from the radial outer end D to the downstream side. Furthermore, an arc R3 connecting the point H of the straight line 225 and the point J of the straight line 226 is provided. Thereby, the radially outer end F of the cylindrical shape and the radially outer end D of the tail tube outlet 222 are smoothly connected, and the radially outer outline of the tail tube 22 is determined.

  Finally, from the tail tube inlet 221 to the radially inner end E and the radially outer end F, a cylindrical shape is formed, and this cylindrical shape reaches the radially inner end C and the radially outer end D of the tail tube outlet 222, and the radial direction The cross-sectional area is monotonously reduced based on the inner outline and the radially outer outline.

  In the production of the transition piece 22, for example, it is divided into four in the axial direction, these are respectively pressed, and later joined by welding to form the transition piece 22.

  In the transition piece 22 of the combustor 2, as shown in FIG. 9, when the flow velocity in the vicinity of the inner wall surface in the radially outer outline and the radially inner outline is viewed, the transition piece 22 (solid line) of this embodiment is used. In this case, the flow velocity from the transition piece inlet 221 to the transition piece outlet 222 becomes maximum at the transition piece outlet 222, and before that, the flow velocity is suppressed so as not to exceed this maximum value, and is monotonically corresponding to the aperture ratio. It turns out that it is increasing stably. On the other hand, in the comparative example (shown by a broken line) in which the cross-sectional area does not decrease monotonously, the flow velocity from the tail tube inlet 221 to the tail tube outlet 222 is fast and shows an unstable change. It is the maximum before 222.

  As described above, in the combustor transition tube and gas turbine of this embodiment, the change in the cross-sectional area from the transition piece inlet 221 to the transition piece outlet 222 is optimized, so that the wall velocity of the combustion gas is reduced. The amount of heat exchanged at the tail tube outlet 222 can be reduced, and the combined efficiency can be improved. Further, in the combustor tail tube design method, an optimum shape of the tail tube 22 that can improve the combined efficiency can be obtained.

1 compressor 2 combustor 21 inner cylinder 22 tail cylinder 221 tail cylinder inlet 222 tail cylinder outlet 23 outer cylinder 24 combustor casing 251 pilot nozzle 252 main nozzle 252b burner cylinder 3 turbine 31 turbine casing 32 turbine stationary blade 321 first stage turbine Stator blade 322 Blade portion 33 Turbine rotor blade 351 Inner shroud 352 Outer shroud 4 Rotor Din Cross section area of tail cylinder inlet Dout Cross section area of tail cylinder outlet Dout / Din Restriction ratio Hin Radial direction of upstream end of inner shroud and outer shroud Dimensions (upstream blade height)
Hout Radial dimension of downstream opening of first stage turbine vane (downstream blade height)
Hin / Hout radial dimension ratio (blade height ratio)
R Rotor axis S Combustor center line

Claims (1)

Setting the angle of the center line of the combustor with respect to the axis of the rotor of the gas turbine;
Next, a step of setting a squeezing ratio from the tail tube inlet into which the combustion gas flows into the tail tube outlet through which the combustion gas is sent;
Next, a straight line parallel to the center line is extended downstream from the radially inner end of the transition piece inlet in a manner that maintains the cross-sectional area of the transition piece inlet, and from the radially inner end of the transition piece outlet. Extending a straight line parallel to the axis to the upstream side and connecting each straight line with an arc to form a radially inner outline;
Next, a step of smoothly connecting from the radially outer end on the downstream side of the cylindrical shape in which the cross-sectional area of the tail tube inlet is maintained to the radially outer end of the tail tube outlet to form a radially outer contour line; and ,
And a step of monotonically decreasing a cross-sectional area from the downstream side of the cylinder to the outlet of the tail cylinder and monotonously reducing a cross-sectional area according to the radially inner outline and the radially outer outline. Design method.

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