JP5852185B2 - Channel structure and gas turbine exhaust diffuser - Google Patents

Description

  The present invention relates to a flow path structure and a gas turbine exhaust diffuser.

  As is well known, a type of flow path structure is known in which a structure extends from a wall surface forming a flow path in a direction intersecting with a main flow direction along a main flow of a fluid flowing through the flow path.

  For example, in a kind of exhaust diffuser of a gas turbine, a bearing that supports a rotor is provided inside an exhaust casing, and an annular space around the bearing serves as an exhaust passage. A strut that extends from the exhaust casing and holds the bearing is disposed (for example, Patent Document 1).

JP 2004-190664 A

  By the way, in the said flow-path structure, since the flow-path cross-sectional area changed, there existed a problem that a pressure loss would arise.

  For example, in a kind of the exhaust diffuser of the gas turbine described above, the range in which the struts are disposed in the main flow direction of the exhaust gas is such that the struts occupy a part of the flow path in the cross section of the flow path. As the flow proceeds from upstream to downstream, the cross-sectional area of the flow path decreases rapidly and then increases. For this reason, there has been a problem that a relatively large pressure loss occurs when the exhaust gas passes through the area where the struts are disposed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a flow channel structure and a gas turbine exhaust diffuser that suppress the occurrence of pressure loss.

In order to achieve the above object, the present invention employs the following means.
That is, in the flow channel structure according to the present invention, a plurality of structures extend from the wall surface forming the flow channel in a direction intersecting with the main flow direction along the main flow of the fluid flowing through the flow channel, and the flow intersecting the main flow. A flow path structure in which the cross-sectional area of the flow path changes as it proceeds in the main flow direction because the structure occupies a part of the flow path in the path cross section, and a plurality of the structures are: A recessed portion forming region is provided in each of the plurality of structures . The recessed portions are disposed in the flow path at intervals in the circumferential direction, and recessed portions are formed in the wall surface over a range including the structures in the main flow direction and the circumferential direction. has the concave portion forming region of each of a plurality of said structures are arranged at intervals in the circumferential direction, the recess, after becoming gradually deeper nears to the structure in the circumferential direction, the circumferential gradually as it gets farther away from the structure in the direction Characterized in that it becomes shallow.
According to this configuration, since the concave portion is formed on the wall surface over the concave portion forming region including the structure in the main flow direction, the cross-sectional area of the flow path is increased by the amount of the concave portion compared to the case where the concave portion is not formed. .
That is, in the range where the structure in the mainstream direction is formed, at least a part of the decrease in the cross-sectional area due to the structure can be offset by the increase in the cross-sectional area due to the recess. Thereby, since the change in the cross-sectional area becomes gentler than that in the case where the concave portion is not formed, generation of pressure loss can be suppressed.
Furthermore, the upstream and downstream of the structure in the main flow direction will increase the cross-sectional area of the flow path as compared with the case where no recess is formed, so the effect of pressure changes at the front and rear edges of the structure will be reduced. Can be relaxed.

Further, when the length from the front edge to the rear edge of the structure in the main flow direction is L, the concave portion is spaced from the rear edge by a distance of 0.4 L from the front edge to the upstream side. It is formed in a range up to a position separated by a distance of 0.4 L on the downstream side.
According to this configuration, since the concave portion is formed in a range from a position separated by a distance of 0.4 L upstream from the front edge to a position separated by a distance of 0.4 L downstream from the rear edge, pressure loss is reduced. It can be effectively deterred.

Further, the concave portion is formed in a range from a position separated by a distance of 0.2 L upstream from the front edge to a position separated by a distance of 0.2 L downstream from the rear edge.
According to this configuration, the concave portion is formed in a range from a position 0.2 L away from the front edge to the upstream side to a position 0.2 L away from the rear edge to the downstream side. It can be suppressed more effectively.

A gas turbine exhaust diffuser according to the present invention has any one of the flow channel structures described above.
According to this configuration, since any one of the above-described flow path structures is provided, the diffuser performance can be improved, and as a result, the performance and efficiency of the gas turbine can be improved.

  According to the present invention, occurrence of pressure loss can be suppressed.

1 is a half sectional view showing a schematic configuration of a gas turbine 1 according to an embodiment of the present invention. 1 is an enlarged cross-sectional view of a main part of a gas turbine 1 according to an embodiment of the present invention, showing a main part I in FIG. It is principal part expanded sectional drawing of the exhaust diffuser 10 which concerns on embodiment of this invention, Comprising: The II-II sectional view taken on the line in FIG. 2 is shown. It is a line graph which shows the change of the cross-sectional area of the exhaust flow path P of the exhaust diffuser 10 which concerns on embodiment of this invention, Comprising: The position of a mainstream direction is shown on a horizontal axis, and the cross-sectional area of the exhaust flow path P is shown on the vertical axis | shaft. Yes. FIG. 5 is a line graph showing a change in the cross-sectional area of the exhaust passage P of the exhaust diffuser 10 according to the embodiment of the present invention, and is an enlarged view of a main part III of FIG. It is an effect explanatory view of exhaust diffuser 10 concerning the embodiment of the present invention, and the horizontal axis shows the start / end position of a crevice formation field, and the vertical axis shows diffuser performance improvement amount. FIG. 5 is an enlarged cross-sectional view of a main part showing a modified example of the exhaust diffuser 10 according to the embodiment of the present invention, corresponding to FIG. 3.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a half sectional view showing a schematic configuration of a gas turbine 1 according to an embodiment of the present invention.
As shown in FIG. 1, the gas turbine 1 is schematically composed of a compressor 2, a combustor 3, and a turbine 4, and a rotor 5 includes a compressor casing 2 a of the compressor 2 and a turbine casing 4 a of the turbine 4. It is inserted.

The compressor 2 includes a blade row composed of compressor stationary blades 2b arranged in an annular shape on the inner periphery of the compressor casing 2a, and a blade row composed of compressor moving blades 2c arranged in an annular shape on the outer periphery of the rotor 5. The compression channels are alternately stacked in the direction of the rotation center axis S, and a compression flow path is formed so as to pass through these blade rows. The cascade composed of the compressor moving blades 2c and the cascade composed of the compressor stationary blades 2b have a multistage structure in which a pair (stage) adjacent in the direction of the rotation center axis S forms a pair.
The compressor 2 adiabatically compresses the air A taken inside from the upstream side to the downstream side of the compression flow path.

  The combustor 3 is disposed between the compressor 2 and the turbine 4. The high-pressure air A compressed by the compressor 2 is mixed and burned, and the combustion gas G is sent to the turbine 4. Yes.

The turbine 4 includes a cascade of turbine stationary blades 4b arranged annularly on the inner periphery of the turbine casing 4a, and a cascade of turbine rotor blades 4c arranged annularly on the outer periphery of the rotor 5. The combustion gas flow path R is formed so as to pass through these blade rows.
The turbine 4 converts the thermal energy of the combustion gas G into rotational energy of mechanical work through the rotor 5 by flowing the combustion gas G generated in the combustor 3 downstream while expanding.

  As described above, the rotor 5 is inserted through the compressor casing 2a and the turbine casing 4a, and one end side is connected to a generator (not shown), and the generator is driven by the rotational energy generated by the turbine 4 as power. To supply.

  The gas turbine 1 having such a schematic configuration includes an exhaust diffuser 10 connected to the downstream side of the turbine blade 4c at the final stage of the turbine casing 4a.

2 is an enlarged cross-sectional view showing a main part I in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line II-II in FIG.
As shown in FIG. 2, the exhaust diffuser 10 is a cylindrical shape that is provided inside the exhaust casing 10 a connected to the turbine casing 4 a and the journal bearing 7 that pivotally supports the rotor 5. A protective casing 11, a plurality of struts (structures) 12 extending from the exhaust casing 10 a to the inside of the protective casing 11 and holding the journal bearing 7 from the periphery, and provided on the downstream side of the struts 12. And a manhole (structure) 13 provided for maintenance.
In the exhaust diffuser 10, the direction of the rotation center axis S is the main flow direction along the main flow of the exhaust gas E.

The exhaust casing 10a is configured such that the inner peripheral wall surface (wall surface) 10b gradually increases in diameter in the main flow direction from the upstream side to which the turbine 4 is connected toward the downstream side.
The protective casing 11 is provided coaxially with the exhaust diffuser 10 and is formed to have substantially the same diameter from the upstream side to which the turbine 4 is connected to the downstream side in the main flow direction.

  An annular exhaust passage P is formed between the exhaust casing 10 a and the protective casing 11 by the inner peripheral wall surface 10 b of the exhaust casing 10 a and the outer peripheral wall surface 11 b of the protective casing 11. The exhaust passage P has the outer peripheral wall surface 11b of the protective casing 11 formed to have substantially the same diameter, while the inner peripheral wall surface 10b of the exhaust casing 10a gradually increases in diameter as it goes downstream. The cross-sectional area that intersects the main flow direction gradually increases as it goes from the upstream side to the downstream side (see FIG. 4).

Each strut 12 includes a strut body 12a that holds the journal bearing 7, and a strut cover 12b that covers the strut body 12a with combustion gas G and protects it from heating. The strut cover 12b extends from the protective casing 11 toward the exhaust casing 10a.
The manhole 13 allows the outside of the exhaust casing 10a to communicate with the inside of the protective casing 11 (accommodating space).
The strut cover 12b and the manhole 13 extend in a direction intersecting the mainstream, and in order to reduce the mainstream resistance in the exhaust passage P, the cross-sectional shape is a wing shape (streamline type).

  As shown in FIG. 2, the exhaust casing 10 a has an upstream recess formation region (recess formation region) 20 and a downstream recess formation region (recess formation region) 30.

  In the upstream recess formation region 20, an upstream inner peripheral recess (recess) 21 formed on the inner peripheral wall surface 10 b of the exhaust casing 10 a and an outer peripheral wall surface of the protective casing 11 (over the range including the struts 12 in the main flow direction). An upstream peripheral recess (recess) 22 formed in the wall surface 11b is formed.

  As shown in FIG. 3, these upstream recesses (upstream inner peripheral recess 21 and upstream outer peripheral recess 22) are positions where the struts 12 respectively extend out of the inner peripheral wall surface 10 b and the outer peripheral wall surface 11 b in the flow path cross section. It is formed over the range including.

As shown in FIG. 2, these upstream recesses gradually become shallower after becoming gradually deeper from one side in the main flow direction to the other side. Moreover, as shown in FIG. 3, after becoming gradually deeper from one to the other in the circumferential direction, it becomes gradually shallower.
Further, the positions of the upstream recesses extending in the main flow direction are set as follows when the length of the strut 12 in the main flow direction is L1. That is, in the main flow direction, 0.2 L1 away from the strut leading edge 12 c located upstream of the strut 12 upstream from the position 0.2 L1 away from the strut trailing edge 12 d located downstream of the strut 12 0.2 L1 away from the downstream. It extends to the position.

  As shown in FIG. 2, the downstream recess forming region 30 includes a downstream inner peripheral recess (recess) 31 formed in the inner peripheral wall surface 10b and an outer peripheral wall surface 11b over a range including the manhole 13 in the main flow direction. A formed downstream outer peripheral recess (recess) 32 is formed.

These downstream recesses (downstream inner peripheral recesses 31 and downstream outer periphery recesses 32) are each formed over a range including the position where the manhole 13 extends in the flow path cross section (see FIG. 3).
Further, as shown in FIG. 2, these downstream recesses become gradually shallower after becoming gradually deeper in the mainstream direction, and gradually getting shallower after becoming gradually deeper in the circumferential direction as shown in FIG. It has become.

  When the length of the manhole 13 in the mainstream direction is L2, these downstream recesses are located in the mainstream direction from a position 0.2 L2 upstream from the manhole leading edge 13c located at the uppermost stream of the manhole 13 in the mainstream direction. Extends from the manhole trailing edge 13d located on the most downstream side to a position 0.2 L2 away from the downstream side.

  4 is a line graph showing a change in the cross-sectional area of the exhaust flow path P of the exhaust diffuser 10, and FIG. 5 is an enlarged view of a main part III of FIG. In FIG. 4, the horizontal axis indicates the position in the main flow direction, and the vertical axis indicates the cross-sectional area of the exhaust passage P. 4 and 5, the locus indicated by the solid line indicates the exhaust flow path P, and the locus indicated by the broken line does not include the upstream recessed portion forming region 20 and the downstream recessed portion forming region 30, the strut 12, and the manhole 13. The change in the cross-sectional area of the first hypothetical flow path PX is assumed, and the second hypothetical flow in the case where the locus indicated by the alternate long and short dash line is assumed to have no upstream recess formation region 20 and downstream recess formation region 30 is shown. The change of the cross-sectional area of the path PY is shown.

  As shown in FIG. 4, the upstream concave portion and the downstream concave portion are located between the first hypothetical channel PX and the second hypothetical channel PY in the central part of the change path of the cross-sectional area of the exhaust channel P. As such, its depth is formed. More precisely, as shown in FIG. 5, the change in the cross-sectional area of the exhaust passage P between the strut leading edge 12c and the strut trailing edge 12d and between the manhole leading edge 13c and the manhole trailing edge 13d. Is formed so as to be located between the first assumed flow path PX and the second assumed flow path PY.

As shown in FIG. 4, the change in the cross-sectional area of the exhaust passage P is as follows.
First, the cross-sectional area of the exhaust passage P increases as the inner peripheral wall surface 10b of the turbine 4 increases in diameter as it proceeds downstream from the inflow portion of the exhaust gas E. Thereafter, when reaching the upstream recess formation region 20, the increase in the cross-sectional area due to the upstream recess is added to the increase in the cross-sectional area due to the expansion of the inner peripheral wall surface 10b, and the increase rate of the cross-sectional area increases. Next, when the strut leading edge 12c is reached, the decrease in the cross-sectional area due to the strut 12 occupying the exhaust flow path P exceeds the increase in the cross-sectional area due to the upstream recess and the expansion of the inner peripheral wall surface 10b. The cross-sectional area increase rate turns negative. Then, after the cross-sectional area of the exhaust passage P decreases to a position near the middle of the strut 12 in the main flow direction, the cross-sectional area increases while depicting a trajectory opposite to the above. When the strut trailing edge 12d is reached, the cross-sectional area of the exhaust passage P is gently reduced by increasing the cross-sectional area due to the expansion of the inner peripheral wall surface 10b more than the decrease of the cross-sectional area of the upstream recess. The locus is only an increase in the cross-sectional area due to the diameter expansion of the wall surface 10b.
The same applies to the downstream recess formation region 30.

Next, the operation of the exhaust diffuser 10 having the above configuration will be described.
As shown in FIG. 2, the combustion gas G that has passed through the final stage turbine blade 4 c flows into the exhaust passage P. Since the exhaust passage P gradually increases in diameter as it goes downstream, the dynamic pressure of the exhaust gas E is converted to a static pressure.

  The exhaust gas E that has reached the most upstream side of the upstream recess formation region 20 flows toward the downstream strut 12. At this time, a pressure distribution in which the pressure gradually increases toward the strut leading edge 12c due to the collision of the exhaust gas E is formed on the upstream side in the main flow direction of the strut leading edge 12c. And the upstream outer circumferential concave portion 22 increase the cross-sectional area of the exhaust flow path P, so that the pressure gradient becomes relatively gentle.

  When the exhaust gas E reaches the strut leading edge 12c, the strut 12 occupies the cross section of the exhaust flow path P, so the cross sectional area of the exhaust flow path P decreases. The cross-sectional area of the exhaust flow path P is the largest in the vicinity of the center in the mainstream direction, in other words, at the position where the blade thickness of the strut 12 having the airfoil cross-sectional shape is maximized, and then gradually increases. .

  In these cases, as shown in FIGS. 4 and 5, the decrease in the cross-sectional area of the exhaust passage P is offset by the increase in the cross-sectional areas of the upstream outer peripheral recess 22 and the upstream inner peripheral recess 21. Compared with the flow path PY, the change in the cross-sectional area of the exhaust flow path P becomes gentle. For this reason, the pressure fluctuation of the exhaust gas E becomes relatively gentle, and the pressure loss generated in the exhaust gas E becomes relatively small.

  When the exhaust gas E flows downstream from the strut trailing edge 12d, the increase in the cross-sectional area due to the expansion of the inner peripheral wall surface 10b is reduced by the decrease in the cross-sectional area between the upstream inner peripheral recess 21 and the upstream outer recess 22. After the increase, the cross-sectional area of the exhaust passage P is gently reduced, and then increases due to the diameter expansion of the inner peripheral wall surface 10b. Even at this time, the cross-sectional area of the exhaust passage P changes relatively gently. For this reason, the pressure fluctuation of the exhaust gas E becomes relatively gentle, and the pressure loss generated in the exhaust gas E becomes relatively small.

  Similarly, when the exhaust gas E passes through the manhole 13 (downstream recessed portion forming region 30), the generated pressure loss is relatively reduced due to the same action as when passing through the strut 12 (upstream recessed portion forming region 20). Get smaller.

As described above, according to the exhaust diffuser 10 according to the embodiment of the present invention, the upstream inner peripheral recess 21 is formed on the inner peripheral wall 10b over the upstream recess forming region 20 including the strut 12 in the main flow direction. Since the upstream outer peripheral concave portion 22 is formed in 11b, the upstream inner peripheral concave portion 21 and the upstream outer peripheral concave portion are compared with the second assumed flow path PY in which the upstream inner peripheral concave portion 21 and the upstream outer peripheral concave portion 22 are not formed. The cross-sectional area of the exhaust flow path P increases by the amount of 22.
That is, at least part of the decrease in the cross-sectional area due to the strut 12 can be offset by the increase in the cross-sectional area due to the upstream inner peripheral recess 21 and the upstream outer peripheral recess 22. Thereby, since the change of the cross-sectional area of the exhaust flow path P becomes gentler than that of the second hypothetical flow path PY, generation of pressure loss of the exhaust gas E can be suppressed.
Further, the upstream and downstream of the strut 12 in the main flow direction, the cross-sectional area of the exhaust passage P increases compared to the second hypothetical passage PY, so the pressure at the strut leading edge 12c and the strut trailing edge 12d. The effects of change can be mitigated.

Since the upstream inner circumferential concave portion 21 and the upstream outer circumferential concave portion 22 are formed so as to include a position where the strut 12 extends in the flow path cross section, a partial region in which the strut 12 is included in the flow path cross section. The cross-sectional area of can be increased. Thereby, compared with the case where the upstream inner circumferential recess 21 and the upstream outer circumferential recess 22 are formed at positions spaced apart from the strut 12 in the circumferential direction, the fluid colliding with the strut 12 can be quickly transferred into the upstream side. Since it can escape to the peripheral recessed part 21 and the upstream outer peripheral recessed part 22, a pressure loss can be reduced effectively.
Furthermore, in the main flow direction, the cross-sectional area of the flow path partially increases compared to the case where the second hypothetical flow path PY is not formed upstream of the strut leading edge 12c and downstream of the strut trailing edge 12d. The influence of the pressure change at the strut leading edge 12c and the strut trailing edge 12d can be greatly reduced.

  In addition, a part of the center of the change path of the cross-sectional area of the exhaust passage P in the range in which the struts 12 extend in the main flow direction is the change of the cross-section area of the first assumed flow path PX and the second assumption. Since the upstream inner circumferential concave portion 21 and the upstream outer circumferential concave portion 22 are formed so as to be between the change trajectories of the flow path PY, the change in the cross sectional area of the exhaust flow path P is the first. It approximates the change in the cross-sectional area of the assumed flow path PX, and pressure loss can be effectively suppressed.

  Further, the upstream inner circumferential recess 21 and the upstream outer circumferential recess 22 extend from a position 0.2 L away from the strut leading edge 12 c to the upstream side to a position 0.2 L away from the strut trailing edge 12 d. Since it is formed in the range, pressure loss can be more effectively suppressed.

FIG. 6 is a correlation diagram between the recessed portion formation region and the diffuser performance improvement amount. FIG. 6 shows the result of confirming the amount of improvement in the diffuser performance by changing the upstream start position and the downstream end position of the upstream recess formation region 20.
As shown in FIG. 6, as the upstream start position and the downstream end position of the upstream recess formation area 20 are increased, they gradually increase and become the highest in the vicinity of 0.2L1. Then, it gradually decreases, and the amount of improvement in the diffuser performance decreases from around 0.4L1.
In this way, the upstream inner circumferential recess 21 and the upstream outer circumferential recess 22 are separated from the strut leading edge 12c by a distance of 0.2L1 upstream and from the strut trailing edge 12d by a distance of 0.2L1 downstream. Therefore, the diffuser performance can be greatly improved, and the performance and efficiency of the gas turbine can be improved.

  Even in the manhole 13 where the downstream recessed portion forming region 30 is located, the downstream inner peripheral recessed portion 31 and the downstream outer peripheral recessed portion 32 exhibit the same effects as the upstream inner peripheral recessed portion 21 and the upstream outer peripheral recessed portion 22, so that the pressure loss Can be effectively deterred.

  Note that the operation procedure shown in the above-described embodiment, various shapes and combinations of the constituent members, and the like are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

  For example, in the above-described embodiment, the upstream concave portion (the upstream inner peripheral concave portion 21 and the upstream outer peripheral concave portion 22) and the downstream concave portion (the downstream inner peripheral concave portion 31 and the downstream outer peripheral concave portion 32) are provided. Only one of the recess and the downstream recess may be provided, or the recess forming region may be provided only on either the inner peripheral wall surface 10b or the outer peripheral wall surface 11b.

  In the above-described embodiment, the upstream inner circumferential recess 21 and the upstream outer circumferential recess 22 are separated from the strut leading edge 12c by a distance of 0.2L1 upstream from the strut trailing edge 12d by a distance 0 downstream. Although formed in a range up to a position 2L1 apart, as shown in FIG. 6, a good improvement in diffuser performance is recognized if it is a range up to a position 0.4L1 away. Accordingly, the upstream inner circumferential recess 21 and the upstream outer circumferential recess 22 are moved from a position separated by a distance of 0.4 L1 upstream from the strut leading edge 12 c to a position separated by a distance of 0.4 L1 downstream from the strut trailing edge 12 d. You may form in a range. The same applies to the downstream inner circumferential recess 31 and the downstream outer circumferential recess 32.

Further, in the above-described embodiment, the upstream inner peripheral recess 21 and the upstream outer recess 22 include the position where the manhole 13 extends so as to include the position where the strut 12 extends in the cross section of the flow path. Although the downstream inner circumferential recess 31 and the downstream outer circumferential recess 32 are respectively formed, as shown in FIG. 7, at least one or more recesses 40 are included in a range not including the struts 12 and the manholes 13 in the flow path cross section. It may be formed.
As shown in FIG. 7, the recess 40 may be provided only on the outer peripheral wall surface 11b, or may be provided only on the inner peripheral wall surface 10b or on both.
Further, in the upstream recess formation region 20, only the recess 40 may be provided instead of the upstream inner periphery recess 21 and the upstream outer periphery recess 22. Similarly, in the downstream recess formation region 30, only the recess 40 may be provided instead of the downstream inner periphery recess 31 and the downstream outer periphery recess 32.

  Moreover, although the case where the flow path structure according to the present invention was applied to the exhaust diffuser 10 of the gas turbine 1 was described in the above-described embodiment, other parts of the gas turbine 1 (for example, suction of air A of the compressor) The flow channel structure according to the present invention may be applied to a flow channel or the like or other fluid machines.

DESCRIPTION OF SYMBOLS 1 ... Gas turbine, 10 ... Exhaust diffuser, 10b ... Inner peripheral wall surface (wall surface), 11b ... Outer peripheral wall surface (wall surface), 12 ... Strut (structure), 12c ... Strut front edge (front edge), 12d ... Strut rear edge (Rear edge), 13 ... manhole (structure), 13c ... manhole front edge (front edge), 13d ... manhole rear edge (rear edge), 20 ... upstream recess formation area (recess formation area), 21 ... upstream side Circumferential recesses (recesses), 22 ... upstream outer periphery recesses (recesses), 30 ... downstream recess formation regions (recess formation regions), 31 ... downstream inner periphery recesses (recesses), 32 ... downstream outer periphery recesses (recesses), 40 ... Recess, E ... Exhaust gas (fluid), P ... Exhaust flow path

Claims (4)

A plurality of structures extend from the wall surface forming the flow path in a direction intersecting the main flow direction along the main flow of the fluid flowing through the flow path, and the structure is in the cross section of the flow path intersecting the main flow. By occupying a part of the range, the cross-sectional area of the flow path changes as it proceeds in the mainstream direction,
The plurality of structures are arranged in the flow path at intervals in the circumferential direction,
For each of the plurality of structures, there is a recess formation region in which a recess is formed on the wall surface over a range including the structure in the mainstream direction and the circumferential direction.
The recessed portion forming regions for each of the plurality of structures are arranged at intervals in the circumferential direction,
The flow path structure according to claim 1, wherein the recess gradually becomes deeper as it approaches the structure in the circumferential direction, and gradually becomes shallower as it moves away from the structure in the circumferential direction .   When the length from the front edge to the rear edge of the structure in the main flow direction is L, the concave portion is located downstream from the rear edge by a distance of 0.4 L from the front edge to the upstream side. 2. The flow path structure according to claim 1, wherein the flow path structure is formed in a range up to a position separated by 0.4 L.   3. The concave portion is formed in a range from a position separated by a distance of 0.2L upstream from the front edge to a position separated by a distance of 0.2L downstream from the rear edge. 2. The flow channel structure according to 1.   A gas turbine exhaust diffuser comprising the flow channel structure according to any one of claims 1 to 3.

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