Patent Publication Number: US-2023145667-A1

Title: Labyrinth seal and gas turbine

Description:
TECHNICAL FIELD 
     The present disclosure relates to a labyrinth seal and a gas turbine. 
     BACKGROUND ART 
     In rotary machines, such as gas turbines, a labyrinth seal may be located between a rotary body and a stationary body to prevent a gas from passing and leaking through between the rotary body and the stationary body. The labyrinth seal may include a seal fin that is located at one of a structure of the rotary body and a structure of the stationary body and extends to the other of the structure of the rotary body and the structure of the stationary body (see PTL 1). By using the seal fin, a gap (hereinafter referred to as an “opposing gap”) between the structure of the rotary body and the structure of the stationary body can be made small, and as a result, a leakage amount of gas can be suppressed. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Laid-Open Patent Application Publication No. 2019-49346 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, according to the labyrinth seal including the seal fin, by the rotation of the rotary body, a tip of the seal fin is brought into contact with an opposing surface and is worn away. As a result, the opposing gap gradually increases in size, and the effect of suppressing the leakage amount of gas by the seal fin gradually deteriorates. To be specific, there is a limit to the suppression of the leakage amount by reducing the size of the opposing interval using the seal fin. 
     The present disclosure was made under these circumstances, and an object of the present disclosure is to provide a labyrinth seal and a gas turbine, each of which can effectively suppress a leakage amount of gas at an outlet portion. 
     Solution to Problem 
     A labyrinth seal according to one aspect of the present disclosure includes: a first structure; and a second structure opposed to the first structure. The first structure includes: seal fins located at intervals in an axial direction and extending toward the second structure; a downstream wall surface located downstream of a most downstream one of the seal fins and extending toward the second structure, a tip of the downstream wall surface being located at a side of a tip of the most downstream seal fin, the side being close to the second structure in a radial direction; and a first outlet surface extending from the tip of the downstream wall surface toward a downstream side in the axial direction. The second structure includes: a second outlet surface opposed to the first outlet surface, a radial gap being between the first outlet surface and the second outlet surface; and a cavity surface located upstream of the second outlet surface in the axial direction and adjacent to the second outlet surface, the cavity surface being recessed in a direction away from the first structure. 
     According to this configuration, the gas having passed through the most downstream seal fin collides with the downstream wall surface, then flows along the downstream wall surface, and further flows along the cavity surface. With this, a vortex is generated in a downstream space surrounded by the most downstream seal fin, the downstream wall surface, and the cavity surface. As a result, even when the dimension of the gap between the first downstream surface and the second downstream surface which is the outlet of the downstream space is slightly large, the outflow of the gas through the gap between the first downstream surface and the second downstream surface can be suppressed. Therefore, according to the above labyrinth seal, a leakage amount of gas at an outlet portion can be effectively suppressed. 
     A gas turbine according to one aspect of the present disclosure includes the above labyrinth seal. 
     Advantageous Effects of Invention 
     The present disclosure can provide a labyrinth seal and a gas turbine, each of which can effectively suppress a leakage amount of gas at an outlet portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a sectional view of a labyrinth seal according to Embodiment 1. 
         FIG.  2    is a sectional view of the labyrinth seal according to Embodiment 2. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     Hereinafter, embodiments of the present disclosure will be described. First, a labyrinth seal  100  according to Embodiment 1 will be described. 
       FIG.  1    is a sectional view of the labyrinth seal  100  according to Embodiment 1. The labyrinth seal  100  is located at a rotary machine, such as a gas turbine. More specifically, the labyrinth seal  100  is located between a stationary body, such as a casing, and a rotary body, such as a shaft. Therefore, the labyrinth seal  100  has an annular shape. 
     In  FIG.  1   , a paper surface left-right direction is an axial direction of the labyrinth seal  100 , and a paper surface upper-lower direction is a radial direction of the labyrinth seal  100 . Moreover, a paper surface upper side is a radially outer side of the labyrinth seal  100 , and a paper surface lower side is a radially inner side of the labyrinth seal  100 . Furthermore, in  FIG.  1   , a paper surface left side is a high pressure side, and a paper surface right side is a low pressure side. To be specific, a gas flows from the paper surface left side to the paper surface right side. Thus, the paper surface left side is an upstream side of the gas, and the paper surface right side is a downstream side of the gas. 
     As shown in  FIG.  1   , the labyrinth seal  100  according to the present embodiment includes a first structure  10  and a second structure  20 . In the present embodiment, the first structure  10  is located on an outer peripheral portion of the rotary body, and the second structure  20  is located on an inner peripheral portion of the stationary body. Hereinafter, the first structure  10  and the second structure  20  will be described in order. 
     First Structure 
     The first structure  10  is located on the outer peripheral portion of the rotary body as described above and has a cylindrical shape. The first structure  10  includes an inlet surface  11 , an inclined surface  12 , a downstream wall surface  13 , a first outlet surface  14 , and seal fins  15 . 
     The inlet surface  11  is a portion located at a most upstream side of the first structure  10  and is located upstream of a most upstream one of the seal fins  15 . The inlet surface  11  of the present embodiment extends in parallel with the axial direction. To be specific, a radial position of the inlet surface  11  in the axial direction is constant. 
     The inclined surface  12  is a portion located downstream of the inlet surface  11  and adjacent to the inlet surface  11 . In the present embodiment, the inclined surface  12  is inclined such that a downstream portion thereof is located at the radially outer side of an upstream portion thereof. In a sectional view, the inclined surface  12  of the present embodiment is inclined linearly but may be inclined stepwise. Moreover, in a sectional view, the inclined surface  12  may have a curved shape or a shape that is a combination of a linear shape and a curved shape. 
     The downstream wall surface  13  is a portion located downstream of the inclined surface  12  and adjacent to the inclined surface  12 . A base end portion of the downstream wall surface  13  of the present embodiment is continuous with the inclined surface  12  and is curved. A tip portion of the downstream wall surface  13  of the present embodiment extends toward the second structure  20 . Moreover, a tip of the downstream wall surface  13  is located at a side (the radially outer side in the present embodiment) of a tip of a most downstream one of the seal fins  15 , the side being close to the second structure  20  in the radial direction. Moreover, an axial distance between the downstream wall surface  13  and the most downstream seal fin  15  is equal to an axial distance between the adjacent seal fins  15 . 
     The first outlet surface  14  is a portion located downstream of the downstream wall surface  13  and adjacent to the downstream wall surface  13 . The first outlet surface  14  is located at a most downstream side of the first structure  10 . A radial position of the first outlet surface  14  of the present embodiment in the axial direction is constant. To be specific, the first outlet surface  14  extends from the tip of the downstream wall surface  13  toward the downstream side in the axial direction. However, the radial position of the first outlet surface  14  in the axial direction does not have to be constant. Moreover, in the present embodiment, an angle between the downstream wall surface  13  and the first outlet surface  14  is smaller than 90°. 
     The seal fins  15  extend from the first structure  10  toward the second structure  20 . A radial gap is between each seal fin  15  and the second structure  20 . The seal fins  15  are located on the inclined surface  12 . The seal fins  15  are located at regular intervals in the axial direction. The seal fins  15  may extend in the radial direction or may extend in a direction inclined relative to the radial direction. 
     In a sectional view, a tip of the seal fin  15  has an acute angle. However, the shape of the tip of the seal fin  15  is not limited to this. Moreover, the seal fins  15  of the present embodiment are the same in shape and size as each other. However, the shape and size of the seal fin  15  are not especially limited. Furthermore, the first structure  10  of the present embodiment includes four seal fins  15 . However, the number of seal fins  15  included in the first structure  10  is not especially limited. 
     The dimension of the radial gap between the first outlet surface  14  and the second structure  20  (second outlet surface  22 ) is larger than the dimension of the radial gap between the seal fin  15  and the second structure  20 . 
     Second Structure 
     The second structure  20  is a structure opposed to the first structure  10 . The second structure  20  is located on the inner peripheral portion of the stationary body and has a cylindrical shape. The second structure  20  includes step surfaces  21 , the second outlet surface  22 , and a cavity surface  23 . 
     The step surfaces  21  are located so as to correspond to the above-described seal fins  15 . Therefore, the step surfaces  21  are opposed to the respective seal fins  15 . A radial gap is between each step surface  21  and each seal fin  15 . Moreover, the second structure  20  of the present embodiment includes four step surfaces  21 , the number of which is equal to the number of seal fins  15 . However, the number of step surfaces  21  included in the second structure  20  is not especially limited. 
     Moreover, the step surfaces  21  extend in parallel with the axial direction. To be specific, a radial position of each step surface  21  in the axial direction is constant. Furthermore, the step surface  21  that is located at the downstream side is located at the radially outer side. Therefore, the entirety of the step surfaces  21  is inclined so as to be located at the radially outer side as it extends toward the downstream side. 
     The second outlet surface  22  is located at a most downstream side of the second structure  20 . The second outlet surface  22  is opposed to the first outlet surface  14 . Moreover, a gap is between the first outlet surface  14  and the second outlet surface  22 . As described above, the dimension of the radial gap between the first outlet surface  14  and the second outlet surface  22  is larger than the dimension of the radial gap between the seal fin  15  and the second structure  20 . 
     A radial position of the second outlet surface  22  of the present embodiment in the axial direction is constant. Therefore, even when the relative positions of the first structure  10  and the second structure  20  in the axial direction slightly deviate from each other, the dimension of the radial gap between the first outlet surface  14  and the second outlet surface  22  does not change and is maintained constant. 
     The cavity surface  23  is connected to a most downstream one of the step surfaces  21 . Moreover, the cavity surface  23  is located upstream of the second outlet surface  22  and is adjacent to the second outlet surface  22 . To be specific, the cavity surface  23  is located between the most downstream step surface  21  and the second outlet surface  22 . The cavity surface  23  is recessed in a direction away from the first structure  10  (in the present embodiment, outward in the radial direction). To be specific, when viewed from the first structure  10 , a bottom portion of the cavity surface  23  is located farther than the second outlet surface  22 . 
     In a sectional view, the cavity surface  23  of the present embodiment is curved. However, the cavity surface  23  may have another shape, such as a shape defined by straight lines connected to each other in a sectional view. Moreover, a radial distance from a downstream end portion of the most downstream step surface  21  to the bottom portion of the cavity surface  23  is larger than a radial dimension of the most downstream seal fin  15 . Furthermore, a boundary between the second outlet surface  22  and the cavity surface  23  is located downstream of a boundary between the downstream wall surface  13  and the first outlet surface  14  in the axial direction. 
     The second structure  20  is such that when each seal fin  15  is regarded as a reference, a portion of the second structure  20  which is located downstream of the seal fin  15  does not overlap the seal fin  15  when viewed in the axial direction. For example, when the most upstream seal fin  15  is regarded as a reference, a portion of the second structure  20  which is located downstream of the most upstream seal fin  15  is located at the radially outer side of the most upstream seal fin  15 , and the most upstream seal fin  15  and the portion of the second structure  20  which is located downstream of the most upstream seal fin  15  do not overlap each other when viewed in the axial direction. Therefore, the rotary body and the stationary body can be assembled by inserting the rotary body into the stationary body in the axial direction without bringing portions of the first structure  10  and portions of the second structure  20  into contact with each other. 
     Flow of Gas 
     Next, the flow of the gas passing through between the first structure  10  and the second structure  20  will be described. Herein, a space  30  surrounded by the most downstream seal fin  15 , the downstream wall surface  13 , and the cavity surface  23  is referred to as a “downstream space.” In this case, the air having passed through a gap between the downstream seal fin  15  and the second structure  20  which is an inlet of the downstream space  30  flows along the axial direction and then collides with the downstream wall surface  13 . After that, the flow of the gas is divided into the flow toward the radially outer side and the flow toward the radially inner side. 
     The gas flowing toward the radially inner side generates a first vortex V 1  in a region located at the radially inner side of the tip of the most downstream seal fin  15 . On the other hand, the gas flowing toward the radially outer side flows along the downstream wall surface  13 , and then, flows along the cavity surface  23  across a gap between the first outlet surface  14  and the second outlet surface  22  which is an outlet of the downstream space  30 . With this, the gas generates a large second vortex V 2  in a region located at the radially outer side of the tip of the most downstream seal fin  15 . As a result, the flow (arrow shown by a broken line in  FIG.  1   ) of the air passing through the outlet of the downstream space  30  is suppressed, and therefore, a leakage amount of gas at an outlet portion of the labyrinth seal  100  can be effectively suppressed. 
     Moreover, in the present embodiment, the boundary between the second outlet surface  22  and the cavity surface  23  is located downstream of the boundary between the downstream wall surface  13  and the first outlet surface  14  in the axial direction. Furthermore, the angle between the downstream wall surface  13  and the first outlet surface  14  is smaller than 90°. Therefore, the gas flowing along the downstream wall surface  13  toward the radially outer side easily separates from the first outlet surface  14 . As a result, the area of the passage at the outlet of the downstream space  30  becomes practically small, and therefore, the flows of the air passing through the outlet of the downstream space  30  is further suppressed. 
     Embodiment 2 
     Next, a labyrinth seal  200  according to Embodiment 2 will be described.  FIG.  2    is a sectional view of the labyrinth seal  200  according to Embodiment 2 and corresponds to  FIG.  1    of Embodiment 1. In  FIG.  2   , the same reference signs are used for the same components as in  FIG.  1    and corresponding components to  FIG.  1   , and explanations of the above-described components are omitted. 
     The labyrinth seal  100  according to Embodiment 1 and the labyrinth seal  200  according to Embodiment 2 are different from each other in that: in Embodiment 1, the first structure  10  is located on the outer peripheral portion of the rotary body, and the second structure  20  is located on the inner peripheral portion of the stationary body; and in Embodiment 2, the first structure  10  is located on the inner peripheral portion of the stationary body, and the second structure  20  is located on the outer peripheral portion of the rotary body. 
     In the labyrinth seal  200  according to the present embodiment, unlike Embodiment 1, the inclined surface  12  is inclined such that the downstream portion thereof is located at the radially inner side of the upstream portion thereof. Moreover, the entirety of the step surfaces  21  is inclined so as to be located at the radially outer side as it extends toward the downstream side. 
     In the present embodiment, the first structure  10  includes the downstream wall surface  13 , and the second structure  20  includes the cavity surface  23 . Therefore, the gas generates the large second vortex V 2  in a region located at the radially inner side of the tip of the most downstream seal fin  15  in the downstream space  30 . As a result, the flow (arrow shown by a broken line in  FIG.  2   ) of the air passing through the outlet of the downstream space  30  is suppressed, and therefore, the leakage amount of gas at the outlet portion of the labyrinth seal  100  can be effectively suppressed. 
     Operational Advantages 
     The foregoing has described the labyrinth seal according to Embodiment 1 and the labyrinth seal according to Embodiment 2. As described above, the labyrinth seal according to each embodiment includes: a first structure; and a second structure opposed to the first structure. The first structure includes: seal fins located at intervals in an axial direction and extending toward the second structure; a downstream wall surface located downstream of a most downstream one of the seal fins and extending toward the second structure, a tip of the downstream wall surface being located at a side of a tip of the most downstream seal fin, the side being close to the second structure in a radial direction; and a first outlet surface extending from the tip of the downstream wall surface toward a downstream side in the axial direction. The second structure includes: a second outlet surface opposed to the first outlet surface, a radial gap being between the first outlet surface and the second outlet surface; and a cavity surface located upstream of the second outlet surface in the axial direction and adjacent to the second outlet surface, the cavity surface being recessed in a direction away from the first structure. 
     According to this configuration, the gas having passed through the most downstream seal fin collides with the downstream wall surface, then flows along the downstream wall surface, and further flows along the cavity surface. With this, a vortex is generated in a downstream space surrounded by the most downstream seal fin, the downstream wall surface, and the cavity surface. As a result, even when the dimension of the gap between the first downstream surface and the second downstream surface which is the outlet of the downstream space is slightly large, the outflow of the gas through the gap between the first downstream surface and the second downstream surface can be suppressed. Therefore, according to the above labyrinth seal, a leakage amount of gas at an outlet portion can be effectively suppressed. 
     In the labyrinth seal according to the embodiment, the cavity surface is curved in a sectional view. 
     According to this configuration, since the gas smoothly flows along the cavity surface, a further strong vortex can be generated in the downstream space, and therefore, the leakage amount of gas at the outlet portion of the labyrinth seal can be further effectively suppressed. 
     Moreover, in the labyrinth seal according to the embodiment, a boundary between the second outlet surface and the cavity surface is located downstream of a boundary between the downstream wall surface and the first outlet surface in the axial direction. 
     According to this configuration, the gas flowing along the downstream wall surface toward the radially outer side easily separates from the first outlet surface. As a result, the flow of the air passing through the outlet of the downstream space can be further suppressed, and therefore, the leakage amount of gas at the outlet portion of the labyrinth seal can be further effectively suppressed. 
     Moreover, in the labyrinth seal according to the embodiment, an angle between the downstream wall surface and the first outlet surface is smaller than 90°. 
     Also in this configuration, the gas flowing along the downstream wall surface toward the radially outer side easily separates from the first outlet surface. As a result, the flow of the air passing through the outlet of the downstream space can be further suppressed, and therefore, the leakage amount of gas at the outlet portion of the labyrinth seal can be further effectively suppressed. 
     Moreover, in the labyrinth seal according to the embodiment, the second structure includes surfaces opposed to the respective seal fins, and a radial distance from a downstream end portion of the surface of the second structure which is opposed to the most downstream seal fin to a bottom portion of the cavity surface is larger than a radial dimension of the most downstream seal fin. 
     According to this configuration, the flow of the air is largely changed by the cavity surface. Therefore, a further strong vortex can be generated in the downstream space, and therefore, the leakage amount of gas at the outlet portion of the labyrinth seal can be further effectively suppressed. 
     Moreover, the gas turbine according to the embodiment includes the above-described labyrinth seal. 
     REFERENCE SIGNS LIST 
       10  first structure 
       13  downstream wall surface 
       14  first outlet surface 
       15  seal fin 
       20  second structure 
       22  second outlet surface 
       23  cavity surface 
       100 ,  200  labyrinth seal