Abstract:
A gas turbine includes a compressor, a combustor, and a turbine. The turbine includes a honeycomb seal disposed so as to be secured to a casing side in a clearance between the casing and turbine blades rotating around a rotating shaft and a seal fin that is provided on an end face of each of the turbine blades facing the honeycomb seal. The seal fin extends in a direction perpendicular to the rotating shaft. The honeycomb seal is formed by a plurality of corrugated sheet metals overlapped with each other at walls of nodes thereof and the walls of the nodes are blazed with each other. Each of the corrugated sheet metals has trapezoids formed in alternating fashion. A longer direction of each wall of the nodes of the honeycomb seal is angled with respect to the rotational direction of the turbine blades.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gas turbine that is provided with an abradable honeycomb seal installed to reduce the leakage of working fluid from a clearance between turbine blades and a casing. 
     2. Description of the Related Art 
     In a gas turbine mainly including a compressor, a combustor, and a turbine, high-temperature combustion gas flows between turbine blades installed on a rotating shaft and stator vanes installed on a stationary casing side. It is desirable to prevent the combustion gas from leaking from the turbine blade tip clearance in terms of the performance of the turbine. To meet such request, a gas turbine provided with an abradable honeycomb seal secured to the casing side is generally used. This honeycomb seal is manufactured in the following manner: a thin sheet metal is processed to form a corrugated shape in which trapezoids are alternately continued; a plurality of the corrugated thin sheet metals are overlapped at their walls of node, the walls of node being brazed with each other; and the abradable honeycomb seal provided with a number of approximately hexagonal voids are manufactured. 
       FIG. 7  is a schematic view exemplifying a seal structure located at the tip of a gas turbine blade B using an abradable honeycomb seal H. The honeycomb seal H is secured to a shroud S on a casing C side at a portion facing a seal fin F installed on the tip of the rotating turbine blade B. A clearance between the tip of the seal fin F and the honeycomb seal H is maintained as little as possible. The leakage of combustion gas at the tip of the turbine blade B is accordingly suppressed. 
     As illustrated in  FIG. 8 , the whole of the honeycomb seal H is generally configured as follows: a corrugated thin sheet metal P is processed such that trapezoids are alternately continued; a plurality of the corrugated thin sheet metals P are overlapped at their walls of node K; and the walls of node K are brazed with each other (at the brazed places R) so that the corrugated thin sheet metals P are secured to each other. 
     The honeycomb seal H is formed of a material relatively softer than the turbine blade B. The honeycomb seal H comes into contact with the rotating turbine blade B when the rotating turbine blade B extends in the radial direction perpendicular to the rotational axis due to thermal expansion. As a consequence, the honeycomb seal H is easily abraded by the seal fin F arranged on the tip of the turbine blade B. Accordingly, while avoiding the damage and vibration of the turbine blade B, the clearance between the turbine blade B and the honeycomb seal H is kept constant whereby the leakage of combustion gas is suppressed. 
     Incidentally, as regards the securing of the honeycomb seal H to the shroud S on the casing C side, as illustrated in  FIG. 8 , the honeycomb seal H is generally secured to the shroud S via the brazed place R in such a manner that the longer direction of the wall of node K (also the longer direction of the brazed place R extending in the Y 1  direction in  FIG. 8 ) may coincide with the rotational direction (the Z direction in  FIG. 8 ) of the turbine blade B. The reason of this securing method is as follows: the corrugated thin sheet metals P formed with press working or other methods are secured to the shroud S so as to extend in the rotational direction of the turbine blade B. Hence, the securing-workability of the corrugated thin sheet metals will be satisfactory and manufacturing efficiency will be enhanced. 
     However, in the securing configuration of the honeycomb seal H described above, the walls of node K and the brazed places R which are abraded when the seal fin F abrades the honeycomb seal H become larger in length. The abradability of the honeycomb seal H by the seal fin F will be degraded accordingly. 
     When the rotating seal fin F comes into a situation of contact with the brazed place R, the abradability of the honeycomb seal H by the seal fin F significantly lowers compared with the case of contact with only the corrugated thin sheet metal. In fact, the thickness of the seal fin F is equal to or greater than that obtained by addition of the thickness of the brazed place R to the thickness of the two walls of node K. The seal fin F therefore will simultaneously abrade the two walls of node K and the brazed place R between the walls along the longer direction. 
     As illustrated in  FIG. 8 , the brazed place R of the honeycomb seal H is linear because the wall of node K is one side of a trapezoid. The longer direction of the brazed place R and the sliding direction of the seal fin F along with the rotational direction of the turbine blade B (and the seal fin F) are almost the same direction. Thus, a distance becomes long in which the seal fin F comes into contact with and slides along the brazed place R with low abradability. In addition, the abradability of the honeycomb seal H by the seal fin F lowers because of the formation in which the longer direction of the brazed place R independently faces the slide of the seal fin F. 
     The seal fin F may be abraded by the brazed place R in some cases. With the seal fin F being abraded, the leakage of the combustion gas from the abraded portion increases, which directly leads to a decrease in the performance of the gas turbine. 
     SUMMARY OF THE INVENTION 
     As countermeasures to such problems, JP-2011-226559-A proposes a structure in which the brazed place of the honeycomb seal is limited to a portion on the base material side, so that a seal fin and the brazed place do not directly slide with each other. JP-2002-309902-A proposes a technology in which a material having a melting point lower than the softening temperature of a rotor blade material is used for a honeycomb seal. 
     However, these conventional technologies require a honeycomb seal having a special shape and material and have problems in terms of economic efficiency, abradability, and durability. 
     Also, JP-2005-163693-A discloses a sealing device in which a honeycomb wall cross-section, which is a cross-section of a wall of a honeycomb seal, extends in an obliquely inclined manner with respect to a honeycomb seal sectional line. This sectional line shows the cross-section of an envelope plane formed by the tip of the honeycomb seal. 
     The technology disclosed in JP-2005-163693-A aims to reduce a leakage amount of fluid between a stationary member and a rotating member. The technology is nothing but simply tilting the wall of the honeycomb seal rising up from the stationary member such as a casing. The technology fails to solve the above-described problem in which the seal fin of the turbine blade is abraded by the brazed places of the honeycomb seal. 
     The present invention has been made in view of the above problem and aims to provide a gas turbine that can solve the problem in which a seal fin of a turbine blade is abraded by the brazed places of a honeycomb seal. 
     In order to achieve the aforementioned aim, a gas turbine according to an aspect of the present invention comprises: a compressor, a combustor, and a turbine which includes a honeycomb seal disposed so as to be secured to a casing side in a clearance between a casing and a turbine blade rotating around a rotating shaft extending in a longitudinal direction of the casing, and a seal fin provided on an end face of the turbine blade facing the honeycomb seal, the seal fin extending in a direction perpendicular to the rotating shaft, wherein the honeycomb seal is formed by a plurality of corrugated thin sheet metals overlapped with each other at each wall of node, the wall of node being brazed with each other, each of the corrugated thin sheet metals having a trapezoid alternately continued, and wherein a longer direction of the wall of node of the honeycomb seal is tilted with respect to the rotational direction of the turbine blade. 
     The gas turbine according to the present invention is such that the longer direction of the wall of node of the corrugated thin sheet metal forming the honeycomb seal, that is, the longer direction of the brazed place whereby the walls of node are secured to each other is tilted with respect to the rotational direction of the turbine blade. The abradability of the honeycomb seal by the turbine blade and the seal fin can be improved and the abrasion of the seal fin by the honeycomb seal can be suppressed accordingly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating the overall configuration of a gas turbine according to the present invention, its upper part above a centerline being illustrated in longitudinal cross-section; 
         FIG. 2  is an enlarged view of an II-portion of  FIG. 1 , illustrating shrouds on a casing side, turbine blades, and seal fins; 
         FIG. 3  is a schematic view illustrating a honeycomb seal and explains a first relation between the honeycomb seal and the rotational direction of a turbine blade (a honeycomb seal securing structure according to a first embodiment); 
         FIG. 4  is a view for explaining a second relation between a honeycomb seal and the rotational direction of a turbine blade (a honeycomb seal securing structure according to a second embodiment); 
         FIG. 5  is a view for explaining a honeycomb seal securing structure according to a third embodiment; 
         FIG. 6A  is a side view for explaining a seal fin according to another embodiment; 
         FIG. 6B  is a view illustrating the seal fin as viewed from arrow (b) in  FIG. 6A ; 
         FIG. 7  is a view illustrating shrouds on a casing side, turbine blades and seal fins in a conventional gas turbine; and 
         FIG. 8  is a view illustrating a honeycomb seal applied in  FIG. 7  and explains a relation between the honeycomb seal and the rotational direction of the turbine blade. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of a gas turbine according to the present invention will hereinafter be described with reference to the drawings. 
     [An Embodiment of a Gas Turbine] 
     &lt;The Overall Configuration of the Gas Turbine&gt; 
       FIG. 1  is a schematic view illustrating the overall configuration of a gas turbine according to the present invention, its upper part above a centerline being illustrated in longitudinal cross-section.  FIG. 2  is an enlarged view of an II-portion of  FIG. 1 , illustrating shrouds on a casing side, turbine blades, and seal fins. 
     As illustrated in  FIG. 1 , a gas turbine  100  generally includes: a compressor  10  which compresses air sucked (from an X-direction) to generate compressed air; a combustor  20  which burns the compressed air from the compressor  10  together with fuel to generate high temperature and pressure combustion gas; and a turbine  30  which is driven by the combustion gas jetted from the combustor  20 . 
     The power obtained at the turbine  30  is transmitted to and drives a generator and the like not shown connected to a rotating shaft  4  and is used as drive force for the compressor  10 . 
     The turbine  30  has the rotating shaft  4  at the center of a casing  1  which partially houses the compressor  10  and the combustor  20 . The rotating shaft  4  can be rotated around a rotational axis L 1  (a longitudinal axis of the casing  1 ). A plurality of turbine blades  5 A,  5 B,  5 C are mounted on the circumference of the rotating shaft  4 . 
     Turbine stator vanes  3 A,  3 B,  3 C are secured to the inner wall side of the casing  1 . These turbine stator vanes  3 A,  3 B,  3 C and the turbine blades  5 A,  5 B,  5 C secured to the circumference of the rotating shaft  4  are alternately installed in the direction of the rotational axis L 1  so as to configure respective stages. In the gas turbine  100  illustrated by way of example, the turbine  30  is a one-shaft turbine having three-stage blade rows and includes the first-stage stator vane  3 A, the second-stage stator vane  3 B, the third-stage stator vane  3 C, the first-stage rotor blade  5 A, the second-stage rotor blade  5 B, and the third-stage rotor blade  5 C. However, the gas turbine according to the present invention is not limited to the one-shaft gas turbine. The present invention may be applied to a two-shaft gas turbine having a high-pressure turbine and a low-pressure turbine. Further, the number of stages is not limited to the three stages and shall not be restrictive. 
     As illustrated in  FIG. 2 , a plurality of stages of shrouds  2  are annularly provided in the rotational direction of the turbine blades at respective positions between the turbine blades  5 A- 5 C for all the stages and the casing  1  so as to define an outer circumferential wall of a passage for high temperature and pressure combustion gas in order to prevent the combustion gas from coming into direct contact with the casing  1 . 
     These shrouds  2  are secured to the inner wall of the casing  1 . The stator vanes  3 A- 3 C are each integrally supported by the corresponding shrouds  2  of a plurality of stages. 
     The turbine blades  5 A- 5 C are greater in blade length as they go toward the rear stages on the downstream side of the flow direction of the combustion gas, thus their strength against vibration stress or bending stress encountered when the turbine blades  5 A- 5 C are subjected to the flow of the combustion gas tends to be lower as they go toward the rear stages. To improve such a tendency, for example, the second and third stage turbine blades  5 B and  5 C are provided with annular shroud covers  5 B′ and  5 C′, respectively, at their tips. In addition, the turbine blades  5 B adjacent to each other in the rotational direction (the circumferential direction) thereof are integrated by the shroud cover  5 B′. Similarly, the turbine blades  5 C adjacent to each other in the rotational direction thereof are integrated by the shroud cover  5 C′. Accordingly, the stiffness of the each blade row is enhanced. 
     It is desirable that clearances between the turbine blades  5 A- 5 C and the corresponding shrouds  2  be narrow as much as possible in terms of the performance of the gas turbine. Seal fins  6  which generally linearly extend parallel to the rotational direction of the turbine blade are therefore provided on the radially outside surfaces of the shroud covers  5 B′,  5 C′ so as to project toward the corresponding shrouds  2 . 
     The clearance between the seal fin  6  and the shroud  2  may be too small. In such a case, when the lengths of the turbine blades  5 A- 5 C is increased due to the thermal expansion during operation, the seal fin  6  and the shroud  2  may be likely to come into contact with each other, which will probably lead to the breakage of or damage to the turbine blades  5 A- 5 C. To prevent such breakage or damage, a honeycomb seal  7  is secured to the inner circumferential side of the shroud  2  so as to face the seal fin  6  with a clearance defined on the radial outside of the seal fin  6 . 
     A detailed description will now be given of the honeycomb seal and a securing structure of the honeycomb seal to the shroud according to embodiments. 
     Honeycomb Seal and its Securing Structure According to a First Embodiment 
       FIG. 3  is a schematic view illustrating a honeycomb seal and explains a first relation between the honeycomb seal and the rotational direction of a turbine blade (a honeycomb seal securing structure according to a first embodiment) 
     The honeycomb seal  7  has a hexagonal honeycomb structure configured in the following manner. Corrugated thin sheet metals  71  are each formed such that trapezoidal concavities and convexities are alternately continued. A plurality of the corrugated thin sheet metals  71  are joined to each other. Honeycomb shapes including approximately hexagonal voids and walls of node are continued to provide the hexagonal honeycomb structure. The hexagonal honeycomb structure is brazed to the shroud  2 . 
     To manufacture the honeycomb seal  7 , a thin sheet material is pressed to form a corrugated thin sheet metal  71 . The corrugated thin sheet metals  71  are joined to each other through welding, brazing, or other methods to form the hexagonal honeycomb structure. Thereafter, a sheet-like brazing filler metal is held between the sticking surface of the shroud  2  and the honeycomb structure. These remaining in this state are heat-treated in a furnace to melt the sheet-like brazing filler metal. This heat treatment allows the molten sheet-like brazing filler metal to enter between the walls of node  71   a  of the corrugated thin sheet metals  71  adjacent to each other through minute gaps due to capillary action, the metal being to be hardened subsequently. Brazed places  72 , formed between the walls of node  71   a , ensure the stiffness of the honeycomb seal  7  which forms a honeycomb seal surface in contact with the seal fin  6 . 
     In the brazed place  72 , the brazing filler metal has penetrated to the tip of the wall of node  71   a  of the corrugated thin sheet metal  71  so as to firmly join the walls of node  71   a , thereby achieving the maintenance of the shape and stiffness of the honeycomb seal  7 . 
     As illustrated in  FIG. 3 , a setting angle θ between the longer direction (the Y 1  direction and also the longer direction of the brazed place  72 ) of the wall of node  71   a  and the rotational direction (the Z direction) of the turbine blades  5 A- 5 C is set to 90 degrees in the formation in which the honeycomb seal  7  is secured to the shroud  2 . 
     The following formation will be easily understood through comparison with the securing formation of the conventional honeycomb seal H illustrated in  FIG. 8 . The seal fin  6  on the tip of the turbine blade comes into contact with the honeycomb seal  7  to abrade the honeycomb seal  7  when the securing formation of the honeycomb seal  7  illustrated in  FIG. 3  is applied. At this time, the seal fin  6  passes the two walls of node  71   a  which are a part of the honeycomb seal  7  in the thickness direction of the walls and passes the brazed place  72  between the walls of node  71   a  in the thickness direction of the brazed place  72 . 
     In short, the seal fin  6  passes the walls of node  71   a  at the shortest distance and passes the brazed place  72  at the shortest distance as well. 
     As described above, the seal fin  6  abrades the shortest portions of the walls of node  71   a  and brazed place  72  of the honeycomb seal  7 . In particular, the seal fin  6  abrades the shortest portion of the hard brazed place  72 . A problem is accordingly effectively solved in which the seal fin  6  is broken or damaged at the time of abrading the honeycomb seal  7 . 
     Incidentally, the illustrated securing structure of the honeycomb seal  7  is a simple structure improved after modification of the arrangement mode of the honeycomb seal  7 . The manufacturing costs of the turbine will not be increased due to the improved structure for this reason. 
     Honeycomb Seal Securing Structure According to a Second Embodiment 
       FIG. 4  is a view for explaining a second relation between a honeycomb seal and the rotational direction of a turbine blade (a honeycomb seal securing structure according to a second embodiment). 
     The arrangement formation of the honeycomb seal illustrated in  FIG. 4  is such that a setting angle θ between the longer direction (the Y 1  direction) of the wall of node  71   a  and the rotational direction (the Z direction) of the turbine blades  5 A- 5 C is set at a range from 30 degrees to less than 90 degrees. 
     A length in which the walls of node  71   a  and the brazed place  72  are abraded by the seal fin  6  is greater than that in the case where the setting angle θ is 90 degrees. However, the study of the present inventors shows that if the setting angle θ is within a range equal to or greater than 30 degrees, an effect of preventing the breakage of the seal fin  6  can sufficiently be attained. 
     Honeycomb Seal Securing Structure According to a Third Embodiment 
       FIG. 5  is a view for explaining a honeycomb seal securing structure according to a third embodiment. 
     The securing structure of the honeycomb seal illustrated in  FIG. 5  is as follows: for example, as illustrated in  FIGS. 3 and 4 , a setting angle θ between the longer direction (the Y 1  direction) of the wall of node  71   a  and the rotational direction (the Z direction) of the turbine blades  5 A- 5 C is set at a range from 30 to 90 degrees. In addition to this securing structure of the honeycomb seal  7 , the wall of node  71   a  and the brazed place  72  are tilted at a tilt angle θ′ in a range between 15 degrees and 45 degrees in the rotational direction (the Z direction) of the turbine blade with respect to a vertical axis L 2  perpendicular to the rotating shaft  4 . 
     The study of the present inventors shows that since the honeycomb seal  7  has the tilt angle tilted in the rotational direction of the turbine blade in such an angle range, a load received by the seal fin  6  can further be reduced when the seal fin  6  abrades the honeycomb seal  7 . The effect of preventing the breakage of the seal fin  6  can further be enhanced. 
     Seal Fins According to Other Embodiments 
     Descriptions are next given of seal fins of other embodiments.  FIGS. 6A and 6B  are views for explaining a seal fin of another embodiment,  FIG. 6A  being a side view illustrating the seal fin,  FIG. 6B  being a view illustrating the seal fin as seen from arrow “b” in  FIG. 6A . 
     As illustrated in  FIGS. 6A and 6B , a seal fin  6 ′ is partially provided with thickened portions  6   a  formed by a hard material overlaid (the hard material being an abrasion-resistant alloy or ceramics, for example) 
     The thickened portions  6   a  made of the hard material are provided to project leftward and rightward from the side walls of the seal fin  6 ′. The abradability of the honeycomb seal  7  can further be enhanced in this manner. 
     Although an illustration is omitted, a seal fin may be applied that is further provided with a projection projecting upward from the upper end surface of the seal fin depicted in  FIG. 6A . 
     A seal fin may be formed with a coating layer made of a hard material on the whole circumference thereof. 
     [Experiments to Confirm the Effect of the Honeycomb Seal Constituting a Part of the Gas Turbine and its Securing Structure According to the Present Invention, and the Results of the Experiments] 
     The inventors conducted experiments in the following manner. The securing structure of the honeycomb seal illustrated in  FIG. 3 ; specifically, the securing structure of the formation was manufactured in which a setting angle θ between the longer direction of the wall of node of the corrugated thin sheet metal and the rotational direction of the turbine blade was set at 90 degrees. In addition, a load acting on the seal fin when the honeycomb seal was abraded was measured. 
     The conventional securing structure illustrated in  FIG. 8  was also manufactured as a comparative example. The same experiment was performed and a load acting on the seal fin at that time was measured. 
     The results of the comparison between both the measurement values show that the maximum load acting on the seal fin in the securing structure illustrated in  FIG. 3  is about ½ of the maximum load acting on the seal fin in the comparative example illustrated in  FIG. 8 . It is verified that the effect of enhancing abradability of the honeycomb seal and the effect of preventing the breakage of the seal fin can sufficiently be expected. 
     The present inventors further conducted an experiment in the following manner. A honeycomb seal was manufactured which had the structure having the tilt angle illustrated in  FIG. 5  in addition to the securing structure illustrated in  FIG. 3 . In addition, the maximum load acting on the seal fin was measured. 
     The honeycomb seals whose tilt angle θ′ was sequentially varied from 15 to 45 degrees are manufactured in this experiment. Moreover, the maximum loads acting on the seal fins when the respective honeycomb seals were applied were measured. 
     The result shows that if the setting angle θ shown in  FIG. 3  is 90 degrees and the tilt angle θ′ is equal to zero, the maximum load acting on the seal fin is approximately ½ of the conventional structure illustrated in  FIG. 8  as described above. Meanwhile, If the tilt angle θ′ is 15 degrees, the maximum load acting on the seal fin can further be reduced by approximately 5%. If the tilt angle θ′ is 45 degrees, the maximum load acting on the seal fin can further be reduced by approximately 30%. 
     It is confirmed through the experimental results that the application of the illustrated honeycomb seal securing structure can produce the effect of enhancing abradability of the honeycomb seal and the effect of preventing the breakage of the seal fin.