Patent Publication Number: US-11028699-B2

Title: Gas turbine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Korean Patent Application No. 10-2018-0016173, filed on Feb. 9, 2018, the entire contents of which are incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a gas turbine. 
     2. Description of the Background Art 
     Generally, a turbine is a machine that converts kinetic energy of fluid such as water, gas, steam, etc. into mechanical work. Particularly, such a turbine generally includes a turbo-type machine in which a plurality of blades is installed on the periphery of a rotor so that steam or gas is directed onto the blades to create an impulse or reaction force, rotating the rotor at high speed. Examples of such turbines include a hydraulic turbine that utilizes the energy of elevated water, a steam turbine that uses the energy of the steam, an air turbine that uses the energy of high-pressure compressed air, and a gas turbine that uses energy of high-temperature and high-pressure gas. 
     Among them, the gas turbine includes a compressor section, a combustor section, a turbine section, and a rotor section. The compressor section includes a plurality of compressor vanes and a plurality of compressor blades which are alternately arranged. The combustor section supplies fuel to the air compressed in the compressor and ignites a fuel-air mixture with a burner to generate combustion gas of high temperature and high pressure. The turbine section includes a plurality of turbine vanes and a plurality of turbine blades which are alternately arranged. The rotor section is formed to pass through the center of the compressor section, the combustor section, and the turbine section, and both ends of the rotor section are rotatably supported by bearings such that one end is connected to a drive shaft of a generator. The rotor section includes a plurality of compressor disks coupled with the compressor blades, a plurality of turbine disks coupled with the turbine blades, and a torque tube transmitting torque from the turbine disks to the compressor disks. 
     In the gas turbine according to this configuration, the compressed air in the compressor is mixed with the fuel in the combustion chamber and combusted, thereby being converted into a high-temperature combustion gas. The generated combustion gas is injected toward the turbine section so that the combustion gas passes through the turbine blades to create a rotating force, thereby rotating the rotor section. 
     Since these gas turbines have no reciprocating mechanism such as piston of four-stroke engine, so that there is no mutual friction component like a piston-cylinder, the gas turbines have advantages that consumption of lubricating oil is extremely small, an amplitude feature which is characteristic of reciprocating machine is greatly reduced, and the gas turbines are able to operate at high speed. 
     Unlike the compressor section, the turbine section is in contact with a combustion gas at a high temperature and a high pressure, so that the turbine section requires a cooling means for preventing damage such as deterioration. To this end, the turbine section further includes a cooling path through which compressed air is additionally supplied from a portion of the compressor section to the turbine section, wherein the cooling path communicates with a turbine blade cooling path formed inside the turbine blade. 
     However, such a conventional gas turbine has a problem in that the tip end of the turbine blade is not cooled, thereby making it difficult to maintain the clearance between the tip end of the turbine blade and an inner circumferential surface of a housing of the gas turbine, and degrading the gas turbine efficiency. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a gas turbine capable of cooling the tip end of a turbine blade. 
     According to an aspect of the present invention, a gas turbine may include a housing in which combustion gas flows; a rotor section rotatably installed in the housing; and a turbine blade configured to rotate the rotor section by receiving a rotational force from the combustion gas and to be cooled by a cooling fluid flowing in a cooling path, the turbine blade including a tip side provided with a tip cooling hole through which a portion of the cooling fluid in the cooling path is discharged from the turbine blade. 
     The tip cooling hole may include a first tip cooling hole formed in a pressure surface of the turbine blade to communicate with the cooling path. 
     The tip side of the turbine blade may include a first inclined surface for facilitating the formation of the first tip cooling hole. 
     The tip side of the turbine blade may include a first inclined surface formed between an end surface of the turbine blade and the pressure surface of the turbine blade, such that the first inclined surface is inclined with respect to each of the end surface and the pressure surface. 
     The first tip cooling hole may extend through the turbine blade from the cooling path to the first inclined surface. 
     The first tip cooling hole may extend in a direction perpendicular to the first inclined surface. 
     The tip cooling hole may include a second tip cooling hole formed in a suction surface of the turbine blade to communicate with the cooling path. 
     The tip side of the turbine blade may include a second inclined surface for facilitating the formation of the second tip cooling hole. 
     The gas turbine may further include a squealer rib extending centrifugally from the tip side of the turbine blade, between an end surface of the turbine blade and a suction surface of the turbine blade. 
     The second tip cooling hole may extend through the turbine blade from the cooling path to a surface of the squealer rib. 
     The squealer rib may include an upper rib surface that is spaced apart from the end surface of the turbine blade, wherein the second tip cooling hole extends through the turbine blade from the cooling path to the upper rib surface. 
     The squealer rib may further include a second inclined surface formed between the end surface and the upper rib surface such that the second inclined surface is inclined with respect to each of the end surface and the upper rib surface. 
     The second inclined surface may be spaced apart from the second tip cooling hole. 
     The second tip cooling hole may extend in a direction parallel to the second inclined surface. 
     The squealer rib may include an upper rib surface that is spaced apart from the end surface of the turbine blade; an outer rib surface that is coplanar with the suction surface of the turbine blade; and a third inclined surface formed between the upper rib surface and the outer rib surface such that the third inclined surface is inclined with respect to each of the upper rib surface and the outer rib surface. 
     The second tip cooling hole may extend through the turbine blade from the cooling path to the third inclined surface. 
     The second tip cooling hole may extend in a direction perpendicular to the third inclined surface. 
     The squealer rib may further include an inner rib surface forming a back surface of the outer rib surface, wherein the inner rib surface is parallel to the outer rib surface and is spaced apart from the second tip cooling hole. 
     According to an embodiment of the present invention, there is provided a gas turbine including a housing in which combustion gas flows; a rotor section rotatably installed in the housing; and a turbine blade configured to rotate the rotor section by receiving a rotational force from the combustion gas and to be cooled by a cooling fluid flowing in a cooling path. The turbine blade may include a tip side provided with a tip cooling hole through which a portion of the cooling fluid in the cooling path is discharged from the turbine blade, and an inclined surface for facilitating formation of the tip cooling hole. 
     According to an embodiment of the present invention, there is provided a gas turbine including a housing in which combustion gas flows; a rotor section rotatably installed in the housing; and a turbine blade configured to rotate the rotor section by receiving a rotational force from the combustion gas and to be cooled by a cooling fluid flowing in a cooling path, the turbine blade including a tip side provided with a tip cooling hole through which a portion of the cooling fluid in the cooling path is discharged from the turbine blade. The tip cooling hole may include a first tip cooling hole formed in a pressure surface of the turbine blade; and a second tip cooling hole formed in a suction surface of the turbine blade. The tip side of the turbine blade may include a squealer rib protruding centrifugally from the tip side of the turbine blade, between an end surface of the turbine blade and the suction surface of the turbine blade; and a first inclined surface formed between the end surface and the pressure surface, such that the first inclined surface is inclined with respect to each of the end surface and the pressure surface. The squealer rib may include an upper rib surface that is spaced apart from the end surface of the turbine blade; an outer rib surface that is coplanar with the suction surface of the turbine blade; an inner rib surface forming a back surface of the outer rib surface; and one of a second inclined surface inclined with respect to each of the end surface and the upper rib surface, and a third inclined surface inclined with respect to each of the upper rib surface and the outer rib surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a gas turbine according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of the tip of a turbine blade in the gas turbine of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along line A-A in  FIG. 2 ; and 
         FIG. 4  is a cross-sectional view showing the tip of a turbine blade in a gas turbine according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIGS. 1-3  show a gas turbine according to an embodiment of the present invention.  FIG. 2  shows the tip of a turbine blade in the gas turbine of  FIG. 1 , and  FIG. 3  is a cross-sectional view taken along line A-A in  FIG. 2 . 
     Referring to  FIG. 1 , the gas turbine according to an embodiment of the present invention may include a housing  100 , a rotor section  600  rotatably installed in the housing  100 , a compressor section  200  that receives a rotating force from the rotor section  600  to compress the air introduced into the housing  100 , a combustor section  400  that mixes the fuel with the air compressed by the compressor section  200  and ignites a fuel-air mixture to generate a combustion gas, a turbine section  500  that rotates the rotor section  600  by receiving a rotational force from the combustion gas generated from the combustor section  400 , a generator that operates in association with the rotor section  600  for generating electricity, and a diffuser through which the combustion gas passed through the turbine section  500  is discharged. 
     The housing  100  includes a compressor housing  110  in which the compressor section  200  is accommodated, a combustor housing  120  in which the combustor section  400  is accommodated, and a turbine housing  130  in which the turbine section  500  is accommodated. Here, the compressor housing  110 , the combustor housing  120 , and the turbine housing  130  may be sequentially arranged from the upstream side to the downstream side in a flow direction of fluid. 
     The rotor section  600  may include a compressor disk  610  accommodated in the compressor housing  110 , a turbine disk  630  accommodated in the turbine housing  130 , a torque tube  620  accommodated in the combustor housing  120  to connect the compressor disk  610  and the turbine disk  630 , and a tie rod  640  and a fastening nut  650  coupling the compressor disk  610 , the torque tube  620 , and the turbine disk  630 . 
     The compressor disk  610  may consist of a plurality of compressor disks, which are arranged along an axial direction of the rotor section  600 . That is, the compressor disks  610  may be arranged in multiple stages. 
     Each of the compressor disks  610  may have a substantially disk shape, a periphery of which is provided with a compressor disk slot into which a compressor blade  210 , which will be described later, may be fitted. The compressor disk slot may be formed in the form of a fir-tree to prevent the compressor blade  210  from being detached from the compressor disk slot in the radial direction of rotation of the rotor section  600 . 
     Here, the compressor disk  610  and the compressor blade  210  are typically coupled in a tangential type or an axial type. In this embodiment, the compressor disk  610  and the compressor blade  210  are formed to be coupled in an axial type. Accordingly, the compressor disk slot may consist of a plurality of compressor disk slots, which may be radially arranged along the circumferential direction of the compressor disk  610 . 
     The turbine disk  630  may be formed similar to the compressor disk  610 . That is, the turbine disk  630  may consist of a plurality of turbine disks, which may be arranged along the axial direction of the rotor section  600 . That is, the turbine disks  630  may be arranged in multiple stages. 
     Each of the turbine disks  630  is formed in a substantially disk shape, a periphery of which is provided with a turbine disk slot into which a turbine blade  510 , which will be described later, may be fitted. 
     The turbine disk slot may be formed in the form of a fir-tree to prevent the turbine blade  510  to be described later from being detached from the turbine disk slot in the radial direction of rotation of the rotor section  600 . 
     Here, the turbine disk  630  and the turbine blade  510  are typically coupled as a tangential type or an axial type. In this embodiment, the turbine disk  630  and the turbine blade  510  are formed to be coupled in an axial type, although the present invention is equally applicable to a disk and blade coupled as a tangential type. The turbine disk slot may consist of a plurality of turbine disk slots, which may be radially arranged along the circumferential direction of the turbine disk  630 . 
     The torque tube  620  is a torque transmission member for transmitting the rotational force of the turbine disk  630  to the compressor disk  610 . The torque tube  620  may be provided at either end with a protrusion to respectively couple one end of the torque tube  620  to the farthest downstream compressor disk  610  and the other end to the farthest upstream turbine disk  630 , that is, to each of the two disks adjacent to the torque tube  620 . Grooves for engaging with the protrusions are respectively formed in the two adjacent disks  610  and  630  to prevent their relative rotation with respect to the torque tube  620 . 
     The torque tube  620  may be formed in the shape of a hollow cylinder so that the air supplied from the compressor section  200  may flow through the torque tube  620  to the turbine section  500 . Further, the torque tube  620  may have features rendering it resistant to deformation and distortion, which may occur in a gas turbine continuously operated for a long period of time, and rendering it easily assembled and disassembled for maintenance. 
     The tie rod  640  is formed to pass through the plurality of compressor disks  610 , the torque tube  620 , and the plurality of turbine disks  630 , and has one end fastened to the farthest upstream compressor disk  610  and the other end protruding from the farthest downstream turbine disk  630  to be engaged with the fastening nut  650 . Here, the fastening nut  650  tightens the farthest downstream turbine disk  630  towards the compressor section  200  to minimize the distance between the farthest upstream compressor disk  610  and the farther downstream turbine disk  630  by compressing the compressor disks  610 , the torque tube  620 , and the turbine disks  630  in the axial direction of the rotor section  600 . Accordingly, axial movement and relative rotation of the plurality of compressor disks  610 , the torque tube  620 , and the plurality of turbine disks  630  can be prevented. 
     Meanwhile, in the present embodiment, one tie-rod  640  passes through the center of the plurality of compressor disks  610 , the torque tube  620 , and the plurality of the turbine disks  630 , although the present invention is not limited to this configuration. That is, separate tie rods  640  may be respectively provided on the compressor section  200  and the turbine section  500 , a plurality of tie rods  640  may be disposed radially along the circumferential direction, or a combination of these configurations may be used. 
     Both ends of the rotor section  600  may be rotatably supported by bearings, with one end connected to a drive shaft of a generator. 
     The compressor section  200  may include a compressor blade  210  rotated along with the rotor section  600  and a compressor vane  220  fixed to the housing  100  to align the flow of air flowing into the compressor blade  210 . 
     The compressor blade  210  may consist of a plurality of compressor blades, which may be disposed in each of the multiple stages of the compressor disks  610  and may be arranged radially along the rotation direction of the rotor section  600  in each stage. 
     Each of the compressor blades  210  may include a plate-shaped platform portion, a root portion extending centripetally from the platform portion, and an airfoil portion extending centrifugally from the platform portion. The platform portion of one compressor blade  210  may be in contact with a neighboring platform portion, serving to maintain a gap between the airfoil portions. The root portion may be formed as a so-called axial type in which the root portion is inserted into the compressor disk slot along the axial direction of the rotor section  600  as described above. The root portion may be formed in a fir-tree shape corresponding to the compressor disk slot. 
     In this embodiment, the root portion and the compressor disk slot have a fir-tree configuration, but the present invention is not limited to this and may have a dovetail configuration or the like. Alternatively, the compressor blade  210  may be fastened to the compressor disk  610  by using fasteners such as keys or bolts. The compressor disk slot may be larger than the outline of the root portion so as to form a gap facilitating the engagement of the root portion with the compressor disk slot. 
     Although not separately shown, the root portion and the compressor disk slot are fixed by separate fins so that the root portion is prevented from being detached in the axial direction of the rotor section  600  from the compressor disk slot. 
     The airfoil portion of the compressor blade  210  may be configured to have an airfoil optimized according to the specification of a gas turbine, and may include a leading edge positioned on the upstream side of the compressor blade  210  to meet with the introduced air, and a trailing edge positioned on the downstream side of the compressor blade  210  toward the exiting air. 
     The compressor vane  220  may consist of a plurality of compressor vanes, which may be disposed according to each of the multiple stages of the compressor disks  610  and may be arranged radially along the rotation direction of the rotor section  600  in each stage. Here, the compressor vanes  220  and the compressor blades  210  may be alternately arranged along the flow direction of air. 
     Each of the compressor vanes  220  includes a platform portion, the respective platform portions collectively forming an annular shape along the rotating direction of the rotor section  600 , and an airfoil portion extending from the platform portion in the radial direction of rotation of the rotor section  600 . 
     The platform portion includes a root side platform that is proximal to the airfoil portion of the compressor vane and is fastened to the compressor housing  110  and a tip side platform that is distal to the airfoil portion opposite to the rotor section  600 . Here, although the platform portion of the compressor vane according to the present embodiment includes the root side and tip side platforms for more stably supporting the airfoil portion of the compressor vane by supporting both the proximal and distal sides of the airfoil portion, the present invention is not limited to this. That is, the compressor vane platform portion may be formed to include only the root side platform to support only the proximal side of the compressor vane airfoil portion. 
     Each of the compressor vanes  220  may further include a root portion of the compressor vane for coupling the root side platform and the compressor housing  110 . 
     The airfoil portion of the compressor vane  220  may be configured to have an airfoil optimized according to the specification of a gas turbine, and may include a leading edge positioned on the upstream side of the compressor vane  220  to meet with the introduced air, and a trailing edge positioned on the downstream side of the compressor vane  220  toward the exiting air. 
     The combustor section  400  mixes the air introduced from the compressor section  200  with fuel and combusts a fuel-air mixture to produce a high-temperature and high-pressure combustion gas. The combustor section  400  may be formed to increase the temperature of the combustion gas up to the heat resistance limit that the combustor section  400  and the turbine section  500  are able to withstand during an isobaric combustion process. 
     Specifically, the combustor section  400  may consist of a plurality of combustors, which may arranged along the rotational direction of the rotor section  600  in the combustor housing  120 . Each combustor of the combustor section  400  includes a liner into which air compressed in the compressor section  200  flows, a burner that injects fuel into the air flowing into the liner and combusts the fuel-air mixture, and a transition piece through which the combustion gas generated in the burner is guided to the turbine section  500 . 
     The liner may include a flame chamber constituting a combustion chamber, and a flow sleeve that surrounds the flame chamber to form an annular space. 
     The burner may include a fuel injection nozzle disposed at one end of the liner so as to inject fuel into the air flowing into the combustion chamber and an ignition plug provided on a wall of the liner to ignite the fuel-air mixture in the combustion chamber. 
     The transition piece may have an outer wall cooled by the air supplied from the compressor section  200  so as to prevent the transition piece from being damaged by the high temperature combustion gas. That is, the transition piece may be provided with a cooling hole through which air is injected into the transition piece for cooling. The air that has cooled the transition piece flows into the annular space of the liner and passes through cooling holes provided in the flow sleeve to collide with the outer wall of the liner. 
     Here, although not shown in the drawings, a deswirler serving as a guide may be disposed between the compressor section  200  and the combustor section  400  to adjust a flow angle of the air flowing into the combustor section  400  to a designed flow angle. 
     The turbine section  500  may be formed similarly to the compressor section  200 . 
     That is, the turbine section  500  includes a turbine blade  510  rotated together with the rotor section  600 , and a turbine vane  520  fixed to the housing  100  to align a flow of air flowing into the turbine blade  510 . 
     The turbine blade  520  may consist of a plurality of the turbine blades, which may be disposed in each of the multiple stages the turbine disks  630  and may be arranged radially along the rotation direction of the rotor section  600  in each stage. 
     Each of the turbine blades  510  may include a plate-shaped platform portion, a root portion extending centripetally from the platform portion, and an airfoil portion extending centrifugally from the platform portion. The platform portion of one turbine blade  510  may be in contact with a neighboring platform portion, serving to maintain a gap between the airfoil portions. The root portion may be formed in a so-called axial type in which the root portion is inserted into the turbine disk slot along the axial direction of the rotor section  600  as described above. The root portion of the turbine blade may be formed in a fir-tree shape corresponding to the turbine disk slot. 
     In this embodiment, the root portion and the turbine disk slot have a fir-tree configuration, but the present invention is not limited to this and may have a dovetail configuration or the like. Alternatively, the turbine blade  510  may be fastened to the turbine disk  630  by using fasteners such as keys or bolts. The turbine disk slot may be larger than the outline of the root portion of the turbine blade so as to form a gap facilitating the engagement of the root portion with the turbine disk slot. 
     Although not separately shown, the root portion and the turbine disk slot are fixed by separate fins so that the root portion is prevented from being detached in the axial direction of the rotor section  600  from the turbine disk slot. 
     The airfoil portion of the turbine blade  510  may be configured to have an airfoil optimized according to the specification of a gas turbine, and may include a leading edge positioned on the upstream side of the turbine blade  510  to meet with the introduced combustion gas, and a trailing edge positioned on the downstream side of the turbine blade  510  toward the exiting combustion gas. 
     The turbine vane  520  may consist of a plurality of turbine vanes, which may be disposed according to each of the multiple stages of the turbine disks  630  and may be arranged radially along the rotation direction of the rotor section  600  in each stage. Here, the turbine vanes  520  and the turbine blades  510  may be alternately arranged along the flow direction of air. 
     Each of the turbine vanes  520  includes a platform portion, the respective platform portions collectively forming an annular shape along the rotating direction of the rotor section  600 , and an airfoil portion extending from the platform portion in the radial direction of rotation of the rotor section  600 . 
     The platform portion of the turbine vane includes a root side platform that is proximal to the airfoil portion of the turbine vane and is fastened to the turbine housing  130  and a tip side platform that is distal to the airfoil portion of the turbine vane opposite to the rotor section  600 . Here, although the platform portion of the turbine vane according to the present embodiment includes the root side and tip side platforms for more stably supporting the airfoil portion of the turbine vane by supporting both the proximal and distal sides of the airfoil portion of the turbine vane, the present invention is not limited to this. That is, the turbine vane platform portion may be formed to include only the root side platform to support only the proximal side of the turbine vane airfoil portion. 
     Each of the turbine vanes  520  may further include a root portion of the turbine vane for coupling the root side platform portion and the turbine housing  130 . 
     The airfoil portion of the turbine vane  520  may be configured to have an airfoil optimized according to the specification of a gas turbine, and may include a leading edge positioned on the upstream side of the turbine vane  520  to meet with the introduced combustion gas, and a trailing edge positioned on the downstream side of the turbine vane  520  toward the exiting combustion gas. 
     Here, unlike the compressor section  200 , the turbine section  500  is in contact with a combustion gas at a high temperature and a high pressure, so that the turbine section  500  requires a cooling means for preventing deterioration and other damage. 
     To this end, the gas turbine according to the present embodiment further includes a cooling path through which compressed air is additionally supplied from a portion of the compressor section  200  to the turbine section  500 . The air in the cooling path will be hereinafter referred to as a cooling fluid. The cooling path may have an external path (which extends outside the housing  100 ), an internal path (which extends through the interior of the rotor section  600 ), or both an external path and an internal path. 
     The cooling path communicates with a cooling path  512  (see  FIG. 3 ) formed in the turbine blade  510 , so that the turbine blade  510  can be cooled by the cooling fluid. 
     Like the turbine blade  510 , the turbine vane  520  may be formed to be cooled by receiving a cooling fluid from the cooling path. 
     The tip of a turbine blade  510  occurs on the tip side of each turbine blade  510 . The turbine section  500  requires a gap between the tip side of the rotating turbine blades  510  and an inner circumferential surface of the turbine housing  130  opposing the turbine blade tips, so that the turbine disks  630  and the turbine blades  510  can rotate smoothly. 
     As the gap between the tip side of the turbine blade  510  and the inner circumferential surface of the turbine housing  130  increases, it is advantageous in terms of preventing interference between the turbine blade  510  and the turbine housing  130 , but disadvantageous in terms of the leakage of combustion gas. As the gap decreases, it is advantageous in terms of in terms of the leakage of combustion gas, but disadvantageous in terms of preventing interference between the turbine blade  510  and the turbine housing  130 . Meanwhile, the flow of the combustion gas injected from the combustor section  400  is divided into a main flow passing through the turbine blade  510  and a leakage flow passing through the gap between the turbine blade  510  and the turbine housing  130 . Therefore, as the gap increases, the leakage flow is increased to reduce the gas turbine efficiency, but interference between the turbine blade  510  and the turbine housing  130  due to thermal deformation or the like and resultant damage can be prevented. On the contrary, as the gap between the tip side of the turbine blade  510  and the inner circumferential surface of the turbine housing  130  decreases, the leakage flow is reduced to improve the gas turbine efficiency, but there is an increased risk of interference between the turbine blade  510  and the turbine housing  130  and damage may occur. 
     Accordingly, the gas turbine according to the present embodiment may further include a sealing means that secures a proper gap to minimize the deterioration of the gas turbine efficiency while preventing damage caused by interference between the turbine blades  510  and the turbine housing  130 . 
     The sealing means may include a squealer rib  516  protruding centrifugally from the tip side of the turbine blade  510 . 
     Consistent with the present invention, the squealer rib  516  may be formed on a pressure surface  510   a  of the turbine blade  510  as well as on a suction surface  510   b  of the turbine blade  510 . To minimize an abnormal flow occurring due to the squealer rib  516 , however, the squealer rib  516  may be formed only on one side of the turbine blade  510 , preferably on the suction surface  510   b , as shown in the embodiment per  FIGS. 2 and 3 . That is, the squealer rib  516  according to this embodiment may be disposed to protrude centrifugally from the turbine blade  510 , between an end surface  510   c  of the turbine blade  510  and the suction surface  510   b  of the turbine blade  510 . 
     Similarly, the turbine section  500  may further include a sealing means for blocking leakage between the turbine vane  520  and the rotor section  600 . 
     In the gas turbine according to this configuration, the air introduced into the housing  100  is compressed by the compressor section  200 , and the air compressed by the compressor section  200  is mixed with the fuel by the combustor section  400  to generate a fuel-air mixture. The fuel-air mixture is combusted by the combustor section to produce a combustion gas, which is then introduced into the turbine section  500  through the turbine blades  510  to rotate the rotor section  600 , and is discharged to the atmosphere through the diffuser. The rotor  600 , which is rotated by the combustion gas, can drive the compressor section  200  and the generator. That is, a portion of the mechanical energy obtained from the turbine section  500  may be supplied to the compressor section  200  as energy required to compress the air, and the remainder may be used to generate electric power using the generator. 
     The gas turbine according to the present embodiment may be configured such that a gap between the tip side of the turbine blade  510  (more precisely, the airfoil portion of the turbine blade) and the inner circumferential surface of the turbine housing  130  is maintained at a predetermined level (distance) so that the tip side of the turbine blade  510  can be sufficiently cooled. 
     Specifically, although the turbine blade  510  is cooled by the cooling path  512  of the turbine blade, since the tip side of the turbine blade  510 , which directly influences the gap between the tip side of the turbine blade  510  and the inner circumferential surface of the turbine housing  130 , is disposed remotely with respect the cooling path  512  of the turbine blade  510 , the tip side of the turbine blade cannot be sufficiently cooled with the cooling path  512  of the turbine blade. As a result, there is a high risk of a collision between the tip side of the turbine blade  510  and the inner circumferential surface of the turbine housing  130  due to thermal expansion. In addition, when the gap between the tip side of the turbine blade  510  and the inner circumferential surface of the turbine housing  130  is increased for the purpose of safety, the gas turbine efficiency may be lowered. 
     Considering this, in the present embodiment, as illustrated in  FIGS. 2 and 3 , the tip side of the turbine blade  510  may be provided with tip cooling holes  514   a  and  514   b  through which a portion of the cooling fluid flowing through the cooling path  512  of the turbine blade is discharged to the outside of the turbine blade  510  so as to sufficiently cool the tip side of the turbine blade  510 . This configuration can prevent a collision between the tip side of the turbine blade  510  and the inner circumferential surface of the turbine housing  130  while preventing the gap between the tip side of the turbine blade  510  and the inner circumferential surface of the turbine housing  130  from being increased. 
     Referring to  FIGS. 2 and 3 , the tip cooling holes  514   a  and  514   b  of the turbine blade may include a first tip cooling hole  514   a  formed in the pressure surface  510   a  of the turbine blade  510  so that the tip side of the turbine blade  510  is effectively cooled, and a second tip cooling hole  514   b  formed in the suction surface  510   b  of the turbine blade  510 . 
     The first tip cooling hole  514   a  may extend through the turbine blade  510  from the cooling path  512  inside the turbine blade  510  to the junction of the end surface  510   c  of the turbine blade  510  and the pressure surface  510   a  of the turbine blade  510 . 
     The first tip cooling hole  514   a  according to this configuration can cool the tip side of the turbine blade  510  with the cooling fluid passing through the first tip cooling hole  514   a.    
     The first tip cooling hole  514   a  may form an air curtain with a cooling fluid discharged from the first tip cooling hole  514   a , so that leakage gas flowing from the pressure surface  510   a  of the turbine blade  510  to the suction surface  510   b  of the turbine blade  510  through the tip gap between the tip side of the turbine blade  510  and the inner circumferential surface of the housing  100  can be reduced. Thus, the high-temperature leakage gas can be prevented from contacting the tip side of the turbine blade  510 . Then, the leakage gas can be cooled. Accordingly, the tip side of the turbine blade  510  (precisely, the end surface  510   c  of the turbine blade  510 ) can be prevented from being excessively heated by the leakage gas. 
     Here, the first tip cooling hole  514   a  may be formed by drilling toward the suction surface  510   b  of the turbine blade  510  at a slant with respect to the radial direction of the rotor section  600  so as to communicate with the cooling path  512  of the turbine blade formed at the center of the turbine blade  510 . 
     If the end surface  510   c  and the pressure surface  510   a  were to form a right-angled corner, a drilling process performed from such a corner would be performed unstably and defects would occur. Therefore, in consideration of this, in the present embodiment, in order to facilitate the formation of the first tip cooling hole  514   a , a first inclined surface S 1  may be formed between the end surface  510   c  and the pressure surface  510   a . The first inclined surface S 1  is inclined with respect to each of the end surface  510   c  and the pressure surface  510   a . Thus, in the present embodiment, the first tip cooling hole  514   a  extends through the turbine blade  510  from the cooling path  512  to the first inclined surface S 1 . Then, since the drilling process is performed from the first inclined surface S 1 , the drilling process can be stably performed. Therefore, failures can be reduced and the first tip cooling hole  514   a  can be easily formed. 
     The first inclined surface S 1  may be formed to be perpendicular to the extending direction of the first tip cooling hole  514   a  of the turbine blade in order to allow the drilling process to be more stably performed. 
     The second tip cooling hole  514   b  of the turbine blade may extend through the turbine blade  510  from the cooling path  512  of the turbine blade to a surface of the squealer rib  516 . 
     Specifically, the squealer rib  516  may include an inner rib surface  516   a , an outer rib surface  516   b , and an upper rib surface  516   c . The inner rib surface  516   a  forms a back surface of the outer rib surface  516   b . The outer rib surface  516   b  is coplanar with the suction surface  510   b  of the turbine blade  510 . The upper rib surface  516   c  is spaced apart from the end surface  510   c  by the same centrifugal distance that the squealer rib  516  protrudes from the end surface  510   c  of the turbine blade  510 . The second tip cooling hole  514   b  extends through the turbine blade  510  from the cooling path  512  to the upper rib surface  516   c.    
     The second tip cooling hole  514   b  according to this configuration can cool the tip side of the turbine blade  510  more effectively by using the cooling fluid passing through the second tip cooling hole  514   b . That is, although the tip side of the turbine blade  510  is cooled by the cooling fluid passing through the first tip cooling hole  514   a  as described above, the tip side of the turbine blade  510  can be additionally cooled by the cooling fluid passes through the second tip cooling hole  514   b  of the turbine blade. 
     The second tip cooling hole  514   b  may form an air curtain with a cooling fluid discharged from the second tip cooling hole  514   b , so that leakage gas flowing from the pressure surface  510   a  of the turbine blade  510  to the suction surface  510   b  of the turbine blade  510  through the tip gap between the tip side of the turbine blade  510  and the inner circumferential surface of the housing  100  can be further reduced. That is, although the leakage gas is reduced by the cooling fluid discharged from the first tip cooling hole  514   a  as described above, the leakage gas can be further reduced by the cooling fluid passing through the second tip cooling hole  514   b . Thus, the high-temperature leakage gas can be prevented from contacting the upper rib surface  516   c  and the outer rib surface  516   b . Then, the leakage gas can be further cooled. Accordingly, the upper rib surface  516   c  and the outer rib surface  516   b  can be prevented from being heated by the leakage gas. 
     Here, the second tip cooling hole  514   b  may be formed by drilling toward the pressure surface  510   a  of the turbine blade  510  at a slant with respect to the radial direction of the rotor section  600  so as to communicate with the cooling path  512  of the turbine blade formed at the center of the turbine blade  510 . 
     If the inner rib surface  516   a  and the outer rib surface  516   b  were to be parallel to each other (for example, if the inner rib surface  516   a  were to extend in a directly radial direction), interference between the inner rib surface  516   a  and the second tip cooling hole  514   b  may occur. That is, part of the second tip cooling hole  514   b  may be exposed (disconnected) by the outer rib surface  516   b . On the other hand, if the second tip cooling hole  514   b  were to be curved or bent to avoid the above problem, processing the second tip cooling hole would be difficult and manufacturing cost would increase. Furthermore, if the thickness of the squealer rib  516  (the distance between the inner rib surface  516   a  and the outer rib surface  516   b ) were to be increased, a flow of fluid may be disturbed by the squealer rib  516 . 
     Therefore, in consideration of the above, in the present embodiment, in order to facilitate the formation of the second tip cooling hole  514   b , a second inclined surface S 2  may be formed between the end surface  510   c  of the turbine blade and the upper rib surface  516   c . The second inclined surface S 2  is inclined with respect to each of the end surface  510   c  and the upper rib surface  516   c . That is, inner rib surface  516   a  may be inclined with respect to each of the end surface  510   c  and the upper rib surface  516   c . The second inclined surface S 2  may be spaced apart from the second tip cooling hole  514   b  so as to prevent a portion of the second tip cooling hole  514   b  from being exposed (disconnected). Accordingly, it is not required to curve or bend the second tip cooling hole  514   b , so that the second tip cooling hole  514   b  can be easily formed and increased manufacturing cost can be avoided. Further, it is not required to increase the thickness of the squealer rib  516 , so that a flow of fluid is not disturbed by the squealer rib  516 . 
     The second inclined surface S 2  may preferably be parallel to the second tip cooling hole  514   b  so as to ensure that the second inclined surface S 2  is more reliably spaced apart from the second tip cooling hole  514   b.    
     According to this configuration, in the gas turbine according to the present embodiment, the first tip cooling hole  514   a  and the second tip cooling hole  514   b  are formed, so that the tip side of the turbine blade  510  can be sufficiently cooled. As a result, the gap between the tip side of the turbine blade  510  and the inner circumferential surface of the housing  100  can be easily maintained, and the gas turbine efficiency can be prevented from being degraded. 
     As the first and second inclined surfaces S 1  and S 2  are formed, the first and second tip cooling holes  514   a  and  514   b  can be easily formed. 
     In the meantime, in the present embodiment, although the second tip cooling hole  514   b  is inclined from the upper rib surface  516   c  to the cooling path  512  of the turbine blade so that the inner rib surface  516   a  is inclined (to form the second inclined surface S 2 ), the present invention is not limited to this configuration. 
     That is, as illustrated in  FIG. 4 , the inner rib surface  516   a  may be parallel to the outer rib surface  516   b  (to omit the second inclined surface S 2 ), a third inclined surfaced S 3  may be provided between the upper rib surface  516   c  and the outer rib surface  516   b , and the second tip cooling hole  514   b  may extend through the turbine blade  510  from the cooling path  512  to the third inclined surface S 3 . Here, the third inclined surface S 3  is inclined with respect to each of the upper rib surface  516   c  and the outer rib surface  516   b.    
     In this case, like the first tip cooling hole  514   a  and the first inclined surface S 1 , the drilling process is performed from the third inclined surface S 3 , so that the drilling process can be stably performed. Accordingly, failures can be reduced, and the second tip cooling hole  514   b  can be easily formed. Here, the third inclined surface S 3  may preferably be formed to be perpendicular to the extending direction of the second tip cooling hole  514   b  so that the drilling process can be stably performed. 
     In this case, the inner rib surface  516   a  is required to be parallel with the outer rib surface  516   b  such that the width of the upper rib surface  516   c  is not excessively narrowed while the thickness of the squealer rib  516  is not excessively increased, and to be spaced apart from the second tip cooling hole  514   b  such that the second tip cooling hole  514   b  is not exposed (disconnected). 
     While the exemplary embodiments of the present invention have been described in the detailed description, the present invention is not limited thereto, but should be construed as including all of modifications, equivalents, and substitutions falling within the spirit and scope of the invention defined by the appended claims.