Patent Publication Number: US-11655730-B2

Title: Strut structure of gas turbine, an exhaust diffuser and gas turbine including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2019-0034660, filed on Mar. 26, 2019, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     Field 
     Apparatuses and methods consistent with exemplary embodiments relate to a strut structure of a gas turbine, an exhaust diffuser and the gas turbine including the same. 
     Description of the Related Art 
     A turbine is a mechanical apparatus that obtains a rotational force by an impulse force or a reactive force by using a flow of a compressive fluid such as steam or gas, and includes a steam turbine using steam, a gas turbine using high temperature combusted gas, and the like. 
     The gas turbine includes a compressor, a combustor, and a turbine. The compressor includes an air inlet configured to receive air, and a plurality of compressor vanes and a plurality of compressor blades which are alternately arranged in a compressor casing. 
     The combustor supplies fuel to the air compressed by the compressor and ignites the fuel mixture by a burner to generate a high temperature and high pressure combusted gas. 
     The turbine includes a plurality of turbine vanes and a plurality of turbine blades which are alternately arranged in a turbine casing. Further, a rotor is disposed to penetrate central portions of the compressor, the combustor, the turbine, and an exhaust chamber. 
     The rotor is rotatably supported at both ends thereof by bearings. A plurality of disks are fixed to the rotor to connect each blade. A drive shaft of a generator is coupled to the end portion of the exhaust chamber side. 
     A gas turbine does not have a reciprocating mechanism such as a piston which is usually provided in four stroke engines. That is, the gas turbine has no mutual frictional portion, such as a piston-cylinder, thereby consuming extremely low lubricating oil, significantly reducing an amplitude of vibration, unlike the reciprocating machine. Therefore, high speed driving of the gas turbine is possible. 
     Briefly describing an operation of the gas turbine, the air compressed by the compressor is mixed with fuel, the fuel mixture is combusted to generate a high temperature combusted gas, and the generated combustion gas is discharged to the turbine side. The discharged combustion gas generates the rotational force while passing through the turbine vanes and the turbine blades, and therefore, the rotor rotates. 
     SUMMARY 
     Aspects of one or more exemplary embodiments provide a strut structure of a gas turbine, an exhaust diffuser and the gas turbine including the same, which may delay a generation of flow separation of the strut by the exhaust gas generated while the exhaust gas collides with the surface of the strut and reduce the pressure loss inside an exhaust diffuser. 
     Additional aspects will be set forth in part in the description which follows and, in part, will become apparent from the description, or may be learned by practice of the exemplary embodiments. 
     According to an aspect of an exemplary embodiment, there is provided a strut structure of a gas turbine, the strut structure being formed in an annular exhaust passage formed between an inner casing and an outer casing of the gas turbine, the strut structure including: a strut housing configured to include a lower end which is connected to the inner casing and an upper end which is connected to the outer casing; and a strut groove configured to be formed on at least one end of the upper end and the lower end of the strut housing to connect a front end and a rear end thereof. 
     A lower inner fillet may be formed on an upper surface of the inner casing, an upper inner fillet may be formed on a lower surface of the outer casing, and the upper inner fillet and the lower inner fillet may be partially inserted into the strut housing, and a portion not inserted into the strut housing may form the strut groove. 
     The lower end of the strut housing may be connected to the inner casing through the lower inner fillet, and the upper end of the strut housing may be connected to the outer casing through the upper inner fillet. 
     The strut groove may include a groove pattern formed on at least any one of the lower inner fillet or the upper inner fillet. 
     The strut groove may include a protrusion pattern formed on at least any one of the lower inner fillet or the upper inner fillet. 
     The strut groove may be formed by bending or cutting at least any one of the upper end and the lower end of the strut housing inward. 
     According to an aspect of another exemplary embodiment, there is provided an exhaust diffuser including: an inner casing configured to include a bearing housing surrounding a tie rod provided in a turbine; an outer casing configured to be spaced apart from the inner casing and include an annular exhaust passage through which an exhaust gas flows; and a strut structure formed in the annular exhaust passage formed between the inner casing and the outer casing. The strut structure may include a strut housing configured to include a lower end which is connected to the inner casing and an upper end formed to be connected to the outer casing; and a strut groove configured to be formed on at least one end of the upper end and the lower end of the strut housing to connect a front end and a rear end thereof. 
     A lower inner fillet may be formed on an upper surface of the inner casing, an upper inner fillet may be formed on a lower surface of the outer casing, and the upper inner fillet and the lower inner fillet may be partially inserted into the strut housing, and a portion not inserted into the strut housing forms the strut groove. 
     The lower end of the strut housing may be connected to the inner casing through the lower inner fillet, and the upper end of the strut housing may be connected to the outer casing through the upper inner fillet. 
     The strut groove may include a groove pattern formed on at least any one of the lower inner fillet or the upper inner fillet. In the exhaust diffuser of the gas turbine according to an exemplary embodiment, the strut groove may be formed by bending or cutting at least any one of the upper end and the lower end of the strut housing inward. 
     The strut groove may include a protrusion pattern formed on at least any one of the lower inner fillet or the upper inner fillet. 
     The strut groove may be formed by bending or cutting at least any one of the upper end and the lower end of the strut housing inward. 
     The exhaust diffuser of the gas turbine may further include an exhaust gas guide member configured to guide the exhaust gas to flow in a direction parallel to a long axis of the strut housing. 
     According to an aspect of another exemplary embodiment, there is provided a gas turbine including: a compressor configured to compress air externally introduced; a combustor configured to mix the compressed air with fuel and to combust the air and fuel mixture; a turbine configured to generate power with the gas supplied from the combustor, and include a turbine vane configured to guide the combustion gas on a combustion gas path through which the combustion gas passes and a turbine blade rotated by the combustion gas on the combustion gas path; and an exhaust diffuser configured to rotate the turbine blade and to exhaust the combustion gas. The exhaust diffuser may include an inner casing configured to include a bearing housing surrounding a tie rod provided in the turbine; an outer casing configured to be spaced apart from the inner casing and include an annular exhaust passage through which an exhaust gas flows; and a strut structure formed in the annular exhaust passage formed between the inner casing and the outer casing. The strut structure may include a strut housing configured to include a lower end which is connected to the inner casing and an upper end which is connected to the outer casing; and a strut groove configured to be formed on at least one end of the upper end and the lower end of the strut housing to connect a front end and a rear end thereof. 
     A lower inner fillet may be formed on an upper surface of the inner casing, an upper inner fillet may be formed on a lower surface of the outer casing, and the upper inner fillet and the lower inner fillet may be partially inserted into the strut housing, and a portion not inserted into the strut housing may form the strut groove. 
     The lower end of the strut housing may be connected to the inner casing through the lower inner fillet, and the upper end of the strut housing may be connected to the outer casing through the upper inner fillet. 
     The strut groove may include a groove pattern formed on at least any one of the lower inner fillet or the upper inner fillet. In the gas turbine according to an exemplary embodiment, the strut groove may be formed by bending or cutting at least any one of the upper end and the lower end of the strut housing inward. 
     The strut groove may include a protrusion pattern formed on at least any one of the lower inner fillet or the upper inner fillet. 
     The strut groove may be formed by bending or cutting at least any one of the upper end and the lower end of the strut housing inward. 
     The gas turbine may further include an exhaust gas guide member configured to guide the exhaust gas to flow in a direction parallel to a long axis of the strut housing. 
     According to one or more exemplary embodiments, it is possible to delay the generation of flow separation of the strut by the exhaust gas generated while the exhaust gas collides with the surface of the strut and to reduce the pressure loss inside the exhaust diffuser. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects will become more apparent from the following description of the exemplary embodiments with reference to the accompanying drawings, in which: 
         FIG.  1    is a diagram illustrating an interior of a gas turbine according to an exemplary embodiment; 
         FIG.  2    is a diagram conceptually illustrating a cross section of the gas turbine according to an exemplary embodiment; 
         FIG.  3    is a diagram illustrating an exhaust diffuser including a strut structure of the gas turbine according to an exemplary embodiment; 
         FIG.  4    is a side diagram illustrating the strut structure of the gas turbine according to an exemplary embodiment; 
         FIG.  5    is a front diagram illustrating the strut structure of the gas turbine according to an exemplary embodiment; 
         FIGS.  6 A,  6 B,  6 C, and  6 D  are diagrams illustrating the strut structures of the gas turbine according to an exemplary embodiment and a related art strut structure; 
         FIG.  7    is a side diagram illustrating a strut structure of a gas turbine according to another exemplary embodiment; 
         FIGS.  8  and  9    are front diagrams illustrating the strut structure of the gas turbine according to another exemplary embodiment. 
         FIG.  10    is a diagram illustrating an exhaust diffuser according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various modifications and various embodiments will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the disclosure. It should be understood, however, that the various embodiments are not for limiting the scope of the disclosure to the specific embodiment, but they should be interpreted to include all modifications, equivalents, and alternatives of the embodiments included within the spirit and scope disclosed herein. 
     The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of the disclosure. The singular expressions “a”, “an”, and “the” are intended to include the plural expressions as well, unless the context clearly indicates otherwise. In the disclosure, the terms such as “comprise”, “include”, “have/has” should be construed as designating that there are such features, integers, steps, operations, elements, components, and/or combinations thereof, not to exclude the presence or possibility of adding of one or more of other features, integers, steps, operations, elements, components, and/or combinations thereof. Further, throughout the specification, “on” means to be located above or below the target portion, and does not necessarily mean to be located with respect to the gravity direction. 
     Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. It should be noted that the same components in the accompanying drawings are denoted by the same reference numerals as possible. Further, detailed descriptions of well-known functions and configurations that may obscure the gist of the disclosure will be omitted. For the same reason, in the accompanying drawings, some components have been exaggerated, omitted or schematically illustrated. 
       FIG.  1    is a diagram illustrating an interior of a gas turbine according to an exemplary embodiment, and  FIG.  2    is a diagram conceptually illustrating a cross section of the gas turbine according to an exemplary embodiment. 
     Referring to  FIGS.  1  and  2   , a gas turbine  1  according to an exemplary embodiment includes a compressor  10 , a combustor  20 , and a turbine  30 . The compressor  10  serves to compress the received air at high pressure, and delivers the compressed air to the combustor  20 . The compressor  10  including a plurality of compressor blades radially installed rotates the compressor blade by receiving a portion of power generated by the rotation of the turbine  30 , and the air is compressed and moved to the combustor  20  by the rotation of the compressor blade. A size and installation angle of the blade may be changed according to an installation position. 
     The air compressed by the compressor  10  is moved to the combustor  20  to be mixed with fuel through a plurality of combustion chambers and fuel nozzle modules arranged in an annular shape and combusted. The high temperature combustion gas is discharged to the turbine  30 , and the turbine is rotated by the combustion gas. 
     The turbine  30  is arranged in multiple stages through a center tie rod  400  that axially couples a turbine rotor disk  300 . The turbine rotor disk  300  includes a plurality of turbine blades  100  arranged radially. The turbine blade  100  may be coupled to the turbine rotor disk  300  in the manner such as a dovetail. Further, turbine vanes  200  fixed to a housing are provided between the turbine blades  100  to guide the flow direction of the combustion gas passing through the turbine blades  100 . 
     As illustrated in  FIG.  2   , in the turbine  30 , the turbine vanes  200  and the turbine blades  100  may be arranged alternately along an axial direction of the gas turbine  1 . The high temperature combustion gas passes through the turbine vane  200  and the turbine blade  100  along the axial direction and rotates the turbine blade  100 . 
     For example, after rotating the turbine blade  100 , the combustion gas may be exhausted to an outside through an exhaust diffuser. Alternatively, in a combined power generation system, the combustion gas exhausted through the exhaust diffuser flows into a steam turbine through a heat exchanger to be used for another power generation. Here, the combustion gas exhausted through the exhaust diffuser is also referred to as exhaust gas. 
     When the exhaust gas flows from the gas turbine into the steam turbine, the hydraulic pressure and flow rate of the exhaust gas are important factors. That is, when flowing into the steam turbine, the exhaust gas should be maintained above a certain pressure, and the pressure recovery is essential for the smooth operation of the steam turbine. 
     In the related art strut constituting the exhaust diffuser of the gas turbine, if the exhaust gas collides with the strut, a flow separation phenomenon has occurred in which the surface of the strut is separated by the exhaust gas, and the inner pressure loss of the exhaust diffuser has been caused by this flow separation phenomenon. 
       FIG.  3    is a diagram illustrating an exhaust diffuser including a strut structure of the gas turbine according to an exemplary embodiment,  FIG.  4    is a side diagram illustrating the strut structure of the gas turbine according to an exemplary embodiment, and  FIG.  5    is a front diagram illustrating the strut structure of the gas turbine according to an exemplary embodiment. 
     Referring to  FIG.  3   , the exhaust diffuser  1000  including the strut structure of the gas turbine includes an inner casing  1100 , an outer casing  1200 , a strut housing  1300 , and a strut groove  1400 . 
     A bearing housing  1110  surrounding the tie rod  400  provided in the turbine is formed inside the inner casing  1100 . The bearing housing  1110  surrounds the tie rod  400  in a cylindrical shape and extends a predetermined length along the axial direction. The bearing housing  1110  is provided with a bearing rotating in a rolling contact state with the outside of the tie rod  400  therein, and the bearing reduces the friction of the rotating tie rod  400  and support the load, thereby seeking stable rotation and operation of the tie rod  400 . 
     The outer casing  1200  is spaced at a predetermined distance apart from the inner casing  1100 . The annular space between the inner casing  1100  and the outer casing  1200  forms an exhaust passage (F) through which the exhaust gas rotating the turbine blade  100  flows. 
     A plurality of power struts (PS) are arranged radially in the outside circumferential direction of the bearing housing  1110 . The inner casing  1100  and the outer casing  1200  are supported by the power strut (PS) while maintaining the interval therebetween. 
     The power strut (PS) extends in a vertical direction from the outside of the bearing housing  1110  when viewed from a rear with respect to the axial direction of the tie rod  400 . The power strut (PS) may have an ellipse shape having a long axis extending in the axial direction of the bearing housing  1110  and include an empty space therein when viewed from a top by cutting a cross section laterally. 
     A lower inner fillet  1410  is formed on an upper surface of the inner casing  1100 , and an upper inner fillet  1420  is formed on a lower surface of the outer casing  1200 . The lower inner fillet  1410  and the upper inner fillet  1420  are inserted into the strut housing  1300 . At this time, a portion of the lower inner fillet  1410  and a portion of the upper inner fillet  1420  are not inserted into the strut housing  1300 , and are formed to be exposed to the exhaust passage (F). 
     The strut housing  1300  is formed to be spaced at a predetermined distance apart from the outer circumferential surface of the power strut (PS) to surround the outer circumferential surface of the power strut (PS). A shape of the strut housing  1300  may be a shape corresponding to the shape of the outer circumferential surface of the power strut (PS). A lower end of the strut housing  1300  may be connected to the inner casing  1100  through the lower inner fillet  1410 , and an upper end of the strut housing  1300  may be connected to the outer casing  1200  through the upper inner fillet  1420 . The strut housing  1300  prevents the power strut (PS) from being exposed to the high temperature exhaust gas to protect the power strut (PS). 
     The sizes of the outer circumferential surfaces of the lower inner fillet  1410  and the upper inner fillet  1420  may be smaller than the size of the outer circumferential surface of the strut housing  1300 . Therefore, the portions of the upper and lower inner fillets  1410 ,  1420  which are not inserted into the strut housing  1300  and the upper and lower end portions of the strut housing  1300  form a step, and the step forms the strut groove  1400 . As a result, the strut groove  1400  may connect a front end  1301  and a rear end  1302  of the strut housing  1300 . The strut structure includes the strut housing  1300  and the strut groove  1400 . 
     It is understood that the strut groove  1400  is not limited to being formed by coupling of the lower and upper inner fillets  1410 ,  1420  and the strut housing  1300 . The strut groove  1400  may be formed by bending the upper end and/or the lower end of the strut housing  1300  inward, or cutting inward them. 
     After rotating the turbine blade  100 , the exhaust gas that is exhausted may be exhausted to another power generation system through the exhaust diffuser  1000 . 
     If the exhaust gas flows vertically to the front end  1301  of the strut housing  1300 , that is, if it flows in a direction parallel to the long axis of the elliptical strut housing  1300 , the exhaust gas colliding with the front end  1301  is branched to flow along the surface of the strut housing  1300 , thereby delaying the occurrence of flow separation. 
     However, the exhaust gas does not flow vertically to the front end  1301  of the strut housing  1300 , and collides with the front end  1301  while having a predetermined angle, for example, an angle of about 20 to 30 degrees with respect to the long axis of the strut housing  1300 . In this case, the exhaust gas does not flow along the surface of the strut housing  1300  and leaves the surface to lower the speed and develops a boundary layer. The development of this boundary layer results in the flow separation and the pressure loss. 
     The strut structure includes the strut groove  1400  connecting the front end and the rear end of the strut housing  1300 , and a portion of the exhaust gas flowing at a predetermined angle to the front end  1301  of the strut housing  1300  delays the development of the boundary layer due to the turbulent effect through the vortex generation of the strut groove  1400 . As described above, the development of the boundary layer may be delayed, thereby reducing the occurrence of flow separation and reducing the pressure loss. 
       FIGS.  6 A,  6 B,  6 C, and  6 D  are diagrams illustrating the strut structures of the gas turbine according to an exemplary embodiment and a related art strut structure together. 
       FIG.  6 A  is a related art strut structure in which no strut groove is formed, and  FIG.  6 B  is a related art strut structure in which an outer fillet is formed on the upper and lower ends of the strut housing  1300  and no strut groove is formed. 
       FIG.  6 C  is the strut structure in which the strut groove is formed, and  FIG.  6 D  is the strut structure that inserts the inner fillet into the upper and lower ends of the strut housing  1300  to form the strut groove. 
     The result of modeling and simulating each strut structure of  FIGS.  6 A,  6 B,  6 C, and  6 D  is as in Table 1 below. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 FIG. 6A 
                 FIG. 6B 
                 FIG. 6C 
                 FIG. 6D 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Static 
                 0.752 
                 0.753 
                  0.779 
                  0.784 
               
               
                   
                 Pressure 
                   
                   
                   
                   
               
               
                   
                 Recovery 
                   
                   
                   
                   
               
               
                   
                 Pressure 
                 3.51 
                 3.46 
                 
                   3.25 
                 
                 
                   3.07 
                 
               
               
                   
                 Loss [%] 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, it may be seen that the pressure loss rate of the strut structure including the strut groove (i.e.,  FIGS.  6 C and  6 D ) is 3.25%, 3.07%, respectively, which is lower than 3.51%, 3.46% of the pressure loss rate of the strut structure in which no strut groove is formed (i.e.,  FIGS.  6 A and  6 B ). In particular, the strut structure in which the inner fillet is inserted into the upper and lower ends of the strut housing  1300  to form the strut groove (i.e.,  FIG.  6 D ) has the lowest pressure loss rate, thereby being the most preferred embodiment. 
       FIGS.  7  to  9    are diagrams illustrating a strut structure of a gas turbine according to another exemplary embodiment. 
     Referring to  FIG.  7   , a strut structure of a gas turbine includes a strut housing  2300  and a strut groove  2400 . 
     Because the structure of the strut housing  2300  is substantially the same as the strut housing  1300  of  FIG.  4   , a detailed description thereof will be omitted. 
     A lower inner fillet  2410  and an upper inner fillet  2420  are inserted into an inner circumferential surface of the strut housing  2300 , and a portion thereof is inserted to be exposed to the exhaust passage (F), and the exposed portion forms the strut groove  2400 . 
     The strut groove  2400  may connect the front end  2301  and the rear end  2302  of the strut housing  2300 . The strut groove  2400  further includes strut patterns  2401 ,  2402 . For example, the strut groove  2400  includes a groove pattern  2401 , which is in a form of channel  2411 , as in  FIG.  8    or a protrusion pattern  2402  as in  FIG.  9    on the lower inner fillet  2410  and the upper inner fillet  2420 . The groove pattern  2401  or the protrusion pattern  2402  may connect the front end  2301  and the rear end  2302  of the strut housing  2300 . 
     The strut structure includes the strut groove  2400  connecting the front end and the rear end of the strut housing  2300 , and the strut groove  2400  includes the groove pattern  2401  or the protrusion pattern  2402 , such that a portion of the exhaust gas flowing at a predetermined angle to the front end  2301  of the strut housing  2300  may add the turbulence effect by the groove pattern  2401  or the protrusion pattern  2402  in addition to the turbulence effect through the vortex generation of the strut groove  2400 , thereby further delaying the development of the boundary layer. 
       FIG.  10    is a diagram illustrating an exhaust diffuser according to another exemplary embodiment which includes the strut structure of the above-described exemplary embodiments. 
     Referring to  FIG.  10   , an exhaust diffuser  3000  of the gas turbine includes an inner casing  3100 , an outer casing  3200 , a strut housing  3300 , a strut groove  3400 , and an exhaust gas guide member  3500 . 
     In the exhaust diffuser  3000  of the gas turbine, because the inner casing  3100 , the outer casing  3200 , the strut housing  3300 , and the strut groove  3400  are substantially the same as the inner casing  1100 , the outer casing  1200 , the strut housing  1300 , and the strut groove  1400  of  FIG.  3   , a detailed description thereof will be omitted. 
     The exhaust gas guide member  3500  is a member configured to guide a flow direction of the exhaust gas flowing into the strut housing  3300 . The exhaust gas guide member  3500  guides the flow direction of the exhaust gas to flow in a direction parallel to the long axis of the elliptical strut housing  3300 . Here, the “direction parallel” means to guide to flow at a smaller angle by further narrowing the flow angle of the exhaust gas that collides with the front end  3301  of the strut housing  3300  while having an angle of about 20 to 30 degrees with respect to the long axis of the strut housing  3300 . 
     The exhaust gas guide member  3500  may be formed on at least any one of an outer circumferential surface (i.e., an upper surface) of the inner casing  3100  and an inner circumferential surface (i.e., a lower surface) of the outer casing  3200 . The exhaust gas guide member  3500  may be a plate-shaped member having a predetermined height and may be arranged in plural on the outer circumferential surface of the inner casing  3100  and the inner circumferential surface of the outer casing  3200  at predetermined intervals in a circumferential direction thereof. 
     The exhaust diffuser  3000  may guide the flow direction of the exhaust gas to flow in a direction parallel to the long axis of the elliptical strut housing  3300  so that the exhaust gas flows through the surface of the strut housing  3300 , thereby delaying the development of the boundary layer. Therefore, it is possible to delay the occurrence of flow separation and reduce the pressure loss. 
     Further, the exhaust diffuser  3000  includes the strut groove  3400  connecting the front end and the rear end of the strut housing  3300 , such that a portion of the exhaust gas flowing at a predetermined angle to the front end  3301  of the strut housing  3300  delays the development of the boundary layer due to the turbulence effect through the vortex generation of the strut groove  3400 . As described above, the development of the boundary layer may be delayed, thereby reducing the occurrence of flow separation and reducing the pressure loss. 
     While one or more exemplary embodiments have been described with reference to the accompanying drawings, it is to be understood by those skilled in the art that various modifications and changes in form and details may be made therein without departing from the spirit and scope as defined by the appended claims. Accordingly, the description of the exemplary embodiments should be construed in a descriptive sense only and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.