Patent Publication Number: US-11022311-B2

Title: Fuel nozzle with turning guide and gas turbine including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2017-0085080 filed in the Korean Intellectual Property Office on Jul. 4, 2017, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a fuel nozzle with a turning guide and a gas turbine including the fuel nozzle and the turning guide, and more particularly to the fuel nozzle in which the airflow of compressed air introduced into the fuel nozzle is guided by the turning guide. 
     Description of the Related Art 
     A gas turbine is a power engine that generates a hot gas through combustion of a compressed air and a fuel. The gas turbine rotates a turbine with the hot gas. The gas turbine is used for a combined-cycle power generation and a cogeneration. 
     The gas turbine is roughly divided into a compressor, a combustor, and a turbine. The compressor compresses an incoming air to a high pressure by receiving a part of power generated from a rotation of the turbine. The compressed air is transmitted to the combustor. The combustor mixes and burns the compressed air with the fuel to generate a flow of high-temperature combustion gas and injects it into the turbine. The injected combustion gas rotates the turbine to obtain a rotational force. 
     Specifically, the air compressed by the compressor flows into the combustor, and the fuel is injected through swirl vanes arranged in each fuel nozzle and is then mixed with the air. A mixture of fuel and air is burned in a combustion chamber located at a downstream of each fuel nozzle assembly, and the combustion gas is discharged through a hot gas path within the turbine. 
     Meanwhile, it is important to maintain uniform airflow as the compressed air is introduced into the fuel nozzle assembly and as the air is supplied to the fuel nozzles. This uniform flow of air is needed to uniformly mix the air with the fuel. Further, in order to make a stable combustion, it is needed to combust the uniform mixture of the air and fuel. 
     However, when the compressed air is introduced into the fuel nozzle assembly, the directionality of the airflow is inherently changed. Also, a small region can be created at where the airflow is slowed or the pressure is low, i.e., an air pocket. A region, where the flow rate of air through a fuel nozzle is low, may cause a flame anchoring in the fuel nozzles, thereby damaging fuel nozzle components. In addition, the low flow of air supplied to the fuel nozzle may invite partial changes in the mixture of air and fuel, thus increasing a combustion temperature or creating excessive nitrogen oxides (NOx). 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a fuel nozzle in which a turning guide enables a uniform flow of air when compressed air is supplied to the fuel nozzle, thereby preventing creation of an air pocket, to provide the turning guide for the same, and to provide a gas turbine including the fuel nozzle with turning guide. 
     It is an object of the present invention to provide a fuel nozzle in which a turning guide facilitates a more uniform supply of air into the fuel nozzle, thereby realizing stable combustion and reducing nitrogen oxides, to provide the turning guide for the same, and to provide a gas turbine including the fuel nozzle with turning guide. 
     According to an embodiment of the present invention, a fuel nozzle may include a central body having an outer wall; a shroud concentrically disposed with respect to the central body and configured to surround the central body while maintaining a space for an air passage between an inner wall of the shroud and the outer wall of the central body; a rim formed on one end of the shroud and forming an air inlet communicating with the air passage; and a turning guide including a turning separator disposed in the air inlet. 
     The turning separator may have an angle of coverage of the rim in a circumferential direction of 40 to 240 degrees. 
     The turning guide may further include at least one outer separator connected to a lateral end of the turning separator and extending outwardly from the turning separator in a radial direction, and at least one inner separator connected to a lateral end of the turning separator and extending inwardly from the turning separator in a radial direction. The at least one outer separator may be connected to the lateral end of the turning separator and extending outwardly from the turning separator in the radial direction. 
     At least one of the turning separator, the inner separator, and the outer separator may have a plurality of openings formed according to a pattern. 
     A horizontal length of a downstream end of the inner separator and a horizontal length of a downstream end of the outer separator may have a ratio of 4:1 to 1:1. 
     The turning separator may have at least one opening. The at least one opening may be arranged according to an airflow travel distance. 
     The turning guide may further include at least one plate-shaped separator connected to a lateral end of the turning separator and extending from the turning separator in a radial direction. The at least one plate-shaped separator may be formed in a streamlined shape. 
     The outer separator may be tilted at an angle of ±10 degrees in a circumferential direction of the turning separator. 
     The turning separator may have a lower portion formed to be inclined with respect to one of the central body and the shroud. 
     The fuel nozzle may further include a plurality of swirl vanes disposed at a specific interval on an outer circumferential surface of the central body, wherein a lower end of the turning guide is spaced apart from an upper end of the plurality of swirl vanes. 
     According to an embodiment of the present invention, a turning guide may be disposed in the above fuel nozzle and may include a turning separator, disposed in the air inlet and arranged along a circumferential direction of the air inlet, including a lower portion facing an inner wall of the shroud and an upper portion facing an outer surface of the rim. 
     According to an embodiment of the present invention, a fuel nozzle assembly may comprise a plurality of the above fuel nozzles. 
     According to an embodiment of the present invention, a gas turbine may include a compressor for compressing incoming air; a combustor for mixing fuel with the compressed air and burning the mixture, the combustor including a combustion chamber and a fuel nozzle assembly disposed in the combustion chamber; and a turbine for generating a turning force by a combustion gas received from the combustor, wherein the fuel nozzle assembly includes a plurality of the above fuel nozzles. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic view illustrating a gas turbine including a fuel nozzle assembly according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view schematically showing a fuel nozzle assembly according to an embodiment of the present invention; 
         FIG. 3  is a perspective view showing a fuel nozzle assembly including a fuel nozzle according to an embodiment of the present invention; 
         FIG. 4  is a perspective view showing a fuel nozzle according to an embodiment of the present invention; 
         FIG. 5A  is a perspective view showing a turning guide according to an embodiment of the present invention, and  FIG. 5B  is a cross-sectional view taken along line CL-CL of  FIG. 5A ; 
         FIG. 6  is a cross-sectional view of a fuel nozzle according to an embodiment of the present invention, schematically showing a distributed flow of air flowing through an air inlet of the fuel nozzle; 
         FIGS. 7A and 7B  are perspective views of a fuel nozzle according to the present invention, respectively showing turning separators according to range of coverage; 
         FIG. 8  is a perspective view of a turning guide having inner separators according to an embodiment of the present invention; 
         FIG. 9  is a perspective view of a turning guide having outer separators according to an embodiment of the present invention; 
         FIGS. 10A and 10B  are perspective views of a turning guide according to the present invention, respectively showing inner and outer separators according to inclination angle; 
         FIGS. 11A and 11B  are perspective views of a turning guide according to the present invention, respectively showing turning separators according to the inclination direction of a lower portion; 
         FIG. 12  is a perspective view of a turning guide having openings according to an embodiment of the present invention; 
         FIGS. 13A and 13B  are perspective views of a turning guide according to the present invention, respectively showing openings formed in the turning separators according to pattern; 
         FIGS. 14A and 14B  are perspective views of a turning guide having inner and outer separators with curved surfaces according to an embodiment of the present invention, respectively showing the separators with and without openings; and 
         FIG. 15  is a perspective view of a turning guide having obliquely angled openings according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood that the present invention is not intended to be limited to embodiments disclosed herein and includes various modifications, equivalents, and/or alternatives of the disclosed embodiments. 
     Terminology used herein is merely for the purpose of describing particular embodiments and is not intended to limit the invention. Singular forms utilizing “a,” “an,” and “the” are intended to include plural forms unless the context clearly dictates otherwise. In addition, terms such as “comprise,” “include,” and “have” are intended to specify the presence of stated elements, components, operations, functions, features, steps, or the like, without excluding the presence or possibility of additional other elements, components, operations, functions, features, steps, or the like. 
     The following description of embodiments may omit descriptions of techniques that are well known in the art or not directly related to the present disclosure. This is to clearly convey the subject matter of the present disclosure by omitting unnecessary explanation. For the same reason, some elements in the drawings may be exaggerated, omitted, or schematically illustrated. Also, the size of each element does not entirely reflect the actual size. In the drawings, the same or corresponding elements are denoted by the same reference numerals. 
     Referring to  FIG. 1 , a gas turbine  1  according to an embodiment of the present invention may include a compressor  10  for compressing incoming air with a high pressure, a combustor  20  for mixing and burning the compressed air and fuel, and a turbine  30  for generating a turning force by a combustion gas. The combustor  20  includes a fuel nozzle assembly, which includes a plurality of fuel nozzles. 
     Referring to  FIG. 2 , a fuel nozzle assembly  100 ′ may include a casing  210 , a cap sleeve  220 , an end plate  230 , and a fuel nozzle  100 . 
     As shown in  FIG. 2 , the casing  210  forms an outer wall of the fuel nozzle assembly  100 ′, has an inner space, and extends in one direction. The casing  210  is generally formed in a cylindrical shape. This shape is, however, exemplary only and not to be construed as a limitation of the present invention. 
     The cap sleeve  220  is disposed inside the casing  210  and formed along the extending direction of the casing  210 . The cap sleeve  220  is separated from the inner wall of the casing  210  by an interposed space forming an annular duct  240 . The cap sleeve  220  is generally formed in a cylindrical or tapered cylindrical shape, which is, however, exemplary only and not to be construed as a limitation of the present invention. 
     The end plate  230  is integrated with the casing  210  at one end of the casing  210  to seal the casing  210 . Further, the end plate  230  may be combined with a manifold for supplying fuel to a central body  110  of the fuel nozzle  100  and to associated valves and the like. In addition, the end plate  230  supports the plurality of fuel nozzles  100  arranged in the casing  210 . 
     Air compressed in the compressor  10  flows through a passage, i.e., the annular duct  240  between the casing  210  and the cap sleeve  220 , and moves along the annular duct  240  until reaching the end plate  230  disposed at the end of the casing  210 . Then, the compressed air turns approximately 180 degrees in the opposite direction (i.e., essentially a U-turn) and flows into each fuel nozzle  100 . 
     When the compressed air is thus redirected to enter each fuel nozzle  100 , airflow may be slowed inside of a fuel nozzle  100  and thereby an air pocket may be created. It is necessary to prevent this phenomenon. 
     As shown in  FIG. 3 , the fuel nozzle assembly  100 ′ includes a plurality of the fuel nozzles  100  arrange in an array. In general, a number of fuel nozzles may be arranged radially around a centrally disposed fuel nozzle. The fuel nozzle  100  of  FIG. 4  may be any one of the array, but for illustrative purposes it may be assumed that the fuel nozzle  100  of the present invention is a radially arranged fuel nozzle. 
     Referring to  FIGS. 2, 3, and 4 , the fuel nozzle  100  includes a central body  110 , a shroud  120 , a rim  130 , and a turning guide  140 . 
     A fuel FF ( FIG. 2 ) is injected through the central body  110 . The fuel FF is supplied from a fuel supply unit, injected into a combustion chamber  250  through the central body  110  and a swirl vane  124 , and burned in the combustion chamber  250  formed in a combustion liner (not shown). The combustion liner exposed to a hot combustion gas is cooled by relatively cool compressed air introduced through the annular duct  240 . The central body  110  may be generally formed in a cylindrical shape, which is, however, exemplary only and not to be construed as a limitation of the present invention. 
     The shroud  120  is concentric with the central body  110  and extends along the longitudinal direction of the central body  110 . The shroud  120  is spaced apart from the central body  110  and is formed to surround the central body  110 . Air flows into a space formed between the central body  110  and the shroud  120 . Although having any practical shape, the shroud  120  of this embodiment has a cylindrical shape which is concentric with the central body  110 . In this case, a cross-section of an air passage  122  formed between the central body  110  and the shroud  120  has an annular shape. 
     The rim  130  is connected to an entrance of the shroud  120  and is formed along the periphery of the entrance to guide the air to the air passage  122 . In order for the compressed air to smoothly enter the fuel nozzle  100  while changing directions, the rim  130  may have a convex curved surface. When each of the central body  110  and the shroud  120  is cylindrical, the rim  130  has an annular shape. An air inlet  131 , through which the compressed air flows, is formed by the convex curved surface of the rim  130  and the juxtaposition of the rim  130  and one end of the central body  110 . 
     The turning guide  140 , which is shown in detail in  FIGS. 5A and 5B , is disposed in the air inlet  131  and is arranged around a portion of surfaces of the shroud  120  and the rim  130 . The turning guide  140  is spaced apart from both the shroud  120  and the rim  130 . The turning guide  140  may be fixed to the central body  110 , the rim  130 , or the shroud  120  through a rib (not shown). The compressed air that reaches the air inlet  131  is introduced and distributed by the turning guide  140 . That is, the turning guide  140  performs a function of distributing a flow of the air flowing into the air inlet  131 , as illustrated in  FIG. 2  and in more detail in  FIG. 6 . 
     Referring to  FIGS. 2 and 6 , when the compressed air is introduced into the air passage  122  of the fuel nozzle  100 , an airflow AF 1  is divided by the turning guide  140  into an airflow AF 2  through a space between the rim  130  and the turning guide  140  and into an airflow AF 3  through a space between the turning guide  140  and the central body  110 . 
     When the turning guide  140  distributes the airflows AF 2  and AF 3 , great airflow moment is created in the space between the rim  130  and the turning guide  140 . Thus, the distribution of divided airflow can suppress the formation of an air pocket in the vicinity of the shroud  120 , which is prone to form in the contemporary art. 
     A plurality of swirl vanes  124  are disposed on the outer circumferential surface of the central body  110  and are arranged at predetermined intervals around the central body  110 . The turning guide  140  is spaced apart from the swirl vanes  124  so as prevent interference between the turning guide  140  and the swirl vanes  124 . Specifically, the lower end of the turning guide  140  and the upper end of the swirl vane  124  are spaced apart from each other by a predetermined distance. 
     As shown in  FIG. 5A , the turning guide  140  includes a turning separator  142  for separating the introduced airflow. The turning separator  142  is disposed to be spaced apart from both the shroud  120  and the rim  130  and is formed in a plate shape having a curved surface. 
     Specifically, the turning separator  142  may be divided into a lower portion  1421  facing the inner wall of the shroud  120  and an upper portion  1422  facing the outer surface of the rim  130 . The lower portion  1421  of the turning separator  142  extends in the same direction as the extending directions of the central body  110  and the shroud  120 , is spaced apart from the swirl vane  124 , and may be disposed parallel to the inner wall of the shroud  120 . 
     The upper portion  1422  of the turning separator  142  extends in the form of curved surface from the lower portion  1421  along the outer surface of the rim  130 . That is, beginning from an upper end of the lower portion  1421 , the upper portion  1422  of the turning separator  142  has a convex curved surface to correspond to a portion of the surface of the rim  130 . The upper portion  1422  of the turning separator  142  may cover the rim  130  such that the surface facing the rim  130  is spaced apart from the outer surface of the rim  130 . Although the upper portion  1422  of the turning separator  142  has an arc shape in this embodiment, this is exemplary only and not to be construed as a limitation of the present invention. Alternatively, the upper portion of the turning separator  142  may have various shapes. 
     Referring to  FIG. 5B , a length l 1  of the lower portion  1421  of the turning separator  142  may be greater than or equal to a vertical component length l 2  of the upper portion  1422 . When the compressed air moves along the annular duct  240  and reaches the end plate  230 , the compressed air turns in the opposite direction (i.e., U-turn) and flows into the fuel nozzle  100 . That is, the compressed air flows into a space between the turning separator  142  and the rim  130  and then flows along the air passage  122  formed by the shroud  120  and the central body  110 . At this time, if the length l 1  of the lower portion  1421  of the turning separator  142  is short, the airflow distribution effect of the turning separator  142  may be weakened. Therefore, in order to maximize the effect of distributing the airflow between the turning separator  142  and the rim  130 , the length l 1  of the lower portion  1421  of the turning separator  142  may be greater than or equal to the length l 2  of the upper portion  1421  of the turning separator  142 . 
     In addition, as shown in  FIGS. 7A and 7B , a range of coverage of the turning separator  142  formed in the air inlet  131  may vary and may be expressed as an angle θ in a circumferential direction of the turning separator  142  with respect to a central axis x ( FIGS. 10A and 10B ). The coverage range may be a little as 40 degrees or as much as 240 degrees and is preferably 60 to 140 degrees. A coverage range of 60 degrees around the central axis x of the central body  110  is exemplified in  FIG. 7A  and a coverage range of 140 degrees is exemplified in  FIG. 7B . 
     If the coverage range of the turning separator  142  is less than 40 degrees, the amount of incoming air divided by the turning separator  142  is small, weakening the airflow distribution effect. On the other hand, if the range of the turning separator  142  is greater than 240 degrees, an undesirable interference of the airflow may occur between neighboring fuel nozzles  100  in the fuel nozzle assembly  100 ′ in which plural fuel nozzles  100  are annularly arranged. Here, when the fuel nozzles  100  are disposed radially about one fuel nozzle in the fuel nozzle assembly  100 ′, the turning guide  140  of each fuel nozzle  100  may be disposed at the outermost position of each fuel nozzle  100  in order to minimize interference by adjacent fuel nozzles  100 . 
     Referring to  FIG. 8 , the turning guide  140  may further include an inner separator  144 . That is, at least one inner separator  144  is disposed at a lateral end of the turning separator  142 . The lateral ends of the turning separator  142  are situated with respect to the circumferential direction, and the inner separator  144  extends inwardly from the turning separator  142  in the radial direction. The inner separator  144  may be in the form of a single inner separator  144  disposed at one lateral end of the turning separator  142 , or a pair of inner separators  144  disposed at both lateral ends of the turning separator  142 . In addition, the inner separator  144  may be formed in a plate shape extending from a corresponding lateral end of the turning separator  142  to the outer surface of the central body  110 . The inner separator  144  may block the air flowing into the space between the turning separator  142  and the central body  110  from fluctuating inwardly and outwardly in the circumferential direction of the turning separator  142 , thereby maintaining the airflow more uniformly. 
     An inward end of the inner separator  144  may be connected to the outer surface of the central body  110 . Although the inner separator  144  is shown as being connected to both lateral ends of the turning separator  142  in this embodiment, this is exemplary only and not to be construed as a limitation. Alternatively, the inner separator  144  may be connected to only one lateral end of the turning separator  142  or to any position of the turning separator  142  other than the lateral ends in the circumferential direction. 
     When the compressed air flows into the air passage  122  of the fuel nozzle  100 , this airflow may be divided by the inner separator  144  in addition to the turning separator  142 . 
     According to another embodiment, as shown in  FIG. 9 , the turning guide  140  may further include an outer separator  146  instead of the inner separator  144 . As in the case of the inner separators  144 , one or two outer separators  146  are connected to one or both lateral ends of the turning separator  142  in the circumferential direction and extend outwardly from the turning separator  142  in the radial direction. Also like the inner separator  144 , the outer separator  146  is formed in a plate shape. The outer separator  146  may block the air flowing into the space between the turning separator  142  and the shroud  120  from fluctuating inwardly and outwardly in the circumferential direction of the turning separator  142 . 
     An outward end of the outer separator  146  may be connected to an inner surface of the shroud  120 . Although the outer separator  146  is shown as being connected to both lateral ends of the turning separator  142  in this embodiment, this is exemplary only and not to be construed as a limitation. Alternatively, the outer separator  146  may be connected to only one lateral end of the turning separator  142  or to any position of the turning separator  142  other than the lateral ends in the circumferential direction. 
     Accordingly, the turning guide  140  of  FIG. 8 or 9  further includes at least one plate-shaped separator  144  or  146  connected to a lateral end of the turning separator  142  and extending from the turning separator  142  in a radial direction. 
     Meanwhile, the outer separator  146  may be formed at an increased angle with respect to the turning separator  142  in the circumferential direction. That is, as shown in  FIG. 10A , the outer separator  146  may be formed to be tilted outwardly at a certain angle (α) in the circumferential direction of the turning separator  142 . In other words, the outer separator  146  may be formed to have an increased angle (α) in comparison with the angle (θ) of the turning separator  142  in the circumferential direction. The tilt angle (α) of the outer separator  146  may be 0 to 10 degrees. When the outer separator  146  is formed to be tilted outwardly with respect to the turning separator  142 , it is possible to change the direction of the airflow. 
     However, if the outer separator  146  is tilted outwardly at an angle of more than 10 degrees with respect to the turning separator  142 , the outer separator  146  may interfere with the flow of the introduced compressed air. This is undesirable. 
     Alternatively, the outer separator  146  may be formed at a reduced angle with respect to the turning separator  142  in the circumferential direction. That is, as shown in  FIG. 10B , the outer separator  146  may be formed to be tilted inwardly at a certain angle (β) in the circumferential direction of the turning separator  142 . In other words, the outer separator  146  may be formed to have a reduced angle (β) in comparison with the angle (θ) of the turning separator  142  in the circumferential direction. The tilt angle (β) of the outer separator  146  may be 0 to 10 degrees. When the outer separator  146  is formed to be tiled inwardly with respect to the turning separator  142 , the compressed air may further flow into the space between the central body  110  and the turning guide  140 . However, if the outer separator  146  is tilted inwardly at an angle of more than 10 degrees with respect to the turning separator  142 , the airflow passage may be narrowed by the outer separator  146 . This is undesirable because of the disruption of the smooth flow of air. 
     As above, by adjusting the tilt angle of the outer separator  146  inwardly or outwardly from the turning separator  142 , it is possible to finely adjust the airflow. 
     In addition, as shown in  FIGS. 11A and 11B , the lower portion  1421  of the turning separator  142  may be formed to incline or curve toward the central body  110  or toward the shroud  120 , that is, inwardly or outwardly. Specifically, when the inner separator  144  is formed in a plate-like shape extending toward or away from the central axis x of the central body  110 , the lower portion  1421  of the turning separator  142  may be bent toward or away from the central body  110 , that is, to become farther from or closer to the shroud  120 . More specifically, the lower end of the lower portion  1421  of the turning separator  142  may be formed to have an inward inclination angle (α) toward the central body  110  or an outward inclination angle (β) toward the shroud  120  with respect to the central axis x of the central body  110 . Each of these angles (α, β) may be from 0 to 10 degrees. 
     As above, by adjusting the lower portion  1421  of the inner separator  146  inwardly or outwardly from the central axis of the central body  110 , it is possible to adjust the airflow with very effective manner. 
     The turning guide  140  may include both the inner separator  144  and the outer separator  146 . As described above, the inner separator  144  is connected to at least one lateral end of the turning separator  142  and extends inwardly in the radial direction, whereas the outer separator  146  is connected to at least one lateral end of the turning separator  142  and extends outwardly in the radial direction. 
     The inner separator  144  and the outer separator  146  have a specific length ratio. Specifically, the horizontal length (a) of a downstream end of the inner separator  144  and the horizontal length (c) of a downstream end of the outer separator  146  may have a ratio of 4:1 to 1:1. That is, the horizontal length (a) of the downstream end of the inner separator  144  may be greater than or equal to the horizontal length (c) of the downstream end of the outer separator  146 . Therefore, within the passage formed by the outer surface of the central body  110  and the inner surface of the shroud  120 , the lower portion of the turning separator  142  is positioned midway in the passage or in the passage closer to the shroud  120 . 
     When the horizontal length (c) of the downstream end of the outer separator  146  is relatively small, a greater amount of air is introduced into the space between the turning guide  140  and the central body  110 . On the other hand, when the horizontal length (c) of the downstream end of the outer separator  146  is increased, the amount of air flowing into the space between the turning guide  140  and the shroud  120  increases. If the horizontal length (c) of the downstream end of the outer separator  146  is greater than the horizontal length (a) of the downstream end of the inner separator  144 , the amount of the air flowing into the space between the central body  110  and the turning guide  140  is insufficient. This is undesirable because the air is not flowing smoothly. 
     According to still another embodiment, as shown in  FIG. 12 , openings  1422 ,  1442 , and  1462  may be formed in the turning separator  142 , the inner separator  144 , and the outer separator  146 . The compressed air that is introduced while being divided by the turning guide  1400  moves in and out through the openings  1422 ,  1442 , and  1462 , thereby being distributed more uniformly. Therefore, the compressed air can remove an air pocket while flowing from a place having a high air density to a place having a low air density. 
     The openings  1422 ,  1442 , and  1462  may be formed in at least one of the turning separator  142 , the inner separator  144 , and the outer separator  146 . That is, the openings may be formed in all three separators as needed, or may be selectively formed only in one or two separators. In addition, the openings may be formed over the entire area of the turning guide  140  without any limitation of their positions. 
     The openings  1422 ,  1442 , and  1462  arranged in the turning guide  140  may be formed with a specific pattern. For example, as shown in  FIG. 13A , the openings  1422 ,  1442 , and  1462  may be formed at regular intervals in the horizontal or vertical direction, or may be formed in a specific shape. In another example, the openings  1422 ,  1442 , and  1462  may be formed to have different sizes in the horizontal or vertical direction. When the sizes of the openings  1422 ,  1442 , and  1462  become larger toward a lower side of either of the inner and outer separators  144  and  146 , as shown in  FIG. 13B , the movement of the compressed air through the openings  1422 ,  1442 , and  1462  may be increased as the air flows downward along the turning guide  140 . In other words, the turning guide  140  has at least one opening arranged according to an airflow travel distance along a surface of one or both of the inner and outer separators  144  and  146 . 
     According to yet another embodiment, as shown in  FIGS. 14A and 14B , each of the inner separator  144  and the outer separator  146  may have a curved surface. That is, rather than formed with a flat surface as described above, at least one of the inner separator  144  and the outer separator  146  may be formed with a curved surface having a convex middle portion to impart a streamlined shape. This may control the separation of airflow around the inner separator  144  and the outer separator  146  and thereby prevent any unnecessary drop of pressure. Even in the inner and outer separators  144  and  146  formed with a curved surface, the above-described openings  1442  and  1462  may be formed respectively. 
     Normally, the openings  1422 ,  1442 , and  1462  are formed perpendicular to the surface of the corresponding separator. However, as shown in  FIG. 15 , the openings  1422 ,  1442 , and  1462  may be formed at an oblique angle with respect to the surface of the corresponding separator. With the openings  1422 ,  1442 , and  1462  thus formed at an oblique angle, the air passing through the openings  1422 ,  1442 , and  1462  has a directionality since each separator itself has a certain thickness. For example, if the openings  1422 ,  1442 , and  1462  are formed obliquely in a downward and inward direction, the air flowing into the turning guide  140  from the outside of the turning guide through the openings  1422 ,  1442 , and  1462  may have a downward stream. The directionality of the airflow may prevent the creation of any undesirable air pocket. 
     According to the present invention as described above, when the compressed air flows into the fuel nozzle assembly, it is possible to make the airflow uniform, thereby suppressing the creation of an air pocket. Since the compressed air is more uniformly supplied to the fuel nozzle, the gas can be stably burned, and thereby the generation of nitrogen oxides can be reduced. It is also possible to prevent a local increase of combustion temperature which may result in the generation of a flame inside the fuel nozzle and damage to fuel nozzle components. 
     While the present disclosure has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken in conjunction with the present disclosure. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the subject matter and scope of the present disclosure.