Patent Publication Number: US-2012034064-A1

Title: Contoured axial-radial exhaust diffuser

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to turbines, and more specifically, to exhaust diffusers for use with gas turbines and steam turbines. 
     Power generation plants often incorporate turbines, e.g., a gas turbine engine. The gas turbine engine combusts a fuel to generate hot combustion gases, which flow through a turbine to drive a load and/or compressor. At high velocities and temperatures, an exhaust gas exits the turbine and enters an exhaust diffuser. The exhaust diffuser may be an axial-radial exhaust diffuser that transitions the flow from an axial direction to a radial direction. Axial-radial exhaust diffusers incorporate internal structural features such as struts and turning vanes. The internal struts hold walls of the diffuser in a fixed relationship to one another and transfer loads from a rotor to a foundation. The internal turning vanes help divert the flow from the axial to radial direction. Unfortunately, the exhaust diffuser design results in significant pressure losses, particularly at the internal struts and turning vanes. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
     In accordance with a first embodiment, a system includes a gas turbine diffuser. The gas turbine diffuser includes an axial diffuser section including a first duct portion having an axial flow path along a centerline of the gas turbine diffuser, wherein the first duct portion has a first cross-sectional area that expands along the axial flow path. The gas turbine diffuser also includes an axial-radial diffuser section coupled to the axial diffuser section, wherein the axial-radial diffuser section includes a second duct portion having a curved flow path along the centerline from the axial flow path to a radial flow path, the second duct portion has a second cross-sectional area that expands along the curved flow path, the curved flow path has a radius of at least greater than or equal to approximately 30 centimeters, and the axial-radial diffuser excludes any turning vane in the second duct portion. 
     In accordance with a second embodiment, a system includes a gas turbine diffuser. The gas turbine diffuser includes an axial diffuser section including a first duct portion having an axial flow path along a centerline of the gas turbine diffuser. The gas turbine diffuser also includes an axial-radial diffuser section coupled to the axial diffuser section, wherein the axial-radial diffuser section includes a second duct portion having a curved flow path along the centerline from the axial flow path to a radial flow path and the axial-radial diffuser section excludes any turning vane in the second duct portion. 
     In accordance with a third embodiment, a method includes axially-radially diffusing an exhaust flow from a turbine through a curved duct along a curved flow path without any turning vanes, wherein the curved flow path has a radius of at least greater than or equal to 2 times a cross-sectional width of the curved duct. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a cross-sectional view of an embodiment of a gas turbine engine sectioned through a longitudinal axis; 
         FIG. 2  is a cross-sectional view of an embodiment of a contoured exhaust diffuser of the gas turbine engine of  FIG. 1  according to an embodiment; and 
         FIG. 3  is a perspective view of an embodiment of a contoured exhaust diffuser of the gas turbine engine of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     The disclosed embodiments are directed toward a turbine diffuser contoured to provide a smooth flow path to transition the flow from an axial to radial direction without a turning vane, while maximizing the pressure recovery in the diffuser. As discussed below, the disclosed turbine diffuser may include an axial diffuser section, an axial-radial diffuser section, and a radial diffuser section. The axial diffuser section includes diverging walls about one or more struts to reduce pressure losses around the struts and to gradually transition to the axial-radial diffuser section. The axial-radial diffuser section includes a vaneless duct with a large radius of curvature to reduce flow separation and pressure losses. For example, the axial-radial diffuser section gradually turns the exhaust flow without any abrupt changes between the axial and radial directions, thereby eliminating the need for internal turning vanes. Instead of a sharp turn or small radius of curvature, the axial-radial diffuser section has the large radius of curvature along radially inward and outwards walls. The radius of curvature may be at least approximately 1 to 100 times a cross-sectional width of the turbine diffuser. For example, the radius of curvature may be greater than or equal to approximately 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10 times the cross-sectional width of the turbine diffuser. In addition, to improved flow performance, the disclosed turbine diffuser eliminates mechanical issues, such as cracks, associated with turning vanes. 
       FIG. 1  is a cross-sectional side view of an embodiment of the gas turbine engine  118  along a longitudinal axis  158 . As appreciated, contoured exhaust diffusers without turning vanes may be used in any fluid flow system that includes rotary machines, such as gas turbine engines and stem turbine engines, and is not intended to be limited to any particular machine or system. As described further below, the contoured exhaust diffuser may be used within the gas turbine engine  118  to maximize diffuser performance by providing a smooth flow path to transition the flow through the diffuser from an axial to radial direction. For example, angles may be disposed near the diffuser inlet to provide early flow diffusion to reduce pressure losses around one or more internal struts and to make the flow path from the axial direction to the radial direction less abrupt and more contoured. Furthermore, the diffuser may include portions that gradually expand along the flow path to further enhance the transition of the flow from an axial to radial flow direction, thus, improving the aerodynamics of the diffuser, while eliminating a source of performance loss (e.g., internal turning vanes). 
     The gas turbine engine  118  includes one or more fuel nozzles  160  located inside a combustor section  162 . In certain embodiments, the gas turbine engine  118  may include multiple combustors  120  disposed in an annular arrangement within the combustor section  162 . Further, each combustor  120  may include multiple fuel nozzles  160  attached to or near the head end of each combustor  120  in an annular or other arrangement. 
     Air enters through an air intake section  163  and is compressed by a compressor  132 . The compressed air from the compressor  132  is then directed into the combustor section  162  where the compressed air is mixed with fuel. The mixture of compressed air and fuel is generally burned within the combustor section  162  to generate high-temperature, high-pressure combustion gases, which are used to generate torque within turbine section  130 . As noted above, multiple combustors  120  may be annularly disposed within the combustor section  162 . Each combustor  120  includes a transition piece  172  that directs the hot combustion gases from the combustor  120  to the turbine section  130 . In particular, each transition piece  172  generally defines a hot gas path from the combustor  120  to a nozzle assembly of the turbine section  130 , included within a first stage  174  of the turbine  130 . 
     As depicted, the turbine section  130  includes three separate stages  174 ,  176 , and  178 . Each stage  174 ,  176 , and  178  includes a plurality of blades  180  coupled to a rotor wheel  182  rotatably attached to a shaft  184 . Each stage  174 ,  176 , and  178  also includes a nozzle assembly  186  disposed directly upstream of each set of blades  180 . The nozzle assemblies  186  direct the hot combustion gases toward the blades  180  where the hot combustion gases apply motive forces to the blades  180  to rotate the blades  180 , thereby turning the shaft  184 . The hot combustion gases flow through each of the stages  174 ,  176 , and  178  applying motive forces to the blades  180  within each stage  174 ,  176 , and  178 . The hot combustion gases may then exit the gas turbine section  130  through an exhaust diffuser  188 . The exhaust diffuser  188  functions by reducing the velocity of fluid flow through the exhaust diffuser  188  while also increasing the static pressure to reduce the work of the gas turbine engine  118 . The exhaust diffuser includes a strut  190  disposed between the walls of the exhaust diffuser  188 . The strut  190  holds the walls in a fixed relationship to another. The number of struts  190  is variable and may range between 1 to 10 or more. The exhaust diffuser  188  includes a contoured shape to transition the fluid flow from an axial to radial direction without any internal turning vane, while also including angles near an inlet  192  of the exhaust diffuser  188  to allow early flow diffusion. 
       FIG. 2  is a cross-sectional side view of the exhaust diffuser  188  of  FIG. 1  further illustrating the angles near the inlet  192  and the contoured shape of the exhaust diffuser  188 . The exhaust diffuser  188  includes an axial diffuser section  202 , an axial-radial diffuser section  204 , and a radial diffuser section  206 . A centerline  208  generally defining the flow path runs from the inlet  192  of the exhaust diffuser  188  toward an outlet  210 . In general, the cross-sectional area of the exhaust diffuser  188  expands downstream along the flow path from the inlet  192  towards the outlet  210 . 
     The axial diffuser section  202  includes a first duct portion  212  having an axial flow path  214  along the centerline  208  of the exhaust diffuser  188 . The first duct portion  212  includes a first wall  216  offset from a second wall  218 . Further, the first wall  216  and the second wall  218  are disposed opposite one another about the axial flow path  214 . The first wall  216  is mounted nearer or proximate relative to a rotational axis, indicated by dashed line  220 , of the turbine  130 , while the second wall  218  is more distal relative to the rotational axis  220 . The first wall  216  extends along the axial flow path  214  at a first angle  222  relative to the rotational axis  220  of the turbine  130 . In certain embodiments, the first angle  222  may be a negative angle that ranges between approximately 0 to 8 degrees, 2 to 6 degrees, or 4 to 5 degrees. For example, the first angle  222  may be at least equal to or greater than approximately 2, 4, 6, or 8 degrees, or any angle therebetween. In addition, the second wall  218  extends along the axial flow path  214  at a second angle  226  relative to the rotational axis  220 . In certain embodiments, the second angle  226  may be a positive angle that ranges between approximately 16 to 20 degrees or 17 to 19 degrees. For example, the second angle  226  may be at least equal to or greater than approximately 16, 17, 18, 19, or 20 degrees, or any angle therebetween. In the illustrated embodiment, the first angle  222  and the second angle  226  are not 0 degrees. In some embodiments, the first angle  222  is less than or equal to approximately 8 degrees, and the second angle  226  is greater than or equal to approximately 16 degrees. 
     Due to the first and second angles  222  and  226 , respectively, the first wall  216  and the second wall  218  diverge from one another along the axial flow path  214 . As a result of the divergence of the first wall  216  and the second wall  218 , the first duct portion  212 , as  FIG. 2  illustrates, includes a first cross-sectional area  228  (i.e., perpendicular to centerline  208 ) that expands along the axial flow path  214  between the first wall  216  and the second wall  218 . The expansion of the cross-sectional area  228  across the flow path may provide early flow diffusion that reduces the pressure losses in diffuser performance across strut  190 . Further, this expansion smoothes the flow path transition from the axial to radial direction, as described below. 
     The axial diffuser section  202  is coupled to the axial-radial diffuser section  204 . The axial-radial diffuser section  204  transitions the flow from the axial diffuser section  202  to the radial diffuser section  206 . The axial-radial diffuser section  204  includes a second duct portion  230  having a curved flow path  232  along the centerline  208  from the axial flow path  214  to a radial flow path  234 . The second duct portion  230  includes a first curved wall  236  offset from a second curved wall  238 . Further, the first curved wall  236  and the second curved wall  238  are disposed opposite one another about the curved flow path  232 . The first curved wall  236  is mounted nearer or proximate relative to the rotational axis  220  of the turbine  130 , while the second curved wall  238  is more distal relative to the rotational axis  220 . The first and second angles  222  and  226  extend toward the first and second curved walls  236  and  238 , respectively. Indeed, in some embodiments, the first and second angles  222  and  226  may extend directly to the first and second curved walls  236  and  238 , respectively. The extension of the angles  222  and  226  to the curved walls  236  and  238  makes the flow path transition from the axial diffuser section  202  to the axial diffuser section  204  more aerodynamic, thereby reducing pressure losses in diffuser performance normally associated with sharp transitions in the flow path direction. 
     The first curved wall  236  curves along the curved flow path  232  with a first radius of curvature  240 , while the second curved wall  238  curves along the curved flow path  232  with a second radius of curvature  242 . The average of these radii  240  and  242  may be defined by an average radius of curvature  243  relative to the centerline  208  along the curved flow path  232 . In certain embodiments, the radii of curvature  240 ,  242 , and  243  may vary along the lengths of the first curved wall  236  and the second curved wall  238 . Accordingly, centers  241  of the radii  240 ,  242 , and  243  may shift to increase or decrease the radii  240 ,  242 , and  243 . At certain points along the length of the second duct portion  230 , the first radius of curvature  240  and the second radius of curvature  242  may be different from each other, while at other points the first radius of curvature  240  and the second radius of curvature  242  may be the same. Alternatively, the first radius of curvature  240  and the second radius of curvature  242  may be different along the entire lengths of the first curved wall  236  and the second curved wall  238 . In certain embodiments, the difference between the first radius of curvature  240  and the second radius of curvature  242  may range between approximately 0 to 50 percent, 10 to 40 percent, or 20 to 30 percent. For example, the difference may be approximately 15, 20, 25, 30, or 35 percent, or any percent therebetween. In certain embodiments, the first radius of curvature  240  may be larger than the second radius of curvature  242 . In alternative embodiments, the second radius of curvature  242  may be larger than the first radius of curvature  240 . In other embodiments, the first radius of curvature  240  and the second radius of curvature  242  may be the same. 
     In certain embodiments, the first radius of curvature  240  may range approximately from 30 centimeters to 390 centimeters, 80 to 340 centimeters, 130 to 390 centimeters, 180 to 300 centimeters, or 220 to 260 centimeters. For example, the first radius of curvature  240  may be approximately 30, 40, 50, 60, 70, 80, 90, or 100 centimeters, or any distance therebetween. In some embodiments, the first radius of curvature  240  may be at least greater than or equal to approximately 100 centimeters. In certain embodiments, the second radius of curvature  242  may range approximately from 30 centimeters to 510 centimeters, 80 to 460 centimeters, 130 to 410 centimeters, 180 to 360 centimeters, or 230 to 310 centimeters. For example, the second radius of curvature  242  may be approximately 30, 40, 50, 60, 70, 80, 90, or 100 centimeters, or any distance therebetween. In some embodiments, the first radius of curvature  240  may be at least greater than or equal to approximately 100 centimeters. In certain embodiments, the radius  243  of the curved flow path  232  may range approximately from 30 centimeters to 450 centimeters, 80 to 400 centimeters, 130 to 350 centimeters, 180 to 300 centimeters, or 220 to 260 centimeters. For example, the radius  243  may be approximately 30, 40, 50, 60, 70, 80, 90, or 100 centimeters, or any distance therebetween. In some embodiments, the radius  243  may be at least greater than or equal to approximately 30 centimeters. In other embodiments, the radius  243  may be at least greater than or equal to approximately 100 centimeters. 
     The curvature of the walls  236  and  238  provides a smoother, more aerodynamic, flow path transition that eliminates the need for an internal turning vane in the second duct portion  230 . Thus, the axial-radial diffuser section  204  excludes any internal turning vane. Indeed, the first and second curved walls  236  and  238 , respectively, diverge from one another along the curved flow path  232  to allow greater diffusion during the transition from the axial to radial direction. The curved second duct portion  230  has a second cross-sectional area  244  (i.e., perpendicular to the centerline  208 ) that expands along the curved flow path  232  between the first curved wall  236  and the second curved wall  238 . In other words, the cross-sectional area  244  has a cross-sectional width  246  that expands along the curved flow path  232 . The expansion of the cross-sectional width  246  within the axial-radial diffuser section  204  allows diffusion of the flow to increase, while also transitioning the flow from an axial to radial direction. 
     In the certain embodiments, the radii  240 ,  242 , and  243  may be at least approximately 1 to 100, 1 to 50, 1 to 25, or 1 to 10 times the cross-sectional width  246  of the curved flow path  232 . For example, radii  240 ,  242 , and  243  may be at least greater than or equal to approximately 1.5, 2, 3, 4, 5, 6, 7, 8, 9, or 10 times the cross-sectional width  246 . 
     From the axial-radial diffuser section  204 , the flow is transitioned to the radial diffuser section  206 . The axial-radial diffuser section  204  is coupled to the radial diffuser section  206 . The radial diffuser section  206  includes a third duct portion  248  having a radial flow path  234  along the centerline  208  of the diffuser  188 . The third duct portion  248  includes a first vertical wall  250  offset from a second vertical wall  252 . Further, the first vertical wall  250  and the second vertical wall  252  are disposed opposite one another about the radial flow path  234 . The diverging first and second curved walls  236  and  238  of the second duct portion  230  extend into the first vertical wall  250  and second vertical wall  252 , respectively. The first vertical wall  250  also diverges from the second vertical wall  252  along the radial flow path  234 . As a result, the third duct portion  248  includes a third cross-sectional area  254  (i.e., perpendicular to the centerline  208 ) that expands along the radial flow path  234  between the first vertical wall  250  and the second vertical wall  252  to increase diffusion and diffuser performance. From the radial diffuser section  206 , the flow is directed to the outlet  210  of the diffuser  188 . 
       FIG. 3  is a perspective view of the exhaust diffuser  188  illustrating the contours and expansion of the diffuser  188 . The exhaust diffuser  188  includes the axial diffuser section  202 , the axial-radial diffuser section  204 , and the radial diffuser section  206 , as described above. The axial diffuser section  202  includes the first and second walls  216  and  218 . The axial-radial diffuser section  204  includes the first and second curved walls  236  and  238 . Both the first and second walls  216  and  218 , as well as, at least portions of the first and second curved walls  236  and  238  include a semi-annular curvature in a circumferential direction, as indicated by arrow  262 , transverse to the longitudinal axis  158  of the gas turbine engine  118 . The annular curvature of the walls  216 ,  218 ,  236 , and  238  allows for the annular distribution of the exhaust diffuser  188  around the exit of the turbine  130 . In some embodiments, one or more exhaust diffusers  188  may be distributed around the exit of the turbine  130 . As shown in  FIG. 3 , the exhaust diffuser  188  includes a third wall  264  and a fourth wall  266  that follow the flow path generally defined by the centerline  208 . The third wall  264  and the fourth wall  266  are disposed opposite from each other and located between the first wall  216  and the second wall  218 , the first curved wall  236  and the second curved wall  238 , and the first vertical wall  250  and the second vertical wall  252  along the length of the diffuser  188 . The third wall  264  and the fourth wall  266  diverge from each other from the inlet  192  in a downstream direction  268  to the outlet  210 . Also, the cross-sectional area of the exhaust diffuser  188  (i.e., perpendicular to the downstream direction  268 ) expands downstream from the inlet  192  to the outlet  210  of the diffuser  188  in both a vertical dimension  270  and a horizontal dimension  272 . The dimension  270  may be defined as a radial dimension relative to axis  158 , whereas the dimension  272  may be defined as a circumferential dimension relative to the axis  158 . 
     In accordance with certain embodiments, the exhaust diffuser  188  above may be operated in conjunction with the turbine  130 . For example, a method of operation may include axially-radially diffusing an exhaust flow from the turbine through a curved duct along the curved flow path  232  without any turning vanes, wherein the curved flow path  232  has an enlarged radius  243  to reduce flow separation and pressure losses. In some embodiments, the radius  243  may be at least greater than or equal to approximately 30 centimeters and/or 1 to 10 times the width  246 . In other embodiments, the radius  243  may be at least greater than or equal to at least 2 times the width  246 . Also, in the method, axially-radially diffusing the exhaust flow may include expanding the exhaust flow between the first curved wall  236  and the second curved wall  238  that curve along the curved flow path  232 . As discussed above, the first curved wall  236  may be oriented nearer to the rotational axis  220  of the turbine  130  than the second curved wall  238 . The method may further include axially diffusing the exhaust flow prior to axially-radially diffusing the exhaust flow. Axially diffusing the exhaust flow includes expanding the exhaust flow between a first angled wall  216  and a second angle wall  218  that are angled relative to the axial flow path  214 . As discussed above, the first angled wall  216  may be oriented nearer to the rotational axis  220  of the turbine  230  than the second angled wall  218 . 
     Technical effects of the disclosed embodiments include providing angled walls  216  and  218  to provide early flow diffusion to reduce the pressure losses across the struts  190 . In addition, the angled walls  216  and  218  allow for a smoother transition from the axial diffuser section  202  to the axial-radial diffuser section  204  to decrease pressure losses during the axial to radial shift in flow direction. Providing an axial-radial diffuser section with curved walls  236  and  238  also smoothes the axial-to radial transition, while eliminating the need for turning vanes. Further, diverging walls along the axial diffuser section  202 , the axial-radial diffuser section  204 , and the radial diffuser section  206  allows the flow to expand along the flow path and to increase diffuser performance. Overall, the aerodynamic design of the diffuser  188  improves diffuser performance, while eliminating a source of performance loss and mechanical problems (i.e., the turning vanes). 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.