Patent Publication Number: US-2013239585-A1

Title: Tangential flow duct with full annular exit component

Description:
STATEMENT REGARDING FEDERALLY SPONSORED DEVELOPMENT 
     Development for this invention was supported in part by Contract No. DE-FC26-05NT42644, awarded by the United States Department of Energy. Accordingly, the United States Government may have certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a flow duct assembly for combustions gasses generated by combustor cans in a gas turbine engine. In particular, this invention relates to an assembly with discrete flow paths configured to receive discrete combustion gas flows from each combustor, where the discrete flow paths merge into a full annular exit component configured to unite the discrete combustion gas flows, where a construction of the full annular exit component is independent of a number of the discrete flow paths. 
     BACKGROUND OF THE INVENTION 
     Various emerging designs for flow duct assemblies direct discrete flows of combustion gases from a respective can of a can annular combustor toward the first row of turbine blades. In conventional can annular gas turbine engines, a first row of turbine vanes properly orients and accelerates the combustion gases for delivery onto the first row of turbine blades. However, some of the emerging designs utilize a geometry of the flow duct assembly to properly orient and accelerate the discrete combustion gas flows, which obviates the need for a first row of turbine vanes. In some of these emerging designs without first row vanes the flow duct assemblies include a plurality of discrete gas flow ducts and a common duct structure, where one duct is associated with a respective can combustor and where all of the ducts lead to the common duct structure which is in turn disposed immediately upstream of the first row of turbine blades. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a prior art subassembly of a flow duct assembly 
         FIG. 2  is an embodiment of the flow duct assembly 
         FIG. 3  is an alternate embodiment of the flow duct assembly of  FIG. 2 . 
         FIG. 4  is an alternate embodiment of the flow duct assembly. 
         FIG. 5  is an alternate embodiment of the flow duct assembly of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present inventor has recognized that flow duct assemblies that accelerate combustion gases to a speed appropriate for delivery onto the first row of turbine blades incur substantially more mechanical loads than do conventional transition ducts. This is due to a greater difference in static pressure of compressed air outside of the flow duct assembly than a static pressure of the combustion gases inside the flow duct assembly. In conventional gas turbine transition ducts leading from a can combustor to a first row vane, combustion gases may enter the transition duct at, for example, approximately 0.2 mach and may leave the transition duct at, for example, approximately 0.3 mach. Within the first row vane assembly the combustion gases are subsequently accelerated to a speed appropriate for delivery onto a first row of turbine blades, which may be, for example, approximately 0.8 mach. However, in the emerging designs for flow duct assemblies where no first row of vane assembly is used, in order to properly accelerate the combustion gases for delivery onto the first row of turbine blades the flow duct assembly itself must accelerate the combustion gases from approximately 0.2 mach to approximately 0.8 mach. Since it is known that as a fluid accelerates it will exhibit a decreasing static pressure, (everything else remaining the same), within the flow duct assembly in a region of accelerated combustion gases, (the accelerated region), the accelerated combustion gases will exhibit a much lower static pressure. Consequently, a static pressure difference between the compressed air outside of the assembly and the combustion gases in the accelerated region will be much greater than any pressure difference present in a convention transition duct. This relatively large pressure will manifest as a greater mechanical load on the flow duct assemblies than is present on traditional transition ducts. This greater mechanical load will occur from a point in the flow duct assemblies at which and downstream of where the acceleration of the combustion gases occurs. In one embodiment (see  FIG. 1 ) a common duct structure will experience the greater mechanical load since it is at a downstream end of the flow duct assembly and combustion gases traveling there through have already been accelerated significantly. Further, these increased pressure loads then require complicated support structure and thickened side flanges. In addition to the mechanical loads, there are thermal loads resulting from the complex geometry and the differences in thermal loading. 
     The present inventor has also recognized that these increased mechanical and thermal loads may result in a loss of efficiency when used in flow duct assemblies designed using assembly techniques associated with individual transition ducts typically used in gas turbine engines using can annular combustors. Specifically, since the assembly techniques used with individual transition ducts were never meant to withstand the increased mechanical loads that the emerging flow duct assemblies must withstand, there are previously unrecognized inadequacies present in the assembly techniques associated with conventional transition ducts when applied to the emerging flow duct assembly designs. 
     Similarly, annular combustors are comparable to conventional transition ducts in that the annular combustors have not been designed to accelerate the combustion gases because they also rely on the first row of vanes to accelerate the combustion gases. Accordingly, they were not designed to accommodate the increased mechanical loads and therefore their designs also suffer from previously unrecognized inadequacies when applied to the emerging flow duct assembly designs. 
     As a result of this recognition the inventor has created a flow duct assembly that does not suffer from the same inadequacies associated with prior flow duct assembly designs. In particular, in contrast to the prior art assembly techniques, where the flow duct assembly may include as many subassemblies as there are combustors, all bolted together circumferentially to form the flow duct assembly, the present invention provides for the common duct assembly to be made up of a hoop structure, where the hoop structure includes as few as one hoop structure component. In certain emerging flow duct assembly designs the common duct assembly may form an annular chamber where the discrete combustion gas flows may unite prior to delivery onto the first row of turbine blade. 
     The inventor has further recognized that in some cases it may be advantageous to separate portions of the flow duct assembly. For example, those portions that define an outer portion of the flow duct assembly may be separated from those portions that define an inner portion of the flow duct assembly. In a typical turbine, inner support structures may support the inner portion of the flow duct assembly, while outer support structures may support the outer portion of the flow duct assembly. However, thermal grown of the inner support structure may be different than thermal growth of the outer support structure, resulting in relative displacement between the two. If the flow duct assembly is rigid, relative movement of the supports attached to the flow duct assembly may cause stresses in the supports and/or the flow duct assembly. Further, due to their different locations, there may be relative thermal growth between the inner portion of the flow duct assembly and a outer portion may themselves grow at different rates than each other and thereby generate thermally induced stresses. To alleviate this, the inventor has developed an embodiment of the flow duct assembly where the inner portion and the outer portion are connected to each other via a less rigid connection which can accommodate the relative displacement without generating excessive stresses. 
     As seen in  FIG. 1 , a subassembly  10  of the prior art flow duct assembly may include a cone  12  and an integrated exit piece (IEP)  14  connected to the cone  12  at cone/IEP joint  15 . The integrated exit piece may include several features. One feature is a throat region  16  that may serve any or all of several functions, including: collimating a combustion gas flow entering the throat region; transitioning a cross section of the combustion gas flow entering the throat region  16  from circular to more of a quadrilateral shape with rounded corners when exiting; and further accelerating the combustion gasses in addition to an acceleration that occurs within the cone section. Another feature may be an annular chamber segment  18 . When all of the subassemblies  10  are assembled into the prior art flow duct the annular chamber segments  18  together form an annular chamber. If it takes, for example, twelve subassemblies to form the prior art flow duct assembly, then each annular chamber segment  18  forms a portion  24  of the annular chamber that equates to 1/12 of the annular chamber. 
     Each annular chamber segment  18  has a circumferentially upstream end  20  and a circumferentially downstream end  22 , with respect to a circumferential direction  26  of flow of combustion gasses within the annular chamber. Since combustion gases exiting the annular chamber, and therefore the annular chamber portion  24 , have been accelerated to approximately 0.8 mach, a static pressure P 1  of the accelerated combustion gasses in the annular chamber portion  24  is less than a static pressure P 2  of the combustion gases within the cone traveling at approximately 0.2 mach. In turn, the static pressure P 2  of the combustion gases in the cone is less than a static pressure P 3  of compressed air surrounding the prior art flow duct assembly and subassembly  10 . (P 1 &lt;P 2 &lt;P 3 .) 
     Each annular chamber segment  18  includes a segment axially upstream wall  30 , (with respect to an axial direction  38  of travel of combustion gases within the annular chamber segment  18 ), a segment radially outer wall  32 , and a segment radially inner wall  34 . The segment upstream wall  30  forms a portion of the annular chamber upstream wall. The segment radially outer wall  32  forms a portion of the annular chamber radially outer wall. Similarly, the segment radially inner wall  34  forms a portion of the annular chamber radially inner wall. It can be seen that each of these segment walls  30 ,  32 ,  34  separates a region of relatively high static pressure P 3  from a region of relatively low static pressure P 1 . 
     As a result of the pressure difference, and the open ended geometry of the annular chamber segment  18 , (and hence of the annular chamber), the segment radially outer wall  32  and segment radially inner wall  34  will be urged toward the region of relatively low pressure P 1 . In the prior art embodiment shown, this may result in a situation where an axial downstream end  36  of the segment radially outer wall  32  is urged radially inwardly as shown by arrow  40 . An upstream end  42  of the segment radially outer wall  33 , however, is fixed to the segment upstream wall  30  at a radially outer end  44  of the segment upstream wall  30 . This may create mechanical stresses the two segment walls  30 ,  32 , because the segment upstream wall  30  acts similar to a moment arm about an intersection  46  of the segment upstream wall  30  and the segment radially outer wall  32 . Similarly, an axial downstream end  50  of the segment radially inner wall  34 , may be urged radially outward as shown by arrow  52 . Since an upstream end  54  of the segment radially inner wall  34  is fixed to the segment upstream wall  30  at a radially inner end  56 , the segment radially inner wall  34  may also act similar to a moment arm about an intersection  58  of the segment radially inner wall  34  and the segment upstream wall  30 . This may also create mechanical stresses the two segment walls  30 ,  34 . 
     Under conventional transition duct methodology, where any pressure difference P 1 :P 3  was not as great, it was thought that the subassemblies  10  could simply be joined together to create the flow duct assembly. Specifically, it was thought that a downstream end  22  of one subassembly  10  could be bolted, pinned, or otherwise conventionally joined to the upstream end  20  of a circumferentially downstream adjacent subassembly  10 . This was repeated for each subassembly  10  until the flow duct assembly was formed. However, modeling, testing and experimentation have informed designers that the pressure difference is so great that using these conventional joining techniques may result in shortened life of the flow duct assembly, and under certain circumstances may not be sufficiently strong to withstand the mechanical forces induced by the pressure differences P 1 :P 3 . The pressure difference is so great that in some embodiments it is believed that despite being joined to adjacent subassemblies  10  the downstream end  36  of the segment radially outer wall  32  and the downstream end  50  of the segment radially inner wall  34  may yield to the point where they would buckle and possibly meet each other. 
     The inventor has recognized that this failure may be due at least in part to the conventional joining techniques being used. These conventional joining techniques were in accord with conventional combustor design ideologies where it is preferred to have modular designs so when maintenance is required, a single subassembly  10  requiring maintenance could be removed from the combustor through a small opening in the combustor casing. The conventional joining of subassemblies  10  permits this and this greatly simplifies maintenance because it eliminates the need to remove the engine casing, which can be expensive and time consuming, in order to perform this maintenance. 
     In addition to potentially not providing adequate structural support the inventor has recognized other drawbacks associated with the traditional joining techniques. For example, since each joint provides a leakage path, having a joint at each subassembly  10  would decrease engine efficiency since more air would leak. Further, machining the individual components, and in particular the IEP portion, is difficult and time consuming, and the geometry of the IEP portion makes it difficult to properly apply a thermal barrier coating (TBC). The hoop structure of the present invention is stronger, provides fewer leakage paths, and is easier to manufacture. 
       FIG. 2  shows an embodiment of the present invention where the flow duct assembly  100  includes one inlet cone  102  for each combustor (not shown) and the hoop structure  104  made of a single hoop segment  105 . The inlet cone  102  includes an inlet end  106  configured to receive combustion gases from a respective combustor can, an acceleration region  108  indicated generally in which all of the acceleration of the combustion gases occurs, and a throat region  110  indicated generally, where the combustion gases may be collimated, the cross section reshaped, and where a portion of the acceleration may occur. 
     Each inlet cone  102  also includes an outlet  112  configured to deliver the received combustion gases to the hoop structure  104 . The annular hoop structure  104  shares a common axis with the rotor (not shown) of the gas turbine engine. The inlet cone outlet  112  meets a respective hoop structure inlet  114  and form an inlet cone/hoop structure joint  116  (indicated generally in  FIG. 2  though the mating components are spaced apart). A construction of the inlet cone/hoop structure joint  116  may take any form known to those of ordinary skill in the art. For example, there may be fasteners such as bolts, flanges, pins etc. Alternately, the inlet cones  102  may even be welded to the hoop structure  104 . A welded assembly would provide good mechanical resistance to pressure induced loads, but it would be less effective with respect to thermal isolation of the components. Also visible in  FIG. 2  is a location of the throat region  110 , which in this embodiment is disposed in the inlet cone  102  upstream of the inlet cone/hoop structure joint  116 , while the throat region  16  of  FIG. 1  is disposed in the IEP, which is downstream of the cone/IEP joint  15 . 
     The hoop structure  104  in this embodiment includes a radially outer wall  118 , a radially inner wall  120 , both sharing a common axis with the gas turbine engine rotor (not shown), and upstream wall segments  122 . In this embodiment the radially outer wall  118  and the radially inner wall  120  are connected by the upstream wall segments  122 . Thus, the upstream wall segments  122  thus form a non continuous upstream wall  124 , where upstream wall segments  122  are disposed between respective hoop structure inlets  114 . Since both the radially outer wall  118  and the radially inner wall  120  are continuous, single-piece hoop-shaped components, stresses resulting from the pressure difference P 1 :P 3  manifest as a much more uniform hoop stress in each of the walls  118 ,  120 , as opposed to the moment arm of the conventional assembly techniques. Hoop stress resulting from the pressure difference P 1 :P 3  in a hoop shaped component is much less detrimental to the hoop shaped component than is the moment arm/cantilever type stress of the conventional design. Consequently, the hoop structure disclosed herein redistributes stresses in a more manageable manner and this redistribution overcomes the newly discovered weaknesses in the conventional joining techniques when applied to the newly emerging flow duct assembly designs. 
     In the single piece embodiment of  FIG. 2 , maintenance to the hoop structure  104  that cannot be accomplished while the flow duct assembly  100  is in the gas turbine engine would require substantial effort, including removing all of the engine casing upper halves, lifting the rotor shaft, and removing other components from the rotor shaft in order to slide the unitary hoop structure  104  off the shaft for maintenance. However, in other embodiments, such as that shown in  FIG. 3 , the hoop structure  104  may be made of more than one hoop segment. For example, there may be two hoop segments  130 ,  132 . In such an embodiment the two hoop segments may be joined using conventional joining techniques, but with only two places for joining the loss in strength would not be enough to render the design unsatisfactory. The aerodynamic inefficiency due to the two leakage paths would also not significantly reduce engine performance. However, losses and effort related to maintenance would be substantially reduced. In particular, with a two piece design only the combustor/mid engine casing may need to be removed, at which point one of the hoop segments could be lifted out, and then the second could be rotated around the rotor shaft and then be lifted out. In this manner the hoop structure  104  may be removed without the tremendous effort associated with lifting the rotor shaft out of place. These maintenance benefits greatly outweigh any losses that may occur by splitting a single piece hoop structure into two pieces. The embodiment of  FIG. 3  shows two hoop segments.  130 ,  132 , but more than two may be used as necessary. As the number of hoop segments increases so do the losses in strength and engine performance. However, so long as the number of hoop segments is not the same as the number of combustors, and in particular less than the number of combustors, then the losses are not as great as that of flow duct assemblies utilizing subassemblies  10 . 
     In an alternate embodiment, as opposed to the embodiment of  FIGS. 2-3  where the radially outer wall  118  and the radially inner wall  120  are connected by the upstream wall segments  122 , in the embodiment of  FIG. 4  the radially outer wall  118  and the radially inner wall  120  are not directly connected to each other. Instead, an integrated inlet cone  138  has an integrated outlet  140  that serves at least two functions. Similar to the outlet  112  of the embodiment of  FIGS. 2-3 , the integrated outlet  140  delivers the combustion gas flow to the hoop structure  104 . In addition, the integrated outlet  140  spans the gap  141  between the radially outer wall  118  and the radially inner wall  120 , and secures the radially outer wall  118  and the radially inner wall  120 . There are no upstream wall segments  122  between the integrated outlets  140  in this embodiment. By eliminating these upstream wall segments  122 , the moment arm/cantilever effect of the conventionally joined flow duct assemblies brought about by the upstream wall segments  122 , also present to a lesser degree in the embodiments of  FIGS. 2-3 , is essentially eliminated. The integrated outlets  140  themselves will span the radially outer wall  118  and the radially inner wall  120  and as a result there may still be some moment arm effect, but it is expected that it will be mitigated by a tolerance present in an integrated inlet cone/hoop structure joint  142  (indicated generally in  FIG. 4  though the mating components are spaced apart). As a result, in this embodiment the pressure difference P 1 :P 3  may be taken as more of a hoop stress within each of the radially outer wall  118  and the radially inner wall  120 . 
     The integrated outlets  140  would not only span and secure the radially outer wall  118  and the radially inner wall  120  to each other, but without the intervening upstream wall segments  122 , each integrated outlet  140  would also secure to circumferentially adjacent integrated outlets  140 . For example, for a given integrated inlet cone  144 , a circumferentially downstream edge  146  of the integrated outlet  140  of the given integrated inlet cone  144  secures to a circumferentially downstream adjacent integrated inlet cone  148  at a circumferentially upstream edge  150  of the integrated outlet  140  of the downstream adjacent integrated inlet cone  148 . Likewise, a circumferentially upstream edge  152  of the integrated outlet  140  of the given integrated inlet cone  144  secures to a circumferentially upstream adjacent integrated inlet cone  154  at a circumferentially downstream edge  156  of the integrated outlet  140  of the upstream adjacent integrated inlet cone  154 . In this manner when the integrated inlet cones  138  are fully assembled it can be envisioned that they form an assembly which is secured to the radially outer wall  118  and the radially inner wall  120 . 
     In such an embodiment each integrated inlet cone outer wall  158  may have radially outer edges  160 ,  162  that may secure to edges  164 ,  166  (respectively) that are present on each outer wall segment base  168  remaining on the radially outer wall  118 . At the integrated outlet  140  a radially inner side may have tapered to an integrated inlet cone radially inner edge  170 , which may secure to an inner wall segment base region  172  present on the radially inner wall  120 . As a result, since each integrated outlet  138  is secured circumferentially to each other, is secured on a radially outer side to the radially outer wall  118 , and is secured on a radially inner side to the radial inner wall  120 , the assembly is complete. Using the improved hoop design for the radially outer wall  118  and the radially inner wall  120  would provide improved support for the integrated outlets  140 . Consequently there would still be an increase in mechanical strength and an increase in engine efficiency. 
     The particular geometry disclosed is only exemplary and other geometries may be used. Further, for each integrated inlet cone/hoop structure joint  142  there may be one or more than one way of joining each integrated inlet cone  138  to each of the walls  118 ,  120 . For example, a combination of pins and/or bolts etc may be used for each integrated inlet cone/hoop structure joint  142 . So long as in such an embodiment the walls  118 ,  120  are not secured to each other via upstream wall segments  122 , the geometry and way of securing components together may be varied and still be within the scope of the invention. 
       FIG. 5  shows the embodiment of  FIG. 4 , where the radially outer wall  118  and the radially inner wall  120  may themselves be made of two or more segments. For example, the radially outer wall  118  may be made of radially outer wall segments  180 ,  182 . Likewise, the radially inner wall  120  may be made of radially inner wall segments  184 ,  186 . Here again, in such an embodiment the wall segments may be joined using conventional joining techniques, but with only two places for joining the loss in strength would not be enough to render the design unsatisfactory. The aerodynamic inefficiency due to the two leakage paths would also not significantly reduce engine performance. However, losses and effort related to maintenance would be substantially reduced. More than two wall segments may be used as necessary. As the number of wall segments increases so do the losses in strength and engine performance. However, so long as the number of wall segments is not the same as the number of combustors, and in particular less than the number of combustors, then the losses are not as great as that of flow duct assemblies utilizing subassemblies  10 . 
     Accordingly, it has been disclosed that the improved design of the hoop structure  104  of the flow duct assembly  100  provides for increased structural strength. This increased strength enables the hoop structure  104  to withstand the significantly increased mechanical brought about by pressure differences not present in gas turbine engines utilizing conventional transition ducts while decreasing the complexity of the support structure. The increased structural strength also increases the lifespan of the hoop structure  104 , as well as the flow duct assembly  100 , thereby decreasing a life-cycle-cost. The additional strength also allows for elimination of the thickened flanges associated with the flow duct systems employing subassemblies  10  and associated conventional joining techniques. Since the thickened flanges are more difficult to cool, this in turn permits more effective cooling, thereby increasing the flow duct system&#39;s  100  ability to handle the thermal loads generated by the combustion gases. In addition, in embodiments where the inner and outer walls are not connected by a wall segment, the hoop design better accommodates relative movement of the inner and outer walls resulting from thermal growth of the walls themselves and/or the support structures etc. This in turn reduces mechanical loads on the hoop structure and increases its lifespan. Further, the hoop design reduces manufacturing costs because the hoop design components are easier to manufacture, and it is easier to apply a TBC and perform associated laser drilling. In addition, elimination of a joint for every combustor decreases the number of leakage paths, which increases engine efficiency. Consequently, the hoop structure design represents an improvement in the art. 
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.