Strut cover for a turbine

A turbine operable to convey a flow of exhaust gas along a central axis includes a strut having a flow portion positioned within the flow of exhaust gas and a strut cover having a length and positioned to surround the flow portion of the strut, the strut cover including a leading-edge portion, a mid-chord portion, and a trailing-edge portion. The mid-chord portion has a uniform cross-section, and the trailing-edge portion has a trailing-edge center positioned such that the mid-chord portion and the trailing-edge portion define a master chord plane. The leading-edge portion defines a leading-edge nose, and the leading-edge portion is twisted with respect to the master chord plane and the leading-edge nose along the length defines a curve that is not coincident with the master chord plane.

BACKGROUND

Turbine engines, including gas turbines and steam turbines include an exhaust section in which a working fluid is exhausted from the turbine. In the case of gas turbines, the working fluid is a flow of combustion gas while a steam turbine exhausts a flow of steam and/or water vapor. Often, struts are placed in this exhaust flow to support components such as bearings that are positioned in the flow. These struts can interfere with the flow and create an increased backpressure that reduces the efficiency of the turbine.

BRIEF SUMMARY

In one construction, a turbine operable to produce a flow of exhaust gas along a central axis includes a strut having a flow portion positioned within the flow of exhaust gas and a strut cover having a length and positioned to surround the flow portion of the strut, the strut cover including a leading-edge portion, a mid-chord portion, and a trailing-edge portion. The mid-chord portion has a uniform cross-section, and the trailing-edge portion has a trailing-edge center positioned such that the mid-chord portion and the trailing-edge portion define a master chord plane. The leading-edge portion defines a leading-edge nose, and the leading-edge portion is twisted with respect to the master chord plane and the leading-edge nose along the length defines a curve that is not coincident with the master chord plane.

In another construction, a turbine includes an exhaust portion having an inner flow liner and an outer flow liner that cooperate to define an annular flow space, the annular flow space arranged to receive a flow in a flow direction. A strut cover is positioned in the annular flow space and has a length normal to the flow direction between the inner flow liner and the outer flow liner. The strut cover includes a uniform mid-chord portion that defines a master chord plane, a trailing-edge portion having a trailing-edge center that resides on the master chord plane, and a leading-edge portion having a leading-edge nose that is twisted with respect to the master chord plane such that the leading-edge nose intersects the master chord plane at no more than one point along the length.

In still another construction, a turbine includes an exhaust portion having an inner flow liner and an outer flow liner that cooperate to define an annular flow space. A strut has a flow portion positioned in the annular flow space and extending along an axis between the inner flow liner and the outer flow liner. A strut cover is positioned in the annular flow space and extends between the inner flow liner and the outer flow liner, the strut cover surrounding the flow portion and including a leading-edge portion, a mid-chord portion, and a trailing-edge portion that cooperate to define a plurality of cross-sections normal to the axis. Each cross-section defines a camber line and the camber lines in the mid-chord portion and the trailing-edge portion overlay one another and the camber lines in the leading-edge portion do not overlay one another.

DETAILED DESCRIPTION

Various technologies that pertain to systems and methods will now be described with reference to the drawings, where like reference numerals represent like elements throughout. The drawings discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged apparatus. It is to be understood that functionality that is described as being carried out by certain system elements may be performed by multiple elements. Similarly, for instance, an element may be configured to perform functionality that is described as being carried out by multiple elements. The numerous innovative teachings of the present application will be described with reference to exemplary non-limiting embodiments.

Also, it should be understood that the words or phrases used herein should be construed broadly, unless expressly limited in some examples. For example, the terms “including,” “having,” and “comprising,” as well as derivatives thereof, mean inclusion without limitation. The singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The term “or” is inclusive, meaning and/or, unless the context clearly indicates otherwise. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Furthermore, while multiple embodiments or constructions may be described herein, any features, methods, steps, components, etc. described with regard to one embodiment are equally applicable to other embodiments absent a specific statement to the contrary.

Also, although the terms “first”, “second”, “third” and so forth may be used herein to refer to various elements, information, functions, or acts, these elements, information, functions, or acts should not be limited by these terms. Rather these numeral adjectives are used to distinguish different elements, information, functions or acts from each other. For example, a first element, information, function, or act could be termed a second element, information, function, or act, and, similarly, a second element, information, function, or act could be termed a first element, information, function, or act, without departing from the scope of the present disclosure.

In addition, the term “adjacent to” may mean: that an element is relatively near to but not in contact with a further element; or that the element is in contact with the further portion, unless the context clearly indicates otherwise. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Terms “about” or “substantially” or like terms are intended to cover variations in a value that are within normal industry manufacturing tolerances for that dimension. If no industry standard is available, a variation of twenty percent would fall within the meaning of these terms unless otherwise stated.

FIG.1illustrates an example of a gas turbine engine100including a compressor section102, a combustion section106, and a turbine section110arranged along a central axis114. The compressor section102includes a plurality of compressor stages116with each compressor stage116including a set of rotating blades118and a set of stationary vanes120or adjustable guide vanes. A rotor122supports the rotating blades118for rotation about the central axis114during operation. In some constructions, a single one-piece rotor122extends the length of the gas turbine engine100and is supported for rotation by a bearing at either end. In other constructions, the rotor122is assembled from several separate spools that are attached to one another or may include multiple disk sections that are attached via a bolt or plurality of bolts.

The compressor section102is in fluid communication with an inlet section124to allow the gas turbine engine100to draw atmospheric air into the compressor section102. During operation of the gas turbine engine100, the compressor section102draws in atmospheric air and compresses that air for delivery to the combustion section106. The illustrated compressor section102is an example of one compressor section102with other arrangements and designs being possible.

In the illustrated construction, the combustion section106includes a plurality of separate combustors126that each operate to mix a flow of fuel with the compressed air from the compressor section102and to combust that air-fuel mixture to produce a flow of high temperature, high pressure combustion gases or exhaust gas128. Of course, many other arrangements of the combustion section106are possible.

The turbine section110includes a plurality of turbine stages130with each turbine stage130including a number of rotating turbine blades104and a number of stationary turbine vanes108. The turbine stages130are arranged to receive the exhaust gas128from the combustion section106at a turbine inlet132and expand that gas to convert thermal and pressure energy into rotating or mechanical work. The turbine section110is connected to the compressor section102to drive the compressor section102. For gas turbine engines100used for power generation or as prime movers, the turbine section110is also connected to a generator, pump, or other device to be driven. As with the compressor section102, other designs and arrangements of the turbine section110are possible.

An exhaust portion112is positioned downstream of the turbine section110and is arranged to receive the expanded flow of exhaust gas128from the final turbine stage130in the turbine section110. The exhaust portion112is arranged to efficiently direct the exhaust gas128away from the turbine section110to assure efficient operation of the turbine section110. The exhaust portion112also includes one or more strut assemblies200that will be discussed in greater detail with regard toFIG.2. Many variations and design differences are possible in the exhaust portion112. As such, the illustrated exhaust portion112is but one example of those variations.

A control system134is coupled to the gas turbine engine100and operates to monitor various operating parameters and to control various operations of the gas turbine engine100. In preferred constructions the control system134is typically micro-processor based and includes memory devices and data storage devices for collecting, analyzing, and storing data. In addition, the control system134provides output data to various devices including monitors, printers, indicators, and the like that allow users to interface with the control system134to provide inputs or adjustments. In the example of a power generation system, a user may input a power output set point and the control system134may adjust the various control inputs to achieve that power output in an efficient manner.

The control system134can control various operating parameters including, but not limited to variable inlet guide vane positions, fuel flow rates and pressures, engine speed, valve positions, generator load, and generator excitation. Of course, other applications may have fewer or more controllable devices. The control system134also monitors various parameters to assure that the gas turbine engine100is operating properly. Some parameters that are monitored may include inlet air temperature, compressor outlet temperature and pressure, combustor outlet temperature, fuel flow rate, generator power output, bearing temperature, and the like. Many of these measurements are displayed for the user and are logged for later review should such a review be necessary.

FIG.2is an enlarged cross-sectional view of a strut assembly200. It should be understood that most gas turbine engines100include several strut assemblies200that are similar to or identical to the one illustrated inFIG.2. Typically, the strut assemblies200are positioned at a common axial location and distributed equally around the central axis114of the gas turbine engine100(e.g., four strut assemblies200would be ninety degrees apart). Of course, other arrangements and spacing are possible including unequal spacings, axially varying spacing, and even varying alignments of the different strut assemblies200.

Each strut assembly200includes a strut210and a strut cover500arranged to cover the strut210. In the illustrated construction, the strut210includes a first end that is fixedly attached to an outer casing202and a second end that is fixedly attached to a bearing casing206for a bearing (not shown). A flow portion216of the strut210extends between an inner flow liner208and an outer flow liner204where it is potentially exposed to the exhaust gas128. Of course, each end could be attached to a different component as may be required by the design of the gas turbine engine100. Attached as described, the strut210serves to rigidly attach the outer casing202and the bearing casing206, thereby providing the necessary support for the bearing casing206and the rotor122which is supported by the bearing. The strut210passes through the outer flow liner204and the inner flow liner208and may or may not be attached to one or both of the outer flow liner204and the inner flow liner208. The outer flow liner204and the inner flow liner208cooperate to define an annular flow space218through which the exhaust gas flows in a flow direction222.

In many constructions, one or more of the struts210are hollow to provide a passage between the interior of the gas turbine engine100and the exterior. The passage is often used to direct instrument wires, air lines, lubricant lines and the like. For example, in the illustrated construction, one of the struts210would include lubricant lines that direct lubricant fluid to and from the bearing. In addition, vibration sensors within the bearing often require wires to pass the signals from the sensors to the exterior of the gas turbine engine100where they can be routed to the control system134.

In some constructions, cross-strut assemblies are provided between some or all the adjacent pairs of strut assemblies200. The cross-strut assemblies provide additional support and stability if needed. Each cross-strut assembly includes a cross-strut (often referred to as a gusset) and may include a cross-strut cover if the cross-strut is in the exhaust flow. The cross-strut provides the desired structural support and can be any shape, cross-section, or configuration desired. For example, box beams, I-beams, or solid beams could be employed as cross-struts.

The cross-strut cover surrounds or at least partially surrounds the cross-strut and is aerodynamically shaped to reduce any backpressure increase that might be caused by the cross-strut if it were in the flow of exhaust gas exiting the turbine. The cross-strut cover does not necessarily provide any structural support and can therefore be made from a thin sheet material. However, some constructions may use a more rigid or thicker material for the cross-strut cover such that it does provide some structural support. It should be noted that many gas turbine engine100constructions do not include or require cross-strut assemblies.

In preferred constructions, each strut210is welded to the outer casing202and the bearing casing206. However, some constructions may use other attachment means such as fasteners. Similarly, each cross-strut is preferably welded to the struts210between which the cross-strut extends.

With continued reference toFIG.2, the strut cover500extends from the outer flow liner204to the inner flow liner208and covers the strut210. As illustrated inFIG.2, each strut cover500cooperates with the outer flow liner204and the inner flow liner208to define two wall fillets220. Of course, other constructions could omit one or both of the wall fillets220.

Each strut cover500is aerodynamically shaped and covers one of the struts210so that the shape of the strut210can be selected for strength and stiffness without concern for aerodynamics. Thus, each strut210could be formed from a box beam, I-beam, solid beam, channel beam, or any other shape or combination of shapes desired.

The aerodynamic shape of the strut cover500includes a curved or elliptical leading-edge portion504and a narrower curved or elliptical trailing-edge portion620. Tapered surfaces extend between the leading-edge portion504and the trailing-edge portion620to define a mid-chord portion622(illustrated inFIG.6) to complete the shape.

In the illustrated construction, the leading-edge portion504extends along the length of the strut cover500and maintains a uniform axial position. Thus, the leading-edge portion504is substantially normal to the central axis114. In the illustrated construction, the trailing-edge portion620is arranged normal to the central axis114. Of course, in some constructions, one or both of the leading-edge portion504and the trailing-edge portion620may have a taper or lean such that the leading-edge portion504and/or the trailing-edge portion620defines an oblique angle with respect to the central axis114. For example, the strut cover500illustrated inFIG.6andFIG.7includes a tapered or leaning trailing-edge portion620.

FIG.3illustrates a first arrangement of a plurality of strut assemblies300which includes three separate strut assemblies200arranged about 120 degrees apart (circumferentially) from one another (i.e., within typical manufacturing tolerances). As illustrated inFIG.3, each of the strut assemblies200extends along an axis that is oblique to a radial axis of the gas turbine engine100. Specifically, each strut assembly200extends from the inner flow liner208to the outer flow liner204along a line or axis that is tangent to the bearing casing206. More specifically, the master chord plane302of each strut assembly200is arranged to be tangent to the bearing casing206.

While three equally spaced, non-radial strut assemblies200are illustrated inFIG.3, other arrangements could vary the spacing between the strut assemblies200, could include additional strut assemblies200, or could include one or more radially arranged strut assemblies200.

FIG.4illustrates a second arrangement of a plurality of strut assemblies400that includes six strut assemblies200arranged around the circumference of the bearing casing206. The arrangement includes a top-dead-center strut assembly200and a bottom-dead-center strut assembly200arranged along master chord planes302that are coincident with a radial plane that intersects the central axis114. Two additional strut assemblies200are arranged along master chord planes302that are coincident with radial planes in the upper portion of the gas turbine engine100. The final two strut assemblies200are arranged along non-radial master chord planes302in the lower portion of the gas turbine engine100.

As with the arrangement ofFIG.3, other arrangements could include different or equal spacing between the strut assemblies200, additional or fewer strut assemblies200, and more or fewer radially aligned master chord planes302.

It is important to note that the arrangement, positioning, or number of strut assemblies200employed in the gas turbine engine100are not critical to the arrangement of the strut cover500as the arrangements described with regard toFIG.5throughFIG.7are not affected by any of these factors.

FIG.5is an axial view of one of the strut covers500looking in the flow direction222of the exhaust gas128. A master chord plane302(sometimes referred to as a skeleton plane or a center plane) is illustrated as a plane that passes through the full length of the strut cover500and substantially bisects the strut cover500. A leading-edge nose502is defined as the locus of the furthest upstream points (i.e., the leading-edge center604) of the leading-edge portion504of the various cross-sections taken parallel to the flow direction of the strut cover500. As illustrated inFIG.5, the leading-edge nose502defines a curve that does not reside on or coincide with the master chord plane302but rather is offset from and, in this construction crosses the master chord plane302at no more than one location.

It should be noted that some constructions could include a leading-edge nose502that defines a curve that never crosses the master chord plane302with preferred constructions including a single crossing. In some constructions, multiple crossings could occur with the leading-edge nose502resembling a parabola, a hyperbola, or a higher order curve.

FIG.6better illustrates the aerodynamic shape of one possible arrangement of the strut cover500. Specifically,FIG.6illustrates five cross-sections each taken at a different distance from the inner flow liner208to better illustrate the variation in the shape of the strut cover500over the length of the strut cover500.

FIG.6illustrates a master chord plane302that substantially bisects the various cross-sections (i.e., with the exception of the leading-edge portion504which is not necessarily bisected). The master chord plane302is parallel to the general direction of flow and provides a reference for the various cross-sections.

The master chord plane302defines a camber line for each cross-section having a leading-edge center604and a trailing-edge center614on the master chord plane302. A camber line is defined as the locus of points halfway between a first curved edge616and a second curved edge618that define the complete strut cover500. For a symmetrical strut cover500having a leading-edge center604that is not twisted, the camber line is located on the master chord plane302. The camber lines of the other cross-sections are generally coincident with the master chord plane302from the trailing-edge center614to a point near the leading-edge portion504where the camber line will diverge slightly to match the twist of the leading-edge portion504for each cross-section.

A first cross-section602is taken along line1-1ofFIG.5at a point near the intersection of the strut cover500and the inner flow liner208. The first cross-section602defines a trailing-edge center614that intersects the master chord plane302and a leading-edge nose502that is offset from the master chord plane302. The distance between the trailing-edge center614and the leading-edge center604of the first cross-section602defines a first length624of the strut cover500.

A second cross-section606of the strut cover500is taken along line2-2ofFIG.5at a point near the intersection of the strut cover500and the outer flow liner204. The second cross-section606also defines a trailing-edge center614that falls on the master chord plane302and a leading-edge center604that is offset from the master chord plane302. The distance between the trailing-edge center614and the leading-edge center604of the second cross-section606defines a second length of the strut cover500. The second length626is shorter than the first length624as the strut cover500includes a tapered or leaning trailing-edge portion620.

A third cross-section608of the strut cover500is taken along line3-3ofFIG.5at about the midpoint of the strut cover500. The third cross-section608also defines a trailing-edge center614that falls on the master chord plane302and a leading-edge center604that is offset from the master chord plane302. The distance between the trailing-edge center614and the leading-edge center604of the third cross-section608defines a third length of the strut cover500. The third length is between the first length624and the second length626.

A fourth cross-section610of the strut cover500is taken along line4-4ofFIG.5at a point between the first cross-section602and the third cross-section608of the strut cover500. The fourth cross-section610also defines a trailing-edge center614that falls on the master chord plane302and a leading-edge center604that is offset from the master chord plane302. The distance between the trailing-edge center614and the leading-edge center604of the fourth cross-section610defines a fourth length of the strut cover500. The fourth length is between the first length624and the third length.

A fifth cross-section612of the strut cover500is taken along line5-5ofFIG.5at a point between the second cross-section606and the third cross-section608of the strut cover500. The fifth cross-section612also defines a trailing-edge center614that falls on the master chord plane302and a leading-edge center604that is offset from the master chord plane302. The distance between the trailing-edge center614and the leading-edge center604of the fifth cross-section612defines a fifth length of the strut cover500. The fifth length is between the second length626and the third length.

In the construction illustrated inFIG.5,FIG.6, andFIG.7, the leading-edge nose502crosses the master chord plane302at some point between the first cross-section602and the fourth cross-section610near the fourth cross-section610. Of course, other constructions could include a different arrangement that results in the leading-edge nose502crossing the master chord plane302at a different point. In addition, different twists, including larger twists, smaller twists, and twists in different directions are contemplated, including arrangements in which the leading-edge nose502does not cross the master chord plane302.

The leading-edge portion504of each of the cross-sections is arranged such that regardless of the location of the leading-edge center604, the leading-edge portion504blends into the first curved edge616and the second curved edge618that are aligned in the length direction of the strut cover500for all the cross-sections. Thus, when viewed in the length direction, as illustrated inFIG.6, the first curved edges616of all the cross-sections overlay one another and appear coincident. Similarly, the second curved edges618of all the cross-sections overlay one another and appear coincident.

With continued reference toFIG.6, each of the first curved edges616blends into its respective trailing-edge portion620such that as the first curved edges616approach their respective trailing-edge portion620they diverge from one another. Similarly, each of the second curved edges618blends into its respective trailing-edge portion620such that as the second curved edges618approach the trailing-edge portion620they diverge from one another.

In constructions in which the trailing-edge portion620does not have a lean or a slant, the trailing-edge portions620of each of the various cross-sections will overlay one another and appear to be coincident when viewed in the length direction such as that illustrated inFIG.6.

FIG.7is an enlarged view of the leading-edge portion504of the strut cover500that better illustrates the offsets of the leading-edge portions504of the various cross-sections. As can be seen, the first cross-section602defines a first leading edge center702that is illustrated as being above the master chord plane302. This would correspond with a twist to the left of the master chord plane302or counterclockwise when looking in the direction of flow (i.e., inFIG.5). The fourth cross-section610defines a fourth leading edge center704that is illustrated as falling slightly below the master chord plane302. Thus, the leading-edge nose502crosses the master chord plane302at some point between the first cross-section602and the fourth cross-section610. The remaining cross-sections are offset further below the master chord plane302with the second cross-section606and the fifth cross-section612being very close to one another. The twist of these cross-sections corresponds to a twist to the right or clockwise when looking in the direction of flow (i.e., inFIG.5). Of course, different twist shapes, directions, magnitudes, and crossing points are possible such that the invention should not be limited to the example provided herein. Thus, the strut cover500illustrated inFIG.6andFIG.7has an aerodynamic shape that includes a twist of the leading-edge portion212with respect to the master chord plane302but that also includes a mid-chord portion622and a trailing-edge portion214that are symmetric with respect to the master chord plane302.

In use, a plurality of struts210are attached to the outer casing202and the bearing casing206or other internal component to support the bearing casing206(or any other internal component) in the desired position. The size, shape, and quantity of struts210are selected to provide the desired support and stiffness for the bearing casing206or other internal components. In the illustrated construction, the bearing casing206at least partially supports the rotor122and must provide the necessary strength for that support as well as a sufficient rigidity to minimize unwanted vibrations.

Strut covers500extend between the inner flow liner208and the outer flow liner204and cover the strut210to protect the interior components from direct contact with the exhaust gas128and to provide an aerodynamic shape that reduces losses that could arise in response to flow interruptions caused by the struts210. The strut covers500include a leading-edge portion504that defines a leading-edge nose502that is preferably positioned such that a tangent to the leading-edge nose502is normal to the flow direction.

However, during operation, the flow exiting the turbine section110may have some swirl or spin. The strut covers500are similarly twisted to align the leading-edge nose502normal to the flow at all locations. At some point along the length of the strut covers500the flow exiting the turbine section110is flowing parallel to the central axis114and at this point the leading-edge nose502is aligned with the master chord plane302that divides each strut cover500. Between this point and the inner flow liner208, the leading-edge nose502may be twisted in a first direction and between this point and the outer flow liner204, the leading-edge nose502may be twisted in the opposite direction.