Abstract:
A wall assembly ( 30 ) for separating a first fluid at a highest pressure and lowest temperature outside ( 86 ) the wall assembly from a second fluid at a lowest pressure and highest temperature inside ( 88 ) the wall assembly. The wall assembly ( 30 ) having: a structural cold wall ( 32 ) for exposure to the first fluid and partly defining a first cavity ( 78 ), and a structural cold wall aperture ( 42 ) for creating a first pressure drop ( 52 ); a structural middle wall ( 34 ) partially defining the first cavity ( 78 ) and partially defining a second cavity ( 84 ), and a structural middle wall aperture ( 44 ) for creating a second pressure drop ( 54 ); and a floating wall ( 38 ) for exposure to the second fluid and partially defining the second cavity ( 84 ), and a floating wall aperture ( 46 ) for creating a third pressure drop ( 56 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to construction of thermally loaded components. Specifically, this invention relates to construction of highly thermally loaded gas turbine engine components subject to high mechanical loads resulting from interior pressure differentials. 
     BACKGROUND OF THE INVENTION 
     Conventional gas turbine engines discharge combustion gasses from a combustor to a transition which directs the combustion gasses to the first stage of the turbine. The combustion gasses inside the transition are traveling faster than the pressurized air outside of the transition. This creates a relatively low pressure inside the transition compared to outside the transition. This pressure difference generates a mechanical load which the transition must bear. These mechanical loads must be borne at the same time the transition bears the thermal loads created by the hot combustion gasses inside the transition and the relatively cooler air outside the transition. Some new transition technologies are increasing combustion gas speeds and consequently creating a need for gas turbine engine component structures that can withstand greater mechanical loads while also handling greater thermal loads. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a single flow directing structure. 
         FIG. 2  is a cross section of the thermally isolated hot wall assembly. 
         FIG. 3  is a cross section of an embodiment of a floating wall element with a cooling channel. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Combustion gasses traveling in conventional gas turbine engine transitions commonly travel at speeds up to mach 0.3. Conventional transitions have been developed that can handle the mechanical loads generated by combustion gasses traveling at mach 0.3, but some emerging technologies may produce greater combustion gas speeds which would generate greater mechanical loads that may exceed the capacity of conventional transition designs. The increased speed of the combustion gas in transitions using these emerging technologies results in higher heat transfer coefficients and greater pressure differences from outside the transition to inside the transition. Consequently, these new technology transitions require improved thermal capacity while simultaneously requiring improved mechanical load capacity resulting from the greater pressure drop. 
     A recent design innovation, as disclosed in co-pending and commonly assigned U.S. patent publication no. 201000077719 to Wilson et al., filed on Apr. 8, 2009 and incorporated by reference herein, replaces the conventional transition, seals, and vanes with an assembly of flow directing structures that transports expanded gasses from each combustion chamber to an annular chamber. In the annular chamber the previously discrete flows are no longer separated from each other by walls but are united into a single annular flow prior to entering the first stage turbine blades. By using fewer seals, aerodynamic losses due to seals are reduced. The newer design uses the entire length of the duct to properly orient the flow, while the designs of the prior art used vanes at the end of the duct to orient the flow, which resulted in a relatively abrupt change in the flow direction, and associated energy losses. Further, this newer design reduces costs associated with assembly and maintenance. 
     A single flow directing structure of the assembly of commonly assigned U.S. patent publication no. 201000077719 to Wilson et al. is shown in  FIG. 1  and is representative of emerging technology that is placing increased demands on the structural and thermal load capacity of gas turbine engine components. The assembly is a collection of flow directing structures  12 , one for each combustor can  18 , and each flow directing structure may comprise a cone  14  and an integrated exit piece (IEP)  16 . Alternately, each flow directing structure may be a single component. A cross section of the cone  14  is substantially reduced as the combustion gasses travel in a downstream direction. Consequently the cone is subject to high thermal stress along its entire cone longitudinal axis  22 . This reduction of a gas flow path cross sectional area is significantly greater in this design than in conventional gas turbine engine transition design, but the mass flow rate of combustion gasses remains comparable. The same mass flow rate of combustion gas flowing through a gas flow path with a reduced cross section results in an increase in the speed of the combustion gasses during transit to the first row of blades. The increased combustion gas flow speed reduces pressure inside the flow directing structure. This increased pressure difference results in a greater mechanical load across the flow directing structure. For example, a mach 0.3 combustion gas flow may create approximately a 3% total drop in pressure from outside the transition to inside the transition. A mach 0.8 combustion gas in a flow directing structure  12 , such as in  FIG. 1 , may create approximately a 30% drop in pressure from outside the IEP  16  to inside the IEP  16 , producing considerably greater mechanical load. Furthermore, the higher velocities generate higher heat transfer coefficients, thereby increasing the thermal load on the transition. The increased mechanical loading together with the increased thermal loading may approach, if not exceed, the capacity of conventional single and double wall transition technology. 
     The present inventor has conceived of an innovative wall structure capable of handling both the increased mechanical load and the increased thermal load of the new technology flow directing structure  12 . In the innovative wall structure the mechanical loads induced by pressure differences are borne primarily by the structural components of the wall, while the thermal loads are borne primarily by the thermal components. Furthermore, the junction between the structural components and the thermal components is configured so that the mechanical loads borne by the structural components are essentially isolated from the thermal components, and the thermal loads born by the thermal components are essentially isolated from the structural components. Specifically, the floating wall elements of the floating wall are not solidly affixed to the structural components (i.e. welded etc), but instead are trapped, and free to float, and expand and contract in response to thermal loads and gradients. 
     This configuration may produce several advantages. For example, the assembly uses apertures in respective walls to control a pressure drop across each respective wall. Apertures like these may also be required to provide cooling air for the walls and/or other walls or elements, such as impingement cooling. However, a pattern optimized for creating a certain pressure drop may not be optimal for cooling. A three wall configuration permits two of the walls to bear a majority of any pressure related mechanical load, while aperture patterns in each of the structural walls can be tailored for a desired task. For example, apertures through a cold, structural outer wall may be patterned to produce a desired larger pressure drop, while apertures through a middle structural wall may be tailored to provide impingement cooling of the inner, hot wall. Thus, while apertures in both structural walls would be achieving a pressure drop and cooling in each wall, each wall could be optimized for one task over the other. In short, having multiple structural walls enables a greater choice of aperture patterning and permits both optimal pressure drop control and cooling control not available in prior designs. 
     In addition, during operation thermals may tend to drive the mouth region  20  of the IEP  16  open and/or closed, which is undesirable for aerodynamic reasons. The stronger wall assembly may reduce this phenomenon. Also, the floating wall elements are modular, which means they can be replaced as needed, as opposed to replacing the entire IEP  16  should there be damage to the floating wall, which produces a savings in time and materials. Further, task specific materials can be chosen for the floating wall elements and for the remaining components, and they can be different from each other. In an embodiment, simple shapes for the floating wall elements may result in reduced stress in the floating wall element, which may in turn permit greater material choice. In an embodiment materials being considered include oxide dispersion strengthened alloys, which have superior heat properties, and single-crystal alloys for greater creep and fatigue strength. Also, should a floating wall element  38  sustain damage it can be switched out with a new one while the remainder of the wall assembly remains unchanged. Thus, repairs may be less costly. 
     A cross section of a wall assembly  30  can be seen in  FIG. 2 . The wall assembly  30  includes a structural cold wall  32 , a structural middle wall  34 , a floating wall  36  including at least one floating wall element  38 , and a joining member  40 . A structural cold wall inner side  74  and a structural middle wall outer side  76  partially define a first gap (or cavity)  78 . A structural middle wall inner side  80  and a floating wall outer side  82  partially define a second gap (or cavity)  84 . The structural cold wall  32  includes structural cold wall apertures  42  that transfer air from a region outside the wall assembly  86  to the first gap  78 . The structural middle wall  34  includes structural middle wall apertures  44  that transfer air from the first gap  78  to the second gap  84 . The floating wall elements include floating wall element apertures  46  that transfer air from the second gap  84  to a hot gas flow path  88 . The structural cold wall  32  and the structural middle wall  34  are joined with a joining member  40 . They may be welded, or bolted etc. The manner of connection is only relevant to the extent that it provide sufficient strength to the structural cold wall  32  and the structural middle wall  34 . The joining member  40  has a geometric feature  48  which can receive a floating wall element engaging feature  50 . A specific configuration of the geometric feature  48  and the floating wall element engaging feature  50  is not required. What is required is any configuration catches and “traps” permits the floating wall element  38  in such a manner that the floating wall element  38  is free to float, expand, and contract, yet remain engaged with the geometric feature  48 . The geometric feature  48  may be elongated, such as a slot, so that individual floating wall elements can be removed and/or installed readily. The edges of the wall assembly  30  can be sealed and damped, or lead to other joining members  40  etc. Cooling can be provided as needed with dedicated cooling holes and/or intentional leakage of cooling air from outside the IEP  16  to inside, for example by joining member cooling aperture  70 . 
     Structurally, the three walls are configured such that any mechanical load is isolated, or at least mostly isolated, from the floating wall elements  38 . This means that in an embodiment the structural cold wall  32 , the structural middle wall  34 , and the joining member  40  may bear a majority of the pressure induced mechanical load. While a single, universally ideal mechanical load distribution is not envisioned, what is envisioned is the ability to partially or fully unload the floating wall element of pressure induced mechanical loads by configuring cooling holes in the components such that a structural cold wall pressure drop  52  and a structural middle wall pressure drop  54  are each (or both together are) greater than a floating wall element pressure drop  56 . Specifically, the structural cold wall apertures  42  are of a number, size, and pattern etc that produce a relatively large structural cold wall pressure drop  52  compared to the floating wall element pressure drop  56 . Similarly, the structural middle wall apertures  44  are of a number, size, and pattern etc. that produce a relatively large structural middle wall pressure drop  54  compared to the floating wall element pressure drop  56 . The floating wall element pressure drop  56  is envisioned to be any value up to but not including 50% of the total pressure drop  58 . In an embodiment the floating wall element pressure drop  56  is envisioned to be significantly lower than that, with the substantial majority of the total pressure drop  58  being borne by the structural cold wall  32 , the structural middle wall  34 , and the joining member  40 . Between the structural cold wall  32 , the structural middle wall  34 , and the joining member  40  the majority of the structural load may be distributed in whatever manner is deemed most beneficial in terms of design and materials. In an embodiment the floating wall element pressure drop  56  may be on the order of 33% or less of the total pressure drop  58 . In another embodiment the floating wall element pressure drop  56  may be on the order of 25% or less of the total pressure drop  58 . 
     Thermal loads may be experienced in conventional transition configurations because material exposed to the combustion gasses may expand more than the structural components that support but simultaneously constrain the material exposed to the combustion gasses. The configuration disclosed herein mechanically unloads the floating wall elements  38 , leaving it free to expand and contract unrestrained by the structural elements. As a result, thermal growth differences between the floating wall elements  38  and the structural elements do not produce stress in the floating wall elements  38 . The reduction in thermal stress present in the floating wall elements  38  increases the material and design options for the floating wall elements  38 . Specifically, the floating wall elements  38  may now be optimized for thermal performance characteristics. 
     ODS alloys may work extremely well in configurations such as in an IEP  16  because ODS alloys have superior thermal characteristics. However, it is difficult to produce ODS alloy components with complex geometry. Since the floating wall elements  38  may be of a simple geometry, the floating wall elements  38  may be made of ODS alloy without incurring unacceptable manufacturing losses. Similarly, the relatively simple geometry of the floating wall allows use of single crystal alloys which provide great creep and fatigue strength. 
     The structural cold wall  32  and the structural middle wall  34  can thus be configured to distribute the pressure related mechanical forces among themselves and the joining member  40  by designing and patterning their respective apertures to minimize or at least reduce cooling air there through. The structural cold wall  32  and the structural middle wall  34  may also, because they are exposed to lower temperatures, be designed using thermally inefficient shapes to enhance their strength. 
     The floating wall elements  38  may be cooled using cooling air that travels through the structural middle wall apertures  44 . This may take the form of impingement cooling, where the cooling air is directed onto the floating wall elements  38  via the configuration and location of the structural middle wall apertures  44 . That cooling air may then exit into the combustion gasses through the floating wall element apertures, such as film holes or slots. 
     In a cross section of an alternate embodiment, as shown in  FIG. 3 , the floating wall element  38  may have a cooling channel  64  instead of film holes or slots. Cooling air may enter the cooling channel  64  via a cooling channel inlet  66 , travel through the cooling channel  64 , and exit through a cooling channel outlet  68 . The cooling channel inlet  66  and the cooling channel outlet  68  may be offset from each other so that the cooling fluid does not travel straight through the floating wall element  38 , but instead must turn, or redirect before exiting the floating wall element  38 . The floating wall element  38  may be solid with a cooling channel  64  there through. Alternately the cooling channel  64  may be porous. A porous interior exposes more surface area to the cooling air, increasing cooling. The porous interior may be uniformly porous, or it may be non-uniformly porous. In an embodiment the cooling channel  64  may be more porous away from the surfaces of the floating wall element  38  and more porous toward the surfaces of the floating wall element  38 . Such an embodiment is advantageous in that it may generate very high effective heat transfer resulting in minimizing floating wall element thermal gradients. Finally, the floating wall element may have a thermal barrier coating  72  added. 
     It can be seen that the inventor has devised an innovative solution to a problem resulting from the emergence of new gas turbine engine technology. This technology requires a single component to be able to withstand greater mechanical loads while simultaneously withstanding greater thermal loads. Not only does this wall assembly solve the problem associated with the emerging technology, but it is capable of withstanding structural and thermal loads beyond that which is required of the emerging technology, making it useful for applications with yet even greater mechanical and thermal load requirements. Yet the current wall assembly accomplishes this in a cost effective manner, and provides the further advantage that subsequent repairs are made easy and less expensive due to the modular nature of the floating wall elements. 
     The inventors envision the structure disclosed herein may be used in a variety of environments requiring structural and thermal capacity. Consequently, while the disclosure has focused on new technology such as the flow directing structure of  FIG. 1 , it is not meant to be limited to such an assembly. Any component lending itself to this structure may employ this structure and is considered to be within the scope of the disclosure. For example, but not limiting, conventional transitions could employ this structure, as could combustor liners etc. 
     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.