Patent Application
20120204727
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.
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.
The invention is explained in the following description in view of the drawings that show:
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
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
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
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
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.
