Patent Application
20130302141
Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade assemblies to these high temperatures. As a result, turbine blades must be made of materials capable of withstanding such high temperatures. In addition, turbine blades often contain cooling systems for prolonging the life of the blades and reducing the likelihood of failure as a result of excessive temperatures.
Typically, turbine blades are formed from a root portion having a platform at one end and an elongated portion forming a blade that extends outwardly from the platform coupled to the root portion. The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge. The inner aspects of most turbine blades typically contain an intricate maze of cooling channels forming a cooling system. The cooling channels in a blade receive air from the compressor of the turbine engine and pass the air through the blade. The cooling channels often include multiple flow paths that are designed to maintain all aspects of the turbine blade at a relatively uniform temperature. However, centrifugal forces and air flow at boundary layers often prevent some areas of the turbine blade from being adequately cooled, which results in the formation of localized hot spots. Localized hot spots, depending on their location, can reduce the useful life of a turbine blade and can damage a turbine blade to an extent necessitating replacement of the blade. Thus, a need exists for a cooling system capable of providing sufficient cooling to turbine airfoils.
A turbine airfoil cooling system for a turbine airfoil used in turbine engines is disclosed. In particular, the turbine airfoil cooling system includes a plurality of internal cavities positioned between outer walls of the turbine airfoil. The cooling system may include a plurality of platform cooling openings positioned in a platform of the turbine airfoil. In particular, the first set of cooling openings may create a first cooling path and a second set of cooling openings may be placed in the path of the first cooling path where the first cooling flow will cool the second set of cooling openings. In addition, the second set of cooling openings may create a second cooling path and additional cooling openings may be placed in the path of previous cooling paths, where the “upstream” cooling flows will provide cooling to the “downstream” cooling openings. In addition, the removal of material from the platform results in the platform weighing less. As the platform weighs less, engine performance will improve.
During use, cooling medium may flow into the cooling system from a cooling medium supply source. The cooling medium may reduce the temperature of the platform and local hot spot. The cooling medium may be exhausted through the downstream edge of the platform. The cooling medium may be a fluid and may form a layer of film cooling air immediately proximate to the outer surface of the platform. This configuration of the cooling system cools the platform with both external film cooling and internal convection. As a result, cooling fluids that cool internal aspects of the platform with convective cooling also will cool external surfaces of the platform with convective film cooling. Such use of the cooling fluids increases the efficiency of the cooling fluids and reduces the temperature gradient of the platform across its width. A potential additional benefit is that the more consistent cooling may allow the platform to be created from less exotic materials that may be less costly.
Another advantage is that the first cooling openings provide a cooling flow to additional cooling openings such that the temperature at the additional cooling opening will be lower. Thus, the additional cooling openings will not have to cool such high temperatures. In addition, the cooling flows from the additional cooling openings will be cooler and will be more effective at later cooling openings. Thus, hot spots on the platform may be reduced resulting in more consistent cooling across the entire platform which will result in a longer life for the platform. This use of cooling opening improves the overall platform cooling efficiency, provides more consistent platform temperatures, reduces the platform metal temperature, reduces platform weight and reduces cooling fluid consumption. These and other embodiments are described in more detail below.
a may illustrate a sample airfoil and platform;
a-4d may illustrate some sample cooling opening shapes;
a and 5b may illustrate additional cooling opening shapes;
In
The shape of the cooling openings 302 may take many forms.
Further, the cooling opening 302 may be created as part of a casting process of the platform 204 which may allow for even more variation, precision and shapes for the cooling openings 302. For example, cores may be shaped to match the desired shape of the cooling opening 302. The cores may be made of compressed sand which may be held together with a binder. The cores may be placed in a mold to create a path for molten metal to flow around and logically, the metal may form around the cores leaving a metallic opening in the shape of the cores.
In other embodiments, wax may be manipulated into a shape of the desired platform 204, including the shape and depth of the cooling openings 302. The mold may be formed around the wax. In some embodiments, the wax may be removed to leave a solid mold. In another embodiment, the wax is left in the mold and when the molten metal is poured into the mold, the wax may burn away leaving a very precise shape for the metal to fill. The result may be a very precise mold and a very precise casting with very precise cooling openings 302.
The path of the cooling openings 302 may have a variety of paths. As illustrated in
The depth of the cooling openings 302 also may be any appropriate depth. The first set of cooling openings 302 may be at a first depth and the second set of cooling openings 304 may be at a second depth where the second depth may be greater than the first depth. In this way, the cooling medium from the first set of cooling openings 302 may exit the output of the first set of cooling openings 302 before the output from the second set of cooling openings 304. As illustrated in
The cooling openings 302 may also proceed to change in width along different lengths of the path. As an example, the paths may start narrow and may widen out as the cooling paths come closer to the surface of the platform 204. In this way, the cooling medium may decelerate as it moves from a smaller opening to a larger opening which may provide additional cooling benefits.
In another embodiment, the cooling openings 302 may be positioned in a way that when the turbine is at its operating speed, the cooling medium will flow from cooling openings in earlier rows over holes in later rows. The position of the cooling openings 302 may be determined through computer simulations or through experiments using actual turbines operating at the desired operating speed to ensure that the cooling medium from previous cooling openings 302 will flow across later cooling openings 304 in the path of the cooling medium. In this embodiment, there may be the same number of cooling openings 302 in each row. In addition, the number of cooling openings 302 may vary based on the flow path in the turbine.
The number of rows of cooling openings may vary depending on a number of factors. If the diameter or surface area of the cooling openings 302 is large, less cooling openings 302 may be needed. If the diameter or surface area of the cooling openings is small, more cooling openings 302 may be needed. In addition, the number and size of the cooling openings 302 may depend on the specific application. For example, some turbine platforms may have few “hot spots” on the platform 204 and the temperature variation from the surrounding area on the may be small. In such cases, fewer cooling openings 302 with fewer rows may be useful. In other examples, a turbine platform 204 may have a large hot spot that may be significantly hotter than its surrounding area. In such a case, more cooling openings 302 with additional rows may be needed.
The rows may be linear or non-linear. Based on a review of the air flow through the turbine 18, it may be useful to have the cooling openings 302 in a non-linear pattern. For example, to provide the desired cooling to later cooling openings 304, the prior cooling openings 302 in the flow pattern may be place in a manner to ensure that the flow from the prior holes 302 flows over the later holes 304 and such placement may not necessarily be linear. The flow path through the turbine may have curves and the cooling openings 302304 placement may vary based on the curve.
During use, cooling medium may flow into the cooling system and out of the cooling openings 302 from a cooling medium supply source. The cooling medium may reduce the temperature of the platform 204 and local hot spot. The cooling medium may be exhausted through the downstream edge of the platform 204. The cooling medium may be a fluid and may form a layer of film cooling air immediately proximate to the outer surface of the platform 204. This configuration of the cooling system may cool the platform 204 with both external film cooling and internal convection. As a result, cooling fluids that cool internal aspects of the platform 204 with convective cooling also will cool external surfaces of the platform 204 with convective film cooling. Such use of the cooling fluids increases the efficiency of the cooling medium and reduces the temperature gradient of the platform 204 across its width. A potential additional benefit is that the more consistent cooling may allow the platform 204 to be created from less exotic materials that may be less costly.
Another advantage is that the first cooling openings 302 provide a cooling flow to additional cooling openings 304 such that the temperature at the additional cooling opening 304 will be lower. Thus, the additional cooling openings 304 will not have to cool such high temperatures. In addition, the cooling flows from the additional cooling openings 304 will be cooler and will be more effective at later cooling openings 306. Thus, hot spots on the platform 204 may be reduced resulting in more consistent cooling across the entire platform 204 which may result in a longer life for the platform 204.
The removal of material from the platform 204 results in the platform 204 weighing less. As the platform 204 weighs less, it may be easier to control and maintain. More specifically, as the turbine 18 is spinning at such a high rate of speed, the weight of the platform 204 becomes a great issue as the high speeds amplify the weight and create significantly more forces on the platform 204. By reducing the weight, the forces will be reduced on virtually all the moving parts related to the platform 204, from bearings to forces on the shaft of the turbine 18.
The described arrangement of cooling openings 202 improves the overall platform 204 cooling efficiency, provides more consistent platform 204 temperatures, reduces the platform 204 metal temperature, reduces platform 204 weight and reduces cooling fluid consumption. As a result, cooling fluids that cool internal aspects of the platform 204 with convective cooling also may cool external surfaces of the platform 204 with convective film cooling. Such use of the cooling fluids may increase the efficiency of the cooling fluids and reduces the temperature gradient of the platform 204 across its width.
A potential additional benefit is that the more consistent cooling may allow the platform 204 to be created from less exotic materials that may be less costly. As is known, finding materials are not overly heavy and that can withstand stress while part of the material is at a significantly different temperature is challenging. The difference in temperature causes varying thermal strains, which result in thermal mechanical fatigue. By creating a more uniform temperature over the platform 204, more materials may be able to withstand the stress and last longer.
In accordance with the provisions of the patent statutes and jurisprudence, exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.
