BACKGROUND

The disclosure relates generally to cooled structures of a gas turbine and more specifically systems and methods relating to turbine airfoils.

In a large frame heavy-duty industrial gas turbine engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature may be limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.

The first stage rotor and stator components are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) should be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the cooled surface from the hot gas stream.

The turbine rotor blades are often formed using investment casting and metallic super-alloy materials, which have high tolerance to mechanical stress and strain, as well as thermal stresses and gradients. However, the geometries and features that can be formed via the investment casting process are limited.

SUMMARY

Aspects and advantages of the disclosure will be set forth in part in the following description, or may be learned through practice of the disclosure.

In one embodiment, an airfoil includes an airfoil body portion, an airfoil tip portion disposed radially outward of the airfoil body portion, an airfoil root portion, and a plurality of radial cooling passages extending through the airfoil body portion from the root portion to the tip airfoil portion. The airfoil body portion and the airfoil tip portion are joined at a braze interface or a weld interface. The airfoil tip portion includes at least one manifold fluidly connecting at least one radial cooling passage to at least one other radial cooling passage.

In another embodiment, an airfoil includes an airfoil body portion, an airfoil tip portion disposed radially outward of the airfoil body portion, an airfoil root portion, and a plurality of radial cooling passages extending through the airfoil body portion from the root portion to the airfoil tip portion. The airfoil tip portion includes at least one manifold fluidly connecting at least one radial cooling passage to at least one other radial cooling passage. The manifold is radially outward of at least one joint interface.

In another embodiment, a method of forming an airfoil includes forming an airfoil body portion via investment casting, forming at least one radial cooling passage within the airfoil body using shaped tube electrochemical machining (STEM), forming an airfoil tip portion, and joining the airfoil tip portion to the airfoil body portion.

These and other features, aspects and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure.

