Gas turbine engines, such as turbofan gas turbine engines, may be used to power various types of vehicles and systems, such as, for example, aircraft. Typically, these engines include turbine blades (or airfoils) that are impinged by high-energy compressed air that causes a turbine of the engine to rotate at a high speed. Consequently, the blades are subjected to high heat and stress loadings which, over time, may reduce their structural integrity.
Modern aircraft jet engines have employed internal cooling systems in the blades to maintain the blade temperatures within acceptable limits. Typically, the blades are air cooled using, for example, bleed air from a compressor section of the engine. The air may enter near the blade root, and then flow through a cooling circuit formed in the turbine blade. The cooling circuit typically consists of a series of connected passages that form serpentine paths, which increase the cooling effectiveness by extending the length of the air flow path.
The internal cooling system is formed in the blade during its production. For example, if utilizing a lost wax casting process a ceramic core is produced which includes a pattern for the blade internal cooling circuit. The ceramic core is placed in a wax pattern die and wax is injected around the ceramic core to produce a wax pattern of the turbine blade. The wax pattern is dipped in ceramic slurry and dried forming a mold. The mold is then heated and the wax removed therefrom. Next, the mold is placed in a furnace, heated, and filled with a metal material to produce a turbine blade casting. Typically, the metal material is a nickel base superalloy. After the metal material solidifies and the blade is formed, the mold is removed from the blade outer surface and the internal ceramic core is chemically removed leaving internal cavities that form the cooling circuit of the turbine blade.
At times, for example, during research and development, the cooling circuit may need to be modified. Currently, modifications are made by changing the flow circuit pattern in the internal ceramic core die, and then using the modified core die to produce new ceramic cores, which are then used to produce new wax patterns and eventually new cast turbine blades. Although this process yields high quality blades, it suffers from certain drawbacks. Specifically, current modification processes are relatively expensive and extremely time-consuming, taking up to a year to perform. Consequently, schedules for research and development programs may be significantly delayed.
Attempts to overcome the above-mentioned drawbacks generally have not been successful. Most processes have utilized the blade outer surface features to approximate locations of particular internal core features, and modifications have been made based on those approximations. However, in some cases, the internal core floats around within the outer shell during blade production, and the locations of the particular internal flow features are not accurately identified based on the blade outer surface. Thus, because internal cooling circuit modifications need to be extremely precise, these processes have not yielded favorable results.
Hence, there is a need for a method for modifying an internal cooling circuit of a blade that is relatively simple and efficient to employ. Additionally, it is desirable that the method yield high quality blades. Moreover, it is desirable for the method to be relatively inexpensive to practice.