Root lightening holes with slot

An airfoil includes a dovetail root having a base. A grooved slot is disposed in the base and a plurality of root lightening cavities is disposed in the grooved slot.

TECHNICAL FIELD

The subject matter of the present disclosure relates generally to gas turbine engines and, more particularly, relates to airfoils having root lightening holes used in gas turbine engines.

BACKGROUND

Gas turbine engines include a plurality of airfoils disposed circumferentially around the perimeter of a rotor disk. For optimum performance, it is ideal that the airfoils be light weight and stiff, because, during gas turbine engine operation, the rotating airfoils are often subject to a variety of different forces. For example, the airfoils typically experience centrifugal forces, aerodynamic forces and vibratory stimuli due to the rotation of the airfoils over the various operating speeds of the engine. One conventional way to reduce weight from the airfoil is to create pockets within the airfoil and to fill those pockets with a suitable light weight filler material for completing the aerodynamic profile of the airfoil. The pockets, however, reduce the stiffness of the airfoil. As such, the dovetail root and transition portion of the airfoil are often times solid in order to maintain stiffness in these critical areas.

A creative way to eliminate additional weight from the dovetail root and transition portion of the airfoil without negatively affecting stiffness much is to drill cavities into the base of the dovetail root. During assembly and disassembly of these airfoils from the gas turbine engine, however, the cavities in the base of the dovetail root cause scratching damage to the dovetail slot. Furthermore, the cavities in the base of the dovetail root have the potential to ingest water and other foreign objects during engine operation. If water gets into the cavities, the water has the potential to freeze and create an imbalance in the gas turbine engine due to the fact that not all the airfoils in the rotor disk may have ingested water. This potential imbalance can adversely affect the engine performance and must be avoided to maintain the efficiency of the engine.

Accordingly, there is a need to provide a light weight airfoil that maintains stiffness, avoids damaging other components of the gas turbine engine during assembly and disassembly, and prevents engine imbalance due to foreign object ingestion into lightening cavities of the airfoil.

SUMMARY

In accordance with an aspect of the disclosure, an airfoil is provided. The airfoil may include a dovetail root having a base. A grooved slot may be disposed in the base. A plurality of root lightening cavities may be disposed in the grooved slot.

In accordance with another aspect of the disclosure, the grooved slot extends substantially radially outwardly so as to be offset substantially radially from the base.

In accordance with yet another aspect of the disclosure, a plurality of plugs may be included so that each of the plurality of plugs may be disposed into a corresponding complementary cavity of the plurality of root lightening cavities.

In accordance with still yet another aspect of the disclosure, a corresponding complementary strip may be disposed within the grooved slot.

In further accordance with another aspect of the disclosure, each cavity of the plurality of root lightening cavities may include a counterbore.

In further accordance with yet another aspect of the disclosure, each cavity of the plurality of root lightening cavities may extend through the dovetail root and a transition portion of the airfoil and into an airfoil root of the airfoil.

In accordance with another aspect of the disclosure, a gas turbine engine is provided. The engine may include a rotor disk. A plurality of dovetail slots may be disposed around the perimeter of the rotor disk. Each airfoil of a plurality of airfoils may be include a dovetail root. Each dovetail root may include a base. Each dovetail root may be removably disposed within a complementary dovetail slot of the plurality of dovetail slots. A grooved slot may be disposed in each base. A plurality of root lightening cavities may be disposed in each grooved slot.

In accordance with still another aspect of the disclosure, each grooved slot may extend substantially radially outwardly so as to be offset substantially radially from the base.

In accordance with still yet another aspect of the disclosure, each plug of a plurality of plugs may be disposed into a corresponding complementary cavity of the plurality of root lightening cavities.

In further accordance with another aspect of the disclosure, each corresponding complementary strip of a plurality of corresponding complementary strips may be disposed within the grooved slot of each base.

In further accordance with yet another aspect of the disclosure, each root lightening cavity of the plurality of root lightening cavities may include a counterbore.

In further accordance with still yet another aspect of the disclosure, each root lightening cavity of the plurality of root lightening cavities may extend through the dovetail root and a transition portion of the airfoil and into an airfoil root of the airfoil.

In accordance with another aspect of the disclosure, a method of preventing a dovetail root of an airfoil from scratching a dovetail slot disposed in a gas turbine engine when the airfoil is removed from the engine is provided. The method entails forming a grooved slot in a base of the dovetail root. Another step may be forming a plurality of root lightening cavities in the base. Yet another step may be inserting a plug into each root lightening cavity of the plurality of root lightening cavities.

In accordance with yet another aspect of the disclosure, the method may include forming the grooved slot to extend substantially radially outwardly so as to be offset substantially radially from the base.

In accordance with still another aspect of the disclosure, the method may include disposing a corresponding complementary strip within the grooved slot to prevent foreign material from getting into the plurality of root lightening cavities.

In accordance with still yet another aspect of the disclosure, the method may include forming the plurality of root lightening cavities with a counterbore.

In further accordance with another aspect of the disclosure, the method may include forming the plurality of root lightening cavities to extend through the dovetail root and a transition portion of the airfoil and into an airfoil root of the airfoil.

In further accordance with still another aspect of the disclosure, the method may include the plurality of root lightening cavities being formed with a ball end mill to reduce stress concentration where the cavities terminate.

Other aspects and features of the disclosed systems and methods will be appreciated from reading the attached detailed description in conjunction with the included drawing figures. Moreover, selected aspects and features of one example embodiment may be combined with various selected aspects and features of other example embodiments.

It is to be noted that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting with respect to the scope of the disclosure or claims. Rather, the concepts of the present disclosure may apply within other equally effective embodiments. Moreover, the drawings are not necessarily to scale, emphasis generally being placed upon illustrating the principles of certain embodiments.

DETAILED DESCRIPTION

Throughout this specification the terms “downstream” and “upstream” are used with reference to the general direction of gas flow through the engine and the terms “axial”, “radial” and “circumferential” are generally used with respect to the longitudinal central engine axis.

Referring now toFIG. 1, a gas turbine engine constructed in accordance with the present disclosure is generally referred to by reference numeral10. The gas turbine engine10includes a compressor12, a combustor14and a turbine16. The serial combination of the compressor12, the combustor14and the turbine16is commonly referred to as a core engine18. The core engine18lies along a longitudinal central axis20. A core engine cowl22surrounds the core engine18.

Air enters compressor14at an inlet24and is pressurized. The pressurized air then enters the combustor14. In the combustor14, the air mixes with jet fuel and is burned, generating hot combustion gases that flow downstream to the turbine16. The turbine16extracts energy from the hot combustion gases to drive the compressor12and a fan26, which includes a rotor disk28. A plurality of airfoils30is mounted circumferentially around the rotor disk28. As the turbine16drives the fan26, the airfoils30rotate so as to take in more ambient air. This process accelerates the ambient air32to provide the majority of the useful thrust produced by the engine10. Generally, in some modern gas turbine engines, the fan26has a much greater diameter than the core engine18. Because of this, the ambient air flow32through the fan26can be 5-10 times higher, or more, than the combustion air flow34through the core engine18. The ratio of flow through the fan26relative to flow through the core engine18is known as the bypass ratio.

The fan26and core engine cowl22are surrounded by a fan cowl36forming part of a nacelle38. A fan duct40is functionally defined by the area between the core engine cowl22and the nacelle38. The fan duct40is substantially annular in shape so that it can accommodate the air flow produced by the fan26. This air flow32travels the length of the fan duct40and exits downstream at a fan nozzle42. A tail cone44may be provided at the core engine exhaust nozzle46to smooth the discharge of excess hot combustion gases that were not used by the turbine16to drive the compressor12and the fan26.

Referring toFIGS. 2-5, each of the plurality of airfoils28may include a tip50, an airfoil root52, a pressure surface side54, a suction surface side56, a leading edge58and a trailing edge60. The pressure surface side54and suction surface side56extend in a spanwise direction between the tip50and airfoil root52. The surface sides54,56also extend in a chordwise direction between the leading edge58and the trailing edge60. Each of the plurality of airfoils28also includes a dovetail root62, which is integrally joined to the airfoil root52by a transition portion64.

Each of the airfoils28may include a plurality of pockets66disposed between the pressure surface side54and the suction surface side56. The plurality of pockets66may be filled with a suitable light weight filler so that the filler is coextensive at its outer surface with either the pressure surface side54or the suction surface side56for providing an aerodynamically smooth and continuous contour with either of the surface sides54,56.

A grooved slot68is disposed at the base70of the dovetail root62. The grooved slot68extends along the base70in the chordwise direction of the airfoil28. Further, the grooved slot68extends radially outwardly so as to be offset substantially radially from the base70. A plurality of root lightening cavities72is disposed at the grooved slot68. Each cavity of the plurality of root lightening cavities72may have a substantially cylindrical shape extending substantially radially through the dovetail root62and may extend through the transition portion64and into the airfoil root52. With the grooved slot68offset substantially radially from the base70of the dovetail root62, the plurality of cavities72will not be in jeopardy of causing scratches on the dovetail slot74(shown inFIG. 2), disposed around the perimeter of the rotor disk28, when the dovetail root62is removed from the dovetail slot74. Although the diameter of each of the cavities62may be approximately equal, the depth of the cavities62may vary from one another. The number and shape of the cavities72are designed so as to maintain the stiffness and torsional strength of the airfoil28.

Corresponding complementary plugs76may be disposed into each of the cavities72to prevent water from getting into the cavities72, freezing and causing an imbalance due to the fact that not all of the airfoils28have ingested water. Similarly, the plugs76prevent other foreign objects from entering the cavities72and causing an imbalance or other damage. The plugs76may be molded or extruded from, but not limited to, polyurethane, epoxy or other foam or plastics. Alternatively, a corresponding complementary strip78may be disposed within the grooved slot68to prevent water from getting into the cavities72. The strip78may be, but is not limited to, a polyimide or other suitable tape, a thin metallic strip or a thin plastic strip. The strip78may be used solely or in conjunction with the plugs76.

In certain instances, a cavity72may not be truly radial, but may be offset at a slight angle. In order to facilitate the manufacturing of these offset cavities72, counterbores78may be provided to help align the machine tooling used to create the offset cavities72.

FIG. 6illustrates a flowchart600of a series of steps which may be performed to prevent a dovetail root of an airfoil from scratching a dovetail slot disposed in a gas turbine engine when the airfoil is removed from the engine. Box610shows the step of forming a grooved slot at a base of a dovetail root of an airfoil. The grooved slot may be formed to extend substantially radially outwardly so as to be offset substantially radially from the base. Another step, as illustrated in box612, is forming a plurality of root lightening cavities in the base. Box614illustrates the step of inserting a plug into each root lightening cavity of the plurality of root lightening cavities. Another step may be to dispose a tape within the grooved slot to prevent foreign material from getting into the plurality of root lightening cavities. Further, the plurality of root lightening cavities may be formed with a counterbore. Yet another step may include forming the plurality of root lightening cavities to extend through the dovetail root and a transition portion of the airfoil and into an airfoil root of the airfoil. Moreover, another step may be to apply adhesive to each plug. The plurality of root lightening cavities may be formed with a ball end mill to reduce stress concentration where the cavities terminate.

While the present disclosure has shown and described details of exemplary embodiments, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the disclosure as defined by claims supported by the written description and drawings. Further, where these exemplary embodiments (and other related derivations) are described with reference to a certain number of elements it will be understood that other exemplary embodiments may be practiced utilizing either less than or more than the certain number of elements.

INDUSTRIAL APPLICABILITY

Based on the foregoing, it can be seen that the present disclosure sets forth an airfoil which prevents scratching of a dovetail slot disposed in a gas turbine engine when the airfoil is removed from the engine. The teachings of this disclosure can be employed to reduce and eliminate damage to the dovetail slot during assembly and disassembly of the airfoil from the engine. Moreover, through the novel teachings set forth above, the potential for water and other foreign object and material ingestion into the root lightening cavities is prevented. Preventing foreign objects and materials from entering the root lightening cavities increases the engine performance by maintaining an equal balance between each airfoil of the plurality of airfoils. Furthermore, the present disclosure provides a lighter weight airfoil, which also increases engine performance.