Detachable leading edge for airfoils

Abstract

A replaceable leading edge insert for an: integrally bladed rotor disk in which the insert includes an enlarged base portion that can be inserted into a dovetail shaped slot formed in the rotor disk to secure the insert to the rotor disk against centrifugal loads during the operation of the blade. The blade on the rotor disk is formed without a leading edge and the leading edge insert includes an aft edge of similar shape to the fore edge n the blade such that the insert can be bonded or fastened to the blade along the entire length of the insert from the blade root to the tip. The rotor disk and the insert include a an annular groove formed on the front side in which a retaining ring is inserted to lock the inserts to the rotor disk. The inserts can be made of a different material from the rotor disk and can be formed with a sweep to form a more :aerodynamic and efficient blade.

Description

FEDERAL RESEARCH STATEMENT

None.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to gas turbine engines of a fan/jet or jet type incorporating fan/compressor rotors and turbine rotors and more particularly to airfoils of the fan/compressor and turbines as well as those utilized in integrated bladed rotor (IBR or BLISK) designs and to the construction thereof.

2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98

As one skilled in this technology appreciates, the gas turbine power plant typically incorporates fans and compressor blades for imparting compression to the intake air (straight jet engines do not incorporate fans) which is then delivered to the combustor where fuel is combusted to add heat thereto. Hence, this engine working medium is accelerated before being delivered to the turbine which is mechanically connected to the fan/compressor so that the energy extracted from the engine working medium is converted to power the compressor fan/lades to pressurize the intake air and develop propulsive thrust. The fan blades which essentially is a compressor blade that is typically mounted upstream of the smaller compressor blades, not only serves to pressurize the intake air, but also develops thrust which is added to the overall thrust developed by the engine.

As will become apparent from the description below, this invention is particularly useful in an IBR of a gas turbine engine, but also has potential use for airfoils that are utilized in a noon-IBR configuration. The following description relates to the IBR configuration.

Modern day fan blades are generally highly sophisticated so as to achieve high pressure rations across the stage(s) of fan blades which require swept airfoils and contoured blade shapes to attain the necessary superior aerodynamics. The backward sweep of the airfoil leading edge typically serves to reduce shock losses and noise generation while the forward sweep is typically incorporated to enhance the aerodynamics of the airfoil.

In addition to the aerodynamics of the airfoil, be it a fan, compressor or turbine blade, a concern for the designer and the engine user is the stress concentration of the blade. During operation, the blades and disk rotate and generate substantial centrifugal farces which are carried by the disk. The designer of tie IBR must assure dial the steady tensile stress and the alternating stress are maintained within their limits throughout the entire IBR configuration for the entire operating envelope of the power plant. What is not in the control of the designer is localized stress concentration that is occasioned by blade damage due to foreign object ingestion. Ingested objects, such as grit or sand from the runways, small birds during normal operation may cause chips or nicks in the blades and most commonly in the leading edge. Obviously, because the IBR is a complicated hardware requiring special materials and expensive manufacturing, it is extremely costly to discard an IBR whenever the blade becomes damaged. One damaged blade could cause the entire IBR to be unusable. Since the IBR is an integral unit of the blades and the disk, the removal of the damaged blade for repair purposes is not effective.

While the teachings disclosed in U.S. Pat. No. 5,725,354 issued to Wadia et a on Mar. 10, 1998 and entitled FORWARD SWEPT FAN BLADE relates to a separate leading edge, the present invention differs not only in the construction thereof, but also the design philosophy. To best understand the difference between these two concepts, one should appreciate the teachings ill the Wadia et al reference, supra, where the swept portion of an IBR fan blade is made from a separate composite piece that fits into the portion of the airfoil of the fan blade so as to attain the forward sweep. As is true in all fall blades, the centrifugal loads generated by the disk create predominantly radial centrifugal forces in the blades which cause a steady tensile stress. In addition, the airflow over the blades induces vibration in the airfoil and creates alternating stresses. These stresses, i.e., steady tensile stress and alternating stresses are not uniform and vary over the length, width and thickness of the blade. This situation is exacerbated by indentations on the airfoil such as nicks, chips, cracks and the like caused by sand, dirt, bird ingestion, ect that causes stress concentration. The problem is more complicated when the leading edge is significantly swept forward. While this innovation provides aerodynamic benefits, it changes the center of gravity of the blade and hence complicates the stress design of the airfoil. Hence the purpose of the teachings of the Wadia et al patent, supra, is to provide a design configuration that improves the stress problem by reducing the steady stress along the leading edge of the airfoil which would otherwise occur from effecting forward sweep.

Of significance, the present invention differs from the Wadia et al patent and other known prior art designs by 1) providing a removable leading edge that can be fabricated from the same or different materials, and 2) designing the leading edge as an independent load carrying member where it includes an airfoil portion and an attachment portion (root), such that the loads on the airfoil are transmitted from the airfoil through the root of the leading edge into the disk. Hence, the disk, whether an IBR or a non-IBR fan must be designed to accommodate the root of the leading edge for attachment thereto.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide for the airfoil of a compressor or fan or turbine for a gas turbine engine of the IBR type an improved detachable leading edge.

A feature of the present invention is an improved leading edge that is removable from the IBR and includes an attachment base that is secured to the disk of the IBR.

Another feature of the present invention is the improved detachable IBR leading edge that selves to ground the stresses impacted thereon by the air and engine working medium loadings and the centrifugal loadings through the disk supporting the detachable leading edge. The load that is seen by tie leading edge transmits that load through the leading edge itself and into the disk by way of the leading edge attachment.

A feature of the present invention is to provide a detachable leading edge for an airfoil whether it be an IBR or a non-IBR configuration, so that the leading edge can be repaired or replaced and eliminating the requirement or repairing and/or replacing the entire IBR and is characterized as being relatively simple and economical to fabricate and being removable with sufficient ease.

The forgoing and other features of the present invention will become more apparent from the following description and accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view in elevation illustrating a rotor of the IBR type utilizing the detachable leading edge of the, present invention.

FIG. 2 is a fragmentary exploded view illustrating the leading edge of the present invention.

FIG. 3 is an enlarged fragmentary view in perspective illustrating the details of the leading edge of FIG. 1.

FIG. 4 is a view in elevation of the leading edge of the present invention.

FIG. 5 is a view of a section of the airfoil of the blade of the rotor taken along lines 5-5 in FIG. 4.

FIG. 6 is a partial view in a section taken along the sectional lines 6-6 of FIG. 3.

These figures merely serve to further clarify and illustrate the present invention and are not intended to limit the scope of tie present invention thereof

DETAILED DESCRIPTION OF THE INVENTION

While the present invention in its preferred embodiment describes the fan rotor fabricated in an IBR of a gas turbine engine, as one skilled in this art will appreciate that this invention is applicable to compressor rotors and turbine rotors and is useful where the leading edge is detach-able from an IBR. It will also be understood that the present invention is also applicable to turbines and to IBR and non-IBR con-figurations.

The present invention is best understood by referring to all of the figures where the complete rotor is generally illustrated in FIG. 1 by reference numeral 10 comprising the IBR 12 having a blade 14 integrally formed with the disk 16 and the detachable leading edge 18. The disk 16 can be made from any suitable material that is consistent with the requirements required for suitable operation in a gas turbine engine, as for example a metal alloy such as Inco 718, Waspaloy, titanium and the like or a ceramic or a composite maternal. The central opening 20 serves to receive the engine shaft (not shown). As best seen in FIG. 5, the leading edge 18 is mounted in a lap type fit 31 so that the aft edge or lip 24 is contoured to define a suitable indentation to fit with the complementary contoured fore edge or lip 26 of the main body 28 of the blade 14. a suitable tongue and groove fit or dove-tail configuration could be equally employed. It will be appreciated from the foregoing that the connection of the leading edge 18 to the main body 28 of the airfoil 29 forms a straight or constant arc interface extending from the root to the tip of the airfoil. The components can be either bonded by a suitable adhesive, particularly where a composite material is utilized as the leading edge, or can be fastened with suitable mechanical fasteners such as “winglets” mounted on the pressure side and the like. A bond from an elastomeric adhesive material such as Soundcoat DYAD 606 or 609 or ISD 113 (available from 3M) not only serves as a bonding material but also acts as a damper that reduces vibrations and eliminates flutter.

Of importance in the present invention is that the mounting must assure that there is a smooth load transition between the leading edge and the blade main structure. It wit also be appreciated that the load that the leading edge 18 sees will be transmitted from the main body 30 of the leading edge through the main body 30 to the root attachment 42 where it is then transmitted through the disk 16. As best seen in FIG. 3, the slot 44 is configured similar to a dove-tail to complement the enlarged base portion 48 of the attachment 42 which serves to take up the centrifugal loads on the blade when it is in operation. A suitable retaining ring 50 mounted in an annular groove 56 formed on the face 54 of the disk 16 serves to lock all of the leading edges of the respective circumferentially spaced blades comprising the rotor disk assembly to the disk 16 independently of the structure that supports the main body 28 of the blade 14.

In accordance with the present invention, the leading edge 18 is not only detachable from the main body 28 of the airfoil 29 so that is can be made from a material that is different from the main body 28, it can also be removed when a replacement or repair is necessary. As will be appreciated, the blades, particularly fan blades, are susceptible to erosion, corrosion, or drainage from foreign objects or even pieces of the engine that may become dislodged. Whatever the reason, the damage must be rectified so that the engine can remain flight worthy. In either an IBR configured rotor or a non-IBR configured rotor, the removal of only the leading edge for repair or replacement is desirable. To more fully appreciate this aspect of the present invention, consider the IBR configuration. For example, the F-022 military airplane engines utilize IBRs that contain hollow titanium airfoils that are linear friction welded onto the disk. The current repair process for that IBR requires the removal of the damaged airfoil by a simple cutting operation and welding a new blade in its place. Once the new blade is inserted into the disk, the IBR needs to be reworked to smooth the surfaces and the blade-to-disk transition. Under these circumstances, each blade of the IBR can be replaced but one time as it would otherwise materially affect the structural integrity of the blade and attachment region of the disk.

As is also apparent from the foregoing, the ability to utilize different materials for the leading edge and particularly composite materials, the designer can design the blade to include swept back or swept forward contours to the blade to enhance the aerodynamics and efficiency of the blade.

By virtue of the present invention, the blade designed with a detachable leading edge affords the following advantages over the cited prior art references. The leading edge may be made from a material that is different than the material of the main body of the blade and hence reduce the overall weight of the blade. Because the material selected for the leading edge can be one that is susceptible of providing sweep to the blade, the overall efficiency and aerodynamics of the blade can be improved. The leading edge being mounted directly into the disk lends itself to being utilized in both IBRs and non-IBRs. Because of the smooth transition of the leading edge from the root to the tip of the airfoil along the contoured edge of the main blade portion and the independent attachment to the disk, the loads generated by thermal and centrifugal loadings on the leading edge is transmitted directly through the leading edge to the disk. The removal aspect of the leading edge results in ease of repair, less costly repairs and the ability to remove the leading edge without having to remove the disk which is a maintenance asset. The attachment of the leading edge can be used to provide damping to the IBR through the adhesive or damping bond to reduce vibrations and eliminate flutter.

Although the present invention has been shown and described with respect to detailed embodiments thereof, it will be appreciated and understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.

Claims

1. An integrally bladed rotor disk comprising: a rotor disk;a blade extending from the rotor disk, the blade being without a leading edge;a dovetail slot formed in the rotor disk; and,a detachable leading edge insert forming the leading edge missing from the blade, the detachable leading edge including an attachment portion and the leading edge portion, the attachment portion having an enlarged base portion to fit within the dovetail slot and hold the detachable leading edge insert against centrifugal loads when the blade is in operation.

2. The integrally bladed rotor disk of claim 1, and farther comprising: the detachable leading edge insert forms the leading edge for the blade from the blade root to the blade tip.

3. The integrally bladed rotor disk of claim 1, and further comprising: the blade includes a fore edge and the leading edge insert includes an aft edge; and,the fore edge and the aft edge are secured together by a removable securing means so that the leading edge insert can he removed mid replaced.

4. The integrally bladed rotor disk of claim 3, and further comprising; the fore edge and the aft edge form a lap type fit that extends substantially all along the leading edge portion from root to tip.

5. The integrally bladed rotor disk of claim 3, and further comprising: the removable securing means is an adhesive applied along the interface between the leading edge insert and the blade.

6. The integrally bladed rotor disk of claim 3, and further comprising: the removable securing means is at least one mechanical fastener.

7. The integrally bladed rotor disk of claim 1, and farther comprising: the rotor disk and the attachment portion both include an annular groove on the forward side of the rotor disk; and,a retaining ring inserted into the annular groove to lock the leading edge insert to the rotor disk.

8. The integrally bladed rotor disk of claim 1, and further comprising: the leading edge insert is made from a different material than the rotor disk.

9. The integrally bladed rotor disk of claim 1, and further comprising: the leading edge insert includes sweep for the blade.

10. The integrally bladed rotor disk of claim 4, and further comprising: the lap type fit is longer on the pressure side of the blade than on the suction side.

11. The integrally bladed rotor disk of claim 1, and further comprising: the dovetail slot and the enlarged base portion are of such shape and size to allow for the leading edge insert to be inserted into position on the rotor disk form the front side of the rotor disk.

12. The integrally bladed rotor disk of claim 1, and further comprising: the rotor disk includes a plurality of integrally formed blades each without a leading edge portion;the rotor disk includes a dovetail slot formed therein for each of the blades; anda detachable leading edge insert with an enlarged base portion to fit within the dovetail slot for each of the blades.

13. The integrally bladed rotor disk of claim 12, and further comprising: the rotor disk and the attachment portion of each insert both includes an annular groove on the forward side of the rotor disk; and,a retaining ring inserted into the annular groove to lock the leading edge inserts into the rotor disk.

14. A replaceable leading edge insert for an integrally bladed rotor disk, the integrally bladed rotor disk including a plurality of blades extending from the rotor disk, at least some of the blades being formed without a leading edge the replaceable leading edge insert comprising: a leading edge portion to form the leading edge for the blade;an attachment portion with an enlarged base portion to secure the leading edge insert to the rotor disk against centrifugal loading during operation of the blade;an the leading edge insert having an aft edge of similar shape to a fore edge on the blade such that the leading edge insert can be secured to the fore edge of the blade

15. The replaceable leading edge insert of claim 14, and further comprising: the enlarged base portion is dovetail shaped.

16. The replaceable leading edge insert of claim 14, and further comprising: the attachment portion of the insert including an annular groove for the insertion of a retaining ring to lock the insert to the rotor disk.

17. The replaceable leading edge insert of claim 14, and further comprising: the leading edge insert includes a blade sweep shape.

18. The replaceable leading edge insert of claim 14 and further comprising: the aft edge of the leading edge insert is a lap type shape.

19. The replaceable leading edge insert of claim 18, and further comprising: the lap type shape has a longer pressure side edge than the suction side edge in the chord wise direction of the blade.

20. The replaceable leading edge insert of claim 14, and further comprising: the aft edge of the leading edge insert extends substantially along the entire insert from the root to the tip of the blade.