Interstage Van Seal Apparatus

The present invention relates generally to structures for sealing between static members within a gas turbine engine. More particularly, in one embodiment the present invention defines a vane interstage seal assembly for minimizing flow recirculating or leaking between vane stages in a gas turbine engine. Although the present invention was developed for use in a gas turbine engine certain applications may be outside of this field.

Typically, the rotating components within a gas turbine engine include one or more rotors that rotate relative to a static structure. Examples of various types of static members found in a gas turbine engine include vanes, stators, compressor cases, combustors, turbine cases, vane cases, fan cases, diffusers, combustor cases, and other components. Much of the engine's static structure is in fluid communication with the working fluid, or flow path of the engine. As gas flows along the engine flow path, the pressure of the gas typically changes, increasing within the compressor and decreasing within the turbine, and creating a pressure differential that can lead to fluid leakage at connecting points between members of the static structure.

Present gas turbine engine designs often use segmented static members. For example, static members such as vanes may be circumferentially segmented into arcuate pieces, such as doublets or triplets, and axially limited to a single stage of expansion or compression. A vane assembly of this type would therefore have circumferential gaps or cavities between it's components and others of the same stage and axial gaps or cavities between the vane assembly and vane assemblies of other stages. If these gaps, cavities, and passageways are not properly sealed, some amount of gas will recirculate off the flow path and around the static member. This recirculation decreases the efficiency of the compressor or turbine, and lowers the overall efficiency of the engine.

Various apparatus have been proposed for providing seals within gas turbine engines. Examples of seals can be found in the following U.S. Pat. No. 3,754,766 issued to Asplund, U.S. Pat. No. 5,333,995 issued to Jacobs et al., U.S. Pat. No. 4,573,866 issued to Sandy, Jr. et al., U.S. Pat. No. 4,337,016 issued to Chaplin, U.S. Pat. No. 4,529,355 issued to Wilkinson, U.S. Pat. No. 5,188,506 issued to Creevy et al., U.S. Pat. No. 5,562,408 issued to Proctor et al., U.S. Pat. No. 3,518,020 issued to Lake, and U.S. Pat. No. 5,233,824 issued to Clevenger.

Even with the variety of earlier designs, there remains a need for a vane interstage seal assembly in gas turbine engines. The present invention satisfies this need in a novel and unobvious way.

One form of the present invention contemplates an apparatus for sealing between static members of a gas turbine engine. The apparatus includes a first annular sealing member clamped to a second static member and contacting a first static member for reducing the passage of fluid between the members. The apparatus also includes a second sealing member contacting the first sealing member for reducing the passage of fluid along the second static member.

One object of the present invention is to provide an improved vane interstage seal for a gas turbine engine.

Other objects and advantages of the present invention will be apparent from the following description.

FIG. 1 is a cut-away view of a portion of a gas turbine engine having one embodiment of the present invention positioned therein.

FIG. 2 is a sectional view of the preferred embodiment of the present invention taken along line 2--2 of FIG. 1, with portions of the engine removed for clarity.

FIG. 3 is a cross-sectional view of FIG. 2 taken along line 3--3.

FIG. 4 is an enlarged view of FIG. 1.

FIG. 5 is a view FIG. 1 taken along line 5--5.

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

FIG. 1 shows a portion of a gas turbine incorporating the preferred embodiment of the present invention. A second static member, compressor vane assembly 22, is shown installed by flanges received within pockets defined by a first static member, compressor case 24. A third static member, compressor vane 28, is shown installed by a flange to a fourth static member, bypass case 30. Bypass case 30 is fastened to compressor case 24. Although specific examples of static members are depicted and described, the present invention is also useful with other static members found in gas turbine engines, including stators, combustors, turbine cases, vane cases, fan cases, diffusers, combustor cases, and other nonrotating components.

Arrow 29 is parallel to the centerline of the engine axis, and also depicts the general direction of the primary gas or fluid flow path within the compressor. Air flowing in the primary flow path 29 through the compressor is largely contained between outer flow path 32 and inner flow path 34. A portion of the inner flow path between vanes 22 and 28 is not shown. In that portion, the inner flow path is defined by a plurality of compressor blades (not shown). The outer tips of these compressor blades would pass within close proximity to abradable blade tip seals 36 and 38.

FIG. 1 shows first annular sealing member 20 as installed in the static structure. Second sealing member 26 is shown installed and sealing between portions of second static member, vane 22, and a third static member, vane 28.

FIG. 2 depicts sealing member 20 as seen along line 2--2 of FIG. 1, with sealing member 20 removed from the engine. In the preferred embodiment, sealing member 20 has a generally circular, split construction, and formed from a single piece of sheet metal. Alternatively, sealing member 20 could be fabricated from different pieces that are welded, brazed, or bonded together. It can also be made from nonmetallic materials and various metals, provided the material has characteristics such as strength, coefficient of expansion, hardness and other properties suitable for the environment to which it is exposed. For example, sealing member 20 could be fabricated from a composite or stainless steel when used in a compressor assembly. As another example, sealing member 20 may be constructed from a nickel-based, iron-based, or cobalt-based material when used in a combustion or turbine section of the engine. Sealing member 20 is shown as a single piece, but could be made in two or more segments.

FIG. 3 is a cross sectional view of sealing member 20 of FIG. 2 taken along line 3--3. Sealing member 20 includes a first sealing portion 40 and a flange portion 42, the latter being generally U-shaped. Portion 40 is generally conically shaped, but is not limited to a conical shape. First sealing portion 40 is cantilevered from first leg 42a of flange portion 42. When installed between first static member 24 and second static member 22, seal 40 deforms elastically with sealing contact surface 46 being urged against surface 69 of member 24 (refer to FIG. 4). Surface 46 is formed on a radius of approximately 0.058 inches, although smaller and larger selections of radii work equally well. First sealing portion 40 is unitary or integral with flange portion 42, portions 40 and 42 joining in the vicinity of clamping contact surface 48. Surface 48 is formed on a radius of approximately 0.1 inches, although smaller or larger radii work equally well.

Flange portion 42 is in the approximate shape of the letter "U", incorporating opposing first and second legs 42a and 42c, respectively, joined by common side 42b. Ring 44 is attached to second leg 42c. Ring 44 and second leg 42c are joined at approximately the same angle as the corresponding surfaces of vane 22. In the preferred embodiment, second leg 42c and ring 44 are approximately perpendicular.

Common leg 42b is approximately perpendicular to side 42c. Side 42a is formed at an angle relative to side 42c, causing the open side of the U-shape to converge. Angle 50 is an acute angle in the preferred embodiment. As measured between sides 42c and 42a in the preferred embodiment is about 7.5.degree.. As a result of this convergence, the top of the U-shape is more closed than the bottom, the difference in the width of the "U" providing spring characteristics for flange portion 42 as installed on flange 57. FIG. 4 is a close-up view of FIG. 1 in the vicinity of sealing member 20, showing sealing member 20 installed in an engine. Flange portion 42 clamps around flange 57 of second static member 22. Clamping contact surface 48 is expanded out, and the spring force of flange portion 42 couples sealing member 20 onto flange 57 by friction along the contact surfaces of sides 42a and 42c.

Installation of the sealing member 20 into the assembly consisting of first static member 24 and second static member 22 results in first sealing portion 40 becoming somewhat flattened as sealing contact surface 46 comes into contact with surface 69 of first static member 24. First sealing portion 40 divides and seals various cavities, gaps, and passageways formed by the assembly of static members 22, 24, 28, and 30. The installation of vane 22 within compressor case 24 creates a first passageway 58. The assembly of vane 28 with bypass case 30 and vane 22 forms a second passageway 60. First sealing portion 40 seals a portion of first passageway 58 from second passageway 60, which passageways would otherwise be in fluid communication.

First passageway 58 contains gas 62 within it at a first pressure. The pressure of gas 62 is related to leakage of gas from the flow path of the engine, especially portions of the flow path downstream of first cavity 58. Second passageway 60 contains gas 64 at a second pressure lower than that of gas 62. Gas 62 is in fluid communication with surface 40a of first sealing portion 40, and gas 64 is in fluid communication with surface 40b. As a result of gas 62 being at a higher pressure than gas 64, there is a pressure imbalance across first sealing portion 40. This pressure imbalance creates a pressure load on seal 40 that tends to force sealing contact surface 46 against surface 69 of compressor case 24. This pressure load increases the sealing ability of sealing member 20, provided first sealing portion 40 is not so stiff as to resist deformation from this pressure load.

Second seal 26 is shown installed in the engine between third static member 28, leg 42c, and ring 44. Seal 26 may be of various configurations, and is shown as an "E" or "W" seal. Seal 26 is circular in nature, extending circumferentially around the engine. Vane 22 and vane 28 define an axial gap 73 between second passageway 60 and the primary flow path. Second seal 26 provides a seal between second passageway 60 and the primary flow path.

Third static member 28 also includes feature 70 which has obstructing surface 72 facing sealing member 20. Obstructing surface 72 limits movement of sealing member 20 if there is movement of sealing member 20 due to the pressure imbalance, vibration, thermal cycling or other reasons. Surface 72 is shown spaced apart from sealing member 20.

FIG. 5 is a view of FIG. 1 taken along line 5--5. FIG. 5 shows a section of the front of compressor case 24 with two second static members 22a and 22b attached. Vanes 22a and 22b define circumferential gap 74 between them. Sealing member 20 is shown installed. First sealing portion 40, leg 42b, and ring 44 are shown. Sealing member 20 seals a portion of circumferential gap 74. Each vane 22a and 22b includes opposed, facing pockets 80 and 78, respectively, which have within them axial strip seal 76. Seal 76, located generally above abradable blade tip seal 38, seals high pressure air in cavity 62 that would otherwise leak between adjacent vanes. Seal 76 seals the balance of circumferential gap 74.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.