Damping and sealing system for turbine blades

Abstract

With a gas-turbine engine, a sealing and damping element (9), which is loosely held between two adjacent platforms (6a, 6b) of turbine blades attached to a rotor disk, generally has a cross-section in the form of a straight three sided prism corresponding to an equilateral triangle, however with convex rubbing surface sides. Due to small swiveling movements enabled by the curvature of the sides, an increased rubbing and wear area is created during operation, which is adapted to the blade geometry and can be determined in advance, thus increasing damping and sealing efficiency.

Description

This application claims priority to German Patent Application DE 10 2006 041 322.9 filed Sep. 1, 2006, the entirety of which is incorporated by reference herein.

This invention relates to a damping and sealing system for turbine blades with a sealing and damping element generally in the form of a straight three sided prism with equal sides which, by centrifugal effect, is retained between opposite faces of adjacent platforms of the blades fitted to the rotor of a gas-turbine engine.

Gas-turbine engines feature rotor disks with radially extending blades, having a blade root, a platform and an airfoil, mounted on the periphery of the rotor disks. On the one hand, there is a need to seal the narrow gap remaining between adjoining edges of adjacent platforms to minimize gas exchange between hot gas and cooling air; on the other hand, it is necessary to dampen the vibrations between the rotor disk and the blades, as well as between the blades themselves.

Sealing elements arranged between the blade platforms have been long known, whose cross-section is complementary to the shape of the space remaining between the platforms and which must be installed in this space in a specific orientation. Assembly is accordingly time-consuming and costly, and incorrect orientation of the sealing element considerably affects its sealing and damping efficiency. Moreover, the closely matched form of sealing element and platform gap requires considerable production effort.

For one solution to this problem, Specification U.S. Pat. No. 4,872,812 proposes a sealing and damping element with planar sides arranged about its longitudinal axis, with the cross-section of this sealing and damping element being an equilateral triangle. The regular cross-section of the sealing and damping element enables two each of its surfaces, irrespective of the orientation with which the element is assembled, to be driven into engagement with the respective edges of the adjacent platforms to seal the gap and dampen the vibrations of the respective blades when acted upon by centrifugal force. High sealing and damping efficiency requires, however, close production tolerances and, thus high production effort with regard to the planar form of the mating surfaces on both sides. Moreover, the sealing and damping efficiency can be affected by wear to the planar mating surfaces.

In order to reduce the production and assembly effort, sealing and damping elements with circular cross-section have been proposed which, in any orientation, mate with the side edges of the two adjacent platforms when acted upon by centrifugal force. It was found, however, that round sealing and damping elements wear quite rapidly, as a result of which the sealing and damping efficiency is affected and the sealing and damping elements have to be replaced with considerable effort.

In a broad aspect, the present invention provides a sealing and damping system for turbine blades, which is characterized by a high sealing and damping efficiency, while requiring only low assembly and repair effort.

It is a particular object of the present invention to provide at least one solution to the above problems by a sealing and damping system designed in accordance with the features described herein. Advantageous developments of the present invention become apparent from the present description.

The present invention provides a sealing and damping element in the form of a straight three sided prism with convex sides allowing the sealing and damping element to perform a slight swiveling movement in operation and thus acting as enlarged rubbing surfaces. The increased friction thus obtained results in improved vibration damping. Rubbing wear leads to a mutual conditioning of the contacting mating surfaces. Thus, production tolerances are leveled out and vibration damping and sealing efficiency is further improved. Production inaccuracies are compensated for by the automatic, mutual conditioning of the sealing or rubbing surfaces. Rubbing wear can be taken into account in the design. Therefore, the production and repair effort is low.

The opposite sealing surfaces of the adjacent blade platforms form an acute-angled gap into which the sealing and damping element is automatically forced by the action of centrifugal force, contacting the gap surfaces with two curved rubbing surfaces.

The present invention is more fully described in light of the accompanying drawings. In the drawings,

FIG. 1 is a partial view of a gas turbine with a turbine blade attached to a rotor disk, and

FIG. 2 is a section AA as per FIG. 1 with a sealing and damping element arranged between two blades.

As can be seen from FIG. 1, a rotor 2 is disposed between two stator vanes 1 spaced in flow direction, with turbine blades 4 arranged on the periphery of a rotor disk 3, which includes a blade root 5, a blade platform 6 and an airfoil 7. The detailed representation in FIG. 2 shows two adjoining platforms 6a, 6b of adjacent turbine blades 4. The platform 6a, shown on the right-hand side of the drawing, features a recess 8 in which a sealing and damping element 9 is loosely received. Positioned opposite to the open side of the recess 8—with a very small gap 10 left—is a planar, essentially vertical platform edge 11 of the other platform 6b which prevents the sealing and damping element 9 from falling out of the recess 8. The recess 8 has a sealing surface 12 which extends obliquely upwards. The sealing and damping element 9 is a straight component with the cross-section generally of an equilateral triangle, however with rounded longitudinal edges 13 and with convex—crowned—rubbing surfaces 14 (sealing and damping faces, side faces) between the longitudinal edges 13. One of the edges 13 faces generally upward, as shown in FIG. 2.

The sealing and damping element 9 is loose in the recess 8 at rest. During rotation of the rotor 2, however, centrifugal force acts on the sealing and damping element 9 so that its respective convex rubbing surfaces 14 abut the vertical platform edge 11 and the oblique sealing surface 12. Rotation of the sealing and damping element 9 about its longitudinal axis is thus counteracted. However, the curvature and the rotationally symmetric arrangement of the curved rubbing surfaces 14 about a longitudinal axis allow the sealing and damping element 9 to perform a slight swiveling movement about the longitudinal axis, in consequence of which the curved rubbing surfaces 14 are conditioned, and slightly flattened, by wear in the areas of contact with the platform edge 11 and the oblique sealing surface 12, so that the actual area of rub is increased and adapted to the platform design, and geometrical differences caused by the production process are leveled out. In addition, the slight swiveling movement which the sealing and dampening element is allowed to perform enlarges the area of rub and increases friction. The deliberately effected wear due to friction of the curved rubbing surfaces 14 and the mating surfaces with the two opposite platforms is determinable in advance, and is accounted for in the blade design. By interaction of the above effects, an optimum rubbing surface is provided and, due to high friction, maximum damping and, ultimately, improved sealing efficiency achieved, but with the sealing and damping element being prevented from uncontrolled or premature wear by permanent rotation. The production and repair effort is reduced.

LIST OF REFERENCE NUMERALS

• 1 Stator vane
• 2 Rotor
• 3 Rotor disk
• 4 Turbine blades
• 5 Blade root
• 6 Platform
• 6a Right-hand platform
• 6b Left-hand platform
• 7 Airfoil
• 8 Recess
• 9 Sealing and damping element
• 10 Gap
• 11 Straight, vertical platform edge
• 12 Oblique sealing surface
• 13 Rounded longitudinal edges
• 14 Rubbing surface, curved side face

Claims

1. A damping and sealing system for turbine blades of a gas-turbine engine, comprising:

a sealing and damping element generally in the form of a straight three sided prism with equal side faces which, by centrifugal effect during operation of the gas-turbine engine, is retained between opposing surfaces of adjacent platforms of the blades fitted to a rotor of the gas-turbine engine, wherein the side faces of the sealing and damping element are configured as convex rubbing surfaces to allow for a slight swiveling movement of the rubbing surfaces with respect to the opposing surfaces of the adjacent blade platforms to thereby increase rubbing efficiency.

2. A damping and sealing system in accordance with claim 1, wherein the opposing surfaces of the adjacent platforms form a wedge-shaped, acute-angled gap, in which the sealing and damping element is loosely fixed.

3. A damping and sealing system in accordance with claim 2, wherein the gap is formed by a generally straight platform edge of the one platform and by an oblique sealing surface in a recess of the other platform.

4. A damping and sealing system in accordance with claim 3, wherein the gap surfaces in the rubbing/wear area of the sealing and damping element are dimensioned in a manner commensurate with an amount of wear expected.

5. A damping and sealing system in accordance with claim 4, wherein longitudinal edges of the sealing and damping element are rounded.

6. A damping and sealing system in accordance with claim 1, wherein longitudinal edges of the sealing and damping element are rounded.