EP3015654A1

EP3015654A1 - Turbine assembly

Info

Publication number: EP3015654A1
Application number: EP14190674.3A
Authority: EP
Inventors: Philip David Hemsley
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2014-10-28
Filing date: 2014-10-28
Publication date: 2016-05-04

Abstract

The invention relates to a turbine blade assembly having a set of circumferentially fitted turbine blades (10) that form a set. The assembly includes a shim (20) located between a cavity (40) formed between lateral surfaces of two of the turbine blades (10). Each lateral surface (14) is offset from a radial direction (30) such that the cavity (40) has a reducing circumferential width over the blade root radial height (13) in a radial direction (30) while the shim (20) is a tapered shim (20) with a shape complementary to the shape of the cavity (40).

Description

TECHNICAL FIELD

The present disclosure relates to shims fitted between turbine blade-roots where the blade-roots are circumferentially aligned in a grooved rotor.

BACKGROUND INFORMATION

A conventional form of turbine has a rotor with a channel for receiving complementary shaped roots of circumferentially mounted turbine blades. Steam turbine moving blades require precision profiles that are most economically machined individually and then attached in rows to the turbine rotor. These blades may further include a shroud at a distal end of the blade.
To fit such blades into channels, the roots typically have a parallelogram shapes which allows rotation of the blade root into the channel. To enable access to the last blade, a circumferential gap is typically provided between each root. This allows the blade roots to be closed up to create a larger gap for the last blade. The access gap can be formed by twisting the blade so that the parallelogram-shaped shroud rotates and becomes more circumferentially compact. After assembly of the last blade, the closed up blades are re-distributed and the root gaps have to be filled with shims.
A problem with turbine blades is that low-cycle fatigue, caused by, for example, repeated started-up and shut downs may lead to crack initiation and consequential failure of the whole blade. The last stage blades being the longest and the heaviest are most severely loaded under the centrifugal forces. Such failure can result in the destruction of the turbine.

SUMMARY

A turbine assembly with reduced low cycle fatigue of blade roots caused by repeated start-ups and shutdowns.
It attempts to addresses this problem by means of the subject matter of the independent claim. Advantageous embodiments are given in the dependent claims.
The disclosure is based on the general idea of providing a tapered shim located between tapered blade roots.
According to an exemplary embodiment there is provided a turbine blade assembly of circumferentially fitted turbine blades that are radially displaced from a rotational axis. The circumferentially fitted turbine blades comprise a set having two turbine blades that form a pair. Each blade of the pair having a blade root with a lateral surface that forms a cavity between each pair of turbine blade and a blade root radial height and a shim located in the cavity with a shim radial height. Each lateral face is offset from a radial direction such that the cavity has a reducing circumferential width over its radial height in a radial direction while the shim is a tapered shim with a shape complementary to and slightly larger than the shape of the cavity.
The tapered shim in a tapered cavity has the advantage that it can migrate outwards when the rotor is run up to over speed, and the blades dilate, and then will remain at the higher radius as the rotor runs down again. This builds up a circumferential stress that keeps the stress in the root fastening high even after the rundown of the turbine by replacing centrifugally generated radial force on the blade root fastening by circumferential compression generated radial force, and thus reduces cyclic loading and as a result reduced low cycle fatigue.
Preferably the shim radial height is less than the blade root radial height so as to enable radial movement of the shim exclusively within a radial extension of the cavity. This ensures that the shim does not interfere with the gas flow through the turbine blading.
Other aspects and advantages of the present disclosure will become apparent from the following description, taken in connection with the accompanying drawings which by way of example illustrate exemplary embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example, an embodiment of the present disclosure is described more fully hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of turbine blade assembly according to an exemplary embodiment of the disclosure.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure are now described with references to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosure. However, the present disclosure may be practiced without these specific details, and is not limited to the exemplary embodiment disclosed herein.
An exemplary embodiment shown in Fig. 1 comprises turbine blades 10 that are circumferentially fitted around a rotational axis of a turbine. The assembly includes at least two circumferentially adjacent turbine blades 10 have blade roots 12 and a shim 20 there between.
The blade roots 12 include lateral surfaces 14 that generally face a circumferential direction. In this arrangement adjacent blades 10 have two lateral surfaces 14 that each faces a lateral surface 14 of an adjacent blade root 12 without the lateral surfaces being parallel. That is, the lateral surfaces 14 are offset from the radial direction 30 such that a cavity 40 formed between the adjacent blades 10 by the lateral faces 14 has reducing circumferential width, i.e. a width measured in the circumferential direction 32, in the radial direction 30.
In an exemplary embodiment, the shim 20 is located in the cavity 40 and is a tapered shim 20 with a shape that is complementary to the shape of the cavity 40.
In exemplary embodiment the shim radial height 22 is less than the blade root radial height 13 so as to enable radial movement of the shim 20 exclusively within a radial extension of the cavity 40. That is, the shim's length and taper is such that at either end of its radial movement within the cavity 40, any portion of the shim 20 does not extend outside the cavity 40. This can be achieved, for example, by the circumferentially thickest part of the cavity 40, corresponding to the portion of the cavity 40 closest to the rotational axis 34, being thicker than the circumferentially thickest portion of the shim 20, corresponding to a portion of the shim 20 closest to the rotational axis 34.
Although the disclosure has been herein shown and described in what is conceived to be the most practical exemplary embodiment, the present disclosure can be embodied in other specific. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the disclosure is indicated by the appended claims rather that the foregoing description and all changes that come within the meaning and range and equivalences thereof are intended to be embraced therein.

REFERENCE NUMBERS

10: blade 10
12: blade root 12
13: blade root radial height 13
14: lateral surface 14
20: shim 20
22: shim radial height 22
30: radial direction 30
32: circumferential direction 32
40: cavity 40

Claims

A turbine blade assembly comprising:
a set of circumferentially fitted turbine blades (10) that are radially displaced from a rotational axis of the set, wherein the set comprises:
two turbine blades (10) each having a blade root (12) with:
a lateral surface (14) that forms a cavity (40) between the two turbine blades (10); and

a blade root radial height (13); and

a shim (20) located in the cavity (40) with a shim radial height (22), characterised by:
each lateral surface (14) being offset from a radial direction (30) such that the cavity (40) has a reducing circumferential width over the blade root radial height (13) in a radial direction (30); and

the shim (20) is a tapered shim (20) with a shape complementary to the shape of the cavity (40).
The turbine blade assembly of claim 1 wherein the shim radial height (22) is less than the blade root radial height (13) so as to enable radial movement of the shim (40) exclusively within a radial extension of the cavity (40).