GB2456770A - A stator vane for a gas turbine engine - Google Patents

Abstract

A stator vane 10 for a gas turbine engine comprises a vane body 12, a base 16 and a tang 48 (see figure 4) extending from the base 16. The tang is resilient and may be U shaped so that it can resile relative to the base 16. Also disclosed is a stator vane mounting with a recess arranged to receive a tang of a stator vane, the channel being flared outwardly at a mouth so that it tapers inwardly from the mouth.

Description

A STATOR VANE FOR A GAS TURBINE ENGINE AND A MOUNTING THEREFOR

The present invention relates to a stator vane for a gas turbine engine and a stator vane mounting for a gas turbine engine.

Stator vanes in gas turbines engines are typically mounted between an outer casing and an inner shroud ring as shown in Figure 1. The vane has a main vane body and upper and lower platforms. The upper platform is arranged in a recess in the inner wall of the outer casing. The lower platform is typically located by means of a tang in a so-called "bird beak" slot. An advantage of this arrangement is that the bird beak fixing allows the vane to slide slightly relative to the inner shroud ring as the vane vibrates. This sliding movement causes rubbing at the interface between the stator and the casing and the inner shroud ring. The rubbing action generates frictional forces that serve to dissipate energy in the form of heat. This acts to damp unwanted stator vibrations.

However, the amount of damping achieved is sensitive to the clearance between the tang of the vane and the bird beak slot. The clearances are small so machining tolerances of the bird beak fixing and the stator tang have a significant effect upon the resulting clearance. That, in turn, changes the way that each stator sits relative to its fixing and as such the resultant variable generation of friction causes unpredictable damping levels from vane to vane.

Furthermore, as the engine is used, the rubbing at the interface between the tang and the bird beak slot causes the bird beak slot or the tang to wear which alters the clearance and changes the damping performance of the vane.

It is an object of the invention to provide an improved stator vane for a gas turbine engine.

According to the invention there is provided a stator vane for a gas turbine engine comprising a vane body, a base and a tang extending from the base, at least part of the tang being resilient so that the tang is arranged to resile relative to the base.

In that way, when the tang is arranged in a bird beak slot it is pre-loaded in bending.

This pre-sprung arrangement takes up any variations in clearance. Because the variations in clearance due to machine tolerances and wear are only small absolute values, the flexible resilient nature of the tang of the present invention causes only a small change in loading the tang, giving, in turn, only a small change in friction in the bird beak from vane-to-vane or from new vane to worn vane. A more reliable level of damping is provided as a consequence.

The tang is preferably U-shaped in section with the resilience being provided by the bight part of the U-shape. The tang may be made of resilient material, such as spring steel.

The tang preferably extends from the lower part of the base so as to define a clearance between the underside of the base and the tang.

The tang may extend into a channel which has a tapered mouth to provide a tapered lead into the channel for the tang. This means that the tang can be pre-sprung on assembly.

According to another aspect of the invention there is provided a stator vane mounting for a gas turbine engine comprising a body defining a recess arranged to receive at least part of a base of the stator vane and a channel adjacent the recess arranged to receive part of a tang of a stator vane, the mouth of the channel being flared outwardly so that the channel tapers inwardly from the mouth inwards.

Preferably, both sides of the channel taper inwardly.

Embodiments of the invention will now be described in detail by way of example and with reference to the accompanying drawings, in which:-Figure 1 is a schematic sectional view of a known stator vane and stator vane mounting; Figure 2 is a sectional view through the mounting of the vane of Figure 1 shown to a larger scale; Figure 3 is a schematic sectional view through a stator vane and stator vane mounting in accordance with the invention; Figure 4 is an enlarged sectional view through the mounting part of the vane of Figure 3; Figure 5 is a schematic sectional view of a further stator vane and a stator vane mounting in accordance with the invention; Figure 6 is an enlarged sectional view of the mounting part of the vane of Figure 5; and Figures 7a to c are schematic perspective views of the stator vane of Figures 5 and 6 showing different modes of vibration and the effect on the mounting.

Figures 1 and 2 illustrate a known mounting arrangement for a stator vane in a gas turbine engine. A stator vane 10 has a main vane body 12, an upper platform 14 at one end of the body 12 and a lower platform 16 at the opposite end of the body 12. The engine has an outer casing 18 and an inner shroud ring 20 and the vane 10 is mounted between the outer casing 18 and the inner shroud ring 20. The outer casing 18 has a recess 22 formed therein which receives the upper platform 14 with a small clearance fit.

The inner shroud ring 20 has a vane mounting recess 24 formed therein. The recess 24 is shaped to receive the lower platform with a small clearance fit. A channel 26 is formed at one side of the vane mounting recess 24. Channel 26 forms a so-called "bird beak" slot which is arranged to receive a tang 28 which projects outwardly from the lower platform l6of the vane 10.

Figures 3 and 4 show a stator vane and the stator vane mounting for a gas turbine engine in accordance with the invention. Parts corresponding to parts in Figures 1 and 2 carry the same reference numerals.

In Figure 3, a vane 10 comprises a main vane body 12, an upper platform 14 and lower platform 16. The upper platform is received in a recess 22 of the outer casing 18 in identical fashion to that in Figure 1.

The lower platform is received in a vane mounting recess 24 in a shroud ring 20. In Figure 3 the vane mounting recess 24 is formed in the outer part of the inner shroud ring 20.

The inner shroud ring 20 comprises a shroud ring base 30 with shroud ring side walls 32, 34 extending from the base 30. Side wall 34 has a thickened portion 36 extending from the base 30 towards the upper part of the side wall 34 terminating short of the top of the side waIl 34. A shoulder 38 projects from the side wall 32 inwardly thereof. The side walls 32, 34 and the upper surfaces of the shoulder 38 and thickened portion 36 define the aforesaid recess 24. A slot 40 is formed in the thickened portion 36 of the side wall 34. The slot 40 has a relatively wide mouth 42 which narrows via tapered walls 44, 46 into the main part of the slot which has a constant depth. A resilient tang 48 extends from the underside of the lower platform 16. The resilient tang 48 is U-shaped in section and has a first part 50 which extends from the underside of the lower platform 16, a bight part 52 and a second leg part 54 which extends substantially parallel with the first part 50. The end of the second leg part 54 acts as the tang in this embodiment.

As can be seen in Figures 3 and 4, the tang is arranged to be received in the slot 40.

The geometry of the inner shroud ring 20, the recess 24, the lower platform 1 6, the slot and the tang 48 are arranged so that the tang is pre-loaded, as shown in Figure 4, when it is received in the slot 40. The tapered walls 44, 46 facilitate insertion of the tang into the slot 40 and also effect the pre-loading.

In the arrangement shown in Figure 4, the tang 48 is resiliently biased back towards the underside of the lower platform 1 6 and is held in tension by the walls of slot 40. This tends to pull the platform 16 into the recess 24 so as to take up any tolerance or wear-induced clearance gaps. If, due to manufacturing tolerances the tang 48 were loaded in compression rather than in tension as in Figure 4, ie if it were pressed against the lower wall 46, that, in turn, would push the upper platform 14 more firmly into the outer casing recess 22. Accordingly, it does not matter whether the tang is pre-sprung in tension or compression. In both cases, the damping effect of the interaction of the tang and the inner shroud and/or the platform 14, 16 on the recesses 22, 24 is made more uniformly consistent by the pre-loading of tang 48.

In Figures 5 and 6 a further stator vane in accordance with the invention is shown.

Again, parts corresponding to parts in Figures 1-4 carry the same reference numerals.

Figures 5 and 6 are a slightly less schematic view than Figures 1-4 of a vane 10. In Figure 5 the upper platform 14 has two tangs 28 which can be used to engage corresponding bird beak slots in the outer casing recess 22 (not shown).

The lower platform 1 6 has a first tang 28 which is received in a channel defined by the shoulder 38 and lipped over upper part of the side waIl 34.

The slot 40 opposes the shoulder 38 and is arranged to receive a resilient tang 56. The tang 56 in Figures 5 and 6 differs from that in Figures 3 and 4 in that its resilience is provided by bending about three bending points 58, 60, 62. The tang extends initially downwardly from the lower platform 16, then bends through point 58 away from the slot 40. The tang then bends back on itself through points 60, 62 to enter the slot 40.

In use, the vane is subjected to torsional loads as indicated by the arrow A in Figure 6.

Figures 7a to 7c illustrate various modes of vibration upon the vane 10 of Figures 5 and 6. In Figure 7a, the vane is in its rest position. In Figure 7b, the vane is subjected to torsional forces at a first frequency mode which cause it to twist about its length. In Figure 7c the vane 1 0 is subjected to torsional forces due to vibrating at a second frequency mode. As can be seen, the mounting arrangement allows a degree of twisting of the lower platform 16 (which is exaggerated in the figure for the sake of clarity). This twisting causes friction between the tang 56 and inner walls of the slot 40 and the tang 28 in the inner walls of the channel 26. That friction damps the vibration that might otherwise cause failure of the vane. The provision of the tang 56 maintains the damping force within a more uniform band, regardless of the clearance being affected by the manufacturing tolerances and/or wear.

Claims (7)

1 A stator vane for a gas turbine engine comprising a vane body, a base and a tang extending from the base, at least part of the tang being resilient so that the tang is arranged to resile relative to the base.

2 A stator vane for a gas turbine engine according to claim 1 in which the tang is U- shaped in section with the resilience being provided by the bight part of the U-shape.

3 A stator vane according to claim 1 or 2 in which the tang extends from the lower part of the base so as to define a clearance between the underside of the base and the tang.

4 A stator vane according to any preceding claim in which the tang extends into a channel in a stator vane mounting part.

A stator vane for gas turbine engine according to claim 4 in which the channel has a tapered mouth to provide a tapered lead-in to the channel for the tang.

6 A stator vane mounting for a gas turbine engine comprising a body defining a recess arranged to receive at least part of a base of a stator vane and a channel adjacent the recess arranged to receive part of a tang of a stator vane, the mouth of the channel being flared outwardly so that the channel tapers inwardly from the mouth inwards.

7 That stator vane mounting for a gas turbine engine according to claim 6 in which both sides of the channel taper inwardly.