GB2373024A

GB2373024A - Tip treatment bar coated with a vibration damping material for a casing of a gas turbine engine

Info

Publication number: GB2373024A
Application number: GB0105392A
Authority: GB
Inventors: Andrew Motherwell; Brynley Clark
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2001-03-05
Filing date: 2001-03-05
Publication date: 2002-09-11
Anticipated expiration: 2021-03-05
Also published as: GB2373024B; GB0105392D0; US6648593B2; US20020122718A1

Abstract

A tip treatment bar 16 for use in a gas turbine engine casing (figure 1) has a coating 24 applied to at least part of at least one face of the bar 16. The coating 24 may be applied to a substrate 26 which is attached to the bar 16 or it may be applied directly to the bar 16. The coating 24 may be a hard ceramic coating and it may be applied to the bar or the substrate by plasma spraying. A number of bars 16 may be disposed in an annular array to form a ring, and they may have end supports which are either formed integrally with the bars 16 or separately from them.

Description

-1- TIP TREATMENT BARS FOR GAS TURBINE ENGINES

This invention relates to tip treatment bars of a rotor casing for a gas turbine engine.

W094/20759 discloses an anti-stall tip treatment 5 means in a gas turbine engine, in which an annular cavity is provided adjacent the blade tips of a compressor rotor. The cavity communicates with the gas flow path through the compressor through a series of slots defined between solid tip treatment bars lo extending across the mouth of the cavity.

Such tip treatments are applicable to both fans and compressors of gas turbine engines, and their purpose is to improve the blade stall characteristics or surge characteristics of the compressor.

15 Known tip treatment bars are solid and relatively robust and, in general, have poor damping characteristics. Consequently, they are susceptible to high cycle fatigue failure. As the ends of the blades pass the tip treatment bars, the bars are 20 aerodynamically excited. Vibration is induced in the bars in operation of the engine at a frequency determined by the passage of the blades. The vibrating bars deflect in a generally circumferential direction and consequently fatigue failure tends to be initiated 25 by cracking at the slot ends.

According to the present invention there is provided a tip treatment bar for a gas turbine to which bar a coating is applied.

In an embodiment in accordance with the invention, 30 the coating acts to dissipate strain energy generated by deflection of the bar as it vibrates. Consequently the amplitude of the vibrations is reduced, so combatting high cycle fatigue failure.

The coating may be a hard ceramic coating, such as 35 Magnesia Alumina Spinel. The coating may be applied directly to the material of the bar, for example by

-2- plasma spraying, but alternatively the coating may be applied to a substrate and which is subsequently bonded to the bar.

The tip treatment bars may be made individually 5 and subsequently assembled with end supports to form a tip treatment ring. In another embodiment, a plurality of bars are formed as ring sections by injection moulding and these sections are assembled together to form the ring. Alternatively, the entire ring can be 10 formed by appropriate machining of a single component.

In embodiments in which the hard coating is applied to a substrate, which is bonded onto the tip treatment bar, the substrate may be metal and the coating may be applied to the substrate by plasma 15 spraying. This has the advantage that the coating can be applied to non metallic tip treatment bars, for example those made of composite material, such as an organic matrix composite material, which might not withstand high temperatures of the coating deposition 20 processes such as plasma spraying. The coating may be applied, directly or indirectly, to at least one side of the tip treatment bar.

For a better understanding of the present invention, and to show more clearly how it may be 25 carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a partial axial sectional view of a fan stage in a gas turbine engine; Figure 2 is a view of tip treatment bars suitable 30 for use in the engine of Figure l; Figure 3 is a view of a first embodiment of a coated tip treatment bar; Figure 4 is a view of a second embodiment of a coated tip treatment bar.

35 Figure 5 is a sectional view of a tip treatment ring; and

-3- Figure 6 is a view in the direction of the arrow VI in Figure 5.

Figure 1 represents a fan casing 2 of a gas turbine engine. A fan, represented by a single blade 5 4, is mounted for rotation in the casing 2. Guide vanes 6 and 8 are provided upstream and downstream, respectively, of the fan 4. The casing 2 includes a circumferentially extending chamber 10, which communicates with the main gas flow through the fan 10(represented by an arrow 12) through an array of slots 14 (see Figure 2) defined between tip treatment bars 16 disposed around the casing. The function of the chamber 10 in delaying the onset of stalling of the blades 4 is disclosed in International Patent 15 Publication W094/20759.

The tip treatment bars 16 are supported by annular front and rear end supports 18, 19 to provide a tip treatment ring 20 which is fitted within the casing 2 and extends around the fan 4. By way of example, the 20 end supports 18, 19 and the bars are made from an organic matrix composite material, such as a carbon fibre/bismaleimide composite.

As shown in Figure 2, the tip treatment bars are provided with damping boots 22 as discussed in greater 25 detail in our British Patent No. 0013772.9.

Alternatively, the boots 22 may be dispensed with so that the bars are connected directly to the end supports 18, 19.

As shown in Figure 3, the treatment bar 16 is 30 provided with a coating 24. The coating 24 comprises Magnesia Alumina Spinel and is applied by plasma spraying onto a metal substrate 26 before the metal substrate 26 is applied to the bar 16. After the plasma spraying operation is complete, and the 35 substrate 26 has cooled, the substrate 26 is bonded to the bar 16. In the embodiment of Figure 3, the coating

24 is applied to one side only of the bar 16. In the embodiment illustrated in Figure 4, two oppositely disposed sides of the bar 16 are each provided with a respective substrate 26 and coating 24. In the 5 assembled ring 20 as shown in Figure 2, the surface or surfaces to which the coating 24 is applied face generally circumferentially of the ring.

In operation of the engine shown in Figure l, equipped with the coated tip treatment bars 16 as 10 described with reference to Figure 3 or 4, vibration is induced in the bars 16 at a frequency determined by the passage of the blades 4. The vibrating bars 16 deflect in a generally circumferential direction.

The damping characteristic of the hard coating 24 15 on the tip treatment bars 16 reduces the amplitude of induced vibrations in the tip treatment bars 16. This measure, therefore, reduces the incidence of high cycle fatigue failure in the tip treatment bars 16.

If the material of the tip treatment bar 16 is 20 able to withstand the heat generated in the plasma spraying process, then the coating 24 can be applied directly to the bar 16 without requiring the separate substrate 26. This possibility is illustrated in Figures 5 and 6, which show a tip treatment ring 28 25 which is formed as an integral component from an appropriate alloy.

Since only part of each circumferential surface of each bar 16 is accessible for plasma spraying, in view of the "line of sight" nature of the spraying process, 30 some regions 29 of these surfaces will not receive the coating 24. Nevertheless, the restricted coated area serves, as mentioned above, to reduce the amplitude of vibration so as to minimise high frequency fatigue cracking of the bars 16. If it is desired to apply the 35 coating to the full extent of the circumferential surfaces of the bars 16, the bars 16 can be made and

coated separately, as described with reference to Figures 3 and 4, although, if the bars 16 are made from alloy, the substrate 26 is not required.

The coatings do not contribute significantly to 5 the impact strength of the tip treatment bar under blade or blade tip release conditions. This is desirable since the blade tip containment philosophy is for blade fragments to penetrate the tip treatment casing and be brought to rest by an external 10 containment system such as a Kevlar wrap.

In the described embodiments, the tip treatment bars are solid. The bars may alternatively have a hollow, thin walled configuration.

Claims

-6 Claims

1. A tip treatment bar for a gas turbine, the bar having a coating applied over at least part of at least one face of the bar.

2. A tip treatment bar as claimed in claim 1, in which the coating comprises a hard ceramic coating.

3. A tip treatment bar as claimed in claim 1 or 10 2, wherein the coating is Magnesia Alumina Spinel.

4. A tip treatment bar as claimed in any one of the preceding claims, wherein the coating is applied to a substrate which is bonded to the bar.

5. A tip treatment bar as claimed in claim 4, wherein the substrate is metal.

6. A tip treatment bar as claimed in claim 4 or 20 5, wherein the substrate is bonded to the bar by a low temperature process.

7. A tip treatment bar as claimed in any one of claims 1 to 3, wherein the coating is applied directly 25 to the material of the bar.

8. A tip treatment bar as claimed in any one of claims 4 to C, or in claim 7, wherein the coating is applied to the substrate or to the material of the bar 30 by plasma spraying.

9. A tip treatment bar as claimed in any one of the preceding claims, wherein the coating is applied to one surface of the bar only.

10. A tip treatment bar as claimed in any one of

-7 claims 1 to 8, wherein the coating is applied to two oppositely disposed surfaces of the bar.

11. A tip treatment bar as claimed in any one of 5 the preceding claims, wherein the material of the bar is metal.

12. A tip treatment bar as claimed in any one of claims 1 to 10, wherein the material of the bar is a 10 composite material.

13. A tip treatment bar as claimed in claim 12, wherein the material of the bar is an organic matrix composite material.

14. A tip treatment bar substantially as described herein with reference to, and as shown in, Figures 2 to 4 or Figures 5 and 6 of the accompanying drawings.

15. A tip treatment ring comprising a plurality of tip treatment bars in accordance with any one of the preceding claims, the bars being disposed in an annular array and supported at their ends by end supports.

16. A tip treatment ring as claimed in claim 15, in which each bar has oppositely disposed surfaces which face generally in the circumferential direction of the ring, the coating being applied to one or both 30 of the circumferentially facing surfaces.

17. A tip treatment ring as claimed in claim 15 or 16, wherein the bars are manufactured as separate components which are subsequently assembled with the 35 end supports to form the ring.

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18. A tip treatment ring as claimed in claim 16, in which the coating is applied to the bars prior to assembly of the ring.

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19. A tip treatment ring as claimed in claim 15 or 16, wherein the bars and the end supports are formed integrally.