GB2109865A - Gas turbine engine compressor air intake - Google Patents

Abstract

The intake comprises an arcuate primary duct 14 which communicates with the compressor 17 and which is provided with a frangible wall portion 18. The latter provides a barrier between the primary duct 14 and a secondary duct 21 and is so arranged to be impacted and penetrated by a foreign body, such as a bird which is above a predetermined weight, which has been ingested through the primary duct inlet 15. After penetrating the wall portion 18 the foreign body passes through the secondary duct 21 and is discharged therefrom at 22.

Description

SPECIFICATION Gas turbine engine compressor air intake This invention relates to a gas turbine engine compressor air intake and in particular to a gas turbine engine compressor air intake which is adapted to remove a heavy ingested foreign body, such as a bird or a part thereof, from the air flowing therethrough prior to that air entering the compressor.

The ingestion of heavy foreign bodies such as birds, by the compressor of gas turbine engines can result in serious damage and, in certain cases lead to a total engine shutdown. One solution to the problem of heavy foreign body ingestion has been to provide the compressor air intake with an inertia separator which utilises the inertia of the body to direct it into an engine by-pass duct from whence it is jettisoned. This, however, is undesirable since it necessitates the provision of a permanent air flow through the bypass duct which is detrimental to engine performance.

Moreover, such by-pass ducts can be expensive to manufacture.

It is an object of the present invention to provide a gas turbine engine compressor intake which is adapted to remove a heavy ingested foreign body, such as a bird, from the air flowing therethrough and which prior to ingestion of a heavy foreign body, is not detrimental to engine performance.

According to the present invention, an air intake for a compressor of a gas turbine engine comprises a primary duct having an air inlet and an air outlet, said air outlet being adapted to deliver air from said primary duct to the compressor of the gas turbine engine, said primary duct being at least partially arcuate in cross-sectional form whereby any foreign body above a predetermined weight which is ingested through said air inlet impacts a portion of the wall of said primary duct, said internal wall portion being frangible and defining a barrier between said primary duct and a secondary duct, said secondary duct and frangible wall portion being so adapted and disposed that any such impacting body penetrates said frangible wall portion, enters said secondary duct and is subsequently discharged therefrom at a location remote from said primary duct.

Said portion of the wall of said primary duct is preferably rendered frangible by the provision of lines of weakness therein.

Said portion of said wall of said primary duct may be formed from a sheet of a light alloy, said lines of weakness being constituted by regions of reduced thickness of said sheet.

Said regions of reduced thickness of said sheet may be so arranged that when said sheet is penetrated by a foreign body, it divides along at least some of said lines of weakness to define a plurality of flaps, each of which remains attached to said sheet.

Said portion of the wall of said primary duct, said primary duct and said secondary duct are preferably so configured and dimensioned that said foreign body may be a bird.

Said air intake may be adapted to be located on the underside of a gas turbine engine.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a sectional side view of a gas turbine engine compressor air intake in accordance with the present invention attached to a gas turbine engine.

Figure 2 is a view on arrow A of the air intake shown in Figure 1.

Figure 3 is a view of the frangible portion of the air intake shown in Figure 1.

Figure 4 is a side view of the frangible portion shown in Figure 3 after it has been penetrated by a foreign body.

Figure 5 is a view on section line B-B of Figure.3.

With reference to Figure 1 a gas turbine engine generally depicted by broken lines at 10 is provided with a reduction gearbox 11 having an output drive flange 12 for driving a propellor (not shown). The gas turbine engine 10 and its reduction gearbox 11 are enclosed within a nacelle 13, part of which is shown in Figure 1.

The nacelle 13 also contains a primary duct 14 which has an air inlet 1 5 and an air outlet 16. The air inlet 15, which can also be seen in Figure 2, is of approximately elliptical cross-sectional shape and positioned below the reduction gearbox 11.

The air outlet 16 is generally annular in form and is adapted to deliver air from the primary duct 14 to the compressor 1 7 of the gas turbine engine 10. Thus the primary duct 14 develops from the approximately eliiptical shape of the air inlet 1 5 to the generally annular shape of the air outlet 16. It will be appreciated however that the air inlet 1 5 could be positioned above the reduction gearbox 11 if necessary.

In order to enable the air inlet 15 to be positioned below the reduction gearbox 1 the primary duct 14 is partially arcuate in crosssectional form as can be seen in Figure 1.

Consequently, air which passes through the primary duct 14 on its way to the gas turbine engine compressor 1 7 is directed to follow a tortuous path. If the air passing through the primary duct 14 carries a foreign body, and if that body is above a certain weight, it will not follow the path of the air flow but will instead impact a portion 1 8 of the wall 1 4a of the primary duct 14.

The portion 18 of the wali 14a which is impacted by any such foreign bodies above a certain weight is frangible so as to be penetrated by such bodies. More specifically the wall portion 18, which can be seen in more detail in Figure 3, is made from an aluminium alloy sheet which has been weakened by the provision of lines of weakness 1 9 therein. The lines of weakness 1 9 are formed by chemically etching the wall portion 1 8 to provide local reductions in its wall thickness. The lines of weakness 1 9 are so arranged that those which are adjacent the periphery 20 of the wall portion 1 8 are of greater thickness than the remainder.This is so that if the wall portion 18 is impacted by a foreign body which is above a certain weight, it will divide in the manner shown in Figure 4 to define a plurality of flaps 21 with lines of weakness 19 of greater thickness acting as hinges whilst the remaining thinner lines of weakness 1 9 fracture.

The degree of curvature of the primary duct 14 and the thickness of the lines of weakness 1 9 in the wall portion 18 are selected so that the wall portion 1 8 is impacted and penetrated only by a foreign body which is above a predetermined weight. The value of this predetermined weight is selected so that any foreign body ingested through the air inlet 15 which is of such a weight as to be likely to damage the gas turbine engine 10 if it were to be ingested thereby impacts and penetrates the wall portion 1 8. The most common foreign body of such a weight which is likely to be encountered by a gas turbine engine is a bird. Consequently the wall portion 18 is so dimensioned that if it is so impacted, it opens to define an aperture which is sufficiently large to permit the passage of a bird therethrough.

The wall portion 18, when intact, also defines a barrier between the primary duct 14 and a secondary duct 21. The secondary duct 21 is also enclosed within the nacelle 13 and is provided with an outlet 22 on the underside of the nacelle 13. The secondary duct 21 is downwardly inclined and so dimensioned that if a foreign body impacts and penetrates the wall portion 18, it passes into the secondary duct 21 and is subsequently discharged therefrom through the outlet 22.

It will be seen therefore that if a foreign body above a predetermined weight, such as a bird, is ingested through the air inlet 15, it impacts and penetrates the wall portion 18 before being discharged from the nacelle 13 through the secondary duct 21. Penetration of the wall portion 18 will of course create a by-pass flow for air entering the air inlet 1 5. However this will have only a small effect upon intake performance and consequently upon the performance of the gas turbine engine 10. The damaged wall portion 1 8 could then be replaced at the next convenient opportunity.

The present invention is also applicable to the air intakes of gas turbine engines having more than one compressor. Thus in the case of ducted fan gas turbine engine, it is common to have three compressors in flow series, these being termed the low, intermediate and high pressure compressors. The intermediate and high pressure compressors of such engines are usually of different diameters, the high pressure compressor being of a smaller overall diameter than the intermediate pressure compressor. This necessitates a primary duct interconnecting the outlet of the intermediate pressure compressor with the inlet of the high pressure compressor which is at least partially arcuate in sectional form. Such a primary duct would normally contain stator aerofoil vanes to direct the air from the intermediate compressor into the high pressure compressor. However, any foreign bodies, such as bird portions, which have been ingested by and passed through the intermediate pressure compressor would, if they were above a certain mass, impact the wall of the primary duct between adjacent stator aerofoil vanes. This being so, those impacted wall portions could be made to be frangible so that the foreign bodies would pass through the wall of the primary duct and be ejected from the engine through a suitable secondary duct, one of which would be associated with each frangible wall portion.

Although the present invention has been described with reference to a frangible wall portion 1 8 which is in the form of a weakened sheet of a light alloy material, it will be appreciated that other suitable frangible materials may be employed if it is so desired.

Claims (7)

Claims

1. An air intake for a compressor of a gas turbine engine comprising a primary duct having an air inlet and an air outlet, said air outlet being adapted to deliver air from said primary duct to the compressor the gas turbine engine, said primary duct being at least partially arcuate in cross-sectional form whereby any foreign body above a predetermined weight which is ingested through said air inlet impacts a portion of the wall of said primary duct, said wall portion being frangible and defining a barrier between said primary duct and a secondary duct, said secondary duct and frangible wall portion being so adapted and disposed that any such impacting body penetrates said frangible wall portion, enters said secondary duct and is subsequently discharged therefrom at a location remote from said primary duct.

2. An air intake for a compressor of a gas turbine engine as claimed in claim 1 wherein said portion of the wall of said primary duct is rendered frangible by the provision of lines of weakness therein.

3. An air intake for a compressor of a gas turbine engine as claimed in claim 2 wherein said portion of the wall of said primary duct is formed from a sheet of a light alloy, said lines of weakness being constituted by regions of reduced thickness of said sheet.

4. An air intake for a compressor of a gas turbine engine as claimed in claim 3 wherein said region of reduced thickness of said sheet are so arranged that when said sheet is penetrated by a foreign body, it divides along at least some of said lines of weakness to define a plurality of flaps, each of which remains attached to said sheet.

5. An air intake for a compressor of a gas turbine engine as claimed in any one preceding claim wherein said portion of the wall of said primary duct, said primary duct and said secondary duct are so configured and dimensioned that said foreign body may be a bird.

6. An air intake for a compressor of a gas turbine engine as claimed in any one preceding claim wherein said air intake is adapted to be located on the underside of a gas turbine engine.

7. An air intake for a compressor of a gas turbine engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.