GB2514832A

GB2514832A - Cooling system

Info

Publication number: GB2514832A
Application number: GB201310132A
Authority: GB
Inventors: Sten Brandenburg
Original assignee: Rolls Royce Deutschland Ltd and Co KG
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 2013-06-07
Filing date: 2013-06-07
Publication date: 2014-12-10
Also published as: GB201310132D0

Abstract

An impingement cooling system 70, eg for cooling nozzle guide vanes or static turbine liners in gas turbine engines, comprises an impingement plate 74 with an array of jet holes 82 and a filter plate 72 with an array of filter holes 80, the filter plate 72 being upstream of the impingement plate 74. There is an interspace 76 between the filter plate 72 and the impingement plate 74, such that in use, fluid entering the interspace 76 from a single filter hole 80 is able to pass through at least two jet holes 82 to reduce the likelihood of the jet holes 82 being blocked by particles in the cooling fluid. The plates 72, 74 may be flat, rectangular and parallel. The filter holes 80 and the jet holes 82 may be of the same shape, eg circular. The cross-sectional area of the filter holes 80, which are preferably smaller than the jet holes 82, may be equal to or greater than that of the jet holes.

Description

COOLING SYSTEM

The present invention relates to cooling systems. More specifically the invention relates to an impingement cooling system, a nozzle guide vane and a gas turbine engine. The invention may have application in relation to impingement cooling of surfaces of nozzle guide vanes used in gas turbine engines. The invention is not however limited to such applications and could be used in alternative applications, such as impingement cooling of static turbine liners.

Impingement cooling is a method of cooling a surface by directing (usually multiple) jets of high velocity, low temperature cooling fluid at the surface. The fluid is deflected at the surface, thereafter travelling parallel to it and cooling an additional area of the surface. The jets are produced by passing the fluid through an impingement plate comprising a number of jet holes. Impingement cooling may be particularly useful where there is a limited supply of air or pressure margin and a relatively hot surface to be cooled, for instance the outer walls of nozzle guide vanes.

One potential concern with impingement plates is that the jet holes may become blocked. A particle in the cooling fluid may be sufficient to block a jet hole alone.

Additionally or alternatively particulates may build up on the surface of the impingement plate or at its base, ultimately reducing flow through or blocking one or more jet holes. Blocking jet holes may have significant consequences. An impingement cooled nozzle guide vane may for example have an increased temperature where one or more jet holes are blocked. This may reduce the life of the vane and potentially the life of downstream components (which might experience vibration forcing as a result of damage to the upstream vanes).

Various mechanisms are known for reducing the likelihood of jet hole blockage.

One option is to elongate the shape of the inlet of the jet holes into channels.

This may trap particles at the inlet while allowing gas flow to continue around the blockage. Nonetheless particles of sufficient size to block the jet hole can still enter the channel if orientated correctly.

Another option is to provide a mesh of smaller holes resting on the impingement plate, but this tends to restrict the flow (especially with moderate particulate build-up), with the supply of cooling fluid to each jet hole being consequently limited to a relatively small number of nearby mesh holes. The mesh may also provide a framework for accumulation of particulate matter, accelerating jet hole blockage.

According to a first aspect of the invention there is provided an impingement cooling system comprising optionally an impingement plate optionally with an array of jet holes and optionally a filter plate with optionally an array of filter holes, where, in use, the filter plate is optionally upstream of the impingement plate and where there is optionally at least one interspace between the filter plate and the impingement plate, such that in use, fluid entering the interspace from a single filter hole is optionally able to pass through at least two jet holes.

The provision of the interspace may mean that there is space between the filter plate and impingement plate, allowing fluid flow around an area between the two plates, therefore potentially avoiding flow starvation of a jet hole as the result the blockage of a single (or a proportion of the filter holes). The use of interspaces each allowing a single filter hole to feed multiple jet holes may be a more reliable way of promoting continued fluid flow to more jet holes, than a system where each jet hole can only be reliably fed by a plurality of closely spaced filter holes.

In some embodiments each filter hole has a largest dimension across its inlet smaller than the smallest dimension across the inlet of each jet hole. In this way any debris particle passing through a filter hole may be unable to entirely block a jet hole and may be less likely to bridge a jet hole. Such debris may therefore be more likely to pass through a jet hole regardless of its orientation upon reaching an intake of the relevant jet hole. Blockages of filter holes are therefore more likely than blockages of jet holes.

In some embodiments the filter holes and jet holes are substantially the same shape. They may in particular have a circular cross-section.

In some embodiments there are more filter holes than jet holes. In this way the impact of a blockage at one or more filter holes may be reduced.

In some embodiments the total cross-sectional area of all filter holes is approximately equal to or greater than the total cross-sectional area of all jet holes. In this way the addition of the filter plate may not significantly impact on the overall pressure drop across the cooling system when it is in use.

In some embodiments at least one of the interspaces between the filter plate and impingement plate is arranged to provide a fluid flow path along the surface of the impingement plate, uninterrupted by the filter plate, from one side of the impingement plate to another side of the impingement plate. The fluid flow path may be in fluid communication with multiple jet holes and/or multiple filter holes.

In this way the number of jet holes that may be fed by each filter hole may be increased.

In some embodiments the sides of the impingement plate connected by the fluid flow path are opposite one another.

In some embodiments the fluid flow path is a straight line.

In some embodiments there is no contact between the filter plate and the impingement plate within the area of each plate bounded by the array of filter holes or jet holes respectively. This may mean that neither plate interrupts or prevents the flow of fluid from any filter hole to all jet holes.

In some embodiments the interspace is arranged such that fluid entering the interspace from any single filter hole is able to pass through all jet holes in the impingement plate. In this way, even if structural links or other components are provided between the filter plate and impingement plate, all jet holes are in fluid communication with all filter holes.

In some embodiments the interspace is uninterrupted in the volume between the array of filter holes and the array of jet holes. There may therefore be no structural links or other components between the plates that might impede the free flow of fluid around the interspace. This may allow the interspace to provide uninterrupted flow paths from any filter hole to all jet holes.

In some embodiments the filter plate and impingement plate are substantially flat.

In some embodiments the filter plate and the impingement plate are substantially parallel.

In some embodiments the impingement cooling system is for use in a nozzle guide vane of a gas turbine engine.

According to a second aspect of the invention there is provided a nozzle guide vane comprising an impingement cooling system according to the first aspect of the invention.

According to a third aspect of the invention there is provided a gas turbine engine comprising an impingement cooling system according to the first aspect of the invention.

The skilled person will appreciate that a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention.

Embodiments of the invention will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a sectional side view of a gas turbine engine; Figure 2 is a portion of a gas turbine core showing a nozzle guide vane; Figure 3 is a top sectional view of a prior art nozzle guide vane; Figure 4 is top sectional view of a nozzle guide vane according to an embodiment of the invention; Figure 5 is a schematic perspective view of an impingement cooling system according to an embodiment of the invention.

A gas turbine engine 10 is shown in Figure 1 and comprises an air intake 12 and a propulsive fan 14 which generates two airflows A and B. The gas turbine engine 10 comprises, in axial flow A, an intermediate pressure compressor 16, a high pressure compressor 18, a combustor 20, a high pressure turbine 22, an intermediate pressure turbine 24, a low pressure turbine 26 and an exhaust nozzle 28. A nacelle 30 surrounds the gas turbine engine 10 and defines, in axial flow B, a bypass duct 32.

The high pressure turbine 22 has a single stage of blades which are downstream in airflow A of an array of nozzle guide vanes (NGV5) (not shown). Figure 2 shows an exemplary NGV 40. The NGVs 40 are stationary components (stators) used to direct the airflow A at a desired angle into the blades of the high pressure turbine 22. The NGVs 40 are in a relatively hot environment (being immediately downstream of the combustor 20) and are therefore typically cooled using bleed air C from the high pressure compressor 18. The bleed air C enters a cavity 42 in the NGV 40 from a radially outer orifice 44 (see Figure 3). Once inside the cavity 42, some of the bleed air C is vented through outlet holes 46 in an outer wall 48 of the NGV 40, which may then flow over the exterior surface of the outer wall 48 forming a protective shroud around the NGV 40. Additional bleed air passes through an impingement plate 50 positioned within the NGV cavity 42 having an array of jet holes 52. The jet holes 52 direct the bleed air C onto an interior surface of the outer wall 48, impingement cooling it from the inside. From there the bleed air cools further downstream areas of the outer wall 48 as well as the trailing edge. The jet holes 52 are however susceptible to blockage by particulate matter in the bleed air C. With at least some of the jet holes 52 blocked, cooling effectiveness for the NGV 40 may be significantly reduced, potentially reducing the life of the NOV 40 and blades of the downstream high pressure turbine 22.

Referring now to Figure 4, an NGV 60 according to an embodiment of the present invention is shown. NOV 60 has an outer wall 62 forming an aerofoil shape and defining a cavity 64 within the NOV 60. The cavity 64 is in fluid communication with a radially outer orifice 66 formed in the outer wall and a plurality of smaller outlet holes 68 passing through and distributed around areas of the outer wall 62.

Dividing the cavity 64 there is provided an impingement cooling system (best shown in Figure 5) generally shown at 70. The impingement cooling system 70 comprises a filter plate 72, an impingement plate 74 and an interspace 76 there between. The filter plate 72 and the impingement plate 74 are both rectangular, are of the same size, are parallel to each other and are flat (that is they are not contoured or otherwise shaped). The impingement plate 74 has four sides 78a-d, with sides 78a and 78c being opposite each other, and likewise sides 78b and 78d being opposite each other.

Passing through the filter plate 72 are an array of filter holes 80. Passing through the impingement plate 74 are an array of jet holes 82. The filter holes 80 are of consistent shape and size. The jet holes 82 are also of consistent shape and size. The filter holes 80 and jet holes 82 are circular in shape, but the filter holes are smaller than the jet holes 82. The largest dimension (in this case constant, that is, it's diameter) across an inlet of each filter hole 80 is smaller than the smallest dimension (in this case constant, that is, it's diameter) across an inlet of each jet hole 82. As will be appreciated, in alternative embodiments with non-circular filter 80 or jet 82 holes, the largest or smallest dimension will be respectively the largest or smallest distance that can be measured across the inlet of the hole 80, 82). The total cross-sectional area of all filter holes 80 is greater than the total cross-sectional area of all jet holes 82. Each of the arrays of holes 80, 82 covers substantially the same area of its respective plate 72, 74.

As shown in Figure 4, the filter plate 72 is positioned upstream of the impingement plate 74 (that is air in the cavity 64 encounters the filter plate 72 before the impingement plate 74). Further there are no fluid flow paths around the filter plate 72 or around the impingement plate 74. Therefore the only fluid communication paths from one side of the impingement cooling system 70 to the other is via the filter holes 80, interspace 76 and jet holes 82.

The filter plate 72 and impingement plate 74 are separated (they are not in contact). The interspace 76 (the gap between the plates 72, 74), is uninterrupted in the volume between the array of filter holes 80 and the array of jet holes 82.

That is, there is no contact of, or linking element between, the plates 72, 74 in the volume between the area of each plate 72, 74 bounded by its respective array of holes 80, 82. Consequently there are uninterrupted, straight flow paths, not only along the surface of the impingement plate 74 facing the interspace 76 from all sides 78a-d to all other sides 78a-d, but also from each filter hole 80 to all jet holes 82.

In use, compressor bleed air enters the NGV 60 via the radially outer orifice 66 and passes into the cavity 64. Some of this air is forced out of the outlet holes 68, subsequently passing over the exterior surface of the outer wall 62, at least partially protecting it from hot air leaving the combustor. Some of the air passing into the cavity 64 is also incident on the impingement cooling system 70.

Air passes through the filter holes 80 and into the interspace 76, before passing through the jet holes 82. The impingement cooling system is orientated such that air leaving the jet holes 82 is jetted onto an interior surface of the outer wall 62.

This cools the outer wall 62.

The filter plate 72 does not substantially impact on the pressure drop across the impingement cooling system 70 because the total cross-sectional area of all the filter holes 80 is approximately equal to or greater than the total cross-sectional area of all the jet holes 82.

Where the air incident on the impingement cooling system 70 contains particulates of sufficient size to completely block one or more jet holes 82, these particulates will be prevented from reaching the interspace 76 and jet holes 82 by the filter plate 72. This is as a result of the largest dimension across the inlet of each filter hole 80 being smaller than the smallest dimension across the inlet of each jet hole 82.

As will be appreciates such particulates may completely block a filter hole 80.

Nonetheless there are multiple additional filter holes 80 through which the air may continue to pass. Further the nature of the interspace 76 means that there is a free line of sight from each filter hole 80 to each jet hole 82. Air is therefore free to follow flow paths that are substantially parallel to the plates 72, 74 within the interspace 76, at any distance from either plate 72, 74. Further swirling or irregular flow paths may be followed, potentially with a net displacement of air in a direction parallel to the plates 72, 74. In this way the presence and arrangement of the filter plate 72 relative to the impingement plate 74 may mean that particles that might otherwise block the jet holes 82 are prevented from reaching them. Further adequate air supply to each jet hole 82 may be maintained via non-blocked filter holes 80 (the flow paths necessary for this to occur being unimpeded).

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the various concepts described herein. Any of the features may be employed separately or in combination with any other features and the invention extends to and includes all combinations and sub-combinations of one or more features described herein in any form of impingement cooling system.

Claims

Claims 1. An impingement cooling system comprising an impingement plate with an array of jet holes and a filter plate with an array of filter holes, where, in use, the filter plate is upstream of the impingement plate and where there is at least one interspace between the filter plate and the impingement plate, such that in use, fluid entering the interspace from a single filter hole is able to pass through at least two jet holes.
2. An impingement cooling system according to claim 1 where each filter hole has a largest dimension across its inlet smaller than the smallest dimension across the inlet of each jet hole.
3. An impingement cooling system according to claim 1 or claim 2 where the filter holes and jet holes are substantially the same shape.
4. An impingement cooling system according to any preceding claim where there are more filter holes than jet holes.
5. An impingement cooling system according to any preceding claim where the total cross-sectional area of all filter holes is approximately equal to or greater than the total cross-sectional area of all jet holes.
6. An impingement cooling system according to any preceding claim where at least one of the interspaces between the filter plate and impingement plate is arranged to provide a fluid flow path along the surface of the impingement plate, uninterrupted by the filter plate, from one side of the impingement plate to another side of the impingement plate.
7. An impingement cooling system according to claim 6 where the sides of the impingement plate connected by the fluid flow path are opposite one another.
8. An impingement cooling system according to claim 6 or claim 7 where the fluid flow path is a straight line.
9. An impingement cooling system according to any preceding claim where there is no contact between the filter plate and the impingement plate within the area of each plate bounded by the array of filter holes or jet holes respectively.
10. An impingement cooling system according to any preceding claim where the interspace is arranged such that fluid entering the interspace from any single filter hole is able to pass through all jet holes in the impingement plate.
11. An impingement cooling system according to any preceding claim where the interspace is uninterrupted in the volume between the array of filter holes and the array of jet holes.
12. An impingement cooling system according to any preceding claim where the filter plate and impingement plate are substantially flat.
13. An impingement cooling system according to any preceding claim where the filter plate and the impingement plate are substantially parallel.
14. A nozzle guide vane comprising an impingement cooling system according to any of claims ito 13.
15. A gas turbine engine comprising an impingement cooling system according to any of claims ito 13.
16. An impingement cooling system of the kind set forth substantially as described herein with reference to and as illustrated in of the accompanying drawings.