GB2518379A

GB2518379A - Aerofoil cooling system and method

Info

Publication number: GB2518379A
Application number: GB1316613.7A
Authority: GB
Inventors: Richard Whitton
Original assignee: Rolls Royce Deutschland Ltd and Co KG
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 2013-09-19
Filing date: 2013-09-19
Publication date: 2015-03-25
Also published as: GB201316613D0

Abstract

An aerofoil cooling system 38, especially for a gas turbine engine nozzle guide vane, comprising a baffle 158 and a cooling fluid flow path 154 is disclosed. The baffle is disposed within the cooling fluid flow path, and the cooling fluid flow path comprises an internal passage 146 of an aerofoil. The baffle has a single through bore 162 inset and discrete from an outer perimeter 160 of the baffle that provides the only fluid communication path through the baffle to the cooling fluid flow path on opposite sides of the baffle. Preferably the system includes two cooling fluid sources with the cooling fluid flow path in between. The through bore may be a circular hole in the centre of the baffle. The baffle may be located at one end of the internal passage and include a skirt around the perimeter.

Description

I

AEROFOIL COOLING SYSTEM AND METHOD

The present invention concerns the cooling of aerofoils and mitigation of foreign body ingestion into the cooling systems for aerofoils. More specifically the invention concerns aerofoil cooling systems, aerofoils, gas turbine engines, and methods of cooling aerofoils. The invention may have particular application to nozzle guide vanes for high pressure turbines in gas turbine engines. For simplicity the background to the invention is discussed in terms of issues with such nozzle guide vanes, but the invention is not limited to such applications.

In gas turbine engines, nozzle guide vanes for high pressure turbines are typically exposed to working gas temperatures liable to damage or destroy the guide vane. To combat this, working gas at a lower temperature is bled from the compressor and delivered to an internal passage through the guide vane. This pressurised cooling gas is then used both for impingement cooling of the vanes and to produce a protective shroud around the external surfaces of the vane as it exits a series of cooling fluid holes.

Typically cooling air is delivered to both ends of the guide vane internal passage and these two supplies of cooling air may be at different pressures. In order to maintain the pressure differential between the two sources of cooling air, a baffle is typically provided in the internal passage, or within its vicinity, so as to provide an impediment to fluid communication. Nonetheless it may be desirable that the baffle does not provide a perfect seal, such that it may allow contaminants (e.g. dust and dirt) within the cooling fluid to leave the vane. Otherwise the contaminants may accumulate within the internal passage and particularly on the baffle itself.

Contaminant accumulation can lead to cooling fluid holes becoming constricted or blocked. Dirt tends to rest on internal surfaces andlor it becomes lodged in the cooling fluid holes themselves. This may be due to simple mechanical interlocking of rough shaped dirt. Reactions may also take place between particles and/or particles and the materials of the vane, especially in the relatively hot conditions in and around the vane. Constituents of air such as water vapour, carbon rJioxide and sulphur dbxide can also contribute to reactions.

Typicafly a gap is left around the perimeter of the baffle with a view to aflowing contaminants to pass through the baffle and out of the internal passage. The gap is sized so as the pressure differential across the baffle is substantiafly maintained, in this way cooling fluid holes on one side of the baffle can be supplied with air from one source of cooling air and those on the other side of the baffle can be supplied by another. In theory the perimeter gap should also prevent: fouling of coong fluid holes by the baffle.

n reality however the perimeter gap tends to become blocked by contaminants, especially as it must be relatively thin in order to maintain the pressure differential across the baffle. This may be a particular problem as nearby cooling fluid holes may also be blocked. Further a build-up of contaminants on the baffle itself may reach the height of nearby cooling fluid holes, constricting or blocking them. These problems lead to overheating, increased oxidation and thermal fatigue damage. This may result in loss of material of the vane and increased vibration forcing on the downstream turbine blade.

The problem may be partially overcome by moving the baffle to the end of the internal passage, where temperatures tend to be lower and so the impact of cooling fluid hole constriction is somewhat lessened, Nonetheless it is still desirable to reduce cooling fluid hole blocking further, and there remains the problem of a blocked gap around the baffle.

According to a first aspect of the invention there is provided an aerofoil cooling system comprising optionally a baffle and optionally a cooling fluid flow path, the baffle being optionally disposed within the cooling fluid flow path, the cooling fluid flow path optionally comprising an internal passage of an aerofoil, and where further the baffle optionally has a single through bore optionally inset and discrete from an outer perimeter of the baffle and optionally providing the only fluid communication path through the baffle to the cooling fluid flow path on opposite sides of the baffle. By insetting the through-bore from the perimeter of the baffle (rather than for example providing a gap at the baffle perimeter), the blocking of the through-bore may be less likely, and any blocking of the through bore would be less likely to block or constrict flow to adjacent cooling fluid holes.

In some embodiments the aerofoil cooling system further comprises two cooling fluid sources, the cooling fluid flow path being intermediate and connecting the two cooling fluid sources.

In some embodiments the internal passage is at least partially defined by a JO passage wall having at least one cooling fluid hole passing there through.

In some embodiments the cross-sectional area of the through bore is such that when the aerofoil cooling system is in use, any and each cooling fluid hole on one side of the baffle is supplied by one of the cooling fluid sources and any and each cooling fluid hole on the other side of the baffle is supplied by the other cooling fluid source.

As will be appreciated, it may be desirable to limit the total cross-sectional area available for flow through the baffle. Especially where one of the cooling fluid sources is at a higher pressure than the other, too great a cross-sectional area through the baffle may lead to some cooling fluid holes receMng insufficient cooling fluid and therefore cooling function loss. Specifically, if the baffle does not properly control the location of the interface (or dead zone') between cooling flows from the two cooling fluid sources, it may form elsewhere within the cooling fluid flow path. In this case fluid flow velocity past at least some of the cooling fluid holes may be greater that it would be if the baffle dictated the dead zone' location. This might reduce the pressure margin against ingestion to those cooling fluid holes sufficient to result in cooling function loss. Further the cooling fluid holes may be angled to accept more favourably flow travelling in a particular direction. By way of example flow from the favoured direction might have to turn through only 30° and necessarily therefore flow coming from the opposite direction would be correspondingly less favoured, having to turn through 1500. If the location of the dead zone' is not predictably located by the baffle, the flow direction past a cooling fluid hole might be opposite to that intended, forcing the air to turn through a non-favourable angle. As before, this might reduce the pressure margin against ingestion to the cooling fluid hole sufficiently to result in coohng lunchon loss.

EspeciaUy when assuming a constraint on the total cross-sectional area available for flow through the baffle, it may be desirable to concentrate the limited cross-sectional area available into a single through-bore, thereby potentially increasing the likelihood that debris can pass through the through-bore. This may he advantageous as it may reduce the likelihood of debris being re-circulated around the internal passage, which might ultimately block a cooling fluid hole. It may further reduce the likelihood of the debris blocking the through-bore and/or building up on the baffle (which might ultimately reach the level of adjacent cooling fluid holes).

n some embodiments the through bore cross-sectional area is as large as possible. Increasing the cross-sectional area to the extent possible (given the constraint imposed by fluid cooling holes being supphed as previously slated) may tend to allow larger pieces of debris to fall through the through bore.

n some embodiments the through bore is substantially centralised within the baffle. This may increase the likelihood oF debris falling through the through-bore, and reduce the likelihood of debris accumulating asymmetrically on one or more areas of the baffle.

n some embodiments tle through bore is circular. This may reduce the likelihood of debris blocking the through bore and/or being prevented from falling through it as a result of straddling the through bore in a particular direction.

n sonic embodiments the baffle is intermediate the ends of the internal passage, This may allow the delivery of cooling fluid into the internal passage from both cooling fluid sources, each source supplying cooling fluid holes on that side of the baffle.

in some embodiments the baffle is mid-way between the ends of the internal passage. In this way each cooUng fluid source may supply substantially half of the coohng fiLid holes in the internal passage.

in some embodiments the baffle is positioned at one of the ends of the internal passage. This may reduce the number of cooling fluid holes in the vicinity of the bathe, thereby potentially reducing the number of cooUng fluid holes that might be affected by a build-up of debris on the baffle or by fluid dynamic effects of the bathe. It may also he that the temperature of the aerofo towards the ends of the internal passage is lower than the temperalure towards the centre of the inlernal passage. The aerofoU may be more tolerant of blockages and/or congestion of cooUng fluid holes towards the ends of the internal passage.

n some embodiments the baffle is positioned beyond one end of the internal passage. If the baffle is positioned radiaUy outward of the internal passage, it may be less likely to impact on even the cooling fluid holes towards the end of the internal passage. In particular any build-up of debris on the baffle may take longer to reach the cooling fluid holes.

in some embodiments the baffle is accommodated in or positioned beyond an end plate of the aerofoil. This may allow the baffle to be further removed froni the internal passage and/or cooling fluid holes. The further the baffle is positioned radially outward of the end plate, the longer the debris might have to clear the through bore before it causes a blockage or congestion of one or more cooling fluid holes, It may be for example that particular debris may take some time to clear the through bore, It may be for example that it is ultimately dislodged or broken up by physical shock to the aerofoil, which may take some time to occur. The endplate may for example be an outer platform or shroud.

n sonic embodiments the baffle is provided with a perimetrical skirt extending perpendicularly from the baffle, the skirt adjoining the passage wall. The skirt may therelore be considered to provide a passage extension at one end, the skirt potentially allowing integrity with the internal passage between the passage wall and baffle. The baffle with skirt may therefore be considered to define a containment area which may have a bucket shape.

In some embodiments the baffle is arranged to be detachable and removable from the aerofoil. This may facilitate the emptying and/or cleaning of the containment area. The baffle andlor aerofoil may for example be provided with an attachment mechanism allowing selective detachment and reattactiment (e.g. by clip or fastener).

JO In some embodiments the aerofoil may be a nozzle guide vane. In particular the nozzle guide vane may be a high pressure turbine nozzle guide vane in a gas turbine engine.

According to a second aspect of the invention there is provided an aerofoil in accordance with the aerofoil of the first aspect of the invention.

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

According to a fourth aspect of the invention there is provided a method of managing cooling fluid flow through a cooling fluid flow path optionally comprising an internal passage of an aerofoil, the method comprising the steps of: a) optionally impeding cooling fluid flow with a baffle in the fluid flow path; b) optionally forcing the only fluid communication through the baffle to occur through a single through bore in the baffle, the through bore being optionally inset and discrete from an outer perimeter of the baffle.

In some embodiments the method further comprises supplying cooling fluid to at least one cooling fluid hole in the aerofoil.

In some embodiments the method further comprises impeding cooling fluid flow with the baffle such that any and each cooling fluid hole on one side of the baffle is supplied by one cooling fluid source and any and each cooling fluid hole on the other side of the baffle is optionally supplied by another cooling fluid source.

The skilled person will appreciate that a feature descdbed 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:

JO

Figure 1 is a sectional side view of a gas turbine engine; FIgure 2 is a schematic view of a portion of a gas turbine engine; Figure 3 is a top cross-sectional view of a high pressure turbine nozzle guide vane; FIgure 4 is a perspective view of a portion of an aerofoil according to an embodiment of the invention; Figure 5 is a perspective view of a portion of an aerofoil according to an embodiment of the invention; Figure 6 is a schematic cross-sectional side view showing a cooling fluid hole and associated rib; Figure Ta is a schematic cross-sectional side view showing a cooling fluid hole and associated ribs; FIgure Tb is a schematic front view of the arrangement shown in Figure 7a.

A gas turbine engine 10 is shown in Figure 1 and comprises an air intake 12 and a propulsive fan 14 which generates two airfiows 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.

Referring now to Figure 2 an aerofoil cooling system 38 forming part of the gas turbine engine 10 is shown. A stage 40 of the high pressure turbine 22 is also shown comprising an array of turbine blades 42 (only one shown). Upstream of JO the blades 42 is an array of nozzle guide vanes 44. Referring now also to Figure 3, each nozzle guide vane 44 is of aeroloil cross-section with a pair of end plates at either radial end. The nozzle guide vane 44 is provided with an internal passage 46 extending in a radial direction through its body between the end plates 45. The internal passage 46 is defined at least in part by a passage wall 48. A plurality of cooling fluid holes 50 pass through the passage wall 48 providing fluid communication between the internal passage 46 and the exterior of the nozzle guide vane 44. The internal passage 46 is also in fluid communication with a first 52 and second 53 cooling fluid sources via openings in the end plates 45. The two cooling fluid sources 52, 53 originate in the high pressure compressor 18 and form part of a cooling fluid flow path 54. The cooling fluid flow path 54 also includes the internal passage 46, each end 56 of which is in direct fluid communication with one of the cooling fluid sources 52, 53.

Referring now to Figure 4 a part of the nozzle guide vane 44 is shown with part of the passage wall 48 removed for clarity. Within the cooling fluid flow path 54, intermediate the two cooling fluid sources 52, 53 and within internal passage 46 is provided a baffle 58. The baffle 58 is positioned at one end 56 of the internal passage 46. Although not apparent (in view of part of the passage wall 48 not being shown), the outer perimeter 60 of the baffle 58 seals against the passage wall 48 at all points. The baffle 58 dMdes the cooling fluid flow path 54 into two portions substantially sealing one from the other. Within the body of the baffle 58 there is however a single and solitary through bore 62 inset and discrete from the outer perirneter 60. The through bore 62 is circular and has a diameter of between two and three niifflmetres. The through bore 62 provides the only fluid communication path through the baffle 58 and therefore the only fluid commumcaflon between the two porton of the coohng fluid flow path 54.

in use cooUng air is bleed from the high pressure compressor 18 and passes into the cooling fluid flow path 54. Along separate paths the cooUng air first enters the first 52 and second 53 cooling fluid sources before reaching respective ends 56 of the internal passage 46. The pressure of cooling air in the second cooling fluid source 53 upon reaching its end of the internal passage 46 is higher than the pressure in the first cooling fluid source 52 upon reaching its end ot the inlernal passage 46 (although in other embodiments the reverse may be true). The baffle 58 however provides an impediment to fluid communication between cooUng air originating from the sources 52, 53 of cooling air. Further the crosssectional area of the through bore 62 has been selected such that c-ach cooling fluid hole 50 is supplied by the first source of cooling fluid 52 only. Thus despite the higher pressure of the second source of cooling fluid 53, the baffle 58 provides sufficient impediment that the second source of cooling fluid 53 does not prevent the supply of all cooling fluid holes 50 with cooling air from the first source of cooling fluid 52.

Cooling fluid supplied by Ihe first source of cooling fluid 52 therefore enters the internal passage 46 and leaves via the cooling fluid holes 50. Thereafter it forms a protective shroud of relatively cool air around the nozzle guide vane 44 aerofoil. Further any contaminants (such as dust and dirt) present in the cooling 23 air, may he more likely to escape the internal passage 46 in view of the presence of the through bore 62. Specifically by making the through bore 62 circular and as large as possible, while still ensuring that the cooling fluid holes are only supplied by the first source of cooling fluid 52, contaminants may he less likely to straddle the through bore 62. Further by displacing the through bore 62 from the outer perimeter 60 of the baffle 58, it may be less likely that contaminant will build up on an area remote from the through bore 62. Further it may he less likely that cooling fluid holes 50 in i:he vicinity of the baffle 58 become constricted or blocked.

Referring now to Figure 5 an alternative to the arrangement of Figure 4 is shown. Like features are given like reference numbers in the series 100. The Figure 5 embodiment is similar to that shown in Figure 4 except For the arrangement of the baffle. In the Figure 5 embodiment the baffle 158 is located beyond one end 156 of the internal passage 146 rather than simply at the end 156. As before the baffle 158 spans the cooling fluid flow path 154, providing an impediment to fluid communication. Rather than the outer perimeter 160 of the baffle 158 sealing against the passage wall 148 at all points, it instead seals against a skirt 164 at all points. The skirt 164 extends perpendicularly from the JO outer perimeter 160 of the baffle 158 and is adjoined to the passage wall 148.

The through bore 162 provides the only fluid communication path through the baffle 158.

The baffle 158 with skirt 164 forms a substantially cylindrical bucket shaped containment area (not shown). In alternative embodiments however the containment area may be of any other suitable shape, such as prismatic, hemispherical, conic or pyramidal. The containment area, which extends beyond the end 156 of the internal passage 146, is accommodated outside of the internal passage and radially beyond the end plate of the nozzle guide vane. The locating of the baffle 158 beyond one end 156 of the internal passage 146 means that it is further from the nearest cooling fluid hole 150. Therefore if contaminants build up on the baffle 158 surface there will be a longer period before they constrict or block the cooling fluid holes 150. The additional time may also allow the contaminants to be dislodged (e.g. as a result of mechanical shock) and to exit the vicinity of the internal passage 146 via the through bore 162. Where (as in this case) the baffle 158 with skirt 164 is removable for cleaning, the additional time may also increase the time between required cleaning intervals.

Figure 6 shows an additional optional feature of the nozzle guide vane 44. The cooling fluid holes 50 are positioned immediately downstream of first ribs 66.

The first rib 66 extends substantially perpendicularly into the internal passage 46 from the passage wall 48 and substantially circumferentially around the passage wall 48 (neither upstream nor downstream). The first ribs 66 therefore create a 1 1 shi&d for the downstream coong fluid hole 50. The haUistic effect created by the rib 66 tends to force contaminants away from the downstream cooling fluid hole 50, separaflng the contaminants from the flow. Each hole may he provided with fts own first rib 66, or a single first rib 66 may shield multiple coohng fluid holes 50.

A modification is shown in Figures 7a and 7b with the addition of a second rib 68 immediately downstream of the cooUng fluid hole 50. The second rib 68 extends suhstantiaUy perpendicularly into the internal passage 46 from the passage wall 48 and substantially circumferentially around the passage wall 46 (neither upstream nor downstream). The first 66 and second 68 ribs together form a channel 70 with a width approximately equal to the diameter of the cooling fluid hole 50. t may therefore be that a contaminant particle 72 that might otherwise block the cooling fluid hole 50 will be prevented from entering the) channel JO, impeded by the first 66 and second 68 ribs. Further, even with the contaminant particle 72 trapped at the entrance to the channel 70 immediately above the cooling fluid hole 50, the coohng fluid hole can still receive cooling air around the contaminant particle 72 via the channel 70.

t 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. By way of example the nozzle guide vane may be provided with one or more additional internal passages with similar features to those described herein. Indeed Figure 3 shows 23 a nozzle guide vane with both leading (internal passage 46) and trailing edge internal passages (despite only the leading edge internal passage having been discussed substantively herein). Further the baffles may be located intermediate, at, or beyond an end of each internal passage and each internal passage in a single nozzle guide vane need not have the baffle position in the same place or at the same end, Any of the features may be employed separately or in combination Mth 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 aerofoil cooling system.

IS

Claims

Claims 1. An aerofoil cooling system comprising a baffle and a cooling fluid flow path, the baffle being disposed within the cooling fluid flow path, the cooling fluid flow path comprising an internal passage of an aerofoil, and where further the baffle has a single through bore inset and discrete from an outer perimeter of the baffle and providing the only fluid communication path through the baffle to the cooling fluid flow path on opposite sides of the baffle.JO
2. An aerofoil cooling system according to claim I further comprising two cooling fluid sources, the cooling fluid flow path being intermediate and connecting the two cooling fluid sources.
3. An aerofoil cooling system according to claim 2 where the internal passage is at least partially defined by a passage wall having at least one cooling fluid hole passing there through.
4. An aerofoil cooling system according to claim 3 where the cross-sectional area of the through bore is such that when the aerofoil cooling system is in use, any and each cooling fluid hole on one side of the baffle is supplied by one of the cooling fluid sources and any and each cooling fluid hole on the other side of the baffle is supplied by the other cooling fluid source.
5. An aerofoil cooling system according to claim 4 where the through bore cross-sectional area is as large as possible.
6. An aerofoil cooling system according to any preceding claim where the through bore is substantially centralised within the baffle.
7. A aerofoil cooling system according to any preceding claim where the through bore is circular.
8. An aerofoil cooling system according to any preceding claim where the baffle is positioned at one of the ends of the internal passage.
9. An aerofoil cooling system according to any of claims I to 7 where the baffle is positioned beyond one end of the internal passage.
1O.An aerofoil cooling system according to claim 9 where the baffle is accommodated in or positioned beyond an end plate of the aerofoil.
11.An aerofoil cooling system according to claim 9 or claim 10 where the baffle is provided with a perimetrical skirt extending perpendicularly from the baffle, the skirt adjoining the passage wall.
12. In some embodiments the baffle is arranged to be detachable and removable from the aerofoil.
13.An aerofoil in accordance with any of claims ito 12.
14.A gas turbine engine comprising an aerofoil cooling system according to any of claims Ito 12.
15.A method of managing cooling fluid flow through a cooling fluid flow path comprising an internal passage of an aerofoil, the method comprising the steps of: a) impeding cooling fluid flow with a baffle in the fluid flow path; b) forcing the only fluid communication through the baffle to occur through a single through bore in the baffle, the through bore being inset and discrete from an outer perimeter of the baffle.
16.An aerofoil cooling system of the kind set forth substantially as described herein with reference to and as illustrated in the accompanying drawings.