US 3666251 A
The disclosure of this invention pertains to a heat shield for jet pipes in gas turbine engines. The heat shield comprises a sheet of heat-resisting alloy having flat portions joined by parallel folds and wherein both the flat portions and the folds are formed into corrugations extending at right angles to the folds. In this way the heat shield is two-dimensionally expansible to accommodate differential expansion between the shield and a support structure to which the shield is secured. The shield is impermeable so that cooling air at the "cold" side of the shield may be of lesser pressure than the hot gases in the jet pipe.
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Description (OCR text may contain errors)
United States Patent 45] May 30,1972
McMurtry et al.
 WALL FOR HOT FLUID STREAMS  Inventors: David Roberts McMurtry; Derek Percival Harris, both of Bristol, England  Assignee: Rolls-Royce Limited  Filed: June 15, 1970  Appl. No.: 46,437
 Foreign Application Priority Data June 19, 1969 Great Britain ..30,996/69  US. Cl.. ..263/50, 60/3932, 263/19 C [51 Int. Cl ..F23m 9/00  Field of Search 60/3932; 263/19 C, 50
 References Cited UNITED STATES PATENTS 3,185,460 5/1965 Mescher et al ..263/50 X FOREIGN PATENTS OR APPLICATIONS 1,122,030 5/1956 France ..263/50 Primary Examiner.l0hn J. Camby Attorney-Mawhinney & Mawhinney The disclosure of this invention pertains to a heat shield for jet pipes in gas turbine engines. The heat shield comprises a sheet of heat-resisting alloy having flat portions joined by parallel folds and wherein both the flat portions and the folds are formed into corrugations extending at right angles to the folds. In this way the heat shield is two-dimensionally expansible to accommodate differential expansion between the shield and a support structure to which the shield is secured. The shield is impermeable so that cooling air at the cold side of the shield may be of lesser pressure than the hot gases in the jet pipe.
ABSTRACT 5 Claims, 7 Drawing Figures PATENTEDMAY 30 I972 SHEET 2 OF 2 FIG. 6
MVH/To/F DAVID ROBERTS Hc MURTRX mm- [3) WALL FOR HOT FLUID STREAMS This invention relates to walls for hot fluid streams.
It is known for such walls to comprise a heat shield connected to a support structure. The heat shield, which faces the hot stream, has to be two-dimensionally expansible in relation to the relatively cooler support structure to accommodate differential thermal expansion. Also the heat shield must present a relatively smooth surface to the hot flow to minimize transfer of heat to the heat shield. Usually a flow of cooling fluid is introduced between the heat shield and the support structure.
It is known to construct the heat shield in the form of a plurality of plates individually connected to the support structure. The plates can expand relative to one another and relative to the structure, and cooling fluid is free to pass through gaps between the plates to the hot side thereof there forming a cooling film.
It is sometimes necessary for the wall to be impermeable so that film cooling cannot be used. This applies, for example, when it is desired to use a cooling fluid whose pressure is less than that of the hot flow. However the two-dimensional expansibility and the relative smoothness of the wall must nevertheless be maintained.
It is an object of this invention to provide a wall satisfying these requirements.
According to this invention a wall for a hot fluid stream includes a heat shield comprising flat portions defining the hot" surface of the shield and connected by folds defining between adjacent flat portions a gap so that the flat portions can expand in the direction at right angles to the length of the folds by narrowing of said gap, and wherein both the flat portions and the folds are shaped to define corrugations whose length extends at right angles to the length of the folds so that the flat portions and the folds can expand together in the direction of the length of the folds by narrowing of the corrugations.
An example of a wall according to this invention will now be described with reference to the accompanying drawings wherein:
FIG. 1 is a sectional elevation of a jet pipe for a gas turbine engine, which jet pipe includes said wall.
FIG. 2 is an enlarged detail of FIG. 1
FIG. 3 is a section on the line III-III in FIG. 2.
FIG. 4 is a perspective view of the detail illustrated in FIGS. 2 and 3.
FIG. 5 is a detail of the wall shown in the course of manufacture.
FIG. 6 is a view similar to FIG. 2, but at a reduced scale, showing a modification.
FIG. 7 is a view on the line VII-VII in FIG. 6.
Referring to FIG. 1 there is shown a jet pipe 1 for a gas turbine engine (not shown), the pipe having flame holders 2 for reheat combustion and a heat shield 3 to protect the pipe against the local rise in temperature under reheat conditions. The pipe is double-walled defining an annular space 4 for the flow of cooling air as indicated by an arrow 5.
The pipe 1 and heat shield 3 define a wall for the hot stream of gases passing through the pipe in the direction of the arrow The heat shield 3 is made from a sheet 10 of heat-resisting alloy and comprises flat portions 16a defining the hot" surface 15, Le. the surface exposed to the hot gases, of the heat shield. Between the flat portions the sheet 10 is formed by pressing operations into folds 16 connecting the flat portions. The term flat" in respect of the portions 160 is intended to include the generally cylindrical shape of the shield which may be regarded as flat in relation to the folds 16.
Each fold 16 extends clear of the surface and is shaped so as to define adjacent that surface a gap 17 providing room for thermal expansion of the flat portions in the direction at right angles to the length of the gap 17. The gap 17 is relatively narrow and has substantially square corners 18 so that the surface 15 is not unduly interrupted by the presence of the gap and the creation of undue turbulence in the gas stream passing over the surface 15 is avoided. Preferably the width of the gap 17 is such that it is virtually closed at the maximum operating temperature of the heat shield.
Both the flat portions and the folds are shaped to define corrugations 11 created by electrochemically machining grooves 12 and 13 into the sheet. The corrugations 11 are so placed that their length (as defined by the length of the grooves 12,13) extends at right angles to the length (as defined by the length of the slots 17) of the folds 16. In consequence the corrugations 11 provide room whereby both the flat portions and the folds can expand together in the direction of the length of the folds.
The grooves 12, which extend in the direction 6 of the gas flow, are relatively narrow, and have substantially sharp edges so that also here there is only minimum disruption of the smoothness of the surface 15.
It will be seen that by virtue of the folds and the corrugations the heat shield forms a two-dimensionally expansible structure.
Remote from the surface 15 each fold 16 is broadened into a base 19 by which the sheet 10 can be connected to a supporting structure, in this case a portion 20 of the pipe 1, as by rivets 23 passing through holes 21 in said base. In the proximity of the holes 21 the corrugations are discontinued to provide the necessary strength of material around these holes 21. Such local discontinuity of the corrugations 11 is readily achieved by the use of electrochemical machining for producing the corrugations l 1.
The folds 16 are made by deforming the sheet 10 in two stages indicated in FIG. 5 The sheet is at first pressed into the shape denoted A and has machined thereon surfaces 22 to define the edges 18. Thereafter the corrugations 1 1 are machined, and finally the sheet is pressed into the shape B being the finished shape of the folds 16. The surfaces 22 are machined at such an angle that in shape B they form the sides of the gap 17. In shape A the fold 16 is open sufficiently widely to provide access for machining the grooves 12,13 in the position destined to become the sides of the fold 16 in shape B.
Space 24 (FIG. 1,2) between each flat portion 16a and the adjacent pipe position 20 may be filled with fibrous insulating material such as silica wool to reduce convection in this space and heat radiation from the surface 15. Alternatively the spaces 24 may be connected by holes (not shown) to the space 4 for the cooling air to circulate in the spaces 24.
In cases where the temperature gradient between the surface 15 and the portion 20 is too high for a single heat shield to accommodate differential thermal expansion, then as shown in FIGS. 6 and 7, a second heat shield 25 may be interposed between the heat shield 3 and the pipe portion 20. The heat shield 25 is generally similar to the heat shield 3 but may have fewer corrugations and the gaps of the fold need not be as close as in the case of the shield 3. Also the heat shield 25 has to have rivets 27 for connection to the heat shield 3 as well as the rivets 23 for connection to the pipe portion 20. The spaces 24 of the shield 3 are filled with silica wool 26 and corresponding spaces of the shield 25 may be in direct communication with the space 4, the direction of the folds of the shield 25 being parallel to the air flow 5 as shown in FIG. 6.
It will be seen that there is no communication between the hot flow 6 and the cold flow 5 and the latter can therefore be at a lower pressure than the former. However, in cases where the cold flow has the superior pressure it can be communicated to the interiors of the folds 16, eg by holes through the rivets 23, to cool the folds and eventually pass into the boundary layer of the surface 15 to cool that surface.
The material for the heat shield may be a nickel or cobaltbored alloy, for example an alloy known by the trade name Stellite. Inasmuch as the heat shield is not cooled by a film over the hot" surface, it has to bear the full effects of the hot gas temperatures.
In the present example the heat shield is arranged so that the surface 15 is a cylinder but the heat shield can equally well be adapted for the surface 15 to lie in a plane.
What we claim is 1. A wall for a hot fluid stream including a heat shield comprising flat portions defining the "hot surface of the shield and connected by parallel folds extending clear of said hot surface and defining between adjacent flat portions a gap so that the flat portions can expand in the direction at right angles to the length of the folds by narrowing of said gap, and wherein both the flat portions and the folds are shaped to define corrugations whose length extends at right angles to the length of the folds so that the flat portions and the folds can expand together in the direction of the length of the folds by narrowing of the corrugations.
2. A wall according to claim 1 wherein said folds include bases situated clear of said flat portions and spaced apart in the direction of the length of the folds, the wall further comprising a support member to which the heat shield is secured at said bases, the folds co-operating to position the flat portions in spaced apart relationship to said support member.
3. A wall according to claim 2 wherein a further heat shield is interposed between the first-mentioned heat shield and the support member in a position so that the folds of the further heat shield extend at right angles to those of the first-mam tioned heat shield, the bases of the first-mentioned heat shield being secured to the flat portions of the further heat shield and the bases of the further heat shield being secured to the support member.
4. A wall according to claim 1 wherein the sides of said gap and said hot surface are arranged to define a substantially sharp corner.
5. A wall according to claim 1 wherein the corrugations are defined by grooves in said hot" surface and wherein the sides of said grooves and the hot" surface are arranged to define substantially sharp comers.