GB2482170A

GB2482170A - A duct

Info

Publication number: GB2482170A
Application number: GB201012324A
Authority: GB
Inventors: Mark William Cornborough; Alan Philip Geary
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2010-07-23
Filing date: 2010-07-23
Publication date: 2012-01-25
Also published as: GB201012324D0

Abstract

A duct and a gas turbine engine comprising a duct wherein the duct 2 comprises a plurality of tubular sections 4 arranged in substantially axial alignment and a plurality of elongate strips 14. The elongate strips couple the tubular sections to one another wherein a longitudinal axis of each strip extends substantially in an axial direction. The tubular sections may partially overlap one another in a telescoping arrangement. The tubular sections may be at least partially frustoconical, the tubular sections and/or the elongate strips may be formed from sheet material. One or more of the tubular sections may contain a plurality of cooling holes (18, fig. 3). The duct may be an exhaust duct or a combustor. The duct may be connected to an outer casing (20, fig. 4) by a plurality of mounting brackets (22) wherein the mounting brackets comprise a spacer portion (24) which spaces the duct from the outer casing.

Description

A DUCT

The present invention relates to a duct and particularly, but not exclusively, to a duct which has inherent flexibility so as to alleviate high stresses caused by differential thermal expansion of the duct.

Background

Combustors and exhaust ducts in gas turbine engines channel gases which are at extremely high temperatures. For example, the temperature of the gas entering an exhaust duct may be between 550 and 850°C, and where afterburning is used may exceed 1500°C. In a combustor, the temperatures range from 850 to 170000.

Consequently, these components experience high thermal expansion caused by the extremely high differential temperatures under which they operate.

To allow the component to handle these high temperatures, cooling holes may be provided in the component. A relatively cool fluid is introduced through the cooling holes to produce a film of cool fluid over an inner surface of the component.

Combustors and exhaust ducts are conventionally made from a single piece of material.

The rigidity of this design may produce areas of high stress caused by the thermal expansion of the component. As a result, the component may have a lower than desired service life. Furthermore, single piece constructions are difficult and expensive to manufacture.

Alternatively, the component may be constructed from a plurality of panels or tiles. The panels or tiles are each individually suspended. The panels or tiles are positioned to form the shape of the combustor or exhaust duct. Again, this technique is expensive and requires the positioning of the panels or tiles to be very accurate so as to ensure that all the panels or tiles line up.

The present invention seeks to provide a duct which overcomes some or all of the problems described above.

Statements of Invention

In accordance with a first aspect of the invention, there is provided a duct comprising: a plurality of tubular sections arranged in substantially axial alignment; and a plurality of elongate strips coupling the tubular sections to one another; wherein a longitudinal axis of each strip extends substantially in an axial direction.

The duct may have inherent flexibility provided by this construction so as to alleviate stresses caused by differential thermal expansion.

The tubular sections may partially overlap one another in a telescoping arrangement.

The tubular sections may be at least partially frustoconical. For example, they may taper from one end to the other end.

The tubular sections and/or elongate strips may be formed from sheet material. The tubular sections and/or elongate strips may be manufactured using a laser profiling technique to provide an inexpensive component.

The elongate strips may be coupled to the tubular sections by fasteners located at positions along the length of the elongate strips.

The fasteners may be rivets or nuts and bolts.

One or more of the tubular sections may contain a plurality of cooling holes.

The cooling holes may be at a leading edge of the tubular sections.

There may be at least three tubular sections and each elongate strip may couple the at least three tubular sections together.

The duct may be an exhaust duct or a combustor.

The duct may be connected to an outer casing. The outer casing may provide stiffness to the duct.

The duct may be connected to the outer casing by a plurality of mounting brackets.

The mounting brackets may comprise a spacer portion which spaces the duct from the outer casing. This may allow the duct to expand and contract relative to the outer casing.

Brief Description of the Drawings

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is an end cross-sectional view of a duct in accordance with an embodiment of the invention; Figure 2 is a side cross-sectional view of the duct; Figure 3 is a top view of the duct; Figure 4 is an end cross-sectional view of the duct connected to an outer casing; Figure 5 is a side cross-sectional view of the duct connected to the outer casing; and Figure 6 is a top view of the duct connected to the outer casing.

Detailed Description

With reference to Figures 1 and 2, a duct 2 according to an embodiment of the invention comprises a plurality of tubular sections 4 made from thin sheet material. The tubular sections 4 of the duct 2 are substantially in axial alignment and each have an inner surface 6 which defines a fluid conduit and an outer surface 8. Each tubular section tapers from a first end 10 to a second end 12. The narrower second end 12 of each tubular section 4 is received within the wider first end 10 of an adjacent tubular section 4 to form a telescoping arrangement.

The tubular sections 4 are coupled to one another by four elongate strips 14 which are oriented axially with respect to the tubular sections 4. The elongate strips 14 are spaced evenly around the tubular sections 4 and thus are positioned at 90°, 180°, 270°, and 360° around the tubular sections 4. The elongate strips 14 may be curved to match the curvature of the tubular sections 4 or may be flat.

As shown in Figure 2, each tubular section 4 is connected to each elongate strip 14 by a fastener 16, such as a rivet or nut and bolt. The elongate strips 14 are made from thin sheet material which deforms to the tapering shape of the tubular sections 4 and thus allows firm fastening.

With reference to Figure 3, the tubular sections 4 are each provided with a plurality of cooling holes 18 for supplying a cooling fluid film to the inner surface 6 of the tubular sections 4. The cooling holes 18 are slot-shaped with the slots oriented in an axial direction and are spaced around the circumference of the tubular section 4. The cooling holes 18 are provided adjacent the first end 10 of the tubular section 4, which is a leading edge of the tubular section 4 with respect to the fluid flow through the duct 2.

With reference to Figures 4 to 6, the duct 2 may be attached to an outer casing 20. The outer casing is tubular and thus provides rigidity to the duct 2. The duct 2 is connected to the outer casing 20 via a plurality of mounting brackets 22. Each elongate strip 14 is connected to the outer casing 20 by a pair of mounting brackets 22. Each mounting bracket 22 has a spacer portion 24 which extends perpendicularly from the outer casing 20. The mounting bracket 22 further comprises a support portion 26 at an end of the spacer portion 24. The support portion 26 is essentially a plate against which the elongate strip 14 rests. Where the elongate strip 14 is curved to match the curvature of the tubular section 4, the support portion 26 may also be curved. The spacer portion 24 spaces the duct 2 away from the outer casing 20, providing freedom for the duct 2 to expand due to the temperature of the fluid flowing through the duct 2.

The fastener 16 at the location of each mounting bracket 22 may be an integral part of the mounting bracket 22. For example, a bolt may pass through the tubular section 4 and elongate strip 14, and screw into an internal thread formed in the mounting bracket 22.

In use, a hot fluid flows through the duct 2 inside the inner surfaces 6 of the tubular sections 4. A cooling film is introduced through the cooling holes 18 to maintain the temperature of the tubular sections 4 at an acceptable level. As the tubular sections 4 and elongate strips 14 are made from thin sheet metal, the duct 2 has a large degree of local flexibility, thus allowing the duct 2 to expand and contract in response to the temperature changes. Consequently, the duct 2 of the present invention prevents the formation of stresses and therefore maximizes the service life of the duct 2. Where the duct 2 is connected to the outer casing 20, the spacer portion 24 of the mounting bracket 22 spaces the duct 2 from the outer casing 20 and thus still allows the duct 2 to expand and contract whilst providing increased stiffness.

The flexibility of the duct 2 also allows manufacturing tolerances to be easily accommodated in the assembly process since the duct 2 will deform to fit.

The tubular sections 4 have been described as having a telescoping arrangement, however this need not be the case. Instead, the tubular sections may have a uniform diameter and be coupled by the elongate strips 14 such that the first end 10 of one tubular section 4 is held in contact with the second end 12 of an adjacent tubular section 4.

Although the elongate strips 14 have been said to be spaced evenly around the tubular sections 4, they could be located at any position around the tubular sections 4.

Furthermore, any number of elongate strips 14 may be used instead of the four elongate strips 14 described. The elongate strips 14 may alternatively be located on the inner surface 6 of the tubular sections 4, rather than the outer surface 8.

Several fasteners 16 may be used to connect each tubular section 4 to each elongate strip 14. Furthermore, any number of mounting brackets 22 may be used to connect each elongate strip 14 to the outer casing 20.

Cooling holes 18 are described above as being slot shaped with the slots oriented in an axial direction. In an alternative embodiment, the cooling holes may be slot shaped with the slots orientated at an angle to the axial direction. In further alternative embodiments the cooling holes may be round, oval or triangular. In another alternative embodiment, no cooling holes are provided in the tubular sections 4.

The duct 2 of the present invention is particularly suited for use as an exhaust duct or combustor, but may also be used in other applications for channelling a fluid and is not limited to gas turbine applications. The duct could be used in any application where perfect sealing is not required.

Claims

CLAIMS1 A duct comprising: a plurality of tubular sections arranged in substantially axial alignment; and a plurality of elongate strips coupling the tubular sections to one another; wherein a longitudinal axis of each strip extends substantially in an axial direction.
2 A duct as claimed in claim 1, wherein the tubular sections partially overlap one another in a telescoping arrangement.
3 A duct as claimed in claim 2, wherein the tubular sections are at least partially frustoconical.
4 A duct as claimed in any one of the preceding claims, wherein the tubular sections and/or elongate strips are formed from sheet material.
A duct as claimed in any one of the preceding claims, wherein the elongate strips are coupled to the tubular sections by fasteners located at positions along the length of the elongate strips.
6 A duct as claimed in claim 5, wherein the fasteners are rivets or nuts and bolts.
7 A duct as claimed in any one of the preceding claims, wherein one or more of the tubular sections each contain a plurality of cooling holes.
8 A duct as claimed in claim 7, wherein the cooling holes are at a leading edge of the tubular sections.
9 A duct as claimed in any one of the preceding claims, wherein there are at least three tubular sections and each elongate strip couples the at least three tubular sections together.
10 A duct as claimed in any one of the preceding claims, wherein the duct is an exhaust duct or a combustor.
11 A duct as claimed in any one of the preceding claims, wherein the duct is connected to an outer casing.
12 A duct as claimed in claim 11, wherein the duct is connected to the outer casing by a plurality of mounting brackets.
13 A duct as claimed in claim 12, wherein the mounting brackets comprise a spacer portion which spaces the duct from the outer casing.
14 A duct substantially as described herein with reference to and as shown in the accompanying drawings 15 A gas turbine engine comprising a duct as claimed in any one of the preceding claims.