GB2261281A

GB2261281A - A combustion chamber casing for a gas turbine

Info

Publication number: GB2261281A
Application number: GB9123777A
Authority: GB
Inventors: Achim Schmid
Original assignee: BMW Rolls Royce GmbH
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 1991-11-08
Filing date: 1991-11-08
Publication date: 1993-05-12
Anticipated expiration: 2011-11-08
Also published as: DE4142413A1; GB2261281B; GB9123777D0; DE4142413C2

Abstract

A peripheral rib (4) is disposed on the wall of a combustion-chamber casing upstream of film cooling holes or air-intakes (3), the rib being of zig-zag shape whereby it intensifies the heat transfer between the combustion chamber wall (1) and the cooling air flowing past it. In a particularly simple manner, the zig-zag rib (4) can be made from zig-zag wire which is joined to the wall (1) by welding or soldering. With this arrangement the holes (3) can be parallel to the axis of the combustion-chamber which allows them to be narrower than in the prior art. <IMAGE>

Description

2 __I ') 12 ^1 11 A combustion-chamber casing for a gas turbine The

invention relates to a combustion-chamber casing for a gas turbine comprising at least one peripheral rib on the chamber wall, especially a casing having air intakes disposed in a ring or circle on the cold side downstream of the rib.

A combustion-chamber casing of this construction is shown e.g. in DE 3 200 972 C2. A partial air stream travels through the air intakes, also called "film-cooling holes", into the interior of the conbustion-chanber casing so as to form a "cooling-air film" therein. The air intakes, however, can also serve as 'lair-admixing holes". The rib or ribs disposed upstream of the air intakes are adapted to increase the heat transfer between the chamber wall and the air flowing past it, thus improving the cooling of the combustion-chamber casing.

An investigation into the flow conditions has shown that dissipating turbulent Patches occur at the rib or ribs and move with the main flow. Consequently, the heat conveyed by mass transfer at right angles to the main direction of flow is restricted to a relatively thin boundary layer. The only high heat transfer coefficients which occur at the ribs themselves is therefore when the flow round them is at excess speed.

Accordingly, the aim of the present invention is to provide a method of improving the heat transfer at the cold side of a combustion-chamber casing according to the preamble of claim 1.

To this end, in accordance with the invention, the rib is of zig-zag shape. A preferred feature of the invention is that the rib is made from a zig-zag wire of desired cross-section.

The invention is explained below in detail, by way of example, with reference to the accompanying schematic drawing, in which:

Figure 1 is a partial perspective view of the prior art; Figure 2 shows a preferred embodiment of the invention, likewise in partial perspective view; and Figure 3 is a view of the zig-zag rib, showing how turbulence is produced.

The figures of the drawing show part of the wall 1 of a combustionchamber casing for a gas turbine. A number of air intakes 3 are disposed in a circle in an annular peripheral shoulder 2 on the cold side. Air flows along the cold and hot side of the chamber wall 1 in the direction shown by arrows (WK on the cold side and WH on the hot side). In the prior art (Fig. 1), three annular peripheral ribs 4 are disposed upstream of the air intakes 3. These ribs are designed to increase the heat transfer between the chamber wall 1 and the air flow WK so that the wall 1 is cooled more efficiently. However, quicklydissipating turbulent patches occur at the ribs 4, so that the only appreciable heat transfer occurs in the neighbourhood of the relatively thin boundary layer 5, also sketched in Figure 1. The ribs 4 also increase the expense of manufacturing the combustion-chamber casing. As shown in Fig. 1, the air intakes 3 have to be drilled at an angle to the longitudinal axis 6 to prevent the ribs 4 being damaged by the trailing end of the tool. This results in turbulence in the cooling film downstream of the air intakes, thus greatly reducing their efficiency. It may also be necessary, particularly in the case of air intakes serving as admixture holes, for the ribs 4 to be extensively milled in the region of the admixture holes before drilling or punching.

These disadvantages are obviated in the combustionchamber casing according to the invention as shown in Fig. 2. In the invention, the peripheral rib 4 upstream of the air intake 3 is zig-zag shaped. The rib 4 is pref erably made by the built-up welding (bead welding) or the builtup soldering (hard soldering) of a zig-zag wire of desired cross- section. The connection to the cold side of the chamber wall 1 should preferably be free from shrink holes over a relatively wide base to ensure intensive heat transfer.

The effect of the zig-zag peripheral rib 4 can best be described with reference to Fig. 3. As a result of the zig-zag shape, the rib 4 produces stable vortex "pencils" 7 of f luid. Adjacent "pencils" rotate in opposite directions and thus help to widen the turbulence field. The flow field covered therefore increases with increasing length of travel over the vortex pencils 7, thus producing an intensive mass transfer at right anles to the direction Of f low WK, resulting in high heat transf er coef f icients at the chamber wall 1.

In addition to improving the heat transfer', the illustrated rib 4 can advantageously be made more simply than in the prior art. The process of punching and drilling the air intakes 3 is also simplified. Another possibility is to align the film-cooling holes or air intakes 3 parallel to the longitudinal axis 6 so that the film-producing slot can be made narrower than in the prior art illustrated in Fig. 1. This reduces the mass flow of air required for film cooling. Advantageously, the flow field and consequently the heat transfer field produced by a zig-zag peripheral rib as per Fig. 2 are characterised by geometrical and aerodynamic similarity parameters, which is useful in dimensioning the desired cooling effect. The design can also differ from the embodiment shown, without departing from the scope of the claims.

Claims

1. A combustion-chamber casing for a gas turbine comprising at least one peripheral rib on the chamber wall, especially a casing having air intakes disposed in a circle or ring on the cold side downstream of the rib, in which the rib is zig-zag shaped.

2. A combustion-chamber casing according to claim 1, in which the rib is made from a zig-zag wire of desired cross-section.

3. A combustion-chamber casing according to claim 1 or claim 2, in which the rib is built-up welded or built-up soldered to the chamber wall.

4. A combustion-chamber casing according to claim 1 substantially as described herein with reference to the accompanying drawing.

5. A gas turbine having a combustion-chamber casing as described in any one of claims 1 - 4.