GB2298245A

GB2298245A - A turbine blade arrangement comprising a cooled shroud band

Info

Publication number: GB2298245A
Application number: GB9503574A
Authority: GB
Inventors: Neil Milner Evans
Original assignee: BMW Rolls Royce GmbH
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 1995-02-23
Filing date: 1995-02-23
Publication date: 1996-08-28
Anticipated expiration: 2015-02-23
Also published as: GB9503574D0; DE19601819A1; GB2298245B

Description

2298245 - 1 A turbine-blade arrangement comprising a cooled shroud band

The invention relates to a turbine blade arrangement comprising a cooled shroud band having at least one circumferential sealing rib and a coolingair distribution duct extending substantially in the peripheral direction in each shroud-band segment associated'with a turbine blade, a number of cooling-air bores leading from the distribution duct to the trailing edge of the shroud-band segment. Examples of the prior art are to be found in WO 94/11616 or US 4 940 388. The last-mentioned citation discloses a shroud-band segment with a "fence" or "wall" which extends at an angle to the longitudinal axis of the turbine. In a conventional construction, the sealing effect of a fence or wall of this kind in reducing the leakage flow between the shroud band and the adjacent casing or duct wall is more advantageous than that given by simple sealing ribs in the peripheral direction, but the fence or wall is disproportionately expensive to manufacture.

The aim of the present invention is to disclose steps for adequately reducing the leakage flow even without a fence or wall and with a conventional sealing rib, optionally provided with a radial seal.

To this end, a number of branch ducts are provided and extend from the leading flank of the sealing rib to the cooling-air distribution duct. Advantageous other features are disclosed in the sub-claims and also in the following description of a preferred embodiment shown in the accompanying

2 drawings, in which Figure 1 is a section through a shroud-band segment; and Figure 2 is an outside view of the shroudband segment shown in Figure 1.

Reference 1 denotes a shroud-band segment of a partially-shown turbine blade 2. The segment 1 co-operates in a known manner with the segments of the adjacent turbine blades to form a circumferential shroud band. The aim is to seal, in optimum manner, the gap between the shroud band and the casing or duct wall 3 diagrammatically indicated in Figure 1, i.e. to reduce to a minimum the leakage flow represented by arrows 4 through the gap 3. Consequently, each shroud-band segment 1 is provided in a conventional manner with sealing ribs 5, 6, 7 extending in the peripheral direction so as to co- operate with the sealing ribs on the adjacent shroud-band segments to form circumferential sealing ribs 5, 6, 7 as before. Each individual sealing rib 5, 6, 7 constitutes an obstacle or hindrance to the leakage flow 4.

As can be seen, the turbine blade arrangement described comprises a cooled shroud band 1, i.e. each shroud-band segment 1 has a system 8 of cooling-air ducts connected to cooling-air ducts 9 inside the turbine blade 2. More specifically, the illustrated shroud-band segment has three cooling-air distribution ducts 8a, 8b, 8c extending substantially in the peripheral direction and closed at their ends, e.g. by welding. A number of cooling-air bores 8d branch off from the distribution duct 8a and lead to the surface of the shroud-band segment 1. Similarly, the two distribution ducts 8b, 8c are connected to one another via a number of cooling-air bores 8e. Finally, additional cooling-air bores 8f lead from the distribution duct 8c to the trailing edge la of the shroud-band segment and open at the trailing edge la thereof in a shape similar to a swirl nozzle.

As can be seen, the cooling-air distribution duct 8c is in the neighbourhood of the trailing sealing rib 7 of the shroud-band segment 1. Starting from the leading flank 7a of the sealing rib 7, a number of branch ducts 10 lead to the cooling-air distribution duct 8c. As a result of the pressure conditions in the gap between the shroud-band segment 1 and the tunnel wall 3 on the one hand and in the system 8 of cooling-air ducts on the other hand, some of the leakage flow 4 which previously passed the sealing rib 6 flows through the branch ducts 10 into the cooling-air distribution duct 8c, where it mixes with the flow of cooling air. The cooling-air flow thereby constitutes an additional obstacle or hindrance to the leakage f low 4. This also especially applies when, depending on the pressure conditions, some of the cooling-air f low in the distribution duct 8c travels through the branch ducts 10 into the region between the two sealing ribs 6, 7.

The flow of cooling air in the distribution duct 8c always reduces the leakage flow 4 in the region of the sealing rib 7. Best results are obtained if each branch duct 10 opening into the distribution duct 8c is associated with a cooling-air bore 8f of substantially equal diameter and branching off substantially opposite to it. The diameter can - 4 be 1.6 mm in the case of the cooling-air bores 8f and also of the branch ducts 10. However, these and other details can be designed differently from the embodiment shown.

Claims

C L A I M

S 1. A turbine blade arrangement comprising a cooled shroud band having at least one circumferential sealing rib (5, 6, 7) and a cooling-air distribution duct (8c) extending substantially in the peripheral direction in each shroud-band segment (1) associated with a turbine blade (2), a number of cooling-air bores (8f) leading from the distribution duct (8c) to the trailing edge (1a) of the shroud-band segment (1), characterised in that a number of branch ducts (10) start from the leading flank (7a) of the sealing rib (7) and lead to the cooling-air distribution duct (8c).
2. A turbine blade arrangement according to claim 1, characterised in that each branch duct (10) opening into the cooling-air distribution duct (8c) is associated with a cooling-air bore (8f) which has substantially the same diameter and branches off substantially.opposite to it.
3. A turbine blade arrangement according to claim 1 or claim 2, characterised in that the mouth openings of the cooling-air bores (8f) are in the form of swirl nozzles.