GB2298246A

GB2298246A - Turbine-blad-tip-sealing arrangement comprising a shroud band

Info

Publication number: GB2298246A
Application number: GB9503575A
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: DE19601818C2; GB9503575D0; GB2298246B; DE19601818A1

Description

1 2298246 A turbine-blade arrangement comprising a shroud band The

invention relates to a turbine blade arrangement comprising a shroud band with at least one circumferential sealing rib, as known for example from WO 94/11616. The aim, by means of one or more circumferential sealing ribs on the shroud band, is greatly to reduce losses through leakage via the gap between the shroud banl and the wall of the casing or duct through which flow takes place.

The aim of the present invention is to disclose steps for still further reducing these leakage losses. To this end, the sealing rib has a circumferential slot, and a stream of air is supplied to the base of the slot and flows out at the top edge of the sealing rib. Advantageous other features are disclosed in the sub-claims.

According to the invention, the leakage flow is reduced by an air stream which flows substantially transversely with respect to the leakage flow between the wall of the casing or duct and the top edge of the sealing rib (s) and which f lows out of the aforementioned top edge. As a result, turbulence occurs in the gap between the casing or duct wall and the top edge of the sealing rib (s), and this turbulence hinders the leakage flow. Optionally the flow of air supplied to the bottom region of the slot can be branched off from the leakage flow upstream of the sealing rib(s), or alternatively the air flowing into the slot can be obtained from a cooling-air duct provided in the turbine blade, or preferably in the shroud band, for supplying air to cool these components.

The invention will now be explained in detail with reference to a preferred embodiment shown in the accompanying drawings, in which:

Figure 1 is a part section through a shroud band segment associated with a turbine blade in accordance with the invention; Figure 2 is a view X of Figure 1; and Figure 3 is a section taken on the line A-A in Figure 1.

Reference 1 denotes a turbine blade, more especially that used in a highpressure turbine or an aircraft gas turbine. The turbine blade carries a shroud-band segment 2, hereinafter also called a shroud band 2, and cooperates in a known manner with the other shroud-band segments of the adjacent blades to form a circumferential shroud band. At the top, the shroud band 2 has three sealing ribs 3, 4, 5 disposed one behind the other in the axial direction of the turbine. The ribs 3, 4, 5 are adapted to seal the gap on the side of the diagrammatically-indicated casing or duct wall 6 and thereby greatly reduce the leakage air flow represented by arrows 7. The sealing effect is improved by an additional air flow 8 from the top edge 5a of the sealing rib 5 into the gap between the sealing rib 5 and the wall 6. violent turbulence consequently occurs in the gap between the leakage air flow 7 and the air flow 8, thus further throttling the leakage air flow 7.

To obtain a uniform distribution of the air flow 8 around the entire periphery of the rotating shroud band 2 or of the likewise rotating sealing rib 5, the sealing rib 5 has - 3 a likewise circumferential slot 9 through which the sealing air flow 8 is guided. Consequently the air flow 8 from the slot 9 enters the gap between the tunnel wall 6 and the top edge Sa of the sealing ribs.

The air flow 8 can be supplied from various sources. A f irst embodiment is shown in Figures 1 to 3, in which a number of branch ducts 10 from a cooling-air duct 11 in the shroud band 2 open into the bottom region 9a of the slot 9. The shroud band in Figures 1 to 3 is provided with a cooling-air duct 11 and an entire cooling-air duct system 12 which supplies the cooling-air duct 11 and, in turn, is connected to a coolingair duct system (not shown) inside the air-cooled turbine blade 1. The air flow 8 is thus supplied from the flow of cooling air guided through the turbine blade 1 and the shroud band or segment 2.

The detailed manufacturing process can be as follows: firstly, the slot 9 is formed in a sealing rib 5, which is made wider than a conventional sealing rib without a slot. Next, the branch ducts 10 are manufactured, e. g. by drilling or electro-erosion. Preferably the branch ducts 10 enter the slot 9 at an inclined angle, as shown especially in Figure 3. By this means, the air flow 8 exhausts in the peripheral direction, i.e. opposing the direction of the rotating shroud band 2, imposing additional torque to the rotating stage to that of the blades in the neighbourhood of the top edge 5a of the sealing rib 5 so that the desired turbulence of the two air flows 7 and 8 is reliably produced in the gap between the top edge 5a and the tunnel wall 6. Finally, in the turbine-blade 4 arrangement shown in Figures 1 to 3, the cooling-air supply duct 13, which for manufacturing reasons extends through the cooling-air duct 11, is closed by welding on the trailing edge 2a of the shroud band 2 so that substantially the entire cooling-air flow is available as the air flow 8.

In the previously-explained embodiment, the sealing rib 5 formed with the circumferential slot 9 is on the trailing-edge side 2a of the cover shroud 2, since the leakage air flow 7 here has already been throttled by the upstream sealing ribs 3 and 4. The additional sealing effect is thus intensified by the air 8 flowing transversely into the gap.

The disclosed steps are a simple method of increasing the sealing effect in the gapregion between a turbine-blade shroud band 2 and the adjacent casing or duct wall 6. The additional expense is kept relatively low, and of course a number of details, particularly constructional, can deviate from the embodiment shown without departing from the scope of the claims.

4

Claims

C L A I M S

1. A turbine blade arrangement comprising a shroud band (2) with at least one circumferential sealing rib (5), characterised in that the sealing rib (5) has a circumferential slot (9), whereby a stream of air (8) supplied to the base (9a) of the slot (9) is able to flow. out at the top edge (5a) of the sealing rib (5).

2. A turbine blade arrangement according to claim 1, having at least one cooling-air duct (11) in the shroud band (2), characterised in that branch ducts (10) extend from the cooling-air duct (11) and open into the bottom region (9a) of the slot (9).

3. A turbine blade arrangement according to claim 1 or claim 2, characterised in that the branch ducts (10) open into the slot (9) at an inclined angle.

A turbine blade arrangement according to any one of the preceding claims, characterised in that a number of circumferential sealing ribs (3, 4, 5) are disposed on the shroud band (2), and the sealing rib (5) formed with the circumferential slot (9) is situated on the trailing edge (2a) of the shroud band (2).