This application claims priority to German Patent Application DE10161292.3, filed Dec. 13, 2001, the entirety of which is incorporated by reference herein.
This invention relates to a shroud for the support of roots of variable stator vanes in the high-pressure compressor of a gas turbine.
More particularly, the present invention relates to a shroud as it is used for the inner support of variable stator vanes primarily in the area of the high-pressure compressors of present-day turbofan engines.
Such shrouds are usually made of aluminium, steel alloy or titanium. A design of this type is exemplified in U.S. Pat. No. 5,062,767.
The shrouds normally consist of two parts so that there is a front and a rear shroud segment. These shroud segments are annular. For weight reduction, an axial annulus is provided in these shroud segments which is produced by turning machining, for example. In order to reduce air swirls, vibrations and noise generation, the annulus is provided with a rubber filling in the state of the art. This filling is applied by way of vulcanization.
Such rubber fillings are disadvantageous in several respects. One disadvantage is the high effort required for production involving a manual special process which is time-consuming and, therefore, expensive. This special process normally comprises several operations, in particular cleaning, priming, filling, heat-treatment and removal of surplus rubber material as well as subsequent re-cleaning of the segments of the shroud. Quality problems may arise from lack of adhesion or from bubbling of the rubber material. In operation, the rubber filling is susceptible to failure since it is subject to ageing and tends to develop cracks at the joints. Furthermore, the rubber filling has a relatively high weight.
In a broad aspect, the present invention provides a shroud of the type specified at the beginning which, while avoiding the disadvantages of the state of the art, features simplicity of design, easy and cost-effective production and, in particular, light weight.
It is a particular object of the present invention to provide a solution to said problems by a combination of the features described herein, with further objects and advantages of the present invention becoming apparent from the description below.
The present invention, therefore, provides for an annular cover arranged in the area of the opening of the annulus, this annular cover being provided with assembly openings. In addition, provision is made for a tubular support arranged in the spacing between the assembly recess of the cover and the corresponding assembly hole of the shroud segment.
The shroud according to the present invention features a variety of merits.
In accordance with the present invention, the rubber filling, which features the above-mentioned disadvantages, is replaced by an annular cover. Compared with a rubber-filled shroud segment, the shroud segment thus provided features a very similar or identical outer contour. Accordingly, the acoustic properties and the flow conditions, which may give rise to air swirls and vibrations, develop very favourably and at least achieve the values known from state-of-the-art shrouds.
A major advantage of the solution according to the present invention is the simple and rapid manner in which it can be produced. The expensive operations required for the application of the rubber filling can now completely be dispensed with. This results in a clear cost advantage over the state of the art.
Another major advantage lies in the fact that no materials that are susceptible to ageing, such as rubber, are applied. This provides for increased reliability and life.
Still another advantage is the weight reduction obtained owing to the absence of a filling with rubber or any other filling material.
Changes to the design of the shroud segments are not required since the cover according to the present invention is fitted into the area of the mouth of the annulus. This enables existing shroud segments to be converted accordingly upon removal of the rubber filling.
It is also advantageous that the cover can be removed and re-installed at any time, for example for maintenance or other work.
In a particularly favourable form of the present invention, the cover is designed essentially as a flat ring. This ring may simply be made of sheet metal, for example aluminium or titanium. It is also particularly favourable to profile the cover at least at its rims. Such edging or flanging may give a particularly favourable clamping effect or an interference fit, thus ensuring the operational safety of the cover fitted into the annulus.
In order to avoid vibrations and similar occurrences, additional stiffening measures may be applied, such as beading or the like.
The support is preferably cup-shaped or hat-shaped. Like the cover, it can be made of sheet metal by rolling or deep-drawing or a similar shaping process. It is also particularly favourable if the free rim area of the support is profiled for retention of the cover, for example by bending or flanging. Thus, the support locates the cover and restrains it against the shroud segment, ensuring safe attachment. Restraint is applied via the fixing bolts which are also used for clamping the two shroud segments of the shroud. The supports are preferably dimensioned such that they are slightly shorter than the depth of the annulus of the shroud segments. This clearance may be 0.5 mm, for example. Accordingly, restraint is applied to the cover by way of the bolted connection.
The covers and the supports may be one-part or multi-part. The covers and/or supports may also be made of a plastic or similar material, for example by injection moulding, instead of a metallic material as described above.