This invention relates to an intermediate-stage seal carrier of a high-pressure jet-engine turbine, said seal carrier having a supporting area for vane retainers.
In particular in the case of high-pressure turbines, appropriate means must be provided for creating a seal between a rotor and a stator. Therefore, the area upstream of the second turbine stage is of particular interest as regards the present invention. In accordance with prior art, an intermediate-stage seal carrier is attached at the radially inward end areas of the vanes. Said intermediate-stage seal carrier is suitably designed in such a way to conduct the air, which is also used for sealing, from an intermediate disc area into the area between the stator and the rotor.
In the solution according to the state of the art, an intermediate-stage seal carrier is located freely movable relative to the vanes by way of a spoke-type centering arrangement. This arrangement provides for thermal and stress characteristics of the seal carrier and, in consequence, the seal between stator and rotor which are superior to those of other, firmly bolted or riveted solutions according to the state of the art. For free movability, axial clearance must be provided between the vane retainers and the intermediate-stage seal carrier. This clearance is liable to incur sealing problems and leakage. Therefore, sealing between the vane retainers and the intermediate-stage seal carrier is accomplished by way of a groove, this groove being provided on the outer circumference of the intermediate-stage seal carrier. Said groove comprises an upstream and a downstream wall between which the individual vane retainers are inserted. In this arrangement, a line contact is formed between the vane retainers and the circumferential annular groove. According to prior art, the line contact can occur at the upstream or at the downstream side of the groove, i.e. at the upstream or at the downstream wall, depending upon the pressure differential prevailing across the intermediate-stage seal carrier in the intermediate disc area. Furthermore, the design known from prior art provides for a secondary sealing effect by way of a small gap between the vane retainers and the groove, should the line-contact force not be sufficient to ensure an adequate sealing effect.
Therefore, it is irrelevant whether the direction of the pressure force changes or the pressure force is very small. This arrangement is mainly used for low-pressure turbines, where the pressure differentials are only minor and subject to major variation. In the case of high-pressure turbines, however, higher pressure differentials may be encountered.
Specification GB 2 222 856 A describes a sealing arrangement of a gas turbine in which a seal carrier is firmly attached by means of bolting, riveting or in another manner. Accordingly, the sealing effect between a vane retainer and an intermediate-stage seal carrier is accomplished by the fasteners and a non-positive/positive lock between the vane retainer and a single wall of the intermediate-stage seal carrier. Hence, a different technical principle is applied in which neither a spoke-type centering arrangement nor a further, second annular wall is required.
A disadvantage of the known design lies in the high effort which is necessary to produce the annular groove with a high accuracy of fit. To achieve this accuracy, the intermediate-stage seal carrier must be machined mechanically in a suitable manner. This incurs high production costs.
A further, major disadvantage arises from the assembly or installation of the vanes to the intermediate-stage seal carrier. Since the fitting tolerances of the groove are very close, high accuracy of fit must be ensured for the installation of the vane retainers.
A further disadvantage is the relatively high total mass.
In a broad aspect, the arrangement of the present invention provides an intermediate-stage seal carrier of the said design which provides reduced mass and simple and cost-effective manufacture as well as reliable operation and long life.
In accordance with the present invention the solution to the said problem is provided by the features cited in the main claim. Further advantageous embodiments will become apparent from the subclaims.
It is a particular object of the present invention to provide a supporting area with a single annular wall upstream of the vane retainers, with the said annular wall abutting the vane retainers.
The design embodiments in accordance with the present invention provide various, significant benefits.
The intermediate-stage seal carrier thus features only one upstream annular wall which provides for the sealing between the vane retainers and the intermediate-stage seal carrier. It was found that the pressure differential across the intermediate-stage seal carrier will always be high on the high-pressure turbine considered herein and that the said high pressure differential will permanently provide for a sufficiently high pressure force against the vane retainers in operation. Accordingly, the upstream annular wall will always be pressed against the vane retainers. Said pressure differential, which is in the range of six bar for example, has proved to be sufficient to ensure reliable sealing in a line-contact area.
The intermediate-stage seal carrier in accordance with the present invention will, therefore, ensure an adequate sealing effect with only one annular wall.
Since two walls and an interpositioned groove, as known from prior art, are omitted, the present invention provides for a considerable reduction in mass, which may lie in the range of 500 g for the intermediate-stage seal carrier.
Since the vane retainers need not be inserted into the narrow, close-tolerance fitting groove, the present invention also facilitates assembly to a considerable extent.
In accordance with the present invention, it is particularly advantageous when the upstream annular wall is provided with openings for the installation of locating pins. Said locating pins provide for fixation of the intermediate-stage seal to the vane retainers.
To ensure reliable fixation of the locating pins, it may be particularly favourable when mounting bosses are provided for the installation of the locating pins downstream of the vane retainer in the supporting area. Said bosses have no sealing function, but are used for mechanical fixation only. Consequently, they can be designed for low weight and their exteriors machined to no or only low standards of fit.
Since, according to the invention, the upstream annular wall abuts the vane retainers, only the abutting face of the annular wall must be machined dimensionally accurate. A close-tolerance fitting groove need not be produced.
This will lead to a considerable reduction in the manufacturing costs for the intermediate-stage seal carrier. In addition, the intermediate-stage seal carrier according to the present invention can simply be produced as a casting, whereas the solutions according to the state of the art mostly require extensive cutting machining effort.
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