Rotor for a compressor

A rotor (20) for a compressor, in particular in a gas turbine, has a number of rotor blades (25) which are arranged around the rotation axis of the rotor (20) in the form of a rim and are each held in a circumferential recess (21) on the rotor (20) by a blade root (26), with the blade root (26) having a widening lower part (27) which engages behind two shoulders (24) that are formed on the side walls of the recess (21). In such a rotor, the life is lengthened in that the recess depth (T) of the recess (21) is substantially greater than a minimum recess depth (Tmin) which results in the rotor (20) having sufficient strength in the area of the blade attachment for starting, based on the predetermined material characteristics of the rotor (20) and the operating conditions of the compressor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of turbomachines, and in particular to a rotor for a compressor.

2. Brief Description of the Related Art

Rotors for high-pressure compressors, as are used in particular in gas turbines, generally have a multistage blade system, which includes blade rims which are arranged one behind the other in the axial direction. Each blade rim contains a large number of rotor blades, which are arranged on and attached to the circumference of the rotor. Each of the rotor blades is seated by means of a blade root in a circumferential groove, which is in the form of a recess in the rotor. One such rotor is known, for example, from the document DE-A1-196 15 549.

FIG. 1also shows how a single rotor blade is mounted in a rotor according to the prior art: the rotor blade15has a blade section12which projects radially outwards and a blade root16, which are separated from one another by a platform18. The rotor blade15is mounted in the rotor10by means of the blade root16. A circumferential groove, in the form of a recess11which has a recess depth T, is provided for attachment of the rotor blades. Shoulders14with a shoulder depth A are formed on the side walls within the recess11. The blade root16has a widening lower part17with a cross-sectional contour in the form of an inverted “T”, by means of which it engages behind the shoulders14of the recess11. The centrifugal force which acts on the rotor blade15during rotation of the rotor10is in this case transmitted via contact surfaces13to the shoulders14of the recess11.

In order to avoid the recesses11for the rotor blades weakening the mechanical strength of the rotor any more than necessary, the recesses11in the prior art have a minimum recess depth T=Tmin,1. This minimum recess depth Tmin,1allows the shoulder14to have a shoulder depth A which is just sufficient to allow sufficient initial strength of the rotor10in the area of the shoulders14in the prevailing extreme operating conditions (high rotation speeds, temperatures up to 500° C. ) and with the characteristics of the chosen rotor material.

Now, however, it has been found in practice that the use of a recess with the minimum recess depth Tmin,1can lead to the rotor10being stressed beyond the permissible strength limits in the area of the recess11, and this can lead to a reduction in the rotor life.

SUMMARY OF THE INVENTION

One aspect of the present invention thus includes providing a rotor for a compressor which addresses this life problem.

Another particularly advantageous aspect of the present invention includes providing the recess with a recess depth which is substantially greater than the minimum recess depth, and to adapt the blade root accordingly.

The recess depth should preferably be more than 10% greater than the minimum recess depth. In particular, it has been proven for the recess depth to be about 40% greater than the minimum recess depth.

One preferred refinement of the invention is characterized in that cutouts are provided in the blade root in order to reduce the weight. This makes it possible to compensate for increases in the weight of the rotor blade resulting from the lengthened blade root, and to reduce the forces which occur during operation.

In one preferred development of the refinement, a cutout is provided in the blade root, above the lower part, in the form of a hole which passes through the blade root in the circumferential direction, with the hole, in particular, being in the form of an elongated hole which extends in the radial direction.

However, it may also be advantageous for cutouts to be provided on the lower face of the lower part of the blade root, in order to reduce the weight.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the exemplary embodiment of the invention illustrated inFIG. 2, the rotor blade25is mounted in the rotor20by the blade section22, the platform28and the blade root26, by a recess21. In this case as well, side shoulders24are once again formed in the recess21, behind which the widened lower part27of the blade root26engages, and is supported on the contact surfaces23when centrifugal forces occur.

In order to make it possible to better absorb the load which occurs in this case on the shoulders24, and thus to overcome the life limit which results from strength problems, the recess21is now formed with a recess depth T which is substantially greater, in particular at least, 10% greater, than the minimum recess depth Tmin,2used in the prior art.

This makes it possible to increase the shoulder depth of the shoulders24to a value B which is substantially greater than the shoulder depth A with the already known mounting as shown inFIG. 1. In the exemplary embodiment shown inFIG. 2, the recess depth T is at least, approximately 40% greater than the minimum recess depth Tmin,2, as has been proven in practice.

The increase in the recess depth T and in the shoulder depth B also results in an increase in the height of the blade root26. Lengthening the blade root26necessarily also increases the blade weight, which would lead to increased centrifugal forces and thus to increased mechanical loads on the rotor20. It is therefore particularly advantageous for at least a portion of the weight increase which is caused by the extension to be counteracted again by suitable measures. The measures comprise material being cut away on the rotor blade25in the area of the blade root26by the provision of at least one cutout at points which are not critical to the mechanical strength. A first preferred type of cutout is an elongated hole19, which passes through the blade root26in the circumferential direction and extends in the radial direction. The elongated hole19is in this case arranged in the thin section of the blade root26, and is located in the centre, between the two shoulders24. A second preferred type of cutout is rounded depressions29, at the edge, on the lower face of the lower part27of the blade root26. Both types of cutouts19,29may optionally be implemented individually or may be combined with one another, in order to achieve the desired reduction in weight by reducing the amount of material.

LIST OF REFERENCE SYMBOLS

A,B Shoulder depth

T Recess depth