Apparatus for adjusting stator blades

[57] ABSTRACT

The adjustably mounted stator blades are movable in a linear manner by means of adjusting rings which are both rotatable about the axis of the turbomachine and slidable longitudinally, i.e. axially, of the turbomachine. The adjusting rings are interconnected by resilient twistable strips which are each anchored in a pivotal manner on the stator blade support. The adjusting rings are driven by servo pistons which are connected to one of the adjusting rings.

Claims, 4 Drawing Figures

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PATF?’Trn JUL C 1975

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SHEET

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W’’T^rn JUL 8 1975

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SHEET 2

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s ί’ΛΤΕΗΤΕΠ JUL 8 ms

SHEET 3

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Fig.3

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APPARATUS FOR ADJUSTING STATOR BLADES

This invention relates to an apparatus for adjusting stator blades and particularly to an apparatus for ad justing stator blades of multi-stage axial turbomachines.

As is known, axial turbomachines have been constructed with stator blades, particularly the stator blades of at least individual stages, which are adjustable in order to improve the part load characteristics of the turbomachines so as to enable very small minimum loads to be operated or, for example, in the case of gas turbine plants, to reduce the starting power which must be supplied by an auxiliary drive.

Generally, various types of adjusting mechanisms 15 have been used to carry out this function. For example, some adjusting mechanisms have used a rotatable adjusting ring to adjust the blades of one stage by connecting the ring to each blade over a lever. In addition, the adjusting rings of the individual stages have been 20 coupled to each other through connecting elements which are rotatably mounted at their downstream ends on the casing of the turbomachine so as to be adapted for simultaneous adjustment in the same sense. Further, the adjusting mechanisms have been constructed 25 so that the angles of rotation above which the blades of the individual stages are to be pivoted through a specific distance of an adjusting mechanism should be in a practically linear relationship, for example, so that the angle for the stages with a higher pressure dimin- ³⁰ishes with a linearly diminishing function. This relationship may be obtained by using levers of different length for the individual stages between the blades and their adjusting rings, which may for example, be combined into a sleeve.

Constructions have also been known in which a rod which is pivotably supported on the casing is pivoted in one plane for the purpose of adjusting the stator blades of a plurality of stages practically in a linear relationship. In this case, the adjusting rings are rotated by the aforementioned pivoting action; the rotation is then transmitted to the blades via trunnions and levers which extend at least substantially axially. Since the pivoting motion of the rod in this construction does not proceed parallel to the rotating motion of the adjusting ⁴³rings, a mechanism is required which has large tolerances and substantial clearance between the individual elements which move relative to each other. The known construction is therefore completely unsuitable for a large number of stages. Also, the construction is ⁵⁰not suitable if the accuracy requirements of blade adjustment are only slight increased. Furthermore, owing to the inaccurate guiding of the individual motions, the known adjusting mechanism is liable to jam or at least become cumbersome, that is, it may require very large ^³adjusting forces. In principle, it is possible to eliminate these disadvantages by providing ball joints and concentric bearing systems for the rings with respect to the machine body; however, this results in a very complex „ and expensive construction.

Accordingly, it is an object of the invention to provide a simply constructed adjusting device in which the relations between the adjusting angles for the adjusted stator blades is also substantially linear.

It is another object of the invention to avoid any need for expensive equipment to ensure accurate blade adjustment and easy mobility of adjustment.

it is another object of the invention to provide a simple accurate apparatus for adjusting the positions of the adjustably mounted stator blades of an axial turbomachine.

It is another object of the invention to avoid the need for ball joints in the adjustable stator blades of a turbomachine.

Briefly, the invention is directed to a multi-stage axial flow turbomachine having a casing and a plurality of 10 stages of adjustable stator blades mounted about a longitudinal axis. In accordance with the invention, an apparatus is provided in this turbomachine for adjusting the adjustable stator blades in each stage. This apparatus includes a plurality of adjusting rings which are connected to the stator blades by levers. The rings are rotatably mounted in concentric relation about the longitudinal axis of the turbomachine and each is mounted adjacent a respective stator stage. The levers connect each blade of a stage to the adjacent ring. In addition, a plurality of resilient twistable strips are secured across and to the rings and each strip is pivotally mounted at one end on the casing. A drive means is also secured to at least one adjusting ring for rotating the ring and the other rings via the twistable strips. As the rings are rotated, they simultaneously move axially under the influence of the twistable strips and cause the stator blades, which are supported between the two axial extreme positions of the adjacent adjusting ring, to turn in a linear pattern.

By contrast to the known construction described above, the blade adjustment of the present construction is obtained by the axial motion of the adjusting ring which is imposed in linearly diminishing manner by rotation of the rings with the aid of the strips in accordance with requirements.

If the apparatus is to be adjusted by a motor drive, one of the upstream disposed adjusting rings is driven because the adjusting forces are relatively small for relatively large angles of rotation in the rings which are the first as seen in the flow direction.

The twistable strips, preferably stamped from thin spring steel sheet, tend to kink if they are stressed in compression with the distance between two adjusting rings is excessive. This kinking can, however, be prevented in a simple manner by securing the strips between two adjusting rings to a support collar which is floatingly disposed between the rings.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates in a sectional view of the first stages of a compressor of a gas turbine plant and an apparatus according to the invention, the view being a longitudinal section along a vertical axial plane of the machine;

FIG. 2 illustrates an enlarged detail of FIG. 1;

FIG. 3 illustrates a view taken on line III—III of FIG. 4 through an adjusting ring, the sectional plane being disposed slightly before or behind that of FIG. 2 as seen in the circumferential direction of the ring to show the ring cross-section in the zone of its bearing elements instead of the connection of the ring to one of the strips; and

FIG. 4 illustrates a perspective schematic view showing the method of operation of the adjusting apparatus of the invention by reference to two adjustable stator blade rows, only one blade being shown for each row.

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Referring to FIG. 1, the compressor has a suction end which is associated with a gas turbine (not shown) and in which a plurality of stages 1-5 of stator blades 6, 7 are mounted. The blades 6 of the inlet stator stage 1 and the blades 7 of the first four stator blades stages 2-5 are adjustably constructed while the stator blades 8 of the higher compression stages are fixed. The blades 6, 7 are pivotally supported by means of a dry bearing system 9 in a stator blade support 10 which is divided along a horizontal axial plane as viewed and concentrically surrounds a rotor 12 which supports rotor blades 11.

The adjustable blades 6, 7 are adjusted via an adjusting apparatus which includes annular adjusting rings 16 connected to the adjustable blades 6, 7 by means of levers 13 which are of identical construction for manufacutring reasons and are retained in the blade roots 15 by means of screw fasteners 14. To this end, sliding blocks 17, e.g. of rectangular shape which are supported on spigots that are welded to the free ends of the levers 13 engage in corresponding annular grooves 18 of the rings 16. The rings 16 themselves, whose diameter becomes smaller for the higher pressure stages, are supported by means of lateral flange extensions 20 (FIG. 3) on three bearing elements 19 (FIG. 3) which are uniformly distributed circumferentially about the rings 16 and are covered with dryrunning material represented in block form in FIG. 3. The bearing elements 19, in turn, are mounted on corresponding extensions 21 on the outside of the stator blade support 10.

The adjusting rings 16 of the individual stages 1-5 are also divided along their horizontal plane and are connected to each other by means of free resiiiently twistable strips 22 e.g. three as shown which are distributed over the circumference. The downstream end of each strip 22 is pivotably supported in corresponding extensions 25 in the blade support 10 by means of spigot mountings 23 which are of a construction that is identical to that for the connections 24 between the rings 16 and the strips 22 and which will be described subsequently.

Since the axial distance between the inlet stator stage 1 and the first stator blade row 2 is relatively large, there is a risk that the strips 22 will be kinked over this relatively long axial length when subjected to impact or thurst loadings. Thus, in order to increase stability, a floating support ring 27 (FIG. 1), that is, a ring which is secured only by means of mountings 26 in the strips 22, is provided between the stages 1 and 2.

The adjusting apparatus is driven by means of two servo pistons 28 (FIG. 1) which are mounted laterally on the ring 16 of the second stage 2, one end of the pistons 28 being supported in the compressor casing 10 and the other end being adapted to act with clearance on a bifurcated extension of the aforementioned ring 16 which is situated close to the horizontal parting plane.

The mounting means 24 are disposed in eyelet extensions 30 (FIG. 2) of the rings 16 and, in the same way as the mounting means 23 and 26, are provided with a spigot 32 which is secured by means of a pin 31 against rotation in the eyelet 30. The spitot 32 additionally bears by means of a shoulder 33 upon the extension 30. In the zone of the strips 22, the spigot 32 is surrounded by a clamping or reinforcing element 34 via an interposed layer of dry running material. The reinforcing el4 ement 34 comprises two parts and bears on the other annular surface of the shoulder 33, the two parts being bolted to each other while clamping the strip 22. The elements 34 are retained with a clearance on the spigot 32 via a washer 36 by means of a screw bolt 35 which is screw mounted into the spigot 32.

The method of operation of the apparatus is illustrated by the perspective sketch of FIG. 4 which illustrates the path 40 and 41 of two rings 16 from a first position shown in dash dot form into a second position shown in solid form and vice versa when rotated in the direction indicated by the double arrow 42. The strips 22 which may comprise stamped sheet metal strips of approximately 60 millimeters (mm) width and 1.5 millimeters (mm) thickness will be subjected to twisting as indicated in FIG. 4 while the rings 16, in addition to rotating, carry out an axial sliding motion on the bearing elements 19 with a linear interdependence, owing to the axial displacement of the rings 16, the sliding blocks 17 which are supported in the annular groove 18 of the rings 16 cause pivoting of the levers 13 and of the blades 7 which are coupled thereto. For small pivoting angles, which are ensured between the axial extreme positions of their associated adjusting rings 16 and by the position of the levers 13 in the circumferential direction with respect to the blade support 9 by virtue of the arrangement of the blade stages 1 to 5, it follows that the linear path of the adjusting rings 16 is almost identical to the arcuate path of the levers 13. In accordance with requirements, there will then be a practically linear relationship for these angles between the pivoting angles of the individual blade stages.