Gap control arrangement for a gas turbine

Abstract

A screw-type gap control arrangement for a gas turbine with at least one row of variable vanes 2 and with a gas-wetted surface 4 adjacent to a blade row, wherein the surface 4 has essentially the form of a spherical surface ring and, at the same time, a contraction of a gas path with an aerodynamically favorable form of an annulus is obtained.

Description

This application claims priority to German Patent Application DE10 2005 040 574.6 filed Aug. 26, 2005, the entirety of which is incorporated by reference herein.

DESCRIPTION

This invention relates to a gap control arrangement for a gas turbine.

From the state of the art, various solutions for gap control of variable stator vanes of a compressor of a gas turbine are known.

Document GB 2 235 730 A provides for gap control on the casing by way of an adjustable outer shroud. Setting of the respective shroud segment is there accomplished by way of an actuating mechanism mounted on the casing. Accordingly, the casing and the inner shroud form the boundary surfaces for the gas flow.

Document DE 42 137 16 A1 provides for a spherical design of the inner vane tip end of the variable stator vane and the opposite wall, with the axis of the variable stator vanes being vertical to the machine axis.

Document US 2002/0061249 A1 provides for local, spherical recesses in the casing for each variable stator vane. The variable stator vane axes are there inclined towards the machine axis to obtain a more favorable aerodynamic design of the local beads.

Besides a small gap between the variable stator vanes and the casings or the inner shroud, respectively, it is also important to avoid protrusions, bends and discontinuities in the gas path as these can cause flow loss and separation.

As is generally known, compression of air by the compressor rotor blades requires a gradual contraction of the gas path and, therefore, a tapering of the casing and/or the inner shrouds which, in particular on the forward stages, can be quite large. The front rows of stator vanes of the compressor are mostly variable. However, during variation of these stator vanes, the gap between the casing and the variable stator vane and between the inner shroud and the variable stator vane is subject to change on conventional designs. Such gap formation is disadvantageous and incurs aerodynamic losses.

Documents DE 42 137 16 A1 und US 2002/0061249 A1 address this problem. The disadvantage of these design variants though, is the gas path geometry, which, as described before, should be free of protrusions, bends and discontinuities.

In a broad aspect, the present invention provides a gap control arrangement of the type specified at the beginning above, which while being characterized by simple design and easy and cost-effective manufacture, provides for a minimization of the gap, minimizes aerodynamic losses and at the same time enables an aerodynamically optimized shaping of the gas path.

It is a particular object of the present invention to provide solution to the above problems by a combination of the features described herein. Further advantageous embodiments of the present invention will become apparent from the description below.

According to the present invention, the radial height difference of the annulus is obtained by a spherical segment, with the spherical segment being sectioned before or behind the equator, respectively. The rotary axis of the variable stator vanes passes through the center of the sphere and is inclined at an angle (α) towards the machine axis. The radius of the spherical segment (R_sphere) results from the radial distance of the vane tip at the intersection of the stator vane rotary axis (R_ma) to the machine rotary axis divided by sin (α). Angle (α) is, according to the present invention, selected such that the desired constriction of the flow path is obtained.

Furthermore, it is favorable to set the angle of the rotary axis such that the leading edge of the radially outer end of the variable stator vane is covered by the screw. The gap formed between the trailing edge of the radially outer end of the stator vane and the casing during rotation of the variable stator vane can be minimized by opposition of the inclination of the annulus in the axial direction and the inclination of the annulus in the circumferential direction. Following the spherical area of the inner shroud is the gas path geometry of the subsequent rotor disk. Since the spherical segment does not lie within the area of the sphere equator, no turning point will exist within the gas path. At the intersection of the annulus segment of the adjacent rotor, a curvature discontinuity may exist. This discontinuity is placed such that it will lie within the required running gap between the stationary inner shroud and the rotor. The latter is not feasible on single-end borne variable stator vanes since no running gap exists on these.

The present invention accordingly provides that the respective gas-wetted surface adjacent to the vane row has essentially the form of a spherical surface ring. In accordance with the present invention, this specially formed gas-wetted area can be provided either on the casing, on the inner shroud or on the rotor (single-end bearing arrangement of the variable stator vane). The present invention is, therefore, applicable to both the radially inner area of the vane and the radially outer area of the vane.

The inventive form of the spherical surface ring is defined by the surface of a flat disk cut from a sphere surface. Accordingly, this surface is uniformly curved in the axial direction.

It is particularly favorable if the rotary axes of the variable stator vanes are arranged vertical to the gas-wetted surface. This ensures that the rotary axis always passes through the sphere center. The surfaces of the variable stator vanes which are in contact with the spherical area of the gas-wetted surfaces are cut by a slightly larger sphere. Thus, a constant gap is achieved between the casing or the inner shroud/rotor, respectively, and the respective axially outer or axially inner end of the vane in each rotary position of the vane.

It is also particularly favorable if the gas-wetted surface is axially inclined to the horizontal plane comprising the rotary axis of the gas turbine. Accordingly, the spherical surface ring is not located in the equator of the sphere, but laterally offset. This enables the flow cross-section of the compressor to be tapered or constricted. Since the rotary axis of the variable stator vane passes through the sphere center, the rotary axis is inclined axially forward.

The gap control arrangement according to the present invention accordingly provides for precise gap control. The gap here remains constant throughout the range of variation of the vane. This results in smaller gaps in the operating point of the compressor, increasing efficiency and reducing aerodynamic losses.

It will be appreciated that, according to the present invention, a slight departure from the form of a spherical surface can be allowed, so that the ideal form is substantially provided. This is also covered by the present invention.

This invention is more fully described in the light of the accompanying drawings showing a preferred embodiment. In the drawings,

FIG. 1 is a schematic partial sectional side-view of a variable compressor vane,

FIG. 2 is a perspective partial view of a vane row with casing and inner shroud,

FIG. 3 is a schematic side-view of the inner shroud and of the vane,

FIG. 4 is a perspective view of the representation of FIG. 3,

FIG. 5 is an enlarged partial view, analogously to the representation of FIG. 3,

FIG. 6 is another enlarged partial view of the arrangement according to the present invention,

FIG. 7 is a perspective view illustrating the spherical surface ring,

FIG. 8 is an enlarged partial representation of the inventive vane with screw,

FIG. 9 is a schematic partial sectional side-view of another embodiment, and

FIG. 10 is an enlarged partial view of the embodiment shown in FIG. 9.

The gap control arrangement according to the present invention comprises a state-of-the-art casing 1 of a gas turbine to which—via a screw 10 and an actuating mechanism, which is not further detailed herein as it is known from the state of the art—a vane 2 is fitted. This vane is part of a compressor, as again known from the state of the art.

The radially inward area of the vane 2 can be located on an inner shroud 3, as shown in FIG. 3, or face a rotor drum, as shown in FIG. 1. FIG. 1 further contains a representation of a rotary axis 7 of the vane 2 and the gaps 8 or clearances 8 at the ends of the vane 2.

The present invention provides that, for aerodynamic reasons, a gas-wetted surface 4 (see FIG. 2, for example) of the casing 1 and/or the inner shroud 3 is axially inclined to the engine rotary axis, so that the gas path contracts as the airstream is compressed (see FIG. 1).

According to the present invention, the radially inner end of the variable stator vane and the gas-wetted surface 4 of the inner shroud 3 are designed spherically. The radius of the sphere (R_sphere) for cutting the stator vane tip is, according to the present invention, equal to the radial distance from the machine axis to the vane tip at the nodal point of the stator vane rotary axis (R_ma) divided by the sine of the angle of inclination of the stator vane rotary axis 7 to the machine axis (α). That is:
R_sphere=R_ma/sin(α)

The inclination of the rotary axis 7 is, according to the present invention, selected such that the required height difference between the leading and the trailing edge at the axially sectioned inner shroud is provided 3.

The example shown in the Figures assumes an ascending gas path. A corresponding design is also possible with a descending gas path.

Also, in a favorable development, the portion 5 of a screw 9 of the vane 2 that would otherwise lie within the gas flow is, according to the present invention, cut by the form of a sphere and is, therefore, is not in and does not obstruct the gas flow.

In a favorable development, with a single-end borne stator vane 12, the area 6 of the rotor is also designed spherically according to the above criteria, so that a uniform running gap is obtained with the spherical radially inner end of the stator vane. Area 6 corresponds to at least the maximum axial extension of the variable stator vane in its range of variation.

The gas-wetted surfaces are annular or circular in a section transverse to the engine axis, as indicated by the reference numeral 5 of FIG. 4.

According to the present invention, the rotary axis 7 of the variable stator vane (vane 2) is arranged such that it is vertical to the surface of the inner shroud 3. Thus, the rotary axis 7 of vane 2 is inclined axially forward, depending on the required inclination of the gas-wetted surface 4.

In the axial direction, the gas-wetted surface 4 is designed such that, according to the present invention, it has the same curvature (reference numeral 6 in FIG. 3) as in circumferential direction (reference numeral 5 of the circular form according to FIG. 4). The gas-wetted surface 4 is, therefore, a spherical sector, or a spherical surface ring, as becomes apparent from the representation of a sphere 9 in FIG. 7.

Vane 2 (stator vane), arranged with a clearance (gap 8) to the inner shroud 3, is designed such that the end of the vane 2 is also a part of a spherical surface. The clearance or gap 8, respectively, is, therefore, only dependent on the manufacturing tolerances and thermal expansion. Moreover, the clearance remains constant with each variation or setting of the vane 2 since two spherical surface parts are moved relative to each other.

FIG. 5 shows the variable stator vane in the fully opened state, while FIG. 6 shows the stator vane in the fully closed state. As can be seen, the gap 8 remains constant in both operating states.

Similarly, the part of a screw 10 of the vane 2 which would otherwise lie within the gas flow will, in a favorable development, be cut by the form of a sphere, as a result of which it will not be in and not obstruct the gas flow. In other words, a gas flow exposed portion of the screw of the vane is cut by the form of the sphere so as not to extend into and impede the gas flow.

Therefore, the present invention enables requirements on the gas path surface for continuity and incidence angle in the gas-flown area of the rotor to be realized.

The above description was written in relation to the inner shroud 3. Obviously, the radially inner surface of the casing 1 and the radially outer end area of the vane 2 can also be designed in the spherical form described.

In a favorable development of the present invention, the variable stator vane is single-end borne (FIG. 12), that is, supported by a single end in a cantilever manner. As such, the stator vane has no inner screw. The radially inner area of the variable stator vane faces the drum of the rotor 11. The opposite surfaces of the variable stator vane 12 and of the rotor 11 are spherical, as described above.

LIST OF REFERENCE NUMERALS

• 1 Casing
• 2 Variable stator vane
• 3 Inner shroud
• 4 Gas-wetted surface
• 5 Circular form
• 6 Curvature
• 7 Rotary axis
• 8 Gap/clearance
• 9 Sphere
• 10 Screw
• 11 Rotor with integrated blades/conventional rotor with circumferential grooves for rotor blades
• 12 Single-end borne variable stator vane

Claims

1. A screw-type gap control arrangement for a gas turbine with at least one row of variable stator vanes, which at a radially outer end are held by a casing and which are located at a radially inner end on an inner shroud, with the radially inner end of the variable stator vane and a gas-wetted surface of the inner shroud being designed spherically, wherein

a radius of a sphere for cutting a stator vane tip is equal to a radial distance from a machine axis to the vane tip at a nodal point of a stator vane rotary axis divided by a sine of an angle of inclination of the stator vane rotary axis to the machine axis,

a radius of the sphere for cutting the inner shroud is smaller than the radius for cutting the inner stator vane tip, to compensate for tolerances or thermal movements,

the angle of inclination is selected such that an aerodynamically required radial height difference between a leading and a trailing edge at the axially sectioned inner shroud is provided, and

a distance of all points on the axially sectioned inner shroud to the machine axis is smaller than the sphere radius.

2. A screw-type gap control arrangement in accordance with claim 1, wherein curvature discontinuities in the gas path are placed in a gap between the inner shroud 3 and a subsequent rotor stage.

3. A screw-type gap control arrangement in accordance with claim 2, wherein a gas flow exposed portion of a screw of the vane is cut by the form of a sphere so as not to extend into and impede the gas flow.

4. A screw-type gap control arrangement in accordance with claim 3, wherein the optimal spherical form is obtained in a hot engine state, and a cold-state geometry produced by machining deviates from the ideal form.

5. A screw-type gap control arrangement in accordance with claim 2, wherein the optimal spherical form is obtained in a hot engine state, and a cold-state geometry produced by machining deviates from the ideal form.

6. A screw-type gap control arrangement in accordance with claim 1, wherein the optimal spherical form is obtained in a hot engine state, and a cold-state geometry produced by machining deviates from the ideal form.

7. A screw-type gap control arrangement in accordance with claim 1, wherein a portion of a screw of the vane lying within the gas flow is cut by the form of a sphere and does not impede the gas flow.

8. A screw-type gap control arrangement in accordance with claim 7, wherein the optimal spherical form is obtained in the a engine state, and a cold-state geometry produced by machining deviates from the ideal form.

9. A screw-type gap control arrangement for a gas turbine with at least one row of single-end borne variable vanes, which at a radially outer end are held by a casing and at a radially inner end seal against a rotor, with the radially inner end of the variable vane and an area of the rotor being designed spherically, wherein

a radius of a sphere for cutting a stator vane tip is equal to a radial distance from a machine axis to the vane tip at a nodal point of a stator vane rotary axis divided by a sine of an angle of inclination of the stator vane rotary axis to the machine axis,

a radius of a sphere for cutting the rotor in the area is smaller than the radius for cutting the inner stator vane tip, to compensate for tolerances or thermal movements,

the angle of inclination is selected such that an aerodynamically required radial height difference in the area of the rotor is provided, and

a distance of all points in the area to the machine axis is smaller than the sphere radius.

10. A screw-type gap control arrangement in accordance with claim 9, wherein the optimal spherical form is obtained in a hot engine state, and a cold-state geometry produced by machining deviates from the ideal form.