EP2229506A1

EP2229506A1 - Magnetic device for damping blade vibrations in turbomachines

Info

Publication number: EP2229506A1
Application number: EP08864578A
Authority: EP
Inventors: Christoph Hermann Richter
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2007-12-21
Filing date: 2008-11-25
Publication date: 2010-09-22
Anticipated expiration: 2028-11-25
Also published as: EP2072755A1; ATE514837T1; JP2011506840A; EP2229506B1; CN101952554A; WO2009080433A1; US8568088B2; CN101952554B; US20100278636A1; JP5143236B2

Abstract

The turbo-machine has a blade (1) e.g. turbine blade, aligned along a blade axis (7) and rotatably arranged at a rotation axis, and a housing arranged at the blade. An induction plate (3) is arranged in a blade tip, and magnets (5) e.g. bar magnets, arranged in the housing. The plate is aligned in a plane formed by the rotation axis and a radial direction and made of electrically conductive material. A magnetic northpole and a magnetic southpole lie in a circular path. The path is aligned rotation symmetric to the rotation axis and runs along a circumferential surface of the housing.

Description

description

Magnetic device for damping blade vibrations in turbomachines

The invention relates to a turbomachine, in particular a steam turbine, comprising a turbine blade rotatably arranged about an axis of rotation and directed along a blade axis, a housing arranged around the turbine blade, an induction plate arranged in the turbine blade tip and a magnet arranged in the housing.

Hydraulic turbines, steam and gas turbines, wind turbines, centrifugal pumps and centrifugal compressors as well as propellers are summarized under the collective term turbomachinery. All these machines have in common that they serve the purpose of extracting energy from one fluid in order to drive another machine or, conversely, to supply energy to a fluid in order to increase its pressure.

In a turbomachine, the energy conversion takes place indirectly and makes its way over the kinetic energy of the flow medium. In a turbine, for example, the flow medium flows through fixed vanes, increasing the velocity and thus the kinetic energy of the flow medium at the expense of its pressure. The shape of the vanes creates a velocity component in the circumferential direction of the impeller. The fluid releases its kinetic energy to the rotor by varying the amount of velocity and the direction as it flows through the channels formed by the blades. The impeller is driven by the resulting forces.

The rotating blades in a turbomachine are designed without resonance for the largest possible operating conditions. If the operating conditions change, eg due to volume Current changes, the blades can be excited to vibrate, which could lead to failure of the blades, if vibration resonances lead to high mechanical stresses. Various devices have been developed to dampen these vibrations. For example, it is known to couple vanes to each other to thereby dampen vibrations.

In DE 199 37 146 Al, a turbomachine is provided in which permanent magnets are incorporated in the blade tip in order to couple adjacent turbine blades by magnetic forces.

EP 0 727 564 B1 discloses a turbomachine having a turbine blade and a housing arranged around the turbine blade, wherein magnets made of rings in the housing are arranged on the circumference of the inner surface of the housing. The turbine blades have a conductive material on the tips, which allows vibrations to be reduced as these turbine blades move about the magnet.

EP 1 596 037 likewise discloses a turbine blade arrangement with which vibrations are to be reduced.

The vibrations of the blades are undesirable because they can lead to material fatigue of the blade and the rotor claw. Any one thousand point of improved logarithmic attenuation decrement is desirable. For example, shroud blades have a total loss of 0.5% log dec. Doubling this size results in halving the resonant amplitudes, which may mean that one mode is less tunable. This also allows the permissible speed range to be widened.

The available measures for damping the vibrations have the disadvantage that they are comparatively need a lot of space. However, this space is usually not available. Another limiting factor is the high centrifugal forces that occur in turbomachinery. The vibration damping methods by magnetic

Forces are caused, such. In EP 0 727 564 B1, DE 199 37 146 A1 and EP 1 596 037 A2 have the disadvantage that the forces generated by eddy currents do not distinguish between a movement of the turbine blade tip in the main movement and a disturbing oscillatory movement. In other words, a movement of the blade in the direction of rotation, i. in the circumferential direction is influenced by the magnetic forces that lead to eddy currents, which is undesirable. An oscillating movement, not in the circumferential direction, for example in the axial direction, is intended to be damped by magnetic forces which lead to eddy currents.

It would be desirable to have a device that dampens vibrations of a blade, the device no

Influence on the movement of the blade in the main direction, i. in the circumferential direction.

At this point, the invention begins, whose task is to provide a turbomachine that allows effective damping of blade vibrations.

This object is achieved by a turbomachine, in particular a steam turbine, comprising a turbine blade rotatably arranged about a rotary pocket and directed along a blade axis, a housing arranged around the turbine blade, an induction plate arranged in the turbine blade tip and a magnet arranged in the housing, wherein the Induction plate is aligned in a plane which is formed by the rotation axis and a radial direction. An essential feature of the invention is that so-called induction plates are arranged in the blade tip. Such induction plates are made of a suitable material. Whereby this material is electrically conductive and therefore suitable for causing eddy currents.

These induction plates are aligned along a plane formed by the axis of rotation and a radial direction. Of course, this plane is not stationary, i. this plane rotates around the axis of rotation. The induction plate is optimal for attenuation, d. H. parallel to

Rotary axis and aligned parallel to the radial direction. Since the radial direction is changed over time in operation, i. With the rotational frequency rotating about the axis of rotation, the induction plate is always aligned perpendicular to the opposite housing. A magnet arranged in the housing is aligned in such a way that the magnetic field acts in the direction of the induction plates. A movement of the induction plate by this magnetic field causes eddy currents in the induction plate, which leads to a development of a counter magnetic field, which is formed according to the Lenzsch'en rule opposite to the external magnetic field, resulting in a counterforce, which eventually leads to a damping.

Further advantageous developments are specified in the subclaims.

So it is advantageous that the magnetic north pole and the magnetic south pole of the magnet lies on a circular path, wherein the circular path is rotationally symmetrical about the axis of rotation. Since turbomachines usually have a high degree of symmetry, it is necessary for the applied magnetic field to be based, so to speak, on the existing symmetry. A magnetic field not oriented along the circular path would lead to undesirable side effects. For example, a desired blade movement could be slowed down. The magnetic field can be generated by a permanent magnet or electrically. The electrically generated magnetic field may advantageously be achieved by an axisymmetric coil having a field orthogonal to the plates.

Advantageously, the circular path runs along an inner peripheral surface of the housing. By this measure, the magnetic field is further homogenized or formed symmetrically. This symmetrical magnetic field leads to a targeted damping of unwanted blade vibrations.

The magnet is in this case advantageously horseshoe-shaped or U-shaped. The magnetic field of a magnet is strongly dependent on its geometric shape. Thus, the magnetic field of a bar magnet is different than the magnetic field of a horseshoe-shaped magnet. The magnetic field of a bar magnet is inhomogeneous compared to the horseshoe-shaped or U-shaped magnet. An arrangement of the horseshoe-shaped or U-shaped magnet on the housing, wherein the legs of the housing are arranged in a circular path, leads to a relatively homogeneous field through which the induction plate is moved.

In a further advantageous embodiment, a plurality of magnets are used, wherein the magnets are arranged in the circumferential direction to a first magnetic circuit row behind the other. An eddy current only occurs when the movement of the induction plate is perpendicular to an external magnetic field. A movement of the induction plate in parallel to an external magnetic field does not lead to eddy currents and thus not to a damping of the blade vibration. A single magnet naturally has a more or less large stray field, which in addition to parallel also has vertical components to the direction of movement of the induction plate. This means that the induction plate moving through this single magnetic field of a single magnet temporarily transits a parallel portion of the magnetic field. Be like in proposed this advantageous development, several magnets arranged one behind the other in the circumferential direction, the individual, caused by the individual magnets, magnetic fields are arranged to a common magnetic field formed in the circumferential direction. This common magnetic field leads to a nearly homogeneous field in the circumferential direction, with the magnetic field lines being aligned almost circularly along the circumference. A movement of the induction plate in the circumferential direction is thus aligned parallel to the magnetic field, whereby no eddy currents are generated. A movement of the induction plate in this direction thus does not lead to disturbing forces, which are caused by the magnetic field. Now only those movements are braked, which have a component which are directed transversely to the magnetic field lines. Such movements are, for example, vibrations in the axial direction. Since this waveform has a component that is perpendicular to the magnetic field, this vibration is decelerated by the external magnetic field.

In a further advantageous development, a number of n magnets are provided in the circumferential direction, where n represents a whole positive number, the magnets being arranged at a regular distance from one another - n, where u represents the circumference of the inner circumferential surface. This results in the number of magnets being adjusted to the circumference. It is advantageous if the magnets are arranged at equidistant intervals on the circumference. This increases the homogeneity or symmetry of the magnetic field. A non-equidistant arrangement of the magnets would lead to inhomogeneities in the magnetic field, which leads to disturbing eddy currents in the induction plates, which occur during the movement of the induction plates in the main direction.

In a further advantageous development, a second series of magnetic circuits comprising a plurality of circumferentially arranged arranged magnets provided, wherein the second magnetic circuit row is arranged in the axial direction in front of the first magnetic circuit row. Advantageously, n magnets are provided in the second magnetic circuit row, wherein the magnets are arranged in u at a regular distance from one another - one behind the other. This is another measure to homogenize the magnetic field in the inner housing virtually along the blade tip. As a result, movements in the main direction are not affected, whereas movements caused by disturbing vibrations are damped.

In a further advantageous development, the magnets of the second magnetic circuit row are arranged offset to one another with respect to the magnets of the first magnetic circuit row. This leads to a homogenization of the magnetic field along the circumferential direction in the housing of the turbomachine. Movement of the induction plate in the main direction is not affected thereby, whereas movements of the induction plate are damped transversely to the main direction.

The invention has, inter alia, the advantage that no rubbing parts are needed to dampen vibrations. In the known methods usually a connection is established between the individual blades, which inevitably leads to a friction in the connecting pieces, which lead to wear.

Another advantage of the invention is that it is applicable to titanium blades. In addition, the device according to the invention is very effective, whereby high attenuation values can be achieved.

The invention will be explained in more detail with reference to an embodiment. In this case, components with the same reference numerals have the same effect. Show it :

FIG. 1 shows a perspective view of a blade tip with an arrangement of a magnet,

2 shows an enlarged view of an induction plate with magnetic field,

FIG. 3 shows a perspective view of a cover strip with an induction plate,

FIG. 4 shows a side view of the cover plate from FIG. 3 with a plurality of induction plates,

FIG. 5 shows a top view of the cover plate with induction plates,

FIG. 6 is a side view of a plurality of blades,

FIG. 7 shows a schematic view of the arrangement of the magnets,

Figure is a schematic representation of a magnet,

FIG. 9 shows the magnetic field of a magnet,

FIG. 10 depiction of a staggered magnetic field by a magnet,

11 shows a representation of the magnetic field by a plurality of magnets that are generated and distributed in a staggered manner and distributed in the circumferential direction.

FIG. 1 shows a blade 1. This blade 1 may be a turbine blade or a compressor blade. The blade 1 is arranged on a rotor, not shown. The arrangement of rotor and blade 1 is a in Figure 1 not shown rotation axis 23 rotatably mounted. In operation, a rotation about this axis of rotation 23 is carried out at a rotational frequency ω. The main movement of the blade 1 runs along the rotor circulation. One of these major movements superimposed and unwanted movement is the vibration of the blade 1. These disturbing vibrations can be damped by means of eddy currents. The arrangement of the induction plates 3 and the magnetic field lead to no force components braking the main movement, since these brake the motor.

The blade 1 has a shroud 2, in which induction plates 3 are arranged. The shroud 2 is arranged on an airfoil 4. The rotor with the blades 1 is rotatably mounted in a turbomachine, which is not shown. Around the rotor and the blades 1, a housing is arranged. The housing has a magnet 5. In FIG. 1, for the sake of clarity, only the magnetic north pole N and the magnetic south pole S are depicted. The blade 1 carries out a disturbing oscillation in the axial direction 6. The induction plate 3 is hereby aligned in a plane which is formed by the rotation axis 23 and a radial direction. This radial direction can be represented in FIG. 1 by a blade axis 7. In operation, this blade axis 7 rotates at the rotational frequency ω about the axis of rotation 23.

FIG. 2 shows a single induction plate 3 and its arrangement relative to the magnetic field B of the magnet 5. For reasons of clarity, only the magnetic north pole N and the magnetic south pole S of the magnet 5 are shown in FIG.

The induction _plate 3 performs a desired movement V _red in the circumferential direction 17 and a disturbing movement V _vlb in the axial direction 6. By the movement of the induction plate 3 in the axial direction 6, a Lorenz force acts in proportion to the speed, since the magnetic field B is perpendicular to the induction plate 3. This Lorenz force leads to a Eddy current, which counteracts the movement of the induction plate 3, whereby the vibration of the induction plate 3 is braked.

However, the main movement does not lead to significant eddy currents, since the induction plate 3 is movable in the direction of movement and thus does not oppose the flow of current. As a result, there is no significant Lorenz force that could slow down the main movement.

FIG. 3 shows a view of the shroud 2 with a single induction plate 3. The shroud 2 has recesses which are designed to couple neighboring shrouds 2, so to speak. The induction plates 3 are in this case formed of an electrically conductive material and incorporated into the shroud 2. The shroud 2 and an upper edge 8 of the induction plate 3 is planar with a surface 9 of the shroud, which can be seen in Figure 4, which is a side view in the direction A of Figure 3. The induction plates 3 are advantageously electrically isolated from each other.

In the figure 4 a plurality of induction plates 3 are shown. An increase in the number of induction plates 3 leads to an increase in the effect of eddy current development.

FIG. 5 shows a plan view of the shroud 2 in the direction of the blade axis 7. The blade axis 7 is thus perpendicular to the plane of the drawing. The arrows 10, 11, 12 represent possible undesired vibration directions 10, 11, 12. All of these vibration directions 10, 11, 12 have a component which points in the axial direction 6. The vibrations occurring in this axial direction 6 are decelerated by eddy current effects.

Optimizations can be made with regard to the orientation of the induction plates 3, such that certain modes are primarily attenuated. Also are combinations of Arrangements on one or different blades 1 in the composite conceivable.

The magnet 5 is, as shown in Figure 8, horseshoe-shaped or U-shaped. The magnet 5 has for this purpose a long edge 13 and two short edges 14 and 15. The short edge 14 is bent by approximately an angle α of 120 ° with respect to the long edge 13. Similarly, the short edge 15 is bent by the angle α of approximately 120 ° with respect to the long edge 13. The angle α may have a value range between 90 ° and 160 ° in alternative embodiments of the magnet 5. The short edge 14 is designed as a magnetic north pole and the short edge 15 as a magnetic south pole. Between the magnetic north pole N and the south magnetic pole S, a magnetic field B is formed, which for physical reasons on the shortest distance between the magnetic north pole and the magnetic south pole S has a homogeneous distribution. In a radial direction 16, the magnetic field B becomes inhomogeneous. The inhomogeneity of the magnetic field B in the radial direction and thus also in a circumferential direction 17 is eliminated by arranging a plurality of magnets 5 in the circumferential direction 17 on the housing. The magnetic field B is thereby homogeneous in the circumferential direction 17.

In the figure 9, the magnetic field B of a magnet 5, not shown, is shown. FIG. 9 shows the magnetic field B in the axial direction 6 in the region of the shroud 2. It can clearly be seen that the field line from the magnetic north pole to the magnetic south pole takes on a circular path-like shape. The cover bands 2 move in the circumferential direction 17 through this magnetic field B. In the black-and-white representation of the magnetic field selected in FIG. 9, white symbolizes a strong magnetic field and black or dark a weak magnetic field.

FIG. 10 shows the magnetic field B of a magnet 5 offset in the circumferential direction 17. The same applies to the representation of the magnetic field B in FIG as in FIG. 9. Here, too, the magnetic field lines are circular.

Finally, FIG. 11 shows a magnetic field B, which can be seen by a superposition of a plurality of magnetic fields of the individual magnets 5. It can be clearly seen that, in particular at a certain height, which is identified at -1 for example, the magnetic field in the circumferential direction 17, which is represented by the X-axis, is unambiguously homogeneous. Accordingly, an induction plate moved in this X direction does not experience a disturbing magnetic deflection force in the form of the Lorenz force because the magnetic fields and the direction of movement are parallel to each other.

The Y-axis in FIGS. 9, 10 and 11 represent a spatial arrangement. For example, the upper edge of Figure 9, 10 and 11 could symbolize the housing. The Y-axis points in the direction of the blade axis 7, which points in the radial direction 16. The magnets 5 are designed as permanent magnets or as electrically controlled magnets.

The magnets 5 are arranged one behind the other in the circumferential direction 17, which leads to a first series of magnetic circuits 18. In this case, a number of n magnets 5 in the circumferential direction 17 are provided, wherein an n represents a positive integer. The magnets 5 are arranged at a regular distance from - behind one another, where u the n

Scope of the inner circumferential surface represents. When viewed in the axial direction 6, behind the first magnetic circuit row 18, a second magnetic circuit row 19 comprising a plurality of magnets 5 is arranged. The second magnetic circuit row 19 comprises a plurality of circumferentially arranged 17 magnets 5 in a row. The second circle of magnetic circuits u 19 has magnets 5 arranged at a regular distance from one another in succession. Furthermore, another third magnetic circuit row 20 are arranged in the axial direction 6 behind the second magnetic circuit row 19. This third series of magnetic circuits 20 also comprises a plurality of magnets 5, which are arranged at a regular distance from one another - one behind the other.

So that the magnetic field is formed as homogeneous as possible, the second magnetic circuit row 19 is arranged offset from the first magnetic circuit row 18. The third magnetic circuit row 20 is in turn offset against the second magnetic circuit row 19. The displacement of the third magnetic circuit row 20 relative to the second magnetic circuit row 19 and the displacement of the second magnetic circuit row 19 relative to the first magnetic circuit row 18 should be equidistant. The offset 21 may be an entire long edge 13. The offset 21 may be half a long edge 13. Likewise, in an alternative embodiment, the offset may be one quarter of the long edge 13. The distance 22 results inevitably from the size of the magnet 5, in particular the long edge 13 and the number n of magnets and the circumference u, since the magnets 5 at equidistant intervals 22 to one another Magnetic circuit row 18, 19, 20 are arranged.

In the figure 6 is a view in the axial direction 6 on the

Shovel 1 and the magnets 5 can be seen. The axial direction 6 is perpendicular to the plane of the drawing. The blades 1 rotate about the axis of rotation 23. The arrangement of the magnets 5 corresponds to the arrangement of Figure 7. The arrangement of the magnets in Figure 6 is shown only symbolically. The magnets 5 are arranged around the entire inner surface of the housing. Of course, the north magnetic poles N and the south magnetic poles S of the individual magnets 5 on a circular path 24, wherein the circular path 24 is rotationally symmetrical about the axis of rotation 23 is directed. The circular path 24 extends along an inner peripheral surface of the housing.

Claims

claims

1. Turbomachine, in particular steam turbine, comprising a about an axis of rotation (23) rotatably arranged and along a blade axis (7) directed blade (1), arranged around the blade (1) housing, arranged in the blade tip induction plate (3) and a magnet (5) arranged in the housing, characterized in that the induction plate (3) is aligned in a plane which is formed by the rotation axis (23) and a radial direction (16).

2. Turbomachine according to claim 1, wherein the magnetic north pole (N) and the magnetic south pole (S) of the magnet (5) lie on a circular path (24), wherein the circular path (24) rotationally symmetrical about the rotation axis (23) is.

3. Turbomachine according to claim 2, wherein the circular path (24) runs along an inner peripheral surface of the housing.

4. Turbomachine according to claim 1, 2 or 3, wherein the induction plate (3) is formed of an electrically conductive material.

5. Turbomachine according to one of the preceding claims, wherein the magnet (5) is formed horseshoe-shaped.

6. Turbomachine according to one of the preceding claims, wherein the magnet (5) is U-shaped.

7. turbomachine according to one of the preceding claims, wherein a plurality of, in the circumferential direction (17) seen, magnets (5] in succession to a first magnetic circuit row (18) are arranged.

8. Turbomachine according to claim 7, wherein a number of n magnets (5) in the circumferential direction (17) are provided, wherein n represents a positive integer, and the magnets u

(5) are arranged at a regular distance from one behind the other, where u represents the circumference of the inner peripheral surface.

9. Turbomachine according to claim 7 or 8, wherein a second magnetic circuit row (19) comprising a plurality of circumferentially arranged (17) magnets (5) are arranged, wherein the second magnetic circuit row (19) in the axial direction of the first magnetic circuit row (18 ) is arranged

10. Turbomachine according to claim 9, wherein n magnets in the second magnetic circuit row (19) are provided and u the magnets (5) at a regular distance from - are arranged one behind the other.

11. Turbomachine according to claim 10, wherein the magnets (5) of the second magnetic circuit row (19) offset from the magnets (5) of the first magnetic circuit row (18) are arranged.