DE102017114153B4 - Electromagnetic vibration exciter to excite vibrations in the blades of a blade ring - Google Patents

Abstract

Electromagnetic vibration exciter (1) for exciting the blades (21) of a rotating blade ring (2) with at least one iron core (10, 13, 14) which is at least partially, preferably continuously, in the circumferential direction (U) over a circumferential angle (ϑ) ring-shaped is designed, wherein the iron core (10, 13, 14) is also designed to be arranged in the circumferential direction (U) perpendicular to the blades (21), so that at least one upper side (13a, 14a) of the iron circle (10, 13, 14) at least in sections, preferably continuously, at a distance (d (ϑ)) in height (Z) from the blades (21), and with at least one field coil (15) which is designed to be electrically supplied and an electromagnetic field to generate, which runs at least in sections through the iron core (10, 13, 14), through the blades (21) and over the distance (d (ϑ)), characterized in that the distance (d (ϑ)) over the Circumferential angle l (ϑ) has at least one change in height (Z).

Description

The present invention relates to an electromagnetic vibration exciter for vibrating the blades of a blade ring according to claim 1.

In the case of units such as gas turbines, steam turbines or aircraft engines, blades are used to effect a power transmission between a rotating or rotatable shaft of the unit and a working medium. These blades of the unit can also be referred to together as a blade ring or as a blading. Depending on the above Use case can e.g. speak of turbine, stator or compressor blades.

During operation, the individual blades of the blading can be excited to vibrate. The excitation can be caused by inhomogeneities in the flow with the working medium, e.g. take place in the air. The resulting vibrations can have a negative effect on the service life of the blades, as long periods of stress can cause cracks, which can ultimately lead to fatigue failure of the individual blades. A short-term overload with very high vibration amplitudes can also result in a forced break in an individual blade. Both types of fracture of at least a single blade can usually lead to failure of the entire unit.

In order to avoid such breaks, the blades of a blading can be designed to be robust enough so that they do the above. Can withstand vibrations permanently and even with short-term heavy loads. For this, it is necessary for the design of the blades of the blading to know as precisely as possible the vibration behavior of the blades when excited by the flow.

To design the vibration behavior of e.g. Turbine blading is carried out in addition to numerical simulations and experimental tests. These mainly serve to validate the developed calculation programs. In other words, the result of the numerical simulation under certain boundary conditions is compared with the measurement results of an experimental test under the same boundary conditions and the numerical simulation program is adapted accordingly so that the simulation results correspond as closely as possible to the measurement results. It can then be assumed that the real conditions of the application can be simulated with sufficient accuracy using the numerical simulation program, so that the numerical simulation program can be used to design a blading that can withstand the real conditions.

For this purpose, the blading is usually put into an oscillation state that is as defined as possible in an experimental test by a force excitation. The comparison with the results of a numerical simulation program can easily be carried out by performing a simulation with the same force excitation.

As an experimental test, an experimental test with a real flow in a centrifugal bunker or on a real unit is unfavorable for this, as such an experimental test can be associated with high costs and with high uncertainties and critical operating conditions often cannot be considered.

Therefore, concepts for the excitation of rotating blades by means of experimental tests generally aim to generate an excitation force profile which only contains certain excitation frequencies EO _{i in} order to generate the above-mentioned excitation state of the blades. The excitation force profile of a blading is in many cases periodic over its circumference. It can thus be described by a Fourier series, which describes the spatial force curve over the circumference of the blade ring. This spatial force curve consists of a sum of harmonic terms with an excitation frequency EO _i and a phase position phi _i .

A widely used variant of the excitation of a rotatable blading consists in installing permanent magnets fixed to the housing below the blades of the blading, which attract each blade when it passes the permanent magnet. One or more permanent magnets can be arranged around the circumference. The rotating blades are then excited during operation by force pulses that are generated by the permanent magnets when a blade of the blades passes a permanent magnet. As many force pulses act on each blade per revolution as there are individual permanent magnets. The fundamental harmonic excitation frequency EO ₁ thus corresponds to the number of magnets if these are arranged equidistantly.

In order to clarify the problem, a blade ring is to be considered as an example, which is correspondingly excited with a force curve of the excitation frequency EO ₁ = 4. 1 shows the normalized course of the idealized excitation force that a single blade of a blading experiences during a revolution over four permanent magnets. The single pulses are as a first approximation Square-wave signals are modeled over the circumferential angle ϑ. 2 shows this signal in the frequency domain.

In addition to the non-interfering constant term EO ₀ = 0, the desired excitation frequency EO ₁ = 4 is clearly included. However, the first harmonic EO ₂ = 8, which forms an interference term, is only slightly less pronounced. All higher harmonics EO ₃ etc. only decrease slowly in their amplitude. This form of excitation thus has the disadvantage that the harmonics EO ₂ etc. excite the blades to vibrate, which can disturb the oscillation shape of the desired excitation frequency EO ₁ = 4 to be examined.

Also in the 2 to recognize that a large part of the energy provided flows into the higher excitation frequencies EO ₂ etc., which is no longer available for excitation of the desired excitation frequency EO ₁ . This means that strong permanent magnets have to be used and the stronger the fewer permanent magnets are used. The use of fewer, strong permanent magnets, however, puts a great deal of stress on the individual blades. The actual excitation force curve does not represent an ideal rectangular function as in 1 However, the fundamental problem remains even with a real curve of the excitation force, even if the amplitudes of the harmonics EO ₂ etc. decrease compared to the fundamental harmonic excitation frequency EO ₁ .

The rotating blade ring can be excited by electromagnets instead of permanent magnets. For non-magnetic blade materials, the excitation in the rotating system can also be done with magnets. The explained fundamental problem of jerky excitation and the undesired excitation frequencies EO ₂ etc. that arise as a result are usually also present in these variants.

In connection with the use of electromagnets, the impulsive excitation can be completely avoided by using a non-rotating blade ring. In this variant, a shovel is always above the same electromagnet. However, the use of a non-rotating test bench has the disadvantage that dynamic effects such as "spin softening" and "stress stiffening" cannot be created or can only be created with great effort. Likewise, damping structures such as sub-platform dampers and shroud coupling cannot be used realistically due to the lack of centripetal acceleration. Therefore, especially for the design of blade rings with damping structures, the test stands with rotating blades described above are to be preferred as test vehicles.

The disadvantage of the test stands with rotating blades or with a rotating blade ring, however, is that the excitation with individual (permanent or electro) magnets can result in undesirable heating of the blades. This is caused by eddy currents, which inevitably arise in the blades when moving due to a spatially changing magnetic field. These eddy currents can lead to the melting of the blade tips. These eddy currents are stronger, the more discontinuous the magnetic field in space. The fact that the blades are exposed to a magnetic field with large gradients by the individual magnets therefore leads to strong eddy currents.

In addition to the excitation concepts described above, there are also excitation concepts based on fluid forces that are generated by air or oil jets. In such test stands, however, the excitation forces that act on the individual blades cannot be set as precisely and reproducibly as with magnetic excitation, which is why this excitation concept is usually to be preferred.

The DE 43 34 799 A1 relates to a device for testing the rotor blades of a turbo machine, in particular a turbine, with a motor-driven, rotatably mounted shaft train on which a wheel disk is non-rotatably arranged, on which the rotor blades are releasably anchored. All blades can be heated. Furthermore, an electromagnetic shaking device is provided with which vibrations can be impressed on the rotor blades via the rotating shaft assembly.

The GB 934 164 A describes an apparatus for testing a fan wheel that may possibly be used in a turbine. The device consists of a series of force-generating devices such as jets of liquid that emit oil, water or steam, or DC magnets, equidistantly spaced around a plate coaxial with the wheel, the groups of devices being excited in various combinations to create blade vibration patterns to simulate generated by internal turbine components when the wheel is in operation. Pairs of magnetic poles are mounted on a base which is removably attached to the plate, with the paddle and magnetic gap adjustable. Vibration detection means such as piezocrystals or strain gauges can be attached to various points on the blades and wheel, with their output being routed via slip rings to measuring devices such as a cathode ray oscilloscope. The wheel can be driven by an electric motor at different speeds rotated, and the entire system can be operated in a vacuum chamber.

The DE 868 674 B describes a method for the excitation of vibratory bodies, in particular of blades in fluid flow machines such. B. steam turbines, axial compressors, etc. for the purpose of determining natural frequencies, resonance-dangerous excitation areas, the associated oscillation forms and testing for fatigue strength. The method is characterized in that the body is excited at several points, both in terms of frequency and phase position, in a freely selectable manner, the body to be examined being at rest apart from the vibrations to be examined.

One object of the present invention is to provide an electromagnetic vibration exciter for vibrating the blades of a blade ring of the type described at the beginning, so that the explained harmonics EO ₂ etc. in the excitation force profile can be eliminated or at least reduced in such a way that the excitation of the blading only with desired frequencies can be done. At least an alternative to known electromagnetic vibration exciters of this type is to be created.

According to the invention, the object is achieved by an electromagnetic vibration exciter for vibrating the blades of a blade ring with the features of claim 1. Advantageous further developments are described in the subclaims.

The present invention thus relates to an electromagnetic vibration exciter for vibrating the blades of a blade ring with at least one iron core which is at least partially, preferably continuously, annular in the circumferential direction over a circumferential angle inkel. In this way, as will be explained in detail below, discontinuities in the magnetic field can be avoided or at least reduced compared to an arrangement of individual magnets in order to avoid or at least reduce the heating of the blades caused by the individual magnets.

The iron core is also designed to be arranged in the circumferential direction perpendicular to the blades, so that at least one upper side of the iron circle at least in sections, preferably continuously, is at a height from the blades. This distance can also be referred to as the air gap, as is common with magnetic circuits. The upper side of the iron circle is understood to mean the side that points towards the distance or towards the air gap.

The electromagnetic vibration exciter also has at least one field coil which is designed to be supplied electrically and to generate an electromagnetic field which runs at least in sections through the iron core, through the blades and over the distance. The field coil can preferably consist of several turns of enamelled copper wire, the ends of which can be led to the outside and connected to a voltage source. The field coil can be operated with direct voltage or with alternating voltage by means of the voltage source. In other words, by means of the electrical field coil, a magnetic circuit can be closed from the iron core via the air gap into the blades and from there via the air gap back into the iron core at another point. The distance or the air gap has at least one change in height over the circumferential angle ϑ.

The present invention is based on the knowledge that the force of attraction of an electromagnet depends not only on the parameters of the field coil, such as diameter, number of turns and coil current, but also on the distance between the structure to be attracted, here the blades, from the iron core. The following applies to the attraction of a simple electromagnet: $$\mathrm{F.}=\frac{{\mathrm{<figure-callout\; id="2"\; label="U\; m"\; filenames="DE102017114153B4\_0008.png"\; state="\{\{state\}\}">U\; </figure-callout>}}_m^{}}{2{\mathrm{<figure-callout\; id="0"\; label="\mu "\; filenames="DE102017114153B4\_0007.png"\; state="\{\{state\}\}">\mu </figure-callout>}}_0\mathrm{<figure-callout\; id="2"\; label="A.\; R.\; m"\; filenames="DE102017114153B4\_0008.png"\; state="\{\{state\}\}">A.\; </figure-callout>}{\mathrm{R.}}_m^{}{}_2^{}}$$

Here Um is the magnetic voltage, µ _{0 is} the magnetic field constant, A is the cross-sectional area of the magnetic circuit, ie here the surface of the iron core, and R _{m is} the magnetic resistance of the magnetic circuit. The magnetic voltage Um can be generated by the field coil, which in turn can contribute significantly to the generation of the magnetic attraction force F.

angegeben werden, d bezeichnet dabei den Abstand der anzuziehenden Struktur, d.h. der Schaufeln, vom Eisenkern.The magnetic resistance of the magnetic circuit R _m , neglecting the magnetic resistance R _{m of} the iron core, as $${\mathrm{R.}}_m=\frac{2d}{{\mu }_0\mathrm{A.}}$$

are given, d denotes the distance between the structure to be attracted, ie the blades, from the iron core.

If you combine these two equations, it becomes clear that the magnetic Attractive force F, which acts between the surface of the iron core and the blades, is inversely proportional to the square of the distance, i.e. the air gap: $$\mathrm{F.}\propto \frac{1}{{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="DE102017114153B4\_0008.png"\; state="\{\{state\}\}">d</figure-callout>}}^2}$$

It has been known so far in the previously described experimental tests or their electromagnetic vibration exciters that they have, on the one hand, individual magnets which are arranged in the circumferential direction and are spaced from one another. An iron core which at least in sections, preferably continuously, is annular in the circumferential direction over a circumferential angle ϑ is not previously known.

Furthermore, the individual magnets have hitherto been arranged at identical distances from the blades so that, viewed in the circumferential direction, there is a constant air gap over the entire extension of the blades or the electromagnetic vibration exciter. In contrast to this, according to the invention, the distance or the air gap has at least one change in height over the circumferential angle ϑ. In this way, the generation of the magnetic attraction force can be influenced as a function of the circumferential angle ϑ in such a way that the explained harmonics EO ₂ etc. in the excitation force profile can be eliminated or at least reduced. As a result, the blades of the blade ring can only be excited with the desired fundamental harmonic excitation frequency EO ₁ , if possible.

In other words, an angle-dependent distance d (ϑ) or air gap d (ϑ) is created according to the invention, which compared to the previously known constant distance h ₀ , which can be an arbitrarily selectable zero distance h ₀ , with the height h (ϑ) des Iron core is related as follows: $$d\left(\vartheta \right)=H_0-H\left(\vartheta \right)$$

angeregt werden, so ist erfindungsgemäß der über den Umfangswinkel ϑ veränderliche Verlauf der Höhe h(ϑ) des Eisenkerns und damit des Abstands d(ϑ) bzw. Luftspalts d(ϑ) gegenüber den Schaufeln zu $$h\left(\vartheta \right)=h_0-\frac{\alpha }{\sqrt{F_0+F_1\text{sin}\left(E{0}_1\vartheta \right)}}$$

auszulegen. Hierbei ist α eine Konstante, welche die übrigen Einflussparameter der allerersten Gleichung, siehe weiter oben, berücksichtigt.Let a sinusoidal magnetic attraction force as an example of a steady harmonic magnetic attraction force $${\mathrm{F.}}_1=\widehat{\mathrm{F.}}sin\left(\mathrm{E.}{0}_1\vartheta \right)$$

are excited, according to the invention the course of the height h (ϑ) of the iron core and thus the distance d (ϑ) or air gap d (ϑ) relative to the blades, which varies over the circumferential angle ϑ $$H\left(\vartheta \right)=H_0-\frac{\alpha }{\sqrt{{\mathrm{F.}}_0+{\mathrm{F.}}_1\text{sin}\left(\mathrm{E.}{0}_1\vartheta \right)}}$$

to interpret. Here is α a constant which takes into account the other influencing parameters of the very first equation, see above.

It is preferably also possible, instead of exciting the blades with only one frequency, to excite several frequencies of interest at the same time. For this purpose, only the course of the height h (ϑ) has to be designed for a force course that is formed as a combination of sine terms of several frequencies. The course of the height h (ϑ) can also be designed for further, arbitrary forms of excitation, which do not only have to be sinusoidal or cosinusoidal.

According to one aspect of the present invention, the distance over the circumferential angle ϑ has a plurality of changes in height. In this way, the freedom of design for varying the magnetic force of attraction over the distance can be further increased.

According to a further aspect of the present invention, the change or changes in height in the circumferential direction is continuous, at least in sections, preferably continuously. In this way, a harmonic excitation can be made possible, which can come as close as possible to the defined test excitations that are to be reproduced experimentally. Furthermore, the eddy currents described above, which can result from discontinuities, can be avoided.

According to a further aspect of the present invention, the distance over the circumferential angle ϑ at least in sections, preferably continuously, has a harmonious profile in height. In this way, a harmonic excitation of the magnetic force of attraction can be ensured, which can be advantageous for the reasons already described above.

According to a further aspect of the present invention, the distance over the circumferential angle ϑ corresponds at least in sections, preferably continuously, in height to a profile of a Fourier-transformable function. In this way, all Fourier transformable functions can be used, which can significantly increase the scope for implementing the knowledge described above.

According to a further aspect of the present invention, the change or changes in height in the circumferential direction is, at least in sections, preferably continuously, abruptly. In this way, alternative suggestions can be created in comparison to continuous curves. For example, suggestions can be reproduced in this way, as they can occur in reality due to the overrun of the guide vanes of an aircraft engine.

According to a further aspect of the present invention, the iron core is U-shaped, so that the iron core forms an interior space that is open at the top, the field coil being arranged within the interior space. This enables a compact electromagnetic vibration exciter, which can be arranged and operated in a corresponding test stand perpendicular to the blades or to the blade tips. The magnetic circuit can get from the field coil through one leg of the U-profile and the distance or air gap above it into the blades and from there back to the field coil via the other distance and the other leg of the U-profile.

According to a further aspect of the present invention, the iron core has a base ring with a radially inner leg and a radially outer leg, the two legs delimiting the interior on both sides, and the iron core has an inner profile ring which is placed on the radially inner leg of the base ring is arranged, and an outer profile ring which is arranged on the radially outer leg of the base ring, wherein the top of the inner profile ring and / or the top of the outer profile ring forms the top of the iron core or form. In this way, the electromagnetic vibration exciter according to the invention can be implemented in that a base ring which is always the same is used as the base element, which is U-shaped and accommodates the field coil in its interior, as already described above. Depending on the application, this basic element can then be adapted to the desired form of excitation by means of appropriately designed profile rings.

Thus, the two profile rings can each have a profile that can generate the desired magnetic attraction force by changing its height and thus the distance over the circumferential angle ϑ. As a result, the basic element can be adapted once or several times by exchanging the profile rings to different excitation profiles and used for this. In other words, a new set of profile rings can be provided for each excitation frequency or combination of excitation frequencies, through the use of which the base ring can be adapted.

According to a further aspect of the present invention, the inner profile ring and / or the outer profile ring is / are arranged interchangeably on the base ring. In this way, as already mentioned above, the base ring can be flexibly adapted as a basic element to different applications, in that only the profile rings have to be exchanged. This can avoid the production and storage of one-piece iron cores with different spacing profiles over the circumferential angle ϑ, as a result of which the costs for using the present invention can be significantly reduced.

According to a further aspect of the present invention, the upper sides of the profile rings have the same or a different course over the circumferential angle ϑ at least in sections, preferably continuously. If, which is preferable, the same course of the distances is selected for the two profile rings, then these courses or the resulting stimuli are in phase with one another. If, however, profile rings with the same but offset in the circumferential direction of the height are used as a further possibility for using the present invention, an excitation with different force amplitudes of the two profile rings can take place. Alternatively, different heights can be combined with each other, which can create further design options.

According to a further aspect of the present invention, the iron core is closed in the circumferential direction except for a lead-through for the electrical connections of the field coil and the profile rings in the circumferential direction are continuously closed in an annular manner. As a result, the electrical connections of the field coil can be passed through in the lower area of the base ring, the magnetic flux of which does not directly merge into the spacing, in order to be able to arrange them within the U-shaped profile of the base ring and still be able to supply them electrically. At the same time, the iron core in the area of the two profile rings, which are directly adjacent to the distance to the blades, can be designed to be continuously closed in the circumferential direction in order to achieve a continuous and uninterrupted magnetic flux between the iron core and the blades. In this way, strong gradients, which result from discontinuities in the magnetic field and can lead to the blades heating up, can be avoided or at least reduced.

According to a further aspect of the present invention, the profile rings are positively locked, preferably each by a plug connection, and / or non-positively, preferably each by at least one pair of centering pins on the Legs of the base ring held. In this way, a simple but nevertheless secure hold can be made possible, which at the same time can be canceled again in a non-destructive manner if the profile rings are to be exchanged, as described above.

According to a further aspect of the present invention, the profile rings are defined in the radial direction and / or in the circumferential direction on the legs of the base ring, preferably each positioned by at least one pair of centering pins. In this way, on the one hand, positioning can take place in the radial direction in order to align the two profile rings with respect to the axis of the vertical direction of the electromagnetic vibration exciter. In other words, a radial centering of the two profile rings can be achieved in this way. On the other hand, the two profile rings can be aligned with one another in the circumferential direction in order to achieve a desired phase offset or to avoid a phase offset.

According to a further aspect of the present invention, the inner profile ring and / or the outer profile ring has a ferromagnetic material with high permeability, preferably consists or consists of a ferromagnetic material with high permeability. As a result, the magnetic field can be guided or guided as effectively as possible.

• 1 ein Diagramm der magnetischen Kraft über den Umfangswinkel bei einer permanentmagnetischen Anregung gemäß des Standes der Technik;
• 2 ein Diagramm der Kraftamplitude über der Frequenz des Diagramms der 1;
• 3 eine perspektivische schematische Darstellung eines Schaufelkranzes;
• 4 eine perspektivische schematische Darstellung eines erfindungsgemäßen elektromagnetischen Schwingungsanregers;
• 5 einen schematischen Querschnitt des erfindungsgemäßen elektromagnetischen Schwingungsanregers;
• 6 eine schematische Draufsicht auf einen Basisring des erfindungsgemäßen elektromagnetischen Schwingungsanregers;
• 7 ein Diagramm der magnetischen Anziehungskraft über den Umfangswinkel für ein erstes Profil des Eisenkerns des erfindungsgemäßen elektromagnetischen Schwingungsanregers;
• 8 ein Diagramm der magnetischen Anziehungskraft über den Umfangswinkel für ein zweites Profil des Eisenkerns des erfindungsgemäßen elektromagnetischen Schwingungsanregers;
• 9 ein Diagramm der magnetischen Anziehungskraft über den Umfangswinkel für ein drittes Profil des Eisenkerns des erfindungsgemäßen elektromagnetischen Schwingungsanregers;
• 10 ein Diagramm der magnetischen Anziehungskraft über den Umfangswinkel für ein viertes Profil des Eisenkerns des erfindungsgemäßen elektromagnetischen Schwingungsanregers;
• 11 ein Diagramm der magnetischen Anziehungskraft über den Umfangswinkel für ein fünftes Profil des Eisenkerns des erfindungsgemäßen elektromagnetischen Schwingungsanregers; und
• 12 ein Diagramm der magnetischen Anziehungskraft über den Umfangswinkel für ein sechstes Profil des Eisenkerns des erfindungsgemäßen elektromagnetischen Schwingungsanregers.

Several exemplary embodiments and further advantages of the invention are explained below in connection with the following figures. It shows:

• 1 a diagram of the magnetic force over the circumferential angle with a permanent magnetic excitation according to the prior art;
• 2 a diagram of the force amplitude over the frequency of the diagram of FIG 1 ;
• 3 a perspective schematic representation of a blade ring;
• 4th a perspective schematic representation of an electromagnetic vibration exciter according to the invention;
• 5 a schematic cross section of the electromagnetic vibration exciter according to the invention;
• 6th a schematic plan view of a base ring of the electromagnetic vibration exciter according to the invention;
• 7th a diagram of the magnetic attraction force over the circumferential angle for a first profile of the iron core of the electromagnetic vibration exciter according to the invention;
• 8th a diagram of the magnetic attractive force over the circumferential angle for a second profile of the iron core of the electromagnetic vibration exciter according to the invention;
• 9 a diagram of the magnetic force of attraction over the circumferential angle for a third profile of the iron core of the electromagnetic vibration exciter according to the invention;
• 10 a diagram of the magnetic attraction force over the circumferential angle for a fourth profile of the iron core of the electromagnetic vibration exciter according to the invention;
• 11 a diagram of the magnetic attraction force over the circumferential angle for a fifth profile of the iron core of the electromagnetic vibration exciter according to the invention; and
• 12 a diagram of the magnetic attractive force over the circumferential angle for a sixth profile of the iron core of the electromagnetic vibration exciter according to the invention.

1 shows a diagram of the magnetic force over the circumferential angle ϑ with a permanent magnetic excitation according to the prior art. 2 shows a diagram of the force amplitude versus frequency of the diagram of FIG 1 . These figures and their diagrams have already been explained at the beginning, so that this is not to be repeated here.

3 shows a perspective schematic representation of a blade ring 2 , which can also be referred to as blading. Such a blade ring 2 can be used with units such as gas turbines, steam turbines or aircraft engines in order to effect a power transmission between a rotating or rotatable shaft of the unit and a working medium. The shovel ring 2 is rotationally symmetrical to the axis of the vertical direction Z which also called height Z can be designated. In the radial direction r which is perpendicular from the axis of the vertical direction Z extends away, has the blade ring 2 a blade body in the middle 20th on, with which the blade ring 2 can be attached to the unit. A plurality of identically constructed and aligned blades extend radially outward 21st which are in contact with the working medium during operation. These are evenly distributed and uniformly in the circumferential direction U, which is oriented perpendicular to the radial direction r spaced from each other. In the circumferential direction U, the circumferential angle ϑ extends around the axis of the vertical direction Z .

4th shows a perspective schematic representation of an electromagnetic vibration exciter according to the invention 1 . 5 shows a schematic cross section of the electromagnetic vibration exciter according to the invention 1 . 6th shows a schematic plan view of a base ring 10 of the electromagnetic vibration exciter according to the invention 1 .

The electromagnetic vibration exciter 1 has a base ring 10 on, which is U-shaped open at the top. The base ring 10 forms a radially inner leg 10a and a radially outer leg 10b from which each protrude vertically upwards and radially between them an interior space 10c of the base ring 10 form. Inside the interior 10c is a field coil 15th arranged from several turns of enamelled copper wire, see 5 , their electrical connections (not shown) via a bushing 12 out and can be connected there to a power supply unit (not shown) as a voltage source.

On the inner thigh 10a of the base ring 10 is an inner profile ring 13th arranged, which the first leg 10a in height Z extended upwards. A corresponding outer profile ring 14th is on the outer thigh 10b arranged. The base ring 10 , the inner profile ring 13th and the outer profile ring 14th together form the iron core 10 , 13th , 14th of the electromagnetic vibration exciter 1 and are therefore formed from a ferromagnetic material with high permeability. The two profile rings 13th , 14th each close with a top 13a , 14a towards the top, which share the top 13a , 14a of the iron core 10 , 13th , 14th in height Z form. The two profile rings 13th , 14th are in the circumferential direction U annularly closed while the base ring 10 by performing 12 is interrupted.

Above the tops 13a , 14a of the iron core 10 , 13th , 14th are the shovels 21st of the blade ring 2 arranged, see 5 so that the tops 13a , 14a of the iron core 10 , 13th , 14th in the circumferential direction U perpendicular to the blades 21st are arranged. Between the tops 13a , 14a of the iron core 10 , 13th , 14th and the shovels 21st or their underside, there is a distance d (ϑ), which can also be referred to as an air gap d (ϑ). The magnetic field lines that go through the field coil 15th generated during operation, thus flow from the base ring 10 through, for example, its inner leg 10a in the inner profile ring 13th , over its top 13a they exit into the air gap d (ϑ). From there the magnetic field lines enter the blades 21st and flow radially outward through the blades 21st through to above the outer profile ring 14th exit into the air gap d (ϑ) formed there. Via this air gap d (ϑ) the magnetic field lines pass over the top 14a of the outer profile ring 14th into this and from there into the base ring 10 back on so that the magnetic field lines close.

According to the invention, on the one hand, the two profile rings 13th , 14th closed in a ring, so that a magnetic force of attraction F in the circumferential direction U continuously on the shovels 21st can work. This can result in gradients and the resulting heating of the blades 21st be avoided.

According to the invention, on the other hand, the two profile rings 13th , 14th with a height h (ϑ) of its upper side which varies over the circumference U or over the circumferential angle ϑ 13a , 14a formed so that the distance d (ϑ) or air gap d (ϑ) varies, see 5 . This is also in the 4th to be recognized by the perspective view, so that there is a minimum 16 of height h (ϑ) and a maximum 17th the height h (ϑ) are marked. By changing the height h (ϑ) over the circumferential angle ϑ, the distance d (ϑ) or the air gap d (ϑ) can be varied accordingly over the circumferential angle ϑ, which influences the magnetic attraction force F (ϑ) over the circumferential angle ϑ results. By generating the magnetic attraction force F (() in this way, a significantly more pronounced oscillation of the fundamental harmonic excitation frequency EO ₁ , ie a stronger amplitude of the fundamental harmonic excitation frequency EO ₁ , can be excited than the interfering harmonics EO ₂ .

Here are the profile rings 13th , 14th designed to be removable, in order to have different profiles of height h (ϑ) on one and the same base ring 10 to be able to realize. The profile rings 13th , 14th can do this from above onto the base ring 10 can be put on and removed again upwards. Each profile ring has both for holding and for alignment in the radial direction r and in the circumferential direction U 13th , 14th on its underside a pair of diametrically opposite recesses in the form of two bores (not shown), in each of which a centering pin can be received (not shown). The base ring 10 has the corresponding four recesses on its top 11 as holes 11 on, in which the centering pins (not shown) can be received.

The 7th to 12 each show a diagram of the magnetic attraction force F (ϑ) over the circumferential angle ϑ for a first to sixth profile of the iron core 10 , 13th , 14th of the electromagnetic vibration exciter according to the invention 1 . By different harmonic progressions, constant magnetic attractive forces F (ϑ) can be exerted, which, for example, can have a sinusoidal progression, cf. 7th . The 8th shows, for example, a Fourier series in the form of the superposition of several harmonic functions with different frequencies. However, discontinuous, interrupted courses are also possible in order to consider such magnetic excitations, cf. 9 and 11 . For example, the 9 discrete characteristics that follow a harmonious function. The 10 shows the course that results from a random surface profile. The 11 shows a single sawtooth curve. Furthermore, the 12 two phase-shifted functions of the profile rings 13th , 14th .

In this way, according to the invention, various magnetic excitations with comparatively large amplitudes of the desired fundamental harmonic excitation frequency EO _{1 can be} applied to the blades in a targeted manner 21st of a blade ring 2 can be exercised in order to compare the measurement results resulting therefrom, e.g. with the results of a simulation program for the design of blades 21st to compare and thereby improve the simulation program.

In other words, the present invention succeeds in producing a precisely defined, continuous excitation force profile F (ϑ) on a blading 2 to impress. This is currently not possible with existing suggestion concepts. The disadvantage of existing excitation concepts of the occurrence of higher harmonic, disruptive excitation frequencies EO ₂ etc., explained at the beginning, can be avoided with the present invention much better than previously known. This makes it possible for the first time to know and control the excitation force profile F (ϑ) as precisely as possible in experimental tests. In particular, it can validate the calculation programs for simulating the dynamic behavior of blading 2 be improved.

The resulting magnetic field is when a corresponding course of the upper sides is selected 13a , 14a the profile rings 13th , 14th about the scope U steady and has no strong gradients. This also causes the very strong heating of the blades mentioned at the beginning 21st avoided by excitation with individual magnets.

In addition to university research, the present invention can also be used in the industrial design process, for example by turbine manufacturers. As a result of the better possibility of validating the calculation programs with the present invention, actually executed blading can be achieved 2 be designed to be safer and more time-efficient in the future. The higher accuracy in the design process can lead to better properties of the blades 21st lead, which ultimately increases the efficiency of the turbine or the engine.

List of reference symbols

α

constant

A.

Cross-sectional area of the magnetic circuit or surface of the iron core 10 , 13th , 14th of the inner profile ring 13th or the outer profile ring 15

d (ϑ)

Distance of the inner profile ring 13th and / or the outer profile ring 15th from the shovel 21st in height Z over the circumferential angle ϑ; Air gap

F (ϑ)

magnetic attraction over distance d (ϑ) over the circumferential angle ϑ

h (ϑ)

variable thickness or height of the iron core 10 , 13th 14th of the inner profile ring 13th and / or the outer profile ring 15th in height Z over the circumferential angle ϑ

h ₀

Zero distance in height Z ; height Z the smallest minimum 16

µ ₀

magnetic field constant

r

radial direction to vertical direction Z

R _m

magnetic resistance of the iron core 10 , 13th , 14th

ϑ

Circumferential angle around vertical direction Z

U

Circumferential direction perpendicular to the radial direction r

U _m

magnetic tension

Z

vertical direction; height

EO _i

i-th excitation frequency

EO ₀

constant term of the excitation frequencies

EO ₁

first or fundamental harmonic excitation frequency

EO ₂

second excitation frequency or first harmonic

EO ₃

third excitation frequency or second harmonic

1

electromagnetic vibration exciter

10

Base ring of the iron core

10a

radially inner leg of the base ring 10

10b

radially outer leg of the base ring 10

10c

Interior of the base ring 10

11

Plug connection receptacle; Recesses or holes for centering pins

12

Bushing for electrical connections of the field coil 16

13

inner profile ring of the iron core

13a

Top of the inner profile ring 13th

14th

outer profile ring of the iron core

14a

Top of the outer profile ring 14th

15th

Field coil

16

Minimum of height h (ϑ) or maximum of distance d (ϑ)

17th

Maximum of height h (ϑ) or minimum of distance d (ϑ)

2

Blade ring; Blading

20th

Blade body

21st

Shovels

Claims (14)

Electromagnetic vibration exciter (1) for exciting vibrations of the blades (21) of a rotating blade ring (2), with at least one iron core (10, 13, 14) which, at least in sections, preferably continuously, in the circumferential direction (U) over a circumferential angle (ϑ) is ring-shaped, the iron core (10, 13, 14) also being designed to be arranged in the circumferential direction (U) perpendicular to the blades (21), so that at least one upper side (13a, 14a) of the iron circle (10, 13 , 14) at least in sections, preferably continuously, at a distance (d (ϑ)) in height (Z) from the blades (21), and with at least one field coil (15) which is designed to be electrically supplied and a to generate an electromagnetic field which runs at least in sections through the iron core (10, 13, 14), through the blades (21) and over the distance (d (ϑ)), characterized in that the distance (d (ϑ) ) about the scope swinkel (ϑ) has at least one change in height (Z). Electromagnetic vibration exciter (1) according to Claim 1 , characterized in that the distance (d (ϑ)) has a plurality of changes in height (Z) over the circumferential angle (ϑ). Electromagnetic vibration exciter (1) according to Claim 1 or 2 , characterized in that the change (s) in height (Z) in the circumferential direction (U) is / are at least in sections, preferably continuously. Electromagnetic vibration exciter (1) according to one of the preceding claims, characterized in that the distance (d (ϑ)) over the circumferential angle (ϑ) at least in sections, preferably continuously, has a harmonic course in height (Z). Electromagnetic vibration exciter (1) according to one of the preceding claims, characterized in that the distance (d (ϑ)) over the circumferential angle (ϑ) at least in sections, preferably continuously, in height (Z) corresponds to a curve of a Fourier transformable function. Electromagnetic vibration exciter (1) according to one of the preceding claims, characterized in that the change (s) in height (Z) in the circumferential direction (U) is / are at least partially, preferably continuously, abruptly. Electromagnetic vibration exciter (1) according to one of the preceding claims, characterized in that the iron core (10, 13, 14) is U-shaped, so that from the iron core (10, 13, 14) an upwardly open interior (10c) is formed, wherein the field coil (15) is arranged within the interior (10c). Electromagnetic vibration exciter (1) according to Claim 7 , characterized in that the iron core (10, 13, 14) has a base ring (10) with a radially inner leg (10a) and a radially outer leg (10b), the two legs (10a, 10b) forming the interior (10c ) limit radially on both sides, and that the iron core (10, 13, 14) has an inner profile ring (13) which is arranged on the radially inner leg (10a) of the base ring (10), and an outer profile ring (14) which is arranged on the radially outer leg (10b) of the base ring (10), the top (13a) of the inner profile ring (13) and / or the top (14a) the outer profile ring (14) the top (13a, 14a) of the Iron core (10, 13, 14) forms / form. Electromagnetic vibration exciter (1) according to Claim 8 , characterized in that the inner profile ring (13) and / or the outer profile ring (14) is / are arranged interchangeably on the base ring (10). Electromagnetic vibration exciter (1) according to Claim 8 or 9 , characterized in that the upper sides (13a, 14a) of the profile rings (13, 14) over the circumferential angle (ϑ) at least in sections, preferably continuously, have the same or a different course. Electromagnetic vibration exciter (1) according to one of the Claims 8 to 10 , characterized in that the iron core (10, 13, 14) is closed in the circumferential direction (U) except for a bushing (12) of the electrical connections of the field coil (15), and that the profile rings (13, 14) in the Circumferential direction (U) are continuously closed in a ring. Electromagnetic vibration exciter (1) according to one of the Claims 8 to 11 , characterized in that the profile rings (13, 14) are held positively, preferably each by a plug connection, and / or non-positively, preferably each by at least one pair of centering pins, on the legs (10a, 10b) of the base ring (10). Electromagnetic vibration exciter (1) according to one of the Claims 8 to 12 , characterized in that the profile rings (13, 14) in the radial direction (r) and / or in the circumferential direction (U) defined on the legs (10a, 10b) of the base ring (10), preferably each by at least one pair of Centering pins, are positioned. Electromagnetic vibration exciter (1) according to one of the Claims 8 to 13th , characterized in that the inner profile ring (13) and / or the outer profile ring (14) has / have a ferromagnetic material with high permeability, preferably consists of a ferromagnetic material with high permeability.

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