EP1624251A1 - apparatus for reducing thermoacoustic oscillations in combustion chambers with adjustable resonance frequency - Google Patents

Abstract

A method for damping thermo acoustic vibrations, especially in the combustion chamber of a gas turbine engine uses at least one Helmholtz resonator (2) of a fixed volume and connected to the combustion chamber via a duct (5) with variable transmission. This enables the control system to vary the resonant frequency to match a range of operating conditions. The duct can comprise a number of sub ducts selected y a movable baffle, a rotating/sliding baffle to vary the effective length of the duct, or any suitable means.

Description

The present invention relates to a device for damping acoustic oscillations in combustion chambers of a gas turbine with a resonator with variable resonance frequency, as well as a gas turbine.

A gas turbine plant comprises in the simplest case a compressor, a combustion chamber and a turbine. In the compressor there is a compression of sucked air, which is then admixed with a fuel. In the combustion chamber, the mixture is combusted, the combustion exhaust gases being supplied to the turbine, from which energy is withdrawn from the combustion exhaust gases and converted into mechanical energy.

Fluctuations in fuel quality and other thermal or acoustic disturbances, however, lead to fluctuations in the amount of heat released and thus the thermodynamic performance of the system. There is an interaction of acoustic and thermal disturbances, which can oscillate. Such thermoacoustic oscillations in the combustors of gas turbines - or turbomachines in general - present a problem in the design and operation of new combustors, combustor parts and burners for such gas turbines.

The exhaust gases produced during the combustion process have a high temperature. The combustion exhaust gases are therefore diluted with cooling air to lower the temperature to a level acceptable for the combustion chamber wall and the turbine components. However, dilution can lead to higher emissions of pollutants. To reduce pollutant emissions from gas turbines, the cooling air mass flow is in modern systems reduced. This also reduces the acoustic damping, so that thermoacoustic vibrations can increase. This can lead to a aufschaukelnden interaction between thermal and acoustic disturbances that bring high loads of the combustion chamber with it and can partially cancel the reduction of pollutant emissions.

To reduce thermoacoustic vibrations, therefore, in the prior art e.g. Helmholtz resonators used for vibration damping of the combustion chambers of gas turbines, which - within a certain frequency band - effectively dampen the amplitude of vibrations. At more deviant frequencies, the effect decreases significantly with increasing frequency difference.

In particular, by the use of different fuels, but also in the partial load range or e.g. when starting the system, the frequencies shift under which increased thermoacoustic vibrations occur. If the damping device remains the same, it then does not work in the most favorable operating point calculated in advance and can no longer optimally damp the occurring thermoacoustic oscillations. This leads in addition to the disadvantages already described also to a higher noise pollution.

From DE 100 04 991 A1, a Helmholtz resonator for speed-dependent damping of the intake or exhaust noise of an internal combustion engine has become known, in which the throat leading to the resonator chamber is flowed through by combustion air. In the neck, two spaced-apart lateral openings are provided whose cross-section is variable. By changing the size of the lateral openings, the resonant frequency can be adjusted in this known resonator. This solution requires a resonator neck of considerable length since the two side openings are spaced apart. A Implementation of this solution on gas turbines is not always possible because the structural requirements of gas turbines differ from those of an internal combustion engine for eg motor vehicles.

The object of the present invention is therefore to provide a device for damping thermoacoustic oscillations in combustion chambers of gas turbines, wherein the resonant frequency for damping thermoacoustic oscillations in gas turbines can be changed with structurally simple means.

According to the invention, this object is achieved by a device for damping thermoacoustic oscillations in combustion chambers of a gas turbine according to claim 1 and by a gas turbine according to claim 9. The dependent claims contain advantageous embodiments of the invention.

A device according to the invention for damping thermoacoustic oscillations, in particular thermoacoustic oscillations in a combustion chamber of a gas turbine, comprises at least one Helmholtz resonator whose resonant frequency is variable. The Helmholtz resonator has a resonator neck, wherein at least one dimension of the resonator neck is variable.

Thus, according to the invention, a dimension of the resonator neck is directly influenced. Because a dimension of the resonator neck can be changed directly, the frequency of the resonator can be adjusted by simple means. In the known state of the art, however, the outer dimension of the resonator neck remains unchanged.

In a development, at least the effective cross-sectional area of the resonator neck can be changed. This can be achieved in particular by the fact that the cross-sectional area of the resonator neck itself is variable. The resonator neck advantageously comprises at least one or more resonator tubes. In particular, at least the cross-sectional area of at least one resonator tube is then variable.

In another development of the invention, at least the effective length of the resonator neck is variable. Preferably, in particular, the length of one or more tubes forming the resonator neck is variable. For this purpose, a tube can be made shorter and / or extendable. This can be done for example via two couplable parts that can be connected in series to extend the resonator neck or shorten.

In particular, a change of both the cross section and the length of the resonator neck can be made to set the resonant frequency of the Helmholtz resonator.

In one embodiment of the invention, the resonator neck comprises at least two resonator tubes. In this case, each of the tubes ends on one side in the resonator chamber and preferably on the other side in the combustion chamber. In this embodiment, the resonator neck is formed by two, three or more resonator tubes. In a simple case, one of the resonator tubes can be closed in order to change the frequency.

beschreiben. Dabei ist c die Schallgeschwindigkeit im Medium, V das Volumen der Resonatorkammer, L die Länge und S die Querschnittsfläche des Resonatorhalses.The resonant frequency of a Helmholtz resonator can be approximated by the equation $${f=c/\left(2\pi \right)(S/\left(\mathit{L\; V}\right))}^{½}$$

describe. Here, c is the speed of sound in the medium, V the volume of the resonator chamber, L the length and S the cross-sectional area of the resonator neck.

By closing a part of the resonator neck, the cross-sectional area S is reduced, whereby the resonance frequency is reduced, and vice versa. By extending the resonator neck, the resonance frequency is also reduced and increased by shortening.

When the cross-sectional area of the resonator neck changes, a partial closing of the resonator neck as a whole or of one or more resonator tubes is also possible. This can e.g. be realized by changing the free flow cross-section of one or more resonator tubes.

If e.g. two or more resonator tubes are provided, then the dimensions of the individual resonator tubes may be the same or different. It is possible that only the dimension of one of a plurality of resonator tubes is changeable.

The adjustment of the resonator can be possible in all embodiments manually with a suitable tool or by hand after opening the turbine housing. Even if this can be done only during the standstill of the machine, the adjustment with a relatively low installation effort is feasible, especially compared to the cost of replacing entire resonators.

In a preferred embodiment, at least one movable control element is provided, which cooperates with the resonator neck. Preferably, the control element cooperates with the opening of at least one resonator tube. Preferably, the control is movable, in particular it is rotatable and / or displaceable.

It is also possible that a controlled adjustment of the dimension (s) of the resonator neck takes place by means of a control device. The adjustment can also be done automatically and also regulated. It is possible, for example, an electric motor, which moves the respective control to one or more Adjust the dimensions of the resonator neck. The use of a hydraulic actuator is possible. By a controlled automatic adjustment of the effort for subsequent adjustment of the resonant frequency is kept particularly low.

Particularly preferred is a controlled adjustment, so that an automatic adjustment of the control is effected in dependence on the determined thermoacoustic oscillations. Then an effective damping can be ensured within the control range.

The inventive manual or automatic adjustability is particularly advantageous in the prototype testing and also during commissioning. A significant advantage of the ease of adjustability results not only from the operation with different fuels, but also under widely varying operating conditions, e.g. due to significant ambient temperature changes.

The control element may have one or more control openings, e.g. have different dimensions. In particular, control openings with different diameters and / or different lengths are possible. Preferably, control openings of different dimensions cooperate with at least one opening of the resonator neck.

It is possible that the control element has a substantially conical shape. Preferred is e.g. an embodiment as a pin with a substantially conical end 15, which forms a closure cone. By introducing such a control element into a resonator tube, the free cross-sectional area of the resonator tube can be effectively changed.

Preferred developments are those in which the position of the control element can be controlled and / or regulated from the outside.

Furthermore, the object of the invention is also achieved by a gas turbine with a device according to the invention for damping thermoacoustic oscillations.

Although the invention is described herein in its entirety with respect to gas turbines, the use is not limited to gas turbines. It is also possible to use the invention in other turbines, turbomachines, combustion chambers and boiler systems.

• Fig. 1 ein erstes Ausführungsbeispiel für die erfindungsgemäße Vorrichtung in einer stark schematischen Darstellung;
• Fig. 2 ein zweites Ausführungsbeispiel für die erfindungsgemäße Vorrichtung in einer stark schematischen Darstellung;
• Fig. 3 ein drittes Ausführungsbeispiel für die erfindungsgemäße Vorrichtung in einer stark schematischen Darstellung;
• Fig. 4 ein viertes Ausführungsbeispiel für die erfindungsgemäße Vorrichtung in einer stark schematischen Darstellung; und
• Fig. 5 ein fünftes Ausführungsbeispiel für die erfindungsgemäße Vorrichtung in einer stark schematischen Darstellung.

Further features, characteristics and advantages of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings.

• 1 shows a first embodiment of the device according to the invention in a highly schematic representation.
• 2 shows a second embodiment of the device according to the invention in a highly schematic representation.
• 3 shows a third exemplary embodiment of the device according to the invention in a highly schematic representation;
• 4 shows a fourth exemplary embodiment of the device according to the invention in a highly schematic representation; and
• Fig. 5 shows a fifth embodiment of the device according to the invention in a highly schematic representation.

In the exemplary embodiments described below with reference to the figures, identical components are given the same reference numerals for the sake of clarity.

FIG. 1 shows a first exemplary embodiment of the device according to the invention for damping acoustic vibrations in a combustion chamber of a gas turbine.

The device 1 comprises a Helmholtz resonator 2, which has a resonator chamber 3 and a resonator neck 4, via which the Helmholtz resonator 2 is connected to a combustion chamber of a gas turbine.

In the illustrated embodiment, the Helmholtz resonator 2 is designed substantially cylindrically symmetrical with respect to a longitudinal or central axis. However, embodiments are also possible which have no symmetry.

The resonator neck 4 is formed in total by three independent resonator tubes 5, 6 and 7, which, viewed from the combustion chamber, protrude into the resonator chamber 3. The three resonator tubes have a tube length 5a, 6a and 7a, respectively. In the exemplary embodiment, the tube length is the same in each case.

The cross-sectional area of the resonator neck 4 is influenced by the individual open cross-sectional areas 5b, 6b, 7b of the three independent resonator tubes 5, 6 and 7. A partial closing of one or more of the resonator tubes 5, 6, 7 changes the effective cross-sectional area of the resonator neck 4, which is composed of the cross-sectional areas 5b, 6b and 7b. It is thus possible to adjust the resonator frequency.

A control disk 8 is provided, which is rotatably mounted about a rotation axis 12. In the exemplary embodiment, the axis of rotation 12 and the central center axis coincide. The cross-sectional areas 5b, 6b, 7b of the three resonator tubes 5, 6 and 7 are different in this embodiment. The largest cross-sectional area 5b has the resonator tube 5, the smallest cross-sectional area 7b the resonator tube. 7

On the control disk 8 openings 9, 10 and 11 are provided, which are axially aligned with the resonator tubes 5, 6 and 7 are aligned by the control disk 8 is rotated accordingly. With different cross-sectional areas of the resonator tubes 5, 6 and 7, a resonator tube or a plurality of resonator tubes 5, 6, 7 can then be opened by targeted rotation of the control disc 8, while the remaining resonator tubes remain closed in order to adapt the resonant frequency to the given conditions. Here in the exemplary embodiment, the control disk is arranged in the resonator chamber 3 in total.

In order to increase the adjustable range, it may also be possible via suitable structural designs to simultaneously open two or even all three resonator tubes. A partial firing of individual resonator tubes is possible by a corresponding angular position.

The adjustment can be made during breaks by means of a suitable tool by hand or during operation. In preferred embodiments, a controller (not shown) is provided, by means of which an adjustment can be controlled. An automatic adjustment or regulation is possible. This can be done online during the operation. With a fully automatic control can take place a continuous or at intervals, adjustment to the strongest vibration frequency.

The cross-sectional areas 5b, 6b and 7b of the resonator tubes 5, 6 and 7 may also be the same in other embodiments. By partially or completely opening a second or third resonator tube, the cross section of the resonator neck 4 as a whole is varied, and a suitable attenuation frequency can be set.

By (partially) opening a larger resonator tube, a dimension of the resonator neck 4 is changed. The cross-sectional area of the resonator neck 4 is increased, which increases the resonance frequency of the Helmholtz resonator 2. Therefore, by changing a dimension of the resonator neck, an effective change in the resonant frequency of the resonator is possible, so that the resonator 2 can be adapted to the vibrations to be damped. As a result, changed conditions, such as an altered fuel composition, reacts and an adjustment of the resonant frequency are performed.

In the description of the exemplary embodiments illustrated in FIGS. 2, 3, 4 and 5, essentially only the differences from the exemplary embodiment according to FIG. 1 will be discussed.

In the exemplary embodiment according to FIG. 2, the device 1 comprises a Helmholtz resonator 2 with a resonator chamber 3 and a resonator neck 4, which in turn is formed by three resonator tubes 5, 6 and 7, which also here have different cross sections.

The control is designed here as a control slide 13. Instead of a spool 13 but can also be used a rotatable camshaft. By means of the control slide 13, the openings 9, 10 and 11, a targeted opening and closing of the three resonator tubes 5, 6 and 7 is possible. By a targeted influencing of the cross section of the three resonator tubes, a dimension of the resonator neck 4 can be effectively changed, whereby the resonance frequency of the resonator 2 is changed.

The spool 13 may be performed through a side opening in the Helmholtz resonator 2 and displaced along the control direction 14. It is also possible, the control slide 13 is completely received by the Helmholtz resonator 2 in all control positions.

The embodiment shown in Figure 3 shows a third embodiment, in which also a device 1 with a Helmholtz resonator 2, which has a resonator 3 and a resonator neck 4, is provided. The resonator neck 4 in this exemplary embodiment comprises only a single resonator tube 5.

In this embodiment, a targeted change of the effective flow cross-section of the resonator tube 5 is possible by means of a control cone 15. For this purpose, the control cone 15 is moved along the control direction 16. As a result, the resonator tube 5 partially - or completely if necessary - are closed. In a partial closure, an annular gap remains open. The effective flow cross section depends on how deep the control cone 15 is lowered into the resonator tube 5. Changing the effective flow area affects the resonant frequency.

In other embodiments, a plurality of resonator tubes 5 may also be provided, e.g. two, three, four or more, each having an adjustable by means of a control cone effective flow cross-section.

In the exemplary embodiments shown in FIGS. 4 and 5, a respective Helmholtz resonator 2 with a resonator chamber 3 and a resonator neck 4 formed by a respective resonator tube 5 is shown. In these exemplary embodiments, the length of the resonator neck 4 is influenced, as a result of which an effective frequency change of the resonator 2 is likewise possible.

To change a length of the resonator neck 4, a control is provided in each case. In the example of Figure 4 the control element is a control disk 17 rotatable about an axis of rotation 18 and in the example according to FIG. 5 a control valve 23 is provided as a control element, which is displaceable along a control direction 24. The thickness of the control disk 17 varies over its circumference, while the thickness of the control slide varies over its length. The change in thickness can take place continuously or in stages.

In the control disk 17 and the spool 23 through holes 9, 10 and 11 are present, for example. Can be realized as through holes. At the location of a first bore 9, the respective control element 17 or 23 has a thickness 20, at the location of a second bore 10 a thickness 21 and at the location of a third bore 11 a thickness 22, wherein the thickness 22 is greater than the thickness 21 and the thickness 20 has the smallest dimension.

The respective bores can be brought into a position aligned with the resonator tube 5. In FIGS. 4 and 5, in each case the first bore 9 is shown in alignment with the resonator tube 5. The resonator neck 4 in this case has a total length 25, which results from the length 19 of the resonator tube 5 and the thickness 20 of the control disk 17 and the spool 23, that is, the length of the respective aligned hole 9. When aligning the bore 10, the total length 25 results as the sum of the length 19 and the thickness 21, and when adjusted to the opening or bore 11 results in the total length 25 as the sum of the length 19 and the thickness 22nd

Unlike in Figures 4 and 5, also control discs or spools may be present with more than three openings, in which each opening has a different length.

Claims (9)

Device (1) for attenuating thermoacoustic oscillations, in particular for attenuating thermoacoustic oscillations in a combustion chamber of a gas turbine, with at least one Helmholtz resonator (2) whose resonant frequency is variable, the Helmholtz resonator (2) having a resonator neck (4) characterized in that at least one dimension (25) of the resonator neck (4) is variable. Device (1) according to claim 1, characterized in that at least the effective cross-sectional area of the resonator neck (4) is variable. Device (1) according to claim 1 or 2, characterized in that at least the length (25) of the resonator neck (4) is variable. Device (1) according to at least one of the preceding claims, characterized in that the resonator neck (4) has at least one resonator tube (5, 6, 7). Device (1) according to claim 4, characterized in that at least one movable control element (8) is present, which cooperates with the resonator tube for changing the dimension of the resonator neck. Device (1) according to claim 5, characterized in that the control element (8) is movable, in particular rotatable and / or displaceable. Device (1) according to claim 5 or 6, characterized in that the control element (8) has control openings (9, 10, 11) of different dimensions (20, 21, 22), in particular of different diameters and / or different lengths. Device (1) according to claim 4 or 5, characterized in that the control element (8) has a substantially conical shape (15). Gas turbine with at least one combustion chamber and at least one device connected to the combustion chamber for damping thermoacoustic vibrations according to one of claims 1-8.

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