DAMPER FOR A COMBUSTOR ASSEMBLY OF A GAS TURBINE ASSEMBLY, COMBUSTOR ASSEMBLY COMPRISING SAID DAMPER AND METHOD FOR MANUFACTURING A DAMPER FOR A COMBUSTOR ASSEMBLY

Abstract

 A damper for a combustor assembly (3) of a gas turbine assembly (1) is provided with:
at least two damping volumes (32, 35) defined by respective damping bodies (31, 34); the damping volumes (32, 35) being interconnected in fluidic communication;
at least one perforated connecting plate (36) connecting the two damping volumes (32, 35);
at least one perforated end plate (38) configured to connect at least one of the two damping volumes (32, 35) with a combustion chamber (16; 14) of the combustor assembly (3);
the perforated connecting plate (36) and the perforated end plate (38) being provided with a plurality of openings (42);
the openings (42) being dimensioned so as to operate in a low Strouhal regime according to the following formula

wherein:
• ω is the angular frequency correlated to the frequency to damp according to the following relation ω=2πf;
• R_H is the equivalent radius of one of the openings (42);
• U_b is the velocity of the flow through one of the openings (42).

Description

TECHNICAL FIELD

[0001] The present invention relates to a damper for a combustor assembly of a gas turbine assembly and to a combustor assembly of a gas turbine comprising said damper. In particular, the present invention relates to a damper for a sequential combustor assembly.

[0002] The present invention relates also to a method for manufacturing a damper for a combustor assembly.

BACKGROUND

[0003] As known, a gas turbine power plant comprises a compressor, a combustor assembly and a turbine.

[0004] In particular, the compressor is supplied with air and comprises a plurality of blades compressing the supplied air. The compressed air leaving the compressor flows into a plenum, i.e. a closed volume delimited by an outer casing, and from there into the combustor assembly. In the combustor assembly the compressed air and at least one fuel are combusted.

[0005] The resulting hot gas leaves the combustor assembly and is expanded in the turbine performing work.

[0006] In order to achieve a high efficiency, high temperatures are required during combustion. However, due to these high temperatures, high NOx emissions are generated.

[0007] In order to reduce these emissions and to increase operational flexibility, sequential combustor assemblies can be used.

[0008] In general, a sequential combustor assembly comprises two combustors in series: a first-stage combustor and a second-stage combustor, which is arranged downstream the first-stage combustor along the gas flow.

[0009] Of course, a combustor assembly with a single combustion stage can be also used.

[0010] During operation, inside the combustor assembly pressure oscillations may occur causing mechanical damages and limiting the operating regime. Mostly combustor assemblies, in fact, have to operate in lean mode for compliance to pollution emissions. The burner flame during this mode of operation is extremely sensitive to flow perturbations and can easily couple with dynamics of the combustor to lead to thermo-acoustic instabilities. For this reason, usually, combustor assemblies are provided with damping devices in order to damp these pressure oscillations.

[0011] Known dampers comprise one damper volume that acts as a resonator volume and a neck fluidly connecting the damper volume to at least one inner chamber of the combustor assembly.

[0012] However, these dampers are not sufficiently flexible and are not able to damp broad frequency ranges.

SUMMARY

[0013] The object of the present invention is therefore to provide a damper for a combustor assembly, which is flexible, simple and economical, both from the functional and the constructive point of view.

[0014] According to the present invention, there is provided a damper for a combustor assembly of a gas turbine assembly comprising:

at least two damping volumes defined by respective damping bodies; the damping volumes being interconnected in fluidic communication;

at least one perforated connecting plate connecting the two damping volumes;

at least one perforated end plate configured to connect at least one of the two damping volumes with a combustion chamber of the combustor assembly;

the perforated connecting plate and the perforated end plate being provided with a plurality of openings; the openings being dimensioned so as to operate in a low Strouhal regime according to the following formula

wherein:

is the angular frequency correlated to the frequency to damp according to the following relation

R_H is the equivalent radius of one of the openings (42);

U_b is the velocity of the flow through one of the openings (42) .

[0015] The structure of the damper according to the invention is flexible and can be also compact.

[0016] The flexibility is given by the possibility of damping different frequencies, as the damping volumes can be sized opportunely depending on the needs.

[0017] In other words, thanks to the damper according to the present invention a broadband damping of combustion dynamics is obtained.

[0018] According to a variant of the present invention, at least one of the damping bodies comprises at least one inlet configured to be in fluidic communication with at least one source of air. In this way, air contributes to cool damper bodies and avoid hot gas ingestion, which would de-tune damper bodies and could cause damages to damper bodies.

[0019] According to a variant of the present invention, the at least two damping volumes are interconnected in parallel.

[0020] According to a variant of the present invention, the at least two damping volumes are interconnected in series.

[0021] According to a variant of the present invention, at least one of the damping volumes is a quarter wave tube.
For example, at least one of the damping volumes is dimensioned according to the following formula:

wherein

f is the frequency to damp

L is the axial length of the respective cavity defined by the damper body

c is the speed of sound

δ is an end correction which allows to account for the inertia of the acoustic flow at the end of the volume just outside of the openings.

[0022] According to a variant of the present invention, at least one of the damping volumes is a Helmholtz resonator.
For example at least one of the damping volumes is dimensioned according to the following formula

wherein

f is the frequency to damp

c is the speed of sound

A is the equivalent surface area of the all the openings

V is the damping volume

1 is the thickness of the perforated plate coupled to the damping volume

δ' is an end correction which allows to account for the inertia of the acoustic flow outside and inside the openings.

[0023] According to a variant of the present invention, the damper comprises a first damping body extending along an extension axis and having a first axial length and a second damping body extending along an extension axis and having a second axial length; the ratio between the greater axial length between the first axial length and the second axial length and the smaller between the first axial length and the second axial lengths being substantially integer, preferably even.

[0024] It is also another object of the present invention to provide a reliable combustor assembly for a gas turbine plant where acoustic oscillations are sensibly reduced.

[0025] According to this object the present invention relates to a combustor assembly according to claim 9.

[0026] It is also another object of the present invention to provide a simple and economic method for manufacturing a damper for a combustor assembly for a gas turbine. According to this object the present invention relates to a method for manufacturing a damper according to claim 11.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will now be described with reference to the accompanying drawings, which illustrate some non-limitative embodiment, in which:

• Figure 1 is a schematic representation of a gas turbine assembly;
• Figure 2 is a lateral schematic view with parts in section and parts removed for clarity, of a detail of a combustor assembly of the gas turbine assembly of figure 1;
• Figure 3 is a front schematic view, with parts in section and parts removed for clarity, of a detail of a combustor assembly according to the present invention;
• Figure 4 is a lateral schematic view, with parts in section and parts removed for clarity, of a damper for a combustor assembly according to the present invention;
• Figure 5 represents diagrams relating to the absorption properties of a damper according to the present invention in use in a combustor assembly.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0028] In figure 1 reference numeral 1 indicates a gas turbine assembly. The gas turbine assembly 1 comprises a compressor 2, a sequential combustor assembly 3 and a turbine 5. The compressor 2 and the turbine 5 extend along a main axis A.

[0029] In use, an airflow compressed in the compressor 2 is mixed with fuel and is burned in the sequential combustor assembly 3. The burned mixture is then expanded in the turbine 5 and converted in mechanical power by a shaft 6, which is connected to an alternator (not shown).

[0030] The sequential combustor assembly 3 comprises a first-stage combustor 8 and a second-stage combustor 9 sequentially arranged along the gas flow direction G. In other words, the second stage combustor 9 is arranged downstream the first stage combustor 8 along the gas flow direction G.

[0031] Preferably, between the first stage combustor 8 and the second stage combustor 9 a mixer 11 is arranged.

[0032] The first stage combustor 8 defines a first combustion chamber 14, the second stage combustor 9 defines a second combustion chamber 16, while the mixer 11 defines a mixing chamber 17.

[0033] The first combustion chamber 14, the second combustion chamber 16 and the mixing chamber 17 are in fluidic communication and are defined by a liner 18 (see figure 2 wherein the liner 18 is partially visible), which extends along a longitudinal axis B.

[0034] With reference to figure 2, in the second combustion chamber 16 of the second stage combustor 9 a supply assembly 20 is arranged.

[0035] The supply assembly 20 comprises a central body 21 provided with a plurality of fingers 22 (schematically represented also in figure 3).

[0036] The fingers 22 are preferably defined by streamlined bodies, each of which is provided with a plurality of nozzles 24 and is supplied with air and at least one fuel.

[0037] Referring to figures 2 and 3, the second stage combustor 9 comprises at least one damper 30.

[0038] In the non-limiting example here disclosed and illustrated the second stage combustor 9 comprises a plurality of dampers 30 (in the example here illustrated the dampers are sixteen). Using more than one damper 30 gives the possibility to increase the damping amplitude.

[0039] Preferably, the dampers 30 are arranged about the central body 21 of the supply assembly 20. More preferably, the dampers 30 are evenly distributed about the central body 21.

[0040] Referring to figure 2 and figure 3 the dampers 30 are preferably coupled to a panel 26 surrounding the central body 21 of the supply assembly 20. Preferably the panel 26 is also provided with a plurality of cooling holes 25 evenly distributed along the panel 26.

[0041] It is understood that damper 30 can be arranged also in another portion of the combustor assembly 3.

[0042] For example, damper 30 can be coupled to the liner 18, preferably to the portion of the liner 18 facing the second combustion chamber 16. Damper 30 can also be arranged so as to face into the first combustion chamber 14.

[0043] Referring to figure 4, the damper 30 extends along an extension axis C and comprises a first damper body 31 having a first cavity defining a first damping volume 32, a second damper body 34 having a second cavity defining a second damping volume 35, a perforated connecting plate 36 connecting the first damping volume 32 and the second damping volume 35 and at least one perforated end plate 38. The perforated end plate 38 is configured to connect the first damping volume 32 with the outside of the damper 30 which is in fluidic communication with the first combustion chambers 14 and/or the second combustion chamber 16 of the combustor assembly 3.

[0044] The first damping volume 32 and the second damping volume 35 are interconnected in fluidic communication by the perforated connecting plate 36.

[0045] In the non-limiting example here disclosed and illustrated the first damping volume 32 and the second damping volume 35 are interconnected in series.

[0046] According to a variant not illustrated, the first damping volume 32 and the second damping volume 35 are interconnected in parallel.

[0047] In the non-limiting example here disclosed and illustrated the second damper body 34 is provided with at least one inlet 40 configured to be in fluidic communication with at least one source of air. In particular, the inlet 40 is connected to a plenum (not visible in the attached figures) receiving air from the compressor 2. In the non-limiting example here disclosed and illustrated the second damper body 34 is provided with two or more inlets 40 arranged at the bottom of the second cavity.

[0048] In use, the air enters through the inlets 40, flows into the second damping volume 35, passes through the perforated connecting plate 36, flows into the first damping volume 32 and exits through the perforated end plate 38 into the first combustion chambers 14 and/or the second combustion chamber 16 of the combustor assembly 3.

[0049] The air contributes to cool the first damper body 31 and the second damper body 34 and avoid hot gas ingestion, which would de-tune the first damper body 31 and the second damper body 34 and could cause damages to the first damping body 31 and the second damper body 34. Preferably, the inlets 40 are arranged on opposite sides of the second damper body 34.

[0050] The perforated connecting plate 36 and the perforated end plate 38 have a similar structure. Both the perforated connecting plate 36 and the perforated end plate 38 are provided with a plurality of openings 42.

[0051] In the example here disclosed and illustrated the openings 42 have a circular shape. However according to variants not illustrated the shape of the openings can be different, for example polygonal or oval or oblong, etc.

[0052] The perforated connecting plate 36 and the perforated end plate 38 are both designed so as to operate in a low Strouhal regime. The Strouhal regime is defined by the value of the Strouhal number.

[0053] Here and in the following with the expression "low Strouhal regime" is intended a Strouhal number lower than 0,5.

[0054] In order to operate in a low Strouhal regime, the openings 42 of the perforated connecting plate 36 and of the perforated end plate 38 are dimensioned according to the following condition:

wherein

is the angular frequency correlated to the frequency to damp according to the following relation

RH is the equivalent radius of one of the opening which is calculated as R_H= A/P where A is the cross-sectional area of the flow and P is the wetted perimeter of the cross-section (in the example here disclosed and illustrated the hydraulic radius is the radius of the circular opening 42);

Ub is the bias flow velocity of the flow through one of the openings.

[0055] In use, the perforated end plate 38 faces directly the first combustion chambers 14 and/or the second combustion chamber 16 and therefore is designed to resist to high temperatures. Thickness and material of the perforated end plate 38 are therefore chosen to guarantee high reliability.

[0056] The perforated connecting plate 36 is subjected to high temperatures too although in a lesser way than the perforated end plate 38.

[0057] In the non-limiting example here disclosed and illustrated, the perforated connecting plate 36 and the perforated end plate 38 are made of the same material. For example the perforated connecting plate 36 and the perforated end plate 38 are made with a high temperature resistant material, for example a superalloy as Hastelloy X.

[0058] In the non-limiting example here disclosed and illustrated, the perforated connecting plate 36 and the perforated end plate 38 have a different thickness. The perforated end plate 38 is preferably thicker than perforated connecting plate 36 as facing the combustion chamber.

[0059] With reference to figure 3, the openings 42 are substantially arranged according to a cross mesh pattern. Alternatively, the openings 42 can be substantially arranged according to a square mesh pattern or according to a rectangular mesh pattern or other patterns.

[0060] In the non-limiting example here disclosed and illustrated, the mesh pattern of the perforated connecting plate 36 is identical to the mesh pattern of the perforated end plate 38. In this way the openings 42 of the perforated connecting plate 36 are aligned with the openings 42 of the perforated end plate 38.

[0061] However, the mesh pattern of the perforated connecting plate 36 and of the perforated end plate 38 can be different from each other and the openings 42 of the perforated connecting plate 36 can be misaligned with the openings 42 of the perforated end plate 38. Such a solution is useful when the distance between the perforated connecting plate 36 and the perforated end plate 38 is lower than a threshold. In other words, the openings 42 of the perforated connecting plate 36 are misaligned with openings 42 of the perforated end plate 38 when the length L1 of the first cavity is lower than a threshold.

[0062] With reference to figure 4, the openings 42 of the perforated connecting plate 36 and of the perforated end plate 38 are arranged so as to extend perpendicularly to the plane a₁ a₂ along which the respective perforated connecting plate 36 or the perforated end plate 38 extends.

[0063] The first cavity of the first damper body 31 and the second cavity of the second damper body 34 are dimensioned so as to give to the damper 30 a desired damping effect.

[0064] In the non-limiting example here disclosed and illustrated, the first cavity of the first damper body 31 and the second cavity of the second damper body 34 are cylindrical. According to variants not shown, the first cavity of the first damper body 31 and the second cavity of the second damper body 34 can be also prismatic or can have a shape adjusted on the basis of the space available in the combustor assembly 3.

[0065] The first cavity of the first damper body 31 and of the second cavity of the second damper body 34 are designed so as to be a quarter wave tube.

[0066] The dimensioning of the first cavity of the first damper body 31 and of the second cavity of the second damper body 34 is made, for example, according to the following formula (quarter wave tube formula):

wherein

f is the frequency to damp

L is the axial length of the respective cavity defined by the damper body (L1 for the first cavity, L2 for the second cavity)

c is the speed of sound

δ is an end correction which allows to account for the inertia of the acoustic flow at the end of the volume just outside of the openings.

[0067] According to a variant not shown the dimensioning can be made according to a derivation of the above quarter wave tube formula.

[0068] Alternatively, the first cavity of the first damper body 31 and of the second cavity of the second damper body 34 are designed so as to be a Helmholtz resonator.

[0069] The dimensioning of the first cavity of the first damper body 31 and of the second cavity of the second damper body 34 is made, for example, according to the following formula (Helmholtz formula):

wherein

f is the frequency to damp

c is the speed of sound

A is the equivalent surface area of the all the openings of the respective perforated plate (i.e. the perforated connecting plate 36 for the second cavity dimensioning and the perforated end plate 38 for the first cavity dimensioning)

V is the volume of the cavity

1 is the thickness of the respective perforated plate coupled to the damping volume (i.e. the thickness l_c of the perforated connecting plate 36 for the second cavity dimensioning and the thickness l_e of the perforated end plate 38 for the first cavity dimensioning)

δ' is an end correction which allows to account for the inertia of the acoustic flow outside and inside the openings.

[0070] According to a variant not shown the dimensioning can be made according to a derivation of the above Helmholtz formula.

[0071] The dimensioning is preferably made with the quarter wave formula as it is independent from the features of the respective perforated plates.

[0072] However, if the thickness of the respective perforated plate is greater than a threshold value and/or if the length of the cavity obtained according to the quarter wave formula is not acceptable due to geometrical constraints in the combustor assembly 3, the dimensioning is made using the Helmholtz formula.

[0073] Preferably, the first cavity of the first damper body 31 is dimensioned to damp a first frequency while the second cavity of the second damper body 34 is dimensioned to damp a second frequency different from the first frequency.

[0074] The damper 30 so dimensioned and designed is able to dampen a broad band of frequencies. The damper 30, in fact, is able to damp at least three frequencies: the one depending from the dimensions of the first cavity, the one depending from the dimensions of the second cavity and the one depending from the dimensions of the first cavity plus the second cavity.

[0075] In particular, the relation between the axial length L1 of the first cavity of the first damper body 31 and the axial length L2 of the second cavity of the second damper body 34 influences the response of the damper 30.

[0076] The reflection coefficient, in fact, is mainly driven by the eigenmode of the two cavities together (i.e. L2+L1), while the response is modulated by the dimensions of each cavity L1 and L2.

[0077] The lengths L1 and L2 of the first and the second cavity are therefore sized according to the need. Said lengths can be essentially sized according to three possibilities: L2=L1, L2>L1 and L2<L1.

[0078] Equal lengths L1 and L2 (L2 = L1) can be chosen if a homogeneous damping over the frequency band is required.

[0079] When L2 is different from L1, if the ratio between the lengths (L2/L1 if L2>L1 or L1/L2 if L2<L1) is substantially integer a concordance of modes can be achieved.

[0080] Concordance of modes leads to a higher damping at the frequency of agreement.

[0081] As the damper 30 is broadband, even if the ratio is not exactly integer, the response of the damper 30 does not vary excessively. For example, if L2/L1 = 3.1 instead of 3 the response of the damper 30 is similar. For this reason, the ratio is defined as "substantially integer".

[0082] In particular, if the ratio L2/L1 is an even integer (i.e. L2>L1), the concordance of modes is between the eigenmode of the two cavities together (i.e. L2+L1) and the eigenmode of the first cavity (L1) as shown by the continuous line in Figure 5. Such a solution leads to a high damping in the center of modulation.

[0083] If the ratio L1/L2 is an even integer (i.e. L2<L1), the concordance of modes is between the eigenmode of the two cavities together (i.e. L2+L1) and the eigenmode of the second cavity (L2). Such a solution leads to a damping, which is higher on the edge of the bounces sequence as shown by the dotted line in Figure 5.

[0084] In figure 5 graphs about the reflection coefficient modulus and phase of a damper 30 having the structure above described in use in the combustor assembly 3 are represented.

[0085] The trends of figure 5 regarding the reflection coefficient modulus and phase evidence that the damper 30 is able to damp a broad band of frequencies. The trends shown in figure 5 are relating to values of the lengths L1 and L2, which are inverted. In other words, dotted line represents a solution wherein L2>L1, while continuous line represents a solution wherein the same lengths are inverted (i.e. L2<L1).

[0086] If the ratio L2/L1 or the ratio L1/L2 is an odd integer, the concordance of modes is between the eigenmode of the first cavity L1 and of the second cavity L2.

[0087] As mode concordance increases the damping and the reflection coefficient is mainly driven by the eigenmode of the 2 cavities together (i.e. L2+L1), it is when the eigenmode of the first cavity or of the second cavity has the same frequency as the eigenmode of the two cavities together (i.e. L2+L1) that the damping gets the best increase.

[0088] Finally, it is clear that modifications and variants can be made to the damper and to the combustor assembly described herein without departing from the scope of the present invention, as defined in the appended claims.

Claims

1. Damper for a combustor assembly (3) of a gas turbine assembly (1) comprising:

- at least two damping volumes (32, 35) defined by respective damping bodies (31, 34); the damping volumes (32, 35) being interconnected in fluidic communication;

- at least one perforated connecting plate (36) connecting the two damping volumes (32, 35);at least one perforated end plate (38) configured to connect at least one of the two damping volumes (32, 35) with a combustion chamber (16; 14) of the combustor assembly (3);

the perforated connecting plate (36) and the perforated end plate (38) being provided with a plurality of openings (42); the openings (42) being dimensioned so as to operate in a low Strouhal regime according to the following formula

wherein:

•

is the angular frequency correlated to the frequency to damp according to the following relation

• R_H is the equivalent radius of one of the openings (42);

• U_b is the velocity of the flow through one of the openings (42).

2. Damper according to claim 1, wherein at least one of the damping bodies (31, 34) comprises at least one inlet (40) configured to be in fluidic communication with at least one source of air.

3. Damper according to anyone of the forgoing claims, wherein the at least two damping volumes (32, 35) are interconnected in parallel.

4. Damper according to anyone of the forgoing claims, wherein the at least two damping volumes (32, 35) are interconnected in series.

5. Damper according to anyone of the foregoing claims, wherein at least one of the damping volumes (32, 35) is a quarter wave tube.

6. Damper according to anyone of the foregoing claims, wherein at least one of the damping volumes (32, 35) is a Helmholtz resonator.

7. Damper according to anyone of the foregoing claims, comprising a first damping body (31; 34) extending along an extension axis (C) and having a first axial length (L1; L2) and a second damping body (34; 31) extending along an extension axis (C) and having a second axial length (L2; L1); the ratio (L1/L2; L2/L1) between the greater axial length (L1, L2; L2, L1) between the first axial length (L1; L2) and the second axial length (L2; L1) and the smaller between the first axial length (L1; L2) and the second axial lengths (L2; L1) being substantially integer, preferably even.

8. Combustor assembly for a gas turbine assembly (1) comprising at least one combustion chamber (14; 16) and at least one damper (30) according to anyone of the foregoing claims.

9. Gas turbine assembly comprising a compressor (2), a gas turbine (5) and a combustor assembly (3) as claimed in claim 8.

10. Method for manufacturing a damper (30) for a combustor assembly (3) of a gas turbine assembly (1) comprising the steps of:

- providing at least two damping volumes (32, 35) defined by respective damping bodies (31, 34) extending along a respective extension axis (C); the damping volumes (32, 35) being interconnected in fluidic communication;

- providing at least one perforated connecting plate (36) which has a plurality of openings (42) and connects the two damping volumes (32, 35);

- providing at least one perforated end plate (38) having a plurality of openings (42) and configured to connect at least one of the two damping volumes (32, 35) with a combustion chamber (16; 14) of the combustor assembly (3);

wherein the step of providing least one perforated connecting plate (36) comprises dimensioning the openings (42) to operate in a low Strouhal regime according to the following formula

wherein:

is the angular frequency correlated to the frequency to damp according to the following relation

R_H is the equivalent radius of one of the openings (42);

U_b is the velocity of the flow through one of the openings (42).

11. Method according to claim 10, wherein the step of providing at least two damping volumes (32, 35) comprises dimensioning a first cavity of a first damper body (31) to damp a first frequency, and dimensioning a second cavity of a second damper body (34) to damp a second frequency different from the first frequency.

12. Method according to claim 10 or 11, wherein the step of providing at least two damping volumes (32, 35) comprises dimensioning at least one of the two damping volumes (32, 35) as a quarter wave tube.

13. Method according to anyone of claims from 10 to 12, wherein the step of providing at least two damping volumes (32, 35) comprises dimensioning at least one of the two damping volumes (32, 35) as a Helmholtz resonator.

14. Method according to anyone of claims from 10 to 13, wherein the step of providing at least two damping volumes (32, 35) comprises dimensioning a first cavity of a first damper body (31; 34) having a first axial length (L1; L2) and a second cavity of a second damping body (34; 31) having a second axial length (L2; L1) so as the the ratio (L1/L2; L2/L1) between the greater axial length (L1, L2; L2, L1) between the first axial length (L1; L2) and the second axial length (L2; L1) and the smaller between the first axial length (L1; L2) and the second axial length (L2; L1) is substantially integer, preferably even.

Drawing