Patent Description:
The present invention relates also to a method for manufacturing a combustor assembly with a damper.

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

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.

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

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

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

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.

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

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.

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.

However, these dampers are not sufficiently flexible and are not able to damp broad frequency ranges. Other kind of dampers are disclosed in documents <CIT> and <CIT>.

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

According to the present invention, there is provided a a combustor assembly of a gas turbine assembly as claimed in claim <NUM>.

The structure of the damper of the combustor assembly according to the invention is flexible and can be also compact.

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

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

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.

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

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

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: <MAT> wherein.

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 <MAT> wherein.

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.

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

According to this object the present invention relates to a gas turbine plant according to claim <NUM>.

It is also another object of the present invention to provide a simple and economic method for manufacturing a combustor assembly for a gas turbine with a damper. According to this object the present invention relates to a method for manufacturing a combustor assembly with a damper according to claim <NUM>.

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

In <FIG> reference numeral <NUM> indicates a gas turbine assembly. The gas turbine assembly <NUM> comprises a compressor <NUM>, a sequential combustor assembly <NUM> and a turbine <NUM>. The compressor <NUM> and the turbine <NUM> extend along a main axis A.

In use, an airflow compressed in the compressor <NUM> is mixed with fuel and is burned in the sequential combustor assembly <NUM>. The burned mixture is then expanded in the turbine <NUM> and converted in mechanical power by a shaft <NUM>, which is connected to an alternator (not shown).

The sequential combustor assembly <NUM> comprises a first-stage combustor <NUM> and a second-stage combustor <NUM> sequentially arranged along the gas flow direction G. In other words, the second stage combustor <NUM> is arranged downstream the first stage combustor <NUM> along the gas flow direction G.

Preferably, between the first stage combustor <NUM> and the second stage combustor <NUM> a mixer <NUM> is arranged.

The first stage combustor <NUM> defines a first combustion chamber <NUM>, the second stage combustor <NUM> defines a second combustion chamber <NUM>, while the mixer <NUM> defines a mixing chamber <NUM>.

The first combustion chamber <NUM>, the second combustion chamber <NUM> and the mixing chamber <NUM> are in fluidic communication and are defined by a liner <NUM> (see <FIG> wherein the liner <NUM> is partially visible), which extends along a longitudinal axis B.

With reference to <FIG>, in the second combustion chamber <NUM> of the second stage combustor <NUM> a supply assembly <NUM> is arranged.

The supply assembly <NUM> comprises a central body <NUM> provided with a plurality of fingers <NUM> (schematically represented also in <FIG>).

The fingers <NUM> are preferably defined by streamlined bodies, each of which is provided with a plurality of nozzles <NUM> and is supplied with air and at least one fuel.

Referring to <FIG> and <FIG>, the second stage combustor <NUM> comprises at least one damper <NUM>.

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

Preferably, the dampers <NUM> are arranged about the central body <NUM> of the supply assembly <NUM>. More preferably, the dampers <NUM> are evenly distributed about the central body <NUM>.

Referring to <FIG> and <FIG> the dampers <NUM> are preferably coupled to a panel <NUM> surrounding the central body <NUM> of the supply assembly <NUM>. Preferably the panel <NUM> is also provided with a plurality of cooling holes <NUM> evenly distributed along the panel <NUM>.

It is understood that damper <NUM> can be arranged also in another portion of the combustor assembly <NUM>.

For example, damper <NUM> can be coupled to the liner <NUM>, preferably to the portion of the liner <NUM> facing the second combustion chamber <NUM>. Damper <NUM> can also be arranged so as to face into the first combustion chamber <NUM>.

Referring to <FIG>, the damper <NUM> extends along an extension axis C and comprises a first damper body <NUM> having a first cavity defining a first damping volume <NUM>, a second damper body <NUM> having a second cavity defining a second damping volume <NUM>, a perforated connecting plate <NUM> connecting the first damping volume <NUM> and the second damping volume <NUM> and at least one perforated end plate <NUM>. The perforated end plate <NUM> is configured to connect the first damping volume <NUM> with the outside of the damper <NUM> which is in fluidic communication with the first combustion chambers <NUM> and/or the second combustion chamber <NUM> of the combustor assembly <NUM>.

The first damping volume <NUM> and the second damping volume <NUM> are interconnected in fluidic communication by the perforated connecting plate <NUM>.

In the non-limiting example here disclosed and illustrated the first damping volume <NUM> and the second damping volume <NUM> are interconnected in series.

According to a variant not illustrated, the first damping volume <NUM> and the second damping volume <NUM> are interconnected in parallel.

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

In use, the air enters through the inlets <NUM>, flows into the second damping volume <NUM>, passes through the perforated connecting plate <NUM>, flows into the first damping volume <NUM> and exits through the perforated end plate <NUM> into the first combustion chambers <NUM> and/or the second combustion chamber <NUM> of the combustor assembly <NUM>.

The air contributes to cool the first damper body <NUM> and the second damper body <NUM> and avoid hot gas ingestion, which would de-tune the first damper body <NUM> and the second damper body <NUM> and could cause damages to the first damping body <NUM> and the second damper body <NUM>. Preferably, the inlets <NUM> are arranged on opposite sides of the second damper body <NUM>.

The perforated connecting plate <NUM> and the perforated end plate <NUM> have a similar structure. Both the perforated connecting plate <NUM> and the perforated end plate <NUM> are provided with a plurality of openings <NUM>.

In the example here disclosed and illustrated the openings <NUM> 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..

The perforated connecting plate <NUM> and the perforated end plate <NUM> are both designed so as to operate in a low Strouhal regime. The Strouhal regime is defined by the value of the Strouhal number.

Here and in the following with the expression "low Strouhal regime" is intended a Strouhal number lower than <NUM>,<NUM>.

In order to operate in a low Strouhal regime, the openings <NUM> of the perforated connecting plate <NUM> and of the perforated end plate <NUM> are dimensioned according to the following condition:
<MAT>
wherein.

In use, the perforated end plate <NUM> faces directly the first combustion chambers <NUM> and/or the second combustion chamber <NUM> and therefore is designed to resist to high temperatures. Thickness and material of the perforated end plate <NUM> are therefore chosen to guarantee high reliability.

The perforated connecting plate <NUM> is subjected to high temperatures too although in a lesser way than the perforated end plate <NUM>.

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

In the non-limiting example here disclosed and illustrated, the perforated connecting plate <NUM> and the perforated end plate <NUM> have a different thickness. The perforated end plate <NUM> is preferably thicker than perforated connecting plate <NUM> as facing the combustion chamber.

With reference to <FIG>, the openings <NUM> are substantially arranged according to a cross mesh pattern. Alternatively, the openings <NUM> can be substantially arranged according to a square mesh pattern or according to a rectangular mesh pattern or other patterns.

In the non-limiting example here disclosed and illustrated, the mesh pattern of the perforated connecting plate <NUM> is identical to the mesh pattern of the perforated end plate <NUM>. In this way the openings <NUM> of the perforated connecting plate <NUM> are aligned with the openings <NUM> of the perforated end plate <NUM>.

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

With reference to <FIG>, the openings <NUM> of the perforated connecting plate <NUM> and of the perforated end plate <NUM> are arranged so as to extend perpendicularly to the plane a<NUM> a<NUM> along which the respective perforated connecting plate <NUM> or the perforated end plate <NUM> extends.

The first cavity of the first damper body <NUM> and the second cavity of the second damper body <NUM> are dimensioned so as to give to the damper <NUM> a desired damping effect.

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

The first cavity of the first damper body <NUM> and of the second cavity of the second damper body <NUM> are designed so as to be a quarter wave tube.

The dimensioning of the first cavity of the first damper body <NUM> and of the second cavity of the second damper body <NUM> is made, for example, according to the following formula (quarter wave tube formula): <MAT> wherein.

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

Alternatively, the first cavity of the first damper body <NUM> and of the second cavity of the second damper body <NUM> are designed so as to be a Helmholtz resonator.

The dimensioning of the first cavity of the first damper body <NUM> and of the second cavity of the second damper body <NUM> is made, for example, according to the following formula (Helmholtz formula): <MAT> wherein.

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

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

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 <NUM>, the dimensioning is made using the Helmholtz formula.

Preferably, the first cavity of the first damper body <NUM> is dimensioned to damp a first frequency while the second cavity of the second damper body <NUM> is dimensioned to damp a second frequency different from the first frequency.

The damper <NUM> so dimensioned and designed is able to dampen a broad band of frequencies. The damper <NUM>, 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.

In particular, the relation between the axial length L1 of the first cavity of the first damper body <NUM> and the axial length L2 of the second cavity of the second damper body <NUM> influences the response of the damper <NUM>.

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.

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.

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

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.

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

As the damper <NUM> is broadband, even if the ratio is not exactly integer, the response of the damper <NUM> does not vary excessively. For example, if L2/L1 = <NUM> instead of <NUM> the response of the damper <NUM> is similar. For this reason, the ratio is defined as "substantially integer".

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 <FIG>. Such a solution leads to a high damping in the center of modulation.

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 <FIG>.

In <FIG> graphs about the reflection coefficient modulus and phase of a damper <NUM> having the structure above described in use in the combustor assembly <NUM> are represented.

The trends of <FIG> regarding the reflection coefficient modulus and phase evidence that the damper <NUM> is able to damp a broad band of frequencies. The trends shown in <FIG> 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).

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.

As mode concordance increases the damping and the reflection coefficient is mainly driven by the eigenmode of the <NUM> 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.

Claim 1:
Combustor assembly for a gas turbine assembly (<NUM>) comprising at least one combustion chamber (<NUM>; <NUM>) and
at least one damper (<NUM>); wherein the damper comprises:
- at least two damping volumes (<NUM>, <NUM>) defined by respective damping bodies (<NUM>, <NUM>); the damping volumes (<NUM>, <NUM>) being interconnected in fluidic communication;
- at least one perforated connecting plate (<NUM>) connecting the two damping volumes (<NUM>, <NUM>);
- at least one perforated end plate (<NUM>) connecting at least one of the two damping volumes (<NUM>, <NUM>) with a combustion chamber (<NUM>; <NUM>) of the combustor assembly (<NUM>);
the perforated connecting plate (<NUM>) and the perforated end plate (<NUM>) being provided with a plurality of openings (<NUM>);
characterized in that
the openings (<NUM>) are dimensioned so as to operate in a low Strouhal regime according to the following formula
<MAT>
wherein:
• <IMG>is the angular frequency correlated to the frequency to damp according to the following relation ω=2πf;
• RH is the equivalent radius of one of the openings (<NUM>);
• Ub is the velocity of the flow through one of the openings (<NUM>).