Damper for gas turbine

Abstract

The present invention generally relates to a gas turbine and more in particular it is related to a damper assembly for a combustion chamber of a gas turbine. According to preferred embodiments, the present solution provides a damper assembly including protrusions on a wall of the neck. These protrusions result in a side wall reactance to the acoustic field that has the effect of decreasing the effective speed of sound in the neck. The decrease of the effective speed of sound in the neck is equivalent to an increase of the effective neck length.

Claims

1. A damper assembly for a gas turbine, the damper assembly comprising: a resonator cavity and a neck in flow communication with said resonator cavity, said damper assembly including a plurality of protrusions located on a wall of said neck to contact a flow of a fluid from a combustion chamber to define a side wall reactance to an acoustic field to decrease an effective speed of sound in the neck as the fluid flows through the neck to the resonator cavity; wherein the neck is mounted to a wall of the combustion chamber and is in flow communication with the combustion chamber such that the neck is between the combustion chamber and the resonator cavity so that the flow of the fluid passes from the combustion chamber and into the resonator cavity via the neck; and wherein the plurality of protrusions define a corrugated flow channel for the flow of the fluid as the flow of the fluid passes through the neck to the resonator cavity, the corrugated flow channel being configured to permit relative movement between the resonator cavity and the combustion chamber and accommodate movement of the combustion chamber due to thermal gradients acting in the combustion chamber without negatively impacting a structural integrity of the damper assembly.

2. The damper assembly according to claim 1, wherein said plurality of protrusions are annular-shaped and arranged about a circumference of said neck.

3. The damper assembly according to claim 1, wherein said plurality of protrusions are equally distanced along said neck.

4. The damper assembly according to claim 1, wherein said plurality of protrusions each have a rectangular cross-section.

5. The damper assembly according to claim 1, wherein said plurality of protrusions each have a curved cross-section.

6. The damper assembly according to claim 1, wherein said resonator cavity comprises two volumes in flow communication with each other.

7. The damper assembly according to claim 6, wherein the neck is a first neck and there is a second intermediate neck extending between the two volumes to fluidly connect the two volumes of the resonator cavity, the second intermediate neck configured to decrease an effective speed of sound in the second intermediate neck as fluid flows through the second intermediate neck.

8. The damper assembly according to claim 1, wherein said plurality of protrusions are directed outward of the neck.

9. A damper assembly in a gas turbine, the damper assembly comprising: a first neck in flow communication with a resonator cavity, a plurality of protrusions located on an inner side wall of said first neck which contact fluid passing through the first neck as the fluid moves through the first neck toward or away from the resonator cavity to define; a side wall reactance to an acoustic field to decrease an effective speed of sound in the first neck as the fluid flows through the first neck; wherein the first neck is mounted to a wall of a combustion chamber and is in flow communication with the combustion chamber such that the first neck is between the combustion chamber and the resonator cavity so that the fluid passes from the combustion chamber and into the resonator cavity via the first neck; and wherein the plurality of protrusions define a corrugated flow channel in the first neck through which the fluid flows as the fluid passes through the first neck to the resonator cavity, the corrugated flow channel being configured to permit relative motion between the resonator cavity and the combustion chamber and accommodate movement of the combustion chamber due to thermal gradients acting in the combustion chamber without negatively impacting a structural integrity of the damper assembly.

10. The damper assembly of claim 9, wherein the resonator cavity has a first volume and a second volume that is in fluid communication with the first volume via an intermediate second neck positioned between the first volume and the second volume, the intermediate second neck having a plurality of protrusions that define a corrugated flow path that extends between the first volume of the resonator cavity and the second volume of the resonator cavity, the corrugated flow path of the intermediate second neck being configured to decrease an effective speed of sound in the second intermediate neck as fluid flows through the second intermediate neck.

11. The damper assembly of claim 9, wherein said resonator cavity has a first volume and a second volume that is in fluid communication with the first volume via an intermediate second neck positioned between the first volume and the second volume, the intermediate second neck having a plurality of protrusions that define a corrugated flow path that extends between the first volume of the resonator cavity and the second volume of the resonator cavity, wherein fluid flows along the corrugated flow path of the intermediate second neck as the fluid passes through the second intermediate neck.

12. The damper assembly of claim 9, wherein the plurality of protrusions are annular-shaped and equally distanced along the first neck.

13. The damper assembly of claim 9, wherein the plurality of protrusions have rectangular cross-sections or curved cross-sections.

14. The damper assembly of claim 9, wherein the plurality of protrusions are equally distanced along the first neck.

15. The damper assembly according to claim 1, wherein said neck is a first neck and the resonator cavity has a first volume and a second volume that is in fluid communication with the first volume via an intermediate second neck positioned between the first volume and the second volume, the intermediate second neck having a plurality of protrusions that define a corrugated flow path that extends between the first volume of the resonator cavity and the second volume of the resonator cavity, wherein fluid flows along the corrugated flow path of the intermediate second neck as the fluid passes through the second intermediate neck.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing objects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 shows a schematic side view of a damper according to the prior art;

(3) FIG. 2 shows a schematic side view of a damper assembly according to the present invention;

(4) FIG. 3 shows different embodiments of a damper neck according to the present invention;

(5) FIGS. 4 and 5 show a particular of the geometry of a damper neck according to the present invention;

(6) FIG. 6 schematically shows a side view of a damper according to the present invention comprising a plurality of volumes.

DETAILED DESCRIPTION

(7) With reference to FIG. 1, it is showed a side view of a damper assembly 100 according to the prior art. As known, the damper assembly 100 comprises a resonator cavity 300 in flow communication with a combustion chamber 500 through a neck 400. Typically, the neck 400 has a uniform cross-section, which could be, by way of example, circular or rectangular. The neck 400 has an outer wall 600 which defines a flow channel that hence puts in communication the resonator cavity 300 and the combustion chamber 500.

(8) Making now reference to following FIG. 2, it is schematically shown, a side view of a damper assembly 1 according to the invention. The damper assembly 1 comprises a resonator cavity 3 and a neck 4. The neck 4 puts in fluid communication the resonator cavity 3 with a combustion chamber, schematically denoted with numeral reference 2. In particular, the neck 4 comprises now protrusions 5 located on its outer wall 6. In the example shown, the neck 4 comprises a plurality of protrusions on the outer wall 6, but it will be appreciated that the outer wall 6 may even have only one protrusion, of any shape. Even in this configuration, the damper assembly 1 according to the present invention results in an advantageous effect with respect to a damper assembly according to the known art, where the neck has a uniform cross-section along its longitudinal development. Protrusions are preferably annular-shaped and arranged around the neck 4 of the damper assembly 1. Moreover, protrusions 5 may have a variety of shapes.

(9) In particular, with reference to FIG. 3, protrusions 5 may have a rectangular cross-section, or a more general curved cross-section. Preferably, the annular-shaped protrusions are equally distanced along the neck 4. According to the preferred embodiment here disclosed as a non-limiting case, the neck 4 may have a typical configuration of a corrugated neck. Furthermore, the protrusions 5 are preferably directed outward of the neck 4.

(10) As mentioned above, the protrusions 5 arranged on the neck 4 of the damper assembly result in a side wall reactance to the acoustic field which decreases the effective speed of sound in the neck. The decrease of the effective speed of sound in the neck is equivalent to an increase of the effective neck length.

(11) The effective speed of sound c.sub.eff in a pipe with protrusions has been derived analytically by Cummings [1]. In Cummings model the effect of the fluid in each cavity is limited to the compressibility of the protrusion, or cavity if considered from the internal volume of the neck, in which the pressure is assumed to be uniform and equal to the pressure in the main pipe:

(12) $c_{\mathrm{eff}}=c_0\frac{1}{\sqrt{1+\frac{V_{\mathrm{corr}}}{\mathrm{Sl}}}}$ c.sub.eff=effective speed of sound V.sub.corr=corrugation cavity volume l=corrugation pitch S=surface area of the pipe c.sub.0=speed of sound
The predictions of the model of Cummings have been confirmed experimentally and by means of simulations with an acoustic network model by Tonon et al. [2,3].

(13) With reference to FIG. 4, which shows a particular of an exemplary corrugated geometry chosen for the neck of the damper assembly, the following mathematical relations can be considered with reference to terms above introduced:

(14) $V_{\mathrm{corr}}=\frac{}{2}H\left(2H+D\right)W$$S=\frac{}{4}{D}^2$
Considering a neck with uniform cross-section according to the prior art, with a length L, the resonance frequencies can be expressed as:

(15) $f_{\mathrm{res}}=\frac{1}{2}n\frac{c_0}{L}$$n=1,2,3,\mathrm{.Math.}$
Considering now a corrugated neck, according to the present invention, the resonance frequencies can be similarly expressed as:

(16) $f_{\mathrm{res}}=\frac{1}{2}n\frac{c_{\mathrm{eff}}}{L}$$n=1,2,3,\mathrm{.Math.}$
But since the following relation stands:

(17) $c_{\mathrm{eff}}=c_0\frac{1}{\sqrt{1+\frac{V_{\mathrm{corr}}}{\mathrm{Sl}}}}$
It follows that:

(18) $f_{\mathrm{res}}=\frac{1}{2}n\frac{c_0}{L\sqrt{1+\frac{V_{\mathrm{corr}}}{\mathrm{Sl}}}}=\frac{1}{2}n\frac{c_0}{L_{\mathrm{eff}}}$$n=1,2,3,\mathrm{.Math.}$
And hence the effective neck length is:

(19) $L_{\mathrm{eff}}=L\sqrt{1+\frac{V_{\mathrm{corr}}}{\mathrm{Sl}}}$

(20) With reference to FIG. 5, and choosing, by way of a non-limiting example, the following geometry: W=0.01 (corrugation width) l=0.02 (corrugation pitch) H=0.01 (corrugation depth) D=0.02 (pipe diameter)
It is:

(21) $V_{\mathrm{corr}}=\frac{}{2}H\left(2H+D\right)W=6.28e^{-6}$$L_{\mathrm{eff}}=L\sqrt{1+\frac{V_{\mathrm{corr}}}{\mathrm{Sl}}}=1.414L$
Therefore, the above relation shows that the same Helmholtz damper can be realized with a neck comprising protrusions that is >40% shorter than a uniform, straight neck.
It is further to be emphasised that, advantageously, a corrugated neck presents local rigidity coupled with global flexibility. The flexibility is beneficial to allow relative movement of the resonator cavity with respect to the wall of the combustion chamber where the neck is mounted. Such arrangement allows movement of the combustion chamber due to thermal gradients acting therein without this having a negative impact of the integrity of the damper assembly.

(22) With reference now to the last FIG. 7, it is shown another example of a damper assembly 1 according to the invention, having the corrugated neck 4 in fluid communication with the resonator cavity 3. In this exemplary embodiment, the resonator cavity 3 comprises two volumes 31 and 32 in flow communication with each other. The damper assembly 1 further comprises an intermediate neck 41, having protrusions 5, arranged to connect said two volumes (31, 32).

(23) It will be appreciated that any kind of configuration for a damper assembly can be achieved, by means of any combination of resonator cavities, having a plurality of volumes and being interconnected through intermediate necks having protrusions according to the present invention.
Furthermore, it will be appreciated that a damper assembly according to the present invention, comprising a plurality of resonator cavities, each one comprising one or more volumes, may also comprise a combination of necks with protrusions and necks with a uniform cross-section.

(24) Although the present invention has been fully described in connection with preferred embodiments, it is evident that modifications may be introduced within the scope thereof, not considering the application to be limited by these embodiments, but by the content of the following claims.