Damped combustion cowl structure

The present invention relates to an improved sheet metal structure, and more particularly to an improved cowl damping structure for use in the combustion chamber of a gas turbine engine.

In a combustor of a gas turbine engine, guide vanes direct pressurized air from the compressor. This air moves over the inner and outer liners of the combustion chamber, or combustor, to provide a cooling effect. Gas turbine combustors generally require a combustion cowl for dividing the incoming air into the primary zone dome flow and into the upper and lower combustor annulus air flows. The impinging air from the compressor exit causes the cowl to vibrate mechanically, which leads to high cycle fatigue of the cowl.

In the existing art, a formed sheet metal part is rolled on a forward end to encase a continuous damper wire. Typically gaps or spaces exist between the formed sheet metal part and the damper wire where they are not in contact with each other. The locations where the components are in contact with each other produces a sliding friction force between the wire and the sheet, which dampens the vibration force. Over a long time exposure, the wire-damped cowl having such gaps experiences typical wear problems associated with friction damping systems. The wear causes thinning of the sheet metal that leads to a shortened part life, requiring frequent replacement of the combustion cowl.

It would be desirable, then, to improve the cowl damping structure in a gas turbine combustor, by improving or increasing the contact area between the damper wire and sheet metal to reduce the wear rate of the combustion cowl.

To improve the existing cowl design, a cowl wrap wire process is proposed. The manual spinning process of the existing art is eliminated, and replaced with a controlled die-form operation and heat treat. The heat treat will occur after the first curl of the sheet metal around the wire. After heat treat, a final controlled die-form process is applied to close the sheet metal around the wire. This yields a consistent contact area around the part that is greater than the contact area using the existing art process.

In one embodiment of the present invention, a method for increasing contact area between a damper wire and sheet metal component in a combustion cowl of a gas turbine engine is provided. The method comprises of several steps that include the following. Processing a sheet metal component having a forward diameter at a forward end and an aft diameter at an aft end wherein the forward diameter is smaller than the aft diameter. Placing or situating a damper wire onto the sheet metal component adjacent to the forward end so that an area of contact is created between the damper wire and the sheet metal component. Die-forming a first curl in the sheet metal component around the damper wire prior to heat treat to create a cowl wrap wire structure. Applying a heat treat operation to the cowl wrap wire structure to conform the sheet metal component and the wire thereby increasing the area of contact between the damper wire and the sheet metal component. Then die-forming a final curl in the sheet metal component around the damper wire in the cowl wrap wire structure after heat treat to create a combustion cowl.

In another embodiment of the present invention, a combustion cowl for use on a gas turbine engine is provided. The combustion cowl comprising a sheet metal component, a damper wire, and an area of contact between the sheet metal component and the damper wire. The sheet metal component having a forward diameter at a forward end and an aft diameter at an aft end wherein the forward diameter is smaller than the aft diameter. The damper wire on the sheet metal component is adjacent to the forward end. The area of contact between the damper wire and the sheet metal component is increased by applying a first die-forming operation, a heat treat operation, and a final die-forming operation after the heat treat operation in order to curl the forward end of the sheet metal component around the damper wire.

Accordingly, the present invention provides an effective technique for improving the contact area between the damper wire and sheet metal to reduce the wear rate of the combustion cowl.

FIG. 1 illustrates a cross-sectional view of an engine combustor region showing a combustor structure;

FIG. 2 illustrates a cross-sectional view of a combustion cowl; and

FIG. 3 illustrates a partial view of the combustion cowl from the proposed cowl wrap process.

Referring to FIG. 1, there is illustrated a cross-sectional view of a typical combustor region of a gas turbine engine 10 . The wire-damped combustion cowl wrap technique herein can be applied to such an engine 10 . In engine 10 , the contact area between damper wire 12 and sheet metal 14 is increased which reduces the wear rate on the combustor cowl 28 , associated with combustor 16 . The combustion cowl divides the air incoming into primary zone dome flow of air region 18 into upper and lower combustor annulus air flows 20 and 22 , respectively. Incoming air from the compressor exit 24 causes the combustion cowl to vibrate mechanically. The mechanical vibrations lead to high cycle fatigue of the cowl.

In the prior art, the cowl wrap design produces gaps between the damper wire and sheet metal thereby reducing a sliding friction force between the wire and the sheet, which damps the vibration force. Over a long time exposure, however, the wire-damped cowl experiences typical friction damping system wear problems. The wear causes thinning of the sheet metal that leads to a shortened part life, requiring frequent replacement of the cowl. Such cowl structures have been proposed, for example, in U.S. Pat. No. 5,181,377 issued to Napoli et. al. on Jan. 26, 1993, assigned to the General Electric Company which patent is hereby incorporated herein by reference.

Referring now to FIGS. 1 and 2, there is illustrated in greater detail the proposed combustion cowl 28 having the increase in contact area between the damper wire and the sheet metal. Contact area Z and area of contact Z are used interchangeably in reference to the actual surface area where there is physical contact between the damper wire 12 and sheet metal component 14 . The formed sheet metal component 14 is rolled on a forward end 26 to encase the continuous damper wire 12 . A controlled die-form operation and heat treat wraps the final leg of the sheet around the wire. This reduces the wear rate of the combustion cowl since the gaps in the contact area are eliminated. This controlled die-form yields a consistent contact area around the part that is greater in surface contact area than prior processes. This increased contact area not only significantly reduces wear rate, it also increases part life.

The heat treat occurs after the first curl of the sheet metal 14 around the wire 12 . This heat treat operation conforms the sheet metal component 14 and wire 12 increasing the contact area and also eliminating or minimizing gaps between the damper wire and the sheet metal component. After heat treat, a final controlled die-form process is applied to close the sheet metal around the wire. The proposed cowl wrap wire process eliminates the manual spinning form process of the existing art.

Referring now to FIG. 3, after completion of this cowl wrap wire process, the combustion cowl 28 includes a diameter E measured across zone F of the combustion cowl 28 . Preferably, diameter E can extend anywhere between a maximum value of about 0.25, 0.247, or 0.24 inches to a minimum value of about 0.231, 0.2275, or 0.21 inches; and more preferably diameter E is about 0.239 inches or about 0.2275 inches. Zone F is shown in FIG. 3 on the outer surface of the combustion cowl 28 . Zone F extends from a tangent point P to the edge of the combustion cowl 28 in the same direction from tangent point P as the combustion cowl 28 wraps around the wire 12 . Zone F may end a maximum distance of about 0.03 inches from the edge of the combustion cowl 28 .

In one embodiment of combustion cowl 28 the following preferred parameters apply. The sheet metal 14 is a high temperature metal alloy and has a width or thickness in the range of about 0.03 inches to about 0.05 inches. Preferably the sheet metal 14 has a thickness greater than about 0.03 inches and more preferably between about 0.038 to about 0.042 inches. The wire 12 is made of a high temperature metal alloy and has a diameter in the range of about 0.15 inches to about 0.16 inches. A preferable heat treat temperature is about 2050° F. While a variety of metals can be used for either the wire 12 or the sheet metal 14 , a preferred material is a high temperature metal alloy such as a cobalt based alloy. By way of example, the use of a Haynes-188 material wire 12 and sheet metal component 14 can help in reducing wear rate and improving part life.

In this embodiment, one continuous damper wire 12 is used. The damper wire 12 can be formed into an annular shape and made continuous by use of a welded joint. At any such welded joint, the one continuous damper wire 12 may have a local reduction in the diameter.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. For example, this design can be applied in various environments and to various sheet metal components. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.