Patent Application
20160348537
1. Field
The present application relates to gas turbines, and more particularly to an arrangement and method to minimize flow induced vibration in a gas turbine exhaust diffuser.
2. Description of the Related Art
The turbine exhaust cylinder and the turbine exhaust manifold are coaxial gas turbine casing components connected together establishing a fluid flow path for the gas turbine exhaust diffuser. The fluid flow path includes an inner flow path and an outer flow path defined by an inner diameter delimiting an outer cylindrical surface of the inner flow path and an outer diameter delimiting an inner cylindrical surface of the outer flow path, respectively. Tangential struts are arranged within the fluid flow path and serve several purposes such as supporting the flow path and provide a pathway for lubrication piping. Turbine exhaust cylinder and turbine exhaust manifold tangential struts are arranged in circumferential rows and extend between the outer cylindrical surface and the inner cylindrical surface. For the last row of turbine exhaust cylinder tangential struts in the direction of flow, every other turbine exhaust cylinder tangential strut may be aligned, axially, with a turbine exhaust manifold strut. As an example, there may be six turbine exhaust cylinder tangential struts arranged in a circumferential row and three turbine exhaust manifold tangential struts aligned axially with every other turbine exhaust cylinder strut.
At certain conditions, unsteadiness of the exhaust flow around the tangential struts can cause vibrations of the inner and outer diameter of the turbine exhaust cylinder and the turbine exhaust manifold. The strut flow unsteadiness may cause large oscillations in flow path pressures that force the flowpath structure to vibrate or even resonate strongly. These vibrations are a potential contributor to damage occurring on the flow path of the turbine exhaust manifold and the turbine exhaust cylinder. This damage to the diffuser flow path may require replacement or repair.
Briefly described, aspects of the present disclosure relates to an arrangement to minimize vibrations in a gas turbine exhaust diffuser and a method to minimize pressure oscillations in a gas turbine exhaust diffuser.
A first aspect provides an arrangement to minimize vibrations in a gas turbine exhaust diffuser. The arrangement includes a gas turbine exhaust diffuser. The gas turbine diffuser includes a turbine exhaust manifold connected to a turbine exhaust cylinder establishing a fluid flow path, the fluid flow path bounded radially outward by an outer cylindrical surface and bounded radially inward by an inner cylindrical surface. A first tangential strut is arranged in the turbine exhaust cylinder between the outer cylindrical surface and the inner cylindrical surface. A second tangential strut in the turbine exhaust manifold is disposed downstream from the first tangential strut between the outer cylindrical surface and the inner cylindrical surface. A projection is coupled to the inner cylindrical surface or the outer cylindrical surface and minimizes pressures oscillations in the gas turbine exhaust diffuser such that an unsteadiness of the fluid flow surrounding the second tangential strut is reduced.
A second aspect provides a method to minimize pressure oscillations in a gas turbine exhaust diffuser. The method includes disposing a projection on an outer cylindrical surface or an inner cylindrical surface of a fluid flow path of the gas turbine exhaust diffuser, and coupling the projection to the outer cylindrical surface or the inner cylindrical surface. The fluid flow path is bounded radially outward by an outer cylindrical and bounded radially inward by an inner cylindrical surface. The projection minimizes pressure oscillations in the gas turbine exhaust diffuser such that an unsteadiness of the fluid flow surrounding of the second tangential strut is reduced.
To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods.
The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present disclosure.
In order to prevent the tangential strut flow unsteadiness on a turbine exhaust cylinder strut, a turbine exhaust cylinder strut strip may be used on the turbine exhaust cylinder tangential strut. The flow unsteadiness on the turbine exhaust cylinder tangential strut is driven by transonic shock induced oscillations on a side of the turbine exhaust cylinder strut airfoil. This unsteadiness is mitigated using the turbine exhaust cylinder strut strip which reduces the shock wave. However, the turbine exhaust cylinder strut strip causes fluid flow separation from the turbine exhaust cylinder tangential strut downstream. This fluid flow separation known as a ‘separation bubble’ may negatively interact with the turbine exhaust manifold leading edge flow and may cause pressure oscillations such that the turbine exhaust manifold strut experiences unsteadiness. In order to minimize these pressure oscillations in the gas turbine exhaust diffuser such that an unsteadiness of the turbine exhaust manifold tangential strut is reduced, a projection or a plurality of projections positioned on a surface of the inner diameter or outer diameter is proposed.
As illustrated in the shown embodiment of
More specifically, in an embodiment, a wall strip (210) may be disposed on the inner cylindrical surface (55) in front of the leading edge of the turbine exhaust manifold (140) strut in the shape of a horseshoe as shown. The horseshoe shaped wall strip (210) helps to reduce the interaction of a horseshoe vortex at the leading edge of the turbine exhaust manifold (140) and the fluid flow separation from the turbine exhaust cylinder (190, 195) that is axially aligned with the turbine exhaust manifold (140). In another embodiment, a plurality of wall strips (220) are shown disposed on the inner cylindrical surface (55) in an axial direction between the turbine exhaust cylinder tangential struts (190, 195). The fluid flow separation from a turbine exhaust cylinder (195) that is not aligned with the turbine exhaust manifold (140) may be controlled with the wall strips (220).
Accordingly, the placement of the projections (210, 220) in
The material of the projection (200, 210, 220) may be the same material or essentially the same material as that of the inner or outer cylindrical surface (55, 65). Having the same or essentially the same material as that of the inner or outer cylindrical surface (55, 65) would minimize the differential growth between the projection (200, 210, 220) and the inner or outer cylindrical surface (55, 65) of the gas turbine exhaust diffuser (10). For example, a steel may be used as the material of the projection (200, 210, 220).
In an embodiment, the projection (200, 210, 220) is disposed such that when the fluid flow flows over the projection (200, 210, 220), a specific frequency of the fluid flow is produced. This specific frequency would be different from a surrounding frequency such that the specific frequency would not couple with the surrounding frequency. In essence, a frequency filter would be created in the region of the projection (200, 210, 220).
Referring to
The projection (200, 210, 220) may be disposed between the leading edge of the turbine exhaust cylinder strut (190) and the trailing edge of the turbine exhaust manifold strut (140) with reference to the fluid flow path. Computational fluid dynamic simulations may be used to determine optimal positioning for the projection (200, 210, 220) such that the projection (200, 210, 220) disrupts an interaction of a flow separation downstream of the turbine exhaust cylinder strut and a leading edge flow of a turbine exhaust manifold strut (140).
While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.
