Patent Application
20160130951
This invention relates to cooling for blades for gas turbines, and particularly to providing a cooling system for cooling the join between platform and aerofoil surfaces.
In the process of building gas turbines, it is often necessary to join together two or more pieces to create a built part, such as the platform and aerofoil of a turbine blade. In joining these pieces together, it is not necessarily possible to achieve a perfect fit and a sealed joint, and it is likely that a distinct gap between the single pieces of the built part will remain. In some areas in gas turbines, engine operation and/or different thermal expansion may cause the gap between pieces to open or close. For example, a small gap may appear between the platform part and aerofoil part, with the result that hot gas may enter the gap between two parts, reducing part lifetime. It is therefore critical that parts are kept sufficiently cool. It has been appreciated that it would be desirable to improve the turbine blade design in light of these considerations.
The invention is defined in the appended independent claims to which reference should now be made. Advantageous features of the invention are set forth in the dependent claims.
According to a first aspect of the invention, there is provided a turbine blade for a gas turbine, comprising a platform part and an aerofoil part, the platform part comprising a platform surface arranged to be attached to a corresponding aerofoil surface of the aerofoil part, further comprising a cooling duct for cooling the platform and aerofoil surfaces, the cooling duct comprising at least one cavity in the platform surface and at least one cavity in the corresponding aerofoil surface, and the platform and aerofoil surface cavities are aligned such that when the platform surface and aerofoil surface are touching, the cooling duct remains open. This provides a reliable cooling means that cools both the platform and aerofoil surfaces, as it avoids blockage of the cooling duct that might appear during engine use, be it a steady state blockage or a transient blockage. A coolant flow is therefore generated that can cool both the platform surface and the aerofoil surface, even during complete closure of the gap between the two parts.
Advantageously, the cooling duct additionally comprises at least one inlet duct or inlet groove. Advantageously, the cooling duct additionally comprises at least one outlet duct or outlet groove. Advantageously, the turbine blade additionally comprises at least one turbulator in at least one of the cavities. This provides for a turbulent air flow and can improve cooling.
Advantageously, the platform part is made from a different material to the aerofoil part. Advantageously, the turbine blade comprises a bi-cast joint between the platform part and the aerofoil part. Advantageously, the turbine blade comprises a seal extending between the platform part and the aerofoil part, for at least substantially stopping ingress of hot gas between the platform part and the aerofoil part. Advantageously, the turbine gas additionally comprises a release means to allow a cooling fluid to flow through the seal. This allows for cooling air to exit into the hot gas flow whilst minimising hot gas flow in the opposite direction.
In a further aspect of the invention, a gas turbine is provided comprising a turbine blade as described above.
An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which:
The invention will now be described in the context of a rotating blade, but can equally well be provided in a stationary blade (a vane).
An example is shown in
The platform part 12 may be made of the same material as aerofoil part 14. This invention is particularly suitable for hybrid parts, where the platform part and aerofoil part are made of different materials and the thermal expansion coefficients of the two parts may be different. In a preferred embodiment the platform part and aerofoil part are therefore made of different materials.
The platform surface 16 and the aerofoil surface 18 may be planar or substantially planar, but may also be curved, such as those shown in
The cooling duct 20 may be a single path for a cooling fluid, or may comprise multiple paths extending in various directions across the surfaces. The platform and aerofoil surface cavities are aligned so that they overlap such that when the platform surface and aerofoil surface are touching, the cooling duct that the platform and surface cavities form remains open. This overlap between the cavities allows for the cooling duct to maintain a fluid path even when the platform surface and aerofoil surface are touching. The cooling duct may be part of a larger cooling system, such as a turbine blade cooling system.
The cavities 22, 24 may be various different shapes. In
In
The inlet duct or ducts 26 (or holes) may be provided in various ways, and may be disposed in the platform part, the aerofoil part, or both. Alternatively, there may be no bespoke inlet means at all, with the inlet provided by an integral part of a blade cooling system. For example, the inlet may be provided by a cooling duct that is part of a cooling system for other parts of the blade, and the duct simply passes through a cavity. A portion of the cooling fluid that is flowing through the cooling system cooling duct then ends up flowing through the cooling duct of the present invention.
Similar flexibility exists in the outlet groove or grooves 30, which may be disposed in the platform part, the aerofoil part, or both. Instead of grooves, ducts could be provided, and in some embodiments there could be no separate outlet at all, with the cavities extending all the way to the outside edge of the blade. The outlet may eject the cooling fluid into the hot gas flow, or it may be directed elsewhere for further cooling.
The turbulators 58 may be various shapes, such as ribs, pedestals (pins) or islands disposed within the flow. These turbulators act as heat transfer coefficient enhancing features, improving heat transfer. One or more turbulators may be provided in any given cavity.
Various modifications to the embodiments described are possible and will occur to those skilled in the art without departing from the invention which is defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14192815.0 | Nov 2014 | EP | regional |
