Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1999-08-24
2001-10-23
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
Reexamination Certificate
active
06305903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a cooled vane for a gas turbine or similar device.
BACKGROUND OF THE INVENTION
Such a vane is known, for example, from U.S. Pat. No. 5,498,133 on which the invention is based. It has a vane blade with a suction side and a pressure side wall that are connected via a leading edge and a trailing edge with each other. The walls define the profile form and enclose a cavity used for cooling purposes. The cavity extends essentially radially, and a cooling medium, usually air, flows through it. The flow through the cavity may, for example, be direct. Alternatively, the cavity may be provided with an insert, whereby the air is usually supplied radially to the insert. The perforation in the insert then causes the air to pass between the insert and the suction or pressure side wall and to be guided to the trailing edge.
In the area of the trailing edge, cooling channels are provided that originate from the cavity and end in the form of blow-out openings in the area of the trailing edge. They extend through a vane section that adjoins the trailing edge and is formed by the corresponding sections of the suction side and pressure side wall together. This means that the cooling medium is able to flow from the cavity through the trailing edge area and cool it before exiting at the trailing edge and being mixed into the process gas stream.
Such a cooling concept also can be realized in gas turbine vanes which are manufactured—as is currently preferred—by using casting processes. The cooling channels are hereby created using a core that must be removed from the component, i.e., from the vane, after the casting. When designing cooling channels, it must be noted in this connection that the corresponding cores also must be producable at a reasonable cost. Usually two- or multi-part core form tools into which the core material is pressed in the molten state are used for this purpose. After solidification, the core tool is opened, and the core can be removed. Since the core consists of a number of side-by-side, connected individual cores, a geometry must be chosen for the overall structure that permits an easy removal from the core form tool. Of importance in this connection is the so-called taper angle that causes a side contour of the individual channels originating from the dividing plane and extending backward at an angle. As a result, the cooling channels in vanes of this type usually were located so as to be located centered between the suction side and the pressure side.
In particular in the case of vanes with a thick trailing edge, this concept causes the cooling channels to be relatively far removed from the two outside walls, so that the cooling effect is very limited.
SUMMARY OF THE INVENTION
The invention attempts to avoid the described disadvantages. It is based on the objective of a cooled vane for a gas turbine or similar device of the initially mentioned type which permits an improved cooling effect in the area of the trailing edge and also can be manufactured at a reasonable cost, especially by using casting processes.
According to the invention this is realized in that in a cooled vane a first row of cooling channels is associated with the suction side and a second row of cooling channels is associated with the pressure side. Contrary to previous configurations in which the cooling channels were arranged near the vane center, the cooling channels are now shifted towards the outside walls. The reduced distance between the cooling channel and the outside wall achieves a higher cooling efficiency which manifests itself either through a reduced material temperature with an unchanged use of cooling medium, or which can be used to achieve the same material temperature with a reduced amount of cooling medium.
An improved component strength in the area of the trailing edge can be achieved if, according to a preferred embodiment, the cooling channels of the first row, when seen radially, are arranged laterally offset to the cooling channels of the second row. The reduction of the cross-section in the trailing edge area due to the applied cooling channels can be minimized in this way, so that in particular vanes with a narrow profile can be cooled optimally.
An arrangement that is optimal under this aspect is achieved if the local pitch of the first row and the local pitch of the second row are identical, and the cooling channels of the first row are in each case radially offset to the side from the cooling channels of the second row by an amount corresponding to half the local pitch. This results in a completely regular and symmetrical pattern of arrangement in which the cooling channels of one row each are arranged so as to be exactly centered opposite from the cooling channels of the other row.
According to a further embodiment of the invention, the sum of the maximum width of two opposing cooling channels is smaller than the local pitch at this point. This configuration permits a channel shape which allows the initially described core production in a casting process using a core form tool. The dividing plane of the core form tool hereby can be moved back and forth in each case between the two rows of cooling channels without undercutting and while preserving the required taper angle. The required taper angle and the distance of the two rows from the cooling channels determines the extra amount which must be added to the sum of the two maximum values for the widths of the cooling channels in order to determine the maximum value for the pitch of each row.
Cooling channels with a triangular or trapezoid design are preferred, since these shapes can be produced easily and at low cost.
Additional advantages in regard to the cooling effect are obtained if the cooling channels are constructed so that the maximum width in each case is oriented outward. As a result, the maximum width is oriented so as to directly adjoin the outside walls, that means it is oriented towards the suction side or pressure side, so that the cooling medium is to a greater degree supplied to these areas, i.e., those wall areas which are subject to the strongest thermal stresses. This type of orientation actually does require additional effort when producing the core form tool since the lateral contour progression of the core extends in the opposite direction to the taper angle of the dividing plane. But the increase in cooling efficiency that can be obtained by this more than makes up for this disadvantage.
It is also possible to reduce the maximum height of the cooling channels in relation to the previously centered channels, and to achieve in this way a balanced temperature distribution of the cooling medium and an increase in the speed inside the respective cooling channel. A value for the ratio of maximum height to maximum width from 1.5 to 1.0:1 was found to be the best.
The installation of turbulence generators, in particular in the form of ribs, which is provided in at least part of the cooling channels promises a further improvement. This improves the thermal transfer from the channel wall to the cooling medium, creating a further possibility for optimization.
An exact adjustment to the radial temperature distribution along the vane height is made possible in that the pitch and/or cross-section area of the cooling channels varies in the radial direction. Depending on the local heat input, the distance of the cooling channels of a row can be reduced, especially in the area of the vane center, where the thermal stress is highest. The cross-section area of the cooling channels in the central vane area also can be selected greater than in the area of the vane tip and the vane root.
Because of cost reasons it is advantageous that the vanes are produced as so-called cast vanes, whereby the cooling channels are directly molded on. This eliminates any necessary finishing, for example by drilling or eroding. For this purpose, the cooling channels are formed by a core that is removed after casting and solidification of the vane. For reasons of production technology it
Semmler Klaus
Weigand Bernhard
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Look Edward K.
Nguyen Ninh
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