This invention relates to a blade for a turbine, the blade being added onto a disk in the turbine and being cooled by internal air circulation.
An axial turbine stage is composed of a grid of fixed blades called a distributor and a grid of mobile blades called a wheel. There are single block wheels in which the blades and the disk are all included in the same part. There are also wheels with add-on blades in which the blades and the disk are mechanically assembled together, usually by tripod fittings.
When the wheels operate at high temperature, the blades have to be cooled. This cooling may be done by using air, taken for example from the compressor outlet and routed inside the blades through their attachment to the disk. Cooling air penetrates through the dovetail root of the blade, for example to exit through the opposite end and through one of its faces.
Cooling air drawn off at the compressor outlet is injected through an end plate held in contact with the upstream face of the disk to make the air circuit leak tight. To achieve this, the end plate is often held in place on the disk by a system of hooks called claws.
The hooks also perform another function. They make the cooling air moving towards the compartments rotate at a speed equal to the rotation speed of the turbine rotor. The cooling air then arrives in front of the compartment turning at the same speed as the compartment and enters into the compartment without any secondary effects.
However, these hooks have the disadvantage that they are expensive and have a relatively short life. Therefore, it would be attractive to be able to eliminate them. However, tests have shown that turbine blades are not cooled as well if these hooks are removed.
Document WO-A-99 47792 divulges a turbine blade, the blade having a dovetail root used to fix it in a compartment of the turbine disk. The blade has an internal air cooling circuit comprising air inlet means located on the dovetail root of the blade and facing the compartment, and air outlet means. The dovetail root of the blade is provided with a device for directing cooling air for the blade. This device also evacuates cooling air after it passes inside the blade. The device separates cooling air circuits entering into the blade and exiting from the blade.
Document GB-A-1 605 282 divulges a blade for a turbine, the blade being provided with a dovetail root through which it is added on into a compartment of a disk in the turbine. The blade has an internal air cooling circuit composed of channels, comprising air inlet means located on the dovetail root of the blade and facing the compartment, and air outlet means located at the end of the blade. The dovetail root of the blade is provided with a cooling tube, through which cooling air is brought in from the intake air collector as far as the air inlets.
Document U.S. Pat. No. 4,348,157 divulges a turbine blade added onto a disk through a dovetail root. The blade is provided with an internal air cooling circuit comprising an air inlet orifice. The air inlet orifice is not located on the dovetail root of the blade facing the housing compartment for this dovetail root, but it is in the connecting part between the dovetail root and the blade, in other words in the leg. Passages are provided to bring the cooling air as far as the blade air inlets. These passages may comprise deflectors.
Document U.S. Pat. No. 4,178,129 divulges a turbine blade cooling system by air circulation. Each blade has a dovetail root used to fix it into a compartment of a turbine disk. The blade is provided with an internal air cooling circuit including air inlet means located on the dovetail root of the blade. The cooling air is sent either into a cooling air supply chamber into which the cooling channels open up, or directly into the leading edge channel through a Pitot receiver.
According to document WO-A-99 47792 mentioned above, the incoming cooling air is brought in through a tube-shaped device communicating with the orifices in the cooling channels. The tube-shaped device may be provided with orifices with a size adapted to the orifices in the channels or orifices almost the same width as the compartment. In both cases, it is impossible to prevent the formation of a vortex.
According to document GB-A-1 605 282 mentioned above, an air cooling tube is provided adapted to the width of the compartment. Therefore, it is impossible to prevent the formation of a vortex.
With reference to document U.S. Pat. No. 4,348,157 mentioned above, air arrives directly on a face in which a hole is drilled, which leads to the same conclusion.
With reference to document U.S. Pat. No. 4,178,129 mentioned above, air arrives either directly in a hole (through a Pitot receiver) or directly on a face in which holes are drilled, which leads to the same conclusion.
The inventors of this invention discovered the reason for the drop in cooling efficiency when hooks or claws are eliminated, and they have found a solution to this problem.
The inventors reached the conclusion that when air is no longer guided as far as the compartment, cooling air reaches the compartment at a lower rotation speed than when it is guided. Air is then scooped up and rotates in the compartment forming a vortex as shown in
This invention provides a means of overcoming this problem whenever it is present in a turbine.
Its purpose is a turbine blade, the blade being provided with a dovetail root used to add it into a compartment of a turbine disk, the blade being provided with an internal air cooling circuit comprising air inlet means located on one face of the dovetail root of the blade in front of said compartment, and air outlet means, characterised in that said face of the dovetail root of the blade is equipped with a deflector comprising at least one fin used to guide the cooling air circulating in the bottom of the compartment to regularise the air flow towards the air inlet means.
The presence of such a deflector on the face of the dovetail root of the blade in which the air inlet means are located provides a means of preventing the formation of a vortex.
The deflector may form an integral part of the blade.
The deflector may be an add-on element on the dovetail root of the blade and may be provided with access means to the air inlet means. The access means may comprise at least one calibrated hole.
The fin may be straight or inclined with respect to the main axis of the blade.
According to one advantageous embodiment, the deflector comprises at least one fin used to guide cooling air entering the compartment and at least one fin that guides discharged air towards the centre of the compartment.
The invention will be better understood, and other advantages and special features will become clear after reading the following description given as a non-limitative example, accompanied by the attached drawings in which:
Unlike the blade described in
The presence of a deflector on the lower face of the dovetail root of the blade prevents the formation of a vortex and the creation of a pressure drop.
The deflector may be a part added onto the blade dovetail root by welding or brazing. As a variant, the deflector may form an integral part of the blade.
Cooling air is drawn off at the bottom of the chamber and is accelerated through a series of injectors like injector 31. This air then passes through holes, such as hole 32 drilled on the end plate 17, and then moves up towards the bottom of compartments as shown by the arrows in
In
In
The deflector may also comprise one or several curved fins to guide cooling air along a more variable path.
The deflector 60 in
The same is true for deflectors 70, 80 and 90 shown in
The invention provides a static pressure gain at the centre of the compartment to overcome about 75% of the pressure drop that would have occurred without the add-on arrangement. This improved supply of cooling air to the blade reduces the average temperature of the blade depending on operating conditions and consequently extends its life.
Number | Date | Country | Kind |
---|---|---|---|
01 05289 | Apr 2001 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FR02/01325 | 4/17/2002 | WO | 00 | 10/14/2003 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO02/086291 | 10/31/2002 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4178129 | Jenkinson | Dec 1979 | A |
4348157 | Campbell et al. | Sep 1982 | A |
4626169 | Hsing et al. | Dec 1986 | A |
4820123 | Hall | Apr 1989 | A |
5403156 | Arness et al. | Apr 1995 | A |
6059529 | Schiavo | May 2000 | A |
Number | Date | Country |
---|---|---|
38 35 932 | Apr 1990 | DE |
1 605 282 | Dec 1987 | GB |
99 47792 | Sep 1999 | WO |
Number | Date | Country | |
---|---|---|---|
20040115054 A1 | Jun 2004 | US |