Patent Application
20080219855
This application claims priority to German Patent Application DE 102007012320.7 filed Mar. 9, 2007, the entirety of which is incorporated by reference herein.
This invention relates to a turbine blade having a curved and converging micro-turbine nozzle in its blade root which originates at a cooling-air chamber in the blade root and issues downstream opposite to a direction of rotation of a turbine rotor wheel.
On a gas-turbine engine known from specification U.S. Pat. No. 6,290,464 B1, the blade roots of the turbine blades of the turbine rotor wheel of the first stage are each provided with a cooling-air duct which branches off a cooling-air chamber and issues downstream and through which part of the cooling air fed into the turbine blade is supplied to the next turbine stage. This cooling-air duct, which originates at a cooling-air chamber in the blade root, converges and continuously curves towards the air exit side such that the cooling air exits opposite to the direction of rotation of the turbine rotor wheel. Because of the curvature and convergence of the cooling-air duct resulting in continuous deflection of the cooling air opposite to the direction of rotation of the rotor wheel and the expansion of the cooling air, the cooling air produces power. The micro-turbine so provided in the blade roots is an additional propulsive element for the first turbine rotor wheel. Simultaneously, the cooling air is cooled according to the turbine principle, thus being available with improved cooling effect for the cooling of the turbine wheel of the following turbine stage.
Manufacture of a cooling-air duct of such curvature and convergence towards the air exit side in the blade roots is, however, problematic in that the very slender and also brittle ceramic cores applied in precision casting of turbine blades by the lost-wax process for forming the very thin cooling-air ducts are liable to failure, rendering manufacture by conventional precision casting processes impossible. Also, manufacture of the converging and curved cooling-air duct by cutting machining directly in the blade root is only possible to a limited extent and confined to larger diameters, especially as the smaller diameter is formed by the exit opening. Directly in the blade root, the known casting and mechanical machining processes are only appropriate for the manufacture of cooling-air ducts with larger diameter. However, such larger diameters will entail high cooling-air losses and decrease the efficiency of the turbine. Disposing the micro-turbine nozzles in turbine holding or cover plates, which is also proposed in specification U.S. Pat. No. 6,290,464, is restricted to the design provided for these plates. This bears on the efficiency of the micro-turbine nozzles.
It is a broad aspect of the present invention to provide the micro-turbine nozzle in the blade root such that small duct cross-sections and, thus, low cooling-air losses and improved engine efficiency can be obtained.
The essence of the present invention is that the turbine blade does not form one part with the micro-turbine nozzle, but that a passage duct with large diameter is formed in the area of the blade root provided for the micro-turbine nozzle, which extends from the cooling-air chamber to the downstream side of the blade root, and that said passage duct is produced by drilling, machining or integrally in the casting process, and that a separately produced micro-turbine nozzle element is partly or also completely fitted into this duct, has a converging nozzle with a cross-section which is minimised in size and is flexible, i.e. is adapted to the required operating conditions.
The known precision casting processes for the manufacture of turbine blades whose blade root forms one integral part with the micro-turbine nozzle, only allows large nozzle cross-sections which affect the efficiency of the turbine. An essential advantage of the turbine blade in accordance with the present invention lies in the flexible cross-sectional size of the micro-turbine nozzle which is adaptable to the respective operating conditions by way of a separately produced micro-turbine nozzle element fitted into the passage duct. Other than in the state of the art, the nozzle cross-section is reducible, as a result of which an efficiency-reducing decrease of the pressure of the cooling air supplied is not necessary. The cooling-air mass flow introduced into the space between the two turbine rotor wheels can be set as low as necessary, thereby avoiding cooling air losses and a reduction of turbine efficiency.
The turbine blades 1 are produced in a casting process, actually with passage ducts 6 having a sufficiently large diameter. With its correspondingly large diameter, the ceramic core for casting the passage duct 6 will have adequate strength and will, therefore, not be damaged or destroyed during casting. The passage duct can also be produced by drilling the blade root. The micro-turbine nozzle element 7 is a separate component which is produced in a simple manner, for instance, in a cutting shaping process from a blank which is formed by machining or in a non-cutting shaping process, or by injection molding, or by other methods, and is fitted completely or, as shown here, partly into the passage duct 6 and attached therein by known joining processes, such as brazing. The flow area of the duct 9 of the nozzle element 7 according to the present invention is no longer dictated by the passage duct 6, and can be selectively varied as desired.
Besides reduced manufacturing cost, the now freely selectable size of the flow area of the micro-turbine nozzle allows the cooling air supply to the following turbine stage to be optimally and variably set in accordance with the required operating conditions, at least without unnecessary cooling air losses.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 012 320.7 | Mar 2007 | DE | national |
