Rotary kinetic fluid motors or pumps – With passage in blade – vane – shaft or rotary distributor...
Reexamination Certificate
1999-05-21
2001-02-06
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
With passage in blade, vane, shaft or rotary distributor...
C416S095000
Reexamination Certificate
active
06183193
ABSTRACT:
TECHNICAL FIELD
This invention relates to gas turbine engines and, in particular, to the Tangential On-Board Injection (TOBI) and Radial On-Board Injection (ROBI) nozzle that provides cooling air flow for turbine blades.
BACKGROUND OF THE INVENTION
In gas turbine engines, fuel is burned within a combustion chamber to produce hot gases of combustion. The gases are expanded within a turbine section producing a gas stream across alternating rows of stationary stator vanes and turbine rotor blades to produce usable power. Gas stream temperatures at the initial rows of vanes and blades commonly exceed 2,000° F. Blades and vanes, susceptible to damage by the hot gas stream, are cooled by air compressed upstream within the engine and flowed to the turbine components.
One substantial problem associated with such systems is the transfer of cooling air from stationary cavities within the engine stator to a rotor assembly for subsequent distribution to the interior of the rotor blades. For this purpose, the TOBI nozzle is a well-known device. In particular, an inlet of the TOBI nozzle receives compressed air emanating from the compressor and passes the cooling air through annually spaced passages that impart a swirling movement and directs the discharging stream of cooling air tangentially to the rotating turbine assembly.
The volume and direction of the cooling air are features of the effectiveness of its cooling capacity and its effect to the overall engine performance. It is important that only the correct amount of cooling air be utilized as any additional air could penalize efficiency of combustion while too little air would result in overheating of the turbine blades. Hence, ideally the TOBI nozzle will optimize the use of turbine cooling air.
A TOBI nozzle with adjustable air flow is disclosed in U.S. Pat. No. 4,708,588 entitled TURBINE COOLING AIR SUPPLY SYSTEM, issued to Schwarz et al on Nov. 24, 1987. According to this patent, the amount of cooling air flowable to the turbine blades of a gas turbine engine is made variable in response to the blade requirements by enabling the opening and closing of a portion of injectors of a tangential on-board injection system supplying cooling air to the turbine rotor assembly. Actuator means are provided to rotate an annular ring such that the orifices in the ring align with a number of injectors at conditions of maximum cooling flow requirements, and are in misalignment at conditions requiring a lesser air flow. The turbine cooling air supply system disclosed in this patent requires additional material weight for the annular ring and the actuator means, which are critical and sensitive to a gas turbine engine, particularly used in aircrafts. The control system for a dynamic air flow adjustment increases problems associated with operation stabilities. Overall, the manufacturing cost will increase significantly for such a dynamic adjustable system.
Decreasing the manufacturing costs is another concern. For this purpose, a simple structure for low cost fabrication is desirable. For example, U.S. Pat. No. 4,435,123, entitled COOLING SYSTEM FOR TURBINES issued to Levine on Jul. 2, 1985, discloses a TOBI nozzle fabricated as a unitary structure that is formed by investment casting and may be easily secured in position in the engine. However, the problem encountered with a unitary investment-cast TOBI nozzle is that the temperature differential encountered in proximity to the attachment structure adjacent the turbine stator vanes is more severe than the structural integrity of the casting can tolerate. To utilize the unitary unit, the attachment end of the unit would need to be made of a different material from the investment cast material so that it could tolerate the temperature stress limitations. Obviously, this would require a weldment of the TOBI nozzle which is not only expensive and difficult but it presents problems that should otherwise be avoided.
U.S. Pat. No. 4,526,511 entitled ATTACHMENT FOR TOBI, issued to Levine on Jul. 2, 1985, discloses an improved unitary structure using attachment means which are a shielding ring. The shielding ring is segmented into several pads, circumferentially spaced to permit thermal growth. This ring serves to shield the mounting flange from the high temperature air.
SUMMARY OF THE INVENTION
An object of the invention is to provide a TOBI nozzle with an air flow area that can be adjusted before the TOBI nozzle is installed for operation.
Another object of the invention is to provide a unitary structure of a TOBI nozzle that may be easily secured in position in a gas turbine engine.
A further object of the invention is to provide a TOBI nozzle that is supported by a stator assembly of a gas turbine engine in a cantilevered manner so that the TOBI nozzle is not subjected to thermal stresses caused by temperature differentials and thrust loads.
According to the present invention, a cooling structure adapted to be fixed to a stator assembly of a gas turbine engine between a source of cooling air and a rotor assembly of the engine for directing cooling air flow in a direction of rotation of the rotor assembly and further into the rotor assembly, comprises an annular body including radially spaced-apart outer and inner peripheries, a plurality of cooling air passages that are circumferentially spaced apart, and that are inwardly oriented in the direction of rotation of the rotor assembly for directing the cooling air flow, at least one but not all of the cooling air passages being left closed when the cooling structure is fabricated and the cooling air passages left closed being adapted to be selectively machined open to satisfy an air mass flow requirement determined after the cooling structure is fabricated.
Preferably, the cooling air structure further has an annular upstream wall and an annular downstream wall wherein the annular upstream wall extends outwardly to form a bell mouth that provides a smooth transition for the cooling air flow, and the annular upstream wall is mounted at an end of the bell mouth to the stator assembly to provide a cantilevered support for the cooling structure.
The cooling structure is preferably an integral single unit fabricated using a casting process.
In general terms, a TOBI nozzle according to one aspect of the invention comprises a plurality of passages for the intake of cooling air. The TOBI nozzle is fabricated such that a number of the passages are left closed. Before the TOBI nozzle is installed in the gas turbine engine for operation, one or more of the left closed passages may be selectively machined open, which depends on whether a cooling air mass flow enabled thereby does not satisfy a predetermined mass flow requirement. The cooling air mass flow enabled by the fabricated TOBI nozzle may be determined by a cooling air flow test. A ROBI nozzle could also be fabricated in a similar fashion.
This invention also provides a method for optimizing cooling air flow through a TOBI or ROBI nozzle for delivering cooling air to a turbine rotor assembly in a gas turbine engine, comprising: fabricating the TOBI or ROBI nozzle with a plurality of passages for intake of cooling air, the TOBI or ROBI nozzle being fabricated such that a number of the passages are left closed; determining cooling air mass flow requirements for the rotor assembly of a particular gas turbine engine; and selectively machining open one or more of the left closed passages as a result of the cooling air mass flow determination in the previous step.
The performance of the gas turbine engines is improved when the TOBI nozzle with adjustable flow area to optimize cooling air flow therethrough is used. The unitary structure of the TOBI or ROBI nozzle according to the invention can be easily fabricated using the casting process with low manufacturing cost, and is advantageously not subjected to thermal stress caused by temperature differentials. The adjustable flow area feature also enables the TOBI nozzle to be broadly applicable in different types of engines which have various cooling air mass flow req
Glasspoole David Frederick
Schraenen Yvan
Astle Jeffrey W.
Look Edward K.
Pratt & Whitney Canada Corp.
Rodriguez Hermes
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