1. Field of the Invention
This invention relates to a variable area turbine nozzle and, more particularly, to a variable area turbine nozzle for use in a multistage turbine engine.
2. Description of the Related Art
In the design of gas turbine engines, the flow through the engine is varied by a plurality of stator vanes and rotor blades. Typically, these vanes and rotors are fixed at particular positions and angles in order to accomplish the appropriate flow function through the various stages of the turbine engine. There have been attempts to vary the flow path through the turbine engine by varying the angle of the vanes to improve the efficiency and operation of the turbine engine.
U.S. Pat. No. 4,135,362 issued to Glenn discloses a split-shaft gas turbine engine having a variable vane and support assembly to provide a flow path between the last stage of a gas generator and the first stage of a low-pressure turbine. The '362 patent discloses the use of a variable vane having a hollow passage to allow a support strut to pass therethrough for supporting the vane and the inner strut. The strut is also hollow which provides a passage for cooling air to the inner strut of the turbine in the vicinity of the variable vane. The rotation of the vane is through sleeve bearings. The '362 design is complex and does not address prolonged field operation.
U.S. Pat. No. 2,819,732 issued to Rapaetz discloses a variable area turbine entrance nozzle having moveable vanes which are rotated in the middle stage of a turbine engine. The moveable vanes are sealed against the outer casing and rotor to prevent any leakage of air therethrough. Again the '732 design is not for prolonged field operation.
What is needed is a design which can vary the vane angles of a stage of a turbine engine which provides long life in the field before overhaul. Such long life should provide up to 25,000 hours of running time between repair intervals.