Closed circuit steam cooled bucket

Abstract

In a gas turbine bucket having a shank portion, a radial tip portion and an airfoil having leading and trailing edges and pressure and suction surfaces, and an internal fluid cooling circuit, an improvement wherein the internal fluid cooling circuit has a serpentine configuration including plural radial outflow passages and plural radial inflow passages. The radial outflow passages, in one example, are shaped to have aspect ratios of about 3.3 to 1 and Buoyancy Numbers of <0.15 or >0.80. A method of determining a configuration for steam cooling passages for a bucket stage in a gas turbine is also provided which includes, in one example, the steps of: a) determining combustion gas inlet temperature and mass flow rate of combustion gases passing through the gas turbine stage; b) taking into account Coriolis and buoyancy secondary flow effects in the steam coolant caused by rotation of the bucket stage; and c) configuring the radial outflow coolant passages to have a size and shape sufficient to produce aspect ratios of about 3.3 to 1 and Buoyancy Numbers in the radial outflow passages of <0.15 or >0.80.

Dependencies are inferred from the claim text.