Leakage control structure

Claim 1

An improved leakage control structure for use in the fluid flow path of a turbine comprising: a diaphragm including a stationary nozzle ring upstream from an adjacent bucket wheel, the bucket wheel including a plurality of radially extending buckets; the buckets connected at their tip portions by at least one bucket cover circumferentially disposed about the bucket tips; a fluid leakage path defined by a pair of axially extending boundaries including the radially outer circumferential surface of the bucket cover and a radially inner, annular diaphragm portion downstream from the nozzle ring; first and second axial stepped portions formed on one of the pair of boundaries upstream of the connections and further including an annular radially extending side surface therebetween; a first annular fin extending radially from the other of said boundaries toward the first stepped portion and terminating in a tip portion closely adjacent the first stepped portion to form a clearance therebetween; a second annular fin extending radially from the other of said boundaries toward the second stepped portion and terminating in a tip portion closely adjacent the second stepped portion; and, the first and second annular fins axially positioned substantially upstream from the mid-point between the bucket leading and trailing edges.