Patent ID: 8147180

Claim:
An axial flow turbine stage structure comprising: an annular diaphragm inner ring; an annular diaphragm outer ring arranged radially outside and coaxially with the diaphragm inner ring and separated from the diaphragm inner ring by an annular flow path interposed therebetween; a plurality of stationary blades arranged peripherally at intervals in the annular flow path and rigidly secured to the diaphragm inner ring and the diaphragm outer ring; and a plurality of moving blades rigidly secured to the outer periphery of a rotatable rotor and arranged peripherally at intervals respectively at axially downstream sides of the stationary blades; wherein a plurality of through holes are formed in the diaphragm outer ring so as to allow axial upstream side and axially downstream side of the stationary blades to communicate with each other, the cross sectional area of each of the through holes being varied in the axial direction of the turbine so as to be increased at an inlet thereof in order to allow fluid to flow through the through holes smoothly.