An axial turbine includes a plurality of stages each comprising a plurality of stationary blades arranged in a row along the turbine circumferential direction and a plurality of moving blades in a row parallel to the stationary blades, each of the moving blade being disposed downstream of a respective one of the corresponding stationary blade in a flow direction of a working fluid so as to be opposed to the corresponding stationary blade. Herein, each of the stationary blades is formed so that the intersection line between the outer peripheral portion of the stationary blade constituting a stage having moving blades longer than moving blades in a preceding stage and a plane containing the central axis of the turbine, has a flow path constant diameter portion that includes at least an outlet outer peripheral portion of the stationary blade and that is parallel to the turbine central axis.
1. An axial turbine comprising:
a turbine rotor;
a stationary body inner wall located outside of said turbine rotor;
stationary blades provided on an inside of said stationary body inner wall; and
moving blades provided on said turbine rotor;
wherein a plurality of turbine stages is formed by said stationary blades and said moving blades, each of said turbine stages comprising said stationary blades adjacent to each other along a turbine circumferential direction and said moving blades adjacent to each other along the turbine circumferential direction, said moving blades being opposed to said stationary blades downstream of said stationary blades along a flow direction of a working fluid;
wherein the form in the meridional plane of said stationary body inner wall at which specific stationary blades are provided, is formed so that the working fluid having passed through the stationary blade outer peripheral portion becomes a flow along a central axis of the axial turbine, the flow having a restrained outward velocity component in the turbine radial direction, said specific stationary blades are stationary blades, the radial height at a stationary blade outlet is higher than the radial height thereof at a stationary blade inlet and are in the turbine stage having a moving blade front-end peripheral velocity Mach number larger than 1.0; and
wherein the relative inflow velocity with respect to the moving blade in the same turbine stage can be reduced lower than the sound velocity.