Axial flow turbine

Abstract

To provide an axial flow turbine that can eliminate a circumferential velocity component of a leakage flow effectively, and attempt to collect motive power. A shroud of the axial flow turbine includes: an annular first protruding portion protruding toward the upstream side in a rotor's axis direction; an annular second protruding portion that is positioned on the outer side in the rotor's radius direction relative to the first protruding portion, protrudes toward the upstream side in the rotor's axis direction, and is longer than the first protruding portion; a circulating-flow generating chamber formed between the first protruding portion and the second protruding portion; and guide plates positioned in the circulating-flow generating chamber. The circulating-flow generating chamber is configured to generate a circulating flow such that part of leakage flow is allowed to collide with the tip surface of the first protruding portion to be directed to the outer side in the rotor's radius direction, and thereafter collide with the inner circumferential surface of the second protruding portion to be directed to the inner side in the rotor's radius direction. The guide plates are inclined opposite the rotor's rotation direction relative to the inward direction in the rotor's radius direction.