Axial turbine
View Patent ↗An axial turbine includes an upstream turbine stage that includes: a cover disposed at a distal end of an upstream bucket and opposed to an inner wall of an upstream diaphragm outer ring across a gap; and a downstream diaphragm outer ring that is disposed downstream of the upstream turbine stage and that has an inner peripheral-side end wall shaped into a flare. The inner peripheral-side end wall of the downstream diaphragm outer ring has a flare angle formed to be greater than a slant angle of an inner peripheral-side wall of the cover. In the axial turbine, the inner peripheral-side end wall of the downstream diaphragm outer ring is formed to have a meridional shape that has at least one inflection point between the upstream turbine stage and a downstream turbine stage and such that a tangent at the inflection point with respect to a steam flow direction has a positive gradient.
1. An axial turbine, comprising:
an upstream turbine stage including:
a plurality of upstream nozzles arrayed in a tangential direction between an upstream diaphragm outer ring and an upstream diaphragm inner ring;
a plurality of upstream buckets disposed on an outer peripheral side of a turbine rotor and arrayed in the tangential direction; and
a cover disposed at a distal end of at least one of the upstream buckets and opposed to an inner wall of the upstream diaphragm outer ring across a gap; and
a downstream turbine stage including:
a downstream diaphragm outer ring disposed downstream of the upstream turbine stage, the downstream diaphragm outer ring having an inner peripheral-side end wall shaped into a flare;
a plurality of downstream nozzles arrayed in the tangential direction between the downstream diaphragm outer ring and a downstream diaphragm inner ring; and
a plurality of downstream buckets disposed on the outer peripheral side of the turbine rotor and arrayed in the tangential direction,
the inner peripheral-side end wall of the downstream diaphragm outer ring having a flare angle formed to be greater than a slant angle of an inner peripheral-side wall of the cover,
wherein the inner peripheral-side end wall of the downstream diaphragm outer ring has a meridional shape curved into an S-shape that has an inflection point between the at least one of the upstream buckets and a front edge of the downstream nozzle such that a tangent at the inflection point with respect to a steam flow direction has a positive gradient.
2. The axial turbine according to claim 1 ,
wherein a radius position of the inner peripheral-side end wall of the upstream diaphragm outer ring, the radius position being opposed to an outer peripheral-side wall of the cover, is located outer side in a radius direction than a minimum radius position of the inner peripheral-side wall of the downstream diaphragm outer ring.
3. The axial turbine according to claim 1 ,
wherein the meridional shape of the inner peripheral-side end wall of the downstream diaphragm outer ring disposed between the upstream turbine stage and the downstream turbine stage is formed using a Bezier curve.