US Patent 11629608 Axial flow turbine

To provide an axial flow turbine that can reduce circumferential pressure differences to reduce loss. The axial flow turbine includes: stator blades arrayed in the circumferential direction; and a diaphragm inner ring having an outer circumferential surface that interconnects the stator blades on their inner-circumference side and constitutes a wall surface of a main flow path. The outer circumferential surface of the diaphragm inner ring has depressed portions. Each depressed portion is formed in an area that is on the downstream side of a throat where the distance between a suction surface of one stator blade of a pair of adjacent blades and a pressure surface of other stator blade of the pair of adjacent blades becomes the shortest, and that lies in the circumferential direction within a range of a throat position on the suction surface of the one stator blade to a downstream edge position of the one stator blade. The area includes a downstream edge position of the outer circumferential surface in the axial direction.