Turbopump capable of balancing axial thrust

A turbopump comprising:

• a casing;
• a rotational shaft rotatably supported on the casing;
• and
• an impeller mounted on a side of the rotational shaft and pressurizing a fluid flowing into the impeller from an inlet of the casing, the impeller including:
• a front shroud,
• a rear shroud provided axially apart from the front shroud, forming a passage through which the fluid flows between the front shroud and the rear shroud, and forming an internal space with the casing, and
• a first protrusion protruding axially from the rear shroud and forming a clearance with the casing,
• a second protrusion protruding axially from the rear shroud and formed radially outward of the first protrusion,
• wherein axial thrust is controlled as the clearance formed between the impeller and the casing in a length direction of the rotational shaft varies according to a fluid pressure difference between front and rear sides of the impeller;
• wherein the casing includes an opposing surface facing the rear shroud and forming the internal space with the rear shroud, and a projection extending from a side of the opposing surface toward the second protrusion, and wherein the projection includes:
• a first extension extending axially forward from the casing, and
• a first end portion extending radially inward from the first extension,
• wherein the second protrusion includes:
• a second extension extending axially rearward from the rear shroud, and
• a second end portion extending radially outward from the second extension;
• wherein the second protrusion and the projection overlap each other in at least one of an axial direction and a radial direction, wherein the first end portion and the second end portion overlap each other in the axial direction, and the first end portion overlaps the rear shroud in the radial direction, wherein the fluid discharged from the impeller flows into the internal space through:
• a clearance between the first end portion and the rear shroud;
• a space formed by the first extension, the first end portion, the second extension, and the second end portion;
• and a clearance between the first extension and the second end portion.