The Francis wheel, with blades forming fluid flow ducts round a central axis of rotation, has intermediate ribs (6) between pairs of adjacent blades, each rib lying basically parallel to the direction of the flow and perpendicular to the blades. The ribs extend between the blade leading (2a) and trailing (2b) edges to form a circular assembly with blade sections (2c, 2d) on either side of it, so that the fluid is separated into inner (E1) and outer (E2) flows.
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