Patent ID: 7736128

Claim:
A runner for a Francis-type hydraulic turbine, comprising a band, a crown and a plurality of blades having a curved shape and being attached to the band and the crown, each blade comprising an inlet flow dividing edge adapted to face upstream in the turbine and an outlet edge adapted to face downstream from the turbine towards a draft tube, the outlet edge extends between the crown and the band, and each blade comprising at least one stress relieving groove cut through the blade from the outlet edge adjacent at least one of the crown and the band, the groove presenting an opening across the outlet edge, the groove extending a predetermined distance from the outlet edge into the blade to transfer load from the outlet edge of the blade adjacent the at least one of the crown and the band to an end portion of the groove in the blade, and the groove extending obliquely with respect to a rotational axis of the turbine, wherein the groove in each blade comprises two stress relieving grooves, one of the stress relieving grooves located adjacent the crown and the other of the stress relieving grooves located adjacent the band.