Francis-type hydraulic turbine wheel equipped with a tip-forming member, and method of reducing fluctuations using such a wheel

A Francis wheel for a turbine or a hydraulic turbine pump, the wheel comprising:

• a plurality of vanes arranged on a crown and having a tip-forming member attached to a central region of the crown radially inside the vanes, the crown defining a wet surface for guiding a flow passing between the vanes, the tip-forming member having a radial wall defining an internal volume, the radial wall being provided with at least one opening for diverting a fraction of the flow passing between the vanes towards the internal volume of the tip-forming member, the tip-forming member including a frustoconical annular skirt which encloses the internal volume of the tip-forming member and towards which the fraction of the flow is diverted, and in that at least one fin is arranged inside the internal volume of the tip-forming member and extends as far as an edge of the skirt delimiting an outlet opening from the tip-forming member for the fraction of the flow that is diverted towards the internal volume, the at least one fin modifies a flow path of the fraction of the flow within the internal volume to direct the fraction of the flow through the outlet opening;
• a plurality of spaced openings in the tip-forming member for diverting a fraction of the flow and wherein a sum of areas of entrance regions into the plurality of openings for diverting the flow is greater than or equal to 25% of an area of an external surface of the tip-forming member;
• and
• wherein a vertical position of the tip-forming member in relationship to the crown is fixed.

A method of reducing fluctuations in a flow interacting with a wheel of a hydraulic machine, comprising steps of:

• causing a fraction of the flow to penetrate into the internal volume of a tip-forming member belonging to a Francis wheel for a turbine or a hydraulic turbine pump, the wheel including a plurality of vanes arranged on a crown and having a tip-forming member attached to a central region of the crown radially inside the vanes, the crown defining a wet surface for guiding a flow passing between the vanes, the tip-forming member having a radial wall defining an internal volume, the radial wall being provided with at least one opening for diverting a fraction of the flow passing between the vanes towards the internal volume of the tip-forming member, the tip-forming member including a frustoconical annular skirt which encloses the internal volume of the tip-forming member and towards which the fraction of the flow is diverted, and in that at least one fin is arranged inside the internal volume of the tip-forming member and extends as far as an edge of the skirt delimiting an outlet opening from the tip-forming member for the fraction of the flow that is diverted towards the internal volume, the at least one fin modifies a flow path of the fraction of the flow within the internal volume to direct the fraction of the flow through the outlet opening, and a plurality of spaced openings in the tip-forming member for diverting a fraction of the flow and wherein a sum of areas of entrance regions into the plurality of openings for diverting the flow is greater than or equal to 25% of an area of an external surface of the tip-forming member;
• diverting the flow through the at least one opening;
• modifying a path of the flow using the at least one fin within the tip-forming member;
• directing the fraction of the flow to exit from the tip-forming member through an axial opening in such a way that fraction of the flow is directed as it exits from the tip-forming along an axis parallel to an axis of rotation of the wheel;
• and
• fixing the tip-forming member in a vertical relationship to the crown.