Abstract: A hydraulic turbine including: a passageway permitting liquid to pass through the turbine; a draft tube defining a portion of the passageway through which liquid normally flows in a vortex flow path during optimal turbine operating conditions; a rotatable runner mounted upstream of the draft tube and rotating about a central axis passing through the runner and extending into the draft tube; at least one nozzle head device positioned relative to the central axis of the runner and adjacent to an upper portion of the draft tube, the at least one nozzle head device has at least one nozzle from which a corresponding control jet of high velocity liquid is injected axially downstream of the runner and into liquid flowing into the upper portion of the draft tube during part load turbine operation, so as to mitigate breakdown of the vortex flow path.