Hydraulic Stability Problem of Francis Turbine

When Francis turbine operates in the off design condition, the flow in the runner will be separated and vortex will appear. It will cause vibration at the units and adjacent concrete structures. Fatigue cracks of parts may be created. Recently, the hydraulic stability problem has been concerned extensively along with the increasing of specific speed and capacity or other cases(the head variation in a large range, the operating condition is off the design point, poor manufacturing quality and insufficient air admission, etc.). The preliminary analysis on hydraulic stability of Francis turbine has been carried out,and some suggestions have been proposed in this paper.