Fatigue of piston rod caused by unsteady, unbalanced, unsynchronized blade torques in a Kaplan turbine

The stresses in Kaplan turbine piston rod were analyzed to predict failure conditions based on the 3D unsteady flow through the Kaplan turbine. The results show that the predicted stress concentration position in the rod agrees well with the actual fracture position. The mean stress and the dynamic stress in the rod varied greatly with operating conditions. The dynamic stress reached 46.0 MPa at the high head low output condition, which caused the final rod failure. The mean of the dynamic stresses in the rod increase with increasing blade angle error, but the amplitudes decrease.