Failure investigation of a Kaplan turbine blade

In this paper, an uncommon failure of a Kaplan turbine blade has been analyzed. After the monitoring system detected a sudden increase in vibration levels, the turbine was inspected. The inspection showed that a large crack occurred on one blade starting from the leading-edge side root hole. Moreover, the tip of the blade was also found broken. A comprehensive analysis of the crack surfaces, broken parts and the vibration data revealed a fatigue problem probably caused by rubbing between the blade and the nearby wall. The effect of contacts on the stress distribution of the blade was investigated through a numerical model of the turbine blade. To validate this numerical model an experimental modal analysis was done on a non-damaged blade and the results showed a good agreement with the numerical results. Stress distribution analysis showed that when applying a contact force, the stress at the leading-edge root hole increases drastically. Therefore, experimental evidences as well as numerical simulations confirm that the crack occurred due to rubbing between the blade tip and the nearby wall. •A large crack was discovered in a Kaplan turbine blade.•A failure investigation of the crack was performed.•Experimental research on the dynamic behavior of a Kaplan turbine blades was carried out.•A numerical model of the Kaplan turbine blade was validated and used for studying the origin of the crack.•Rubbing between the blade and the stationary wall was demonstrated to be the cause of the crack appearance.