Failure investigation of a Kaplan turbine blade

Abstract

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 nondamaged 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.