Deformation and Stress of a Runner in Large Francis Turbines Under Wide-Load Operating Conditions

During partial-load operation, hydroelectric units are frequently subjected to hydraulic vibrations caused by pressure fluctuations within the turbine. These vibrations can result in deformation of the runner blades and, in severe instances, lead to crack formation. Over the years, research efforts have primarily focused on specific operating conditions, with relatively insufficient attention paid to the study of operational stability under broad-load operation. This study investigates the recurrent occurrence of crack damage in the runner blades of a Francis turbine installed at a major hydropower station. The issue emerges in response to the operational requirements of a modern power system, which mandates wide-load operation across varying heads (154.6 m, 197 m, 229.4 m) and guide vane openings (10%, 25%, 50%, 70%, 100%). To inform the development of optimized operational control strategies, this work examines the deformation and von Mises stress distribution patterns on the runner blades under these wide-load conditions. The findings reveal that the maximum blade deformation predominantly occurs in the mid-section of the trailing edge under most operating scenarios, while the peak von Mises stress consistently appears near the band at the trailing edge. Both peak deformation (1.99 mm) and peak von Mises stress (170.92 MPa) were observed at the maximum head (229.4 m) under 100% guide vane opening. Notably, significant deformation and stress levels were also encountered at openings below 25% under low-head conditions. On the basis of the research results, suggestions for ensuring the safe and stable operation of power station units under wide-load conditions were proposed.