Effect of part-load operation and high-pressure in condenser on the pressure fluctuation frequency of the steam turbine to analyze L-2 blade failure

Abstract

Steam turbines are indispensable in large-scale power generation due to their high efficiency and long service life. However, the low-pressure stages are particularly prone to flow-induced vibrations under off-design conditions. In a 315 MW steam turbine operating at a thermal power plant, multiple intermittent failures were reported in the L-2 stage blades. To determine the root cause, many steady and transient three-dimensional CFD simulation were conducted under varying load levels and condenser pressures. Pressure fluctuations caused by vortex shedding were analyzed using Fast Fourier Transform (FFT) and compared against the blade's natural frequency obtained from modal analysis. The simulations suggest that the simultaneous occurrence of part-load operation and increased condenser pressure may be associated with strong vortical excitations propagating into the L-2 stage. The dominant frequencies, approaching approximately 190 Hz, closely match the blade's natural frequency, promoting a possible resonance-type response. The findings help identify critical operating regimes and provide practical insight for preventing fatigue-related failures.