ON THE IMPACT OF SIMULATION APPROACHES ON THE PREDICTED AERODYNAMIC DAMPING OF A LOW PRESSURE STEAM TURBINE ROTOR

The determination of the aerodynamic damping is a major task in predicting flutter stability and therefore safety margins for turbine operation. Throughout the current work the energy method is employed to predict the aerodynamic damping for a last stage rotor blade numerically. The focus is put on the prediction of the aerodynamic damping with different traveling wave mode representations and on the influence of the blade fixation at the root. The Fourier transformation-method, the influence coefficients-method and a direct traveling wave mode calculation are employed. The investigated rotor geometry was taken from the open literature, a root was designed and an iterative process was installed to determine the cold blade geometry. It became apparent, that the influence-coefficients-method is capable of predicting the overall stability curve computationally efficient, whereas the Fourier-transformation-method showed advantages in the identification of the least stable point for a finer mesh. Nevertheless, all methods predicted a potential flutter risk for the current operating point. The influence of the additional blade root with a completely fixed support on the aerodynamic damping is minor.