A Correlation Between Vibration Stresses and Flow Features of Steam Turbine Long Blades in Low Load Conditions

Abstract

The vibration stress of long steam turbine blades during low load operating conditions is examined in this paper. A series of experiments has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressure fluctuation. It is found that a steady pressure distribution over the blade tip is much to do with the unsteady pressure and fluctuation of the vibration stress. A precise investigation of unsteady wall pressure near blade tip explains the relationship between pressure fluctuation and the vibration stress, and reveals the existence of particular frequency which affects blade axial modes. Blade to blade flow mechanisms and aerodynamic force and properties during low load operating condition were investigated by a steady CFD simulation. FFT of aerodynamic force by another steady full arc CFD simulation provides various pattern of harmonic excitation which account for the behavior of vibration stresses well. The mechanism of the rapid stress increase and a step drop were examined by considering CFD results and measured unsteady pressure data together.