Faced with the present transformation of the world economy, steam turbine manufacturers are seeking ways to remain competitive in their respective markets. Having longer Low Pressure (LP) blades and seeking for higher rotating speeds have always been two effective methods to improve the Steam Turbine efficiency, therefore to reduce steam consumption and related plant costs. Both trends have increased the risk of failure for forced response due to the occurrence of resonance or to the decrease of alternating stress margins. Because of large uncertainties in the estimation of friction damping and aerodynamic excitation, the prediction of dynamic response of the long blades in the LP section is still a challenge for the analytical tools; therefore, expensive activities for experimental validation are usually required. In order to reduce design costs and time, a set of tools has been developed and validated using the test data collected during a full-scale test vehicle campaign in steam (Low Pressure Development Turbine - LPDT). In this study, the validation activity related to the blade response due to nozzle stimulus is reported. As a first step, a steady state CFD analysis was performed at the operating conditions where significant response was observed, caused by the resonance with the Nozzle Passing Frequency (NPF). Then, an unsteady CFD analysis of the bucket blade was conducted considering the perturbation due to the nozzles. Subsequently, the computed unsteady pressure distribution on the blade airfoil was mapped onto a finite element model and forced response analyses were performed to estimate the bucket dynamic response. The predicted response was compared against measured test data and good correlation was found.
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