Operational Modal Analysis of Francis Turbine Runner Blades Using Transient Measurements

Abstract

Abstract To prevent dynamic amplification or resonance during normal operation, which could result in large blade deformations and premature fatigue failure, structural mode frequencies are predicted using numerical models during design. However, such numerical models could benefit from validation using data obtained during commissioning. Here, we propose the use of asynchronous transient experimental measurements to identify regions where interaction between structural modes and Rotor-Stator Interaction (RSI) harmonics can be detected. From these regions, modal parameters can be estimated and compared with numerical predictions. This paper presents the methodology used to extract these modal parameters and estimate their uncertainties using data from a Francis runner recently commissioned by Hydro-Québec.