ESTIMATION OF THE FLUIDELASTIC INSTABILITY BOUNDARY FOR STEAM-GENERATOR TUBES SUBJECTED TO TWO-PHASE FLOWS

The estimation of tube wear due to vibration-induced tube-support impacting remains an important problem for operating steam generators. For fluidelastic excitation this requires a realistic model for the excitation fluid forces. Recently the authors (Mureithi et al., 2008) have presented detailed force measurements in a rotated triangular tube bundle subjected to air-water two-phase flow. The data provides new potential to designers to estimate expected fluid dynamic loads for two-phase flow conditions. In particular, the data may be used for quantitative estimation of critical velocities for fluidelastic instability the most important excitation mechanism for steam generator tube bundles. In the work reported here the fluid force field is employed along with the quasi-steady vibration stability model, adapted to two-phase flows, to model the two-phase flow problem and predict the critical instability velocity for a steam-generator U-tube subjected to non-uniform two-phase flow. The implication of the present model, with respect to improved estimation of tube wear is discussed in the paper.