STV-16 Calculating Fluidelastic Instability of U-Tubes Near Inlet Nozzles

K. J. Farrell

The challenges of a rules-based vibration screening in Xist® have often led to excessive conservatism for U-tubes positioned near the inlet nozzle. In this study, we simulated shellside diabatic flow over the U-bend portion of the bundle for a number of nozzle locations using computational fluid dynamics (CFD). Using the simulation results with an idealized mode shape for the U-span, we computed the fluidelastic instability (FEI) ratio and compared the results to those generated by Xvib® and Xist. Our FEI values closely matched those from Xvib and were substantially lower than those from Xist. The favorable comparison with the finite element results of Xvib validated our synthesized mode-shape approach because Xvib directly solves the discretized equation of motion for the eigenvalues and eigenvectors. We generalized the analysis procedure to improve the Xist 6.0 vibration screening procedure for TEMA E and J shells when the inlet nozzle is adjacent to the U-bend region. Ratios of heat transfer to pressure drop were nearly independent of the relative position of the nozzle and U-bend for typical flow rates.