Theoretical investigation of fluidelastic instability of a rotated triangular tube array in two-phase flow

Fluidelastic instability of a tube array is extremely important to the security of a nuclear power plant. Lots of experimental analyses were conducted on the fluidelastic instability of a tube array subjected to two-phase flow in the transverse direction. Streamwise fluid-elastic instability of a tube array has been ignored for a long time until recently observations of streamwise tube failure in a steam generator in the USA. However, there are a few theoretical analysis to calculate the critical velocity. Therefore, the streamwise fluidelastic instability of a rotated triangular tube array was studied in this paper. A mathematical model of a tube array with seven tubes was established. A program based on the model was written, and an experiment was conducted to verify the program. The numerical results were in good agreement with the experimental data. The critical velocity of streamwise fluidelastic instability considering the two-phase flow was determined by the eigenvalue analysis. The numerical results illustrate that void fraction has an obvious effect on the critical velocity and the instability mode of the streamwise fluidelastic instability of a tube array. The influences of tube natural frequency were also investigated within void fraction range from 0 to 80%. The results indicate that void fraction and tube natural frequency are the key factors in streamwise fluidelastic instability.