Numerical investigation of the cross flow fluidelastic forces of two-phase flow in tube bundle

This paper presents a numerical model to predict the unsteady fluid forces in a parallel triangular array subjected to two-phase flow. The numerical model utilizes the RANS formulation with aid of Spalart-Allmaras turbulence model, while the physics of the two-phase flow are modeled by the mixture model, drift-flux model, and the interfacial area concentration concept. This numerical model was utilized to simulate an air-water flow in tube array with various air void fractions. The predicted fluid force coefficients were compared with the available experimental data. The comparison showed a good agreement in terms of the force magnitude and phase at various reduced flow velocities. The obtained force coefficients were employed in a Hybrid analytical-CFD model representing a kernel of 7 tubes. The stability was investigated by studying the eigen values of the system as a function of the flow velocity. In addition, the stability thresholds were examined by simulating the same 7 flexible tubes kernel in cross flow using the direct flow/structure coupling. The predicted stability threshold obtained via these two models agrees very well with the experimental counterparts. They represent a lower bound for the stability data. These results are very promising and represent an important step towards an analytical frame work to accurately predict the stability of tube arrays.