An investigation of time lag causing fluidelastic instability in tube arrays

This paper presents an in-depth study of the time lag in a normal triangular tube array subjected to cross-flow. A Computational Fluid Dynamics (CFD) model was developed to simulate the flow inside the tube bundle. A moving tube with a prescribed sinusoidal oscillation was utilized for a range of reduced flow velocities from 1 to 40. An attempt was made to capture the temporal variation of the flow channel dimensions. The results were studied and interpreted in the framework of the flow cell model of Lever and Weaver. The flow channel dimensions were then used to extract the channel area perturbation amplitude and phase lag.The computed time lag was used in tube stability simulations and a stability threshold was computed for a mass damping parameter range of 10–200. Using the proposed time lag in a time domain implementation of the flow cell model yielded a better prediction of the stability threshold. However, the results show that the original time lag postulation by Lever and Weaver had captured the main essence of the time lag predicted in this study. The difference lies in the time quantification variation along the flow due to the additional influence of the flow separation in the upstream tube.