TURBULENT STRUCTURE STUDY ON FLOW-INDUCED VIBRATION IN TEE JUNCTION PIPE

Flow-Induced Vibration (FIV) caused by turbulent flow inside a pipe could lead to fatigue failure with shell mode vibration. Our previous study investigated the excitation source of the FIV for tee junctions experimentally to understand the FIV mechanism and provided Power Spectral Density (PSD) profiles of pressure fluctuation. In the.present study, "experiments were performed with more extensive measurement points for both 90- and 45-degree tees to understand a more detailed mechanism. PSD plots were provided, featuring different pressure fluctuation characteristics at each measurement point among both angle tees. It also emerged that the PSD level declined with increasing distance from the impingement point. Unsteady Computational Fluid Dynamics (CFD) simulations with the Large Eddy Simulation (LES) model were also performed to understand the turbulent structure for the tee junctions. The frequency characteristic of the simulated pressure fluctuation effectively matched those of the experiments at each measurement point, which implies that CFD simulation with an LES model could reveal reasonable predictions of the FIV excitation source for tee junctions. Simulation results showed that the relatively large vortex shed from the branch pipe impinged periodically on the main pipe bottom and the large vortex was dissipated downstream. These vortex behaviors would be the main mechanism generating the FIV excitation source.