Abstract
Knowledge of turbulent flows in rod bundles is important for improving safety analysis codes for nuclear reactors. In this study, we therefore measured liquid velocity in single-phase and bubbly flows by installing a small LDV probe into a rod of a 2×2 rod bundle. The local time-averaged velocity and turbulent intensity were obtained from 10,000 instantaneous velocities at each measurement point. The Reynolds shear stress in the rod gap was evaluated from velocity data measured from two directions. The experimental results showed that (1) the turbulence is enhanced due to the presence of bubbles at a low liquid volume flux, whereas the turbulence modification due to bubbles is not clear at a high liquid volume flux, and (2) the Reynolds shear stress can be evaluated by measuring velocities from two different angles between the horizontal plane and the optical axis of the LDV not only for single-phase flow but also for bubbly flow.
