Measurements of turbulent flows in a 2×2 rod bundle

Abstract

Abstract Turbulence models such as the k – ɛ model have been used in numerical predictions of turbulent flows in rod bundles. However, the validation of the turbulence models is not an easy task mainly due to the lack of experimental data on turbulent flows in rod bundles. In this study, we therefore measured three-dimensional velocity and turbulence intensities of water flows in a 2 × 2 rod bundle by using a particle image velocimetry (PIV) system. The diameter and pitch of the rods were 20 and 25 mm, respectively. The mean velocity ranged from 1 to 2 m/s. To measure the velocity distributions in the subchannels, the rod in the measurement region was made of fluorinated ethylene propylene (FEP) resin, the refractive index of which is almost the same as that of water. The time-averaged velocity and turbulent intensities at each measurement point were obtained from 10,000 instantaneous velocities. Time-series velocity distributions were also acquired to understand the motion of turbulence eddies in the subchannel. The experimental results indicate that the axial mean velocity along the line normal to the rod in the inner subchannel agrees well with the one-seventh power law, and that the velocity fluctuation in the direction normal to the rod wall becomes weak in the rod gap. Numerical simulations using the k – ɛ models were carried out to examine their applicability to the turbulent flow in the rod bundle. They gave reasonable predictions for the distribution of the axial velocity in the rod bundle and the flow rate in each subchannel.