Examination Method for Flow Fields in Piping Systems of Nuclear Power Plants Using Computational Fluid Dynamics

We developed an examination method that uses computational fluid dynamics (CFD) to investigate the effects of a complex pipe geometry on flow fields. Two kinds of pipe model with different geometries are simulated to test the developed method. The simulation models were split into several computational regions to reduce the computation time. The simulation results showed that the fluctuation of the flow rate depended on the pipe geometry, which qualitatively agreed well with the experimental results. The simulation results of one of the two models showed a swirling flow around the orifice with large fluctuations of the flow rate. It was found that the swirling flow caused velocity fluctuations in the recirculation zone around the tap positions, which resulted in the large fluctuations of the flow rate. We also investigated the mechanisms generating the swirling flow. The simulation results showed that the high velocity of the flow along the wall was caused by the valve and the bend pipe. The high-velocity flow then moves along the pipe wall of the tee, which causes the flow to swirl. These results show that the developed method can be used to evaluate the flow fields in piping systems.