This paper is intended to validate the numerical simulation tool, which is Unsteady Reynolds Averaged Navier-Stokes equation (U-RANS) approach with the Reynolds Stress Model using a commercial computational fluid dynamics code, by applying to the flow through a single short-elbow in the 1/10 and 1/3 scale water experiments simulating the Japan Sodium-Cooled Fast Reactor (JSFR) hot-leg piping. An additional objective of this paper is to investigate the effect of outlet condition at which the coolant overflows a partition wall in the upper part of an intermediate heat exchanger in the JSFR design.

The numerical results were in good agreement with the 1/10 and 1/3 scale experimental data indicating time-averaged velocity distributions, flow field visualization, and power spectral densities of pressure fluctuation. These comparisons can conclude that the U-RANS numerical simulation tool was validated with its applicability to a single short elbow flow. The numerical simulation has also shown that the unsteady flow fields in the short elbow flow, which was characterized by a cyclic secondary flow and the subsequent horseshoe vortex.

In this study, the effect of the outlet condition was also examined through the numerical simulation. At the outlet of the pipe, the simulation modeled the partition wall in the upper part of the intermediate heat exchanger, which has never been simulated in the experiments. The numerical simulation results were compared between with and without the intermediate heat exchanger at the pipe outlet in terms of the time-averaged velocity distribution, pressure fluctuation power spectral density, and so on. In the result, no significant difference between them was observed, so that it can be said that the effect of the outlet condition is negligibly small.

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