Numerical simulation of the IAEA benchmark regarding ROCOM PTS test cases

The development, verification and validation of CFD codes in respect to Nuclear Power Plant (NPP) safety and design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. Therefore, a set of ROCOM CFD-grade test data were made available to set up an International Atomic Energy Agency (IAEA) benchmark, relating to PTS scenarios. The benchmark deals with the injection of the relatively cold Emergency Core Cooling (ECC) water which can induce buoyancy-driven stratification. Data obtained from the PTS experiment were compared in the study presented here with predictions obtained from CFD software. In addition a test case without buoyancy forces was selected to show the influence of density differences. Compared to the earlier study, significant progress was made in the development of CFD codes concerning both numerical aspects and physical modelling; here especially the treatment of turbulence. The CFX code (and turbulence modelling approaches) shows a respectable qualitative agreement with the experimental data. The dominant mixing phenomena have been treated correctly. Further, experimental and numerical analysis together seems necessary to better understand the flow behaviour under momentum driven flow conditions at low velocities.