Study on the Applicability of k-ε Model to Nuclear Safety Problems

Two equation models such as k-ε model, which use the eddy-viscosity assumption, are widely used for industrial CFD applications. They offer a good compromise between complexity, accuracy and robustness. However, this model cannot be expected to perform well in the cases such as impinging jets, flow separation in a strong adverse pressure gradient, strongly swirling flows and buoyant driven flow. A Reynolds Stress model may show the improved prediction for rotating flow, secondary flow and buoyant flow by solving a transport equation for the independent Reynolds stresses. In this study, to assess the applicability of k-ε model to the typical nuclear safety problems such as the complex flow phenomena inside either the fuel assembly or the reactor vessel, simulation was performed using the commercial CFD software, ANSYS CFX R.14 and the predicted results with k-ε model were compared with the measured data and the computational results with more complex turbulence models. In this study, to assess the applicability of k-ε model to the typical nuclear safety problems such as the complex flow phenomena inside either the fuel assembly or the reactor vessel, simulation was performed using the commercial CFD software, ANSYS CFX R.14 and the predicted results with k-ε model were compared with the measured data and the computational results with more complex turbulence models. The major conclusion can be summarized as follows: (1) Complex flow pattern inside either the fuel assembly or the reactor vessel was locally different depending on turbulence models. (2) Prediction performance of k-ε model was at least equivalent to that of more complex turbulence models such as SSG Reynolds Stress model and SAS-SST model