Validation of a system code (GAMMA+) using standard k-ε model for multi-dimensional turbulent flows in various geometries

The GAMMA+ (General Analyzer for Multi-component and Multi-dimensional Transient Application) has been developed as a safety analysis tool for non-light water reactors (non-LWRs). Multi-dimensional turbulence modeling capabilities in system codes are essential for analyzing rapid transients in non-LWR nuclear systems with large cores operating in turbulent regimes. While some system codes employ the mixing-length model due to its implementation simplicity, the standard k-ε model is preferred for its superior accuracy and robustness in practical flow applications. This study presents the implementation of the standard k-ε model into GAMMA+, utilizing a square matrix that consists of the temporal differences of the pressure, the temperature, k and ε. Validation of the implemented model encompassed various single-phase flow configurations: flows in a pipe, a plate channel, and a backward-facing step with adiabatic wall conditions; forced convection flows including a pipe, an abruptly expanded pipe, and a backward-facing step with heat flux conditions; and natural convection flows in cavities with fixed temperature boundaries. Comparative analyses against experimental data, Direct Numerical Simulation (DNS) results, and Reynolds-Averaged Navier Stokes (RANS) simulations from well-known computational fluid dynamics (CFD) codes demonstrate the successful implementation of the standard k-ε model in GAMMA+ for multi-dimensional turbulent flow simulations.