Development of Best Practice Guidelines for CFD in Nuclear Reactor Safety

Assessment of a common nonlinear eddy-viscosity turbulence model in capturing laminarization in mixed convection flows

“…Keshmiri et al [11,12] recently tested a wide range of RANS turbulence models and found that the k-ω-SST model [14] and the nonlinear eddy-viscosity model (NLEVM) of Craft, Launder, and Suga [15] completely failed to capture the laminarization phenomenon present in ascending mixed convection flows. This was a particularly significant finding, since these two models are commonly used in several commercial CFD codes and are "recommended" by various industrial best practice guidelines for a wide range of applications [13,16]. Indeed, contrary to expectation associated with some of the more recent turbulence models tested, it was demonstrated that the original "low-Reynolds number" model of Launder and Sharma [17] was, in general, the superior model.…”

Assessment of CFD Codes Used in Nuclear Reactor Safety Simulations

“…Conversely, doubling the mesh density, say from 200 to 400 in each coordinate direction, again keeping total runtime constant, means that the number of processors has to be increased by a factor of 16. Given these statistics, it is evident that the pursuit of quality and trust in the application of CFD to transient NRS problems, adhering strictly to the dictates of a Best Practice Guidelines philosophy of multi-mesh simulations [87], will stretch available computing power to the limit for some years to come. In the mid-term, compromises will have to be made: for example, examining mesh sensitivity for a restricted part of the computational domain or to a specific period in the full transient.…”

Transient computational fluid dynamics analysis of emergency core cooling injection at natural circulation conditions

“…This is less than the thermocouple uncertainty of ± 2.75 K. As a consequence, the medium-sized grid was chosen for the production calculations. It should be added that further grid refinement studies would be required to accurately quantify the solution errors as described by Mahaffy (2007). The comparison of calculations with first-order upwind and second-order high-resolution discretisation schemes are shown in Fig.…”

“…Following the OECD/NEA Best Practice Guidelines (Mahaffy et al, 2007), three hexahedral grids with increasing resolution were generated to perform sensitivity studies. In the first refinement step the number of elements was mainly increased in the cold leg.…”