Scaling and connection with computational fluid dynamics

Abstract

Scaling is used in the nuclear industry to support the design of test facilities and provide experimental results that are related to the full-scale prototype (nuclear power plant) during postulated accident scenarios. Test results are used to support the validation of the thermal-hydraulics system codes and developed models. Test facilities sizes and complexity span from basic and separate effect tests to integral effect tests. Computational Fluid Dynamics (CFD) can provide more detailed information about velocity and temperature fields than thermal-hydraulics system codes. However, practical CFD domain sizes are limited by the number of control volume cells - resulting in demanding memory and computational time requirements. Validated CFD models, based on well-instrumented basic and separate effect test results, are currently used only to support the development of small portions of sub-systems (modules) of nuclear power plants. Further development of CFD software compatible with high-performance computing platforms will enable applications of CFD for bigger and more complex domains such as portions, or entire, integral test facilities. In combination with scaling analysis methods developed for scaling integral test facilities in the nuclear industry, validated CFD models will be able to support improvements of the thermal-hydraulics system codes. The paper addresses the connection between the derivation of dimensionless groups (based on nondimensionalization of equations used for CFD) and hierarchical and time scaling approaches used to develop test facilities. This helps the validation process and scalability of CFD codes when they are applied to the reactor scale. Several examples related to single-phase flows present how CFD is used to support scaling and extrapolation of distorted test results.