Modeling of a numerical wall function for single-phase CFD-simulations within a LWR-containment

Safety analyses for nuclear power plants support manufactures and regulatory authorities in defining recommendations for emergency protection measures during accidents and to point out potentials for plant upgrades. To analyze the course of a loss of coolant accident (LOCA), in the future spatially resolved Computational Fluid Dynamics (CFD) models should be used increasingly to describe the gas flow mixing and the resulting pressure load for the containment. In such scenarios the modeling of the steam concentration in the gas mixture is necessary which requires a fine spatial grid discretization at the walls in CFD calculations. Today and in the foreseeable future only a limited grid size is possible within reasonable calculating times, due to the enormous temporal and spatial scales. Therefore the use of wall functions is necessary for such coarse grids to limit the information loss by modeling the boundary layers in the CFD calculation. As actual wall functions only cover the specifics of wall condensation inadequately, the Fully Integrated BoUndary Layer (short: FIBULA) wall function is developed and presented in this thesis. The FIBULA is derived from the governing equations for mass, energy and steam species and the Cebeci turbulence model and covers wall normal convection (suction) and buoyancy among other things. The numerical solutions of the FIBULA are prototypically provided in a lookup-table and implemented as wall functions for velocity and steam mass fraction in ANSYS CFX 16.Using the FIBULA velocity wall function in cases with suction and buoyancy, the momentum flux (wall shear stress) is now calculated more accurately on coarse grids. Furthermore the condensation rates are calculated independently from the near wall grid resolution up to a nondimensional wall distance of y${}^{+}$= 10 instead of y${}^{+}$ = 2 when the FIBULA is used as wall function in the wall condensation model. This confirms the concept of a numerical, parametrical wall function for CFD calculations considering condensation and buoyancy. The present work forms the basis for implementing a condensation specific wall function in LOCA CFD simulations in the future.