Numerical simulation of density driven flows (PTS)

Buoyancy driven mixing was investigated under simulated natural circulation conditions at the test facility ROCOM.
A transition matrix from momentum to buoyancy-driven flow experiments was selected for validation of the CFD software ANSYS CFX.
Buoyancy generated source and dissipation terms were proposed and introduced into the balance equations for the turbulent kinetic energy .
The results of the experiments and of the numerical calculations show that mixing strongly depends on buoyancy effects: At higher Froude numbers (Fr>1.5) the injected slug propagates in the circumferential direction around the core barrel. With lower Froude numbers (Fr<0.85) buoyancy effects reduce this circumferential propagation at lower mass flow rates and/or higher density differences. The ECC water falls in an almost vertical path and reaches the lower downcomer sensor directly below the inlet nozzle.