A numerical tool has been implemented at Arcelor Research to evaluate the influence of different process parameters on the stability of the flow in the CC mould and on steel cleanliness. The key parameter to improve steel cleanliness is hydrodynamics. It is generated in the mould and naturally unsteady, even if maintaining the process parameters at a constant value. In order to maintain a stable mould flow that allows inclusions removal while avoiding the creation of new defects, process parameters should be optimized or some actuators should be proposed and adapted. The new numerical tool affords a better understanding of the phenomena in the CC mould when some modifications or variations are imposed.