Irreversible energy losses of flow through porous and perforated plates

For a realistic numerical simulation of a hypothetical core disruptive accident (HCDA) it is often important to take into account perforated plates. Inclusion of the plates drastically changes the loading pattern of the containment and a significant amount of the fluid's energy is dissipated as it passes through the plates. At present the PISCES-2DELK program simulates the perforated plates explicitly by defining the geometric boundary and the fluid passages. This boundary is attached to a movable structure, thereby ensuring the correct fluid-structure interaction. Equally important as the correct fluid-structure interaction is the energy dissipation, associated with fluid flow through the narrow passages. This aspect will be treated in this paper. Simple PISCES-2DELK calculations will illustrate that the fluid undergoes an internal energy rise, well beyond the reversible component (de=-pdv). The excess energy can be marked as heating of the fluid and is therefore irreversible. Furthermore, as the flow through the narrow passages tends to a 'stationary state', an a posteriori computed energy loss factor Csub(D) levels off to a value which corresponds to those common in the literature. The method of explicitly defining the geometric boundaries of perforated/porous structures is advantageous, for the following reasons: (a) it takes into account volume occupying effects of the perforated/porous plates: (b) it is equally applicable for the dynamic and for the more or less stationary state; and (c) it simulates the fluid-structure interaction and energy dissipation of the fluid, without any a priori assumptions about energy loss factors. (orig.)