The 3D model was reconstructed from available 2D CAD files. Hex/prism-dominated meshes between 180?600k elements were created for the exhibition rooms (in fire/smoke applications the flow is buoyancy-driven and the thermal boundary layers are not of primary importance, the mesh need not be fine near the walls) for the exhibition rooms.
The mathematical model solved for the turbulent flow with buoyant heat transfer for a mixture of gases containing air and various combustion components (CO, CO2, H2O). The fire was simulated as a small cube in space, containing volumetric sources for heat and gases, according to a standard 3-stage fire model (quadratic power growth, constant maximum power & exponential decay) with appropriate coefficients corresponding to fast-rate fires of 3.5 [MW] peak thermal power. The smoke model was actually a mathematical link with combustion gases production based on established empirical models found in the literature and fire regulations. The effect of smoke detection and fire-fighting was also modeled by monitoring the predicted temperature at the sprinklers head locations. When the sprinkler activation temperature was exceeded a conservative cooling source, corresponding to the evaporation of only 10 [%] of the sprayed water, was applied in the space underneath the sprinkler head.
The boundary conditions of the model, i.e. open/closed doors, fresh air inflow rates, smoked air extraction rates and flow through cracks, were determined by the corresponding evacuation plans and dedicated smoke-extraction ventilation system, designed for each space under investigation. Special post-processing routines were created to calculate the local values of visibility, Total Cumulative Dose (TDC) for heat stroke and CO lethality, in order to assess the available time for escape in any location inside the public areas of the NMMA. The simulations were performed up to 15 [min] after the fire outburst, over-adequate for the escape of the last museum visitor.
All simulations proved the effectiveness of the proposed emergency ventilation system. Only in one occasion an outlet vent was oversized in the final system, compared to the base design, in order to eliminate even the unlikely risk of insufficient smoke extraction.
The results of the fire scenario in the small exhibition room in the basement, are shown in the animations below.