Assessment of Thermal Boundary Condition in FDS Simulation for Underground Car Park
Both Fire Dynamic Simulator (FDS) and Smokeview (SMV) were adopted to predict the heat distribution and the smoke propagation. The data are important for determining the required tenability limit in an underground car park during fire. The credibility of FDS result depends heavily on the numerical setting and the imposed boundary conditions. The present study explored the influence of different thermal boundary conditions, i.e. adiabatic and constant wall temperature boundary conditions. The grid-independent Heat Release Rate (HRR) and the vertical temperature profiles on some selected locations were firstly obtained. It was found that the R2 of the inert thermal boundary condition was the highest (89.4%). Meanwhile, the R2 of the adiabatic thermal boundary condition was 87.5%. Therefore, the constant wall temperature boundary condition was adopted for subsequent analysis.On the other hand, the temperature distribution was dependent on the imposed thermal boundary condition as well. For adiabatic condition, the smoke took lesser time to reach the floor. However, for constant temperature boundary condition, the smoke layer remained at the upper level and the smoke concentration was low near the end wall. Also, the predicted critical velocity for the case of constant temperature boundary condition was much lower than that of adiabatic boundary condition. In general, lower critical velocity indicates that the hot gases would reside at the upper level longer.
Index Terms - Adiabatic, constant temperature, critical velocity, underground car park.