Advances in Simulation Capability for Complex Geometry

We describe our effort on the enhancement of fire simulation capability around complex geometry within the Fire dynamics Simulator (FDS). An efficient algorithm based on spatial intersection and polygon/polyhedral reconstruction is developed to define a boundary conforming cut-cell mesh around geometrically complex objects in three dimensions. These target geometries do not need to lay on the FDS grid planes. A conservative finite volume unstructured discretization of the energy and scalar transport equations (chemical species) on this cut-cell grid is implemented. We explore the implicit solution for transport of chemical species, addressing stability issues arising in small cells close to the object, as well as explicit time integration by means of linking small cells to larger neighbors. Velocity reconstruction on faces near the solid surfaces is done using a direct forcing immersed boundary method (IBM). Finally, tight conservation defined by the pressure Cartesian unstructured discretization and solution is also evaluated, as a counterpart to the global pressure solution method present in FDS. A description of the work done on the above areas is provided, together with a simulation example.