The objective of the simulation studies was to demonstrate the capability of GASFLOW /1/ to predict flows and gas distributions in buildings and to perform some parameter studies. GASFLOW is a finite-volume computer code for solving transient, three-dimensional , compressible, Navier-Stokes equations for multiple gas species. It calculates the transport, mixing, and combustion of gases and aerosols in geometrically complex domains.
The first analysis was done for a subway station, a facility with complex geometry. Two main situations were considered, each with multiple cases. The first one was a bounding situation, where maximum and minimum inflow velocities into the station were used as time-independent boundary conditions. In the second situation the velocity boundary conditions were time-dependent and describe a more realistic sequence with trains reaching and leaving the station. After steady-state calculation for the different situations a neutral gas and a gas that is heavier than air were released at six different locations in the subway station, and the gas distribution depending on the different boundary conditions was analyzed.
The second analysis involved a hangar with a heating, ventilation, and air conditioning (HVAC) system. GASFLOW calculated the distribution of a gas that was released in the HVAC system. The study was a sensitivity analysis, with the changing parameters being meteorological data (wind outside the building), flow rates in the HVAC system, and flows through leaking doors. For calm wind conditions outside the hangar the results are very similar to the base case; for leakage changes of +/- 20% the results are basically identical. The biggest difference in the results compared with the base case was observed for the cases where the flow in the HVAC system was changed. Also for a high wind of outside the hangar and a big change in leakage we can see significant changes. They are caused by a changed flow pattern inside the hangar.
GASFLOW is a valuable tool for simulating and visualizing the release and distribution of gases in buildings and can be applied to analyses of accidents with hazardous gases. The results show complex flow and concentration fields caused by internal structures and varying boundary conditions.
References
1. J. R. Travis, K. L. Lam, and T. L. Wilson, "GASFLOW: A Three-Dimensional Finite-Volume Fluid-Dynamics Code for Calculating the Transport, Mixing, and Combustion of Flammable Gases in Geometrically Complex Domains," LA-UR-94-2270, July 11, 1994.