For more information:
tezduyar@gmail.com

Numerical Simulation of the Dispersion of Air Contamination in a Subway Station
Daniel Clark
Following the poison gas attack in the Tokoyo Subway earlier this year,
Professor Tezduyar's group has conducted a numerical simulation of the spread
of such a gaseous subsance through a subway station. The simulation was
performed on the T3D supercomputer with a computational scheme which
simultaneously solved the continuity and NavierStokes equations for the
velocity field of the incompressible flow and with these results solved an
advectiondiffusion equation with a single source term to determine the density
distribution of the air contaminant in the subway tunnel. The results of this
computation were then postprocessed to determine the spread of density
isosurfaces with time over 80 time steps.
The simulation was initially conducted for a mesh of 187,612 nodes and
1,116,992 finite elements (shown below) with slip allowed along the surface of
the tunnel (to avoid a discontinuity with the entering wind at the tunnel
mouth) and a noslip boundary condition applied to the body of the subway
station. A wind was assumed to be blowing steadily down the tunnel from one
mouth with a natural boundary condition applied at the other mouth, while a
suction was also applied to the four roof vents. Currently, the simulation is
being repeated for a modified mesh of 138,017 nodes and 795,327 element and
staggered entrance ways (shown at bottom). In this case, a wind is assumed to
be blowing in one entrance and out of the other with both tunnel mouths now
natural boundaries. For both simulations, the following parameters were assumed
to be relevent: Re = 350,000, Pr = 0.72, and Le = 1.0.
