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Flow Past the Pentagon: Building Resolving Large-Eddy Simulations
and Comparison with Wind Tunnel Experiments
Piotr Smolarkiewicz
NCAR
Abstract
We perform large-eddy simulations (LES) of the flow past the scale
model of the Pentagon building. Calculations are accomplished using two
different methods to represent the edifice. The first method employs
the standard Gal-Chen and Somerville terrain-following coordinate
transformation, common in small- to mesoscale atmospheric simulations.
The second method uses the immersed boundary approach, in which
fictitious body forces in the equations of motion are used to represent
the building by attenuating the flow to stagnation in an arbitrarily
short time compared to the time step of the model. Both methods are
implemented in the same hydrodynamical code (EULAG) using the same
nonoscillatory forward-in-time (NFT) incompressible flow solver based
on the multidimensional positive definite advection transport
algorithms (MPDATA). The two solution methods are compared to wind
tunnel data collected for neutral stratification. Profiles of the
first and second-order moments at various locations around the building
show good agreement with the wind tunnel data. Although both methods
appear viable tools for LES of urban flows, the immersed boundary
approach is computationally more efficient. The results of these
simulations demonstrate that, contrary to generally accepted beliefs,
continuous mappings such as the Gal-Chen and Somerville transformation
are not inherently limited to gentle slopes.
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