Séminaire mercredi 7 dec 10h30 / Seminar Wednesday Dec 7 10h30 

Conférencier/Lecturer: Piotr Smolarkiewicz
                       NCAR, Boulder, Colorado

        Sujet/Subject: Flow past the Pentagon: building resolving large-eddy
                       simulations and comparison with wind tunnel experiments.

         Presentation: Anglais/English
            Lieu/Room: Grande salle du premier étage CMC 

                 iweb: http://iweb.cmc.ec.gc.ca/rpn/SEM 
                  web: http://collaboration.cmc.ec.gc.ca/science/rpn/SEM/index.php

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                                 RESUME / ABSTRACT 

Building-resolving large-eddy simulations (LES) of the flow past the
Pentagon are accomplished using two different methods to represent the
edifice. The first method employs the standard Gal-Chen & 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 arbitrary 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 MPDATA transport algorithms.

Both solution methods are compared to wind tunnel data collected for a
scale model of the Pentagon for neutral stratification.  Profiles of
the first and second-order moments at various locations around the
Pentagon 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. A simulation for a
stratified case (Fr=U/Nh=1; representative of nocturnal flows) is also
presented. It shows substantial differences from the neutral case.