Collection of abstracts 13th GAMM-Seminar Kiel on Numerical Treatment of Multi-Scale Problems January 24th to 26th, 1997.

Friday, January 24th, 1997

Discretization of Advection on an ARAKAWA-C-grid with Internal Boundaries

Small-scale meteorological models which simulate the airflow around buildings usually are only able to deal with obstacles that are resolved by the model grid; i.e., a grid box is always either completely covered by a building or completely within the fluid domain. On the other hand, in the last years CFD methods have been developed in aircraft engineering that are able to take into account arbitrarily shaped internal boundaries, although with a rather simple grid structure. We present an adaption of such a method to an Arakawa-C-grid, focussing our attention on the advective processes. In this method, the momentum and scalar fluxes are weighted with the relative coverage of the grid surfaces. The instability problem that arises from cut cells with only a small coverage of free fluid can be avoided by redistributing parts of the flux divergence to the neighboring cells. This advection routine will later on be part of a large numerical model (MITRAS) which will be used to calculate the transport of pollutants in urban areas.