The TA Luft dispersion program AUSTAL makes it possible to use externally calculated flow and turbulence fields for a TA Luft calculation with AUSTAL. For this, however, the flow and turbulence fields must be available in a defined format. One use case for externally calculated wind fields is when the influence of buildings has to be taken into account according to TA Luft.

With the add-on module "Interface MISKAM wind and turbulence fields for AUSTAL" it is possible to convert flow and turbulence fields calculated with the MISKAM model into a format readable by AUSTAL and to store them in a wind field library. The interface works on a project-related basis and enables both the recalculation of flow and turbulence fields with subsequent conversion into a wind field library for AUSTAL and the conversion of existing MISKAM flow and turbulence fields into a wind field library for AUSTAL.

The add-on module is integrated directly into the basic version of WinMISKAM and can be called up directly via the menu. With the help of a "WIZARD", the user is guided in five steps to the calculation of the MISKAM wind fields with subsequent conversion of the flow and turbulence fields into the format readable by AUSTAL. All the necessary data and parameters are saved in a project file so that the calculation and conversion steps can be retraced later.

In addition to the MISKAM flow fields, it is also possible to convert the velocity fluctuation fields and exchange coefficients into the wind field library for AUSTAL.

As the model physics of the MISKAM and AUSTAL flow and dispersion models differ, there are restrictions when dealing with MISKAM wind fields for AUSTAL calculations:

• The flow model in MISKAM does not calculate with the boundary layer profiles prescribed in TA-Luft. In addition, wind rotation with height is NOT taken into account.
• Only an equidistant calculation grid is permissible for AUSTAL. This means that the wind fields calculated with MISKAM in the inner investigation area must also have an equidistant computational grid.
• MISKAM wind fields cannot be calculated for topographically structured terrain. MISKAM is not validated for these cases. Only the use case of buildings in flat terrain is supported by the interface.
• In MISKAM, not all stability classes occurring in nature are taken into account in a physically meaningful way. MISKAM is validated for neutral cases (dT/dz = 0). For stable classes (dT/dz > 0), the results are physically meaningful. For unstable classes (dt/dz < 0), MISKAM has inadequate model physics. Therefore, unstable cases are not supported by the interface.
• Calculations with a nested computational grid are not yet supported by the interface, as the total computational effort could not be significantly minimized. In principle, it would be possible to use nested computational grids from MISKAM in AUSTAL.