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# Basic Geometry Requirements for Pedestrian Wind Comfort

Pedestrian wind comfort analysis in SimScale is based upon the Lattice Boltzmann Solver by Pacefish®$$^1$$ and therefore has few geometry requirements in terms of quality, and by that, generally speaking, open geometry, overlapping, and coinciding geometry is ok. However, it is also highly automated, streamlined, and tuned specifically for wind comfort based upon validation projects such as the AIJ cases, best practices from industry in both CFD and wind tunnel methodology, and guidelines and standards. Therefore, to get the most out of the solver, a few considerations need to be given about the tested geometry.

## Orientation

SimScale’s PwC analysis type requires some basic orientation rules which most tools comply with by default. However, if you are creating geometry from scratch in a software that is often used for 3D modelling rather than building or environment orientated it is important to consider these.

The geometry should have the Z+ direction as the up orientation, i.e. Z-axis points to the sky. Also, although not strictly required, the PWC analysis type uses the Y-axis by default to orientate to North, this can be corrected in the platform, but usually, geometries are also created with this in mind.

## Sizing and Regions

Geometry should be uploaded in real physical sizing, i.e. scaled-down models should not be uploaded. The default unit is meters, and therefore, when and if exporting STL geometry, you should ensure that this unit is used in the model beforehand.

You can also select units when uploading STL’s to the SimScale platform. This can be done by matching the unit in the CAD and the SimScale platform, but care should be taken to get this right.

Cell sizing is currently done using reference sizing based upon the building of interest and the building maximum height. Therefore, it is recommended that a region of interest no more than 400 $$m$$ is used, to approach the target resolution of 0.5-1 $$m$$ when meshing. Click here to learn more about mesh settings in PWC analysis.

The region of interest should include, in most use cases, the newly proposed building or buildings and the region in which their presence or design might affect the pedestrian’s comfort. The area of interest should include your main buildings of interest and surrounding buildings and can be detailed if you need it.

The surrounding region is likely to affect the aerodynamics significantly in the region of interest so it is advised that the surrounding buildings are present but do not need to have any detail, they can be block representations. Beyond that, the buildings and obstacles will be modeled using a standard wind profile, correcting the exposure to the terrain (ranging from open terrain to the city center).

The PWC analysis type is capable of dealing with geometry intersecting the bounding box, therefore if the bounding box representing the fluid domain limits has geometry outsides of its bounds it will not be included in the solution.

City of London Guidelines

There may be specific restrictions regarding the geometry in use for wind comfort analysis based on the location. Here you can find a set of standard guidelines for the geometry and the mesh when analyzing pedestrian wind comfort in the City of London.

Our Knowledge Base articles have a great collection of articles associated with CAD issues in PWC analysis. Explore them now!

References

Last updated: June 14th, 2021