When dealing with Urban Areas not only the model (of a single skyscraper or a whole neighborhood) is relevant. You need to include the terrain or topography in your simulation to get reliable results.
Look at the following image. The streamlines represent the particles of wind in the lower level, near to ground level. The edge of the topography is affection the wind behavior in a non-desirable way because it does not represent how wind would flow in the real world.
In order to correctly run a wind simulation with Ingrid Cloud, you have to choose one of the following methods:
1. Take away topography, placing the model directly on ground level. If you’re interested in understanding how your design is affecting wind in a different direction or if there are no relevant surroundings, that’s the best option.
2. Amplify the ratio of the area in at least five times by including surrounding buildings. That will place the geometry borders further away from your area of interest. Consequently, the wind that reaches the main part of the geometry won’t be affected by the turbulence caused in the edge of the model.
In summary, Ingrid Cloud understands topography as part of the model, and it affects the wind behavior in a non-desirable way. So, if the geometry contains considerable volume underneath the area of interest, you have to take that away.