CFD for Urban Design

During the urban design phase, critical decisions about the building cubature are made and a wind analysis for the estimation of wind velocities and other aerodynamic characteristics is being performed:

  • wind speed perceived by building occupants or pedestrians in the close vicinity
  • pressure distribution on building faces for the estimation of pressure difference between building surfaces which is the driving force for natural ventilation achievement
  • achievement of natural ventilation under adverse weather conditions (i.e. low wind velocities for stable (night) and unstable (extreme solar radiation) atmospheric conditions).

According to site wind data, a number of significant directions and magnitudes of wind speeds have been considered in order to compose a simulation matrix for the CFD analysis. Simulation results are interpreted by visualizing the flow field and summing up the results to comprehensive graphical representations which will assist the KPI‐based evaluation phase.


The wind comfort indices are related to wind speed and turbulence intensity as they are perceived by the building occupants or the pedestrians around building. From a list of suitable KPIs along with KRIs as more significant have been chosen the wind speed at building entrances and exits and the wind speed at the city canyons around the building.

In order to obtain the KPIs related to wind velocity, all resulting velocities at the sites of interest are taken into consideration. The simulation results are synthesized by applying frequencies (fij) of occurrence for each of the wind directions and wind speed magnitudes, as weighting factors.


The occurrence frequencies are coincident to the corresponding frequencies obtained by the site wind‐rose.

External aerodynamics in the urban environment, air flow and pressure