Average Wind Speed

The averageWindSpeed field represents the long-term, weighted average of the local wind speed \(U_{local}\) over a given period (annual, seasonal, or monthly). It combines CFD simulation results with observed wind statistics to provide a realistic picture of the wind environment across the computational domain.

How is it computed?

1. Wind Directions

   • The simulation runs for 8 or 16 evenly spaced directions, covering the full 360°.
   • Each direction provides a local wind speed distribution on the computational mesh.

2. Wind Statistics (Weibull Distribution)

   • For each wind direction, the observed wind climate is described using Weibull parameters:

     • Shape factor \(k\)
     • Scale factor \(c\)

   • From these parameters, the mean wind speed is derived analytically:

     $$ \mathbb{E}[S] = c \cdot \Gamma!\left(1 + \frac{1}{k}\right) $$

3. Weighted Local Wind Speed Contribution

   • For each direction, the local contribution is:

     $$ U_{\theta} = \frac{occurrence_{\theta}}{100} \times \left(\frac{U_{\text{local, simulated}}}{U_{\text{met, simulated}}}\right) \cdot \mathbb{E}[S] $$

   • Where:

     • \(U_{\text{local, simulated}}\) is the CFD wind speed at the site.
     • \(U_{\text{met, simulated}}\) is the reference meteorological wind speed used in simulations.
     • \(occurrence_{\theta}\) is the frequency of that wind direction in percent.

4. Aggregation

   • The weighted contributions from all wind directions are summed to form the averageWindSpeed field.

Why it matters

The averageWindSpeed field provides critical insight into the prevailing wind environment at a site:

• Urban Planning → informs building placement and street layout.
• Safety Assessments → highlights areas prone to high winds that could pose risks to people and structures.
• Environmental Studies → supports analysis of wind impact on vegetation, air quality, and outdoor comfort.

By combining local CFD simulations with statistical wind data, this field bridges short-term flow patterns and long-term wind climate.