Forma Wind and Microclimate Analysis

[sina_rahimi]

Hi,

I have two questions regarding Forma’s wind and microclimate analysis.

1. I understand that Forma uses OpenFOAM with the simpleFoam solver for CFD component and applies Atmospheric Boundary Layer (ABL) conditions for detailed wind analysis. I was wondering what the initial condition for wind velocity is. Is it assumed to be 3 m/s, or if ERA5 data is used, which data is considered for U? Does it take the average value over eight years (2013–2020), or another period? Also, are the results tied to a specific time of year or a particular year?
2. I assume that the results from the detailed wind analysis are also used for the microclimate analysis. If that is the case, and the wind analysis is run under steady-state conditions, how does the microclimate analysis produce UTCI values for different hours between 8 a.m. and 8 p.m.?

I appreciate your help in clarifying these points and helping me better understand the workflow.

Thank you!

[tord.ekern · Accepted solution]

Hi!

1. The boundary condition at the inlet for the OpenFOAM simulation uses a speed of 3 m/s at 10 m reference height. The results shown in the analysis UI are however scaled using the inlet wind speed selected in the UI (linearly scaling wind fields like this is common practice for urban wind flows). By default the inlet wind speed used in the UI is the median speed from the speed distribution shown in the right hand side panel for the selected direction in the wind rose (more on the wind rose here). The wind rose and speed distribution data used by default are from Global Wind Atlas, which provides wind distribution estimates based on ERA5 data from 2008-2017 (i.e. not tied to a specific year or time of year, more info here). As mentioned in the wind rose article, it is possible to upload your own wind data if you want results matching a particular time period.

2. The detailed wind analysis is indeed used by the microclimate analysis. However, the analysis also uses radiation estimates based on ERA5 data along with calculated sun and daylight exposure, as well as other weather data inputs like air temperature, and these parameters do vary throughout the day. More on how this analysis works here.

Hope this helps!