WIND Specification

Created with software version 2020.1

To follow along with this tutorial, download the relevant files here.

1. Introduction

FDS version 6.6.0 added a new WIND namelist to describe wind and atmospheric conditions. Support for WIND was included in PyroSim 2018.1. The new WIND namelist is described in Chapter 10 of the FDS User Guide. The FDS User Guide describes the wind_example.fds input file:

The computational domain is a flat landscape that is 1 km x 1 km x 100 m LxWxH. There are various rectangular blocks scattered about to represent buildings. The wind speed varies with height as shown in the first plot of Fig. 10.1 in the FDS User Guide. The wind also turns a full 360◦ in 50 s, starting and ending in the westerly direction, 270◦. This turn of the wind is not realistic, but this case is intended to test the ramp and mean forcing functionality.

Figure 1 shows the geometry of the problem. The wind initially blows from left to right.

pyro scrn wind model
Figure 1. Geometry of wind example. The wind blows from the side boundaries.

To run this problem in PyroSim:

  • Save the wind_example.fds input file that is provided above. You can also download this file directly from the NIST verification examples.
  • In PyroSim, on the File menu click Import FDS/CAD File and select wind_example.fds. PyroSim will inform you how it handled any unsupported data. In this case, the data is added to the Additional Records section of each object. All data is handled correctly.
  • After the file is imported, you can run PyroSim. No other action is required.

To explore where the WIND parameters were added to PyroSim:

  • On the Analysis menu, click Simulation Parameters.
  • Click the Environment tab and click the Edit button associated with Configure Wind.
  • Now you can see which parameters have been set. To match the wind_example.fds input file, the Wind Profile has been set to Morin-Obukhov Similarity, the Thermal Stability has be set to Very Unstable, for Landscape\(z_{0}\) has been set to 0.01, and the Speed is 5.
  • Click the Speed Change over Time tab. Click the Edit Values button for Horizontal Speed to see the time history table.
  • Close the Wind Parameters dialog.
  • Other parameters that have been changed are the Start Time and End Time on the Time tab and the DT_DEVC_LINE on the Misc tab.
  • Close the Simulation Parameters dialog.

The vents on the boundary also have special properties. If you edit the properties for one of these vents, you will notice that:

  • The Surface type is PERIODIC.
  • The WIND option has been added on the Advanced tab.

After you run the simulation, you can plot results. At 30 seconds, the wind has swirled around the obstructions, as shown in Figure 2.

pyro scrn wind velocity
Figure 2. Wind vectors at 30 seconds.

To download the most recent version of PyroSim, please visit the PyroSim downloads page and click the link for the current release. If you have any questions, please contact support@thunderheadeng.com.