How do you use SimScale?

Here, we’ll take a look at the most straightforward way to use SimScale. To make the process easier, we’ve given you step-by-step instructions.

Instructions for using SimScale

1. Create a (free) account on www.simscale.com. Note: for free accounts all projects are public.
2. Create a new project and import your model. This can be e.g. a file from Revit, AutoCAD, or a similar programme, or a general format like .SAT or .STL.
3. Select your imported geometry and click “Edit in CAD mode”.
4. Use the “Flow Volume > External” option to create the wind tunnel we will be simulating. For the size, you can use the following rules of thumb based on the tallest building (Hmax).
   • Height of the wind tunnel: 6 x Hmax
   • Free space on the downwind side of your building(s): 15 x Hmax
   • Free space on other sides: 5 x Hmax
   • Use the “seed face” option and select the roof of any building.
5. Select all buildings (or, select the new wind tunnel, right click, and invert the selection) and delete these.
6. Click Finish or Export to return to the wind simulation interface.
7. Select the new geometry that has been creased and click “Create simulation”, then choose Flow (incompressible).
8. Go through the Settings menu at the left hand side as explained in the following steps.
9. Material: assign the pre-defined Air material to the wind tunnel.
10. Initial conditions: this can be skipped for now.
11. Boundary conditions (BC):
    • Downwind face of the wind tunnel: “Pressure outlet” BC with type “Fixed value” and pressure 0 Pa.
    • Both sides and the roof of the wind tunnel: “Wall” BC with the option “Slip”. (The air can move freely here as we assume it is only touching more air that is also moving.)
    • Upwind face: “Velocity inlet” BC. Use the navigation cube (bottom right) to identify if the wind is moving along the X or Y axis. If the wind is coming in the same direction as the arrows on the navigation cube, you will enter a positive number for the wind speed. If it is going the opposite direction you enter a negative number. Set the wind speed to 0 for the other two directions.
    • Wind speed: to represent that wind speeds are higher further up, you can use the following formula: U = -5 * log((z)/1.5) / log((10)/1.5) m/s Where -5 is the input wind speed that was measured at 10 meters above the ground. The value of 1.5 is a factor representing the roughness of the ground.
12. Mesh: use the “Hex dominant” algorithm, “Internal” meshing mode, “Automatic mesh sizing”. The mesh fineness controls the resolution of the simulation; a finer mesh can give better results but takes more time to calculate everything.
13. Under “Simulation Runs” you can start a new simulation. Provide a name that helps you recognize what this run is, e.g. “Existing buildings – wind from north”.
14. After the run is complete, check the convergence plots for the run. If the lines are (almost) horizontal towards the right of the graph this means that the simulation has found a stable solution and you can continue with visualizing the results. If the lines are still going up and down you can add more runs by clicking on the run in the menu on the left and using the “Continue run” button next to “Post-process results”.
15. Under the run you performed, go to “Solution Fields”. Here you can add a number of different visualization options. The most useful ones for us are “Cutting plane” and “Particle trace”.
16. Add a new cutting plane, choose “Z” for orientation and under position enter a value of 1.5 m for Z. This will gives us a map of the wind speeds at the pedestrian level. You can adjust the colour scale by dragging the arrows on the colour bar at the bottom. Adjust the scale so you can easily see the differences in wind speeds in the map. You can also add vectors (arrows) showing how the wind moves.
17. Add a new particle trace. This will allow you to pick a point on the wind inlet face. From here, virtual “smoke” is added to the wind that helps you see how the wind is moving. You can adjust the number of particles and what they look like using the options provided. This feature is particularly useful to help understand how high wind speeds in some areas are being created.