SimScale Settings

Hi, in the previous video, I showed you how to import your model into SimScale and generate the wind tunnel from that. So now we’ll go over all the settings we need to make to set up our simulation. So with the new wind tunnel geometry selected, you simply click on create simulation and choose incompressible flow.

And then in the menu on the left, we just go through all the different steps here. Materials is quite simple.

We only have one body in this simulation: the wind tunnel, so that material should be air and we just leave all the default settings as they are. The initial conditions we can skip for now. You can use these sometimes to speed up the simulation a little bit, but it’s fine to ignore them for now. Then, the boundary conditions are used to define what is happening on the edges of this simulation domain, including, for example, the input wind speed. And that can be defined using a velocity inlet boundary condition. And you can simply click on the face of the wind tunnel that the wind should be coming from.

We then need to specify the wind direction - the wind speed, sorry - along the different axes in the model. So you see in the cube on the bottom right here that the X-axis is from left to right as we’re looking now, Z this vertical and Y is depth-wise in this case. So if the wind is coming from this face here, then what we do is that we leave the velocities along the Y and Z directions as zero and for X we need to specify what the wind speed should be. Since winds moves more quickly higher up from the ground, we need to specify some formula to represent that.

So we can do that through this button here, and then we can either specify the table or formula. And here is a formula that I’ve prepared before. This is a standard formula that you can find for these wind speeds. So in this case, we have a reference wind speed of 5 meters a second that we measured at a reference height of 10. So you can adjust those values based on what scenario you want to test or based on local measured data.

And this factor of 1.5 that appears here represents the roughness of the ground, where two is a typical factor for a very dense urban area and very low numbers, close to zero, are associated with a large open plains or seas, for example. For the reference wind speeds, in this case, I’ve written minus 5, and that is because we want to wait to be coming from the right hand side of the simulation domain here. That’s why we look again at this cube. We see that the X-axis that the origin of the axis is on the left hand side and it is running right.

So if we specified this velocity as 5 meters a second, that would be going out of the domain at this face. So we specify minus 5 instead so it goes into the simulation domain.

Then on the opposite side of the velocity inlet, we need to specify a pressure outlet. And we do that the same way. And then we specify a pressure outlet with a fixed value of zero. It just means that the winds will be free to flow out of the model from that face. We then specify the sides and the top of the wind tunnel, and since we assume there is just more air on those sides, we can have a free flowing air along those faces. So we specify the wall boundary condition with the velocity set to slip. Then for all the faces that remain, we need to specify again a wall but with a no slip condition.

And, you can either select all of those faces manually, but it will be quite a lot of work, so it’s easier to just select all the faces that we have already assigned boundary conditions to. And then you can simply right click to invert that selection and then we are left with just the grounds and all of the building faces. And there we once again add a wall boundary condition, but this time we say that there is no slip, so basically the very first layer of air, the first millimeter of the air along these faces will not be moving, so these faces are imparting friction against the wind.

Those were some of the basic settings, and in the next video, we’ll go over how to set up the computational mesh that we use and how to start the simulation.