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SimScale: Tips and tricks

In this video, Dr. Ico Broekhuizen shares some tips and tricks for urban wind simulations in SimScale.
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Hi, in this video, I will go over a few useful tips and tricks for simulating wind around buildings using SimScale. As you may have already realized when setting up these boundary conditions, If you want to change the direction of the wind, then what you have to do is when you are creating this wind tunnel volume, make sure that you follow the same guidelines for the dimensions, but rotate by 90 degrees. And then you can specify the velocity inlet and the pressure outlet on different faces than you did before.
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However, if you want to simulate the winds coming from the Northeast, for example, you would need to have the wind coming from come from this corner, which you can’t set up directly here. So one way in which you can do this is if you go to your geometry in CAD mode in SimScale.
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So here we have the buildings that we had before. If this is also showing you the wind tunnel, you can delete it from the history pane on the left here. Then we switch to the select volume mode, select all of the buildings. And then here under transform we have an option to rotate all of the buildings. And then we will want to rotate them around the Z axis, which is the vertical axis. As you can see in this cube, in the bottom right. And then if you rotate, for example, the building by 45 degrees.
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That means that the main sides of the wind tunnel that it then creates, rather than representing north, east, south and west, is that they will represent north east, south east and so on. And other than that, you can just continue the same setup for the simulation as you were doing before.
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When you are working with the mesh, as I said in another video, you can use this dropdown menu to adjust how fine the mess should be. And the finer the mesh, the more precise the results will be, but the longer it will take to get to them. So sometimes it is useful to use a finer mesh, but only in specific areas of the model. For example, if you’re working in particular with a building or a particular square, for example.
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If you want to do that, you go to this refinements option here and you can choose between a few different ways of doing this. So you can either use the region refinement that allows you to define a cylinder or a sphere, or a box in which you really use a finer mesh than in the rest of the model. You can also use surface refinement, in which case you can then click on the faces of, for example, some buildings that are relevant to your particular case. And you can also do the same with the feature refinements.
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And finally, there’s the inflate inflate boundary option which basically will mean that any face where you have a wall specified that uses the no slip option. So the ground and all of the building faces that we set up before in the boundary conditions - that you will create a number of extra layers on all of those faces. So this is quite useful for us because the things that are happening near the ground and near the buildings are most relevant for us. So you can add a number of boundary layers to all of those faces to increase the resolution of the simulation around those and get more precise results.
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One case where you might want to do that is, for example, if you are looking at the results of your simulation and if you have used a a rather coarse grid, it may be so that, for example, around the corners of some buildings, when you look at the wind speeds it will, it may be so that it looks quite - the wind speeds look quite blocky. And if that’s the case, it might be worth refining the mesh in that area. So you get a more smooth picture. For example here, around this sharp corner here, you might want to do that.

SimScale offers many options to precisely control the wind simulation. In this video, Dr. Ico Broekhuizen explains a few that are particularly useful for urban wind simulation.

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