# Creating Topological Entities for the mesh

**URL:** <https://www.simscale.com/forum/t/creating-topological-entities-for-the-mesh/32738>\
**Category:** Project Support\
**Created:** [July 15, 2016, 7:28pm UTC](https://www.simscale.com/forum/t/creating-topological-entities-for-the-mesh/32738 "2016-07-15T19:28:53Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![averma](https://www.simscale.com/forum/letter_avatar/averma/32/6_22734026db12803ebb3e059622ac3534.png) [@averma](https://www.simscale.com/forum/u/averma)\
**Post date:** [July 15, 2016, 7:28pm UTC](https://www.simscale.com/forum/t/creating-topological-entities-for-the-mesh/32738/1 "2016-07-15T19:28:53Z")

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Hello,

I am new user to SimScale and I was trying to simulate flow through wind turbine. I copied this project from @jprobst. The link to my project is [https://www.simscale.com/workbench?publiclink=ef655f23-3c87-44ba-85d2-bd6317a0e251](https://www.simscale.com/workbench?publiclink=ef655f23-3c87-44ba-85d2-bd6317a0e251).

I am having issues to create Topological entities during mesh. The geometry does not have any inlet section or outlet section. It just has the wind turbine. But, it is necessary to various inlet/outlet sections before the mesh. I am unable to create them as I see no option. It is done in “wind-turbine mesh” mesh, but I do not know how (because I just copied it 😛 ). So if somebody can tell how to create them during the mesh process, it will be really nice.

PS: I have tried directly the mesh operation without creating the inlet. But the mesh is only made on the wind turbine and not outside of it.

Thanks in advance  
Abhishek VERMA

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**Author:** ![oscarcorripio](https://www.simscale.com/forum/user_avatar/www.simscale.com/oscarcorripio/32/6518_2.png) [@oscarcorripio](https://www.simscale.com/forum/u/oscarcorripio)\
**Post date:** [July 15, 2016, 7:40pm UTC](https://www.simscale.com/forum/t/creating-topological-entities-for-the-mesh/32738/2 "2016-07-15T19:40:31Z")

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Hi Averma,

I usually define inlets and outlets and the rest of the BCs after the mesh is done. The topological features created before the mesh are usually more for defining different mesh regions of different constrains. For a turbine blade you would want to do an external mesh and then you define the faces during the simulation designer section. I recommend you try some of the homeworks and tutorials to get more used to Simscale. Here’s a good post for that:

> [@A Collection of SimScale Resources](https://www.simscale.com/forum/t/a-collection-of-simscale-resources/30801):
>
> For those of you who are new to SimScale (or new to our forum), I wanted to create a collection of resources to make getting started a little easier. Have a look around and happy simulating! What is SimScale SimScale is revolutionizing the computer-aided engineering sector by providing full access to engineering simulation in your web browser. Powerful cloud-based engineering simulation platform supporting solid mechanics, computational fluid dynamics, and thermal analysis. Ideal for collabor…

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**Author:** ![jprobst](https://www.simscale.com/forum/user_avatar/www.simscale.com/jprobst/32/766_2.png) [@jprobst](https://www.simscale.com/forum/u/jprobst)\
**Post date:** [July 17, 2016, 2:27pm UTC](https://www.simscale.com/forum/t/creating-topological-entities-for-the-mesh/32738/3 "2016-07-17T14:27:43Z")

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Hi @averma,  
as mentioned by @oscarcorripio the inlet and outlet faces will only show up after the meshing was done. There are 2 meshing algorithms which will create the box for you:

- Hex-dominant automatic for external flow (only CFD)
- Hex-dominant parametric (only CFD)

Both have a box named “\_BaseMeshBox” which sets the dimensions of the background mesh, respectively the location of the inlet and outlet faces. This is also demonstrated in the tutorials posted above.

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**Author:** ![averma](https://www.simscale.com/forum/letter_avatar/averma/32/6_22734026db12803ebb3e059622ac3534.png) [@averma](https://www.simscale.com/forum/u/averma)\
**Post date:** [July 24, 2016, 10:33pm UTC](https://www.simscale.com/forum/t/creating-topological-entities-for-the-mesh/32738/4 "2016-07-24T22:33:15Z")

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Thank you @jprobst and @oscarcorripio for your replies. You were right that we need to create topological entities after the mesh. I made a mistake earlier and kept the material point inside the CAD model and was unable to create an external mesh. This is why I got confused and thought we need to define the boundaries (topological entities) during the meshing phase. But later, I was able to make the mesh. Once again. thank you. 😃