# Boundary Layer Modelling **URL:** \ **Category:** Using SimScale\ **Created:** [June 20, 2018, 5:40pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656 "2018-06-20T17:40:45Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Kai\_himself](https://www.simscale.com/forum/letter_avatar/kai_himself/32/6_22734026db12803ebb3e059622ac3534.png) [@Kai\_himself](https://www.simscale.com/forum/u/Kai_himself)\ **Post date:** [June 20, 2018, 5:40pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/1 "2018-06-20T17:40:45Z")
Hello, i have a problem to creat a “good” Mesh with my Model. It’s about this project here: [_Deleted by author_] With the standart Meshing options i get a “Stairway” at the tilted surfaces. ![Layer%20with%20Steps](https://www.simscale.com/forum/uploads/default/original/3X/5/2/52089cdf49dabc98e89e4a2dc18bdbf993e3b84b.jpg) This is exactly what this tutorial is about, > [@Session 1 of CFD Master Class](https://www.simscale.com/forum/t/session-1-of-cfd-master-class/42428): > > Tutorial Updated 2018-02 Recording [[CFD Master Class: Wall Modelling & Drag and Flow Separations] ](https://www.youtube.com/watch?v=5bMYaIRHXlM)Introduction The CFD Master Class: Session 1 explores the methodology of correctly defining the first cell wall distance, and its effect on results obtained using the wall modelling technique and assessing the resulting near wall velocity. During this session we shall explore the concept of Y+, how to predict the wall distance Y from an approximated Y+ and how to correct your mesh… I try different solutions (Mesh 1 till 8) from the tutorial but it wont work. i gave up at Mesh 8, with this results. ![1%20View](https://www.simscale.com/forum/uploads/default/original/3X/1/7/171942c20a53832b7b1a7e36a994989da1935287.JPG) ![2%20View](https://www.simscale.com/forum/uploads/default/original/3X/8/b/8bf4e5bf3029f9cda12a4ae0b074b932901c4ab7.JPG) The simulation at Mesh 8 stops at 10%. How can I creat a good Mesh ? Greetz Kai ---
**Author:** ![jousefm](https://www.simscale.com/forum/user_avatar/www.simscale.com/jousefm/32/34908_2.png) [@jousefm](https://www.simscale.com/forum/u/jousefm)\ **Post date:** [June 20, 2018, 8:50pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/2 "2018-06-20T20:50:22Z")
Hi Kai (@Kai_himself)! Nice to see you again 🙂 Thanks for your post and detailed description of your problem! I will have a look at that and also tag my colleagues and well known PowerUsers @Get_Barried & @vgon_alves here who might give you some useful input here. Cheers, Jousef ---
**Author:** ![vgon\_alves](https://www.simscale.com/forum/user_avatar/www.simscale.com/vgon_alves/32/20574_2.png) [@vgon\_alves](https://www.simscale.com/forum/u/vgon_alves)\ **Post date:** [June 21, 2018, 4:46am UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/3 "2018-06-21T04:46:54Z")
Hi @Kai_himself & @jousefm, Aims to imrpove your mesh, I suggest to start implemanting some inflation into fluid-valve contact region. I saw that you tried it but your inflate b.layers in mesh 8 were not loaded successfuly. ![b%26a](https://www.simscale.com/forum/uploads/default/original/3X/e/a/ea0fd0d6492fc7eeb71981dcd1b67a8975d2019c.jpg) **EDIT1:** ![b%26a3](https://www.simscale.com/forum/uploads/default/original/3X/b/b/bb24eab8c6198c633febef0b192354789434fd5c.png) ![b%26a2](https://www.simscale.com/forum/uploads/default/original/3X/1/2/123525c8b8ca84d18bf27ffa34bc48d5c0fedac2.png) You can also add some “vicinity” refinement regions to gradually refine your mesh according to the valve and flow direction adding one more cartesian box in addition to the one added. **What I did above is too far away of a good mesh** , but I think it can be a good begin. **EDIT2:** It is running OK at least for 100 [s]. I canceled it with the purpose to preserve core hours 🙂 . You can find the project [here][_Deleted by author_]. The mesh is called “_90 60 150 mesh_”. Maybe [this](https://www.simscale.com/workbench/?pid=6781135185634606370#tab_0-0) project helps you to see these steps I mentioned above. Please, let me know if it was useful in some way. Cheers, Vinícius ---
**Author:** ![Get\_Barried](https://www.simscale.com/forum/user_avatar/www.simscale.com/get_barried/32/20599_2.png) [@Get\_Barried](https://www.simscale.com/forum/u/Get_Barried)\ **Post date:** [June 21, 2018, 10:00am UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/4 "2018-06-21T10:00:42Z")
Hi @Kai_himself, Just to add on to what was mentioned by Vinícius. If you refer to the figure below you will notice that you basically have a broken mesh based on the very high illegal cell count. This is what is causing your simulation error. ![image](https://www.simscale.com/forum/uploads/default/original/3X/f/4/f4ed9ff5f8a56c05929a2dcfc8f0fd034fcc11ee.png) From the same mesh’s meshing log, you will also notice that your layers are not showing up as Vinícius has mentioned. ![image](https://www.simscale.com/forum/uploads/default/original/3X/e/c/ec1d162d718a65820939e7f115be93928e75c135.png) This post [here](https://www.simscale.com/forum/t/y-yplus-generate-wall-spacing-for-cfd/82451) should help you with regards to layer generation. The issue with illegal cells seems to be with the geometry. Your pipe has a gap between the inner and outer surface along with the hollow cap that is interfering with the inner and outer pipe surface. The presence of this coupled with the sharp edges along with the high refinement levels all equate to the very high illegal cell count you encountered. Do refer below. ![image](https://www.simscale.com/forum/uploads/default/original/3X/3/d/3dfc08be589abd70c542e2777ab3216cd174744d.png) A good way to mitigate this issue would be to either create a simple pipe assembly with just one inner surface and a cap with no thickness or to close the gaps within the geometry (for the cap and the pipe itself) by filling in the gaps. Cheers. Regards, Barry ---
**Author:** ![Kai\_himself](https://www.simscale.com/forum/letter_avatar/kai_himself/32/6_22734026db12803ebb3e059622ac3534.png) [@Kai\_himself](https://www.simscale.com/forum/u/Kai_himself)\ **Post date:** [June 21, 2018, 5:53pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/5 "2018-06-21T17:53:01Z")
@vgon_alves and @Get_Barried, Thank you very much, i will try it and get back to you 🙂 Greetz Kai ---
**Author:** ![Kai\_himself](https://www.simscale.com/forum/letter_avatar/kai_himself/32/6_22734026db12803ebb3e059622ac3534.png) [@Kai\_himself](https://www.simscale.com/forum/u/Kai_himself)\ **Post date:** [June 28, 2018, 5:10pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/6 "2018-06-28T17:10:58Z")
@vgon_alves and @Get_Barried, so i make a new geometry, only existing out of surface until the umbrella. I use your values, refinements etc. [Here](https://www.simscale.com/workbench/?pid=2931523305998705569#tab_0-0) is the link to the new project. The picture shows the first test simulation. Did you know how i improve the mesh at the begin of the umbrella ? ![Kite](https://www.simscale.com/forum/uploads/default/original/3X/b/0/b08d4cee0ba6b2eaf9c257091710bb62363bd82f.jpg) Thank you Kai 🙂 ---
**Author:** ![1318980](https://www.simscale.com/forum/user_avatar/www.simscale.com/1318980/32/9637_2.png) [@1318980](https://www.simscale.com/forum/u/1318980)\ **Post date:** [June 28, 2018, 9:34pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/7 "2018-06-28T21:34:45Z")
Better refinement on that edge will help Kai, also if you add a feature refinement that goes say one level finer than the end, then you have a better chance of inflating the layers around the geometry. Good luck, Darren ---
**Author:** ![Kai\_himself](https://www.simscale.com/forum/letter_avatar/kai_himself/32/6_22734026db12803ebb3e059622ac3534.png) [@Kai\_himself](https://www.simscale.com/forum/u/Kai_himself)\ **Post date:** [July 4, 2018, 4:09pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/8 "2018-07-04T16:09:10Z")
I wanted to report back shortly, i add a surface refinement to the front and back at the umbrella. This should be ok for now. Thank you for your help. Greetz Kai ![Mesh](https://www.simscale.com/forum/uploads/default/original/3X/b/3/b3a51c31f8f7a6b8074adbdd8b066d887dde2563.JPG) ![Mesh%201](https://www.simscale.com/forum/uploads/default/original/3X/8/9/893ba1180371c8068f68ffe1ecab175390eea6a1.JPG) ---
**Author:** ![1318980](https://www.simscale.com/forum/user_avatar/www.simscale.com/1318980/32/9637_2.png) [@1318980](https://www.simscale.com/forum/u/1318980)\ **Post date:** [July 4, 2018, 5:01pm UTC](https://www.simscale.com/forum/t/boundary-layer-modelling/82656/9 "2018-07-04T17:01:21Z")
Hi @Kai_himself, Glad you got the mesh you wanted, looking forward to seeing the simulation! Best, Darren