n23012 meshing problem.....
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Hello everybody,
I hope that you all are fine and enjoying the CFD world. I have been working on gmsh on the airfoil n23012. I have found this example on the internet, and try to understand how can make an unstructured mesh since it is essential to have a good mesh in order to get reasonable results. However, when I used the command gmshToFoam and then checkMesh, SimpleFoam has given me a message tells that the mesh is not ok. I made print screen for both the mesh and the error on the gnu terminal wishing from somebody how is able to help me out in this issue. Regards, Attachment 36212 Attachment 36213 |
Try get better mesh with good skewness and aspect ratio
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Hey Khamllag,
you said you are trying to create an unstructured mesh !! but the mesh you have posted looks like a structured one. On a first look the mesh doesn't look very good, you need to read about skewness and aspect ratio at least before creating your next mesh. There should not be quick jumps in cell sizes the mesh should have smooth transitions like the attached picture below all the best, Hasan KJ |
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Attachment 36221 Regards, |
Did you put the front and back part of your mesh as empty in the constant/polyMesh/boundary file?
I would also say that the mesh is not very well done, I would try to put the inlet as circle, that would help to improve the inlet cells. I would also start using a mucho more coarse mesh which should give less problemas when talking about high aspect ratio cells near the airfoil wall. |
For a basic mesh you dont need to waste your time reading books skwness aspect ratio are explained here http://en.wikipedia.org/wiki/Types_of_mesh
Yes, I did have good results for the pictures posted but there is some small inconsistencies that I am trying to figure out you can have an eye on this thread for more info http://www.cfd-online.com/Forums/ope...provement.html But at some point in time you need to get to basics of what is happening by reading some books then you will understand it better. And yeah also Look at C-mesh it is very effective for airfoils. http://www.cfd-online.com/Wiki/NACA0012_airfoil Quote:
1) if you are using a rectangular mesh you have to tilt the airfoil in the geometry but you donot have to make any changes in the 0/U file you just have to use a normal fixed value as inlet Code:
INLET 2) The other way is to have a geometry of a C-mesh with airfoil at Zero angle of attack and use to 0/U file to control the flow angle, the angle of the flow at which it gets to the airfoil. Code:
INLET All the best, Hasan K.J |
skwness aspect ratio
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Thank you again for your kind explanations and taking the time. You were to the point. However, I still have a question about using this equation: "Based on the deviation from normalized equilateral angle This method applies to all cell and face shapes and is almost always used for prisms and pyramids" Attachment 36223 Could you please show me how to use it in order to create a good mesh for the airfoil example? Finally, I have been using gmsh for about two weeks, and in fact I am having some difficulties controlling the mesh since it has many commands that are not obvious. I have found the manual on the internet and try it to follow it, but it is not easy to understand. Have you read the manual about gmsh? Regards, |
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Hey Khamllag,
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However i dont think skewness was your main problem with your mesh it was the aspect ratio where you had very very long rectangle cells (square cells are optimal) All the best, Hasan K.j |
n23012
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Thank you again for your time, Attachment 36232 |
Hey Khamllag,
I am sorry I am not familiar with Gmsh. For staters from your first image, just increasing the number of nodes on the x and y-axis would sort out your problem with aspect ratio. Just play around with it that is how you learn, play with number of nodes on x and y axis till it approximately looks like the image i shared in my first comment. Have fun all the best. Hasan K.J |
Hey Alhasan,
Do you have the mesh file for the picture that you have shown it to me? It will be nice to check and compare the experiential results with CFD. I just want to change it to the openFoam. Thank you again... |
Hey,
I have compared my mesh with experimental results and they are not good enough like I have mentioned in my previous comments and I am still waiting for that question to be answer here http://www.cfd-online.com/Forums/ope...provement.html My mesh will do you no good and I am still working on it, you have to create your own mesh for your case as mine is NACA0012 and I have meshed using ICEM and Salome. Best of Luck, Hasan K.J |
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