[ICEM] Meshing an airfoil using C grid, some curves have no elements

tmartin · November 16, 2011, 16:46

Hi there, new to this forum and to CFD more generally.

I'm trying to mesh a NACA0012 according to the instructions given in http://www.youtube.com/watch?v=EknKVAJGEJ8 (though with a larger far-field) in order to export to FLUENT for solving.

Now, the above video creates the far field as one part and associates three of the edges to curves at once. I really don't understand how this can be made to work with FLUENT, as the only way I'd got FLUENT to work in the past is using separate parts/families for inlet, outlet, top and bottom as the video annotation suggests. Anyway, when I import into FLUENT as in the video, I find that I don't have any zones to create, for example inlet (velocity-inlet) BCs - the inlet simply does not appear in the list, only OUTLET and BOTTOM.

If I right click the INLET or TOP in ICEM, I'm told that there are no elements associated with either of them. OUTLET and BOTTOM are okay though. I ungrouped the curve, and associated the edges to the curves individually and renamed the parts INLET, OUTLET, TOP and BOTTOM and re-built the mesh. Unfortunately, when I export the mesh into FLUENT, the same thing happens.

I've got FLUENT working with an H grid mesh before so I get the feeling it's to do with the C grid somehow... I'm basically just really confused. Would very much appreciate any help and I will do my best to add more detail if I can.

raj.cfd · November 16, 2011, 18:42

Hi,

1. You can import NACA0012 body co-ordinates in any of the CFD pre-processing software.
2. The farfield as a rule of thumb is 15-20 times chord length . create one.
3. You can generate C-grid, O-grid or H-grid or mixture of them and / or structured or unstructured.
4. Divide airfoil into different segments, segment 1 - leading edge, seg-2, from leading edge to suction side just before the trainling edge and similarly at the pressure side as well. connect this to the far feild boundary.
5. C-grid at leading edge, suction and pr. side and H-grid at the trailing edge can be generated.
6. Make sure to have a fine mesh gradient at the airfoil boundaries , since you will solve one equation model to capture very fine viscous effects at the boundaries.

tmartin · November 16, 2011, 18:45

Thanks Raj. I have a mesh generated already, far field is about 20x the chord, etc etc. The problem is that when I take export to FLUENT I can't add boundary conditions to the inlet, it doesn't appear as a zone under the boundary conditions tab. ICEM says there are no elements associated with the inlet for some reason, even though it really does look like it.

The only difference between what I've done already and what you suggested is the separate curves for pressure and suction sides, could this have an effect?

raj.cfd · November 16, 2011, 18:58

Probably before taking it to fluent, you need to have different named selections like inlet, outlet, farfield, pr. side, suc. side etc etc in your pre-processing software and also depends if you are meshing it as a single body mesh or multibody mesh..

November 16, 2011, 16:46	Meshing an airfoil using C grid, some curves have no elements	#1
tmartin New Member Tom Join Date: Nov 2011 Posts: 2 Rep Power: 0	Hi there, new to this forum and to CFD more generally. I'm trying to mesh a NACA0012 according to the instructions given in http://www.youtube.com/watch?v=EknKVAJGEJ8 (though with a larger far-field) in order to export to FLUENT for solving. Now, the above video creates the far field as one part and associates three of the edges to curves at once. I really don't understand how this can be made to work with FLUENT, as the only way I'd got FLUENT to work in the past is using separate parts/families for inlet, outlet, top and bottom as the video annotation suggests. Anyway, when I import into FLUENT as in the video, I find that I don't have any zones to create, for example inlet (velocity-inlet) BCs - the inlet simply does not appear in the list, only OUTLET and BOTTOM. If I right click the INLET or TOP in ICEM, I'm told that there are no elements associated with either of them. OUTLET and BOTTOM are okay though. I ungrouped the curve, and associated the edges to the curves individually and renamed the parts INLET, OUTLET, TOP and BOTTOM and re-built the mesh. Unfortunately, when I export the mesh into FLUENT, the same thing happens. I've got FLUENT working with an H grid mesh before so I get the feeling it's to do with the C grid somehow... I'm basically just really confused. Would very much appreciate any help and I will do my best to add more detail if I can.

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November 16, 2011, 18:42		#2
raj.cfd New Member raj Join Date: Nov 2011 Posts: 22 Rep Power: 14	Hi, 1. You can import NACA0012 body co-ordinates in any of the CFD pre-processing software. 2. The farfield as a rule of thumb is 15-20 times chord length . create one. 3. You can generate C-grid, O-grid or H-grid or mixture of them and / or structured or unstructured. 4. Divide airfoil into different segments, segment 1 - leading edge, seg-2, from leading edge to suction side just before the trainling edge and similarly at the pressure side as well. connect this to the far feild boundary. 5. C-grid at leading edge, suction and pr. side and H-grid at the trailing edge can be generated. 6. Make sure to have a fine mesh gradient at the airfoil boundaries , since you will solve one equation model to capture very fine viscous effects at the boundaries.

November 16, 2011, 18:45		#3
tmartin New Member Tom Join Date: Nov 2011 Posts: 2 Rep Power: 0	Thanks Raj. I have a mesh generated already, far field is about 20x the chord, etc etc. The problem is that when I take export to FLUENT I can't add boundary conditions to the inlet, it doesn't appear as a zone under the boundary conditions tab. ICEM says there are no elements associated with the inlet for some reason, even though it really does look like it. The only difference between what I've done already and what you suggested is the separate curves for pressure and suction sides, could this have an effect?

November 16, 2011, 18:58		#4
raj.cfd New Member raj Join Date: Nov 2011 Posts: 22 Rep Power: 14	Probably before taking it to fluent, you need to have different named selections like inlet, outlet, farfield, pr. side, suc. side etc etc in your pre-processing software and also depends if you are meshing it as a single body mesh or multibody mesh..