[GAMBIT] Boundary layer meshing problems

gambiss · January 29, 2011, 11:03

Hi

I am having trouble making a boundary layer around an aerofoil as I want a y+ as 1 so structure mesh at first (1% of the chord) then unstructure out from that (modelling a VAWT turbine with three blades).

Does anyone have any suggestion how to do this, as when I try it boundary layer function does go around the blade, and just make lines across it.

Thanks

-mAx- · January 31, 2011, 02:31

first mesh edges from your airfoil

gambiss · January 31, 2011, 13:49

Cheers. Now when I try to mesh, I either get error: boundary layer is to high, then when I reduce it says: that mesh is not possible without interference.

I have taken off the auto smooth default. Is their anything else I should do?

Thanks

-mAx- · February 1, 2011, 01:52

can you post a picture with the BL you try to attach

gambiss · February 6, 2011, 15:12

Still having problems, is this a fault of my meshed edge or? An gambit error, as some times it seems to work with out hassle... and see that other people are having simular problem...

https://picasaweb.google.com/1157392...56072322986802
https://picasaweb.google.com/1157392...56075170157810
https://picasaweb.google.com/1157392...56075170157810

Thanks for you help in advance!

-mAx- · February 7, 2011, 02:19

if you deselect the trailing edge in the BL-surface list, does the error remain?

gambiss · February 7, 2011, 07:01

If you mean, not creating a boundary layer around the trailing edge then no, this doesn't work either!

But unsure of what you mean!

-mAx- · February 7, 2011, 07:54

no I mean, don't pick the trailing edge, when you select edges where the BL will be attached.
Does the error remain?

Quote:

Originally Posted by gambiss

Now when I try to mesh, I either get error: boundary layer is to high, then when I reduce it says: that mesh is not possible without interference. Thanks

gambiss · February 7, 2011, 08:08

Yes, now it will mesh, is there any way to get it create a boundary layer around the whole blade?

Thanks!

-mAx- · February 8, 2011, 01:58

ok that means the error comes from this edge.
Try to add more nodes on this edge.
If it don't help, try to merge the edge with the 2 others (both sides), and perturb nodes distribution

gambiss · February 8, 2011, 05:42

I've managed to Mesh it now, but, it is really skewed next to the blade, is this just from the position of the nodes and is the only way to solve this adjusting them?

Or is there a simpler way!?

Thanks for all you help, I really appreciate it!

-mAx- · February 8, 2011, 05:51

post a picture

gambiss · February 8, 2011, 06:01

https://picasaweb.google.com/1157392...56384960415330

https://picasaweb.google.com/1157392...56392982700834

-mAx- · February 8, 2011, 06:04

something is weird.
Can you provide me the dbs file?

gambiss · February 8, 2011, 06:59

http://www.fileswap.com/dl/eQjBziUI/...again.zip.html

-mAx- · February 8, 2011, 08:30

ok I kept the parameters from your BL and your SF.
But first, you absolutely need to split your domain into several smallest surfaces.
Indeed you have 3 airfoils, so I would isolate each airfoil with a split (circle in my example)
Then Gambit will have less difficulty to mesh surfaces, especially when you impose a thin BL.
So I meshed one airfoil with this method (you choosed tri), but here you can easily mesh it with hexa.
I would mesh it with hexa ,then you can have more control on the aspect ratio between last cell layer from your BL and cells outside the BL.
Sans titre.jpg Sans titre2.png Sans titre3.jpg

gambiss · February 8, 2011, 10:18

Okay, thanks for that! I will reduce my surfaces...

But- I can only select hexa in volume meshing? How do I do it for 2D? :?

-mAx- · February 8, 2011, 10:52

quad or map

gambiss · February 9, 2011, 07:31

Hmm, I've meshing the blades seperately but I still get the same skewed BL around them...

-mAx- · February 9, 2011, 07:58

with quad or tri?
As you saw, with tri I didn't have any problem
post pictures

January 29, 2011, 11:03	Boundary layer meshing problems	#1
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	Hi I am having trouble making a boundary layer around an aerofoil as I want a y+ as 1 so structure mesh at first (1% of the chord) then unstructure out from that (modelling a VAWT turbine with three blades). Does anyone have any suggestion how to do this, as when I try it boundary layer function does go around the blade, and just make lines across it. Thanks

January 31, 2011, 02:31		#2
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	first mesh edges from your airfoil __________________ In memory of my friend Hervé: CFD engineer & freerider

February 1, 2011, 01:52		#4
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	can you post a picture with the BL you try to attach __________________ In memory of my friend Hervé: CFD engineer & freerider

February 7, 2011, 02:19		#6
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	if you deselect the trailing edge in the BL-surface list, does the error remain? __________________ In memory of my friend Hervé: CFD engineer & freerider

February 8, 2011, 01:58		#10
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	ok that means the error comes from this edge. Try to add more nodes on this edge. If it don't help, try to merge the edge with the 2 others (both sides), and perturb nodes distribution __________________ In memory of my friend Hervé: CFD engineer & freerider

January 31, 2011, 13:49		#3
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	Cheers. Now when I try to mesh, I either get error: boundary layer is to high, then when I reduce it says: that mesh is not possible without interference. I have taken off the auto smooth default. Is their anything else I should do? Thanks

February 6, 2011, 15:12		#5
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	Still having problems, is this a fault of my meshed edge or? An gambit error, as some times it seems to work with out hassle... and see that other people are having simular problem... https://picasaweb.google.com/1157392...56072322986802 https://picasaweb.google.com/1157392...56075170157810 https://picasaweb.google.com/1157392...56075170157810 Thanks for you help in advance!

February 7, 2011, 07:01		#7
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	If you mean, not creating a boundary layer around the trailing edge then no, this doesn't work either! But unsure of what you mean!

February 7, 2011, 08:08		#9
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	Yes, now it will mesh, is there any way to get it create a boundary layer around the whole blade? Thanks!

February 8, 2011, 05:42		#11
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	I've managed to Mesh it now, but, it is really skewed next to the blade, is this just from the position of the nodes and is the only way to solve this adjusting them? Or is there a simpler way!? Thanks for all you help, I really appreciate it!

February 8, 2011, 05:51		#12
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	post a picture __________________ In memory of my friend Hervé: CFD engineer & freerider

February 8, 2011, 06:01		#13
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	https://picasaweb.google.com/1157392...56384960415330 https://picasaweb.google.com/1157392...56392982700834

February 8, 2011, 06:04		#14
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	something is weird. Can you provide me the dbs file? __________________ In memory of my friend Hervé: CFD engineer & freerider

February 8, 2011, 06:59		#15
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	http://www.fileswap.com/dl/eQjBziUI/...again.zip.html

February 8, 2011, 08:30		#16
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	ok I kept the parameters from your BL and your SF. But first, you absolutely need to split your domain into several smallest surfaces. Indeed you have 3 airfoils, so I would isolate each airfoil with a split (circle in my example) Then Gambit will have less difficulty to mesh surfaces, especially when you impose a thin BL. So I meshed one airfoil with this method (you choosed tri), but here you can easily mesh it with hexa. I would mesh it with hexa ,then you can have more control on the aspect ratio between last cell layer from your BL and cells outside the BL. Sans titre.jpg Sans titre2.png Sans titre3.jpg __________________ In memory of my friend Hervé: CFD engineer & freerider

February 8, 2011, 10:18		#17
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	Okay, thanks for that! I will reduce my surfaces... But- I can only select hexa in volume meshing? How do I do it for 2D? :?

February 8, 2011, 10:52		#18
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	quad or map __________________ In memory of my friend Hervé: CFD engineer & freerider

February 9, 2011, 07:31		#19
gambiss New Member Emily Join Date: Jan 2011 Posts: 13 Rep Power: 15	Hmm, I've meshing the blades seperately but I still get the same skewed BL around them...

February 9, 2011, 07:58		#20
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	with quad or tri? As you saw, with tri I didn't have any problem post pictures __________________ In memory of my friend Hervé: CFD engineer & freerider

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