
[Sponsors] 
July 22, 2013, 09:04 
Meshing a s809 wing in Gambit

#1 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
Hello everybody,
Im new in CFD so my questions may seem a bit dumb but i cant help it so here it goes!Im currently trying to simulate a 3d multiphase (airstream+rain drops) flow over a s809 wing.So i attempted to mesh the wing and the farfield and the result was a mesh that kept the solution from converging in Realizable ke model of 2nd order.After reading many answers in similar situations in these forums i tried to make a 2nd mesh in order to get convergence.The thing is that although the solution did converge,the results seem to be a bit off the experimental ones plus there is a highly skewed element in my wing which i dont know how to smooth it. I am simulating a S809 wing (initially in single phase flowairand then in multiphase flow) in Re=2x10^6 using kw sst, realizable ke and spalart allmaras turb models. Here are the 2 meshes i used for this simulation: 

July 23, 2013, 02:53 

#2 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
I would appreciate it very much if someone could give me a hint on how to improve the 3.mesh because of its highly skewed element at the trailing edge.Here are the vertices that i used for the airfoil


July 23, 2013, 03:32 

#3 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
post picture of your mesh, and especially where you get skewed elements
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 04:00 

#4 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
thanks for the reply Max,I attach below some pictures


July 23, 2013, 04:04 

#5 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
from your picture 7, it seems you meshed also your wing (solid part).
why?
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 04:08 

#6 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
I am simulating the 3d flow over the wing so i thought that i should have the wing unmeshed for the part where there is the actual wing and have the wing meshed where there should only be the flowfield,in order to study the effects due to induced drag


July 23, 2013, 04:15 

#7 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
if you delete the wing volume, do you see your wing as hollow?
You should have substracted your outer domain with your wing.
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 04:22 

#8 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
Yes Max i deleted the volume of the meshed wing (and the mesh in the face of the wing where z=5/I meshed that face because i got a warning when i tried to export the mesh,concerning boundaries) and theres a hole in my mesh.As for substracting,i didnt substract the wing initially (in 2d mesh) i just created the hole out of its adjacent edges.


July 23, 2013, 04:24 

#9 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
then delete the wing volume, and compute on the rest of the grid
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 04:28 

#10 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
Initially i had my wing unmeshed for 0<z<5(theres the actual wing in the calculations) and had it meshed for 0>z>2(theres only air in calculations).If i delete the wing volume (which is 2<z<0) then theres a hole in the mesh and then we assume that the wing extends from the left to the right side of the flowfield,or?Excuse me for those dumb questions


July 23, 2013, 04:37 

#11 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
what im trying to say is that if i calculate the grid just like that,dont we assume that we have got a wing all over the width of the flowfield and as such we neglect the 3d effects?


July 23, 2013, 04:44 

#12 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
ok I understood
The problem comes from your wing extension. So you have to fix this skew element. You can try to split the trailing edge (sharp angle), and mesh this surface with only one tri element. Then propate this split in the zdirection Untitled.png
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 04:53 

#13 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
So i split the upper and lower edges at the secondtolast node and i create a triangle as you show in your picture.Then i mesh the 2 parts of the wing separately (the whole wing and the last trianglelike part which i have created with the split).For the latter i use 1 tri element.Is that correct?


July 23, 2013, 05:03 

#14 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
yes, it is.
But you will need another split on the right (next to the triangle), especially if you want hexa mesh. Hence the triangle "lock" the thickness of your "wing" with one element. With this second split, you can generate a transition from x elements to one element. Then, as you refined your mesh on the wing, you will also do this refinement on this area
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 05:18 

#15 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
I didnt understand the second split next to the triangle


July 23, 2013, 05:22 

#16 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
on my picture I represented this volume with a rectangle (inside this rectangle you can mesh with tri or pave)
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 05:30 

#17 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
So the wing is split into 3 parts:the first one to the left(the biggest),the 2nd one(the trapezoid one) and the third one (the triangle one)?


July 23, 2013, 05:35 

#18 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
yes:
hexa > tri or pave (transition) > tri (one element) Then another split along (xy) for refinement at the end of the wing
__________________
In memory of my friend Hervé: CFD engineer & freerider 

July 23, 2013, 05:44 

#19 
Member
Nikolaos R.
Join Date: Nov 2009
Posts: 30
Rep Power: 9 
After trying to split the right most area (the triangle one) my geometry changes and the edges seem to be converging


July 23, 2013, 06:01 

#20 
Super Moderator
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 3,186
Rep Power: 33 
wait your angle will be to sharp and will generate skewness.
Question, is your wing section constant? on your picture 7 , the trainling edge is represented in light blue, right?
__________________
In memory of my friend Hervé: CFD engineer & freerider 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
[ICEM] ICEM sizing function >>> Gambit and Ansys meshing  Far  ANSYS Meshing & Geometry  6  March 5, 2013 02:16 
3D wing + wind tunnel hexa structured meshing  icemaniac178  ANSYS Meshing & Geometry  9  October 28, 2010 09:37 
Meshing for 3D wing with tubercle on the leading edge in GAMBIT  nvtrieu  FLUENT  0  August 14, 2010 10:13 
mesh missing after export in gambit  morteza08  ANSYS Meshing & Geometry  1  July 26, 2010 01:10 
mesh missing after export in gambit  morteza08  Main CFD Forum  0  July 23, 2010 02:19 