# 2nd Order Convergence Problem for 3D Airfoil

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September 8, 2015, 08:16
2nd Order Convergence Problem for 3D Airfoil
#1
New Member

Gokce Turkmen
Join Date: Feb 2015
Posts: 3
Rep Power: 11
Hi everyone,

I am working on simulating flow over 3D airfoil. I solved my case in first order Simplefoam but now I want to solve it in second order. But I didnt verify my first order result, it seemed good to me.

I tried different schemes only one of it converged but the residuals were higher than my first order. I used my converged result from first order simplefoam as initial guess. I only changed divergent schemes in simplefoam to increase the order. I put them at the end of this thread. (only the last one worked)

I tried icofoam but courant number diverged after some time. My case is laminar. I used my converged result from first order simplefoam as initial guess. I would be very greatfull if someone help me to solve my problem, because I have been working on this for long time.

I tried the schemes below:
divSchemes
{
default none;
div(phi,k) Gauss linear;
div(phi,epsilon) Gauss linear;
div(phi,R) Gauss linear;
div(R) Gauss linear;
div(phi,nuTilda) Gauss linear;
}
divSchemes
{
default none;
div(phi,U) Gauss linear;
div(phi,k) Gauss linear;
div(phi,epsilon) Gauss linear;
div(phi,R) Gauss linear;
div(R) Gauss linear;
div(phi,nuTilda) Gauss linear;
}
,divSchemes
{
default none;
div(phi,U) Gauss SFCD;
div(phi,k) Gauss linear;
div(phi,epsilon) Gauss linear;
div(phi,R) Gauss linear;
div(R) Gauss linear;
div(phi,nuTilda) Gauss linear;
}
divSchemes
{
default none;
div(phi,U) Gauss limitedLinearV 1;
div(phi,k) Gauss limitedLinear 1;
div(phi,epsilon) Gauss limitedLinear 1;
div(phi,R) Gauss limitedLinear 1;
div(R) Gauss linear ;
div(phi,nuTilda) Gauss limitedLinear 1;
}
divSchemes
{
default none;
div(phi,U) Gauss QUICKV leastSquares;
div(phi,k) Gauss linear;
div(phi,epsilon) Gauss linear;
div(phi,R) Gauss linear;
div(R) Gauss linear;
div(phi,nuTilda) Gauss linear;
}
divSchemes
{
default none;
div(phi,U) Gauss linearUpwindV leastSquares;
div(phi,k) Gauss linear;
div(phi,epsilon) Gauss linear;
div(phi,R) Gauss linear;
div(R) Gauss linear;
div(phi,nuTilda) Gauss linear;
}

I couldnt attach my case file so I am attaching my residualsi checkmesh results and BCs.

0/p
dimensions [0 2 -2 0 0 0 0];

internalField uniform 0;

boundaryField
{
wall
{
}

airfoil
{
}

sides
{
type freestreamPressure;
}

}
0/U
dimensions [0 1 -1 0 0 0 0];

internalField uniform (1 0 0);

boundaryField
{
wall
{
type fixedValue;
value uniform (0 0 0);
}

airfoil
{
type fixedValue;
value uniform (0 0 0);
}

sides
{
type freestream;
freestreamValue uniform (1 0 0);
}

}
Time = 0

Mesh stats
points: 370455
faces: 4159775
internal faces: 4037721
cells: 2049374
boundary patches: 3
point zones: 0
face zones: 0
cell zones: 0

Overall number of cells of each type:
hexahedra: 0
prisms: 0
wedges: 0
pyramids: 0
tet wedges: 0
tetrahedra: 2049374
polyhedra: 0

Checking topology...
Boundary definition OK.
Point usage OK.
Upper triangular ordering OK.
Face vertices OK.
Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
Patch Faces Points Surface topology
airfoil 72504 36528 ok (non-closed singly connected)
sides 2470 1393 ok (non-closed singly connected)
wall 47080 23974 ok (non-closed singly connected)

Checking geometry...
Overall domain bounding box (-0.85 -0.5 -1.66533e-16) (1.05 0.5 0.27)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-1.59378e-17 6.14025e-17 -3.65029e-15) OK.
Max cell openness = 3.74888e-16 OK.
Max aspect ratio = 6.7235 OK.
Minumum face area = 3.48265e-09. Maximum face area = 0.00154965. Face area magnitudes OK.
Min volume = 9.66928e-14. Max volume = 2.01324e-05. Total volume = 0.512781. Cell volumes OK.
Mesh non-orthogonality Max: 58.2936 average: 19.726
Non-orthogonality check OK.
Face pyramids OK.
Max skewness = 0.715771 OK.
Coupled point location match (average 0) OK.

Mesh OK.

End

Thank you
Attached Images
 simplefirst.png (28.4 KB, 22 views) simplesecond.png (58.6 KB, 21 views) ico.png (28.2 KB, 21 views) airfoil1.png (115.6 KB, 20 views) airfoil2.png (98.0 KB, 18 views)

 September 10, 2015, 07:20 #2 Senior Member     Philipp Join Date: Jun 2011 Location: Germany Posts: 1,297 Rep Power: 26 1st order has more numerical dissipation than 2nd order, i.e. you spuriously solve for a case with artificially higher viscosity. Also, you damp all kinds of effects by 1st order schemes. Maybe your case just isn't stationary, which only appears in 2nd order? Edit: Ok, you should post the whole schemes file and also the fvOptions. And some log output would be beneficial. Please use the "code" button (under "->Go Advanced') to post code - don't just copy it to the text box. Also: Why do you specify all the different div-Schemes for a laminar case? This is pretty confusing. __________________ The skeleton ran out of shampoo in the shower.

 Tags 3d airfoil, icofoam problem, simplefoam second order