# 3D Airfoil simulation cd to low kklOmega-Modell

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May 16, 2021, 07:40
3D Airfoil simulation cd to low kklOmega-Modell
#1
New Member

Sebastian
Join Date: May 2021
Location: Germany
Posts: 1
Rep Power: 0
Hi everyone,

I am trying to simulate a NACA 23015 airfoil in OpenFoam 8. The source of the results is a technical report written by NASA "AERODYNAMIC CHARACTERISTICS OF 15 NACA AIRFOIL SECTIONS AT SEVEN REYNOLDS NUMBERS FROM 0.7 x 10^6 TO 9.0 x 10^6"
I started with a opensouce motorbike case and tried to change it for the airfoil simulation. (I am unfortunately an OpenFoam newbie)
The model for the simulation was created in Catia. I am trying to study an "endless airfoil" which means that the model is larger in y-direction than blockmesh.
The airfoil length is 24 inch (0.6096m).

My blockmesh:
vertices
(
(-3 -0.05 -5)
( 8 -0.05 -5)
( 8 0.05 -5)
(-3 0.05 -5)
(-3 -0.05 5)
( 8 -0.05 5)
( 8 0.05 5)
(-3 0.05 5)
);

blocks
(
hex (0 1 2 3 4 5 6 7) (110 1 100) simpleGrading (1 1 1)
);
The origin of the coordinate system is also the origin of the airfoil

After a few tests I noticed that I have to change the turbulence model in a low reynolds model, because my y+ is lower than 5.
I have chosen the kklOmega model. Now my case is running, but I get wrong results. My result for cd should be at 0.007 for a Re=2*10^6 but I get 0.0038. The cl should be 0.1-0.12 and I get 0.141

I am going to add the systems folder so that you can take a look but in the following lines i will summary the most important things:

snappyhexmesh:
refinementBox2
{
type searchableBox;
min (0.35 -0.05 -1);
max ( 4.0 0.05 1);
}

nCellsBetweenLevels 6;

edge refinement: level 9
surface-wise refinement: 8 9
region-wise refinement: levels ((1E15 5))

nSurfaceLayers: 10
min. Thickness: 0.1
finalLayerThickness: 0.3

fv solution

for u,kl,kt and omega:
{
solver smoothSolver;
smoother GaussSeidel;
tolerance 1e-8;
relTol 0.1;
nSweeps 1;
}

residualcontrol
{
p 1e-4; // 1e-2
U 1e-5; // 1e-3
"(kt|kl|epsilon|omega)" 1e-5; // 1e-3
}

fvschemes
divSchemes
{
default none;
div(phi,kt) bounded Gauss upwind;
div(phi,kl) bounded Gauss upwind;
div(phi,omega) bounded Gauss upwind;
}

Please donīt be confused that the airfoil is named motorBike(stl)

I hope you can help me. If you need more information just let me know.

Attached Files
 system.zip (10.5 KB, 5 views)

 May 18, 2021, 18:26 #2 Senior Member   Klaus Join Date: Mar 2009 Posts: 258 Rep Power: 22 It's probably insufficient boundary layer mesh refinement, try y+ < 1, use up to 10000 timesteps and skip residual control.

 May 19, 2021, 16:39 #3 Senior Member     Herpes Free Engineer Join Date: Sep 2019 Location: The Home Under The Ground with the Lost Boys Posts: 932 Rep Power: 12 In addition to Klaus' remarks: I don't want to blame the turbulence model at this point, but the model is transitional model. In your case, do you expect any transition? __________________ The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror

 Tags airfoil 3d, kklomega, low drag, low re correction, yplusras