[vinz]

Hello everybody,

I am trying to run simpleFoam on a 2D multi element airfoil.
I usualy don't have big problems to run simpleFoam but here it crashes straight at the first iteration with this message:

/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 1.6 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
Build : 1.6-f802ff2d6c5a
Exec : simpleFoam -case coarse
Date : Oct 12 2009
Time : 11:49:30
Host : bigbrain13
PID : 2647
Case : ./coarse
nProcs : 1
SigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create mesh for time = 0

Reading field p

Reading field U

Reading/calculating face flux field phi

Selecting incompressible transport model Newtonian
Selecting RAS turbulence model laminar

Starting time loop

Time = 1

#0 Foam::error:rintStack(Foam::Ostream&) in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so"
#1 Foam::sigFpe::sigFpeHandler(int) in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so"
#2 __restore_rt at sigaction.c:0
#3 Foam::divide(Foam::Field<double>&, double const&, Foam::UList<double> const&) in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so"
#4 Foam:perator/(double const&, Foam::tmp<Foam::Field<double> > const&) in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libOpenFOAM.so"
#5 Foam::fvPatch::makeDeltaCoeffs(Foam::Field<double> &) const in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libfiniteVolume.so"
#6 Foam::surfaceInterpolation::makeDeltaCoeffs() const in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libfiniteVolume.so"
#7 Foam::surfaceInterpolation::deltaCoeffs() const in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libfiniteVolume.so"
#8 Foam::fvPatch::deltaCoeffs() const in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libfiniteVolume.so"
#9 Foam::fvPatchField<Foam::Vector<double> >::snGrad() const in "/CFDBB/vincent/OpenFOAM/OpenFOAM-1.6/applications/bin/linux64GccDPOpt/simpleFoam"
#10 Foam::fv::gaussGrad<Foam::Vector<double> >::correctBoundaryConditions(Foam::GeometricField< Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh> const&, Foam::GeometricField<Foam::Tensor<double>, Foam::fvPatchField, Foam::volMesh>&) in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libfiniteVolume.so"
#11 Foam::fv::gaussGrad<Foam::Vector<double> >::grad(Foam::GeometricField<Foam::Vector<double >, Foam::fvPatchField, Foam::volMesh> const&) const in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libfiniteVolume.so"
#12 Foam::tmp<Foam::GeometricField<Foam:uterProduct< Foam::Vector<double>, Foam::Vector<double> >::type, Foam::fvPatchField, Foam::volMesh> > Foam::fvc::grad<Foam::Vector<double> >(Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh> const&, Foam::word const&) in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libincompressibleRASModels.so"
#13 Foam::tmp<Foam::GeometricField<Foam:uterProduct< Foam::Vector<double>, Foam::Vector<double> >::type, Foam::fvPatchField, Foam::volMesh> > Foam::fvc::grad<Foam::Vector<double> >(Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh> const&) in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libincompressibleRASModels.so"
#14 Foam::incompressible::RASModels::laminar::divDevRe ff(Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh>&) const in "/CFDBB/vincent/OpenFOAM//OpenFOAM-1.6/lib/linux64GccDPOpt/libincompressibleRASModels.so"
#15 main in "/CFDBB/vincent/OpenFOAM/OpenFOAM-1.6/applications/bin/linux64GccDPOpt/simpleFoam"
#16 __libc_start_main in "/lib64/libc.so.6"
#17 _start at /usr/src/packages/BUILD/glibc-2.9/csu/../sysdeps/x86_64/elf/start.S:116
segmentation fault

Unfortunately, I don't understand what it says.
Can it come from the mesh or is it something else?
Thanks for any info

Vincent

[vinz]

Hi everybody,

I got my problem solved. It was coming from an exactly zero area face in my mesh which was apparently enough to raise a segmentation fault, certainly due to a division by zero somewhere in the code.
Anyway, I did a new mesh and I get interesting results for only few hours spent on the case.
You'll find attached some pictures of the field as well as the Cp plots over the airfoils and some pics of the mesh.
I've got some other detailed views, so if people are interested I can post them later on. I may write a very small paper on the subject as well.

Regards,

Vincent

[vinz]

Dear OpenFOAMers,

I have a question about simpleFOAM. I know it is solving p/rho instead of p, at least, that's what I understood. However I was wondering which rho is it taking as reference? 1? 1.225? something else?

In fact, I tried to change the value of rho in the transportProperties file, going from 1 to 1.225 or even 0.561, and it doesn't change anything. Is this value taken into account by the code?

My question comes from the fact that in my test case, I have a mach number and a reynolds value. If I want to specify a speed value, I have to play with rho and nu to match my Re. How can I be sure that I match my Mach number? what is the reference temperature taken by the code?

Thanks to anyone who can give me some details about that. Being used to work with compressible flows, I have some difficulties to understand the way simpleFoam works.

Vincent

[Verfblikje]

Dear vinz,

Searching google I found this thread. Could you tell me how you built the mesh? For some time I have been trying to build a 2D multi-element airfoil mesh (double-slotted flap as opposed to slat-flap). However, I have not been able to make one.
I tried Salomé and snappyHexMesh. Since sHM does not have a GUI it is not very straightforward for me. On the other hand, Salomé gives me a very distorted mesh. Could you please give me some tips?

Kind regards,

Nick

/edit: Apologies for bumping old thread

[vinz]

I use GridPro to do my mesh when I need a very good accuracy.

[Verfblikje]

Thanks for the quick reply. However, I am not in a position to buy a piece of software that expensive just yet. Thanks anyways!

[vinz]

I understand. If you are a student or an academic, you can also contact GridPro, they do prices for them.

Good luck for your case.

[MUZ]

hello Vinz, i am simulating flow over naca0012 aerofoil and i am trying to sample pressure data on the aerofoil and conduct a Cp v x/c plot.any ideas how to go about it please.
thank you

[vinz]

At that time I used Tecplot for the post processing of the Cp values.

[MUZ]

thanks for the reply

[vkrastev]

@MUZ
If you don't use (or don't have access to) Tecplot, you can do the job with the sample utility for extracting the pressure data at the airfoil surface and (for instance) gnuplot for postprocess them.

@vinz
I don't know if you have solved your doubts about simpleFoam (I guess so, judging from the date of your post about the matter), but the answer is that the way the solver has been designed does not allow to take into account any kind of Mach effects: it is a purely incompressible approach, in which (as you have already noticed) the pressure gradient is actually solved for p/rho, and not for p. A reference density value can be only taken into account if you have to calculate aerodynamic forces with the forces function. So, if you have to match some experimental low-Mach number conditions, just focus on the right velocity and kinematic viscosity values to be consistent with the Reynolds number.

Best

V.

[MUZ]

hello Vkrastev,
thank you for the reply i used the sample utility in OF to extract the pressures on the airfoil surface. i got x,y,z&p values and non dimensionalised ie Cp=p/0.5*rho*V^2 to get the Cp values but i do not get a good plot for Cp v x/c. i think there is some basic or fundamental mistake i am making but cant seem to figure out. i have posted my sample data.Please could you verify to see where i am going wrong. thank you.
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.0.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object sampleDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

interpolationScheme cell;

setFormat raw;

surfaceFormat raw;

fields
(
p
);

sets
(
);

surfaces
(
naca
{
type patch;
patches (naca_ascii);
interpolate false;
triangulate false;
}
);

// ************************************************** *********************** //

# p FACE_DATA 376
# x y z p
0.174913 -0.038935 0.125 -336.939
0.137808 -0.0423376 0.125 -329.806
0.180226 -0.0384175 0.125 -332.959
0.174956 0.0395397 0.125 -1863
0.18026 0.0389632 0.125 -1828.27
-0.427986 -0.0411248 0.125 2167.09
-0.421859 -0.0424192 0.125 2088.4
0.131682 -0.0428595 0.125 -319.894
-0.428084 0.0415035 0.125 -8583.91
-0.421952 0.0428129 0.125 -8184.66
-0.490817 -0.0159395 0.125 4051.48
0.36885 -0.0179373 0.125 -262.057
-0.491004 0.0161267 0.125 -15161.3
0.368939 0.0184724 0.125 -909.816
-0.486198 -0.019565 0.125 4269.9
0.158914 -0.0404514 0.125 -343.396
0.153577 -0.0409387 0.125 -333.277
0.389933 -0.015475 0.125 -259.064
0.374161 -0.017322 0.125 -258.838
-0.486451 0.0197643 0.125 -14221.8
0.158999 0.0412746 0.125 -1992.55
0.153696 0.0418386 0.125 -2030.14
0.309251 0.0253554 0.125 -1200.49
0.390109 0.0158856 0.125 -796.478
0.37422 0.0178343 0.125 -883.665
0.394773 -0.0149014 0.125 -256.51
-0.44261 0.0378846 0.125 -9512.09
-0.207004 0.0602094 0.125 -4326.2
-0.191657 0.0601673 0.125 -4162.2
-0.212209 0.0601914 0.125 -4363.09
0.395273 0.0152454 0.125 -768.793
-0.499655 -0.00225307 0.125 -4118.55
-0.499705 0.00226808 0.125 -10006.9
0.169582 -0.0394478 0.125 -337.061
0.142923 -0.0418887 0.125 -336.643
0.185412 -0.0379061 0.125 -332.674
0.218097 -0.0345714 0.125 -310.041
0.212772 -0.0351253 0.125 -313.357
0.169637 0.040118 0.125 -1898.23
0.18544 0.0384 0.125 -1793.45
0.218134 0.0349296 0.125 -1612.52
0.21281 0.035486 0.125 -1640.82
-0.432804 -0.0400556 0.125 2262.66
-0.458665 -0.0323429 0.125 3205.68
0.22342 -0.0340136 0.125 -306.798
0.228742 -0.0334536 0.125 -303.171
-0.432984 0.0403963 0.125 -8941.77
-0.458801 0.0326711 0.125 -10290.1
0.223458 0.0343733 0.125 -1585.46
0.228782 0.0338169 0.125 -1559.59
0.358474 -0.0191322 0.125 -262.993
0.363563 -0.0185476 0.125 -262.107
0.496013 -0.0015689 0.125 11.3652
0.357708 0.0198199 0.125 -968.038
0.363855 0.0190824 0.125 -934.911
0.164248 -0.0399529 0.125 -341.022
0.148237 -0.0414159 0.125 -330.755
0.190254 -0.0374232 0.125 -327.408
0.196234 -0.0368205 0.125 -324.359
0.202369 -0.0361972 0.125 -320.245
0.207471 -0.0356738 0.125 -319.734
0.384763 -0.0160838 0.125 -257.942
0.37947 -0.0167036 0.125 -260.159
0.164318 0.0406963 0.125 -1940.41
0.148588 0.0423544 0.125 -2046.93
0.190284 0.0378734 0.125 -1761.97
0.196271 0.0372263 0.125 -1721.95
0.202412 0.0365727 0.125 -1685.94
0.20751 0.0360398 0.125 -1665.95
0.384825 0.0165374 0.125 -825.313
0.379524 0.0171878 0.125 -853.981
-0.437516 -0.0389092 0.125 2389.3
-0.443527 -0.037249 0.125 2605.37
-0.449549 -0.0354567 0.125 2809.33
-0.454148 -0.0339435 0.125 3014.64
0.244071 -0.0318226 0.125 -297.069
0.239228 -0.0323406 0.125 -297.516
0.234046 -0.0328919 0.125 -302.021
-0.437912 0.0391594 0.125 -9085.04
-0.448551 0.0360975 0.125 -9605.16
-0.454415 0.0341748 0.125 -9922.85
-0.185846 0.0601236 0.125 -4105.47
-0.201679 0.0602089 0.125 -4275.14
-0.196467 0.0601926 0.125 -4221.73
-0.217022 0.0601627 0.125 -4433.66
-0.0190183 0.0541865 0.125 -2837.02
0.244606 0.0321758 0.125 -1481.93
0.249452 0.0316832 0.125 -1464.35
0.239416 0.0327082 0.125 -1506.74
0.234105 0.0332605 0.125 -1533.5
0.400112 0.0146423 0.125 -742.25
0.486754 -0.00276903 0.125 109.264
0.492457 -0.00202616 0.125 95.278
0.136479 0.0435394 0.125 -2116.63
0.142455 0.0429547 0.125 -2077.85
-0.34123 -0.0541177 0.125 821.25
-0.378775 -0.0498301 0.125 1282.99
-0.383596 -0.0491636 0.125 1375.36
-0.389624 -0.048276 0.125 1442.89
0.00288606 -0.0525213 0.125 -212.548
0.0082449 -0.0521692 0.125 -219.102
0.045712 -0.04953 0.125 -230.731
0.0889618 -0.0462957 0.125 -274.585
0.0509143 -0.049156 0.125 -238.571
0.0943104 -0.0458744 0.125 -276.616
0.47603 -0.00419555 0.125 38.9129
-0.378833 0.0501761 0.125 -6805.66
-0.389681 0.0486567 0.125 -7160.17
-0.38366 0.049528 0.125 -6999.75
0.00290783 0.0529809 0.125 -2724.72
0.089092 0.0477157 0.125 -2391.29
0.00827355 0.0526859 0.125 -2699.56
0.0458314 0.0506006 0.125 -2560.91
0.0511967 0.0503019 0.125 -2550.32
0.0944201 0.0473266 0.125 -2370.8
0.131632 0.0440136 0.125 -2147.9
0.476233 0.00470107 0.125 -307.194
0.352329 -0.0198351 0.125 -261.777
0.346334 -0.0205188 0.125 -263.65
0.331016 -0.0222537 0.125 -267.711
0.480863 -0.00354681 0.125 69.482
0.34687 0.0211051 0.125 -1022.66
0.331093 0.0229416 0.125 -1112.24
0.351711 0.0205363 0.125 -1000.96
0.481401 0.00399413 0.125 -273.626
0.455296 -0.00709974 0.125 -119.466
0.455346 0.00750996 0.125 -427.877
-0.470107 -0.0280035 0.125 3658.55
-0.475692 -0.025591 0.125 3907.03
0.310003 -0.0246048 0.125 -269.346
0.325702 -0.0228512 0.125 -266.464
-0.470432 0.028249 0.125 -11689.4
0.32578 0.023542 0.125 -1131.37
-0.464468 -0.0301843 0.125 3437.51
-0.357745 -0.0523622 0.125 1090.23
-0.363061 -0.0517691 0.125 1116.82
-0.405984 -0.0455751 0.125 1724.14
-0.400807 -0.0464997 0.125 1615.81
-0.0131649 -0.0535758 0.125 -230.433
-0.0182967 -0.0539113 0.125 -252.754
0.0243113 -0.051062 0.125 -227.877
0.0296658 -0.0506786 0.125 -219.125
0.0729341 -0.0475197 0.125 -257.527
0.0678137 -0.0479047 0.125 -247.621
0.110355 -0.0446021 0.125 -286.346
0.115687 -0.0441793 0.125 -298.077
0.261296 -0.029962 0.125 -284.71
0.30386 -0.0252908 0.125 -274.339
0.266592 -0.0293896 0.125 -283.478
0.282546 -0.0276428 0.125 -275.58
0.287848 -0.0270598 0.125 -273.539
0.460356 -0.00637707 0.125 -79.5929
-0.464642 0.0305135 0.125 -10578.2
-0.406051 0.0459466 0.125 -7645.24
-0.400868 0.0468617 0.125 -7484.34
-0.357817 0.0527762 0.125 -6334.95
-0.363104 0.052167 0.125 -6480.46
-0.0129271 0.0538516 0.125 -2805.88
0.0243701 0.0517954 0.125 -2632.22
0.0297355 0.0514966 0.125 -2610.94
0.0719162 0.04897 0.125 -2476.12
0.0670714 0.0493238 0.125 -2525.96
0.110466 0.0460848 0.125 -2366.33
0.115797 0.0455632 0.125 -2286.67
0.26157 0.0304488 0.125 -1418.46
0.266672 0.029923 0.125 -1399.5
0.282617 0.028267 0.125 -1333.26
0.303262 0.0260125 0.125 -1229.15
0.287933 0.0276942 0.125 -1311.54
0.460417 0.00683442 0.125 -399.168
0.433149 -0.0101535 0.125 -230.16
0.427877 -0.0108367 0.125 -238.33
0.438295 -0.0094706 0.125 -217.282
0.443126 -0.00881167 0.125 -198.201
0.43319 0.0104349 0.125 -558.835
0.427913 0.0111178 0.125 -589.584
0.438346 0.00976617 0.125 -528.973
0.44318 0.00913065 0.125 -502.81
-0.34736 -0.0535206 0.125 950.678
-0.373635 -0.050503 0.125 1239.15
-0.415839 -0.0436822 0.125 1947.37
-0.335255 -0.0546388 0.125 826.04
-0.330408 -0.0550562 0.125 813.045
-0.298488 -0.0572499 0.125 527.94
-0.303845 -0.0569385 0.125 601.57
-0.255505 -0.0590447 0.125 311.068
-0.260889 -0.0588358 0.125 373.891
-0.293125 -0.0575049 0.125 487.549
-0.287753 -0.0577268 0.125 516.858
-0.169331 -0.0595149 0.125 36.9852
-0.174716 -0.0595929 0.125 58.0531
-0.20703 -0.0598352 0.125 115.196
-0.201643 -0.0598281 0.125 109.067
-0.250119 -0.0592089 0.125 257.803
-0.244739 -0.0593413 0.125 271.054
-0.212419 -0.0598274 0.125 131.028
-0.217807 -0.0598004 0.125 144.566
-0.163951 -0.0594275 0.125 29.4754
-0.158564 -0.05933 0.125 8.57843
-0.126287 -0.0584867 0.125 -3.56861
-0.131665 -0.0586302 0.125 5.82357
-0.083274 -0.0572248 0.125 -155.226
-0.0886477 -0.0574359 0.125 -170.47
-0.120909 -0.0583432 0.125 -14.7492
-0.115531 -0.0582028 0.125 -27.9702
-0.00247281 -0.0528733 0.125 -207.52
-0.0351497 -0.0548742 0.125 -191.923
-0.0303088 -0.0546042 0.125 -202.279
-0.0779003 -0.0570138 0.125 -156.55
-0.0725314 -0.0567899 0.125 -184.259
-0.0403625 -0.055165 0.125 -186.519
-0.0457103 -0.0554632 0.125 -195.928
0.0136019 -0.051815 0.125 -228.791
0.0403747 -0.049912 0.125 -225.345
0.0836118 -0.0467082 0.125 -262.748
0.0557559 -0.0488014 0.125 -247.084
0.0616999 -0.0483594 0.125 -243.975
0.0996587 -0.0454502 0.125 -274.202
0.125724 -0.0433621 0.125 -325.021
0.470875 -0.00489905 0.125 3.35084
-0.41591 0.0440573 0.125 -7928.63
-0.3406 0.0545652 0.125 -6054.69
-0.346578 0.0539799 0.125 -6200.74
-0.373679 0.0508635 0.125 -6652.16
-0.335786 0.0550114 0.125 -5995.41
-0.330618 0.0554237 0.125 -5932.69
-0.29851 0.0576133 0.125 -5423.91
-0.303868 0.0573237 0.125 -5492.92
-0.255515 0.0594382 0.125 -4819.25
-0.260898 0.0592612 0.125 -4872.33
-0.29314 0.057867 0.125 -5265.99
-0.28777 0.0581207 0.125 -5156.16
-0.169329 0.0599389 0.125 -3954.44
-0.174687 0.0600082 0.125 -4005.21
-0.250131 0.0595926 0.125 -4771.61
-0.244753 0.0597346 0.125 -4704.8
-0.163946 0.0598604 0.125 -3907.39
-0.158561 0.0597738 0.125 -3860.17
-0.126274 0.0590523 0.125 -3609.15
-0.131653 0.0591865 0.125 -3642.49
-0.0832638 0.057523 0.125 -3297.15
-0.0886359 0.0577545 0.125 -3349.85
-0.120892 0.0589059 0.125 -3587.78
-0.115511 0.0587357 0.125 -3549.81
-0.00245794 0.0532759 0.125 -2753.23
-0.0349856 0.0550692 0.125 -2942
-0.0297714 0.0547792 0.125 -2905.72
-0.0778918 0.0572915 0.125 -3261.83
-0.0725245 0.0570483 0.125 -3238.34
-0.0403333 0.0553668 0.125 -2984.69
-0.0456987 0.0556654 0.125 -3032.21
0.0839713 0.0480896 0.125 -2407.24
0.0136392 0.0523909 0.125 -2676.54
0.040466 0.0508993 0.125 -2575.42
0.056562 0.0500031 0.125 -2544.35
0.0997734 0.0469357 0.125 -2355.57
0.126442 0.0445215 0.125 -2180.07
0.470966 0.00541902 0.125 -336.85
-0.497204 -0.00791832 0.125 1520.83
-0.49375 -0.0129623 0.125 3483.08
0.341491 -0.0210694 0.125 -264.48
0.336314 -0.0216555 0.125 -264.913
0.496366 0.000351585 0.125 -737.826
-0.497349 0.00801548 0.125 -15074.2
-0.493937 0.0131262 0.125 -15852.8
0.341696 0.0217075 0.125 -1048.69
0.336402 0.0223239 0.125 -1079.38
0.417284 -0.0121733 0.125 -251.871
0.422583 -0.0115098 0.125 -245.194
0.449143 -0.00797043 0.125 -158.94
0.417346 0.0124704 0.125 -649.631
0.422618 0.0117983 0.125 -619.915
0.449193 0.00832966 0.125 -464.541
-0.481157 -0.0229234 0.125 4141.57
0.315095 -0.0240362 0.125 -266.946
0.320387 -0.0234454 0.125 -265.933
-0.474677 0.0264832 0.125 -12983.9
-0.480094 0.023804 0.125 -14137.2
0.315392 0.0246816 0.125 -1174.37
0.320487 0.0241228 0.125 -1154.37
-0.352453 -0.0529525 0.125 1032.35
-0.368361 -0.0511598 0.125 1161.48
-0.411062 -0.0446252 0.125 1804.49
-0.395777 -0.0473352 0.125 1528.25
-0.3199 -0.0559171 0.125 641.847
-0.325209 -0.0555037 0.125 746.246
-0.314567 -0.0562693 0.125 627.214
-0.309206 -0.0566039 0.125 637.756
-0.271633 -0.0583922 0.125 456.774
-0.266261 -0.058614 0.125 420.028
-0.277007 -0.0581704 0.125 490.723
-0.28238 -0.0579486 0.125 518.184
-0.185487 -0.0597205 0.125 72.007
-0.180101 -0.059659 0.125 67.1925
-0.190873 -0.0597682 0.125 90.4781
-0.196255 -0.0598044 0.125 91.4034
-0.233973 -0.0595945 0.125 208.354
-0.239361 -0.0594737 0.125 258.518
-0.228584 -0.0596874 0.125 168.982
-0.223196 -0.0597541 0.125 157.563
-0.1478 -0.0590609 0.125 13.7744
-0.153178 -0.0592044 0.125 -7.42864
-0.142421 -0.0589173 0.125 22.0134
-0.137043 -0.0587737 0.125 15.4573
-0.0993964 -0.0577864 0.125 -121.463
-0.0940211 -0.0576255 0.125 -146.246
-0.104774 -0.0579306 0.125 -81.7997
-0.110153 -0.058066 0.125 -51.623
-0.00783163 -0.0532254 0.125 -209.524
-0.0243952 -0.0542744 0.125 -216.67
-0.0617935 -0.0563008 0.125 -186.98
-0.0671642 -0.0565479 0.125 -188.263
-0.0564331 -0.0560446 0.125 -205.365
-0.0510756 -0.0557624 0.125 -218.081
0.0189568 -0.0514452 0.125 -242.805
0.0350203 -0.0502954 0.125 -220.8
0.0782608 -0.047115 0.125 -258.945
0.105007 -0.0450262 0.125 -277.835
0.120883 -0.0437624 0.125 -314.266
0.2562 -0.0305128 0.125 -286.244
0.250059 -0.0311765 0.125 -291.343
0.271911 -0.028811 0.125 -285.039
0.277228 -0.0282276 0.125 -280.827
0.297869 -0.0259567 0.125 -274.173
0.293027 -0.0264901 0.125 -273.168
0.412006 -0.012824 0.125 -253.075
0.406922 -0.013443 0.125 -255.6
0.400774 -0.0141843 0.125 -256.345
0.465609 -0.00563255 0.125 -36.0574
-0.411123 0.0449984 0.125 -7787.09
-0.395837 0.0477018 0.125 -7331.33
-0.352717 0.0533498 0.125 -6261.96
-0.368405 0.0515375 0.125 -6592.6
-0.319927 0.056195 0.125 -5627.8
-0.325281 0.0558087 0.125 -5757.69
-0.314573 0.0565814 0.125 -5555.47
-0.309219 0.0569677 0.125 -5507.86
-0.271652 0.0588675 0.125 -5010.21
-0.266273 0.0590737 0.125 -4959.02
-0.27703 0.0586281 0.125 -5043.43
-0.2824 0.0583745 0.125 -5092.75
-0.179824 0.0600665 0.125 -4048.46
-0.234001 0.0599606 0.125 -4614.31
-0.239365 0.0598612 0.125 -4665.7
-0.228867 0.0600452 0.125 -4548.86
-0.222842 0.0601175 0.125 -4510.2
-0.147794 0.0595743 0.125 -3776.16
-0.153178 0.059678 0.125 -3821.54
-0.14241 0.0594548 0.125 -3744.27
-0.137032 0.0593207 0.125 -3688.96
-0.0993833 0.0581909 0.125 -3422.81
-0.0940086 0.0579852 0.125 -3409.17
-0.104759 0.0583725 0.125 -3452.5
-0.110135 0.0585541 0.125 -3493.84
-0.00779787 0.0535695 0.125 -2781.85
-0.0249298 0.0545114 0.125 -2874.17
-0.0617914 0.0565085 0.125 -3142.74
-0.0671593 0.0567834 0.125 -3197.81
-0.0564234 0.0562335 0.125 -3099.19
-0.0510605 0.0559553 0.125 -3065.92
0.0778589 0.048536 0.125 -2431.12
0.0190048 0.0520941 0.125 -2655.34
0.0351007 0.0511979 0.125 -2592.15
0.0618855 0.0496817 0.125 -2551.14
0.105125 0.0465429 0.125 -2348.15
0.121127 0.0450415 0.125 -2218.78
0.255433 0.0310752 0.125 -1440.3
0.271972 0.0293746 0.125 -1375.52
0.277296 0.0288236 0.125 -1352.46
0.298417 0.0265441 0.125 -1251.86
0.293236 0.0271125 0.125 -1280.17
0.412268 0.0131146 0.125 -676.638
0.406117 0.0138899 0.125 -708.902
0.46568 0.00613177 0.125 -368.349
0.48632 0.00331948 0.125 -280.426
0.491987 0.0025401 0.125 -195.585

[vkrastev]

Originally Posted by MUZ

hello Vkrastev,
thank you for the reply i used the sample utility in OF to extract the pressures on the airfoil surface. i got x,y,z&p values and non dimensionalised ie Cp=p/0.5*rho*V^2 to get the Cp values but i do not get a good plot for Cp v x/c. i think there is some basic or fundamental mistake i am making but cant seem to figure out. i have posted my sample data.Please could you verify to see where i am going wrong. thank you.

Hi,
be aware when you apply the Cp formula: the pressure values you get from the sample utility are not actual p values, but p/rho values. So, to obtain the effective Cp you have to apply the formula:

Cp=p'/(0.5*V^2)

where p' is the sampled pressure value from the incompressible OF solver. Try to replot your Cp vs. x/c graphs and see if they get better.

Best

V.

[MUZ]

Originally Posted by vkrastev

Hi,
be aware when you apply the Cp formula: the pressure values you get from the sample utility are not actual p values, but p/rho values. So, to obtain the effective Cp you have to apply the formula:

Cp=p'/(0.5*V^2)

where p' is the sampled pressure value from the incompressible OF solver. Try to replot your Cp vs. x/c graphs and see if they get better.

Best

V.

Thanks again for the quick reply, i tried it but could not get a good plot. i think the problem would be from my sampling, the x coordinates do not look right my V=43.8m/s
my plot is all scattered.

[vkrastev]

Originally Posted by MUZ

Thanks again for the quick reply, i tried it but could not get a good plot. i think the problem would be from my sampling, the x coordinates do not look right my V=43.8m/s
my plot is all scattered.

If your coordinate system is not alligned with the airfoil chord (x axis not alligned with c) , you'll have to play a bit with the coordinates associated to each p value to obtain properly ordered data for a nice plot. Remember also that the sample utility returns pressure values on both sides of the airfoil, so to have a smooth plot you'll have to separate upper and lower side data and then plot them one by one in the same graph.

Best

V.

[MUZ]

Originally Posted by vkrastev

If your coordinate system is not alligned with the airfoil chord (x axis not alligned with c) , you'll have to play a bit with the coordinates associated to each p value to obtain properly ordered data for a nice plot. Remember also that the sample utility returns pressure values on both sides of the airfoil, so to have a smooth plot you'll have to separate upper and lower side data and then plot them one by one in the same graph.

Best

V.

Thanks vkrastev; you are a star. i will do that and hopefully get a good plot.
Just one more question please i am simulating flow over naca0012 and my cd matches well with exp but my cl does not. i have checked my mesh which is good. for alpha of 10 deg my cl =0.2 whilst exp is 1.1. i have attached my mesh. for my case Re =6x10^6, V=90.249m/s, viscosity =1.811x10^-5kg/ms,rho=1.204kg/m^3. i used spalart almaras turbulent model, snappyhexmesh for meshing,my snappyhexmeshDict. is attached
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 2.0.1 |
| \\ / A nd | Web: www.OpenFOAM.com |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;
snap true;
addLayers true;


// Geometry. Definition of all surfaces. All surfaces are of class
// searchableSurface.
// Surfaces are used
// - to specify refinement for any mesh cell intersecting it
// - to specify refinement for any mesh cell inside/outside/near
// - to 'snap' the mesh boundary to the surface
geometry
{
Naca_ascii.stl
{
type triSurfaceMesh;
name naca;
}

refinementBox
{
type searchableBox;
min (-1 -1 -1);
max ( 5 1 1);
}
};



// Settings for the castellatedMesh generation.
castellatedMeshControls
{

// Refinement parameters
// ~~~~~~~~~~~~~~~~~~~~~

// If local number of cells is >= maxLocalCells on any processor
// switches from from refinement followed by balancing
// (current method) to (weighted) balancing before refinement.
maxLocalCells 1000000;

// Overall cell limit (approximately). Refinement will stop immediately
// upon reaching this number so a refinement level might not complete.
// Note that this is the number of cells before removing the part which
// is not 'visible' from the keepPoint. The final number of cells might
// actually be a lot less.
maxGlobalCells 2000000;

// The surface refinement loop might spend lots of iterations refining just
// a few cells. This setting will cause refinement to stop if <=
// minimumRefine are selected for refinement. Note: it will at least do one
// iteration (unless the number of cells to refine is 0)
minRefinementCells 100;

// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 6;



// Explicit feature edge refinement
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

// Specifies a level for any cell intersected by its edges.
// This is a featureEdgeMesh, read from constant/triSurface for now.
features ();



// Surface based refinement
// ~~~~~~~~~~~~~~~~~~~~~~~~

// Specifies two levels for every surface. The first is the minimum level,
// every cell intersecting a surface gets refined up to the minimum level.
// The second level is the maximum level. Cells that 'see' multiple
// intersections where the intersections make an
// angle > resolveFeatureAngle get refined up to the maximum level.

refinementSurfaces
{
naca
{
// Surface-wise min and max refinement level
level (5 5);
}
}

// Resolve sharp angles on fridges
resolveFeatureAngle 30;


// Region-wise refinement
// ~~~~~~~~~~~~~~~~~~~~~~

// Specifies refinement level for cells in relation to a surface. One of
// three modes
// - distance. 'levels' specifies per distance to the surface the
// wanted refinement level. The distances need to be specified in
// descending order.
// - inside. 'levels' is only one entry and only the level is used. All
// cells inside the surface get refined up to the level. The surface
// needs to be closed for this to be possible.
// - outside. Same but cells outside.

refinementRegions
{
refinementBox
{
mode inside;
levels ((1e15 2));
}
}


// Mesh selection
// ~~~~~~~~~~~~~~

// After refinement patches get added for all refinementSurfaces and
// all cells intersecting the surfaces get put into these patches. The
// section reachable from the locationInMesh is kept.
// NOTE: This point should never be on a face, always inside a cell, even
// after refinement.
locationInMesh (-1 1.2 0);


// Whether any faceZones (as specified in the refinementSurfaces)
// are only on the boundary of corresponding cellZones or also allow
// free-standing zone faces. Not used if there are no faceZones.
allowFreeStandingZoneFaces true;
}



// Settings for the snapping.
snapControls
{
//- Number of patch smoothing iterations before finding correspondence
// to surface
nSmoothPatch 3;

//- Relative distance for points to be attracted by surface feature point
// or edge. True distance is this factor times local
// maximum edge length.
tolerance 4.0;

//- Number of mesh displacement relaxation iterations.
nSolveIter 30;

//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;
}



// Settings for the layer addition.
addLayersControls
{
// Are the thickness parameters below relative to the undistorted
// size of the refined cell outside layer (true) or absolute sizes (false).
relativeSizes true;

// Per final patch (so not geometry!) the layer information
layers
{
"naca.*"
{
nSurfaceLayers 3;
}
}

// Expansion factor for layer mesh
expansionRatio 1.3;

//- Wanted thickness of final added cell layer. If multiple layers
// is the
// thickness of the layer furthest away from the wall.
// Relative to undistorted size of cell outside layer.
// is the thickness of the layer furthest away from the wall.
// See relativeSizes parameter.
finalLayerThickness 0.7;

//- Minimum thickness of cell layer. If for any reason layer
// cannot be above minThickness do not add layer.
// Relative to undistorted size of cell outside layer.
// See relativeSizes parameter.
minThickness 0.25;

//- If points get not extruded do nGrow layers of connected faces that are
// also not grown. This helps convergence of the layer addition process
// close to features.
// Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x)
nGrow 0;

// Advanced settings

//- When not to extrude surface. 0 is flat surface, 90 is when two faces
// make straight angle.
featureAngle 60;

//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 5;

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 1;

// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 3;

// Smooth layer thickness over surface patches
nSmoothThickness 10;

// Stop layer growth on highly warped cells
maxFaceThicknessRatio 0.5;

// Reduce layer growth where ratio thickness to medial
// distance is large
maxThicknessToMedialRatio 0.3;

// Angle used to pick up medial axis points
// Note: changed(corrected) w.r.t 16x! 90 degrees corresponds to 130 in 16x.
minMedianAxisAngle 90;

// Create buffer region for new layer terminations
nBufferCellsNoExtrude 0;


// Overall max number of layer addition iterations. The mesher will exit
// if it reaches this number of iterations; possibly with an illegal
// mesh.
nLayerIter 50;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
//- Maximum non-orthogonality allowed. Set to 180 to disable.
maxNonOrtho 65;

//- Max skewness allowed. Set to <0 to disable.
maxBoundarySkewness 20;
maxInternalSkewness 4;

//- Max concaveness allowed. Is angle (in degrees) below which concavity
// is allowed. 0 is straight face, <0 would be convex face.
// Set to 180 to disable.
maxConcave 80;

//- Minimum pyramid volume. Is absolute volume of cell pyramid.
// Set to a sensible fraction of the smallest cell volume expected.
// Set to very negative number (e.g. -1E30) to disable.
minVol 1e-13;

//- Minimum quality of the tet formed by the face-centre
// and variable base point minimum decomposition triangles and
// the cell centre. Set to very negative number (e.g. -1E30) to
// disable.
// <0 = inside out tet,
// 0 = flat tet
// 1 = regular tet
minTetQuality 1e-30;

//- Minimum face area. Set to <0 to disable.
minArea -1;

//- Minimum face twist. Set to <-1 to disable. dot product of face normal
//- and face centre triangles normal
minTwist 0.05;

//- minimum normalised cell determinant
//- 1 = hex, <= 0 = folded or flattened illegal cell
minDeterminant 0.001;

//- minFaceWeight (0 -> 0.5)
minFaceWeight 0.05;

//- minVolRatio (0 -> 1)
minVolRatio 0.01;

//must be >0 for Fluent compatibility
minTriangleTwist -1;


// Advanced

//- Number of error distribution iterations
nSmoothScale 4;
//- amount to scale back displacement at error points
errorReduction 0.75;
}


// Advanced

// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cellLevel for postprocessing
// 4 : write current intersections as .obj files
debug 0;


// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;


// ************************************************** *********************** //

[vinz]

I would say there is quite some space for improvement regarding your mesh.
Try to look at your solution superimposed on your mesh you should see some jumps in your solution field which are not expected.

You'll certainly need to refine the mesh in the wake region and on the extrado to be sure to capture correctly eventual flow separation.

[MUZ]

Originally Posted by vinz

I would say there is quite some space for improvement regarding your mesh.
Try to look at your solution superimposed on your mesh you should see some jumps in your solution field which are not expected.

You'll certainly need to refine the mesh in the wake region and on the extrado to be sure to capture correctly eventual flow separation.

Thanks very much for the reply. will work on it
cheers
M

[s.m]

Originally Posted by vinz

Hi everybody,

I got my problem solved. It was coming from an exactly zero area face in my mesh which was apparently enough to raise a segmentation fault, certainly due to a division by zero somewhere in the code.
Anyway, I did a new mesh and I get interesting results for only few hours spent on the case.
You'll find attached some pictures of the field as well as the Cp plots over the airfoils and some pics of the mesh.
I've got some other detailed views, so if people are interested I can post them later on. I may write a very small paper on the subject as well.

Regards,

Vincent

hi vinz,
i am working on multi element airfoils and i also use OpenFOAM for it's analyzing.
my Question is that, for setting the "lRef" and "ARef" in functions of forceCoeffs for obtaining the "cd" and "cl" on the slat and main and flap separately, what should we use?
please help me, your answer may help me alot.
Regards.