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September 15, 2012, 12:27 |
SonicFoam - Forces, viscous force too big?
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#1 |
New Member
Join Date: Sep 2012
Posts: 8
Rep Power: 13 |
Im just running a simulation of a rocket flying with Ma=1.7 through air. I use sonicFoam for this, and everything looks quite well when i view it with paraview. (compression, expansion and so on).
But then I try to calculate forces and coefficients and imo I get too high drag forces. Drag is directed to the bottom, therefore negative Z-axis is the drag. Have a look at the output: Code:
forces output: forces(pressure, viscous)((9.821624 11.33696 -398.8834) (0.6874167 -0.04157073 -1979.892)) moment(pressure, viscous)((8.025379 -7.056551 0.2301483) (-0.1572154 -0.5736852 -0.04660123)) forceCoeffs output: Cd = 1.790804 Cl = 0.008503463 Cm = 0.003948905 Cl(f) = 0.0003028264 Cl(r) = 0.008200637 The following settings might be connected to this, but as far as I know they are set correctly for my case :/ Code:
forces { type forces; functionObjectLibs ( "libforces.so" ); outputControl timeStep; outputInterval 1; patches ( rocketbody ); pName p; UName U; rhoName rho; log true; rhoInf 1.16; CofR ( 0 0 0 ); liftDir ( 0 1 0 ); dragDir ( 0 0 -.1 ); pitchAxis ( 1 0 0 ); magUInf 600; lRef 1.500; Aref 0.00636172512351933130788685285114; } forceCoeffs { type forceCoeffs; functionObjectLibs ( "libforces.so" ); outputControl timeStep; outputInterval 1; patches ( rocketbody ); pName p; UName U; rhoName rho; log true; rhoInf 1.16; CofR ( 0 0 0 ); liftDir ( 0 1 0 ); dragDir ( 0 0 -1 ); pitchAxis ( 1 0 0 ); magUInf 600; lRef 1.500; Aref 0.00636172512351933130788685285114; thermophysicalProperties: Code:
FoamFile { version 2.0; format ascii; class dictionary; location "constant"; object thermophysicalProperties; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // thermoType ePsiThermo<pureMixture<constTransport<specieThermo<eConstThermo<perfectGas>>>>>; mixture { specie { nMoles 1; molWeight 28.9; } thermodynamics { Cv 717.5; Hf 0; } transport { mu 14.74e-06; mu=eta/rho ; eta= 17.1e-6, rho=1.16 Pr 0.7; } } EDIT: Ok I found out, viscous force is bigger than the pressure force for rockets, but still, its far too high in total. What could be connected to: I am using LaunderSharmaKE as RAS turbulence model. Last edited by Kryo; September 15, 2012 at 13:02. |
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September 15, 2012, 14:33 |
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#2 |
New Member
Join Date: Sep 2012
Posts: 8
Rep Power: 13 |
sorry for double post, but I found the reason for the high values: Random k-epsilon- boundaries for the turbulence model...
Any idea what to use here? are there any formulas to calculate the correct k and epsilon boundaries? |
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