Hello all,
I am trying to run openfoam with CGS units with a compressible solver, I already tested this solver so I know it works as it should. All my initial conditions are in cgs, so pressure is 10^6 g/cm/s^2 (dimensions [1 -1 -2 0 ...]) and velocity in cm/s (dimensions [0 1 -1 0...]) , to solve a flow in a fluidised bed with air, in order to do so I added in the controlDict
DimensionedConstants
{
unitSet CGS; // SI; // USCS; //
CGSCoeffs
{
universal
{
c c [ 0 1 -1 0 0 0 0 ] 2.99792e+10; // speed of light in vacuum (cm/s)
G G [ -1 3 -2 0 0 0 0 ] 6.67429e-8; // gravitational constant (cm^3/(gs^2))
h h [ 1 2 -1 0 0 0 0 ] 6.62607e-27; // Planck's constant (erg.s)
R R [1 2 -2 -1 -1 0 0 ] 8.314e7; //universal gas constant (erg/mol*K)
}
electromagnetic
{
e e [ 0 0 1 0 0 1 0 ] 4.803204e-10; // elementary charge (statcoulomb)
R R [1 2 -2 -1 -1 0 0 ] 8.314e7; //universal gas constant
}
atomic
{
me me [ 1 0 0 0 0 0 0 ] 9.10938e-28; // electron mass (g)
mp mp [ 1 0 0 0 0 0 0 ] 1.67262e-24; // proton mass (g)
}
physicoChemical
{
mu mu [ 1 0 0 0 0 0 0 ] 1.66054e-24; // atomic mass unit (g)
k k [ 1 2 -2 -1 0 0 0 ] 1.38065e-16; // Boltzman constant (erg/K)
}
standard
{
//- Standard pressure [bar]
Pstd Pstd [ 1 -1 -2 0 0 0 0 ] 1000000; // 1 bar (barye)
//- Standard temperature [degK]
Tstd Tstd [ 0 0 0 1 0 0 0 ] 298.15; // should be same as in SI unit system
}
}
}
however when trying to run the case the density is like 10 g/cm^3, when it should be 1e-3. what is the matter? someone has already done this passage and knows how to help?
every help is greatly appriciated,
Riccardo
NTT1508 | Tue, 04/28/2015 - 02:48
Incompressible Solver
Hi,
I tried an investigation with CGS and SI (Incompressible solver) using tutorial case. Just simply copying the ControlDict file which is already existed in tutorial case. It worked without any problems except results were not relevant to me. See my post below.
http://www.cfdem.com/forums/convert-si-cgs-unit-cfd
http://www.cfdem.com/forums/volumelimit-fixparticletemplate
Regards,
Riccardo Maione | Tue, 04/28/2015 - 08:50
I tried that is what I did,
I tried that is what I did, but this didn't work for me, I think this is related to the pressure and density. I used the input in CGS, so pressure is 1e6 barye and velocity inlet is 5 cm/s. I have been playing quite a lot in order to understand what isn't right
funny thing is that if I use the CGS constants and I set the SI input output (so the initial conditions are in SI), adding this to the controlDict:
DimensionSets
{
unitSet SI; // USCS
SICoeffs
{
// Basic units
kg kg [ 1 0 0 0 0 0 0 ] 1.0;
m m [ 0 1 0 0 0 0 0 ] 1.0;
s s [ 0 0 1 0 0 0 0 ] 1.0;
K K [ 0 0 0 1 0 0 0 ] 1.0;
mol mol [ 0 0 0 0 1 0 0 ] 1.0;
A A [ 0 0 0 0 0 1 0 ] 1.0;
Cd Cd [ 0 0 0 0 0 0 1 ] 1.0;
// Derived units
Hz Hz [ s^-1 ] 1.0;
N N [ kg m s^-2 ] 1.0;
Pa Pa [ N m^-2 ] 1.0;
J J [ N m ] 1.0;
W W [ J s^-1 ] 1.0;
// Some non-symbolic ones
area area [m^2] 1.0;
volume volume [m^3] 1.0;
density density [ kg m^-3 ] 1.0;
acceleration acceleration [ m s^-2 ] 1.0;
kinematicPressure kinematicPressure [ Pa density^-1 ] 1.0;
// Scaled units. Only allowed in dimensionedType (dimensionedScalar,
// dimensionedVector etc.) and UniformDimensionedField, not
// in DimensionedField or GeometricField
cm cm [ m ] 1e-2;
mm mm [ m ] 1e-3;
km km [ m ] 1e3;
// Set of units used for printing. Can be any basic or derived
// but not scaled (only supported for dimensionedScalar, etc)
writeUnits (kg m s K mol A Cd);
}
}
density is ok and 1 kg/m^3. However in order to understand what is going on, I used a string to output the universal gas constant. In this case the constant is ok with the correct value in CGS, but its dimensionality is in Kg and m!
I am a little frustrated
thank you for your reply
Riccardo