Q
I have doubts about specifying sources of 'additional variable'. For example, I have to implement following equation
D(phi)/Dt = S_phi
where phi is dimensionless. Therefore units of source term S_phi are s^1. However when I implemented additional variable as
ADDITIONAL VARIABLE: ICVariance
Option = Definition
Units = [ ]
Variable Type = Specific
END
the units of sources need to be implemented are [kg m3 s1]. Do I need to multiply the source terms Rpi and RDi with density? And what is the difference between specification of 'additional Variable' Volumetric or Specific.
A
Looking at the transient term and source only, for specific AVs the transport equation is
d(rho.phi)/dt = S_phi (1)
and for volumetric AVs it is
d(phi)/dt = S_phi (2)
It might be expected that a dimensionless specific AV should have units of kg^1, and a dimensionless volumetric AV, m^3. However, dimensionless AVs are exactly that (dimensionless) and have dimensions [ ]. From (1) and (2) we therefore see that for dimensionless, specific AVs sources are in units of kg m^3 s^1, whilst for volumetric AVs, they are s^1.
So, to return to your original question, you should multiply your source terms by density.
Q I have doubts about specifying sources of `additional variable`. For example, I have to implement following equation D(phi)/Dt = S_phi where phi is dimensionless. Therefore units of source term S_phi are s^1. However when I implemented additional variable as ADDITIONAL VARIABLE: ICVariance Option = Definition Units = [ ] Variable Type = Specific END the units of sources need to be implemented are [kg m3 s1]. Do I need to multiply the source terms Rpi and RDi with density? And what is the difference between specification of `additional Variable` Volumetric or Specific. A Looking at the transient term and source only, for specific AVs the transport equation is d(rho.phi)/dt = S_phi (1) and for volumetric AVs it is d(phi)/dt = S_phi (2) It might be expected that a dimensionless specific AV should have units of kg^1, and a dimensionless volumetric AV, m^3. However, dimensionless AVs are exactly that (dimensionless) and have dimensions [ ]. From (1) and (2) we therefore see that for dimensionless, specific AVs sources are in units of kg m^3 s^1, whilst for volumetric AVs, they are s^1. So, to return to your original question, you should multiply your source terms by density. 

