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 m-3 s-1]. 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 m-3 s-1]. 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.





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