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Ale July 8, 2002 06:30

UDS source term units
Hi to all,

which are the units of the source terms for user defined scalar in fluent?

If I write a source term for a scalar, e.g. a concentration (kmol/m^3), using mass flow rate as the flux function, the solved equation should be eq. 9.2-3 on page 9-2 of Fluent6 UDF Manual.

According to this equation the units should be kg*m^-3*s^-1*(scalar unit), i.e. for concentration, kg*kmol*m^-6*s^-1. Is that right?

Should I multiply a source term whose units are kmol*m^-3*s^-1 by the density (or by something else) to fit the units used in Fluent?

Is it the same for Fluent4, Fluent5 and Fluent6?

Thanks a lot

Lanre July 8, 2002 15:29

Re: UDS source term units
Source term is always defines as source per unit volume. What at the units of a UDS? You define this. So your source units are (UDS stuff)/m^3

Ola Nordblom July 12, 2002 13:01

Re: UDS source term units

It's more convenient to define your scalar concentration per unit mass of mixture instead of per unit volume. Thus, your scalar should have the unit (kmol/kg), and the source term in the scalar transport equation should have the unit kmol/(m^3*s). In fact, since the convective flux in Fluent is a "mass flow rate", the scalar must be expressed per unit mass to get a correct convective transport.

Of course, after you have solved your scalar equation, you can multiply your results by the density to get the concentration in (kmol/m^3) if you prefer to present your results using that unit.


Ola Nordblom

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