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-   -   UDS source term units (http://www.cfd-online.com/Forums/fluent/29995-uds-source-term-units.html)

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
 
Hi,

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.

Regards,

Ola Nordblom


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