# Source Term

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September 2, 2015, 16:31
Source Term
#1
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Fabricio
Join Date: Dec 2009
Location: Brazil - São Paulo
Posts: 22
Rep Power: 9
I would like to know how is the more practical way to insert a source term as like in the attached figure. The simulation will be transient.

Thanks
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 Differential_equation.jpg (3.7 KB, 23 views)

 September 2, 2015, 17:28 #2 Senior Member   Join Date: Jun 2009 Posts: 604 Rep Power: 14 Source term into what equation ? Separately, may I ask what that expression is trying to model ?

September 2, 2015, 19:57
#3
New Member

Fabricio
Join Date: Dec 2009
Location: Brazil - São Paulo
Posts: 22
Rep Power: 9
Dear Opaque.

This is the entropy generation equation, that it has two terms, the temperature and friction terms.

It's a volumetric term and I don't know hos is the better way to implement it.

Thanks.
Attached Images
 Equation.jpg (8.7 KB, 9 views)

 September 3, 2015, 09:29 #4 Senior Member   Join Date: Jun 2009 Posts: 604 Rep Power: 14 thank you for the explanation about the source term.. Interesting. If you need the component of the gradient of a variable in CFX, you can use CEL expressions to access them following the syntax .Gradient For example, you source term can be written as Code: ```EntropySource = ConductionSource + FrictionSource ConductionSource = Thermal Conductivity * ( (Temperature.Gradient X)^2 + (Temperature.Gradient Y)^2) / Temperature^2 FrictionSource = Dynamic Viscosity * ( 2 * ( Velocity u.Gradient X ) ^2 + 2 * (Velocity v.Gradient Y) ^2 + ... ) / Temperature``` Then, in the subdomain definition select the source for the additional variable you defined, and set Code: ```Source = EntropySource Source Coefficient = < A value if needed to help convergence >``` Hopefully, the source is well behave and requires no/minimal relaxation. Good luck..

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