[Poimsm]

Hi everyone!

I have some questions about UDFs for FLUENT.

1. The general MACRO for defining a source is DEFINE_SOURCE(name, c, t dS, eqn) and I know that you should provide an equation for the derivative dS for solver stability. If the source term only depends on one variable it is clear how the derivative looks like. For example a source for the x-momentum is a constant multiplied with the velocity in x-dircetion. Thus the derivative is dS[eqn] = constant.

But how can you provide the derivative if the source term depends on multiple variables such as

source = C1*x-velocity + C2*y-velocity*z-velocity ?

Do you have to provide the sum of the partial derivatives like

dS[eqn] = C1 + C2*z-velocity + C2*y-velocity?