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-   -   Adding and resolve a differential equation (https://www.cfd-online.com/Forums/cfx/109336-adding-resolve-differential-equation.html)

Luigi November 15, 2012 07:19
Adding and resolve a differential equation
 
I have a transport equation of a scalar C in which it appears another (vectorial) variable i.
Also I have a differential equation of i: div(i)=0.
Can I introduce and resolve this equation in Ansys CFX, or it supports only algebraic equations?

cdegroot November 15, 2012 15:50
Yes you can add additional transport equations in CFX.

Luigi November 16, 2012 04:52
The problem is that I haven't a transport equation, but an additional differential equation to be solved

brunoc November 20, 2012 16:50
Well, \nabla\bullet\textbf{i} = 0 is also a transport equation. Do you mean you want to solve only this equation and not the others?

If that is the case, you can add and the following Expert Parameters to your simulation:

Code:
FLOW: Flow Analysis 1
  EXPERT PARAMETERS:
    solve energy = f
    solve fluids = f
    solve turbulence = f
  END
END
You can also go to 'Insert > Solver > Expert Parameters > Model Over-rides' and disable other equations you see fit.

Cheers

Luigi November 21, 2012 05:51
I have a transport equation of the variable C, in which there is a term containing i; also, I have the equation div i = 0. So, I have a system of two equation. I don't know how I can solve the latter equation

brunoc November 21, 2012 06:29
You have four variables (C, ix, iy, iz) but only two equations. Aren't you missing two extra equations to close your problem?

Luigi November 21, 2012 07:05
I think you're right! Maybe I need others equations. I will study better my problem


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