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-   -   Couple different additional variables (http://www.cfd-online.com/Forums/cfx/129456-couple-different-additional-variables.html)

TrII4d February 5, 2014 14:00

Couple different additional variables
 
hey guys,

is there a way to couple two or more additional variables (AV) with each other?
what i want to do is the following:

i calculated heat flux for all three directions (see http://www.cfd-online.com/Forums/cfx...direction.html) with an additional tensor type "vector" ... so i finally got q_x, q_y and q_z ...

now i want to calculate the gradient X of q_x like this :

\frac{\partial q_x}{\partial x} = \frac{\partial (-\lambda * \frac{\partial T}{\partial x})}{\partial x}

but im not able to write an algebraic equation for this case ... the problem is to handle the two gradients ... this is my actual status :

(- Thermal Conductivity * Temperature.Gradient X).Gradient X

but this is not working ...

another idea is that i calculate \frac{\partial q_x}{\partial x} in an AV tensor type "vector" (name GradQ) and use this AV later, i.e.

GradQ X.Gradient X

but this is not working, too ...

any good ideas? :)

-thanks!

Opaque February 5, 2014 15:37

I assume you got the heat flux vector by doing something similar to

ADDITIONAL VARIABLE: MyHeatFluxVector
Option = Vector Algebraic Equation
Vector xValue = - Thermal Conductivity * Temperature.Gradient X
Vector yValue = - Thermal Conductivity * Temperature.Gradient Y
Vector zValue = - Thermal Conductivity * Temperature.Gradient Z
END

Now you should be able to access the MyHeatFluxVector_x.Gradient X, and any of its components.

NOTICE the syntax to access the components of a vector AV. That is the syntax for AV vector components in the ANSYS CFX Solver. Unfortunately, in CFD-Post you will see MyHeatFluxVector X(Y/Z) instead.

Not sure what you are trying to do with these variables, but if you need them for post-processing only you should be able to do the same in CFD-Post and save you to rerun the case. Create a User Defined variable, and select Vector + Gradient.

Hope the above helps,

TrII4d February 6, 2014 03:28

hi Opaque,

thank you very very much ... this is exactly what i was searching for ...

i read the syntax for a vector AV in the user guide ... but it was not really clear for me ... but now i got it ...


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