[eh65]

hi
I am beginner in fluent. I have a problem that have a convective B.C in outlet as follows:
000.png


that is a independent variable p,v and T.
can anyone help me for this case??
thanks ..

[eh65]

sorry . the equation is :

000.png

[Amir]

Dear friend,

you can consider phi as a scalar and solve a modified UDS equation for that easily and set a Dirichlet BC instead, but I think you meant that phi is a dependent variable.

Bests,

[eh65]

thanks amir
but phi is a independent variable. but i dont know that what to do and begin from which step?
this is the problem of channel that air passes through it.

[Amir]

Originally Posted by eh65

thanks amir
but phi is a independent variable. but i dont know that what to do and begin from which step?
this is the problem of channel that air passes through it.

What's the governing equations and what is phi variable?!

[eh65]

(d/dt)(phi)+ U(d/dx)(phi)= 0
phi is pressure, tempreture and avreaged x-velocity (U)

[Amir]

Originally Posted by eh65

(d/dt)(phi)+ U(d/dx)(phi)= 0
phi is pressure, tempreture and avreaged x-velocity (U)

Ah, sorry I think this is sth different at first. Ok, here note that for some BCs you cannot set both velocity and pressure. But you have 2 choices:
1) using a separate UDS equation but it may face some difficulties in its own BCs
2) write a UDF like this:
phi_new=phi_old-U(d/dx phi)*dt
which is a approximation.

Bests,

[eh65]

thanks
in situation 2 i have to use flux uds?

[Amir]

Originally Posted by eh65

thanks
in situation 2 i have to use flux uds?

No! in this situation you wouldn't need any UDS. you're setting phi directly. (note that you can access gradient operator in UDF)

[eh65]

thanks amir