boundary conditions dependent by the numerical solution

c120613 · September 22, 2011, 12:53

Dear All,

I'm trying to implement in CFX a boundary condition which will be dependent by the solution calculated at the previous timestep. The simulation is transient.

Anyone can help me?

Thank you in advance

singer1812 · September 22, 2011, 13:37

Exactly how are you changing it? On the surface, this is easily done, but I dont know exactly how you want to change it or based on what for the change.

I suggest a search of this forum. There are lots of discussions. Probably no need to rehash.

c120613 · September 22, 2011, 13:49

Hello man,

what I'm saying is that I need to define the static pressure at the outlet of my compressor and this value in turn will change at each timestep of the transient simulation. To calculate it, you need the value of pressure and the mass flow calculated at the previous timestep. Then the previous solution become an input data to calculate the new boundary condition at the next timestep.
In the forums people say something on the time-dependent boundary conditions which are already defined in a separated file, but this is not my case.

Thank you for your attention.

Regards

singer1812 · September 22, 2011, 16:31

So you need something like Poutlet=function(P_old_outlet,mdot_old_outlet)?

Search this forum for threads on "Update Loop = TRANS_LOOP". This might work for what you need to do.

Else you can try user fortran.

September 22, 2011, 12:53	boundary conditions dependent by the numerical solution	#1
c120613 Member Domenico Join Date: Sep 2009 Location: Cranfield Posts: 48 Rep Power: 17	Dear All, I'm trying to implement in CFX a boundary condition which will be dependent by the solution calculated at the previous timestep. The simulation is transient. Anyone can help me? Thank you in advance

September 22, 2011, 13:49	solution dependent by the solution at the previous timesteps	#3
c120613 Member Domenico Join Date: Sep 2009 Location: Cranfield Posts: 48 Rep Power: 17	Hello man, what I'm saying is that I need to define the static pressure at the outlet of my compressor and this value in turn will change at each timestep of the transient simulation. To calculate it, you need the value of pressure and the mass flow calculated at the previous timestep. Then the previous solution become an input data to calculate the new boundary condition at the next timestep. In the forums people say something on the time-dependent boundary conditions which are already defined in a separated file, but this is not my case. Thank you for your attention. Regards

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September 22, 2011, 13:37		#2
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	Exactly how are you changing it? On the surface, this is easily done, but I dont know exactly how you want to change it or based on what for the change. I suggest a search of this forum. There are lots of discussions. Probably no need to rehash.

September 22, 2011, 16:31		#4
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	So you need something like Poutlet=function(P_old_outlet,mdot_old_outlet)? Search this forum for threads on "Update Loop = TRANS_LOOP". This might work for what you need to do. Else you can try user fortran.