Initial conditions

Nabuchadresar · February 11, 2016, 12:24

Hello,
I am working with external flow. So, on "Continua>Physics>initial conditions>velocity" I set the velocity [0 , 7 , 0] m/s.
And, on "Region>Windtunnel>Boundary>Inlet>Physics Values" I set [0 , 7 , 0].

My question, I don't know if this is correct. I need set both with 7m/s or just one?

Schwob77 · February 11, 2016, 14:43

The setting in the initial conditions of the physics continuum is the starting solution of the whole domain. This means that every single cell in the regions that have the physics continnum applied will have that velocity value. As soon as the solver start to run, it will replace the values in the interior cells by the one calculated out of the boundary conditions. The better the initial solution is, the better and fast the solver will converge. So if you don't set the velocity [0 , 7 , 0] m/s there, it can be of advantage but also of disadvantage depending on the expected flow field. If the solution is fully converged, the starting solution shouldn't matter in general anymore.

On the other side you have the boundary conditions. This is the place where you think you know the solution already. So the setting there is absolutely nevessary. These are the faces that will keep their solution as the solver doesn't calculate them. Instead the solver uses them to calculate the solution in the interior field.

Nabuchadresar · February 11, 2016, 21:21

Thank you a lot. I changed to [0 0 0] and the results looks better.

February 11, 2016, 12:24	Initial conditions	#1
Nabuchadresar Member André Luiz Moura Silva Moreira Join Date: Apr 2015 Location: Brazil Posts: 40 Rep Power: 11	Hello, I am working with external flow. So, on "Continua>Physics>initial conditions>velocity" I set the velocity [0 , 7 , 0] m/s. And, on "Region>Windtunnel>Boundary>Inlet>Physics Values" I set [0 , 7 , 0]. My question, I don't know if this is correct. I need set both with 7m/s or just one?

February 11, 2016, 14:43		#2
Schwob77 Member Join Date: Nov 2015 Posts: 38 Rep Power: 10	The setting in the initial conditions of the physics continuum is the starting solution of the whole domain. This means that every single cell in the regions that have the physics continnum applied will have that velocity value. As soon as the solver start to run, it will replace the values in the interior cells by the one calculated out of the boundary conditions. The better the initial solution is, the better and fast the solver will converge. So if you don't set the velocity [0 , 7 , 0] m/s there, it can be of advantage but also of disadvantage depending on the expected flow field. If the solution is fully converged, the starting solution shouldn't matter in general anymore. On the other side you have the boundary conditions. This is the place where you think you know the solution already. So the setting there is absolutely nevessary. These are the faces that will keep their solution as the solver doesn't calculate them. Instead the solver uses them to calculate the solution in the interior field. Nabuchadresar, Derek2580 and CinderellaHP like this.

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February 11, 2016, 21:21		#3
Nabuchadresar Member André Luiz Moura Silva Moreira Join Date: Apr 2015 Location: Brazil Posts: 40 Rep Power: 11	Thank you a lot. I changed to [0 0 0] and the results looks better.