# Problem with modelisation of air flow

Hello !
I'm French so my english might do some mistakes sorry for that !

I'm actually studying in post preparatory school and I have to do some kind of project.

I am working on a problem in our lab : the fact is that the ventilation is working better when all windows and doors are closed. It is 10 m*10m*2m, there are two inlets and two outlets in this lab,
so I would like to do a modelling to show the air flows with a window opened (adding an inlet) and with no windows opened, to know why this problem exists.

So I am actually using your software, I watched some of your videos on youtube. I created a box, 4 cylinders (representing 2 inlets and 2 outlets), I made them stuck on the roof of my box.

The air is not supposed to move at the beginning, so i put as U (0, 0, 0) m.s-1

Then I put in physics an inlet on the upper base of 2 cylinders, and 2 outlets in the base of the two others.

When I am going to results, when I apply U (vectors field), one face becomes blue. Then I go back to U and click arrows, but there are none !

My questions are the following :
-> what did I do wrong ?
-> it is possible to do a 3D modelling ? because when I have to apply U, it is only on one face, or maybe I didn't understand how it works ?

Thank you very much in advance !

Paul

### Velocity initialized to zero

Nothing is wrong. You have initialized your velocity to zero, so that's why you are seeing blue (zero) on your faces and you don't see any vectors (zero again). You have to run your simulation to see the predicted velocity and specify a non-zero velocity either as your reference velocity or at your inlets.

Rather than start with your own simulation I suggest you first actually perform a simulation according to a basic tutorial then you'll see and experience how to setup and run a simulation.

Ok I'll do exactly what is done in this tutorial.
I just have a question : I saw you can add velocity in inlets and outlets. Will it give velocity to the ambiant air or is it just a number to indicate the max amount or air that can be taken out of the room (for example) without creating any moving air ?

Paul

### Inlet or outlet velocity specification

Velocity specified at inlets or outlets determines the air velocity entering (inlet) or exiting (outlet) the flow domain. It is not a maximum. In the tutorial I suggested, the inlet velocity is taken as the reference velocity by default.

### Hi ! I have done the

Hi !

I have done the tutorial and I have some questions now :
-in the tutorial, the inlet and outlet are all aligned with the air velocity.
I mean the air velocity are -10 m.s on Z, and inlet and outlet are taking and giving air in this same direction (Z). Will it work if my inlet and outlet are both located on the ceiling of my room ?

-As the air in my room does not really have velocity in one specific direction, what do you advise me to put as initial velocity ?

-I don't understand why in the video they put particles on a wall and a target for those particles.
In order to see lines representing the moving air, do I necessary have to put particles ?

The computer I'm using to do the modelling does not have access to the internet, but I will try to put screenshots because I'm afraid I am not explaining well enouth ?

Paul

### Use default inlet type and initialize velocity to zero

The default inlet type applies the reference velocity magnitude normal to the inlet direction, so it is independent of your reference velocity direction - it just relies on the reference velocity magnitude. I suggest you leave your outlet as a default type - there's no need to specify a velocity condition, if it's the only outlet then it will exactly match the inlet velocity magnitude by continuity.

You should initialize your velocity to zero as in the tutorial "Incompressible Transient Flow with Heat Transfer" according to section "Set the Initial Velocity for the Simulation".

For streamlines you need to specify a source from which you release particles and a target - usually the volume through which the particles will progress. For more details see "Particles or Streamlines".