[NeoKim]

Hello guys

I'm a new one in Fluent and I've just started learning this software thesedays.

I'm trying to analyse fanless electric fan and here is my 2-D model below.

I made a system that a duct envelope the airfoil(my product)

These are what I did to set up the boundary condition

1. I create half model so I gave one edge symmetry condition
2. The other side is wall
3. The tiny edge of the airfoil is the inlet for velocity inlet.
4. At the tip of the duct(to the flow direction), I gave "outlet" namedselection
5. I don't know the other side of the duct

And here's my question , what should be the proper boundary condition on the other edge of the duct? I mean the other side of "4"edge

I tried Pressure_outlet, Pressure_inlet, outflow, etc but until now It doesn't seem that there is good results, Honestly I don't know what the "good results" would be. So I'm wondering What is the correct boundary type in my model.

Please help me out!!

[D.M]

hi,
actually using axisymmetric for the upper boundary means that everything u got in your geometry gonna turn around your upper axis for 360 degrees (i mean you gonna have a 3D geometry but for lowering the time cost you are using 2D model with axisymmetric BC). so if you want to simulate that , using pressure outlet BCs for both sides of your geometry (right and left) would be ok. if you have problem with your result i dont think the BCs are causing the problem, try to change something else like turbulence model or ... .

[NeoKim]

Originally Posted by D.M

hi,
actually using axisymmetric for the upper boundary means that everything u got in your geometry gonna turn around your upper axis for 360 degrees (i mean you gonna have a 3D geometry but for lowering the time cost you are using 2D model with axisymmetric BC). so if you want to simulate that , using pressure outlet BCs for both sides of your geometry (right and left) would be ok. if you have problem with your result i dont think the BCs are causing the problem, try to change something else like turbulence model or ... .

Thanks again D.M. Actually I wasn't thinking of the axisymmetric for my model because the real product is not like that. This is the fanless electronic fan so as you can find the attachment image, the velocity from the inlet is different depending on the position. I guess only a symmetry on the plane that I draw on the image would be OK.

Frankly, this is my graduation work. Not just analysis but also the experiment. So What i am doing now is for finding reasonable size of the duct and I'm using 2D model for less cost.

Anyway Thanks a lot about the type of boundary.
I will keep trying with the pressure outlet.

Plus, would you mind if I ask why the pressure outlet would be OK? I'm wondering why it is fine if I use the pressure outlet in my model

[LuckyTran]

The second picture was very helpful. 2D with axissymmetric BC is very good way to model this problem.

The right boundary with the ? should be a total pressure inlet (in Fluent, this is simply the pressure inlet) with the pressure equal to ambient/atmospheric. The total/stagnation temperature should also be ambient, depending on whether or not you have an energy equation and equation of state. I recommend the pressure inlet because it specifies the more correct BC, which is total pressure, instead of a pressure outlet (which is a static pressure BC).

That is, with the fan off everything is quiescent at the local ambient pressure. Once you turn on the fan, air moves and hence the static pressure drops upstream of the fan whereas the total pressure is unchanged upstream of the fan.