[mariposa]

I recently want to simulation an axial fan that work like wind tunnel so the input pressure is negative and the output pressure is positif. I also want to input mass flow 32.5 kg/s.
But the problem is, i've trying to make the boundary inlet is mass flow but its still goes false, while the result in input and output get exchange.
Honestly i still confuse how to use boundary condition, like pressure inlet, velocity inlet, massflow, exhaust fan, intake van and also function each of them.
I really need your help guys, please help me.
Thank you

[mCiFlDk]

Originally Posted by mariposa

I recently want to simulation an axial fan that work like wind tunnel so the input pressure is negative and the output pressure is positif. I also want to input mass flow 32.5 kg/s.
But the problem is, i've trying to make the boundary inlet is mass flow but its still goes false, while the result in input and output get exchange.
Honestly i still confuse how to use boundary condition, like pressure inlet, velocity inlet, massflow, exhaust fan, intake van and also function each of them.
I really need your help guys, please help me.
Thank you

Hi mariposa,


Could you share with us a screenshot of the whole bunch of boundary conditions?


Regards.

[vinerm]

Originally Posted by mariposa

I recently want to simulation an axial fan that work like wind tunnel so the input pressure is negative and the output pressure is positif. I also want to input mass flow 32.5 kg/s.
But the problem is, i've trying to make the boundary inlet is mass flow but its still goes false, while the result in input and output get exchange.
Honestly i still confuse how to use boundary condition, like pressure inlet, velocity inlet, massflow, exhaust fan, intake van and also function each of them.
I really need your help guys, please help me.
Thank you

If the flow is incompressible, then it won't matter much whether the pressure is positive or negative. The only difference you will observe is in the flow profile at the boundaries. Just apply a mass flow outlet at the outlet, since that's what fan would be doing; sucking the air. And apply pressure inlet with total pressure of 0 Pa at the inlet. However, the situation would be entirely different if the flow is compressible.

[mariposa]

Hi mariposa,


Could you share with us a screenshot of the whole bunch of boundary conditions?

blade_LI.jpg
Well, firstly i just drew a boundary only in (a) and in (d) but my lecture said that i've to add some new selection name in (b) and (c), so in my BC the (a) i set to mass flow inlet that has 32 kg/s and the pressure is -4336 Pa and in the (d) i set an outflow because i want to know about the outlet pressure.

2 (2).jpg

but in (C) and (d) i get confused because the BC show just like this option

thats why i get confused what should i do with that boundary condition, while in my real data the (a) is -4336 Pa and in (d) is 1236 Pa. thats why i need ur help. thank you

[mariposa]

Originally Posted by vinerm

If the flow is incompressible, then it won't matter much whether the pressure is positive or negative. The only difference you will observe is in the flow profile at the boundaries. Just apply a mass flow outlet at the outlet, since that's what fan would be doing; sucking the air. And apply pressure inlet with total pressure of 0 Pa at the inlet. However, the situation would be entirely different if the flow is compressible.

unfortunely i forgot to mention that my fluid is a compressible air that have density is 0.77 kg/m3

[mariposa]

Originally Posted by mCiFlDk

Hi mariposa,


Could you share with us a screenshot of the whole bunch of boundary conditions?


Regards.

Attachment 78372
Well, firstly i just drew a boundary only in (a) and in (d) but my lecture said that i've to add some new selection name in (b) and (c), so in my BC the (a) i set to mass flow inlet that has 32 kg/s and the pressure is -4336 Pa and in the (d) i set an outflow because i want to know about the outlet pressure.

Attachment 78373

but in (C) and (d) i get confused because the BC show just like this option

thats why i get confused what should i do with that boundary condition, while in my real data the (a) is -4336 Pa and in (d) is 1236 Pa. thats why i need ur help. thank you

[vinerm]

You cannot apply any condition at the interior boundaries, nor are those required. Check with your lecturer why those are required; possibly for data extraction. Or if you wish to rotate the rotor. Then, it has to be interface and you have to slit the boundary or generate non-conformal mesh at the meshing stage. So, check before you proceed.

If the flow is compressible, then you have to set operating pressure as 0 and use only positive pressure values at the boundaries. Do not use negative pressure values. Use mass flow at the outlet and pressure inlet at the inlet. Do NOT use outflow.

[mariposa]

Originally Posted by vinerm

You cannot apply any condition at the interior boundaries, nor are those required. Check with your lecturer why those are required; possibly for data extraction. Or if you wish to rotate the rotor. Then, it has to be interface and you have to slit the boundary or generate non-conformal mesh at the meshing stage. So, check before you proceed.

If the flow is compressible, then you have to set operating pressure as 0 and use only positive pressure values at the boundaries. Do not use negative pressure values. Use mass flow at the outlet and pressure inlet at the inlet. Do NOT use outflow.

Thanks i did like what u said, and for the pressure its correct such like i want. But when i saw the vector, it show that the flow is from Output to Input. So i change the direction vector in mass flow Z=1 (direction from input to Output) but the pressure get decrease. Am i should to increase the pressure inlet ? Thanks