Simulation Air Stream in a System with out Outlet Boundary

MNMK · January 22, 2021, 03:10

Hi,

I would like to simulate a system which does not have any outlet. Infact, air as a media is sucked in my system through a fan, and again like a loop comes into the fan which probably should have a higher rotation speed. I would like to know how is the best model and boundary conditions for simulating this case in cfx?

regards,

ghorrocks · January 22, 2021, 03:44

I don't understand what you are trying to explain.

But the whole point of boundary conditions is you know the state of the fluid at that point, so you can specify it rather than modelling it. If you don't know the conditions at that point you cannot put a boundary condition there.

And a second point - if air goes into a domain and does not leave then air will accumulate in the domain. This will increase the temperature and/or pressure. It also means there is no steady state solution, so it must be a transient simulation.

MNMK · January 22, 2021, 04:23

Hi Ghorrocks,

First of all thank you because of your fast answer. You are absoloutly right. The fluid will accumulate and also its temperature and pressure will increase. Surely, it is a transient simulation. However, I do not understand whether it is possible to simulate a model with out Oulet boundary.

Gert-Jan · January 22, 2021, 05:24

It sure is. Just give it a try.
I have performed calculations with a pump/fan with a closed outlet to determine the shut off head. This is possible in a transient calculation.

January 22, 2021, 03:10	Simulation Air Stream in a System with out Outlet Boundary	#1
MNMK Senior Member Mey Join Date: Dec 2019 Posts: 129 Rep Power: 7	Hi, I would like to simulate a system which does not have any outlet. Infact, air as a media is sucked in my system through a fan, and again like a loop comes into the fan which probably should have a higher rotation speed. I would like to know how is the best model and boundary conditions for simulating this case in cfx? regards,

January 22, 2021, 03:44		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 18,011 Rep Power: 146	I don't understand what you are trying to explain. But the whole point of boundary conditions is you know the state of the fluid at that point, so you can specify it rather than modelling it. If you don't know the conditions at that point you cannot put a boundary condition there. And a second point - if air goes into a domain and does not leave then air will accumulate in the domain. This will increase the temperature and/or pressure. It also means there is no steady state solution, so it must be a transient simulation. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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January 22, 2021, 04:23		#3
MNMK Senior Member Mey Join Date: Dec 2019 Posts: 129 Rep Power: 7	Hi Ghorrocks, First of all thank you because of your fast answer. You are absoloutly right. The fluid will accumulate and also its temperature and pressure will increase. Surely, it is a transient simulation. However, I do not understand whether it is possible to simulate a model with out Oulet boundary.

January 22, 2021, 05:24		#4
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,995 Rep Power: 29	It sure is. Just give it a try. I have performed calculations with a pump/fan with a closed outlet to determine the shut off head. This is possible in a transient calculation.