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rafiktharwat May 15, 2011 05:49

How to simulate a simple fan inside a room ?
i want to simulate a fan inside a room to simply flow the air from its backside to its front side .
to flow the air from and into the room.
knowing its mass flow rate Kg/s
and Air velocity m/s

without involved in the details of simulating its blades or modeling its internal details.

can I simulate it as subdomain or interface or what ... and how?

thanx for your time and help.

ghorrocks May 15, 2011 18:56

Either define a volume and apply a momentum source to it, or define an interface and apply a momentum source on that.

rafiktharwat May 27, 2011 09:56

problems in the momentum source
i want to simulate a jet fan of diameter 0.3 m and length on 2 m
velocity of 18 m/s
mass flow rate of 1.2 m^3/s

when i input the momentum source as momentum per volume
( Mass flow rate * velovity /Volume ) in the direction of the flow axis

the results are not realistic

please advice me with the way of input a momentum source

thnx for help

ghorrocks May 28, 2011 06:39

An alternative approach is to make the inlet of the fan an outlet in your domain and the outlet of the fan an inlet. You can specify the mass flow rate easily that way.

rafiktharwat May 28, 2011 07:06

need to move air inside the room
thanx for reply

but i need the jet fan to move the smoke inside the room
so i need to flow the poluted air inside the room

i need to know the exact setup of the momentum source of the subdomain (the fan)

i have non realastic solution

when i use general momentum source as :

x component = 0 kg m^-2 s^-2
y component = (Mass flow rate * velocity of air from the fan / volume of
the fan) = 150 kg m^-2 s^-2
z component = 0 kg m^-2 s^-2


x component = 0 kg m^-2 s^-2
y component = C *(Mass flow rate * velocity of air from the fan / volume
of the fan) = 15000000 kg m^-2 s^-2
z component = 0 kg m^-2 s^-2

with momentum source coff of 100000 kg m^-3 s^-1

and both

give me non realastic solution with wrong velocities and pressures

thnk u for your help and time

ghorrocks May 28, 2011 07:12

You are not taking into account the momentum of the incoming air. You need to change the velocity component to something like (VF-v) where VF is the velocity of air you want (18m/s) and v is the local control volume velocity in the appropriate direction. This way the source term goes to zero as the velocity of the air approaches the velocity you want.

And you will almost certainly need the mom source coefficient, so use that approach.

rafiktharwat May 28, 2011 07:31

local control volume velocity
thnx very much for reply

but can i know more information about knowing the (local control volume velocity) meaning

and how to know and input it

and if i correctly understand that the momentum source term is equal to [MassFR*(VF-v)/ Volume]

or am i wrong

thnx for help

ghorrocks May 28, 2011 07:41

Yes that is correct. But you have to make sure the sign of the velocity component is correct, so you might need to change the sign, but that is the general idea.

miquiita September 23, 2014 02:29

Local control volume velocity

I am also trying to simulate a fan indoor, a room, but what do you mean by local control volume velocity?

Also I have some issues to start, I know how to do the room and fan in the middle, with two domains. But then for meshing what would be the best idea? Also what would I need from the fan measurments to be put into the model?

Many thanks

ghorrocks September 23, 2014 02:34

Control volumes are defined in the CFX documentation, under the theory manual. I am just referring to the velocity of the control volume.

Why do you need to use 2 domains?

If you are modelling a fan in a room then you need the fan performance curve (pressure rise versus flow rate).

miquiita September 23, 2014 02:51

So I can find a more detail explanation of it it the manual?

Because I am new to the CFX simulation and need to create a simulation of the fan in a room for my thesis. I have done nearly all the tutorials in the guide. But there is nothing of any fans in a indoor environment.

I measured the fan speed and the air velocity of the fan around the room. I can easily get the performance curve of the fan manual. But I dont need the turbulence of the air?

Also I have no idea how to start the modelling. Any suggestions?

I read heaps of treads. But I am really new still at this.

Kind regards and thanks for any help.


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