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Andy June 25, 2008 09:36

How to simulate a fan?

I am quiet new in CFX Simulations. Just used it a bit in my diploma thesis. Now I try to simulate the air-flow in a small box created by a fan. The geometrie of the fan, especially the rotorblades, are not important. It is displayed as a simple cylinder-volume. I know the characteristic line of this fan. With this data, it would be possible to use the CFX Data Point input to create a function and an expression. Right? But how do I use this expression? Do I create a boundary condition or a subdomain? How do I define inlet, outlet or opening?

Thanks fpr your answers.


Amit Roghs June 26, 2008 12:11

Re: How to simulate a fan?
Dear you first need to make the geometric model of the physcial blade.

Then you have to make the fluid model of the domain,i.e. excluding the fan.

After that define the boundary condition as per your requirement of results.

Also you need to specify the speed of the fan.


Amit Roghs

Andy June 27, 2008 03:33

Re: How to simulate a fan?
Thanks Amit Roghs,

but my application ist not the fan. It is just what happens in my "black box" addicted to the air flow. Turbulency is not nescessary. I just want to have an airflow by using the data-line of the fan.

The last days I tried different settings. But I did not find out how to handle the Input Data because of their units. By using a subdomain with general momentum source, the unit is [kg m^-2 s^-2] The units I get from the data.line of the fan are i.e. [Pa] and [l/min]

I hope I could describe my problem a bit better.

Thank you

Amit Roghs June 27, 2008 11:24

Re: How to simulate a fan?
Dear Andy,

I think your problem is that you have a fan at a distance & the wind blowing is concerned to your domain.

You can create a domain of fan ahead of your problem domain & then simulate both of them.

Or else you can simulate the fan domain separetely and then use the result file of it for your problem.

I hope I have understood the problem correctly.

If not then do let me know.


Amit Roghs

Rogerio Fernandes Brito June 28, 2008 13:14

Re: How to simulate a fan?
U can study only the channel that passing the air or use the bladegen and turbogrid! The are the tools that u will need do construct your geometry and input the bc and ic

Andy July 2, 2008 03:48

Re: How to simulate a fan?
Hello Amit,

you nearly understodd my problem correctly :)

I Just need an air flow in my domain. Therefore I want to use the database of a real fan. I hope in this way it is able to approxmiate i.e. the speed ad the pressure. (without turbolency or blade geometrie) I tried to set up a subdomain. But how do I get the input from the data-line of the fan? I just could not handle the units (already written before). The speed solutions doesn't match in any way with my measurements?


Regards, Andy

Andy July 11, 2008 03:35

Re: How to simulate a fan?

some ideas?



Ste July 13, 2008 13:07

Re: How to simulate a fan?

I also am new to CFX and have to model a situation similiar to yours.

So far I have found that if you place a disc like volume in your geometry and then make it a sub-domain, you can specify it as a momentum source (remembering that work done on the fluid is -ve)

But when i had a technical demo from the sales team at ansys they mentioned this could be done with a pressure rise across the volume also which i am yet to figure out.

Hope this helps a bit. If you figure anything out, i'd appreciate it if you post here too? maybe we can crack it!


Andy July 14, 2008 03:39

Re: How to simulate a fan?
Thanks Steve,

this way I did it. Using a sub-domain and momentum source.

I am just trying to get input for the momentum source by the fan data (its a data line about pressure rise across the volume). This is what I try to figure out as you do :)

Perhaps the ansys support can help. If I get new Informations, I will post immediatelly.


Markus July 14, 2008 10:49

Re: How to simulate a fan?
Hello Andy and Ste

I'm also dealing with almost the same problem at the moment. I want to model a fan with a momentum source using pressure/flow rate curve data. Do you know how to implement this?

Additianally in the documentation it say, for modelling a fan the rhie chow option should be checked. What is this option exactely meaning?

Hope, we can solve it soon,


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