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Richard October 9, 2006 10:08

Modelling a fan

I am modelling a fan using a sub domain whith a defined momentum source, momentum source coefficient and redistribute options on. Only my results do not match measurements. The speed in the fan is allmost the same as in reality. The problem is: The air movement is not diverging like in reality. The airspeed is at about 35 meter after the fan still in a range of 6 meters. The measurements show results where at 35 meters the air is moving in a range of 15 meters. So the moving air does not have a lot of influence on the other air. I don't know what i'm doing wrong. I'm using the K epsilon model.

Thanks in advance, Richard

Glenn Horrocks October 9, 2006 17:09

Re: Modelling a fan

Do you mean the jet coming out of the fan is not dissipating as measurements show? To get the dissipation right you will need to have the correct turbulence levels in the jet created by the fan (amungst many other things you will need to get right for an accurate simulation). If you model the fan by a momentum source you will need to put in an appropriate turbulence source as well.

Glenn Horrocks

Richard October 10, 2006 02:08

Re: Modelling a fan
Thanks Glenn,

I ment the jet coming out of the fan indeed. I also didn't put in a tubulence source so that probalbly causes the unrealistic results. I only have no idea what value the Turbulence eddy dissipation or turbulence kinetic energy should be. I also can't find a formula in the maual. Is there a standard formula to calculate these values? Do i also need to set the option for viscous dissipation in the domain on?

Thanks a lot for the help, Richard

Bian October 10, 2006 09:48

Re: Modelling a fan
I have no experience on jet flow, however, I do simulate the fans (from inlet to outlet).

I would say the tubulence source will be a guess or estimate according to flow speed and outlet size. If I work on your problem, I will take the outlet boundary of my fan simulation as the inlet boudary of the jet flow.


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