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ijk June 1, 2010 07:03

fan vs experimental data
 
Hi all,

I am trying to generate a fan curve from experimental data using CFX. I have found that it does not converge steady state so I run it transient.

The fan is an axial fan but I am running in the stalled mixed flow region. I have found that my course mesh using wall functions (yplus100 on blade) is about 15% low in mass flow for a given loading. The steady state is way off.

I have yplus 30 and 1 cases running but they take forever. Perhaps a PHD using CFD was a bad idea.

Are these normal results for CFX? I have some friends who have done similar work with Star CD and they have got transient results within 5%.

I am not 100% that the experimental results are correct as the airflow was measured using anemometers and not a proper venturi setup.

Any advice anyone could give would be much appreciated.

Thanks

ghorrocks June 1, 2010 18:46

Getting accurate results in the stalled region is difficult, so you have a difficult project. That means you can expect long run times.

It also means you may not be able to use a turbulence model to get good results, you may be forced to use DES/SAS to get improvement - but that will just increase your run time more.

There are no simple answers in CFD, especially with difficult work like stall modelling.

I would be very surprised that the difference between your results and Star-CD is purely the solver. I would suggest either the user knew what he was doing better or was lucky.

ijk June 7, 2010 04:42

Thanks Glenn


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