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June 1, 2010, 08:03 |
fan vs experimental data
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#1 |
Member
Join Date: Apr 2010
Posts: 33
Rep Power: 16 |
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 |
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June 1, 2010, 19:46 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144 |
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. |
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June 7, 2010, 05:42 |
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#3 |
Member
Join Date: Apr 2010
Posts: 33
Rep Power: 16 |
Thanks Glenn
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