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Old   March 8, 2000, 19:09
Default Drag Factors
  #1
Nassar Majothi
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Dear All, I am doing a final year degree project to predict the drag factors of various simple automotive shapes, i have currently obtained results that are around 40% away from experimental results. I have tried many solvers and mesh structures, could you please help me with further suggestions on how i may further improve my results. (using Fluent 5) Cheers, Nas.
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Old   March 9, 2000, 00:59
Default Re: Drag Factors
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Bob Anderson
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Are they 40% higher, or 40% lower than experiment? My first guess would be that you are not modeling separation correctly or at all. Are these separated flows? If so, how are you modeling that separation?

Bob
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Old   March 9, 2000, 11:57
Default Re: Drag Factors
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clifford bradford
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also try asking around in the fluent forum
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Old   March 10, 2000, 05:19
Default Re: Drag Factors
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Nassar Majothi
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Thanks for the replies. My results are 40% higher than experimental values, I am modelling seperation, although as i am new to this, i may not be doing it correctly. I am using Reynolds stress equations with non equilibrium boundary conditions. What would be the best way to model seperation? Cheers, Nas.
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Old   March 13, 2000, 06:11
Default Re: Drag Factors
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Ahmed Al-otaibi
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you have to check the base drag..it has major contribution in total drag..
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Old   March 15, 2000, 02:09
Default Re: Drag Factors
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ROOH-UL-AMIN KHURRAM
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Drag estimation is perhaps most difficult field in CFD. And if you are matching it with Wind tunell results it become even more difficult because of WT errors like wall effects and sting effect. First of all you have to get a reliable WT data with corrections. i suggest you should first match the drag coefficient of a simpler shape like a 10 degree cone. By chance I am presently involved in matching the drag coeficient of 10 degree cone with WT data. but I am doing it at supersonic Mach numbers and with various turbulence models, as base drag strongly depend on the Turbulence models. I have got quite interesting results. If you are interested to repeat this study, contact me

regards

khurram R.A
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