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Old   July 2, 2011, 03:27
Default Turbulence modeling
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Hi all
I'm simulating flow around sphere at Re=1E05 with DES(Detached Eddy Simulation) turbulence model. the Y plus=0.2 and time step size=0.008.
The mean drag coefficient is 0.27 and there is large error with experiment data that say Cd=0.42.

whats wrong in my simulation?


Best regards.
omid
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Old   July 2, 2011, 05:31
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Sijal Ahmed Memon (turboenginner@gmail.com)
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use the gamma theta model
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Old   July 2, 2011, 06:51
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Could be dozens of things, not just the turbulence model. Read this FAQ:

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F
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Old   July 4, 2011, 02:37
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Quote:
Originally Posted by omidiut View Post
Hi all
Re=1E05 with DES(Detached Eddy Simulation) turbulence model. the Y plus=0.2 and time step size=0.008.
Best regards.
omid
Hi.
Try to solve it with the timestep of order of 1e-4... it may work..
mesh density along the chord and in downsteam also are important.

good luck
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Old   July 4, 2011, 09:53
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Quote:
Originally Posted by mohammad View Post
Hi.
Try to solve it with the timestep of order of 1e-4... it may work..
mesh density along the chord and in downsteam also are important.

good luck

Hi
Thanks
but its very small! i use timestep value equal 0.008 but the Drag be constant, i think with smaller timestep this problem repeat, whats your idea?
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Old   July 4, 2011, 09:59
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Thanks all
I find something about grid resolution and surface grid spacing in ANSYS CFX- solver theory guide p.81 : DES simulation.

is this problem because of grid induced separation?
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Old   July 4, 2011, 09:59
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Quote:
Originally Posted by omidiut View Post
Hi
Thanks
but its very small! i use timestep value equal 0.008 but the Drag be constant, i think with smaller timestep this problem repeat, whats your idea?
Hi, about the DES timestep I'm sure that it must be small.+ number of nodes in chordwise and Y+ value are important..you can see teh CFX 11 help manual about DES .

regards
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