Turbulence modeling

omidiut · July 2, 2011, 04:27

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

Far · July 2, 2011, 06:31

use the gamma theta model

ghorrocks · July 2, 2011, 07:51

Could be dozens of things, not just the turbulence model. Read this FAQ:

http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

mohammad · July 4, 2011, 03:37

Quote:

Originally Posted by omidiut

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

omidiut · July 4, 2011, 10:53

Quote:

Originally Posted by mohammad

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?

omidiut · July 4, 2011, 10:59

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?

mohammad · July 4, 2011, 10:59

Quote:

Originally Posted by omidiut

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

tias · November 28, 2016, 11:37

I am having a similar issue. did you ever get to the bottom of this?

July 2, 2011, 04:27	Turbulence modeling	#1
omidiut Senior Member omid Join Date: Apr 2011 Posts: 105 Rep Power: 15	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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July 2, 2011, 06:31		#2
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	use the gamma theta model

July 2, 2011, 07:51		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Could be dozens of things, not just the turbulence model. Read this FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

July 4, 2011, 10:59		#6
omidiut Senior Member omid Join Date: Apr 2011 Posts: 105 Rep Power: 15	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?

November 28, 2016, 11:37		#8
tias New Member Join Date: Jun 2016 Posts: 7 Rep Power: 10	I am having a similar issue. did you ever get to the bottom of this?