Turbulence modeling
 

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

use the gamma theta model

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

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

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?

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?

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

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