How estimate k-omega parameters?

WhiteW · December 9, 2015, 04:52

Hi to everybody,
I'm studying the external aerodynamic of an airplane(rhoSimplecFoam) with the velocity of 44.85 m/s.

The simulation converges and the values of pressure and velocity fields seem to be correct.
However the forces (Lift and Drag) are incorrect and I think it is due to the k omega boundary conditions.

How can the turbulence values be estimated?
The setting of the Motorbike case is:
U=20m/s
k=0.24m2/s2
omega=1.78s-1
How have k and omega been estimated in this case?
I'm using the tool: http://www.cfd-online.com/Tools/turbulence.php but I can't find that values.
Thanks in advance,

WhiteW

fabian_roesler · December 11, 2015, 08:34

You could just calculate backwards from the formulas given for free-steam k and omega.
Here is the motorbike setup data:

U = 20 m/s
Tu = 2 %
TuL=0.275 m
nu = 1.5e-05 m2/s

resulting in

k = 0.24 m2/s2
omega = 1.78 1/s

The explanation on how to get those values is pretty good:
http://www.cfd-online.com/Wiki/Turbulence_modeling

Cheers

Fabian

WhiteW · December 12, 2015, 07:16

Thanks Fabian!!

December 9, 2015, 04:52	How to estimate k-omega parameters?	#1
WhiteW Member Join Date: Dec 2015 Posts: 74 Rep Power: 10	Hi to everybody, I'm studying the external aerodynamic of an airplane(rhoSimplecFoam) with the velocity of 44.85 m/s. The simulation converges and the values of pressure and velocity fields seem to be correct. However the forces (Lift and Drag) are incorrect and I think it is due to the k omega boundary conditions. How can the turbulence values be estimated? The setting of the Motorbike case is: U=20m/s k=0.24m2/s2 omega=1.78s-1 How have k and omega been estimated in this case? I'm using the tool: http://www.cfd-online.com/Tools/turbulence.php but I can't find that values. Thanks in advance, WhiteW Last edited by WhiteW; December 9, 2015 at 05:56.

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December 11, 2015, 08:34		#2
fabian_roesler Senior Member Fabian Roesler Join Date: Mar 2009 Location: Germany Posts: 213 Rep Power: 18	You could just calculate backwards from the formulas given for free-steam k and omega. Here is the motorbike setup data: U = 20 m/s Tu = 2 % TuL=0.275 m nu = 1.5e-05 m2/s resulting in k = 0.24 m2/s2 omega = 1.78 1/s The explanation on how to get those values is pretty good: http://www.cfd-online.com/Wiki/Turbulence_modeling Cheers Fabian

December 12, 2015, 07:16		#3
WhiteW Member Join Date: Dec 2015 Posts: 74 Rep Power: 10	Thanks Fabian!!