# k and omega boundary conditions.

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 October 12, 2011, 08:44 k and omega boundary conditions. #1 Member   Join Date: Jul 2011 Posts: 42 Rep Power: 14 Hi, I am relatively new with OpenFoam and I would be grateful if some one can help me please. I am trying to set up a case using simpleFoam and the kOmegaSST model (for a subsonic flow around and airfoil) but I have difficulties defining the boundary conditions for k and omega. My question is what should be the value of the term “value” in the following script ? And also what should be the value for internal field ? For k: dimensions [0 2 -2 0 0 0 0]; internalField uniform ????; boundaryField { airfoil { type kqRWallFunction; value uniform ???; } farfield { type turbulentIntensityKineticEnergyInlet; intensity 0.9; value uniform ????; } frontAndBackPlanes { type empty; } } For Omega: dimensions [0 0 -1 0 0 0 0]; internalField uniform ???; boundaryField { airfoil { type omegaWallFunction; Cmu 0.09; kappa 0.41; E 9.8; value uniform ????; } farfield { type turbulentMixingLengthFrequencyInlet; mixingLength 0.005; k k; value uniform ????; } frontAndBackPlanes { type empty; } } Thank you in advance for your consideration and time. Sincerely, A.D.E

 October 12, 2011, 11:35 #2 Senior Member   Join Date: Apr 2010 Posts: 151 Rep Power: 15 k is the specific turbulent kinetic energy and omega the turbulence length scale. In general it is hard to know how much they are. If you are simulating a wind tunnel with inlet speed U and turbulence intensity x%, then you can guess k = x/100 * U^2 at the inlet boundaries and in the domain. For omega I cannot give you tips, but I read that often omega smooths out independently of the BC's.

 October 13, 2011, 09:42 #3 Senior Member   David Boger Join Date: Mar 2009 Location: Penn State Applied Research Laboratory Posts: 146 Rep Power: 16 Not stated is the fact that "internalField" represents the initial condition or initial guess for the flow field. I suspect the "value" field does not need to be specified in your 0/ directory for many if not all of the boundary conditions you list. On subsequent time steps, that variable may be output and contain the current value of the cell faces on the boundary. __________________ David A. Boger

 October 14, 2011, 05:25 #4 Member   Join Date: Jul 2011 Posts: 42 Rep Power: 14 Hello, Thank you both for your reply. I am currently running a simulation after considering your comments. Can I also ask what does the value of mixingLength represent? For a simulation of a flow in a wind tunnel what value can I use? Thank you, A.D.E

October 14, 2011, 07:52
#5
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Dhondu Pant
Join Date: Nov 2009
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Quote:
 Originally Posted by A.D.E Hello, Thank you both for your reply. I am currently running a simulation after considering your comments. Can I also ask what does the value of mixingLength represent? For a simulation of a flow in a wind tunnel what value can I use? Thank you, A.D.E
Hello

http://www.openfoam.com/docs/user/ca...#x5-120002.1.3

2.1.8.1 Pre-processing

Best regards

 October 31, 2011, 05:00 Cp plots #6 Member   Join Date: Jul 2011 Posts: 42 Rep Power: 14 Hello I would like to plot the Cp curve around an aerofoil in paraFoam can anyone tell me how I can go about it? Thank you in advance A.D.E

 October 31, 2011, 05:01 #7 Member   Join Date: Jul 2011 Posts: 42 Rep Power: 14 Thank you.

 June 30, 2020, 02:45 #8 New Member   Manuel Fermin Fonseca Join Date: Nov 2014 Location: Valencia, Venezuela Posts: 17 Rep Power: 10 Hi A.D.E. hope this above can help you k=3/2*(Ve*I)^2 I=0,16/R_e^(1/8) epsilon=C_mu^(3/4)*k^(3/2)/Dh omega=(k)^(1/2)/Dh for more information see the user guide.