Hi, All
I'm a new user of Ope
Hi, All
I'm a new user of OpenFoam. I just found her several days ago and was interested in its open and robust attributes. After plays with it, i think it has a bright promising if it's help documentation can be strengthened. Now, comes my question: I run the LES case:channel395 and get several results written as files in different directory,e.g. in directory 1000, there are files of P,U,u_0,k,.....etc. My exact question is what's the meaning of U_0,Umean,R,Bmean. Does Umean means the average U with time?? Can anybody help me?? 
Umean is a running average of
Umean is a running average of the velocity field and R is a running average of the 2nd moments (velocity variance av(u'u'). Bmean is a running average of the SGS stress tensor. By running average I mean a continuouslyupdated time average of the quantity.
Most of this is in createAverages.H, which is fairly easy to read once you get used to the syntax. I actually can't find where U_0 is being defined : I'm wondering if its redundant. I'll keep looking. Gavin 
U_0 and the other *_0 fields a
U_0 and the other *_0 fields are the old time values (i.e. timestep previous to U). They are necessary to restart calculations that use second order accurate schemes in time like CrankNicholson.
For the rest,"p" for a incompressible code is pressure devided by density. For a compressible code it is just the pressure (same for mean quantities). "pPrime2Mean" is the mean of the square of the deviatoric part (ppMean) of the pressure and is a good indicator for noise. "nuSgs "is the subgridscale viscosity and "k" is the SGS turbulent kinetic energy. "nuTilda" is a working SGS viscosity that is only used with the Spalartallmaras model. Have I missed anything? 
Hello
Does anyone know what
Hello
Does anyone know what is the definition of the 9 components of Reynolds stress R in OpenFOAM? Thanks! 
Hi all,
I was looking at w
Hi all,
I was looking at what the components of R is and how they are calculated in channelOodles. In createAverages.H, R is created as a symmetric tensor. so the 6 components of R written out by the program are Rxx,Rxy,Rxz,Ryy,Ryz and Rzz. As Dr. Tabor remarks above , R represents the variance of velocity thus the components of R should ; Rxx=ave(u'u') , Rxy=ave(u'v') , Rxz=ave(u',w'), Ryy=ave(v'v') , Ryz=ave(v'w') and Rzz=ave(w'w'). so the dimensions of R should be [0 2 2 0 0 0 0] . But if you look at the output file of R generated by the solver (say channelOodles.C) , then its dimension is [ 0 1 1 0 0 0 0]. Is this correct? Also in createAverages.H, R is calculated as sqr(U)sqr(UmeanPtr()) . thus R seems to be a function of velocity squared and should have dimension of m^2/s^2. and can someone tell me how to get u'u' from sqr(U)  sqr(Umean) . It seems to me this should be square(U  Umean) Thanks a lot kumar 
Hi Kumar,
About your last q
Hi Kumar,
About your last question i can tell you the following (PLEASE SOMEONE CORRECT ME IF I AM WRONG): R is a running average of u'u' so R=<u'u'>=<(uumean)(uumean)> =<(uumean)^2> =<u^2> =<u^2>  2<u.umean> + <umean^2> =<u^2> 2<u>.Umean + Umean^2 =<u^2> 2.Umean^2 + Umean^2 =<u^2>  Umean^2. Cheers, Hadi 
Hi Kumar,
About your last q
Hi Kumar,
About your last question i can tell you the following (PLEASE SOMEONE CORRECT ME IF I AM WRONG): R is a running average of u'u' so R=<u'u'>=<(uumean)(uumean)> =<(uumean)^2> =<u^22u.umean+umean^2> =<u^2>  2<u.umean> + <umean^2> =<u^2> 2<u>.Umean + Umean^2 =<u^2> 2.Umean^2 + Umean^2 =<u^2>  Umean^2. Cheers, Hadi 
Very good!
Thanks for engene, kumar and hadi's explanation. hadi's explanation is especially excellent. This thread shouldn't be forgot. 
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