CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

initial field of turbulence

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 9, 2002, 03:16
Default initial field of turbulence
  #1
Paul
Guest
 
Posts: n/a
Dear all,

I am coding the 2D decay turbulence and coming across a difficult in set the initial homogeneous turbulent field. There is always a large difference between the desired energy spectrum and my numerical spectrum. I also find that the main point is how to randomly generate velocity ( streamfunction or anything else) in the wavenumber space which SHOULD satisfies the condition of complex conjugate. I did refer to the book `Fluid Flow Phenomena' by P. Orlandi and the old paper by S. A. Orszag but still can not get some idea for my codes. If anyone has some experience, please kindly give me some hints.

PS. the procedure described in the `Fluid Flow Phenomena' seems not correct scince one can not get a real function from the RANDOMLY generated streamfuntion which does not satisfies the complex conjugate condition.

Thank you very much!
  Reply With Quote

Old   May 25, 2002, 06:53
Default Re: initial field of turbulence
  #2
Geert
Guest
 
Posts: n/a
It should not be so difficult. I have done the following for 3D turbulence. First give the velocity in spectral space a random complex number, for instance the real and imaginary part have a random value between -1 and 1 (make sure that it is random value between -1 and 1 and not between 0 and 1). Then set the modes U(0,0) U(n/2,0) U(0,n/2) U(n/2,n/2) to zero. Make the velocity field divergence free! Then I calculate the spectrum and modify the amplitudes of the waves so that I get the desired spectrum.

Good luck.
  Reply With Quote

Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Forces in OF15 richard OpenFOAM Running, Solving & CFD 180 July 9, 2018 11:54
TwoPhaseEulerFoam and Boundary conditions raagh77 OpenFOAM Running, Solving & CFD 99 February 6, 2018 19:31
Compressible Nozzle Flow sebastian OpenFOAM Running, Solving & CFD 14 September 21, 2016 11:47
Extrusion with OpenFoam problem No. Iterations 0 Lord Kelvin OpenFOAM Running, Solving & CFD 8 March 28, 2016 12:08
Upgraded from Karmic Koala 9.10 to Lucid Lynx10.04.3 bookie56 OpenFOAM Installation 8 August 13, 2011 05:03


All times are GMT -4. The time now is 03:57.