<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div>Hello everyone,<br></div><div><br data-mce-bogus="1"></div><div>I have been working on the turbulent channel case for some time. But I am quite confused with the filtering technique in the turbChannel.usr. <br data-mce-bogus="1"></div><div>I understand well the filtering technique for improving stability (p101 and p103), thanks to the discussion on the forum. However, is the same technique used in the build_1d_filt ? basically, partly removing the high wavenumber spectral in the expansion ?<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>I have a question about transfer function also:<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div> diag(nx-0) = 0.05 <br> diag(nx-1) = 0.50<br> diag(nx-2) = 0.95<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>It seems to me that the diag(:) would determine how much energy will be removed for the high wave number spectral? but what are the variables fh, fht in the subroutine <br data-mce-bogus="1"></div><div>build_1d_filt (fh,fht,diag,nx,nid) ?<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>it seems quite difficult to apply the more traditional filters like top-hat filter or Gaussian filter in the Nek5000. <br></div><div><br data-mce-bogus="1"></div><div>Lastly, removing high wave number parts of Legendre expansion seems makes no sense physically. After all, the energy spectral of turbulence is represented in Fourier series.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Does anyone has any idea on these puzzles? Any discussion is greatly appreciated. <br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Best regards<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div data-marker="__SIG_PRE__"><div>Bien cordialement<br></div><div><br></div><div>Zhenrong JING<br></div><div><br></div><div>Doctorant (Doctor Candidate)<br></div><div><br></div><div>LHEEA</div><div><br></div><div>Ecole Centrale de Nantes<br></div><div><br></div><div><span class="_Xbe">1 Rue de la Noë, 44321 Nantes, France<br></span></div></div></div></body></html>