# Is there a corrected Gauss gradient scheme?

 Register Blogs Members List Search Today's Posts Mark Forums Read

 November 24, 2011, 09:18 Is there a corrected Gauss gradient scheme? #1 Senior Member     Philip Cardiff Join Date: Mar 2009 Location: Dublin,Ireland Posts: 638 Rep Power: 23 Sponsored Links Hi, I have been looking at the accuracy of the Gauss linear gradient scheme for a simple case compared with the analytical solution, and it is exactly correct for a perfectly orthogonal mesh. But it is inaccurate if the grid is non-orthogonal. Is there any corrected version of the Gauss linear gradient scheme where the non-orthogonality is corrected for explicitly? I have also tried leastSquares but it seems to give strange gradients in the boundary cells. extendedLeastSquares seems to work the best but I am not entirely sure how it works. Philip

 November 27, 2011, 09:54 #2 Senior Member     Philip Cardiff Join Date: Mar 2009 Location: Dublin,Ireland Posts: 638 Rep Power: 23 OK, I found that you can specify explicit correction like this (as described here): Code: ```gradSchemes { grad(U) Gauss skewCorrected linear; }``` This certainly reduces the error on non-orthogonal grids, for my test cases anyway. However, leastSquares gives me much better results on non-orthogonal grids. I was getting strange incorrect gradients in the boundary cells using leastSquares but this was solved by commenting and uncommenting a few lines in OpenFOAM-1.6-ext/src/finiteVolume/finiteVolume/gradSchemes/leastSquaresGrad/leastSquaresVectors.C. I commented the following lines (lines 140 to 151): Code: ``` // Original version: closest distance to boundary //vectorField pd = // mesh_.Sf().boundaryField()[patchi] // /( // mesh_.magSf().boundaryField()[patchi] // *mesh_.deltaCoeffs().boundaryField()[patchi] // ); //if (!mesh_.orthogonal()) // { // pd -= mesh_.correctionVectors().boundaryField()[patchi] // /mesh_.deltaCoeffs().boundaryField()[patchi]; // }``` and uncommented this line (line 155): Code: ``` // Better version of d-vectors: Zeljko Tukovic, 25/Apr/2010 // Experimental: review fixed gradient condition. HJ, 30/Sep/2010 vectorField pd = p.delta();``` Philip fumiya, nero235 and serles like this.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post nico765 OpenFOAM Bugs 27 June 3, 2014 05:29 Ger_US OpenFOAM 8 January 8, 2013 13:29 fuji OpenFOAM 7 December 14, 2010 00:44 subash OpenFOAM 0 May 29, 2010 01:23 waynezw0618 OpenFOAM Running, Solving & CFD 39 March 5, 2009 13:57