# For 2nd order scheme, how to put boundary conditions?

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

 April 28, 2014, 21:58 For 2nd order scheme, how to put boundary conditions? #1 New Member   David Join Date: Feb 2013 Posts: 16 Rep Power: 6 We all know for 1st order scheme, for example upwind, it is easy to set the boundary conditions, for example, if it is a wall, just give it zero for the first cell located on the wall. If it is a 2nd order scheme, for example QUICK, it may require 2 points to calculate, the I may need to calculate the 3rd layer cells, maybe I will need 1st and 2nd layer cells to calculate, now the 1st layer maybe a wall, and value is zero, how about the 2nd layer one? How to put a boundary conditions there? THanks.

 April 30, 2014, 03:03 #2 Member   Join Date: Dec 2012 Posts: 82 Rep Power: 7 Hi As far as I know Quick is 3rd order. Anyway.. The easiest way is surely to change to first order upwind near the wall. For a more sophisticated calculation, where you can't use 1st order consider switching to second order upwind or central differencing, if the peclect number is low enough. Apart from that you will never use the second layer inside a wall for reconstruction if you use 2nd order or 3rd order upwind (Quick). Regards

April 30, 2014, 04:38
#3
New Member

David
Join Date: Feb 2013
Posts: 16
Rep Power: 6
Quote:
 Originally Posted by beer Hi As far as I know Quick is 3rd order. Anyway.. The easiest way is surely to change to first order upwind near the wall. For a more sophisticated calculation, where you can't use 1st order consider switching to second order upwind or central differencing, if the peclect number is low enough. Apart from that you will never use the second layer inside a wall for reconstruction if you use 2nd order or 3rd order upwind (Quick). Regards
Thanks Beer:

By "Apart form that......", you mean never try to use a double layer ghost cells in the wall, right? So looks like downgrade the order near boundary is the only way, right?

The other thing, Is it a good idea to always use central differencing scheme for diffussion item?

 April 30, 2014, 04:51 #4 Member   Join Date: Dec 2012 Posts: 82 Rep Power: 7 Hi Yes and no. You can use as many ghost cells as you want, I personally don't really like them. But what I actually meant was that, assuming you have no convection on the face between the solid cell (or wall) and the fluid cell, there is no need to use the second layer anyway. Just draw a picture of QUICK with 3 cells. It uses 2 upwind cells and one downwind one. Like I said before, the face lies inside the fluid domain and has thus fluid cells left and right of it. Now the second upwind cell is the only one that can be a solid cell, wall, ghost cell or whatsoever. Thus you never use the second layer in that scheme. It can be different at in- and outlets, but I wouldn't use quick on those boundaries either. To central differencing for diffusion: Yes . Honestly I have never seen anybody using a different approach. Just remember to use the cross flux correction or mesh transformation if your mesh is skewed. Regards

 Tags boundary condition, high order scheme

 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 Saturn CFX 48 October 25, 2017 06:07 hinca CFX 15 January 26, 2014 18:11 Anna Tian CFX 1 June 16, 2013 06:28 Far FLUENT 0 May 22, 2011 01:50 Mark CFX 6 November 15, 2004 16:55

All times are GMT -4. The time now is 00:41.