CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > CFX

why momentum residual at wall is not zero

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

Like Tree1Likes
  • 1 Post By ghorrocks

LinkBack Thread Tools Search this Thread Display Modes
Old   February 26, 2019, 13:47
Default why momentum residual at wall is not zero
Join Date: Oct 2013
Posts: 67
Rep Power: 9
lostking18 is on a distinguished road
Hi, there

Recently I ran a cooling channel simulation in CFX as following:
1) I built two meshes for the same cooling channel: one with fine mesh; one with coarse mesh.;
2) I ran a fine mesh simulation and get converged; the flow is steady simulation with no-slip wall boundary condition at the bottom X_Y plane;
3) I set up the coarse meh simulation with the same boundary conditions as the fine mesh simulation, then I use the fine solution as the initial guess to the coarse mesh simulation and ran the simulation for just one time step.

Ideally since the difference between the fine and the coarse simulation is solely the mesh resolution and at the wall for both cases the velocity is 0(no-slip boundary contions), after one time step the momentum residual should be zero because there is no difference in momentum equation between these two simulations. However, I noted that the residual at the wall is not zero. Could you give some explanation on this observation? Is it because the residual is interpolated from the center of the mesh cell? Where does CFX store residual? On the vertex or at the cell center?

Thank you very much!
lostking18 is offline   Reply With Quote

Old   February 26, 2019, 16:33
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,392
Rep Power: 126
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
You should read the CFX documentation on discretisation approach.

The finite volume which includes the wall has the wall on one side and internal faces on the other side. The centroid of this finite volume is therefore off the wall, which means it has a non-zero velocity and therefore a residual.
lostking18 likes this.
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote


residuals, wall bcs

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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
Segmentation fault when using reactingFOAM for Fluids Tommy Floessner OpenFOAM Running, Solving & CFD 4 April 22, 2018 12:30
High Courant Number @ icoFoam Artex85 OpenFOAM Running, Solving & CFD 11 February 16, 2017 13:40
Floating point exception error lpz_michele OpenFOAM Running, Solving & CFD 53 October 19, 2015 02:50
Cannot run the code properly: very large time step continuity error crst15 OpenFOAM Running, Solving & CFD 9 December 14, 2014 18:17
Moving mesh Niklas Wikstrom (Wikstrom) OpenFOAM Running, Solving & CFD 122 June 15, 2014 06:20

All times are GMT -4. The time now is 16:46.