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

High-freq oscillations in residuals

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

Like Tree1Likes
  • 1 Post By Daveo643

LinkBack Thread Tools Search this Thread Display Modes
Old   June 8, 2015, 17:15
Default High-freq oscillations in residuals
New Member
Join Date: Mar 2013
Location: Canada
Posts: 22
Rep Power: 9
Daveo643 is on a distinguished road
Hello there,

I am wondering if someone could help me. I am running a transient simulation and encountering oscillations, particularly in the continuity and energy residuals within a single timestep, when other timesteps are fine. After a few timesteps, these oscillations disappear and return to relative normalcy.

Advanced solution control options are initially left to their defaults (F-Cycle), but I've also variously tried V-Cycle multigrid with and without BCGSTAB stabilization on Flow and Energy.

I've also gone into the text-interface options /solve/set/amg-options/amg-gpgpu-options and played with using different solvers (FGMRES PBICGSTAB AMG), pre-/post-sweeps and smoothers (ILU GS JACOBI).

Thanks in advance!

The second to last timestep showed the beginning of the oscillations with no changes from the start of the simulation and was interrupted. There is nothing physically going on that should cause the oscillations. The Energy under-relaxation factor was reduced from 1 to 0.75 and Density from 1 to 0.9 in the last shown timestep.
Daveo643 is offline   Reply With Quote

Old   November 2, 2015, 12:44
New Member
Join Date: Mar 2013
Location: Canada
Posts: 22
Rep Power: 9
Daveo643 is on a distinguished road
FYI: Resolved by combination of remeshing and stopping the transient simulation before the timestep of observed oscillations/flatlining and reducing underrelaxation factors. Using hybrid initialisation with proper patching also helped overall convergence greatly (0.5X number of iterations to complete entire transient simulation run of 512 timesteps).
cwang likes this.
Daveo643 is offline   Reply With Quote


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
plot residuals pigna OpenFOAM Running, Solving & CFD 2 December 19, 2014 03:32
Residuals high for 2D Convergent divergent nozzle simulation jphoenix FLUENT 0 November 11, 2014 09:12
High Pressure Residuals ArathoN OpenFOAM Running, Solving & CFD 2 May 4, 2014 10:23
High drop in residuals star FLUENT 2 February 16, 2014 07:51
Poor Residuals at Intersection Between Symmetry Plane and Airfoil Leading Edge TWaung CFX 2 February 16, 2010 09:11

All times are GMT -4. The time now is 16:00.