Problem with unwanted oscillations

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

 June 29, 2013, 22:19 Problem with unwanted oscillations #1 New Member   Patricio Javier Valades Pelayo Join Date: Jun 2013 Posts: 5 Rep Power: 4 Hello, I am trying to write my own Finite Volume code for a very simple problem. it is a mass transport problem on a pipe. 1D (axial) Unsteady state for the mass balance equation, only forced convection is considered. The Momentum equation on the pipe is considered plug flow (constant at all radius and all axial positions). In the program I consider an impulse function (delta dirac) of compound A, I made an animation of a plot of Concentration vs Axial Position that changes with time and started and following the pulse (or the evolution of the concentration profile inside the tube). The pulse moves in the expected way (forward) the width of the peak doesnt change (as expected since there is no axial dispersion), HOWEVER, on the trail behind the pulse I notice some "unwanted" oscillations... I am using a 1st order in space approximation for the FV and 4th order Runge-Kutta Method. I don't know what to do to get rid of those oscillations, I already tried moving the segments length in the axial direction and the time step, but nothing happens... I am new to this so all advices are welcome, however I would like to stress that I already checked and reckecked the logic behind the FV volume, and it is all right...maybe some problem with the numerical stability?

June 29, 2013, 22:33
#2
New Member

Join Date: Jun 2013
Posts: 5
Rep Power: 4
Here I attach an image of the concentration profile inside the pipe. at time zero the pulse is at Z=0, this image however is taken at time= 22 seconds. The velocity in the pipe is about 0.7 m/s , so the pulse is at about 15-16 meters (about halfway through the pipe since the pipe is 27 m long).
Attached Images
 unwanted_oscillations.jpg (15.5 KB, 7 views)

 Tags cfl condition, new user, stability problem

 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 Wouter Fluent UDF and Scheme Programming 6 June 6, 2012 04:43 ayhan515 OpenFOAM 2 May 1, 2012 04:29 michujo CFX 4 December 16, 2011 10:00 JFDC FLUENT 1 July 11, 2011 05:59 ParodDav CFX 5 April 29, 2007 19:13

All times are GMT -4. The time now is 19:56.