CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

Oscillation of a upwind scheme

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 20, 2003, 16:00
Default Oscillation of a upwind scheme
  #1
Mehdi
Guest
 
Posts: n/a
I am coding an upwind scheme with adaptative mesh to solve an MHD problem with a strong shock. I am using a 2 stage Runge-Kutta scheme for stepping in time.

I have problem to converge, since my solution start to oscillate very quickly (5 or 6 iterations), the osciallation become verry strong and crash the solution.

These oscillation seems to come from the shock and expand to all the space domain. The oscialltion frequency is the same of the grid, so refining more does'nt change resolve the problem.

- I want to know what kind of solution I have to damp such oscialltion and make my solution converge. - Should I add a terme in d2_U/d_x to add an actificial viscosity in my solver ? What consequence it will have on the final solution.

Thank you
  Reply With Quote

Old   June 20, 2003, 17:29
Default Re: Oscillation of a upwind scheme
  #2
Ravi
Guest
 
Posts: n/a
I assume you are using higher order upwinding. Upwind schemes are subject to oscillations near shocks. You can use some limiter ( e.g. minmod, vanleer..) to restrit the scheme to first order near shocks to make the scheme more dissipative and avoid oscillations.

Typically, they add artificial viscosity for central difference schemes as it has no dissipation..( so the term artificial or numerical viscosity)

I hope this helps.

Ravi
  Reply With Quote

Old   June 23, 2003, 13:55
Default Re: Oscillation of a upwind scheme
  #3
Mehdi
Guest
 
Posts: n/a
Thank you for you answer Ravi

In fact, I am using a second order in space and time upwind MUSCL scheme. during the reconstruction I use a minmod type diffusive limiter to reconstruct the cell's edges variables (Barth limiter). Despite I am forcing this limiter to 0 ( forcing the scheme to be just a first order in space all the time), I still have the same oscillations that are coming form the shock.

Turning on or off the grid refinement doesn't change anything too as I said.

How can I remove such oscillation that make my solution diverge ?

PS : I am simulating a supersonci plasma shock (M=10)

  Reply With Quote

Old   June 24, 2003, 21:51
Default Re: Oscillation of a upwind scheme
  #4
versi
Guest
 
Posts: n/a
Did you experience the so called carbuncle artifact for blunt body in supersonics? there are much work done on it. You can see recent (2002-2003) JCP paper. It seems that all 1D-based Riemann -type scheme will face such "carbuncle artifact" in hypersonics.
  Reply With Quote

Old   June 26, 2003, 11:47
Default Re: Oscillation of a upwind scheme
  #5
Salvador
Guest
 
Posts: n/a
Always depend on the Riemann Solver you are using, Roe's solver and HLL will have carbuncle phenomena and do not predict contact waves. Use HLLC or HLLEM, those are not affected by those phenomena and they are not that much expensive. Anyway using MHD, the Riemann Solver must be different so the problem must be somewhere else (I cannot coment on that) I rember peope dong it have to put artifcats for div B=0 buy I really am not an expert on it. Using MUSCL or other limiter, the damping should be effective (turn MUSCL off) and you shouldn't see the oscillations (first order is quite dissipative).

If you are not using Rieamnn solvers, what are you using?, do you have viscoisty ? or walls? does it work if you turn the lectric/magnetic force off (not solving the M in MHD

  Reply With Quote

Reply

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
2nd order upwind vs 2nd order upwind!!! Far Main CFD Forum 7 March 14, 2013 13:29
Use of upwind scheme for interpolation of u/v quarkz Main CFD Forum 6 August 30, 2011 05:10
Second order upwind is not UPwind!!! Far CFX 9 May 31, 2011 09:21
2nd order upwind scheme (Fluent and CFX) Far FLUENT 0 May 22, 2011 02:50
solution diverges when linear upwind interpolation scheme is used subash OpenFOAM 0 May 29, 2010 02:23


All times are GMT -4. The time now is 05:28.