# transient behavior dependent on time step

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 27, 2008, 14:53 transient behavior dependent on time step #1 Fab Guest   Posts: n/a Hi, I wonder, if one can expect that the transient behavior at a certain probe location is dependend on the chosen time step!? E.g. would a time step size of 0.01sec compared to 0.001sec change the output, when watching the low frequencies around 1Hz? I assume that the output depends more on the numerical diffusion, than on the time step size as long as it runs stable!? Thanks. Fab

 May 29, 2008, 08:04 Re: transient behavior dependent on time step #2 Vinayender Guest   Posts: n/a Hi Fab, When you say that total error depends only on numerical diffusion rather than on time step... Rember when you see MPDE (Modified Partial Differential Equation) for your PDE you see there are spatial derivatives and temporal derivatives in the Trunction Error. That is the error depends not only on the spatial descritisation but also on the time discritisation....As the time step tends to very small your error corresponding to temporal discritisation goes to zero then your error will corresponding to only sptial discritisation....This is all valid for only Unsteady flows... For steady flow, your final steady state solution will NOT depend on your time step provided your scheme is stable and the things will be right as said by you (i.e, the error is because of only spcatial discritisation ) Thanks, Vinayender.

 May 29, 2008, 11:38 Re: transient behavior dependent on time step #3 Fab Guest   Posts: n/a Hi Vinayender, thanks, o.k. I understand this. So actually the time step size determines the diffusion as well and has the same influence as turbulent or viscous diffusion; and the diffusion is proportional to the step sizs. Then it would not be enought just to check the CFL number due to some osziallations, but needs to calculate the diffusion as well!? Thanks! Fab

 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 nileshjrane OpenFOAM Running, Solving & CFD 4 February 25, 2013 05:13 panda60 OpenFOAM Bugs 4 July 8, 2010 10:23 shib FLUENT 0 June 17, 2010 13:07 lr103476 OpenFOAM Running, Solving & CFD 30 November 19, 2007 15:09 Sanjay Padhiar Main CFD Forum 1 March 31, 1999 12:32

All times are GMT -4. The time now is 18:19.

 Contact Us - CFD Online - Privacy Statement - Top