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

advection time scale

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

LinkBack Thread Tools Search this Thread Display Modes
Old   February 23, 2009, 23:43
Default advection time scale
Tanveer ahmad Rubani
Posts: n/a
1.what fraction of Length/Velocity scale should be used for iving value of Physical Time scale in Solver control of ANSYS CFX Pre. 2.Why Physical Time scale value should be less than advection time scale as is mentioned in help for divergence.The advection time scale appears in solver out file under average time scale information.How is advection time calculated. 3.How sensitive is problem convergence to time step. Is is possible that a problem never converges with auto time scale value but will converge with Physical Time scale value.
  Reply With Quote

Old   February 24, 2009, 16:16
Default Re: advection time scale
Glenn Horrocks
Posts: n/a

I assume you are talking about a steady state simulation.

1. One is a starting point but many simulations can use much higher than that. It is problem dependant.

2. Smaller timesteps are less prone to divergence. However once the flow has started and the basic flow pattern is established you can generally use a much bigger timestep.

2a. Advection time is a length scale/velocity scale. The length scale is (I think) the cube root of the total volume and the velocity scale is some sort of average velocity.

3. Problem dependent. Simple simulations are not very sensitive, but numerically unstable simulations can be very sensitive.

3a. Yes. Auto time scale is just a guess, but with physical time scales you can set it to be as high or low as is necessary.

Glenn Horrocks
  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
Advection Time Anne CFX 15 March 1, 2018 16:53
TimeVaryingMappedFixedValue irishdave OpenFOAM Running, Solving & CFD 31 January 25, 2018 03:03
Time Scale and physical time scale mohammad CFX 1 March 23, 2011 17:43
directMapped problem panda60 OpenFOAM Bugs 4 July 8, 2010 10:23
DPM: Particle Tracking Madhukar FLUENT 1 July 24, 2007 03:51

All times are GMT -4. The time now is 21:29.