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

time steps in transient heat transfer in solids

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 5, 2003, 04:04
Default time steps in transient heat transfer in solids
  #1
Mike
Guest
 
Posts: n/a
Hello,

Is there any criteria for the time steps doing transient calculation with heat transfer in solids?

I found one for the convective mass transport saying

2*dt*nu/rho < L^2

L ... mean mesh size dt ... time step rho ... density nu ... dynamic viscosity

Is that criteria correct?

Is it possible to compare the energy-equation with the one for mass transport, so that I get a similar criteria for heat transport in solids?:

2*dt*lambda/(rho*cp) < L^2

L ... mean mesh size dt ... time step rho ... desnity lambda ... heat conduct. of solid cp ... spec. heat

Thanks in advance for every answer Mike
  Reply With Quote

Old   June 5, 2003, 04:58
Default Re: time steps in transient heat transfer in solid
  #2
gorka
Guest
 
Posts: n/a
Hi,

It depends on whether you use an explicit or implicit method for time discretization. Usually:

Explicit: 2*dt*lambda/(rho*cp) < L^2 (as you have pointed out)

Implicit: No restrictions for convergence (only for accuracy)

Semi-implicit (Crank-Nicolson): No retrictions for convergence but a restriction to avoid unphysical results:

dt*lambda/(rho*cp) < L^2

Hope this helps,

Gorka
  Reply With Quote

Old   June 5, 2003, 05:30
Default Re: time steps in transient heat transfer in solid
  #3
Mike
Guest
 
Posts: n/a
Hello,

Thank you very much - that really helps a lot, Gorka.

I have an implicit scheme, so it should be only a question of accuracy.

Do you have any advice how I can measure or see accuracy without having experimental data? Or is there any hint how to choose the time steps in fully imclicit scheme?

Mike
  Reply With Quote

Old   June 5, 2003, 05:47
Default Re: time steps in transient heat transfer in solid
  #4
gorka
Guest
 
Posts: n/a
Hi,

The Implicit scheme is first order accurate unless you use results from the two previous time-steps (n and n-1, being n+1 the new time step, in which you evaluate the terms). Therefore, you should use small time steps if you want to obtain accurate results. Sorry but I donīt know any specific criterium.

Gorka
  Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Upgraded from Karmic Koala 9.10 to Lucid Lynx10.04.3 bookie56 OpenFOAM Installation 8 August 13, 2011 04:03
Domain Imbalance HMR CFX 3 March 6, 2011 21:10
Transient Conjugate Heat Transfer Raja FLUENT 2 September 30, 2008 01:59
transient conjugate heat transfer problem scott CD-adapco 2 March 12, 2007 15:10
time averaged heat transfer in oscillating flow Matthieu Ubas Main CFD Forum 2 November 5, 1999 15:20


All times are GMT -4. The time now is 18:41.