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

 June 20, 2007, 03:08 problems for unsteady calculation #1 olivier Guest   Posts: n/a Hi everybody, I want to do an unsteady calculation for a flow over a flate plate in horizontal duct (like a forward-facing and backward-facing step). -I calculate a steady-state solution before.Is it the best solution ? -I tried with an adaptive time stepping method with the default values. But which is the criteron to determine the best time step size for a fixed time stepping method. -Why my unstedy model give me a steady solution when I visualize my animation? My model is maybe steady or there is a problem in the calculation ? Thanks a lot !!!

 June 20, 2007, 09:13 Re: problems for unsteady calculation #2 Laure Guest   Posts: n/a Hello, I think that if you are that your problem is unsteady, you don't need to calculate a steady-state solution before. You can directly calculate an unsatedy-state solution. For the criterion to determine the best time step size, it is the CFL number. You initialize this criterion in solve -> controls -> solution. Laure

 June 20, 2007, 09:17 Re: problems for unsteady calculation #3 olivier Guest   Posts: n/a Thanks Laure (merci d'avoir répondu et bon courage pour la suite)

 June 21, 2007, 02:13 Re: problems for unsteady calculation #4 James Guest   Posts: n/a Hi, You didn't say whether you were using RANS or LES. With RANS, you might seem to be having a steady state solution at the onset. You'll have to allow it to run for a considerable period of time before you get rid of the steady state behaviour. Hope this helps. James

 June 21, 2007, 02:28 Re: problems for unsteady calculation #5 olivier Guest   Posts: n/a Hi James, I used a k-e model. I don't know which model is the most adapted for this kind of calculation. I'll try a RANS model. Maybe my unsteady calculation didn't work over a rather long periode of time to became unsteady? Thanks James.