# timesteps reqd for the convergence of unsteady flo

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 July 27, 2005, 11:42 timesteps reqd for the convergence of unsteady flo #1 satyam Guest   Posts: n/a hi im simulating the flow past a barge(a displacment vessel) using vof,realizable k-epsilon,unsteady model.iam using maximum iterations per time step as 20 and the time step size as 0.001.can any one suggest me for how many time steps are reqd to acheive the convergence. thanks in advance

 July 28, 2005, 07:33 Re: timesteps reqd for the convergence of unsteady #2 Swarup Guest   Posts: n/a This is completely problem dependent for any model. Swarup.

 July 28, 2005, 07:39 Re: timesteps reqd for the convergence of unsteady #3 satyam Guest   Posts: n/a how can i calculate the min time required

 July 28, 2005, 07:51 Re: timesteps reqd for the convergence of unsteady #4 dirk Guest   Posts: n/a What do you think should the converged solution in your unsteady simulation be ? What do you want to compute ?

 July 28, 2005, 07:56 Re: timesteps reqd for the convergence of unsteady #5 satyam Guest   Posts: n/a i want to compute the total force,convergence of the coefficient of drag

 July 28, 2005, 09:30 Re: timesteps reqd for the convergence of unsteady #6 dirk Guest   Posts: n/a Then you simply have to monitor the development of drag and hope that it reaches a steady state or oscillates around a steady mean value. Dirk

 July 28, 2005, 09:37 Re: timesteps reqd for the convergence of unsteady #7 Swarup Guest   Posts: n/a then you should run simulation until Cd tapers off. do you have a target for total flow time? if so, then you should see that before your flow time is over, you have achieved convergence. further, if you are assuming incompressibility, then you should try to obtain convergence as early as possible. you have time step size deltat and number of iterations per time step to choose from. one more issue is whether your problem is inherently unsteady and has no steady state solution (like free convection)or you are finally interested in obtaining a steady state solution. Swarup

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