iteration

mani20saze · February 2, 2014, 07:32

hi
I want to simulate flow through a pipe by fluent.its a unsteady flow and i choose pressure-velocity coupling as simple. I dont have any idea about how should i fill the time step size and number of time steps and max iteration per time step in panel iterate?

tanks a lot

flotus1 · February 3, 2014, 02:40

Since you expect unsteady flow, there has to be some estimate for the time scale of this unsteadyness.
A good initial guess for the time step size is 1/20th of this time scale. You should still do a sensitivity study with the time step size especially if this is the first simulation of this kind you are doing.

The number of time steps in entirely your choice. Together with the time step size, it determines the total physical time of the simulation. If you want to simulate 20 seconds of real time and your time step size is 0.001s, then you need 20000 time steps.

The maximum iterations per time step have a default value of 20, which is not all that bad. If you chose a sufficuently small time step size, at least for standard simulations that should be enough to achieve convergence.
It is important to keep in mind that this is the MAXIMUM number of iterations. If the convergence criteria are met before this number is reached, the simulation advances to the next time step.
But as for the time step size, I highly recommend to do a sensitivity analysis with this quantity (and the convergence criteria) if this is the first time you do a new kind of simulation.

February 2, 2014, 07:32	iteration	#1
mani20saze New Member sandi Join Date: Feb 2014 Posts: 1 Rep Power: 0	hi I want to simulate flow through a pipe by fluent.its a unsteady flow and i choose pressure-velocity coupling as simple. I dont have any idea about how should i fill the time step size and number of time steps and max iteration per time step in panel iterate? tanks a lot Last edited by mani20saze; February 2, 2014 at 14:22.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[snappyHexMesh] determining displacement for added points	CFDnewbie147	OpenFOAM Meshing & Mesh Conversion	1	October 22, 2013 09:53
how to increase "Newton Pressure Iteration Limit"	kus	CFX	9	April 21, 2013 01:54
[snappyHexMesh] snappyHexMesh aborting	Tobi	OpenFOAM Meshing & Mesh Conversion	0	November 10, 2010 03:23
Parallel runs slower with MTU=9000 than MTU=1500	Javier Larrondo	FLUENT	0	October 28, 2007 22:30
Heat exchanger problem	chiseung	FLUENT	16	October 20, 2001 04:36

February 3, 2014, 02:40		#2
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	Since you expect unsteady flow, there has to be some estimate for the time scale of this unsteadyness. A good initial guess for the time step size is 1/20th of this time scale. You should still do a sensitivity study with the time step size especially if this is the first simulation of this kind you are doing. The number of time steps in entirely your choice. Together with the time step size, it determines the total physical time of the simulation. If you want to simulate 20 seconds of real time and your time step size is 0.001s, then you need 20000 time steps. The maximum iterations per time step have a default value of 20, which is not all that bad. If you chose a sufficuently small time step size, at least for standard simulations that should be enough to achieve convergence. It is important to keep in mind that this is the MAXIMUM number of iterations. If the convergence criteria are met before this number is reached, the simulation advances to the next time step. But as for the time step size, I highly recommend to do a sensitivity analysis with this quantity (and the convergence criteria) if this is the first time you do a new kind of simulation.