Time step for unsteady simulation

Mohankumarg12 · June 29, 2011, 06:18

Hi
I am doing a simulation for defrosting of wind shield using fluent 12.1. In the input I am giving a time dependent temperature profile for 40min. For the unsteady calculation I am giving a time step of 5 sec and with intermediate iteration of 5.
I am also getting solution for time step of 10 sec and I am getting a quicker solution as compare with 5 sec, but I want to know which is right and how to decide the time step for unsteady simulation.

Thanks in advance.

Mohan.G

nikhil · July 2, 2011, 15:40

I would suggest, Monitor the temperature or the heat flux from the wind shield after a particular time interval.

If the difference between these monitored parameters is within some desired critera, say 5-8%, then you can trust the results of the 10 second case.

Another way to deside whether your time step is correct as per grid and convection-diffusion of your physical problem is to check
1. CFL condition OR 2. Grid Fourier Number criterion ( Depending upon a physics of your problem)

CFD criterion needs to be satisfied for negligible diffusion.
Grid Fourier number criterion needs to be satisfied for negligible convection

Mohankumarg12 · July 4, 2011, 00:51

Thank you Nikhil

mecamor · July 4, 2011, 16:03

hello I wanted to see the shock wave generated by a piston. My problem I can not even move my piston with moving wall. thank you for helping me

June 29, 2011, 06:18	Time step for unsteady simulation	#1
Mohankumarg12 Member Mohankumar.G Join Date: Sep 2010 Location: Pune,India Posts: 44 Rep Power: 17	Hi I am doing a simulation for defrosting of wind shield using fluent 12.1. In the input I am giving a time dependent temperature profile for 40min. For the unsteady calculation I am giving a time step of 5 sec and with intermediate iteration of 5. I am also getting solution for time step of 10 sec and I am getting a quicker solution as compare with 5 sec, but I want to know which is right and how to decide the time step for unsteady simulation. Thanks in advance. Mohan.G

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Extrusion with OpenFoam problem No. Iterations 0	Lord Kelvin	OpenFOAM Running, Solving & CFD	8	March 28, 2016 12:08
Superlinear speedup in OpenFOAM 13	msrinath80	OpenFOAM Running, Solving & CFD	18	March 3, 2015 06:36
Orifice Plate with a fully developed flow - Problems with convergence	jonmec	OpenFOAM Running, Solving & CFD	3	July 28, 2011 06:24
Time step in Transient simulation	sandisk	FLUENT	2	February 3, 2011 00:55
Long time CHT transient simulation time step....	JP	CFX	0	May 9, 2008 04:36

July 2, 2011, 15:40		#2
nikhil New Member Nik Join Date: Mar 2010 Location: Michigan Posts: 25 Rep Power: 16	I would suggest, Monitor the temperature or the heat flux from the wind shield after a particular time interval. If the difference between these monitored parameters is within some desired critera, say 5-8%, then you can trust the results of the 10 second case. Another way to deside whether your time step is correct as per grid and convection-diffusion of your physical problem is to check 1. CFL condition OR 2. Grid Fourier Number criterion ( Depending upon a physics of your problem) CFD criterion needs to be satisfied for negligible diffusion. Grid Fourier number criterion needs to be satisfied for negligible convection

July 4, 2011, 00:51		#3
Mohankumarg12 Member Mohankumar.G Join Date: Sep 2010 Location: Pune,India Posts: 44 Rep Power: 17	Thank you Nikhil

July 4, 2011, 16:03		#4
mecamor New Member mecamor Join Date: Jul 2011 Posts: 23 Rep Power: 15	hello I wanted to see the shock wave generated by a piston. My problem I can not even move my piston with moving wall. thank you for helping me