transient analysis from steady data

Cecco · May 21, 2013, 09:10

Hi everybody,
I usually perform steady simulations by CFX without troubles.
Now I need to perform a transient analysis in order to understand the flow field insiede a pump.
I would like to know I can I perform a transient simulation from data of a finished steady run.

Thanks in advance.

oj.bulmer · May 21, 2013, 09:51

Just initialize the transient run using the steady res files in Define Run dialogue box.

OJ

ghorrocks · May 21, 2013, 20:23

And use adaptive time stepping, homing in on 3-5 coeff loops per iteration to set the time step. Probably the most common problem in transient simulation on this forum is people who set a time step size which is way off.

Cecco · May 22, 2013, 04:41

Thanks guys.

Could you please help me to fill out the basic settings tab as you can see in the file attached.
I want to get an animation of my impeller motion and flow field around. Its speed is 8750 rpm. I want to simulate in 10 frames a total time of 0.000403 seconds.

Thank you!

ghorrocks · May 22, 2013, 06:52

Initial timestep=1e-8[s]
max TS=1e20
min TS=1e-20

That will do. The initial TS is almost certainly too small, but it will quickly find the correct size. Next time you run it you can put the correct initial TS in and you will save some time.

For the animation make sure you save transient results files at time intervals suitable for what you want to see.

Cecco · May 22, 2013, 09:00

Thank you so much! I gonna try!

May 21, 2013, 09:10	transient analysis from steady data	#1
Cecco Member Francesco Join Date: Jan 2012 Posts: 31 Rep Power: 14	Hi everybody, I usually perform steady simulations by CFX without troubles. Now I need to perform a transient analysis in order to understand the flow field insiede a pump. I would like to know I can I perform a transient simulation from data of a finished steady run. Thanks in advance.

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May 21, 2013, 09:51		#2
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	Just initialize the transient run using the steady res files in Define Run dialogue box. OJ

May 21, 2013, 20:23		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	And use adaptive time stepping, homing in on 3-5 coeff loops per iteration to set the time step. Probably the most common problem in transient simulation on this forum is people who set a time step size which is way off.

May 22, 2013, 06:52		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Initial timestep=1e-8[s] max TS=1e20 min TS=1e-20 That will do. The initial TS is almost certainly too small, but it will quickly find the correct size. Next time you run it you can put the correct initial TS in and you will save some time. For the animation make sure you save transient results files at time intervals suitable for what you want to see.

May 22, 2013, 09:00		#6
Cecco Member Francesco Join Date: Jan 2012 Posts: 31 Rep Power: 14	Thank you so much! I gonna try!