|
[Sponsors] |
September 14, 2017, 12:35 |
Trn results output frequency
|
#1 |
Member
cfxtwophaseflow
Join Date: Aug 2017
Posts: 46
Rep Power: 9 |
Hi,
I'm doing a transient DNS analysis for an isothermal bubble column. Total time = 150s and the time step = 0.01s. In the output control for Trn results when I change the output frequency form every time step to Time interval=10s. The flow configuration is very different in the two cases. Is there any logical explanation?? Should I select the every time step option to have more accurate results? Thank you |
|
September 17, 2017, 21:57 |
|
#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,841
Rep Power: 144 |
0.01s does not sound like DNS time scales. Where did you establish that time step from?
Writing results files does not affect the simulation. If the simulation result has changed then you changed something in the setup. |
|
September 18, 2017, 11:58 |
|
#3 |
Member
cfxtwophaseflow
Join Date: Aug 2017
Posts: 46
Rep Power: 9 |
thank you for your reply.
For the time step, it was big just to do a test. I did the test an other time and I found out that the trns result frequency doesn't affect the final result. I'm figuring out what did I change. |
|
September 18, 2017, 20:06 |
|
#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,841
Rep Power: 144 |
By DNS you mean direct numerical simulation, don't you? Have you confirmed your mesh and numerics can resolve the Kolmogorov length and time scales? This is very challenging in CFX, it is not a solver which is designed for DNS simulations.
Or do you mean something else by DNS? |
|
September 19, 2017, 02:11 |
|
#5 |
Senior Member
urosgrivc
Join Date: Dec 2015
Location: Slovenija
Posts: 365
Rep Power: 11 |
output control Trn results can and does not influence your results.
that is just to limit the size of the output file if you dont need results at every timestep, you will have only 15 timesteps in cfx post if You chose 10s interval for your 150s long run and if you chose every timestep than you will have 150000 result timesteps and your result file will be aproximately 1000 times larger. and for true dns this will be yet another few fthousant times larger. Are you talking about 150s long DNS run? you do know that quantum computers are not here jet . Oh anyway I think thats imposible. I wonder what the world record is for the logest dns run? If you are realy doing a DNS than the problem with your results is you dont have none and any litle change to the BCs, mesh or domain changes your results as your simulation is not independant of all the wariables (trn result frequency does not). DNS is worlds most expensive way of doing cfd and is not usefull for the normal user. You will probably need to use some kind of turbulence model. nice reading_dns; https://en.wikipedia.org/wiki/Direct...cal_simulation or maybe LES https://en.wikipedia.org/wiki/Large_eddy_simulation Last edited by urosgrivc; September 19, 2017 at 08:59. |
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Improved solver data output / tracking / visualization | chriss85 | OpenFOAM Running, Solving & CFD | 1 | May 13, 2015 08:55 |
Comparing Air numerical results with water experimental results | cristian2009es | Main CFD Forum | 1 | July 2, 2014 19:11 |
mixerVesselAMI2D's mass is not balancing | sharonyue | OpenFOAM Running, Solving & CFD | 6 | June 10, 2013 10:34 |
Questions about data output | aki_yafuji | OpenFOAM Running, Solving & CFD | 3 | September 9, 2010 02:59 |
How to output results for specific elements - HELP | Dan | FLUENT | 0 | January 16, 2009 09:38 |