Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

time dependent turbulent flow and step function

Please login with a confirmed email address before reporting spam

Hi,
I am modeling heat transfer and turbulent fluid flow(RANS) in a pipe.
i could run the model and get reasonable results as long as fluid flow is in laminar regime but converting to RANS model, the process continues for ever and even after one day no progress is made. but still going and not interrupted.

by browsing through the forum i realized i should define a step function so what I did is a step function as follows:
step1
location: 0.025
from:0
to:0.2
smoothing: 0.05
i am not sure if these are correct but my inlet velocity is 0.2m/s. the problem is that when i multiply the inlet velocity with the step function (U0=0.2*step1(t)) comsol does not recognizes it and stays in red. even if i define t=0 as a parameter in advance.

i would appreciate if anyone could help me with this.

ASAL

3 Replies Last Post 2012年2月19日 GMT-5 17:29

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2012年2月15日 GMT-5 17:48
now the model in being run but only 4% progress in 4 days and i think this is going to continue forever.
may this be because of the step function i defined?


ASAL
now the model in being run but only 4% progress in 4 days and i think this is going to continue forever. may this be because of the step function i defined? ASAL

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2012年2月16日 GMT-5 02:04
Hi

turbulence models are tough and really demanding on RAM and processing time, as you often need a very fine mesh.

Sometimes starting from a laminar flow case can help, by gently increasing the velocity

Anyhow you should monitp what is gping on, by looking at the plots wile solving of both velocity and pressure, then you often identify rapidly that the solver is going the wrong direction , and you can stop before haviong waited ages for the progress to move on its sand bar ;)

--
Good luck
Ivar
Hi turbulence models are tough and really demanding on RAM and processing time, as you often need a very fine mesh. Sometimes starting from a laminar flow case can help, by gently increasing the velocity Anyhow you should monitp what is gping on, by looking at the plots wile solving of both velocity and pressure, then you often identify rapidly that the solver is going the wrong direction , and you can stop before haviong waited ages for the progress to move on its sand bar ;) -- Good luck Ivar

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 2012年2月19日 GMT-5 17:29
Hi Ivar,
I have divided it to two studies. stationary for fluid flow and transient for heat transfer and forced the heat transfer to use the stationary results as initial conditions. the model is run but I get very unrealistic results.

i think that step function should work well for me but i could not figure out what the step should be. imagine my velocity is 0.3m/s for a 0.025m diameter pipe.

Regards
ASAL
Hi Ivar, I have divided it to two studies. stationary for fluid flow and transient for heat transfer and forced the heat transfer to use the stationary results as initial conditions. the model is run but I get very unrealistic results. i think that step function should work well for me but i could not figure out what the step should be. imagine my velocity is 0.3m/s for a 0.025m diameter pipe. Regards ASAL

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.