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-   -   particle tracking with droplets (http://www.cfd-online.com/Forums/cfx/22970-particle-tracking-droplets.html)

simone marras August 21, 2006 07:33

particle tracking with droplets
 
Hi everyone, I am trying to simulate the movement of water droplets with a small diameter (400 micron up to 2 mm) in a duct; I tried using the particle tracking approach but apparently i am not setting the problem (B.C., fluids, etc) correctly because it crashes after 1 second of simulation. I also tried following the multiphase tutorial (that doesn't use the particle tracking but the euler-euler approach), but with my cionditions it crashes after about 5 time loops.

Can anyone give me hints on how to set the problem? what can be wrong once i suppose the b.c. are correct? Has anyone even simulate the behavior of water droplets? if yes, how did you set the problem in CFX?

thank you very much,

regards,

Simone Marras

Felix August 21, 2006 09:24

Re: particle tracking with droplets
 
Hello Simone,

what is the error message in your output-file?

Cheers, Felix

simone marras August 21, 2006 09:29

Re: particle tracking with droplets
 
Hi felix, thanks for replying,

it says overflow when it quits.

thanks a lot s.

Felix August 21, 2006 09:42

Re: particle tracking with droplets
 
Have you read the faq on page 706 in _CFXReference.book : "Solver overflow can often occur when an inappropriate timestep has been selected." Maybe your timestep is too small?

Felix

simone marras August 21, 2006 10:11

Re: particle tracking with droplets
 
Actually I haven't yet; I didn't know about it (new to cfx) and starting already with multiphase is not the best of things. My time step is a physical time step of 2 seconds, but i'll be trying an automatic time stepping

thanks again and Ill go thtorugh the FAQs,

s.

Bart Prast August 29, 2006 03:33

Re: particle tracking with droplets
 
Hi Simone, are you doing a two-way coupled simulation? If so the source terms to due drag in case of a high mass load of particles might be a problem. Lower the time step, the particle relaxation and maybe increase the number of iterations between coupling.

Bart

simone Marras August 29, 2006 03:43

Re: particle tracking with droplets
 
Hello Bart, thanks a lot for replying. Actually I am (as suggested in the butterfly valve tutorial), using a large number of particles one-way coupled and a few 2-way coupled, so that the load and time of computation can be reduced. Anyhow, to the first problems I had, it seems that the crashing was due to a bad meshing, and now things seem to be working if I use sand solid particles instead of water droplet. Ill want to set the problem with droplets as next step now that the first solution converges. Of cours,e i also want to evaluate how physical my solution is.

Do you work on water droplets impact for any chance?

thank you very much,

simone

Bart Prast August 29, 2006 03:46

Re: particle tracking with droplets
 
> Do you work on water droplets impact for any chance?

not specifically

Bart


suribabu September 2, 2006 04:09

Re: particle tracking with sand
 
hi iam suribabu. iam doing particle traking analysis using cfx. i want to calculate particle velocity in perticular location. but i saw in cfx post. there is no option for calculating paticle velocity. how to find can u help me


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