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Laminar field as initial state for turbulent two phase pipe flow |
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July 17, 2009, 05:51 |
Laminar field as initial state for turbulent two phase pipe flow
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#1 |
Senior Member
Join Date: Mar 2009
Location: Norway
Posts: 138
Rep Power: 17 |
Hello,
I am setting up a two-phase 40m pipe case, and have so far been successful using the laminar model. I will also have to do a turbulent case, and this is where it gets interesting - say difficult. Not awfully challenging per se, having a working laminar case. So I have been trying to tune the fvSolutions and PISO settings adding correctors to pressure, and using smaller and smaller delta T's, but still - the simulation keeps exploding at about 1.01 seconds every run. I tried to use a an exisiting field for alpha and the phase velocities Ua and Ub - using the result from laminar case @ 1.6 seconds. It seems to run nicely, but then suddenly the Courant number increases from 0.37 to 81 in two iterations, and it fails again. Is this a good way to do it - using a laminar field as initial condition? And should it be chosen closer to 0 or could it be later? Should tune my fvSolutions differently? The laminar case is steady and stabile after about 30 seconds. I attach two photos from the laminar case - the one showing the entire pipe visualize how far the gas has reached by the 1.6 seconds. Any suggestions to this? |
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July 18, 2009, 06:17 |
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#2 | |
Member
Nugroho Adi
Join Date: Mar 2009
Location: norway
Posts: 79
Rep Power: 17 |
Quote:
maybethis thesis report useful for you.Bay, M. O. (2008). "Development of Transient One-Dimensional Solver for Severe Slugging Simulation". M.Sc. Thesis, Aalborg University Esbjerg. Hilsen, Nugroho Adi Stavanger |
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July 21, 2009, 06:26 |
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#3 |
Senior Member
Join Date: Mar 2009
Location: Norway
Posts: 138
Rep Power: 17 |
Thanks, Nugroho Adi
that was an interesting paper for sure - and I believe it may become useful to me later. In this case though, I think my problem is quite simpler than the case in that paper - and the author doesn't seem to use an initial laminar field either |
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July 21, 2009, 10:15 |
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#4 |
Senior Member
Join Date: Mar 2009
Location: Norway
Posts: 138
Rep Power: 17 |
I have found a solution to this, and as courtesy to other users that have (or will have) a similar problem, I'll post the quick solution:
When it comes to slowly increasing Courant numbers, members on this forum have been referring to boundary conditions, and to verify that they are set properly. Though, this was not a solution to me - my case (just a pipe w/two phase flow) is also fairly simple. Until this point I had not been able to use a turbulence model starting from T=0 without crashing in an early stage. As mentioned - the laminar worked well. However, first thing I did was to refine my mesh - so the cells are distributed more evenly. Then - the major change I did was to alter the Divergence schemes in fvSchemes from limitedLinear or limitedLinearV to upwind. Now I am also being told that using upwind (which is a lower order scheme) initially is common. I changed back to the limitedLinear or limitedLinearV after a while (I had just commented them out when adding the upwind alternative) - the simulation is still running so I can't say 100% if it's successful - but so far it hasn't crashed again. |
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Tags |
explode, initial, laminar, turbulent, two phase |
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