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May 23, 2011, 12:59 |
Diverging Turbulence
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#1 |
New Member
Nicholas
Join Date: May 2009
Location: Seattle, USA
Posts: 18
Rep Power: 17 |
Hi All,
I have a transient multiphase simulation with mesh deformation. (See attached pictures) Problem is that the turbulence equations keep diverging. I am modelling a set of water locks that slowly fill with a set of barges inside. The mesh deformation models the movement of the barges with the rising water level. Mesh deformation is linked to move with the position of the average water level. (I defined it on a velocity basis to ensure I got the initial mesh velocity with my first iterations.) No matter what I do, the problem is the same thing every time. I get a good initialization, and then as I step through time, the turbulence residuals slowly get larger. Eventually, after 20 - 120 time steps, depending on what settings I use, the model blows up and crashes. Any ideas why this is happening, and what I can do to stop it? I have tried k-e, k-w, and Spalart-Allmaras. Currently I am using Spalart-Allmaras to try and get it stable. I have an under-relaxation factor 0.60 for my turbulence solver. I have added a linear ramp to the solver, with an initial value of 0.20 ramping up to 0.60 over 12 iterations. No matter what I do, the simulation eventually diverges, and only with turbulence. All other residuals show strong convergence. Further, I only have problems with my lower region (the bottom region shown in my pictures.) This is where the water enters through an extensive set of pipes. The pipes are meant to stop the water velocity and create smooth flow into the lock. Some simulation settings: Rough reynolds number: 1.55x10^5 Average cell size: 5.0 ft Average surface cell size: 1.0 ft Timestep: 0.05 s Iterations between timestep: 45 (120 on initialization) Total solution time: 32.0 s Thanks Last edited by nickninevah; May 24, 2011 at 11:13. |
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Tags |
diverge, divergence, instable, turbulence, unstable |
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