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[sardar.svn]

I am trying to model impeller mixing of high volume fraction of particles in water (transient, Eulerian, DDPM, kwsst, Coupled, injection). The issue is that simulation solves and converges (as per both residuals and monitored variables) for the first flow timestep, but when the flow timestep is bumping to the second one, continuity and k, e residuals fly up to 10 orders of magnitude (!), and then there is this Experiencing convergence difficulties warning before I get floating point exception and simulation is terminated.

 

My background effort to fix the issue has been the following, however, I have tried most of them one at a time, instead of in tandem, to see individual effect each could have had,that's why they are open to discussion if you think so:

• Solving the flow to a stable state before injecting
• refining the mesh ( Watertight/ Polyhedral or Polyhedral Hex Core - Orth: min. 0.3 - avg 0.95  |  Skew: max 0.7 avg 0.04  |  AspR: Max 19.9 - avg 1.75) (I read somewhere tetrahedral mesh should be used to fix this issue. How reliable is this advice?),
• solving for flow timesteps as small as 0.002 [s],
• compromising on injections as small as parcel count of 2 (while keeping DDPM active),
• manipulating URF's of momentum, pressure, k and e for as low as 0.2 (pressure) and 0.5 for the rest, as the manulal says
• increasing number of DPM updates per flow timestep and reducing DPM source URF to make sure DPM sources are fully consumed in each timestep.

Since tank top is open in reality, I define zero-shear wall and escape as boundary condition for top open surface and DPM, which I believe should not be a deal. I am neither brand new to Fluent nor an expert, especially given the fact that I have learned on my own so far. I am thus far coming to the question if such model is ever soluable in Fluent at all? 

But there is nothing else I can either find online, in the Fluent User/Theory Guide or think of on my own.

Can anyone help please?

[Rob]

Continues here  /forum/forums/topic/eulerian-ddpm-floating-point-exception-error-still-persists/