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Divergence in calculation: water-emulsion-injection

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Old   October 8, 2018, 11:30
Default Divergence in calculation: water-emulsion-injection
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Dennis Niemann
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I am simulating a water-emulsion-injection in an 4 stroke gas engine.
The Mesh was build with Fame Engine Plus.

- 315°-526°: exhaust valves open
- 526-534°: valve overlapping
- 534°-772: intake valves open
- 772°-1035: all valves open

The problem is, that my calculation diverges around 360°CA (exhaust valves not full open).
The false report are such as:
- Problem diverges: TKE equation, variable: TKE, material: 1
- Problem diverges: continuity equation, variable: Pressure correction, material: 1

The following modules are activatated: Species Transport, Combustion, Spray, Wallfilm, Thin Walls.

When the modules Spray, Wallfilm and Thin Walls are deactivated, the problem are the same. So I think the problem is an incorrect setting in the solver control.

I have decreased the underrelaxation factors (pressure: 0.1, Momentum: 0.6, TKE: 0.3, Turb. diss. rate: 0.3. I also have tried to change the linear solver of continuity (GSTB/AMG and variated th max iterations), but the problem was still the same.

Here are other settings, which I used:
- Convergence Criteria Pressure: 0.01
- Boundary Condition Inlet: total pressure 1.5bar
- BC outlet: static pressure 1.07bar

It is possible, that the problem for the divergence is the mesh itself?
I use high refinements in valve seats and valve heads.

I am thankful for every recommendation.

Best regards
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Old   October 9, 2018, 03:30
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Stephan Werner
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did You do a dummy run after meshing with FE+? What were the results?

Also a refinement of cells might be necessary, when the valves are almost closed.
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Old   October 9, 2018, 05:24
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Dennis Niemann
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The result of the dummy run were 2 twisted faces.

5°CA after the valves opened and before the valves will close I have used a refinement level 3 at valve heads and the valve seats.

My settings of the refinements are a recommendation of an example case in AVL Fire (case 920)
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4 stroke engine, continuity equation, divergence, gas engine, pressure correction

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