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Free turbulent water jet into liquid metal pool, inlet submerged

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Old   February 21, 2019, 14:46
Default Free turbulent water jet into liquid metal pool, inlet submerged
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elliot stone
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Hi all,

I am having a really hard time attempting to run this simulation and any advic would be great.

The problem can be described as follows - Simulation of a high pressure water jet at 10-20MPa, at critical conditions T~330DegC, injected in a pool of lead bismuth eutectic at around 400-450DegC, Rho=10,0000 at atmospheric pressure. I am considering performing the injection through inlets ranging from 5,10,20mm. from the description its clear that the water jet will evaporate almost instantly from the expansion and incident heat transfer from the lead. Oddly with this problem I have been instructed to perform the simulation under liquid-liquid conditions, at steady state. This means the state of the fluid can be calculated via data extrapolation. Essentially these simulations will be looking into the depth that the water jet penetrates, and use this as a design constraint for distance between reactor core and heat exchangers in lead cooled nuclear reactors.

Surprisingly I am having a hard time finding any literature related to to free jetting into a denser fluid and simulating it...

I'm treating the problem as a steady state axis-symmetric jet with a symmetry at the centre of the inlet.

Modelling
Pressure based solver - steady state, gravity
Multiphase VOF, (Ive considered using open channel and setting a vessel depth)
Thermal
K-e Realizable, standard wall treatment(Although not too relevent), also various issues could be presented as Pr,turb is uncertain to liquid metals.

[U]Boundary conds[U]
Refer to attached image for domain shape and assignment (diagram shows blocking of mesh with inlet block being finest to coarse on the far wall).
its 3 pressure outlouts on the surrounding walls, pressure inlet at constant P 10-20MPa, and symmetry for axis-symmetric representation. (FYI, inlet is injected vertically downwards)

Methods
Coupled (not with volume fractions)
pressure - BFW
momentum 2ndUS
VF - Compressive (which could be an issue ? )
TKE -1stUW
TDR -1stUW
Energy- 2ndUW
Higher order relaxation enabled at default values

Pressure and temp of primary phase, and Vf of 2nd phase = 0 patched in after initialisation from inlet

At this state, I cant get convergence below 10^-2 which is not good. My major concerns here are the boundary conditions, causing the lack of convergence or that there isn't a steady state, i'd previosuly used transcient and was advised against it.

Any advice would be greatly appreciated! Sorry if my description isnt clear for anything, let me know.
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Old   February 22, 2019, 14:39
Angry Is it even possible to simulate turbulent free jet flow as steady state?
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elliot stone
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After some more digging and some more testing, I'm not actually sure whether a steady state free jet is possible ? especially as its being injected vertically downwards, the water will be arrested by buoyancy in the liquid metal which will continually give me VF convergence issues. Regardless I still cant get convergence, currently testing a full model rather then symmetry and results are visibly more agreeable (E.g jet profile). I've tried some open channel simulations and defined an arbitrary depth of 5m, but have still had no luck...

I have a few thoughts related to the simulation though: 1.) is there a treatment for jet boundary layer similar to Y+ wall treatment 2.) If i did produce a transient simulation, would the initial jetting depth produced be reasonable to assume a maximum penetration depth of the jet?
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free jet, jet penetration, liquid metal, turbulent jet, vof

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