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Multiphase inlet/outlet patch definitions

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Old   September 30, 2016, 11:41
Default Multiphase inlet/outlet patch definitions
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John Anonymous
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Hello foamers

I have been trying to determine the appropriate definition of multiphase inlet and outlet patches for a long time and are seeking assistance. This relates to a civil engineering hydraulic structure (fish passage) that I have concerns about and wish to model (I have experience with OpenFOAM). I have known upstream and downstream water levels, however I have no information on velocities or flow rates and therefore my problem is under-constrained based upon my understanding of available OpenFOAM boundary conditions.

The structure operates as an offtake from the main channel of a river and discharges back into the river downstream of an obstruction that necessitates the fish passage and as a result have known water levels. In essence the water from the river 'spills' into and flows through the fish passage structure.

While the geometry of the fish passage (and internal baffles) are relatively simple it is not possible to accurately model the performance of the structure using other 1d and 2d models they are not sufficiently robust, and require a large number of assumptions for this purpose. The image below shows a segment of the fish passage model domain in perspective (the full domain is much longer).

Where blue is the inlet patch, brown is the outlet, red is the baffles, yellow the walls and light blue the atmospheric boundary.

I have seen other posts on the forum that have suggested creating an individual patch for inlet and outlet boundaries but I am not in favour of this approach. I have looked into groovyBC and believe this will be the best approach as it will enable me to use different water surface elevations and will also accommodate a hydrograph being run through the model while using a single multiphase patch. In this model I have specified the multiphase patches using groovyBC but need some assistance in appropriately defining the remaining boundary conditions

The conditions for the model are:
  1. Water surface elevation known at the inlet (z<83.676 water phase) and outlet (z=<83.176 water phase), values above these are air.
  2. Water phase velocity unknown
  3. Water phase flow rate unknown
  4. Hydrostatic pressure of the phases is applicable
Any assistance on the best approach to constrain the boundaries for the velocity and code this in groovyBC (or any alternative approach) will be appreciated?

For brevity a segment of the fish passage base model can be accessed at:

This is a common situation for hydraulic structures in civil engineering and I hope someone has developed an approach that could be applied to this model.

Any and all assistance will be appreciated.

Regards JFM
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groovybc, multiphase boundary, under-constrained

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