How to define Velocity of two phases at Inlet in VOF?

08 August 2019 5 9K Report

Hello, I am simulating slug flow in annulus with inner pipe rotation using VOF in Ansys Fluent. I have one inlet and one outlet.I would want to use velocity inlet specification. I have divided the inlet into 3 regions with air inlet at the centre and water inlets near the pipe walls, so that the volume fraction of a particular phase at an inlet is set to 1 and for the second phase is set to 0 . The outlet is maintained as a single pressure outlet zone. Without dividing the geometry I can generate a hexahedral mesh using nodes at the outlet and inlet and applying the multizone method. I have attached it below

My problem is:

1. When I divide the inlet as described above, the nodes on the inlet are slit up and I cant have a structured hexahedral mesh. Also, the multizone option in this case returns an error: "MultiZone found free block in swept body." Is there a better way of having two inlets on the same surface and still achieve a structured hexa mesh?

2. I decided to use an undivided inlet and specified mass flowrate at the inlet since it allows mass flow for both phases but it leads to low liquid holdup and high pressure drop values than the experimental results. Does this mean the mass flowrate is an inaccurate specification compared to velocity inlet since the domain is relatively incompressible or the difference could be from other reasons? 3. Is it possible to specify velocities of two phases on one inlet?

I would really appreciate your help.

Ammar Abdulkadhim

Dear Mr. Talemwa:

it is possible to specify the velocities of each phases by make a separate inlet for each phase (gas and liquid).

this problem can be solved numerically for 2D as it gives you accurate results and faster more than 3D.

for mesh problem: the 2D will be easier and you can make mesh independent study because of CPU limitations and reduce the iterations time.

finally the validation is the main and the first step in the numerical simulation which illustrates the error of your model (VOF)

Sincerely Yours,

Ammar

Emmanuel Talemwa

Many thanks Ammar Abdulkadhim ,

I would want to study shape and behaviour (hydrodynamics) of the Taylor bubble and slugs around the annulus as the inner cylinder rotates... do you think this is possible in a 2D configuration?

Thanks

Aws Al-Akam

Dear @Emmanuel talemwa

Try to use axisymmetric features in fluent.

You may be able capture the behaviour of the bubble and the slangs.

Regards

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