## Fluids

#### Single bubble growth in an oversaturated water flow – DNS?

• Monta
Subscriber

Hey everyone,
has anyone already had experience with fluent multiphase simulation of the growth of a single bubble until detachement in an oversatured water flow. Problem is considered 2D. See Picture describing the problem (© picture taken from this Paper DOI: 10.1039/C9LC00211A)

My concrete questions to the modelisation are:
1. How can I define an oversaturated water flow (oversaturated with oxygen in my case)
2. Is Fluent solver able to solve the concentration differential equation and determine the mass transfer which leads to growth of the gas bubble
3. I am thinking of using VOF model to capture the change of the interface. Any thoughts about this?
4. How to inject the bubble from a site?
5. Is a direct numerical simulation possible to investigate the physical problem?

I would appreciate any suggestions or thoughts.
Monta

• Rob
Ansys Employee

Have a look in the multiphase sections of the User’s and Theory Manuals. In answer to the questions, yes we can, but it’s not necessarily easy.

Edit: DNS can be used to solve the problem, let us know how you get on writing the core numerics, solver and models!

• DrAmine
Ansys Employee

Oversaturated water flow means for me we have some dissolved oxygen but so much that it might goes to the gaseous phase giving the solubatlity of water / volatility of the component dissolved.  I assume that will be something for Henry's law assuming low concentration of solute. Ansys Fluent can deal with phase change mechanism within a multiphase framework (like built-in Mixture Model, which is similar to VOF) or using your own mass transfer model.

First of all Ansysdoes not claim DNS capabilities for its CFD codes, and these codes have not been tested for DNS and I am pretty sure some discreization schemes generally used in DNS arte not available in Ansys Fluent. Moreover DNS for this of runs is "insane". However you might think that solving thins laminar with high resolution is something like Direct Numerical Solution as you are not using any model. Multiphase DNS is bit more "complex" than Turbulence DNS (Requiring Re^3 numerical operations overhead) as the former can be turbulent too and we need to resolve turbulence scales and mutliphase scales.