# CFX / buoyancy/mixing of water in tank

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 November 25, 2003, 22:50 CFX / buoyancy/mixing of water in tank #1 Christos lorakis Guest   Posts: n/a My problem is as it follows.I have a tank.The lower part of the tank contains water.The upper part of the tank contains water of higher density. Suppose initially two fluids are seperated.Instateneously they mix due to force of gravity. So i want to study the growth rate of the mixing zone. Please i am a begginer and i want help on CFX build for a start. So fat i know my problem characteristics are: Transient Laminar 2D ANALYSIS No slip boundary Hope to hear soon from everybody Thank you all!!!!!!!!!!

 November 26, 2003, 17:30 Re: CFX / buoyancy/mixing of water in tank #2 Glenn Horrocks Guest   Posts: n/a Hi Christos, Your problem is definitely transient, and no slip wall boundaries are probably correct. Your simulation may or may not be laminar, as there will be some sort of laminar to turbulent transition when the initial density difference exceeds some sort of threshold. You will need to determine this for yourself as it is problem dependant. It would be unlikely that your simulation is really 2D. Even though you geometry is 2D, the beauty of fluid mechanics will give you a solution which is 3D. Again, there probably would be transition from 2D laminar to 3D laminar to 3D turbulent, with some sort of threshold between all the different regimes. Enjoy! Regards, Glenn

 November 27, 2003, 12:44 Re: CFX / buoyancy/mixing of water in tank #3 Christos lorakis Guest   Posts: n/a any good ideas how to start building the tank in CFX-pre?PLEASE SOMEONE HELP!!!!!!

 November 28, 2003, 03:26 Re: CFX / buoyancy/mixing of water in tank #4 Pascale Fonteijn Guest   Posts: n/a You have to build a tank in CFX-Build. Mesh it in Build and then import your mesh (.gtm-file) into Pre. In Pre you can only define your problem, e.g., BC's, physical models. Pascale

 November 30, 2003, 10:59 Re: CFX / buoyancy/mixing of water in tank #5 Christos Guest   Posts: n/a In CFX build do you think i should create two solids (one the up and one down), one 3-d region including everything and two 3-d syb regions one for up and one for down ?

 November 30, 2003, 17:32 Re: CFX / buoyancy/mixing of water in tank #6 Glenn Horrocks Guest   Posts: n/a Hi Christos, Your idea would probably work. A better way would be to define your initial condition using a CEL expression, then you can easily move the interface up and down, make the interface sharper or blunter etc etc. If you use sub-domains and define different initial conditions for each sub-domain you will have to do a new mesh if you want to move the interface location. Have a look at CEL expressions in the documentation. Glenn

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