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Old   March 21, 2016, 01:04
Default Advanced Options Tab for flow simulation
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M.A.
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Good Day Sirs!

I'm simulating a multi-phase flow (water and air) on a Banki cross flow turbine.

I'm using Ansys CFX, but didn't have a formal training on.

I need help on the Advanced Options Tab under the Solver Control. So far, the only checked item on my simulation is Global Dynamic Model Control.

Should I include the following settings below? :

Velocity Pressure Coupling -------> Rhie Chow 4th order
Multiphase Control --------> Volume Fraction coupling
Body forces --------> Volume-Weighted

I am using the default setting, wherein none of those three are set.
What is the significance of this?
I read the CFX Guide but could not understand/fully grasp the concepts. I kind of need a layman's explanation, if possible.

Thank you very much Sirs!
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Old   March 21, 2016, 18:19
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Glenn Horrocks
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It is rare for users to need to change these parameters. They are not called advanced options for nothing.

Having said that you often do need to adjust these parameters for free surface flow in my experience. But the optimum settings are different for different types of simulations so the best way to proceed is to do a short benchmark simulation where you try all the options and see which ones have a beneficial effect. You will probably find that one or two of these options will help in your case.

A quick explanation of what they mean:
VP coupling - the velocity and pressure variables are only loosely coupled in the Navier stokes equations. The coupling requires special treatment as naive applications of finite difference gradients leads to numerical instability, so usually a 4th order correction term is used to keep these instabilities under control.

MP Control - This controls whether the equations are solved as velocity and pressure in one matrix and volume fraction in another matrix; or all solved together in one big matrix. Coupled usually works better but not always.

Body forces - I think this is mainly for the surface tension model and control how the body forces from the surface tension are applied to the nodes.
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