Can someone brief what useDDTvoidfraction does?

Submitted by yesaswi92 on Mon, 01/29/2018 - 00:54

Hello,

I am going through the void-fraction tutorial example and found this keyword useDDTvoidfraction in the coupling properties. Can someone briefly explain what role does that play and what its options are. In the file I'm looking at, it has
useDDTvoidfraction b

I can't find the source-code associated with it, neither any documentation.

Thanks.

Yesaswi.

Forums:

alice's picture

alice | Mon, 01/29/2018 - 10:26

Hi Yesaswi,

the keyword is used to determine the way, in which the voidfraction-change-term ddtVoidfraction() is set in the equaions:

https://github.com/CFDEMproject/CFDEMcoupling-PUBLIC/blob/b23726463721d5d83c419b8c0b612950e6c4c7c8/src/lagrangian/cfdemParticle/cfdemCloud/cfdemCloud.C#L914

If it is off the change of the voidfraction per cell is not considered, in case of chosing type a one ads div(Us*(1-voidfraction)) and in case of selecting b the gradient is added directly.

The reason for the default "off" is that this term has, in many cases, little impact on the result, but can cause instabilities (when using the divided voidfraction model, the voidfraction changes non-steadily, which leads to high fluctuations in the gradient...).

Best,

Alice