Asked by Othman Sh on 2020-07-08

Hello,

I have a general question about the flow engine in Yade. I would like to know how the fluid velocity (for example: averageVelocity() function) is calculated? I have read the model documentation in [1] and [2] and similar papers but I couldn't understand how the fluid velocity is obtained numerically.

Also, is the average velocity reported from using averageVelocity() is the same as (u-v) in equation 19 in [2]?

Thank you,
Othman

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 Revision history for this message Robert Caulk (rcaulk) said on 2020-07-09: #1

Hello,

It's an integral of the velocity on the surface of the cell which boils down to estimating the total flowrate crossing the cell boundary and dividing that by the volume. Here is the source code [1].

Cheers,

Robert

 Revision history for this message Othman Sh (othman-sh) said on 2020-07-11: #2

Hi Robert,

I was trying to understand the equations in the source code and link that to the documentation in eq. 19 in [1] but it wasn't clear to me.

" the total flowrate crossing the cell boundary" means that flow rate would have a unit of volume/time, so how is it that dividing this by the cell volume would give a velocity in distance/time unit?

Also, line 123 in the source code [2] reads the following:

cell->info().averageVelocity() = cell->info().averageVelocity() + (facetFlowRate) * (posAvFacet - CGAL::ORIGIN);

I couldn't understand this part: "(facetFlowRate) * (posAvFacet - CGAL::ORIGIN);", what is posAvFacet?

Best,
Othman

 Revision history for this message Othman Sh (othman-sh) said on 2020-07-23: #3

Hi,

I hope someone can answer the questions above, this will be a great help.

Thanks,
Othman

 Revision history for this message Robert Caulk (rcaulk) said on 2020-07-24: #4

>what is posAvFacet?

posAvFacet is the location of the facet.

cell->info().averageVelocity() has units of m^4/s before dividing by volume.

Cheers,

Robert

 Revision history for this message Othman Sh (othman-sh) said on 2020-07-27: #5

Thank you, Robert. This answered my question.