Flow Modulation, mesh, cell and Ksl

Submitted by dbcmih001 on Fri, 03/01/2013 - 23:12

Hi

A professor at my university has brought to my attention that if the momentum transfer term, involving Ksl, is computed as occupying an entire single cell, in which a particle is located i.e. for an unresolved case (particle << cells), this could lead to significant flow evolution errors with simulation time. Is this concern valid? And what additional flags or options are required use to produce best flow modulation results.

Also is this concern also valid (if valid at all) for dilute systems?

Thanks

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cgoniva's picture

cgoniva | Wed, 03/06/2013 - 19:30

Hi,
it is not assumed that "Ksl, is computed as occupying an entire single cell"
That's why you have a voidfraction field.
Cheers,
Chris

dbcmih001 | Thu, 03/07/2013 - 18:34

Thanks for the reply

So just to clarify, when the Ksl field is computed for the continuum field, it is not introduced as a continuum cell? Reason for the confusion is because when running simulations and viewing for example the xy cross sectional plane of a cubic control volume containing very small particles, the Ksl field appears to occupy an entire cell, and only that cell, where the particles are located?

cgoniva's picture

cgoniva | Wed, 03/13/2013 - 10:03

Hi,

It is part of finite volume discretization that values are stored at the cell centres (Have a look at textbooks like Ferziger&Peric). Consequently momentum exchange terms must be stored at cell level - if finer discretization is needed, you need a finer mesh!
Please note that each particle has its own fluid forces, even if they are in the same cell - but for exchange with the flow field, these forces have to be summed-up/averaged (that's the job of the averagingModels).

Cheers,
Chris