About smoothingModel_constDiffSmoothing

Dear CFDEM community,

Has anyone used the smoothing model in CFDEM before? I wonder what's the theory or underlying science for the smoothing approach used in CFDEM?

What I get from the code is that it solves a diffusion equation for the void fraction and the momentum exchange term Ksl.

******************************************************************************
double deltaT = vSmoothField_.mesh().time().deltaTValue();
DT_.value() = smoothingLength_.value() * smoothingLength_.value() / deltaT;

// do smoothing
solve
(
fvm::ddt(vSmoothField)
-fvm::laplacian(DT_, vSmoothField)
);
*******************************************************************************

Is there any guidance on how to choose the smoothingLengthScale and the DT value, and is deltaT here the same as the CFD time step?

I am simulating a pipe flow using DNS/LES-DEM, the particle size is larger than the mesh size, so I am considering the smoothing approach. Attached is a preliminary test of what I get (the void fraction of fluid) using constDiffSmoothing with setting up deltaT as the CFD time step and smoothing length scale equals to 0.0015. Thanks.

Cheers,
Enzu