[Jendrik Weise]

Hi,
that is another potential resolution. I had assumed that, given that Guo forcing was chosen, implementing something along the lines of https://journals.aps.org/pre/abstract/10.1103/PhysRevE.86.036701 had been the intention. To do that correctly though, in accordance with formulas (15) and (16) in that paper, the force/2 addition needs to occur before the averaging step.

In any case though, if there was no intention to implement that model, it would likely make sense to simply switch to a ShanChen forcing scheme to avoid future confusions, which would bring the model in line with the original Shan Chen paper.

Jendrik Weise

[Jendrik Weise]

Having investigated this further, point 2 is merely a result of “force” being actually an acceleration and simply confusingly named. Having now tested 1, correct results are indeed obtained by switching to dynamics along the lines of:

template <typename MOMENTA>
struct Identity {
template<typename DESCRIPTOR>
using type = typename MOMENTA::template type<DESCRIPTOR>;
};

template <typename T, typename DESCRIPTOR, typename MOMENTA=momenta::BulkTuple>
using IdentityForcedBGKdynamics = dynamics::Tuple<
T, DESCRIPTOR,
MOMENTA,
equilibria::SecondOrder,
collision::BGK,
forcing::Guo<Identity>
>;
and adding the forcing momentum adjustments within the processor. I believe altering the default behavior here and documenting this in more detail may indeed by advisable.

• This reply was modified 6 months, 2 weeks ago by Jendrik Weise.

[Jendrik Weise]

I believe the issue with 1. may be the following: internally(elements.h#1095), the Guo forcing adds the term force/2 for each lattice individually, however normally this should happen before the averaging(at least for the Shan-Chen forces), meaning that in a correct explicit forcing implementation all fluids at a given location have the same equilibrium velocity. I have yet to address that potential issue in the code myself so take the above results with a grain of salt.

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