airBubbleCoalescence3d example: adding BounceBack BCs

[mehrdadvasheghanifarahani]

Dear OpenLB community,

I am trying to run the airBubbleCoalescence3d example with solid boundaries at the top and bottom by adding bounce-back boundary conditions. Following the approach from the rayleighTaylor3d example, I made the following modifications:

i) in the prepareGeometry function:

superGeometry.rename( 0,1 );

Vector<T,3> origin1( -2. );
Vector<T,3> origin2( -2., N/2., -2. );
Vector<T,3> origin3( -2., N-1., -2. );
Vector<T,3> extend1( N+3., 2., N+3. );
Vector<T,3> extend2( N+3., N/2+2., N+3. );

IndicatorCuboid3D<T> bottom( extend1, origin1 );
IndicatorCuboid3D<T> top( extend1, origin3 );

superGeometry.rename( 1,3,bottom );
superGeometry.rename( 1,4,top );

superGeometry.clean();

This sets material numbers 3 and 4 for the bottom and top boundaries, respectively, while the bulk fluid remains as material 1.

ii) in the simulate function:

// set periodic boundaries to the domain
cGeometry.setPeriodicity( true, false, true );

So, I disable the peiodicity in y-direction.

iii) in prepareLattice function:

sLattice1.defineDynamics<BulkDynamics>(superGeometry, 3);
sLattice2.defineDynamics<BulkDynamics>(superGeometry, 3);

sLattice1.defineDynamics<BulkDynamics>(superGeometry, 4);
sLattice2.defineDynamics<BulkDynamics>(superGeometry, 4);

setBounceBackBoundary(sLattice1, superGeometry, 3);
setBounceBackBoundary(sLattice1, superGeometry, 4);
setBounceBackBoundary(sLattice2, superGeometry, 3);
setBounceBackBoundary(sLattice2, superGeometry, 4);

and also:

sLatticeOne.defineRho(superGeometry, 3, rhoH2O);
sLatticeTwo.defineRho(superGeometry, 4, rhoH2O);

sLatticeOne.defineRho(superGeometry, 4, rhoN2);
sLatticeTwo.defineRho(superGeometry, 3, rhoN2);

This ensures that the bounceback nodes have densities required to impose the wettability.

However, when I run the simulation, I get NaN values. Could you please advise if any further modifications are needed to correctly implement the bounce-back nodes? I believe I’m implementing something incorrectly in step (iii).

Kind Regards,
Mehrdad Vasheghani Farahani

[luizeducze]

Dear Farahani,

I tried to simulate here the same example with your modifications and it worked. However, I did the simulation using lattice1 for H2O, lattice2 for N2 and lattice3 for O2. Are you trying to simulate just H2O and N2? I will try to disable the O2 phase and see if it breaks.

Kind regards,
Luiz

[luizeducze]

Another thing …

You dont need those lines:

sLattice1.defineDynamics<BulkDynamics>(superGeometry, 3);
sLattice2.defineDynamics<BulkDynamics>(superGeometry, 3);

sLattice1.defineDynamics<BulkDynamics>(superGeometry, 4);
sLattice2.defineDynamics<BulkDynamics>(superGeometry, 4);

When you use the setBounceBack, you are already applying the correct dynamics to the boundary nodes.

Did you applied BulkDynamics for the material number 1?

Kind regards,
Luiz

[Author]

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