# Questions about periodic+freeslip+outflow boundary conditions

Dear all, I’m using Palabos to simulate a 3D turbulent flow with noslip BC on bottom, freeslip on top, periodic on lateral sides, a velocity profile on inlet and outflow BC on outlet. The Re number in my simulation will up to 1e4 so I use smagorinsky model.
But when I combine these BC together, the result always seems unreasonable. Here is one of my codes I tried:

``````
Box3D top    = Box3D(0, nx-1, ny-1, ny-1, 0, nz-1);
Box3D inlet  = Box3D(0, 0, 1, ny-1, 0, nz-1);
Box3D outlet = Box3D(nx-1, nx-1, 1, ny-2, 0, nz-1);

T cSmago = 0.12;

setBoundaryVelocity (lattice, inlet, TurbulentVelocity<T>(parameters) );
initializeAtEquilibrium(lattice, lattice.getBoundingBox(), TurbulentDensityAndZeroVelocity<T>(parameters) );

``````
``````
MultiBlockLattice3D<T, DESCRIPTOR> lattice (
parameters.getNx(), parameters.getNy(), parameters.getNz(),
new SmagorinskyRegularizedDynamics<T,DESCRIPTOR>(parameters.getOmega(), cSmago) );

OnLatticeBoundaryCondition3D<T,DESCRIPTOR>* boundaryCondition
//               = createLocalBoundaryCondition3D<T,DESCRIPTOR>();
= createInterpBoundaryCondition3D<T,DESCRIPTOR>();
//    lattice.periodicity().toggle(0, true); // periodic along the x-axis
lattice.periodicity().toggle(2, true); // periodic along the z-axis

``````

I think there must be something wrong with my definition of BCs. I read some of the topic in this forum but I still can’t make it go right, so any help is highly appreciated.

Another question is when I increase the Re number to around 1e4 or less in simulation of turbulent flow, the velocity field near the newmann BC will become unstable. I tried InterpBC in palabos and the unstability still happen. I wonder is this due to my wrong settings or something else.

Best regard.

1 Like

Hi,

I work on something similar however I have periodic BC which do not work now. When I will have solved that, your problem migth be mine so if you can send your code, I will have a look and who knows, maybe I will find a solution.

Best,

Olivier.