# Answer to Question #27721 in Astronomy | Astrophysics for Omkareshwar Jha

Question #27721

Is it possible to make adibatic wall????

Expert's answer

Adiabatic walls are implemented in Palabos, according to the following idea: the wall implements a boundary condition for the temperature, but the value of the temperature to be imposed on the wall is copied from the nearest neighbor at each iteration. The effect of this is to have a zero temperature gradient along the wall normal, which means, an adiabatic wall.

Use it with care, though, because this boundary condition has not yet been tested very thoroughly. In particular, it doesn't seem to be very stable, numerically, at high Rayleigh number.

// The lattice of the navier-stokes solver

MultiBlockLattice3D<T, NSDESCRIPTOR> nsLattice (

nx,ny,nz,new NSDYNAMICS<T, NSDESCRIPTOR>(nsOmega) );

// The lattice of the temperature solver

MultiBlockLattice3D<T, ADESCRIPTOR> adLattice (

nx,ny,nz,new ADYNAMICS<T, ADESCRIPTOR>(adOmega) );

// .. at this place, create the coupling between temperature and fluid, as usual.

OnLatticeBoundaryCondition3D<T,NSDESCRIPTOR>*

& nsBoundaryCondition = createLocalBoundaryCondition3D<T,NSDESCRIPTOR>();

&

OnLatticeAdvectionDiffusionBoundaryCondition3D<T,ADESCRIPTOR>*

& adBoundaryCondition = createLocalAdvectionDiffusionBoundaryCondition3D<T,ADESCRIPTOR>();

// All outer walls of the rectangular domain shall implement a velocity condition for

// the fluid, and a fixed temperature condition for the temperature.

nsBoundaryCondition -> setVelocityConditionOnBlockBoundaries(nsLattice);

adBoundaryCondition -> setTemperatureConditionOnBlockBoundaries(adLattice);

// On one selected plane (the x-z plane at y=0), turn the temperature condition

// into an adiabatic condition.

Box3D adiabaticWall(0,& nx-1, 0, 0, 1, nz-2);

xint processorLevelBC = 1;

integrateProcessingFunctional (

new FlatAdiabaticBoundaryFunctional3D<T,ADESCRIPTOR,1,-1>,

adiabaticWall, adLattice, processorLevelBC );

Use it with care, though, because this boundary condition has not yet been tested very thoroughly. In particular, it doesn't seem to be very stable, numerically, at high Rayleigh number.

// The lattice of the navier-stokes solver

MultiBlockLattice3D<T, NSDESCRIPTOR> nsLattice (

nx,ny,nz,new NSDYNAMICS<T, NSDESCRIPTOR>(nsOmega) );

// The lattice of the temperature solver

MultiBlockLattice3D<T, ADESCRIPTOR> adLattice (

nx,ny,nz,new ADYNAMICS<T, ADESCRIPTOR>(adOmega) );

// .. at this place, create the coupling between temperature and fluid, as usual.

OnLatticeBoundaryCondition3D<T,NSDESCRIPTOR>*

& nsBoundaryCondition = createLocalBoundaryCondition3D<T,NSDESCRIPTOR>();

&

OnLatticeAdvectionDiffusionBoundaryCondition3D<T,ADESCRIPTOR>*

& adBoundaryCondition = createLocalAdvectionDiffusionBoundaryCondition3D<T,ADESCRIPTOR>();

// All outer walls of the rectangular domain shall implement a velocity condition for

// the fluid, and a fixed temperature condition for the temperature.

nsBoundaryCondition -> setVelocityConditionOnBlockBoundaries(nsLattice);

adBoundaryCondition -> setTemperatureConditionOnBlockBoundaries(adLattice);

// On one selected plane (the x-z plane at y=0), turn the temperature condition

// into an adiabatic condition.

Box3D adiabaticWall(0,& nx-1, 0, 0, 1, nz-2);

xint processorLevelBC = 1;

integrateProcessingFunctional (

new FlatAdiabaticBoundaryFunctional3D<T,ADESCRIPTOR,1,-1>,

adiabaticWall, adLattice, processorLevelBC );

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