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• #1990
Eric
Participant

Dear OpenLB team,

I am now trying to apply a boundary condition as shown below:
[img]https://ibb.co/n382mK[/img]

the top and bottom boundary are characterized by u=u_inf and dv/dy=0. My question is that if there’s Neumann type boundary already implemented in OpenLB? I searched the function library and the only Neumann bc I found is convection boundary, which is however not suitable for this case.

Does that mean I need to create a new boundary class by myself? I am not an expert in C++ so I am a little bit confused on the program structure when assigning a boundary condition. Correct me if I was wrong: the user define a boundary condition via “addXXXBoundary” then the program goes into BoundaryConditionInstantiator2D and then PostProcessorGenerator2D, where the boundary condition algorithm is constructed.

Do I need to create a new addXXboundary function and new boundaryprocessor to create a Neumann type boundary as shown before? Looking forward to hearing from you.

Best regards,
Eric

#2904
mathias
Keymaster

Dear Eric,

addPressureBoundary does the job – you an have a look at the cylinderXd eyamples.

Best
Mathias

#2905
Eric
Participant

Dear Mathias,

Sorry I didn’t make myself clear. The top and bottom boundary has Ux predescribed (dirichlet bc) and dUy/dy=0 (neumann bc) so I guess it is actually a mxied boundary condition. By pressure boudary condition I guess the velocity gradient at all directions is 0 (exactly neumann type bc). Is there any method not to force dUx/dy=0?

Best regards,
Eric

#2906
mathias
Keymaster

No, there isnt one. Best Mathias

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