Re: DESCRIPTOR D2Q9Descriptor
bstep2d uses a BGKDynamics with a D2Q9Descriptor which in the end calls into lbHelpersD2Q9.h.
prepareLattice in bstep2d.cpp tells you which boundaries are used in the example. The variable bulkDynamics corresponds to the BGK fluid dynamics, bounce back is obvious and only the velocity and the pressure boundary require some more work.
By default the example uses local boundaries (273 createLocalBoundaryCondition2D<T,DESCRIPTOR>( sBoundaryCondition ); ) which means that we get a RegularizedBoundaryManager2D and as a Result CombinedRLBdynamics (with MixinDynamics as BGKdynamics). The only difference between the pressure and the velocity boundary in that case is the used boundary momenta.
Which descriptor are you currently missing. Depending on the type of descriptor you might just need to add a new descriptor. There are only a few cases where putting work into the lbHelpers and the corresponding template specializations is ever required.