In this chapter we give an overview of various lifting strategies for lattice Boltzmann models (LBMs). A lifting operator finds for a given macroscopic variable the corresponding distribution functions, mesoscopic variables of the lattice Boltzmann model. This is, for example, useful in coupled LBM and partial differential equation (PDE) models, where one part of the domain is described by a macroscopic PDE while another part is modeled by a LBM. Such a hybrid coupling results in missing data at the interfaces between the different models. The lifting operator provides the correct boundary conditions for the LBM domain at the interfaces. We discuss the accuracy, computational cost and convergence rate of some analytical and numerical lifting procedures.
Keywords: Chapman-Enskog expansion, computational cost, Constrained Runs, hybrid models, initialization, lattice Boltzmann models, lifting operator, macroscopic partial differential equations, numerical Chapman-Enskog expansion, spatial coupling.